Distributed self-balancing control system and control method based on torque-rotating speed droop

Abstract

According to the distributed self-balancing control system and method based on torque-rotating speed droop, distributed motors are laid below a track, and efficient and flexible control over a vehicle and decoupling control over transverse driving force and longitudinal pressure are achieved; establishing a vehicle-machine-electricity coupling dynamic model comprising a loading vehicle, an electromechanical transmission device, a motor and a converter; the torque-rotating speed droop distributed self-balancing control of the rail type gravity energy storage motor is provided, and the rule of the influence of control parameters of a vehicle-machine-electricity coupling system on the stability of the system is analyzed. Compared with a traditional centralized control scheme, plug-and-play and dynamic balance of distributed motors in vehicle operation are achieved under the condition of no communication, and the problem that torque distribution of multiple motors is not uniform in distributed relay driving operation of a rail type gravity energy storage system is solved.

Description

Technical Field

[0001] The present invention relates to the field of multi-motor control of a track-type gravity energy storage system, and in particular to a decentralized self-balancing control system and a control method based on torque-speed droop. Background Art

[0002] In order to solve the problems of fossil energy shortage and environmental pollution, new energy power generation technology has developed rapidly in recent years. The rapid growth of installed capacity of renewable energy such as wind power and photovoltaics has increased the dual uncertainty of power generation and demand due to its volatility and intermittency, causing more serious contradictions between load and power generation. How to deal with it scientifically is a major problem facing people. At present, pumped storage is still the main means of large-capacity energy storage, but there are also constraints such as difficult site selection, high investment cost and long construction period. Whether large-scale energy storage systems can be effectively applied in new power systems depends on the research and development and breakthroughs of new energy storage technologies, and improving the energy density, power density, cycle life and rapid response capabilities of energy storage technologies.

[0003] In recent years, rail-type gravity energy storage, as a new type of energy storage technology, has the advantages of large capacity, long life, fast response speed, low cost per kilowatt-hour, and solves the problem of difficult site selection for pumped energy storage. Rail-type gravity energy storage realizes the mutual conversion between gravitational potential energy and electrical energy through solid media, among which the motor is the core device to realize energy conversion. Therefore, the design technology of multiple motors / generators and their control systems is one of the key technologies of rail-type gravity energy storage.

[0004] This patent aims at the problem of coordinated control of multiple motors in rail-mounted gravity energy storage systems, and proposes a multi-motor distributed torque autonomous balancing control method based on torque droop to improve the stability of the system. The innovations of this paper are: 1) Designing a distributed relay drive scheme for rail-mounted gravity energy storage systems based on a transverse coupling structure; 2) Analyzing the mechanism of the loading vehicle, transmission system and motor dynamics of the rail-mounted gravity energy storage system, and establishing a vehicle-machine-electric coupling model of the rail-mounted gravity energy storage system; 3) Proposing a multi-motor distributed torque self-balancing control strategy based on torque droop, which can achieve autonomous balancing of the torque of each motor without communication.

[0005] Compared with the existing technology, the main differences are as follows:

[0006] Existing rail-type gravity energy storage methods are driven by a single motor, and most of them use rope-type and chain-type structures. These structures have low transmission efficiency and have an adverse effect on the energy efficiency of the system; the use of a single motor solution makes it difficult to expand the system capacity. This patent provides a distributed relay drive solution for a rail-type gravity energy storage system based on a transverse coupling structure, and designs a multi-motor distributed self-balancing control method based on torque droop to achieve torque balance and power output stability among multiple motors. This method realizes plug-and-play and dynamic balancing of distributed motors in vehicle operation without communication, effectively improving the robust autonomous operation capability of the multi-motor coordination system and reducing the investment cost and failure rate of high-bandwidth communications.

[0007] 1. Technical comparison with patent CN118399496A "A method for grid-connecting multiple motors for synthetic gravity energy storage based on greedy algorithm"

[0008] 1. Patent CN118399496A proposes a method for connecting multiple motors to the grid based on a greedy algorithm to synthesize gravity energy storage, which is used to solve the problem that existing solutions are difficult to meet the needs of real-time and high flexibility. The greedy algorithm is used to achieve power smoothing of multiple motors for synthesizing gravity energy storage, ensuring system stability while improving system operating efficiency. However, it is impossible to ensure the speed synchronization and torque synchronization of each motor in the system. In contrast, the present invention achieves torque balance, speed synchronization and power output stability among multiple motors through torque droop control.

[0009] 2. In the patent CN118399496A, a method for connecting multiple motors to the grid based on a greedy algorithm to synthesize gravity energy storage is proposed. It is necessary to select a motor with the smallest impact on the total power demand after power changes, and then adjust its power output to meet the needs of which building, which means that the system needs a centralized controller to meet the motor power regulation. In contrast, the present invention realizes the plug-and-play and dynamic balance of distributed motors in vehicle operation without communication, which enhances the scalability of the system.

[0010] 2. Technical comparison with patent CN115664291A "A sensorless control method for gravity energy storage motor"

[0011] 1. In the sensorless control method of a gravity energy storage motor proposed in patent CN115664291A, the speed reference value in the speed outer loop control process is obtained according to the motor rotation angular velocity reference value, and cannot respond to the power grid power command. In contrast, the present invention compares the power grid power command with the Bingwang strategy, and outputs the speed reference value in the speed outer loop control process after PI transformation, which can realize the function of responding to the power grid power command.

[0012] 2. Patent CN115664291A proposes a sensorless control method for a gravity energy storage motor, which meets the power conversion requirements of the gravity energy storage system and the power system. In a multi-motor application scenario, this control method cannot guarantee torque balance and speed synchronization between the motors; in contrast, the present invention can meet the power conversion requirements of the gravity energy storage system and the power system in single or multi-motor scenarios, and achieve multi-motor torque balance in energy storage and electric states, effectively improving the robust autonomous operation capability of the multi-motor coordination system. Summary of the invention

[0013] In order to overcome the shortcomings of low transmission efficiency and easy wear of the chain transmission structure, the present invention proposes a decentralized self-balancing control system and control method based on torque-speed droop. The rail-type gravity energy storage system studied in the present invention adopts a multi-drive station / power station drive mode. Among them, the drive station / power station is arranged under the downhill track between the high and low altitude material yards, and one is arranged at a certain distance. The drive station / power station mainly includes friction wheels, a transmission system, a motor and a friction wheel clamping device. During the operation of the loading vehicle, the drive plate under the vehicle is matched and connected with the friction wheel, and the clamping device presses the friction wheel against the drive plate, and the power transmission between the vehicle and the drive station / power station is realized through pressure.

[0014] To achieve the above object, the technical solution adopted by the present invention is:

[0015] A decentralized self-balancing control system based on torque-speed droop, including a loading vehicle dynamic model, an electromechanical transmission dynamic model, and a power electronic converter model:

[0016] i) Loading vehicle dynamic model;

[0017] The wheels of the loaded vehicle are regarded as rigid bodies, and the vehicle-machine-electric coupling system dynamics models of the rail-type gravity energy storage system in the energy storage stage and the power generation stage are established, which are expressed as follows:

[0018]

[0019] F mg =mgsinα

[0020]

[0021] F mg =mgsinα

[0022]

[0023] Where, m is the total mass of the vehicle when fully loaded, v is the instantaneous speed of the vehicle, and F mg is the component of the vehicle's gravity along the slope, F fis the total resistance encountered by the vehicle during operation, g is the acceleration of gravity, α is the track slope, is the force between the ith driving station / power station and the vehicle, is the mechanical torque generated between the vehicle and the i-th drive station / power station, r m is the radius of the friction wheel, η is the transmission efficiency;

[0024] The total resistance encountered by the vehicle during operation is expressed as:

[0025] F f =F f1 +F f2

[0026]

[0027] F f2 =μ2F t

[0028]

[0029] Among them, F f1 is the sliding friction between the wheel and the track, μ1 is the dimensionless rolling friction coefficient between the wheel and the track, r is the wheel radius, F f2 is the friction force generated by the positive pressure, F t is the normal pressure between the friction wheel and the vehicle, μ2 is the dimensionless rolling friction coefficient between the friction wheel and the driving plate, and μ3 is the adhesion coefficient between the friction wheel and the driving plate;

[0030] ii) Dynamic model of electromechanical transmission device;

[0031] The transmission mechanism is regarded as an equivalent flexible mechanical element. The inertia of the flexible mechanical element itself is ignored or combined with the inertia of the motor and load, and its elastic effect is equivalent to a torsion spring. The simplified mechanical part of the flexible transmission device is equivalent to a two-mass system of friction wheel-spring-motor.

[0032] For the equivalent spring model:

[0033] T Si =K S (θ i -θ m )+B S (ω i -ω m )

[0034]

[0035] Where: m ,θ m and ω i ,θi are the rotation angular velocity and rotation angle of the friction wheel and motor in the i-th driving station / power station, respectively;

[0036] The following relationship exists between the friction wheel and the vehicle speed:

[0037] v=ω m ·r m

[0038] The torsional moment of a torsion spring is expressed as:

[0039]

[0040] in, K S , B S are the torsional moment, stiffness coefficient and damping coefficient of the spring in the i-th driving station / generating station respectively;

[0041] For the motor end, the torque balance relationship can be obtained:

[0042]

[0043] in, J i , B i are the electromagnetic torque, moment of inertia and damping coefficient of the motor in the i-th drive station / power station respectively;

[0044] The torque equation of permanent magnet synchronous motor can be expressed as:

[0045]

[0046] Among them, n p is the number of pole pairs of the permanent magnet synchronous motor, ψ is the permanent magnet flux, i sd 、i sq is the dq axis component of the stator current, L d , L q is the dq axis inductance component;

[0047] For the friction wheel end, the torque balance relationship is:

[0048]

[0049] in, J m , B m are the electromagnetic torque, moment of inertia and damping coefficient of the friction wheel in the i-th driving station / power station respectively;

[0050] The moment of inertia of the friction wheel itself is neglected, and then we get:

[0051]

[0052] iii) Power electronic converter model;

[0053] The stator winding of the permanent magnet synchronous generator adopts the motor convention, ignoring the hysteresis loss and eddy current. The phase of the permanent magnet magnetic field is consistent with the d-axis. The dynamic mathematical model of the motor-side converter in the dq synchronous rotating coordinate system is:

[0054]

[0055] Among them, L s is the stator inductance, i sd 、i sq are the stator current d-axis and q-axis fundamental components, u sd 、u sq are the d-axis and q-axis components of the stator voltage, R s is the stator resistance, ω e is the electrical angular velocity;

[0056] The dynamic mathematical model of the grid-side converter is expressed as:

[0057]

[0058] Among them, L g is the grid side inductance, i gd 、i gq are the d-axis and q-axis fundamental components of the grid current, v gd 、v gq are the d-axis and q-axis fundamental wave components of the grid voltage, u gd 、u gq is the d-axis and q-axis output voltage of the grid-side converter, R g is the grid side resistance, ω g is the grid angular frequency, C is the DC side capacitance, u dc is the DC side voltage, i dcg and are the DC side currents of the grid-side converter and the i-th motor-side converter respectively.

[0059] The present invention provides a control method for a distributed self-balancing control system based on torque-speed droop, including multi-motor torque-speed droop balancing control, motor vector control, and grid-side converter vector control:

[0060] i) Multi-motor torque-speed droop balancing control;

[0061] The motor speed is fed back based on the collected local motor torque information. It also has the speed synchronization capability and can ensure the torque distribution between motors evenly without communication. Taking the i-th motor as an example, the specific description is as follows:

[0062]

[0063] in, is the motor reference angular velocity, ω * is the given motor angular velocity, n is T e -ω droop coefficient, T e * is the rated torque of the motor; v max and v min are the maximum and minimum values ​​allowed for vehicle speed, ω * It is expressed as:

[0064]

[0065] in, are the proportional integral coefficients of the power link, P * is the grid active power command, P is the grid-connected power; there are two types of motors, It is in electric state, suitable for upward process; In the power generation state, the motors are in the downlink process, and the control laws of the two motors are unified.

[0066] ii) Motor vector control;

[0067] The motor side control adopts i d =0 vector control method, including speed control and stator current control; the motor control model is expressed as:

[0068]

[0069] Among them, k np , k ni is the proportional integral control coefficient of the speed outer loop, k p , k i is the proportional-integral control coefficient of the inner current loop;

[0070] iii) Grid-side converter control;

[0071] The grid-side control adopts a vector control method based on grid voltage orientation, including DC voltage control and output current control; the grid-side converter control model is expressed as:

[0072]

[0073] Among them, k up , k ui is the proportional-integral control coefficient of the DC voltage control loop, k p , k i is the proportional-integral control coefficient of the inner current loop.

[0074] When the system is in steady state, due to the zero steady-state error effect of proportional integral control in the system control model, the relationship between the angular velocity of each motor and the vehicle speed in steady state is expressed as:

[0075]

[0076] That is, each motor has the same reference speed in steady state Then, from the droop formula we can get:

[0077]

[0078] Therefore, the proposed droop control method realizes the angular velocity synchronization of multiple motors and torque balance control without communication;

[0079] A small signal state space model of the system is established for the motor and vehicle dynamics:

[0080]

[0081] Among them, the state variable x and the state matrix A are as follows;

[0082] The state variable x in the small signal state space model is:

[0083]

[0084]

[0085] in:

[0086]

[0087]

[0088] By analyzing the trend of the dominant poles of the state matrix with parameter changes, the influence of control parameters or physical parameters on the system stability and dynamic response is obtained.

[0089] The present invention discloses a distributed self-balancing control system and control method based on torque-speed droop, which is used to solve the problem of uneven torque distribution of multiple motors in the distributed relay drive operation of the rail-type gravity energy storage system. First, a distributed relay drive electromechanical scheme for the rail-type gravity energy storage system based on the lateral coupling structure is designed, and the distributed motor is laid under the track to achieve efficient and flexible vehicles and decoupled control of lateral driving force and longitudinal pressure; secondly, a vehicle-machine-electric coupling dynamics model including loading vehicles, electromechanical transmission devices, motors and converters is established; furthermore, a torque-speed droop distributed self-balancing control of the rail-type gravity energy storage distributed drive station is proposed, and the influence of the control parameters of the vehicle-machine-electric coupling system on the system stability is analyzed. Compared with the traditional centralized control scheme, the present invention realizes the plug-and-play and dynamic balancing of distributed motors in vehicle operation without communication, effectively improves the robust autonomous operation capability of the multi-motor coordination system, and reduces the investment cost and failure rate of high-bandwidth communication. Finally, the feasibility and effectiveness of the present invention are verified by hardware-in-the-loop experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 The distributed relay drive scheme of the rail-type gravity energy storage system based on the transverse coupling structure is shown;

[0091] Figure 2 The transverse coupling motor drive station is shown: (a). Structural diagram; (b). Force diagram;

[0092] Figure 3 The overall electrical design of the rail-type gravity energy storage system is shown;

[0093] Figure 4 The physical structure and control principle diagram of the vehicle-machine-electric coupling of the rail-type gravity energy storage system are shown;

[0094] Figure 5 An equivalent schematic diagram of a flexible transmission device is shown;

[0095] Figure 6 Shows T e -ω droop characteristic curve;

[0096] Figure 7 The characteristic root loci are shown: (a). Droop coefficient; (b). Speed ​​loop proportional gain; (c). Speed ​​loop integral gain;

[0097] Figure 8 The results of the hardware-in-the-loop experiment in the energy storage stage are shown: (a). Motor torque; (b). Motor speed and vehicle speed; (c). Grid-connected current and DC bus voltage;

[0098] Fig. 9The results of the hardware-in-the-loop experiment in the power generation stage are shown: (a). Motor torque; (b). Motor speed and vehicle speed; (c). Grid-connected current and DC bus voltage. DETAILED DESCRIPTION

[0099] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0100] In order to overcome the shortcomings of low transmission efficiency and easy wear of the chain-type transmission structure, the rail-type gravity energy storage system studied in the present invention adopts a multi-drive station / power station drive mode. Among them, the drive station / power station is arranged under the downhill track between the high and low altitude material yards, and one is arranged at a certain distance. The drive station / power station mainly includes friction wheels, a transmission system, a motor and a friction wheel clamping device. During the operation of the loading vehicle, the drive plate under the vehicle is matched and connected with the friction wheel, and the clamping device presses the friction wheel against the drive plate, and the power transmission between the vehicle and the drive station / power station is realized through pressure.

[0101] The present invention provides a distributed relay drive solution for a track-type gravity energy storage system based on a transverse coupling structure. Figure 1 As shown, the transverse coupling motor drive station: (a). Structural diagram; (b). Force diagram as shown Figure 2 As shown in the figure, the overall electrical design of the rail-type gravity energy storage system is as follows Figure 3 As shown in the figure, the physical structure and control principle diagram of the vehicle-machine-electric coupling of the rail-type gravity energy storage system is as follows Figure 4 As shown, the equivalent schematic diagram of the flexible transmission device is as follows Figure 5 As shown, T e -ω droop characteristic curve is as follows Figure 6 shown.

[0102] In view of the high load and low speed characteristics of the rail-type gravity energy storage system, a low-speed, high-torque permanent magnet synchronous motor is selected. The number of power stations and drive stations in the overall electrical scheme of the system is a. In the design scheme, the load-carrying vehicle contacts three drive stations / power stations at the same time. At time T1, it is driven by #1, #2, and #3 drive stations / power stations. After a period of time, it reaches time T2, at which time it is driven by #4, #5, and #6 drive stations / power stations. The number of vehicles running simultaneously in the system determines the size of the system power and also determines the number of grid-side converters.

[0103] The vehicle-machine-electric coupling physical object model of the rail-type gravity energy storage system includes a loading vehicle dynamic model, an electromechanical transmission device dynamic model, and a power electronic converter model.

[0104] i) Loading vehicle dynamic model

[0105] The wheels of the loaded vehicle are regarded as rigid bodies, and the vehicle-machine-electric coupling system dynamics models of the rail-type gravity energy storage system in the energy storage stage and the power generation stage are established, which are expressed as follows:

[0106]

[0107] F mg =mgsinα

[0108]

[0109]

[0110] F mg =mgsinα

[0111]

[0112] Where, m is the total mass of the vehicle when fully loaded, v is the instantaneous speed of the vehicle, and F mg is the component of the vehicle's gravity along the slope, F f is the total resistance encountered by the vehicle during operation, g is the acceleration of gravity, α is the track slope, is the force between the ith driving station / power station and the vehicle, is the mechanical torque generated between the vehicle and the i-th drive station / power station, r m is the radius of the friction wheel, η is the transmission efficiency;

[0113] The total resistance encountered by the vehicle during operation can be expressed as:

[0114] F f =F f1 +F f2

[0115]

[0116] F f2 =μ2F t

[0117]

[0118] Among them, F f1 is the sliding friction between the wheel and the track, μ1 is the dimensionless rolling friction coefficient between the wheel and the track, r is the wheel radius, F f2 is the friction force generated by the positive pressure, F t is the normal pressure between the friction wheel and the vehicle, μ2 is the dimensionless rolling friction coefficient between the friction wheel and the driving plate, and μ3 is the adhesion coefficient between the friction wheel and the driving plate;

[0119] ii) Dynamic model of electromechanical transmission device

[0120] When modeling a flexible transmission device, the transmission mechanism is usually considered as an equivalent flexible mechanical element for the convenience of analysis. The inertia of the flexible mechanical element itself is relatively small compared to the motor rotor and the load, so it is often ignored or combined with the motor and load inertia, and its elastic effect is equivalent to a torsion spring. The simplified mechanical part of the flexible transmission device can be equivalent to a two-mass system of friction wheel-spring-motor.

[0121] For the equivalent spring model:

[0122] T Si =K S (θ i -θ m )+B S (ω i -ω m )

[0123]

[0124] Where: m ,θ m and ω i ,θ i are the rotation angular velocity and rotation angle of the friction wheel and motor in the i-th driving station / power station, respectively;

[0125] The following relationship exists between the friction wheel and the vehicle speed:

[0126] v=ω m ·r m

[0127] The torsional moment of a torsion spring can be expressed as:

[0128]

[0129] in, K S , B S are the torsional moment, stiffness coefficient and damping coefficient of the spring in the i-th driving station / generating station respectively;

[0130] For the motor end, the torque balance relationship can be obtained:

[0131]

[0132] in, J i , B i are the electromagnetic torque, moment of inertia and damping coefficient of the motor in the i-th drive station / power station respectively;

[0133] The torque equation of permanent magnet synchronous motor can be expressed as:

[0134]

[0135] Among them, n p is the number of pole pairs of the permanent magnet synchronous motor, ψ is the permanent magnet flux, i sd 、i sq is the dq axis component of the stator current, L d , L q is the dq axis inductance component;

[0136] For the friction wheel end, the torque balance relationship can be obtained:

[0137]

[0138] in, J m , B m are the electromagnetic torque, moment of inertia and damping coefficient of the friction wheel in the i-th driving station / power station respectively;

[0139] Compared with the motor rotor, the friction wheel's own moment of inertia is very small and can be ignored, which leads to:

[0140]

[0141] iii) Power Electronic Converter Model

[0142] The stator winding of the permanent magnet synchronous generator adopts the motor convention, ignoring the hysteresis loss and eddy current. The phase of the permanent magnet magnetic field is consistent with the d-axis. The dynamic mathematical model of the motor-side converter in the dq synchronous rotating coordinate system is:

[0143]

[0144] Among them, L s is the stator inductance, i sd 、i sq are the stator current d-axis and q-axis fundamental components, u sd 、u sq are the d-axis and q-axis components of the stator voltage, R s is the stator resistance, ω e is the electrical angular velocity;

[0145] The dynamic mathematical model of the grid-side converter can be expressed as:

[0146]

[0147] Among them, L g is the grid side inductance, i gd 、i gq are the d-axis and q-axis fundamental components of the grid current, v gd 、vgq are the d-axis and q-axis fundamental wave components of the grid voltage, u gd 、u gq is the d-axis and q-axis output voltage of the grid-side converter, R g is the grid side resistance, ω g is the grid angular frequency, C is the DC side capacitance, u dc is the DC side voltage, i dcg and are the DC side currents of the grid-side converter and the i-th motor-side converter respectively.

[0148] The multi-motor system distributed self-balancing control method disclosed in the present invention includes multi-motor torque-speed droop balancing control, motor vector control, and grid-side converter vector control:

[0149] i) Multi-motor torque-speed droop balance control

[0150] It can be seen from the working characteristics of the rail-type gravity energy storage system studied by the present invention that the rotor speed of each motor is coupled to the vehicle running speed through the transmission system to synchronize, so the motor speed can be regarded as a global variable of the rail-type gravity energy storage system. Analogous to the inverter power droop control, a unified torque-speed droop control is proposed to solve the torque balance problem. Its working principle is to feedback the motor speed based on the collected local motor torque information. At the same time, it can also have the speed synchronization capability, and can ensure the torque is evenly distributed among the motors in the absence of communication. Taking the i-th motor as an example, the specific description is as follows:

[0151]

[0152] in, is the motor reference angular velocity, ω * is the given motor angular velocity, n is T e -ω droop coefficient, T e * is the rated torque of the motor; v max and v min are the maximum and minimum values ​​allowed for the vehicle speed. * It can be expressed as:

[0153]

[0154] in, are the proportional integral coefficients of the power link, P * is the grid active power command, P is the grid-connected power;

[0155] It is worth mentioning that there are two types of motors in the scheme shown in the figure. It is in electric state, suitable for upward process; It is in the power generation state and works in the downlink process. The control laws of the two motors are unified;

[0156] ii) Motor vector control

[0157] The motor side control adopts i d =0 vector control method, including speed control and stator current control; the motor control model can be expressed as:

[0158]

[0159] Among them, k np , k ni is the proportional integral control coefficient of the speed outer loop, k p , k i is the proportional-integral control coefficient of the inner current loop;

[0160] iii) Grid-side converter vector control

[0161] The grid-side control adopts a vector control method based on grid voltage orientation, including DC voltage control and output current control;

[0162] The grid-side converter control model can be expressed as:

[0163]

[0164] Among them, k up , k ui is the proportional-integral control coefficient of the DC voltage control loop, k p , k i is the proportional-integral control coefficient of the inner current loop.

[0165] When the system is in steady state, due to the zero steady-state error effect of proportional integral control in the system control model, the relationship between the angular velocity of each motor and the vehicle speed in steady state can be expressed as:

[0166]

[0167] That is, each motor has the same reference speed in steady state Then, from the droop formula we can get:

[0168]

[0169] Therefore, the proposed droop control method realizes the angular velocity synchronization of multiple motors and torque balance control without communication;

[0170] A small signal state space model of the system is established for the motor and vehicle dynamics:

[0171]

[0172] Among them, the state variable x and the state matrix A are as follows;

[0173] The state variable x in the small signal state space model is:

[0174]

[0175] in:

[0176]

[0177]

[0178] By analyzing the trend of the dominant poles of the state matrix with parameter changes, the influence of control parameters or physical parameters on the system stability and dynamic response is obtained.

[0179] Brief description of the experimental waveform.

[0180] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments, but is not intended to limit the present invention.

[0181] Figure 2 (a) is the internal structure diagram of the drive station / power station, which mainly includes friction wheels, transmission system, motor and friction wheel clamping device. During the operation of the loaded vehicle, the drive plate under the vehicle is matched with the friction wheel, and the clamping device presses the friction wheel against the drive plate, realizing the power transmission between the vehicle and the drive station / power station through pressure. The force diagram is shown in the figure. Figure 2 As shown in (a), F t 、F m perpendicular to the supporting force;

[0182] Figure 3 This is the overall electrical scheme of the system, where the number of power stations and drive stations is a. In the design scheme, the load-carrying vehicle contacts three drive stations / power stations at the same time. At time T1, it is driven by #1, #2, and #3 drive stations / power stations. After a period of time, it reaches time T2, at which time it is driven by #4, #5, and #6 drive stations / power stations. The number of vehicles running simultaneously in the system determines the size of the system power and also determines the number of grid-side converters;

[0183] Figure 4 The physical structure and control principle diagram of the system. The physical structure of the coupled system includes five parts: power grid, DC bus, motor, transmission device and loading vehicle. The system control algorithm includes motor side converter control and grid side converter control, which mainly includes five parts: 1) motor torque-speed droop control; 2) motor speed control; 3) motor stator current control; 4) DC side voltage control; 5) grid current control;

[0184] Figure 7(a) shows the change of the dominant eigenvalue when the droop coefficient n changes: as n increases, the system characteristic root gradually moves away from the imaginary axis, which means that the system dynamics has a faster decay rate; the influence of the PI control parameters in the motor speed PI controller on the system characteristic root is shown in Figure 7 .(b) and (c) show: It can be seen that a too small proportional coefficient will cause the system characteristic root to be close to the imaginary axis, deteriorating the system stability, while a too large proportional coefficient will cause the system characteristic root to be far away from the real axis, reducing the system damping and causing the system dynamic oscillation. As the integral coefficient increases, the dominant conjugate characteristic root will move away from the real axis and close to the imaginary axis, reducing the system damping and causing potential instability.

[0185] Figure 8 The figure is the result of the hardware-in-the-loop experiment in the energy storage stage of the system. At this time, the motor is working in the electric state. Figure (a) shows the experimental results of the torque of each motor. When motors #2 and #3 are cut in, it can be observed that under the proposed control strategy, the torque of each motor reaches a balanced state after a transient process of about 10s, indicating that the proposed torque droop control can achieve multi-motor torque balance in the electric state. Compared with the cut-in process of motor #3, motor #2 will produce a large torque fluctuation when it is cut in. Therefore, it can be seen from the torque droop control characteristics that a large speed fluctuation of about 32rpm will be generated, and a vehicle speed fluctuation of about 0.4m / s will be generated at the same time. Due to the droop characteristics, the motor speed is always less than the given speed. The experimental results of motor speed and vehicle speed are shown in Figure (b). Figure (c) shows the experimental results of grid-connected current and DC bus voltage. It can be observed that the adopted control strategy ensures the stability of grid-connected current and DC side voltage when the motor is cut in.

[0186] Fig. 9 The hardware-in-the-loop experiment results of the system power generation stage are shown in Figures (a), (b), and (c) respectively, showing the motor torque, motor speed and vehicle speed, grid-connected current and DC voltage experimental results. At this time, the motor is working in the power generation state. It can be seen that in the power generation state, the proposed control strategy can also achieve torque balance of each motor. Due to the droop characteristics, the motor speed is slightly higher than the given speed in the power generation state.

[0187] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A decentralized self-balancing control system based on torque-speed droop, characterized in that: Includes loading vehicle dynamics model, electromechanical transmission dynamics model and power electronic converter model: i) Loading vehicle dynamic model; The wheels of the loaded vehicle are regarded as rigid bodies, and the vehicle-machine-electric coupling system dynamics models of the rail-type gravity energy storage system in the energy storage stage and the power generation stage are established, which are expressed as follows: F mg =mgsinα F mg =mgsinα Where, m is the total mass of the vehicle when fully loaded, v is the instantaneous speed of the vehicle, and F mg is the component of the vehicle's gravity along the slope, F f is the total resistance encountered by the vehicle during operation, g is the acceleration of gravity, α is the track slope, is the force between the ith driving station / power station and the vehicle, is the mechanical torque generated between the vehicle and the i-th drive station / power station, r m is the radius of the friction wheel, η is the transmission efficiency; The total resistance encountered by the vehicle during operation is expressed as: F f =F f1 +F f2 F f2 =μ2F t Among them, F f1 is the sliding friction between the wheel and the track, μ1 is the dimensionless rolling friction coefficient between the wheel and the track, r is the wheel radius, F f2 is the friction force generated by the positive pressure, F t is the normal pressure between the friction wheel and the vehicle, μ2 is the dimensionless rolling friction coefficient between the friction wheel and the driving plate, and μ3 is the adhesion coefficient between the friction wheel and the driving plate; ii) Dynamic model of electromechanical transmission device; The transmission mechanism is regarded as an equivalent flexible mechanical element. The inertia of the flexible mechanical element itself is ignored or combined with the inertia of the motor and load, and its elastic effect is equivalent to a torsion spring. The simplified mechanical part of the flexible transmission device is equivalent to a two-mass system of friction wheel-spring-motor. For the equivalent spring model: T Si =K S (i i -θ m )+B S (oh i -oh m ) Where: m ,θ m and ω i ,θ i are the rotation angular velocity and rotation angle of the friction wheel and motor in the i-th driving station / power station, respectively; The following relationship exists between the friction wheel and the vehicle speed: v=ω m ·r m The torsional moment of a torsion spring is expressed as: in, K S , B S are the torsional moment, stiffness coefficient and damping coefficient of the spring in the i-th drive station / power station respectively; for the motor end, the torque balance relationship can be obtained: in, J i , B i are the electromagnetic torque, moment of inertia and damping coefficient of the motor in the i-th drive station / power station respectively; The torque equation of permanent magnet synchronous motor can be expressed as: Among them, n p is the number of pole pairs of the permanent magnet synchronous motor, ψ is the permanent magnet flux, i sd 、i sq is the dq axis component of the stator current, L d , L q is the dq axis inductance component; For the friction wheel end, the torque balance relationship is: in, J m , B m are the electromagnetic torque, moment of inertia and damping coefficient of the friction wheel in the i-th drive station / power station respectively; the moment of inertia of the friction wheel itself is ignored, and then we get: iii) Power electronic converter model; The stator winding of the permanent magnet synchronous generator adopts the motor convention, ignoring the hysteresis loss and eddy current. The phase of the permanent magnet magnetic field is consistent with the d-axis. The dynamic mathematical model of the motor-side converter in the dq synchronous rotating coordinate system is: Among them, L s is the stator inductance, i sd 、i sq are the fundamental components of the stator current d-axis and q-axis, u sd 、u sq are the d-axis and q-axis components of the stator voltage, R s is the stator resistance, ω e is the electrical angular velocity; The dynamic mathematical model of the grid-side converter is expressed as: Among them, L g is the grid side inductance, i gd 、i gq are the d-axis and q-axis fundamental components of the grid current, v gd 、v gq are the d-axis and q-axis fundamental wave components of the grid voltage, u gd 、u gq is the d-axis and q-axis output voltage of the grid-side converter, R g is the grid side resistance, ω g is the grid angular frequency, C is the DC side capacitance, u dc is the DC side voltage, i dcg and are the DC side currents of the grid-side converter and the i-th motor-side converter respectively.

2. The control method of the decentralized self-balancing control system based on torque-speed droop according to claim 1, characterized in that: Including multi-motor torque-speed droop balance control, motor vector control, grid-side converter vector control: i) Multi-motor torque-speed droop balance control; The motor speed is fed back based on the collected local motor torque information. It also has the speed synchronization capability and can ensure the torque distribution between motors evenly without communication. Taking the i-th motor as an example, the specific description is as follows: in, is the motor reference angular velocity, ω * is the given motor angular velocity, n is T e- Droop coefficient of ω, T e * is the rated torque of the motor; v max and v min are the maximum and minimum values ​​allowed for vehicle speed, ω * It is expressed as: in, are the proportional integral coefficients of the power link, P * is the grid active power command, P is the grid-connected power; There are two types of motors, for T e * >0 is the electric state, which is applicable to the upward process; T e * <0 is the power generation state, working in the downward process, and the control laws of the two motors are unified; ii) Motor vector control; The motor side control adopts i d =0 vector control method, including speed control and stator current control; the motor control model is expressed as: Among them, k np , k ni is the proportional integral control coefficient of the speed outer loop, k p , k i is the proportional-integral control coefficient of the inner current loop; iii) Grid-side converter control; The grid-side control adopts a vector control method based on grid voltage orientation, including DC voltage control and output current control; The grid-side converter control model is expressed as: Among them, k up , k ui is the proportional-integral control coefficient of the DC voltage control loop, k p , k i is the proportional-integral control coefficient of the inner current loop.

3. The control method of the decentralized self-balancing control system based on torque-speed droop according to claim 2, characterized in that: When the system is in steady state, due to the zero steady-state error effect of proportional integral control in the system control model, the relationship between the angular velocity of each motor and the vehicle speed in steady state is expressed as: That is, each motor has the same reference speed in steady state Then, from the droop formula we can get: Therefore, the proposed droop control method realizes the angular velocity synchronization of multiple motors and torque balance control without communication; A small signal state space model of the system is established for the motor and vehicle dynamics: Among them, the state variable x and the state matrix A are as follows; The state variable x in the small signal state space model is: in: By analyzing the trend of the dominant poles of the state matrix with parameter changes, the influence of control parameters or physical parameters on the system stability and dynamic response is obtained.

Images