Control method of new type bidirectional energy conversion device of flywheel energy storage considering device loss

Abstract

The application discloses a flywheel energy storage new-type bidirectional energy conversion device control method in the flywheel energy storage technical field, which considers device loss, and comprises a current planning control method considering motor loss and a 180-degree conduction three-phase natural commutation control method. The control method considers torque constraints during motor operation of the device, the current planning control method is proposed under the condition of not changing the motor operation performance of the device, the motor loss during the working process of the device is reduced, the operation loss of the device is reduced, and the operation performance efficiency of the device is improved; and the 180-degree conduction three-phase natural commutation control is introduced, the switching frequency of the device power device is sufficiently reduced under the condition of slightly changing the current planning control winding current waveform, and the switching loss of the device power device is effectively reduced without significantly increasing the motor copper loss and winding current harmonics.

Description

Technical Field

[0001] This invention belongs to the field of flywheel energy storage technology, specifically relating to a control method for a novel bidirectional energy conversion device for flywheel energy storage that takes into account device losses. Background Technology

[0002] Flywheel energy storage technology boasts advantages such as fast response, high frequency, high efficiency, long lifespan, and environmental friendliness, making it a crucial direction for the development of electric energy storage technology in my country. Modern flywheel energy storage technologies are typically categorized into low-speed flywheels and high-speed flywheels, limited by shaft speeds of 6000–10000 r / min. The advantages of high-speed flywheel energy storage technology lie in its high energy density and high power density. A typical high-speed flywheel energy storage device mainly includes a controller, a bidirectional energy conversion device, a high-speed flywheel motor, a bearing system, a flywheel rotor, and a vacuum chamber.

[0003] The bidirectional energy conversion device is an important component of the high-speed flywheel energy storage device. The performance of the bidirectional energy conversion device directly affects the performance and reliability of the high-speed flywheel energy storage device. Losses and efficiency are important performance indicators for evaluating bidirectional energy conversion devices. The operating efficiency of the device is closely related to the losses that exist during operation. The losses that exist during the operation of the device mainly include power device losses, motor stator losses, and motor rotor eddy current losses.

[0004] Power device losses generally refer to the switching and conduction losses generated by power switching devices during operation. Switching losses are the losses caused by voltage and current tailing effects at the moment of device turn-on and turn-off. Conduction losses are the losses generated during device conduction, generally related to the voltage drop and current during conduction. Switching losses increase with increasing switching frequency, while conduction losses are less affected by frequency variations. Motor stator losses mainly include stator copper losses and stator iron losses. Stator copper losses are the losses caused by heating due to winding resistance when current passes through the stator windings. Stator iron losses are the losses caused by the eddy current effect in the stator core. Motor rotor eddy current losses are the losses caused by the eddy current effect in the rotor core; compared to stator losses, rotor eddy current losses are usually very small.

[0005] The losses during the operation of a bidirectional energy conversion device affect the operating efficiency of the energy storage system, and the magnitude of these losses is crucial to the device's efficient operation. Reducing the operating losses of bidirectional energy conversion devices to achieve high-efficiency energy conversion control is an important research topic in flywheel energy storage technology. Minimizing these losses during operation is of great significance for improving the operating efficiency of bidirectional energy conversion devices. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a novel bidirectional energy conversion device control method for flywheel energy storage that takes into account device losses, so as to solve the problems mentioned in the background art.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A control method for a novel bidirectional energy conversion device for flywheel energy storage that considers device losses is provided. The control method includes a current planning control method that considers motor losses and a three-three natural commutation control method with 180° conduction.

[0009] Preferably, the current planning and control method considering motor losses includes the following steps:

[0010] Based on the output torque of the square wave permanent magnet motor, establish torque constraints for motor loss optimization;

[0011] Based on the relationship between stator copper loss and winding current of the motor, a three-phase current planning and control expression with the motor back electromotive force as the variable is established using the derivative extremum method.

[0012] Preferably, the output torque equation of the square wave permanent magnet motor is as follows:

[0013]

[0014] In the formula, T em For the electromagnetic torque of the motor, ω m Let i be the mechanical angular velocity of the motor. a i b i c e represents the three-phase winding current of the motor. a e b e c The back electromotive force of the three-phase windings of the motor;

[0015] The constraint equation for the motor output torque is as follows:

[0016]

[0017] In the formula, E is the amplitude of the motor back electromotive force, and I is the amplitude of the motor winding current.

[0018] Preferably, the motor stator copper loss equation is expressed as follows:

[0019]

[0020] In the formula, P cu For the stator copper loss of the motor, R e i is the resistance of the motor phase winding. a i b This refers to the stator winding current of the motor.

[0021] The current planning control expression is as follows:

[0022]

[0023] Preferably, the 180° conduction three-three natural commutation control method includes the following steps:

[0024] Based on the schematic diagram of the operating current path under the three-three natural commutation control topology, the voltage-current relationship of the operating current loop is obtained;

[0025] Based on the relationship between the device's operating current and the winding circuit voltage and current, the control formula for the device's operating current is obtained;

[0026] By using the operating current control formula of the device, the duty cycle of the operating current control of the power device in the front-end current chopper topology is obtained to achieve the operating current control of the device.

[0027] Preferably, the voltage-current relationship of the operating current loop is as follows:

[0028]

[0029] In the formula, α is the operating duty cycle of the switching device T7 in the positive chopper mode, and U dc L1 is the DC power supply voltage for the device, U is the DC bus inductance of the device, and L is the voltage at the right end of the DC bus inductance. e This refers to the inductance of the motor phase winding.

[0030] Preferably, the operating current control formula of the device is as follows:

[0031]

[0032] In the formula, i dc This is the operating current of the device's DC bus.

[0033] Preferably, the current control duty cycle is expressed as follows:

[0034]

[0035] The beneficial effects of this invention are:

[0036] 1. The control method of the present invention takes into account the torque constraint of the device motor during operation. The current planning control method proposed without changing the operating performance of the device motor reduces the motor loss during the device operation, reduces the device operating loss, and improves the device operating performance efficiency.

[0037] 2. The control method of the present invention also introduces a 180° conduction three-three natural commutation control, which, under the condition of slightly changing the current planning control winding current waveform, significantly reduces the switching frequency of the device power devices, and effectively reduces the switching losses of the device power devices without significantly increasing the copper loss of the motor and the harmonics of the winding current. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the topology of the novel bidirectional energy conversion device for flywheel energy storage in an embodiment of the present invention;

[0040] Figure 2 This is a waveform diagram of the phase current of the motor winding of the novel bidirectional energy conversion device for flywheel energy storage in this embodiment of the invention when the device adopts 120° conduction natural commutation control.

[0041] Figure 3 This is a waveform diagram of the phase current of the motor winding of the novel bidirectional energy conversion device for flywheel energy storage in this embodiment of the invention when current planning control considering motor losses is adopted;

[0042] Figure 4 This is a schematic diagram comparing the stator copper loss of the motor during the operation of the novel bidirectional energy conversion device for flywheel energy storage in this embodiment of the invention when the 120° conduction natural commutation control method and the current planning control method considering motor losses are respectively adopted.

[0043] Figure 5 This is a schematic diagram of the Fourier analysis of the phase current waveform of the motor winding of the novel bidirectional energy conversion device for flywheel energy storage in this embodiment of the invention when the 120° conduction natural commutation control method is adopted.

[0044] Figure 6 This is a schematic diagram of the Fourier analysis of the phase current waveform of the motor winding of the novel bidirectional energy conversion device for flywheel energy storage in an embodiment of the present invention when the current planning control method considering motor losses is adopted.

[0045] Figure 7 This is a schematic diagram of the topological working current path of the novel bidirectional energy conversion device for flywheel energy storage in this embodiment of the invention under the three-three natural commutation control method with 180° conduction.

[0046] Figure 8This is a schematic diagram of the motor winding current waveform of the device after introducing the 180° conduction three-three natural commutation control method into the current planning control method considering motor losses in the embodiments of the present invention.

[0047] Figure 9 This is a schematic diagram of the switching control signal waveforms of the three-phase bridge arm power devices in the subsequent full-bridge topology of the device before the introduction of the 180° conduction three-three natural commutation control method in the current planning control method considering motor losses in this embodiment of the invention.

[0048] Figure 10 This is a schematic diagram of the switching control signal waveforms of the three-phase bridge arm power devices in the subsequent full-bridge topology after the current planning control method considering motor losses in this embodiment of the invention introduces the 180° conduction three-three natural commutation control method.

[0049] Figure 11 This is a simulation curve of the motor loss of the novel bidirectional energy conversion device for flywheel energy storage under three control methods in the embodiment of the present invention during the energy conversion control process;

[0050] Figure 12 This is a simulation curve of device loss variation during the energy conversion process under three control methods in the embodiments of the present invention. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Please see Figure 1 As shown, this embodiment provides a control method for a novel bidirectional energy conversion device of flywheel energy storage that considers device losses. The novel bidirectional energy conversion device of flywheel energy storage is a two-stage full-bridge topology (DC / DC+full-bridge), including a front-stage current chopper topology, a rear-stage two-level full-bridge topology and a capacitor feedback topology. The capacitor feedback topology is connected between the front and rear topologies. The device has a relatively simple device topology structure, and the device operating current is controlled by the front-stage current chopper topology.

[0053] The specific structure of the flywheel energy storage novel bidirectional energy conversion device topology is as follows:

[0054] The device's front-end current chopper topology consists of power switching devices T7 and T8, capacitor C1, and inductor L1. The topology inserts inductor L1 in series with the DC bus of the device. During the control of the device's operating current, the inductor is inserted into the equivalent motor winding circuit, which improves the problem of low resistance inductance in the high-speed flywheel motor drive control to a certain extent. Therefore, in the device's charge and discharge cycle, good device operating current control can be achieved through front-end current chopper control, suppressing operating current ripple and pulsation.

[0055] The full-bridge topology of the device consists of power switching devices T1, T2, T3, T4, T5, T6 and power diodes D1, D2, D3, D4, D5, D6. The topology uses external power diodes to improve the commutation freewheeling path of the bridge arm and the corresponding operating current measurement scheme. During the operation of the device, the operating current value of the device is obtained by combining the current measurement values ​​at the full-bridge topology m1 and the external commutation freewheeling topology m2, and the change of the device operating current is fed back in real time.

[0056] The capacitor feedback topology of the device consists of power switching device T9 and power diode D. 10 With D 11 The system consists of capacitor C2 and inductor L2. The topology is connected to the DC power supply through inductor L2 and through power diode D. 10 Connected between the preceding and following topologies; the existence of the capacitor feedback topology ensures that the freewheeling path of the DC bus inductor L1 during device operation is achieved through the capacitor feedback circuit. The voltage control of capacitor C2 is achieved through the switching control of power device T9, and further controlled by power diode D. 10 To achieve DC clamping voltage control when the bus inductor is freewheeling.

[0057] The control method for the novel bidirectional energy conversion device of flywheel energy storage that takes into account device losses includes a current planning control method that considers motor losses, and introduces a three-three natural commutation control method with 180° conduction.

[0058] The current planning and control method that considers motor losses includes the following steps:

[0059] Step 1: Starting from the output torque of the square wave permanent magnet motor, establish torque (current) constraints for motor loss optimization;

[0060] The control method considering motor loss optimization aims to reduce motor losses during operation without reducing the motor's load-carrying capacity (output torque). Therefore, the output torque (current) constraint of the motor is considered first. The output torque equation of the square wave permanent magnet motor is as follows:

[0061]

[0062] In the formula, T emFor the electromagnetic torque of the motor, ω m Let i be the mechanical angular velocity of the motor. a i b i c e represents the three-phase winding current of the motor. a e b e c This is the back electromotive force of the three-phase windings of the motor.

[0063] When the device motor adopts the 120° conduction natural commutation control method, based on the variation law of motor back electromotive force and current, the constraint equation of motor output torque (current) can be obtained as follows:

[0064]

[0065] In the formula, E is the amplitude of the motor back electromotive force, and I is the amplitude of the motor winding current.

[0066] Step 2: Starting from the relationship between the stator copper loss and the winding current of the motor, the derivative extremum method is used to establish a three-phase current planning and control expression with the motor back electromotive force as the variable.

[0067] Assume that the resistance of each of the three phase windings of the motor is R. e Combining the constraint equations of the three-phase current relationship of the motor, the stator copper loss equation of the motor can be expressed as follows:

[0068]

[0069] In the formula, P cu R is the stator copper loss (power) of the motor. e This represents the resistance of the motor phase winding.

[0070] From the equation for stator copper loss, it can be found that the stator copper loss corresponds to the stator winding current i. a i b Extreme points exist. The mathematical method of derivative extrema is used to calculate the stator copper loss equation of the motor; the stator copper loss equation of the motor is then applied to the stator winding current i. a i b Taking the partial derivatives, we can obtain the following partial derivative equation for the stator copper loss of the motor:

[0071]

[0072] By combining the constraint equations for the motor output torque (current), the constraint equations for the three-phase current relationship, and the partial derivative equations for the stator copper loss, we can obtain the equation with respect to the motor back electromotive force e. a e b e c The phase winding current programming control expression is as follows:

[0073]

[0074] like Figure 2 and Figure 3 As shown, when the flywheel energy storage novel bidirectional energy conversion device of the present invention adopts the current planning control method that considers motor losses, the stator winding current of the motor operates according to the phase winding current planning control expression. Compared with the 120° conduction natural commutation control method, it has a smoother stator winding current change waveform and has smaller current harmonic components.

[0075] like Figure 4 As shown, when the flywheel energy storage novel bidirectional energy conversion device of the present invention adopts the current planning control method that considers motor losses, the stator winding current of the motor operates according to the phase winding current planning control expression, and the stator copper loss equation of the motor operates at the extreme point. At this time, the motor operates in a situation where the stator winding copper loss is relatively small. Compared with the 120° conduction natural commutation control method, the device has a smaller stator winding copper loss during operation.

[0076] For example Figure 5 and Figure 6 As shown, Fourier analysis was performed on the phase current changes of the motor windings in the novel bidirectional energy conversion device of the flywheel energy storage according to the present invention, using both the 120° conduction natural commutation control method and the current planning control method considering motor losses. Compared with the 120° conduction natural commutation control method, the amplitude of the harmonic components of the phase current in the motor windings is significantly reduced under the current planning control method considering motor losses, and the phase current THD is also greatly reduced. Therefore, the rotor eddy current loss during motor operation is also effectively reduced. The current planning method considering motor losses can result in lower copper losses in the motor windings during device motor operation, while also effectively reducing rotor eddy current losses during operation.

[0077] For example Figure 7 As shown, when the flywheel energy storage novel bidirectional energy conversion device of the present invention is in a 180° conduction three-three natural commutation control method (A-phase upper bridge arm, B-phase upper bridge arm and C-phase lower bridge arm are conducting), the device topology operating current loop consists of a DC power supply, switching device T7, bus inductor L1 and three-phase motor windings in a conducting state; the device's front-stage current chopper topology operates in forward chopper mode, power device T8 operates in the off state, anti-parallel diode D8 is connected in parallel on both sides of the DC bus, power device T7 operates in PWM modulation state, and the front-stage current chopper topology controls the change of the device motor operating current through the duty cycle of the control device T7. When the bidirectional energy conversion device control method considering device losses introduces a 180° conduction three-three natural commutation control method, the specific steps are as follows:

[0078] Step 1: Based on the schematic diagram of the operating current path under the three-phase natural commutation control topology (with the upper bridge arm of phase A, the upper bridge arm of phase B, and the lower bridge arm of phase C conducting), the voltage-current relationship of the operating current loop is obtained as follows:

[0079]

[0080] In the formula, α is the operating duty cycle of the switching device T7 in the positive chopper mode, and U dc L1 is the DC power supply voltage for the device, U is the DC bus inductance of the device, and L is the voltage at the right end of the DC bus inductance. e This refers to the inductance of the motor phase winding.

[0081] Step 2: Based on the relationship between the device's operating current and the winding circuit voltage and current, the device's operating current control formula is obtained as follows:

[0082]

[0083] In the formula, i dc This is the operating current of the device's DC bus.

[0084] Step 3: From the device's operating current control formula, the duty cycle of the power devices in the front-end current chopper topology is obtained to achieve device operating current control. Under the three-three natural commutation control mode with 180° conduction, the current control duty cycle of the device's bus power device T7 is as follows:

[0085]

[0086] like Figure 8 As shown, the flywheel energy storage novel bidirectional energy conversion device of the present invention adopts a current planning control method that considers motor losses. After introducing the 180° conduction three-three natural commutation control method, the working current waveform of the motor winding is similar to that before the introduction. This means that the introduction of the 180° conduction three-three natural commutation current planning control method can significantly reduce the switching frequency of power devices during the device operation process under the condition of slightly changing the current planning control winding current waveform. It can reduce the switching losses of power devices during the device operation process without significantly increasing the motor copper loss and winding current harmonics (related to the motor rotor eddy current loss).

[0087] like Figure 9 , Figure 10 As shown, the current planning control method considering motor losses proposed in this invention introduces a 180° conduction three-three natural commutation control method. Under the condition that the control system has the same current control effect, it effectively reduces the switching frequency of power devices during the operation of the device motor, and can effectively reduce the switching losses generated by the device power devices.

[0088] like Figure 11 , Figure 12 As shown, the control method of the novel bidirectional energy conversion device for flywheel energy storage that considers device losses proposed in this invention has been verified under a simulation model. The operation of the bidirectional energy conversion device under three control methods was simulated and analyzed under the same device motor operation control state. Figure 11 The simulation curves show the motor loss variation of a novel bidirectional energy conversion device with flywheel energy storage during the energy conversion control process under three control methods. Figure 12 Simulation curves of device losses during energy conversion under three control methods are presented. Simulation results demonstrate that the current planning control method considering motor losses has lower device motor losses than the 120° conduction natural commutation control method; the current planning control method introducing 180° conduction three-three natural commutation slightly increases motor losses during device operation; because it effectively reduces the switching frequency and switching losses of power devices during device operation, the current planning control method introducing 180° conduction three-three natural commutation has the lowest device losses among the three control methods; the control method for the flywheel energy storage novel bidirectional energy conversion device considering device losses can, to a certain extent, reduce device operating losses and improve device operating efficiency.

[0089] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A control method for a novel bidirectional energy conversion device using flywheel energy storage, considering device losses, characterized in that: The control methods include a current planning control method that takes into account motor losses and a three-three natural commutation control method with 180° conduction. The current planning and control method that considers motor losses includes the following steps: Based on the output torque of the square wave permanent magnet motor, establish torque constraints for motor loss optimization; Based on the relationship between stator copper loss and winding current of the motor, a three-phase current planning and control expression with the motor back electromotive force as the variable is established by using the derivative extremum method. The output torque equation of the square wave permanent magnet motor is as follows: In the formula, For the electromagnetic torque of the motor, The mechanical angular velocity of the motor. , , This refers to the three-phase winding current of the motor. , , The back electromotive force of the three-phase windings of the motor; The constraint equation for the motor output torque is as follows: In the formula, This represents the amplitude of the motor's back electromotive force. This refers to the amplitude of the motor winding current. The 180° conduction three-three natural commutation control method includes the following steps: Based on the schematic diagram of the operating current path under the three-three natural commutation control topology, the voltage-current relationship of the operating current loop is obtained; Based on the relationship between the device's operating current and the winding circuit voltage and current, the control formula for the device's operating current is obtained; By using the operating current control formula of the device, the duty cycle of the operating current control of the power device in the front-end current chopper topology is obtained to achieve the operating current control of the device.

2. The control method for a novel bidirectional energy conversion device for flywheel energy storage considering device losses according to claim 1, characterized in that, The equation for the stator copper loss of the motor is expressed as follows: In the formula, For motor stator copper losses, The resistance of the motor phase winding is... , This refers to the stator winding current of the motor. The three-phase current planning and control expression is as follows: 。 3. The control method for a novel bidirectional energy conversion device for flywheel energy storage considering device losses according to claim 2, characterized in that, The voltage-current relationship of the operating current loop is as follows: In the formula, Switching device in positive chopper mode The operating duty cycle, The DC power supply voltage for the device. To install DC bus inductance, This is the voltage at the right end of the DC bus inductance. This refers to the inductance of the motor phase winding.

4. The control method for a novel bidirectional energy conversion device for flywheel energy storage considering device losses according to claim 3, characterized in that, The operating current control formula for the device is as follows: In the formula, This is the operating current of the device's DC bus.

5. The control method for a novel bidirectional energy conversion device for flywheel energy storage considering device losses according to claim 4, characterized in that, The current control duty cycle is expressed as follows: 。 6. A novel bidirectional energy conversion device control system for flywheel energy storage considering device losses, characterized in that, The system is used to implement the control method for the novel bidirectional energy conversion device of flywheel energy storage considering device losses as described in claim 1, and the system includes: The constraint module is used to establish motor loss optimization torque constraints based on the output torque of the square wave permanent magnet motor. The first control module is used to control the device based on the established three-phase current programming control expression with the back electromotive force of the motor as the variable. The acquisition module is used to obtain the control formula for the device's operating current based on the relationship between the device's operating current and the winding circuit voltage and current. The second control module is used to obtain the duty cycle of the operating current control of the power device in the front-end current chopper topology of the device based on the device operating current control relationship obtained by the acquisition module, so as to realize the device operating current control.

7. A controller for a novel bidirectional energy conversion device for flywheel energy storage that takes into account device losses, comprising storing a program for operating the control system of the novel bidirectional energy conversion device for flywheel energy storage that takes into account device losses as described in claim 6.

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