1. A high-efficiency potential energy recovery system comprises an oil tank (1), a hydraulic oil pump/motor (2), a motor (3), a power supply assembly (4), a controllable single (change) direction valve (5), a hydraulic oil cylinder (6) and a controller (7), and is characterized in that one side of the controller (7) is electrically connected with the power supply assembly (4), the other side of the controller (7) is electrically connected with the motor (3), the motor (3) is connected with the hydraulic oil pump/motor (2), one side of the hydraulic oil pump/motor (2) is communicated with the oil tank (1), and the other side of the hydraulic oil pump/motor (2) is communicated with the hydraulic oil cylinder (6) through the controllable single (change) direction valve (5);

the electric machine (3) is switchable between motor and generator modes;

the hydraulic oil pump/motor (2) is switchable between oil pump and motor modes;

the controller (7) controls the lifting component connected with the hydraulic oil cylinder (6) to do ascending motion or descending motion by controlling the motor (3) to operate positively or negatively;

when the controller (7) controls the rotating speed of the motor (3) to be zero or in a stop state, the lifting part is in a hovering state.

2. The efficient potential energy recovery system of claim 1, wherein: the controller (7) can control the speed of the lifting component during ascending movement or descending movement by controlling the forward/backward rotation speed of the motor (3).

3. The efficient potential energy recovery system of claim 2, wherein: the controller (7) can control the motor (3) to realize stepless speed regulation.

4. The efficient potential energy recovery system of claim 1, wherein: the motor (3) can operate in 4 quadrants; high-efficient potential energy recovery system when operation in different work condition, motor (3) can be operated under 3 quadrants, specifically do:

when the working condition of the 1 st quadrant (rotating speed n is greater than 0 and torque Te is greater than 0) or the 3 rd quadrant (rotating speed n is less than 0 and torque Te is less than 0) is met, the running mode of the motor (3) is a motor mode;

when the working condition of quadrant 4 (rotating speed n is less than 0 and torque Te is greater than 0) is met, the running mode of the motor (3) is a generator mode;

when n is greater than 0, the motor (3) rotates forwards; when n is less than 0, the motor (3) runs in a reverse rotation mode.

5. The efficient potential energy recovery system of claim 4, wherein: the motor (3) is a permanent magnet synchronous motor or a permanent magnet direct current brushless motor or an alternating current motor or a direct current brush motor or a switched reluctance motor.

6. The efficient potential energy recovery system of claim 4, wherein: the electric machine (3) can control the operation mode of the hydraulic oil pump/motor (2);

when the motor (3) operates under the working condition of quadrant 1, the motor (3) rotates positively to drive the hydraulic oil pump/motor (2) to rotate positively, hydraulic oil flows upwards, the motor (3) is in a motor mode at the moment, and the hydraulic oil pump/motor (2) is in an oil pump mode;

when the motor (3) operates under the working condition of quadrant 3, the motor (3) rotates reversely to drive the hydraulic oil pump/motor (2) to rotate reversely, hydraulic oil flows downwards, but the motor (3) is still in a motor mode and the hydraulic oil pump/motor (2) is still in an oil pump mode because the torque Te is less than 0 at the moment;

when the motor (3) operates under the working condition of quadrant 4, the motor (3) rotates reversely to drive the hydraulic oil pump/motor (2) to rotate reversely, hydraulic oil flows downwards, but the torque Te is greater than 0, the motor (3) is in a generator mode at the moment, and the hydraulic oil pump/motor (2) is in a motor mode.

7. The efficient potential energy recovery system of claim 6, wherein: the hydraulic oil pump/motor (2) is a plunger pump or a piston pump or a gear pump or a vane pump or a screw pump.

8. The efficient potential energy recovery system of claim 1, wherein: the controllable single (change) valve (5) is an electric control single (change) valve, a hydraulic control single (change) valve or an electro-hydraulic single (change) valve.

9. The efficient potential energy recovery system of claim 1, wherein: the power supply assembly (4) further comprises a storage battery (8), and the storage battery (8) is electrically connected with the motor (3) through a controller (7).

10. The efficient potential energy recovery system of claim 9, wherein: the power supply assembly (4) further comprises a super capacitor (9), one side of the super capacitor (9) is electrically connected with the motor (3) through a controller (7), and the other side of the super capacitor (9) is electrically connected with the storage battery (8) through a power supply management unit in the power supply assembly (4).

11. The efficient potential energy recovery system of claim 1, wherein: the hydraulic oil pump/motor system is characterized by further comprising an overflow valve (10), wherein a connector on one side of the overflow valve (10) is communicated with a pipeline between the controllable single (change) direction valve (5) and the hydraulic oil pump/motor (2), and a connector on the other side of the overflow valve (10) is communicated with the oil tank (1) or an external recovery system.

12. The efficient potential energy recovery system of claim 1, wherein: the hydraulic control system is characterized by further comprising an explosion-proof valve (12), wherein the explosion-proof valve (12) is arranged between the controllable single (reversing) valve (5) and the hydraulic oil cylinder (6).

13. The efficient potential energy recovery system of claim 1, wherein: the intelligent control system is characterized by further comprising a human-computer interface (11), wherein the human-computer interface (11) can send control instructions to the controller (7), and the control instructions comprise lifting/hovering/descending instructions of the lifting component and lifting speed instructions of the lifting component.

14. The efficient potential energy recovery system of claim 1, wherein: the man-machine interface (11) comprises an operating handle or a knob or a key or a touch screen.

15. A method of controlling an efficient potential energy recovery system according to any one of claims 1-14 comprising the steps of:

when rising: the power supply assembly (4) supplies power to the motor (3) through the controller (7), according to a lifting instruction and a speed instruction given by the human-computer interface (11), the controller (7) controls the motor (3) to rotate forwards according to a set rotating speed, the motor drives the hydraulic oil pump/motor (2) to rotate forwards (n is more than 0), the motor (3) at the moment needs to output a forward torque (Te is more than 0), the motor operates in a 1 st quadrant, namely a motor mode, the hydraulic oil pump/motor (2) at the moment rotates forwards and operates in an oil pump mode, and hydraulic oil is pushed and lifted to enable the hydraulic oil cylinder (6) to extend and drive the lifting component to ascend;

through the control of the controller (7), the controllable one-way (change) valve (5) is in a power-off (closing) state in the whole lifting process, namely, hydraulic oil can only flow in one direction (upwards); after the motor is ascended to a preset position, the controller (7) controls the motor (3) to enter a stop state or a zero-speed running state;

when in suspension: through the control of the controller (7), the controllable single (change) valve (5) is continuously in a power-off (closing) state, and the hydraulic oil between the controllable single (change) valve (5) and the hydraulic oil cylinder (6) cannot reversely flow back; the motor (3) and the hydraulic oil pump/motor (2) are in a stop state or a zero-speed running state, and hydraulic oil between the controllable single (change) direction valve (5) and the oil tank (1) cannot reversely flow back; in other words, in the hovering process, hydraulic oil is filled between the hydraulic oil cylinder (6) and the oil tank (1) all the time;

when descending: according to a descending instruction given by a human-computer interface (11), the controller (7) controls the controllable one-way (change) valve (5) to be electrified and opened, so that hydraulic oil can reversely flow back through the controllable one-way (change) valve (5); meanwhile, according to a descending instruction and a speed instruction given by a human-computer interface (11), the controller (7) controls the motor (3) to act immediately and reversely rotate at a set rotating speed (n is less than 0);

when the heavy-load operation is carried out (the gravity G of the lifting component and the goods is greater than the sum f of the pipeline resistance and other equivalent resistances), the motor (3) needs to output a forward torque (Te >0), and the motor (3) works in a 4 th quadrant, namely a generator mode; the hydraulic oil pump/motor (2) runs reversely at the moment and works in a motor mode; the motor (3) becomes a generator and charges the power supply assembly (4);

when the vehicle runs under light load (the gravity G of the lifting component and the goods is smaller than the sum f of pipeline resistance and other equivalent resistance), the motor (3) needs to output reverse torque (Te <0), and the motor (3) works in a 3 rd quadrant, namely a motor mode; the hydraulic oil pump/motor (2) at this time is operated in reverse and operated in an oil pump mode.

16. The method of controlling an efficient potential energy recovery system of claim 15, wherein:

the controller (7) controls the hydraulic oil pump/motor (2) to rotate forwards (or reversely) by controlling the motor (3) to rotate forwards (or reversely), so that the lifting component is controlled to ascend (or descend);

the controller (7) controls the rotating speed of the hydraulic oil pump/motor (2) by controlling the rotating speed of the motor (3), so that the displacement/flow of hydraulic oil is controlled, and the ascending speed and/or the descending speed of the lifting component are controlled.

Background

In mechanical equipment, numerous lifting devices such as industrial vehicles (forklifts), excavators, loaders, stacking machines and aerial work platforms drive lifting parts to lift by utilizing a hydraulic system, and the devices can recover the gravitational potential energy of the lifting parts by utilizing the hydraulic system and convert the gravitational potential energy into electric energy to be stored.

The Chinese invention patent with the patent number of 201911373009.6 discloses a high-efficiency potential energy recovery system and a control method thereof, wherein the system comprises an oil tank, a first power supply, a first motor, a lifting oil cylinder and a controller, the first power supply is a storage battery, the first motor can be switched between a motor mode and a generator mode, and the lifting oil cylinder is used for driving a lifting part to lift; the storage battery is electrically connected with the first motor, the first motor is connected with the motor, a first interface of the motor is communicated with the lifting oil cylinder through the valve assembly, and a second interface of the motor is communicated with the oil tank; install first pressure sensor between valve member and the lift cylinder, install the second pressure sensor between motor and the valve member, first pressure sensor, second pressure sensor, valve member and first motor all are connected with the controller electricity.

According to the technical scheme, the pressure difference between the upper side and the lower side of the valve assembly is sensed by the first pressure sensor and the second pressure sensor, and before potential energy is recovered, the pressure on the upper side and the lower side of the valve assembly is balanced by control to prevent the speed difference problem (namely the stalling phenomenon of a lifting component caused by too large difference of oil pressure on two sides of the valve assembly), so that before a first motor in the technical scheme is switched into a generator mode from a shutdown state, the motor mode needs to be started, a period of time is waited for, potential energy recovery can be started until the pressure values of the first pressure sensor and the second pressure sensor are equal, the working efficiency is to be improved, and the equipment structure and the control logic are relatively complex; and the process of equalizing the pressure requires energy consumption, which affects the energy recovery efficiency.

In addition, in order to reduce the energy consumed in the pressure balancing process, the technical scheme also provides an alternative/preferred scheme, the pressure balancing is realized by adding a second motor, a second power supply, a pump (the displacement of the pump is smaller than that of the motor) and a one-way valve, so as to avoid the generation of speed difference, however, the reduction of the displacement means that the pressure balancing process needs longer time, the structure of the equipment is further complicated, the equipment cost is higher, and the practicability needs to be improved.

Disclosure of Invention

The invention aims to solve the problems and provides an efficient potential energy recovery system and a control method thereof, which not only have simple structure but also overcome the technical bias in the prior art, realize the lifting motion of the system by directly controlling a motor through a controller, simultaneously can recover potential energy in the descending process according with conditions, can avoid the speed difference problem under the condition of not needing pressure balance, reduce the cost of the system, improve the potential energy recovery efficiency and improve the practical performance of equipment.

In order to achieve the purpose, the invention adopts the following technical scheme: the system comprises an oil tank, a hydraulic oil pump/motor, a power supply assembly, a controllable single (change) valve, a hydraulic oil cylinder and a controller, and is characterized in that one side of the controller is electrically connected with the power supply assembly, the other side of the controller is electrically connected with the motor, the motor is connected with the hydraulic oil pump/motor, one side of the hydraulic oil pump/motor is communicated with the oil tank, and the other side of the hydraulic oil pump/motor is communicated with the hydraulic oil cylinder through the controllable single (change) valve;

the electric machine is switchable between motor and generator modes;

the hydraulic oil pump/motor is switchable between oil pump and motor modes;

the controller controls the lifting component connected with the hydraulic oil cylinder to do ascending motion or descending motion by controlling the motor to operate in forward rotation or reverse rotation;

when the controller controls the rotating speed of the motor to be zero or in a stop state, the lifting part is in a hovering state.

Preferably, the controller controls the speed of the ascending/descending member in ascending or descending motion by controlling the forward/reverse rotation speed of the motor.

Preferably, the controller can control the motor to realize stepless speed regulation.

Preferably, the motor can operate under the working condition of 3 quadrants:

when the working condition of the 1 st quadrant (rotating speed n is greater than 0 and torque Te is greater than 0) or the 3 rd quadrant (rotating speed n is less than 0 and torque Te is less than 0) is met, the motor running mode is a motor mode;

when the working condition of quadrant 4 (rotating speed n <0, torque Te >0) is met, the motor operation mode is a generator mode;

when n is greater than 0, the motor rotates forwards and the lifting component moves upwards;

wherein when n <0, the motor rotates reversely and the lifting member moves downward.

Preferably, the motor is a permanent magnet synchronous motor, a permanent magnet direct current brushless motor, an alternating current motor, a direct current brush motor or a switched reluctance motor.

Preferably, the electric machine is capable of controlling the mode of operation of the hydraulic oil pump/motor;

when the motor operates under the working condition of quadrant 1, the motor rotates positively to drive the hydraulic oil pump/motor to rotate positively, hydraulic oil circulates upwards, the motor is in a motor mode at the moment, and the hydraulic oil pump/motor is in an oil pump mode;

when the motor operates under the working condition of quadrant 3, the motor rotates reversely to drive the hydraulic oil pump/motor to rotate reversely, hydraulic oil flows downwards, but the motor is still in the motor mode and the hydraulic oil pump/motor is still in the oil pump mode because the torque Te is less than 0;

when the motor operates under the working condition of quadrant 4, the motor rotates reversely to drive the hydraulic oil pump/motor to rotate reversely, hydraulic oil flows downwards, but the torque Te is greater than 0, the motor is in a generator mode at the moment, and the hydraulic oil pump/motor is in a motor mode.

Preferably, the hydraulic oil pump/motor is a plunger pump or a piston pump or a gear pump or a vane pump or a screw pump.

Preferably, the controllable single (change) valve is an electric control single (change) valve, a hydraulic control single (change) valve or an electro-hydraulic single (change) valve.

Preferably, the power supply module further includes a battery electrically connected to the motor via a controller.

Preferably, the power supply module may further include a super capacitor, one side of the super capacitor is electrically connected to the motor through a controller, and the other side of the super capacitor is electrically connected to the storage battery through a power management unit inside the power supply module.

Preferably, the hydraulic oil pump/motor system further comprises an overflow valve, a connector on one side of the overflow valve is communicated with a pipeline between the controllable single (change) valve and the hydraulic oil pump/motor, and a connector on the other side of the overflow valve is communicated with the oil tank or an external recovery system.

Preferably, the hydraulic control system further comprises an explosion-proof valve, wherein the explosion-proof valve is arranged between the controllable single (change) direction valve and the hydraulic oil cylinder.

Preferably, the system further comprises a human-machine interface, wherein the human-machine interface can send control commands to the controller, and the control commands comprise lifting/hovering/descending commands of the lifting component and lifting speed commands of the lifting component.

Preferably, the human-computer interface comprises an operating handle or a knob or a key or a touch screen.

The scheme also comprises a control method of the efficient potential energy recovery system, which comprises the following steps:

when rising: the power supply assembly supplies power to the motor through the controller, the controller controls the motor to rotate forwardly according to a set rotating speed according to a lifting instruction and a speed instruction given by a human-computer interface, the motor drives the hydraulic oil pump/motor to rotate forwardly (n is greater than 0), the motor needs to output forward torque (Te is greater than 0) at the moment and operates in the 1 st quadrant, namely a motor mode, the hydraulic oil pump/motor rotates forwardly at the moment and works in an oil pump mode, and hydraulic oil is pushed and lifted to enable the hydraulic oil cylinder to extend and drive the lifting component to ascend;

through the control of the controller, the controllable one-way (change) valve is in a power-off (closing) state in the whole lifting process, namely hydraulic oil can only flow in one direction (upwards); after the motor is lifted to a preset position, the controller controls the motor to enter a stop state or a zero-speed running state;

when in suspension: the controllable single (change) valve is continuously in a power-off (closing) state under the control of the controller, and hydraulic oil between the controllable single (change) valve and the hydraulic oil cylinder cannot reversely flow back; the motor and the hydraulic oil pump/motor are in a stop state or a zero-speed running state, and hydraulic oil between the controllable single (change) direction valve and the oil tank cannot reversely flow back; in other words, in the hovering process, hydraulic oil is filled between the hydraulic oil cylinder and the oil tank all the time;

when descending: according to a descending instruction given by a human-computer interface, the controller controls the controllable one (change) directional valve to be electrified and opened, so that the hydraulic oil can reversely flow back through the controllable one (change) directional valve; meanwhile, according to a descending instruction and a speed instruction given by a human-computer interface, the controller controls the motor to act immediately and reversely rotate at a set rotating speed (n is less than 0);

when the heavy-load operation is carried out (the gravity G of the lifting component and the goods is greater than the sum f of the pipeline resistance and other equivalent resistances), the motor needs to output a forward torque (Te is greater than 0), and the motor works in a 4 th quadrant, namely a generator mode; the hydraulic oil pump/motor runs reversely at the moment and works in a motor mode; the motor becomes a generator and charges the power supply assembly;

when the motor runs under light load (the gravity G of the lifting component and goods is less than the sum f of pipeline resistance and other equivalent resistance), the motor needs to output reverse torque (Te <0), and the motor works in a 3 rd quadrant, namely a motor mode; the hydraulic oil pump/motor at this time is operated in reverse and operates in the oil pump mode.

Preferably, the controller controls the hydraulic oil pump/motor to rotate forwards (or reversely) by controlling the motor to rotate forwards (or reversely), so as to control the lifting component to ascend (or descend);

the controller controls the rotating speed of the hydraulic oil pump/motor by controlling the rotating speed of the motor, so that the displacement/flow of hydraulic oil is controlled, and the ascending speed and/or the descending speed of the lifting component are controlled.

Compared with the prior art, the invention has the advantages that:

1. the valve component (consisting of a plurality of valves) adopted in the prior art is replaced by a single controllable one-way valve, so that the structure is simpler. In addition, the system directly controls the motor through the controller to realize the lifting movement of the system, and meanwhile, potential energy recovery can be carried out in the descending process according with conditions by utilizing the working characteristics of the motor, and the phenomenon that the lifting part stalls due to large difference of oil pressure at two sides (short for speed difference problem) can be avoided without the pressure balancing process, so that a complex matched structure for balancing pressure is not required, the structure is simpler, the equipment cost is lower, and the popularization is convenient;

2. for efficiency, in the potential energy recovery process, a pressure balancing process is not needed, the controllable single (change) valve can be directly opened, then the potential energy of the hydraulic oil can be recovered and stored in an electric energy form, and the energy recovery efficiency of the equipment is higher;

3. in the prior art, in the energy recovery process, an operating handle is adopted to adjust the torque of a motor (also called motor torque), the implicit meaning of the prior art is the energy recovery process, the rotating speed of the motor is adjusted by manually adjusting (or configuring) the motor torque, and the manually configured motor torque cannot be automatically matched with the load torque, so that the speed instability and even the speed runaway are easy to occur; the invention adopts speed closed-loop control, so that the motor torque can automatically change along with the change of the load torque in the energy recovery process, so that the motor can run at a set rotating speed, in other words, the rotating speed of the motor is controllable and adjustable, the risk of speed runaway is avoided, and the equipment can run at a working point (or interval) with the highest energy conversion efficiency by controlling the rotating speed of the motor, thereby further improving the energy recovery efficiency of the equipment;

in addition, the system controls the rotating speed of the motor through the controller, so that an operator can control the lifting speed under the condition of controlling the stable lifting of the heavy object, and the speed control can be controlled in a stepless manner, so that the working efficiency of the system can be improved, and the effect of stable running of goods in the lifting process can be achieved.

4. In addition, through setting up super capacitor, rise the in-process or descend the in-process, discharge current or charging current when too big, the controller can preferentially start super capacitor and carry out work, avoids the battery to carry out work under the overload condition, has prolonged the life of battery, and in the cost constitution of this kind of equipment, the shared proportion of battery is very big, and the life of extension battery has great economic benefits.

Drawings

Figure 1 is a schematic diagram of an efficient potential energy recovery system provided by the present invention.

Fig. 2 mechanical characteristic curve of quadrant operation of the permanent magnet synchronous motor 4.

Fig. 3 is a schematic diagram of a permanent magnet synchronous motor controller.

FIG. 4 stress analysis diagram of hydraulic oil

In the figure, an oil tank 1, a hydraulic oil pump/motor 2, a motor 3, a power supply assembly 4, a controllable single (change) direction valve 5, a hydraulic oil cylinder 6, a controller 7, a storage battery 8, a super capacitor 9, an overflow valve 10, a human-computer interface 11 and an explosion-proof valve 12.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the scope of protection of the present patent.

In the description of the present invention, it should be noted that the terms "upward", "downward", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted" and "connected" are to be interpreted broadly, e.g., as being detachably connected or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be specifically understood by those of ordinary skill in the art.

In the description of the present invention, it should be noted that, the description of "when the hydraulic oil cylinder and the lifting component descend, and when the lifting component and the cargo are in light load operation (the gravity G of the lifting component and the cargo is less than the sum f of the pipeline resistance and other equivalent resistances), the motor works in the 3 rd quadrant" does not indicate or imply that the potential energy recovery system described in the present invention must satisfy the following characteristics: when the vehicle runs in a light load mode (or in a no-load mode), the gravity G of the lifting component and the goods is smaller than the sum f of pipeline resistance and other equivalent resistance. And therefore should not be construed as limiting the invention.

In the description of the embodiment of the present invention, it should be noted that the description of "the power supply assembly is composed of the storage battery and the super capacitor" does not indicate or imply that the power supply assembly described in the present invention necessarily includes the super capacitor, and in an embodiment, the power supply assembly may not include the super capacitor. And therefore should not be construed as limiting the invention.

In the description of the embodiments of the present invention, it should be noted that the terms "fixed displacement pump" and "variable displacement pump" are defined as follows: in the present invention, a pump whose flow rate/displacement can be adjusted without any other method than adjustment of the rotational speed of the prime mover is defined as a fixed displacement pump; a variable displacement pump is defined as a pump in which "the flow rate/displacement can be changed by changing the variable mechanism or the compression ratio without changing the rotational speed of the prime mover". Obviously, the pump body structure of the constant delivery pump is simpler and the cost is lower.

The present invention will be described in further detail below with reference to specific embodiments and with reference to the attached drawings.

Referring to fig. 1 to 4, the embodiment provides a high-efficiency potential energy recovery system, which includes an oil tank 1, a hydraulic oil pump/motor 2, an electric motor 3, a power supply assembly 4, a controllable single (change) direction valve 5, a hydraulic oil cylinder 6, and a controller 7, wherein one side of the controller 7 is electrically connected to the power supply assembly 4, the other side of the controller 7 is electrically connected to the electric motor 3, the electric motor 3 is connected to the hydraulic oil pump/motor 2, one side of the hydraulic oil pump/motor 2 is communicated with the oil tank 1, and the other side of the hydraulic oil pump/motor 2 is communicated with the hydraulic oil cylinder 6 through the controllable single (change) direction valve 5; the controller 7 controls the lifting component connected with the hydraulic oil cylinder 6 to do ascending motion or descending motion by controlling the motor 3 to operate positively or negatively; when the controller 7 controls the rotating speed of the motor 3 to be zero or in a stop state, the lifting part is in a hovering state.

The motor 3 can be switched between a motor mode and a generator mode, and the motor 3 can be a permanent magnet synchronous motor, a permanent magnet direct current brushless motor, an alternating current motor, a direct current brush motor or a switched reluctance motor.

As an implementable embodiment, the motor 3 is a Permanent Magnet Synchronous Motor (PMSM), and the core function of the controller 7 is Control of the PMSM, which adopts a dual closed-loop Control strategy of the rotation speed/current of the PMSM based on vector Control (FOC).

Referring to fig. 2, the electric machine 3 can operate under 3 quadrant operating conditions:

when the working condition of the 1 st quadrant (the rotating speed n is greater than 0 and the torque Te is greater than 0) or the 3 rd quadrant (the rotating speed n is less than 0 and the torque Te is less than 0) is met, the running mode of the motor 3 is a motor mode;

when the working condition of quadrant 4 (rotating speed n <0, torque Te >0) is met, the running mode of the motor 3 is a generator mode;

when n is greater than 0, the motor 3 rotates forwards and the lifting component moves upwards;

where n <0, the motor 3 reverses and the lifting member moves downward.

The hydraulic oil pump/motor 2 can be switched between an oil pump mode and a motor mode, and the hydraulic oil pump/motor 2 is a plunger pump or a piston pump or a gear pump or a vane pump or a screw pump.

Further, the electric machine 3 can control the operation mode of the hydraulic oil pump/motor 2;

when the motor 3 operates under the working condition of quadrant 1, the motor 3 rotates forwards to drive the hydraulic oil pump/motor 2 to rotate forwards, hydraulic oil flows upwards, the motor 3 is in a motor mode, and the hydraulic oil pump/motor 2 is in an oil pump mode;

when the motor 3 runs under the condition of quadrant 3, the motor 3 rotates reversely to drive the hydraulic oil pump/motor 2 to rotate reversely, hydraulic oil flows downwards, but at the moment, the motor 3 is still in a motor mode and the hydraulic oil pump/motor 2 is still in an oil pump mode because the torque Te is less than 0;

when the motor 3 operates under the condition of quadrant 4, the motor 3 rotates reversely to drive the hydraulic oil pump/motor 2 to rotate reversely, hydraulic oil flows downwards, but the torque Te is greater than 0, the motor 3 is in a generator mode at the moment, and the hydraulic oil pump/motor is in a motor mode.

The controller 7 in the system can control the speed of the ascending movement or descending movement of the lifting component by controlling the forward/backward rotation speed of the motor 3, and the controller 7 can control the motor 3 to carry out stepless speed regulation. The controller 7 is connected with a human-computer interface 11, and the human-computer interface 11 can send control instructions to the controller 7, wherein the control instructions comprise lifting/hovering/descending instructions of the lifting component and lifting speed instructions of the lifting component. Specifically, the human-computer interface 11 includes an operation handle or a knob or a key or a touch screen.

Specifically, as an embodiment, the hydraulic oil pump/motor is a fixed-displacement gear pump. The quantitative gear pump can be switched between oil pump/motor modes, and the rotating speed of the quantitative gear pump can be changed through the motor 3, so that the flow rate/displacement of the quantitative gear pump is changed, and finally the control of the lifting speed is realized.

The controllable one (change) directional valve 5 is an electric control one (change) directional valve or a hydraulic control one (change) directional valve or an electro-hydraulic one (change) directional valve, and the controllable one (change) directional valve 5 can control the hydraulic oil to flow through the valve body only in one direction (upwards) and can also control the hydraulic oil to flow through the valve body in two directions; the hydraulic oil cylinder 6 can drive the lifting component to lift when stretching.

Specifically, as an implementation manner, the controllable one (change) way valve 5 is an electromagnetic directional valve in an electrically controlled one (change) way valve, specifically, a two-position two-way normally closed electromagnetic valve. When the electromagnetic directional valve is powered off (by default), hydraulic oil can only flow in one direction (upwards) in the valve body, namely the direction of a white arrow Lf1 shown in FIG. 1; when the electromagnetic directional valve is electrified, hydraulic oil can flow in two directions in the valve body.

In addition, the system also comprises an overflow valve 10, one side interface of the overflow valve 10 is communicated with a pipeline between the controllable single (change) valve 5 and the hydraulic oil pump/motor 2, and the other side interface of the overflow valve 10 is communicated with the oil tank 1 or an external recovery system, so that the potential energy recovery system can be subjected to constant-pressure overflow, system unloading and safety protection by using the overflow valve 10.

The potential energy recovery system further comprises an explosion-proof valve 12, the explosion-proof valve 12 is arranged between the controllable single (change) direction valve 5 and the hydraulic oil cylinder 6, and when a pipeline on one side, away from the hydraulic oil cylinder 6, of the explosion-proof valve 12 bursts/leaks, the explosion-proof valve 12 can limit the speed of pipeline oil liquid, and an emergency effect of avoiding the lifting component from descending out of control is achieved.

The power supply module 4 in the present system further comprises a battery 8, and the battery 8 is electrically connected to the motor 3 through the controller 7. The power supply assembly 4 may further include a super capacitor 9, one side of the super capacitor 9 is electrically connected to the motor 3 through the controller 7, and the other side of the super capacitor 9 is electrically connected to the storage battery 8 through a power management unit inside the power supply assembly 4.

The scheme also comprises a control method of the efficient potential energy recovery system, which comprises the following steps:

when rising: the power supply assembly 4 supplies power to the motor 3 through the controller 7, according to a lifting instruction and a speed instruction given by the human-computer interface 11, the controller 7 controls the motor 3 to rotate forwardly according to a set rotating speed, the motor drives the hydraulic oil pump/motor 2 to rotate forwardly (n is greater than 0), the motor 3 at the moment needs to output a forward torque (Te is greater than 0), the motor operates in quadrant 1, namely a motor mode, the hydraulic oil pump/motor 2 at the moment rotates forwardly and operates in an oil pump mode, and hydraulic oil is pushed and lifted to enable the hydraulic oil cylinder 6 to extend and drive the lifting component to ascend;

through the control of the controller 7, the controllable one-way (change) valve 5 is in a power-off (closing) state in the whole lifting process, namely, hydraulic oil can only flow in one direction (upwards); after the motor is ascended to a preset position, the controller 7 controls the motor 3 to enter a stop state or a zero-speed running state;

when in suspension: through the control of the controller 7, the controllable one (change) directional valve 5 is continuously in a power-off (closing) state, and the hydraulic oil between the controllable one (change) directional valve 5 and the hydraulic oil cylinder 6 cannot reversely flow back; the motor 3 and the hydraulic oil pump/motor 2 are in a stop state or a zero-speed running state, and hydraulic oil between the controllable single (change) direction valve 5 and the oil tank 1 cannot reversely flow back; in other words, in the hovering process, hydraulic oil is filled between the hydraulic oil cylinder 6 and the oil tank 1 all the time;

when descending: according to a descending instruction given by the human-computer interface 11, the controller 7 controls the controllable one (change) direction valve 5 to be electrified and opened, so that hydraulic oil can reversely flow back through the controllable one (change) direction valve 5; meanwhile, according to a descending instruction and a speed instruction given by the human-computer interface 11, the controller 7 controls the motor 3 to act immediately and operates reversely according to a set rotating speed (n < 0);

(i) when the heavy-load operation is carried out (the gravity G of the lifting component and the goods is greater than the sum f of the pipeline resistance and other equivalent resistances), the motor 3 needs to output a forward torque (Te is greater than 0), and the motor 3 works in a 4 th quadrant, namely a generator mode; the hydraulic oil pump/motor 2 runs in reverse at this time and works in a motor mode; the motor 3 becomes a generator to charge the power supply assembly 4;

(ii) when the motor 3 is in light-load operation (the gravity G of the lifting component and the goods is smaller than the sum f of the pipeline resistance and other equivalent resistances), the motor 3 needs to output reverse torque (Te is less than 0), and the motor 3 works in the 3 rd quadrant, namely a motor mode; the hydraulic oil pump/motor 2 at this time is operated in reverse and operates in the oil pump mode.

Specifically, the controller 7 controls the hydraulic oil pump/motor 2 to rotate forward (or reversely) by controlling the motor 3 to rotate forward (or reversely), so as to control the lifting component to ascend (or descend); the controller 7 controls the rotation speed of the hydraulic oil pump/motor 2 by controlling the rotation speed of the electric motor 3, thereby controlling the displacement/flow rate of the hydraulic oil, and thus the ascending speed and/or the descending speed of the elevating member.

The strategy of the controller for controlling the permanent magnet synchronous motor in the scheme adopts a speed/current double closed-loop control strategy, and the basic principle is explained from 3 aspects as follows, which are respectively as follows: the system comprises a mathematical model of the permanent magnet synchronous motor, a functional block diagram of a permanent magnet synchronous motor controller and stress analysis of a potential energy recovery system under different working conditions.

The mathematical model of the permanent magnet synchronous motor consists of a voltage equation, a torque equation, a motion equation, an electromagnetic power equation and an input power equation, and specifically comprises the following steps:

the voltage equation of the permanent magnet synchronous motor in the dq axis coordinate system can be expressed as follows:

wherein u is_d、u_qAre d-axis voltage and q-axis voltage; i.e. i_d、i_qAre d-axis current and q-axis current; l is_d、L_qAre d-axis inductance and q-axis inductance; r_sIs the stator phase resistance; omega_rIs the rotor electrical angular velocity; psi_fIs a permanent magnet excitation flux linkage; p is the differential operator d/dt

The torque equation of a permanent magnet synchronous motor can be expressed as:

T_e＝n_p[ψ_fi_q+(L_d-L_q)i_di_q] (2)

wherein, T_eIs an electromagnetic torque; n is_pIs the number of pole pairs

When i is_dWhen 0, the torque equation can be simplified as:

T_e＝n_pψ_fi_q＝k_Ti_q (3)

wherein k is_TIs a torque coefficient, usually considered as a constant, electromagnetic torque T_eAnd q-axis current i_qIs in direct proportion.

The equation of motion of a permanent magnet synchronous motor can be expressed as:

wherein, T_e、T_LRespectively electromagnetic torque and motor load torque; j is the sum of the motor inertia and the load inertia; omega is the mechanical angular speed of the rotor, omega-omega_r/n_p。

According to the torque equation and the motion equation of the permanent magnet synchronous motor, when the electromagnetic torque T is obtained_eGreater than motor load torque T_LWhen the motor rotates, the rotating speed of the motor is increased; when electromagnetic torque T_eLess than motor load torque T_LWhen the motor rotates, the rotating speed of the motor is reduced; by controlling the current iq, the electromagnetic torque T can be controlled_eAnd further controlling the rotation speed of the motor to increase or decrease.

The electromagnetic power equation of a permanent magnet synchronous motor can be expressed as:

P_em＝T_eΩ＝ψ_fi_qω_ror

The input power equation of a permanent magnet synchronous motor can be expressed as:

when electromagnetic power P_em>When 0, the permanent magnet synchronous motor works in a motor mode; when electromagnetic power P_em<At 0, the permanent magnet synchronous motor operates in generator mode. When the input power P_in>When the voltage is 0, the power supply assembly (or the storage battery) discharges to the permanent magnet synchronous motor; when the input power P_in<And when the voltage is 0, the permanent magnet synchronous motor charges a power supply assembly (or a storage battery). It should be noted that the motor has stator copper lossThe motor mode of the permanent magnet synchronous motor cannot be fully equivalent to the power supplyA discharge mode of the assembly; the generator mode of a permanent magnet synchronous motor is not fully equivalent to the charging mode of a power supply assembly. Usually the stator copper loss is much smaller than the electromagnetic power, and for simplicity of analysis and description it is assumed that the stator copper loss is equal to zero, i.e. the electromagnetic power P_emEqual to the input power P of the motor_in。

The controller in the scheme adopts a permanent magnet synchronous motor speed/current double closed-loop Control strategy based on FOC (Field-Oriented Control), and the basic principle of the strategy is shown in figure 3. By combining a torque equation and a motion equation of the permanent magnet synchronous motor, the principle of the speed closed-loop control is as follows: speed instruction omega sent by human-computer interface_rRef and the actual rotational speed ω of the motor_rIs err _ ω is calculated_rPerforming speed PID control, wherein the output of the speed PID controller is a Q-axis current reference value i_qRef. When ω is_r_ref>ω_rTime, speed difference err _ ω_r>0, output of speed PID controller i_qRef will be larger, i.e. by increasing the electromagnetic torque T_eAccelerating the permanent magnet synchronous motor; when ω is_r_ref<ω_rTime, speed difference err _ ω_r<0, output of speed PID controller i_qRef will be smaller, i.e. by reducing the electromagnetic torque T_eThe permanent magnet synchronous motor is decelerated; when ω is_r_ref＝ω_rTime, speed difference err _ ω_r0, output of speed PID controller i_qRef will remain unchanged, i.e. electromagnetic torque T_eAnd the speed of the permanent magnet synchronous motor is kept unchanged. The current closed-loop control and the speed closed-loop control are similar in principle and adopt PID control. The control period of the current loop is set to 100us and the control period of the speed loop is set to 1 ms.

The speed/current double-closed-loop speed regulation control strategy of the permanent magnet synchronous motor has the advantages of good speed regulation performance, fast dynamic response (the current loop bandwidth can reach 150-350 hz), small speed fluctuation (within +/-3 percent of speed fluctuation), short transition process, small speed overshoot (within 10 percent), good speed stability and the like; compared with the traditional control strategy for controlling the flow rate of hydraulic oil by a proportional valve, the control strategy has the most remarkable advantages of fast dynamic response and good stability.

The stress analysis of the potential energy recovery system under different working conditions needs to be carried out by the following convention so as to clearly describe the stress analysis of the hydraulic oil:

the hydraulic oil is acted by 3 forces, namely gravity G, resistance F and electromagnetic force F_e(ii) a The permanent magnet synchronous motor is acted by 3 torques which are respectively motor load torques T_GMotor load torque T_fAnd electromagnetic torque T_e. Through the transmission of force and torque arm, gravity G, resistance F and electromagnetic force F_eCan be respectively equivalent to motor load torque T_GMotor load torque T_fAnd electromagnetic torque T_eAnd satisfies the following conditions:

symbol G represents the sum of the gravity of all components such as a hydraulic oil cylinder, a lifting component, goods and the like, and the positive direction of the gravity G is downward;

and f represents the sum of equivalent resistances of all components such as a hydraulic oil pipeline, an electromagnetic directional valve, a hydraulic oil pump/motor, a motor and the like. For simplicity of analysis, power losses such as motor winding resistance losses, motor controller losses, power supply component losses, etc. are also equivalent as a portion of the resistive force. When the lifting component is lifted, the direction of the resistance f is downward; when the lifting component descends, the direction of the resistance f is upward;

symbol F_eForce representing the electromagnetic torque equivalent of the machine, convention F_eThe positive direction of (2) is upward.

When the lifting component operates at a constant speed (the motor operates in a stable state), the following relation is satisfied:

when the lifting component rises at a constant speed (the motor speed n is greater than 0), the following conditions are met:

output power of motorAt the moment, the permanent magnet synchronous motor is in a motor mode; neglecting stator copper loss, the motor input power P_in＝P_em>0, the power supply assembly discharges the motor.

When the lifting component descends at a constant speed (the rotating speed n of the motor is less than 0) and the lifting component runs under light load, the following conditions are met:

output power of motorAt the moment, the permanent magnet synchronous motor is in a motor mode; neglecting stator copper loss, the motor input power P_in＝P_em>0, the power supply assembly discharges the motor.

When the lifting component descends (at a constant speed) (the rotating speed n is less than 0) and operates under heavy load, the following conditions are met:

output power of motorAt the moment, the permanent magnet synchronous motor is in a generator mode; neglecting stator copper loss, the motor input power P_in＝P_em<0, the motor charges the power supply assembly.

Furthermore, according to the electromagnetic power equation of the permanent magnet synchronous motor, the electromagnetic torque T can be obtained_ePermanent magnet synchronous motor electromagnetic power P_emProportional to the speed n, when the motor is in generator mode, the generated power can be reduced by reducing the speed of the motor, so that the storage battery can be chargedThe flow is in a reasonable range, and the service life of the storage battery is further prolonged.

Furthermore, the overcurrent protection (lower than the overflow protection value of the overflow valve) of the controller is set as first-level overload protection, the constant-pressure overflow protection of the overflow valve is set as second-level overload protection, and the overcurrent protection value is lower than the constant-pressure overflow protection value; when the goods are overweight, the controller can quickly respond to the overcurrent protection and automatically stop, so that the overload protection realized by the overflow pressure relief of the overflow valve is avoided, and the energy loss caused by long-time overflow is also avoided.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Although the terms hydraulic oil pump/motor 2, power supply assembly 4, controllable one-way valve 5, human-machine interface 11, explosion-proof valve 12, etc. are used more extensively herein, the possibility of using other terms is not excluded. These terms are used merely to more conveniently describe and explain the nature of the present invention and they are to be interpreted as any additional limitation which is not in accordance with the spirit of the present invention.