Flywheel energy storage machine side converter system control method using an electrically excited synchronous machine

Abstract

The application relates to motor control technology and discloses a flywheel energy storage machine-side converter system control method using an electrically excited synchronous motor, wherein by establishing a bidirectional converter system topological structure of a flywheel energy storage system and a mathematical model of the electrically excited synchronous motor in an ABC three-phase static coordinate system, voltage equations and flux linkage equations in a d-q axis coordinate system are obtained; then based on a double closed-loop control architecture of a voltage outer ring-current inner ring, a machine-side converter system control method is designed to realize independent control of d-axis and q-axis currents; a voltage outer ring controller is designed to provide d-axis, q-axis and excitation current reference values for the current inner ring; and according to different current reference value calculation methods, three control modes of high performance, balance and low power consumption are designed. Through the design of the three control modes of high performance, balance and low power consumption, the flywheel energy storage system can adapt to the operation requirements under different working conditions, and the adaptability and economy of the system are improved.

Description

Technical Field

[0001] This invention relates to a motor control technology, and more particularly to a control method for a flywheel energy storage machine-side converter system using an electrically excited synchronous motor. Background Technology

[0002] A flywheel energy storage system is a physical energy storage device that uses an electric motor to convert electrical energy into the kinetic energy of a flywheel for storage. When needed, the kinetic energy is converted back into electrical energy by a generator. Flywheel energy storage systems have advantages such as high power density, long cycle life, and environmental friendliness, and have broad application prospects in fields such as power system frequency regulation, uninterruptible power supplies, and energy recovery in rail transit.

[0003] Flywheel energy storage motors mainly include permanent magnet synchronous motors (PMSMs) and electrically excited synchronous motors (EMSs). PMSMs are widely used due to their simple structure and high power density, but their fixed and unadjustable air gap magnetic field makes it difficult to suppress no-load losses during standby, resulting in energy waste. Furthermore, permanent magnet materials are at risk of demagnetization, leading to higher costs. In contrast, EMSs, as motors with adjustable excitation, have significant advantages in flywheel energy storage systems: the air gap magnetic field can be controlled by adjusting the excitation current; the motor has a wider full-load operating speed range, a discharge depth of up to 90%, and can be shut off during standby, significantly reducing standby losses.

[0004] However, existing flywheel energy storage system control methods mainly rely on permanent magnet synchronous motors for design, and the control means are relatively simple. In actual operation, flywheel energy storage systems need to cope with a variety of operating conditions. For example, they need to respond quickly when the grid frequency is adjusted, they need to be highly efficient during the energy storage phase, and they need to achieve a balance between performance and efficiency during normal operation.

[0005] Therefore, there is an urgent need for a control method for the flywheel energy storage machine-side converter system designed for the excitation adjustable function of an electrically excited synchronous motor. Summary of the Invention

[0006] To address the shortcomings in existing flywheel energy storage control technologies, this invention proposes a control method for a flywheel energy storage machine-side converter system employing an electrically excited synchronous motor. By establishing a bidirectional converter system topology and a mathematical model of the motor in the dq rotating coordinate system, a control method for the machine-side converter system is designed. A dual closed-loop control method consisting of an outer voltage loop and an inner current loop is adopted. The inner current loop uses feedforward decoupling control. Furthermore, for the outer voltage loop, a multi-mode control method is proposed, including a high-performance mode, a low-power mode, and a balanced mode.

[0007] The technical solution of the invention is as follows: A control method for a flywheel energy storage machine-side converter system employing an electrically excited synchronous motor is provided, which is achieved through the following steps: Step 1: Establish the bidirectional converter system topology of the flywheel energy storage system, including the machine-side converter, DC bus, grid-side converter, electrically excited synchronous motor, and flywheel rotor.

[0008] Preferably, to reduce device switching losses and output waveform harmonics, the machine-side converter adopts a three-phase three-level topology, the grid-side converter adopts a three-phase two-level topology, and a supporting capacitor is connected in parallel to the DC bus. The machine-side converter also includes an excitation system and a pre-charging circuit. The excitation system adopts an H-bridge circuit, and the three-phase UPS supplies power to the excitation system and the machine-side converter pre-charging circuit through uncontrolled rectification.

[0009] Step 2: Establish a mathematical model of the electrically excited synchronous motor in the ABC three-phase stationary coordinate system. Through Clarke transformation and Park transformation, transform the mathematical model to the motor equations in the dq rotating coordinate system to obtain the voltage equations and flux linkage equations in the dq axis coordinate system.

[0010] Preferably, in the dq rotating coordinate system, the d-axis is aligned with the positive direction of the excitation winding flux linkage, and the q-axis leads the d-axis by 90°. Furthermore, the mathematical modeling of the electrically excited synchronous motor is performed according to motor conventions, and the voltage equations for the d-axis and q-axis are as follows:

[0011] in, , These are the voltages along the d-axis and q-axis, respectively. , These are the d-axis and q-axis currents, respectively. For stator resistance, , These are the d-axis and q-axis inductances, respectively. Electric angular velocity, The mutual inductance between the excitation winding and the armature winding is given. The equations for the excitation voltage and flux linkage are as follows:

[0012] in, This is the excitation voltage. For excitation current, For the excitation winding resistance, For the self-inductance of the excitation winding, For excitation flux linkage. Step 3: Based on the dual closed-loop control architecture of voltage outer loop and current inner loop, design the control method of machine-side converter system. The current inner loop adopts feedforward decoupling control, and d-axis current PI controller and q-axis current PI controller are designed respectively to realize independent control of d-axis and q-axis current.

[0013] Preferably, the feedforward decoupling control defines a set of quantities. , As a dq-axis current PI controller, a q-axis current coupling term is added to the output of the d-axis current PI controller. As a feedforward compensation, a d-axis current coupling term is added to the output of the q-axis current PI control. As feedforward compensation, the inner current loop PI controller is as follows:

[0014] in , These are the d-axis and q-axis voltage reference values, respectively. , These are the d-axis and q-axis current reference values, respectively. , These are the proportional and integral coefficients of the d-axis current loop, respectively. , are the proportional and integral coefficients of the q-axis current loop, respectively, and s is the Laplace operator.

[0015] Step 3 also includes excitation current loop control, designing an excitation current PI controller to achieve closed-loop control of the excitation current, wherein the output of the excitation current PI controller is the excitation voltage reference value. :

[0016] in, , These are the proportional and integral coefficients of the excitation current loop, respectively. This is the reference value for the excitation current. This is the actual excitation current.

[0017] Step 4: Design an outer voltage loop controller to provide d-axis, q-axis, and excitation current reference values ​​for the inner current loop. The outer voltage loop is designed with three control modes: high performance, balanced, and low power consumption, based on different current reference value calculation methods. The outer voltage loop dynamically selects or switches the operating mode according to the real-time operating status of the flywheel energy storage system and external commands.

[0018] Preferably, the high-performance control mode aims to improve the system's dynamic response speed and output capability, simulating the operation of a permanent magnet motor, maintaining a constant excitation current, and adjusting... , To maintain stable terminal voltage and power, the excitation current reference value in this mode is established based on the rated power. q-axis current reference value and d-axis current reference value as follows:

[0019] in, Rated power, This is a power reference value. Rated voltage, This represents the peak value of the mutual inductance between the excitation winding and the single-phase armature winding. , For direct-axis and quadrature-axis synchronous inductors, This represents the number of phases of the motor.

[0020] The low-power mode aims to reduce system losses. When the flywheel energy storage system is in standby mode, it does not need to respond to power commands and can shut down excitation. The excitation current is first determined based on the real-time rotational speed. Rated direct-axis current Rated quadrature axis current Rated power Should be compared with reference power Consistent symbols:

[0021] Subsequently, based on the power reference value Scaling proportionally to the inner current loop reference value , , ,Notice It must maintain the same polarity. Always positive Always negative (demagnetizing). Excitation current reference value. q-axis current reference value and d-axis current reference value as follows:

[0022] The balanced mode combines the advantages of fast response speed in high-performance mode and low standby loss in low-power mode. It moderately reduces the excitation current when the flywheel is in standby mode, and builds up the excitation current from no-load when responding to power commands, ensuring fast response. The d-axis and q-axis control methods in this mode are the same as in high-performance mode, and the excitation current reference value is based on the power reference value. The calculated excitation current reference value is... q-axis current reference value and d-axis current reference value as follows:

[0023] The beneficial effects of this invention are as follows: This invention proposes a control method for a flywheel energy storage system using an electrically excited synchronous motor. This method is particularly suitable for electrically excited synchronous motors. By controlling the excitation current, the air gap magnetic field can be flexibly adjusted to achieve efficient operation over a wide speed range. The inner current loop employs feedforward decoupling control, realizing independent control of the d-axis and q-axis currents, improving the system's dynamic response performance and control accuracy. By designing three control modes—high performance, balanced, and low power consumption—it can adapt to the operating requirements of the flywheel energy storage system under different working conditions, improving the system's adaptability and economy. Attached Figure Description

[0024] Figure 1 This is a flowchart of the control method for the flywheel energy storage machine-side converter system using an electrically excited synchronous motor, as described in this invention. Figure 2 This is a schematic diagram of the flywheel energy storage bidirectional converter system, which is the subject of an embodiment of the method of the present invention. Figure 3a This is a simulation curve of the high-performance mode grid connection in an embodiment of the method of the present invention; Figure 3b This is a simulation curve of the low-power mode grid connection in an embodiment of the method of the present invention. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0026] This embodiment takes a 500kW / 125kWh flywheel energy storage-side converter system using an electrically excited synchronous motor as an example, and designs the control method for the system. Its flowchart is as follows: Figure 1 As shown, this can be achieved through the following steps: Step 1: Establish the bidirectional converter system topology of the flywheel energy storage system, including the machine-side converter, DC bus, grid-side converter, electrically excited synchronous motor, and flywheel rotor.

[0027] Preferably, to reduce device switching losses and output waveform harmonics, the generator-side converter adopts a three-phase three-level topology, and the grid-side converter adopts a three-phase two-level topology. A supporting capacitor is connected in parallel to the DC bus. The generator-side converter also includes an excitation system and a pre-charging circuit. The excitation system uses an H-bridge circuit. A three-phase uninterruptible power supply (UPS) supplies power to the excitation system and the generator-side converter's pre-charging circuit through uncontrolled rectification. The topology is as follows: Figure 2 As shown.

[0028] In this embodiment, the DC bus voltage is selected as 900V, the DC bus capacitance is 0.01F, and two 0.02F capacitors are connected in series.

[0029] Step 2: Establish a mathematical model of the electrically excited synchronous motor in the ABC three-phase stationary coordinate system. Through Clarke transformation and Park transformation, transform the mathematical model to the motor equations in the dq rotating coordinate system to obtain the voltage equations and flux linkage equations in the dq axis coordinate system.

[0030] Preferably, in the dq rotating coordinate system, the d-axis is aligned with the positive direction of the excitation winding flux linkage, and the q-axis leads the d-axis by 90°. Furthermore, the mathematical modeling of the electrically excited synchronous motor is performed according to motor conventions, and the voltage equations for the d-axis and q-axis are as follows:

[0031] in, , These are the voltages along the d-axis and q-axis, respectively. , These are the d-axis and q-axis currents, respectively. For stator resistance, , These are the d-axis and q-axis inductances, respectively. Electric angular velocity, The mutual inductance between the excitation winding and the armature winding is given. The equations for the excitation voltage and flux linkage are as follows:

[0032] in, This is the excitation voltage. For excitation current, For the excitation winding resistance, For the self-inductance of the excitation winding, For excitation flux linkage.

[0033] In this embodiment, a stator resistor is included through electromagnetic design. Direct-axis synchronous reactor Quadrature axis synchronous reactor Excitation winding resistance , excitation winding self-inductance Mutual inductance between excitation winding and armature winding .

[0034] Step 3: Based on the dual closed-loop control architecture of voltage outer loop and current inner loop, design the control method of machine-side converter system. The current inner loop adopts feedforward decoupling control, and d-axis current PI controller and q-axis current PI controller are designed respectively to realize independent control of d-axis and q-axis current.

[0035] Preferably, the feedforward decoupling control defines a set of quantities. , As a dq-axis current PI controller, a q-axis current coupling term is added to the output of the d-axis current PI controller. As a feedforward compensation, a d-axis current coupling term is added to the output of the q-axis current PI control. As feedforward compensation, the inner current loop PI controller is as follows:

[0036] in , These are the d-axis and q-axis voltage reference values, respectively. , These are the d-axis and q-axis current reference values, respectively. , These are the proportional and integral coefficients of the d-axis current loop, respectively. , are the proportional and integral coefficients of the q-axis current loop, respectively, and s is the Laplace operator.

[0037] Step 3 also includes excitation current loop control, designing an excitation current PI controller to achieve closed-loop control of the excitation current, wherein the output of the excitation current PI controller is the excitation voltage reference value. :

[0038] in, , These are the proportional and integral coefficients of the excitation current loop, respectively. This is the reference value for the excitation current. This is the actual excitation current.

[0039] In this embodiment, the PI parameter of the d-axis current loop is tuned as follows: , The q-axis current loop PI parameters are consistent with those of the d-axis.

[0040] Step 4: Design an outer voltage loop controller to provide d-axis, q-axis, and excitation current reference values ​​for the inner current loop. The outer voltage loop is designed with three control modes: high performance, balanced, and low power consumption, based on different current reference value calculation methods. The outer voltage loop dynamically selects or switches the operating mode according to the real-time operating status of the flywheel energy storage system and external commands.

[0041] Preferably, the high-performance control mode aims to improve the system's dynamic response speed and output capability, simulating the operation of a permanent magnet motor, maintaining a constant excitation current, and adjusting... , To maintain stable terminal voltage and power, the excitation current reference value in this mode is established based on the rated power. q-axis current reference value and d-axis current reference value as follows:

[0042] in, Rated power, This is a power reference value. Rated voltage, This represents the peak value of the mutual inductance between the excitation winding and the single-phase armature winding. , For direct-axis and quadrature-axis synchronous inductors, This represents the number of phases of the motor.

[0043] The low-power mode aims to reduce system losses. When the flywheel energy storage system is in standby mode, it does not need to respond to power commands and can shut down excitation. The excitation current is first determined based on the real-time rotational speed. Rated direct-axis current Rated quadrature axis current Rated power Should be compared with reference power Consistent symbols:

[0044] Subsequently, based on the power reference value Scaling proportionally to the inner current loop reference value , , ,Notice It must maintain the same polarity. Always positive Always negative (demagnetizing). Excitation current reference value. q-axis current reference value and d-axis current reference value as follows:

[0045] The balanced mode combines the advantages of fast response speed in high-performance mode and low standby loss in low-power mode. It moderately reduces the excitation current when the flywheel is in standby mode, and builds up the excitation current from no-load when responding to power commands, ensuring fast response. The dq axis control method in this mode is the same as in high-performance mode, and the excitation current reference value is based on the power reference value. The calculated excitation current reference value is... q-axis current reference value and d-axis current reference value as follows:

[0046] In this embodiment, by simulating the power response of the system after grid connection, the simulation results of the high-performance mode are as follows: Figure 3a As shown, the simulation results for the low-power mode are as follows: Figure 3b As shown. In high-performance mode, the power response time is approximately 50ms, and the charge / discharge response time is approximately 200ms. The excitation current remains at full load in both power response and standby states, resulting in the fastest response speed. In low-power mode, the power response time is approximately 400ms, and the charge / discharge response time is approximately 700ms. The excitation current in low-power mode is very small, which can significantly reduce standby losses, but the charge / discharge response time is correspondingly increased. The balanced mode has a response speed comparable to the high-performance mode, but in standby mode, the excitation current is slightly lower than the full load value, which can appropriately reduce standby losses, thus balancing the advantages of fast response speed and low standby losses. These results indicate that the control method of the flywheel energy storage machine-side converter system using an electrically excited synchronous motor proposed in this invention is reasonable and reliable.

[0047] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A control method for a flywheel energy storage machine-side converter system employing an electrically excited synchronous motor, characterized in that, This can be achieved through the following steps: Step 1: Establish the bidirectional converter system topology of the flywheel energy storage system, including the machine-side converter, DC bus, grid-side converter, electrically excited synchronous motor, and flywheel rotor; Step 2: Establish a mathematical model of the electrically excited synchronous motor in the ABC three-phase stationary coordinate system. Through Clarke transformation and Park transformation, transform the mathematical model to the motor equations in the dq rotating coordinate system to obtain the voltage equations and flux linkage equations in the dq axis coordinate system. Step 3: Based on the dual closed-loop control architecture of voltage outer loop and current inner loop, design the control method of machine-side converter system. The current inner loop adopts feedforward decoupling control, and designs d-axis current PI controller and q-axis current PI controller respectively to realize independent control of d-axis and q-axis current. Step 4: Design the voltage outer loop controller to provide d-axis, q-axis and excitation current reference values ​​for the current inner loop. The voltage outer loop is designed with three control modes: high performance, balanced and low power consumption, based on different current reference value calculation methods. The voltage outer loop dynamically selects or switches the operating mode according to the real-time operating status of the flywheel energy storage system and external commands.

2. The control method for the flywheel energy storage machine-side converter system using an electrically excited synchronous motor according to claim 1, characterized in that, In the bidirectional converter system topology described in step 1, the machine-side converter adopts a three-phase three-level topology, the grid-side converter adopts a three-phase two-level topology, and the DC bus is connected in parallel with a supporting capacitor; the electrically excited synchronous motor and the flywheel rotor adopt an integrated structure, the motor excitation winding is located on the stator, and the flywheel rotor is supported by a magnetic levitation bearing and operates in a vacuum environment.

3. The control method for the flywheel energy storage machine-side converter system using an electrically excited synchronous motor according to claim 2, characterized in that, The machine-side converter also includes an excitation system and a pre-charging circuit. The excitation system adopts an H-bridge circuit, and the three-phase UPS supplies power to the excitation system and the machine-side converter pre-charging circuit through uncontrolled rectification.

4. The control method for the flywheel energy storage machine-side converter system using an electrically excited synchronous motor according to claim 1, characterized in that, In step 2, the d-axis of the dq rotating coordinate system is aligned with the positive direction of the excitation winding flux linkage, and the q-axis leads the d-axis by 90°. It is stipulated that the mathematical modeling of the electrically excited synchronous motor is performed according to the conventions of electric motors, and the voltage equations for the d-axis and q-axis are as follows: ； in, , These are the voltages along the d-axis and q-axis, respectively. , These are the d-axis and q-axis currents, respectively. For stator resistance, , These are the d-axis and q-axis inductances, respectively. Electric angular velocity, For the mutual inductance between the excitation winding and the armature winding, the equations for the excitation voltage and flux linkage are as follows: ； in, This is the excitation voltage. For excitation current, For the excitation winding resistance, For the self-inductance of the excitation winding, For excitation flux linkage.

5. The control method for the flywheel energy storage machine-side converter system using an electrically excited synchronous motor according to claim 1, characterized in that, The feedforward decoupling control described in step 3 defines a set of quantities. , As a dq-axis current PI controller, a q-axis current coupling term is added to the output of the d-axis current PI controller. As a feedforward compensation, a d-axis current coupling term is added to the output of the q-axis current PI control. As a feedforward compensation, the inner current loop PI controller is as follows: ； in , These are the d-axis and q-axis voltage reference values, respectively. , These are the d-axis and q-axis current reference values, respectively. , These are the proportional and integral coefficients of the d-axis current loop, respectively. , are the proportional and integral coefficients of the q-axis current loop, respectively, and s is the Laplace operator.

6. The control method for the flywheel energy storage machine-side converter system using an electrically excited synchronous motor according to claim 1 or 5, characterized in that, Step 3 also includes excitation current loop control, designing an excitation current PI controller to achieve closed-loop control of the excitation current, wherein the output of the excitation current PI controller is the excitation voltage reference value. : ； in, , These are the proportional and integral coefficients of the excitation current loop, respectively. This is the reference value for the excitation current. This is the actual excitation current.

7. The control method for the flywheel energy storage machine-side converter system using an electrically excited synchronous motor according to claim 1, characterized in that, The high-performance control mode described in step 4 aims to improve the system's dynamic response speed and output capability. It simulates the operation of a permanent magnet motor, maintaining a constant excitation current and adjusting... , To maintain stable terminal voltage and power, the excitation current reference value in this mode is established based on the rated power. q-axis current reference value and d-axis current reference value as follows: ； in, Rated power, This is a power reference value. Rated voltage, This represents the peak value of the mutual inductance between the excitation winding and the single-phase armature winding. , For direct-axis and quadrature-axis synchronous inductors, This represents the number of phases of the motor.

8. The control method for the flywheel energy storage machine-side converter system using an electrically excited synchronous motor according to claim 1, characterized in that, The low-power mode described in step 4 aims to reduce system losses. When the flywheel energy storage system is in standby mode, it does not need to respond to power commands and can shut down excitation. First, the excitation current is determined based on the real-time rotational speed. Rated direct-axis current Rated quadrature axis current Rated power Should be compared with reference power Consistent symbols: ； Subsequently, based on the power reference value Scaling proportionally to the inner current loop reference value , , , Maintain the same polarity. Always positive Always negative (demagnetizing); excitation current reference value q-axis current reference value and d-axis current reference value as follows: 。 9. The control method for the flywheel energy storage machine-side converter system using an electrically excited synchronous motor according to claim 1, characterized in that, The balancing mode described in step 4 involves moderately reducing the excitation current when the flywheel is idle. When responding to a power command, the excitation current builds up from no-load, ensuring a fast response. In this mode, the dq-axis control method is the same as in the high-performance mode, and the excitation current reference value is based on the power reference value. The calculated excitation current reference value is... q-axis current reference value and d-axis current reference value as follows: 。

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