A virtual synchronous machine based converter control method and device and a computer readable storage medium

Abstract

The present application belongs to the technical field of flexible direct current power transmission, and particularly relates to a converter control method and device based on a virtual synchronous machine and a computer readable storage medium. For the scenario of multiple converters in parallel in a sending-end converter station or a receiving-end converter station, the reactive power difference between the converter and other converters in parallel in the same pole, and the reactive power difference between the two poles in the converter station where the converter is located are used to calculate the reactive power difference adjustment amount of the converter when the reactive power in the converter station is balanced. In the virtual excitation control part, the control voltage of the converter is generated, and the calculation parameters include the AC bus voltage instruction value, the AC bus voltage actual value, the converter reference voltage, and the reactive power difference adjustment amount. The dynamic balance of the reactive power of each converter is achieved, the phenomenon of reactive circulating current of the converter is avoided, and the stability of the system under the scenario of multiple converters in parallel is improved.

Description

Technical Field

[0001] This invention belongs to the field of flexible DC transmission technology, specifically relating to a converter control method, device, and computer-readable storage medium based on a virtual synchronous machine. Background Technology

[0002] In flexible DC transmission projects, multiple converters are used in parallel within the converter station to improve transmission capacity and quality. Taking two converters connected in parallel as an example... Figure 1 As shown, the sending-end renewable energy power station is connected to the AC bus of the sending-end converter station at a voltage level of 66kV. The two converters at the sending-end converter station, WFMMC1 and WFMMC2, are connected in parallel to the same AC bus and are connected to the corresponding converters at the receiving-end converter station via pole 1 (positive) line, pole 2 (negative) line, and a metallic return line, respectively. The two converters at the receiving-end converter station, GSMMC1 and GSMMC2, are also connected in parallel to the same AC bus and connected to the same receiving-end power grid. The two converters at the sending end control the AC voltage and frequency, providing grid-connected AC voltage for the sending-end renewable energy. The two converters at the receiving end control the DC voltage, providing a stable DC voltage for the flexible DC transmission system.

[0003] For scenarios involving multiple converters in parallel, the paper "Control Strategy for Bipolar Flexible DC Converter Stations Connected to Isolated New Energy Power Plants" proposes a coordinated control method for AC voltage and frequency droop of bipolar converter units (referred to as dual U / f droop control). Both converters adopt reactive power / AC voltage (Q / U) droop control to adjust the amplitude balance of the AC bus voltage of the two converters, and both converters adopt active power / AC frequency (P / f) droop control to adjust the phase synchronization of the AC bus voltage of the two converters. However, due to the differences in the primary and secondary equipment involved in the control loops of each converter, and the fact that each converter's control device independently controls reactive power, the reactive power command value Qref of each converter remains consistent, and the sum of the reactive power of the converters is constant. This leads to inconsistencies in the reactive power of each converter. The deviation between the reactive power and the reactive power command value of one converter is greater than zero, while the deviation between the reactive power and the reactive power command value of another converter is less than zero. This results in a large reactive power circulation between the two converters, making it impossible to achieve reactive power balance among multiple converters. This may lead to the reactive power of the converters exceeding the limit, affecting the stable operation of the system. Summary of the Invention

[0004] The purpose of this invention is to provide a converter control method, device, and computer-readable storage medium based on a virtual synchronous machine, in order to solve the problem that existing converter control methods cause reactive power circulation between converters, affecting the stable operation of the system in scenarios with multiple converters in parallel.

[0005] To address the aforementioned technical problems, this invention provides a converter control method based on a virtual synchronous machine. The method uses virtual synchronous machine control to obtain the converter's voltage command value. The virtual synchronous machine control includes a virtual mechanical control section, a reactive power differential adjustment section, a virtual excitation control section, and a converter voltage control section. The virtual mechanical control section is used to calculate the phase angle. The reactive power differential adjustment section is used to calculate the reactive power differential adjustment amount of the converter based on the actual reactive power difference between the converter and other converters connected in parallel at the same pole, and the actual reactive power difference between the two poles within the converter station. The virtual excitation control section is used to calculate the converter control voltage based on the AC bus voltage command value, the actual AC bus voltage value, the converter's reactive power differential adjustment amount, and the converter reference voltage. The converter voltage control section is used to calculate the converter voltage command value based on the phase angle and the converter control voltage.

[0006] Furthermore, the calculation process of the reactive power differential adjustment amount of the converter is as follows: the first adjustment amount allocated to the converter is calculated based on the actual difference in reactive power between the two poles in the converter station where the converter is located and the number of converters in the pole where the converter is located. The sum of the actual differences in reactive power between the converter and other converters connected in parallel with the same pole is calculated as the second adjustment amount. The first adjustment amount and the second adjustment amount are superimposed to obtain the reactive power difference of the converter. The reactive power differential adjustment amount of the converter is obtained based on the reactive power difference of the converter and the reactive power differential adjustment coefficient.

[0007] Furthermore, the formula for calculating the reactive power differential regulation of this converter is as follows:

[0008]

[0009] Where ΔQ is the reactive power differential regulation of this converter, k0 is the reactive power differential regulation coefficient, m is the number of converters in the pole where this converter is located, and n is the number of converters in the other pole. i Q represents the actual reactive power value of the i-th converter within the pole where this converter is located. opj Let q be the actual reactive power value of the j-th converter in the other pole. i This represents the difference in actual reactive power between this converter and the i-th converter connected in parallel with the same pole.

[0010] Furthermore, the calculation process of the converter control voltage is as follows: the difference between the AC bus voltage command value and the AC bus voltage actual value is subjected to PI control, and the value after PI control is superimposed with the reactive power differential adjustment of the converter and the converter reference voltage to obtain the converter control voltage.

[0011] Furthermore, the phase angle is determined based on the converter active power command value, the actual converter active power value, the reference angular velocity of the AC grid, the inertia time constant of the virtual synchronous machine, and the damping of the virtual synchronous machine.

[0012] Furthermore, the formula for calculating the phase angle is as follows:

[0013]

[0014] Among them, T J ω is the inertia time constant of the virtual synchronizer; ω is the angular velocity of the virtual synchronizer; t is time; ω0 is the reference angular velocity of the AC power grid; P ref θ is the active power command value of the converter, P is the actual AC active power value of the converter; D is the damping of the virtual synchronous machine; θ is the phase angle of the virtual synchronous machine.

[0015] The beneficial effects of the above technical solution are as follows: This invention is a pioneering invention. For scenarios involving multiple converters connected in parallel within a sending-end or receiving-end converter station, it calculates the reactive power differential adjustment amount of the converter when the reactive power within the converter station is balanced, based on the actual reactive power difference between the converter and other converters connected in parallel at the same pole, and the actual reactive power difference between the two poles within the converter station. When generating the control voltage of the converter in the virtual excitation control section, in addition to the AC bus voltage command value, the actual AC bus voltage value, and the reference voltage of each converter, the reactive power differential adjustment amount is also superimposed on the calculated parameters. This achieves dynamic balance of reactive power for each converter, avoids the phenomenon of reactive power circulation in the converters, and improves the stability of the system in scenarios involving multiple converters connected in parallel.

[0016] To address the aforementioned technical problems, the present invention also provides a converter control device based on a virtual synchronous machine, comprising a processor for executing computer instructions to implement the converter control method based on a virtual synchronous machine described above.

[0017] Furthermore, the actual reactive power values ​​of the converters are transmitted between the converter control devices via optical fiber communication.

[0018] The beneficial effects of the above technical solution are as follows: This invention is a pioneering invention. For scenarios where multiple converters are connected in parallel within a sending-end or receiving-end converter station, the control device of each converter calculates the reactive power differential adjustment amount of the converter when the reactive power is balanced within the converter station, based on the actual reactive power difference between the converter and other converters connected in parallel at the same pole, and the actual reactive power difference between the two poles within the converter station. When generating the control voltage of the converter in the virtual excitation control section, the calculated parameters, in addition to the AC bus voltage command value, the actual AC bus voltage value, and the reference voltage of each converter, also include the reactive power differential adjustment amount. This achieves dynamic balance of reactive power for each converter, avoids the phenomenon of reactive power circulation in the converters, and improves the stability of the system in scenarios where multiple converters are connected in parallel.

[0019] To address the aforementioned technical problems, the present invention also provides a computer-readable storage medium storing computer-executable instructions, which, when executed, implement the converter control method based on a virtual synchronous machine described above.

[0020] The beneficial effects of the above technical solution are as follows: This invention is a pioneering invention. For scenarios involving multiple converters connected in parallel within a sending-end or receiving-end converter station, it calculates the reactive power differential adjustment amount of the converter when the reactive power within the converter station is balanced, based on the actual reactive power difference between the converter and other converters connected in parallel at the same pole, and the actual reactive power difference between the two poles within the converter station. When generating the control voltage of the converter in the virtual excitation control section, in addition to the AC bus voltage command value, the actual AC bus voltage value, and the reference voltage of each converter, the reactive power differential adjustment amount is also superimposed on the calculated parameters. This achieves dynamic balance of reactive power for each converter, avoids the phenomenon of reactive power circulation in the converters, and improves the stability of the system in scenarios involving multiple converters connected in parallel. Attached Figure Description

[0021] Figure 1 This is a block diagram of two converters connected in parallel in the prior art;

[0022] Figure 2 This is a block diagram of a converter control based on a virtual synchronous machine according to an embodiment of the method of the present invention;

[0023] Figure 3 This is a waveform diagram of reactive power balance control for multiple converters according to an embodiment of the method of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0025] This invention calculates the reactive power differential adjustment amount of the converter when the reactive power is balanced within the converter station, based on the actual reactive power difference between the converter and other converters connected in parallel at the same pole, and the actual reactive power difference between the two poles within the converter station. When generating the control voltage of the converter in the virtual excitation control section, the calculated parameters, in addition to the AC bus voltage command value, the actual AC bus voltage value, and the reference voltage of each converter, also include the reactive power differential adjustment amount. This achieves dynamic reactive power balance among the converters, avoids the phenomenon of reactive power circulation in the converters, meets the stable control requirements of AC voltage, reactive power, active power, and frequency for multiple converters, and improves the stability of the system in multi-converter parallel scenarios. Simultaneously, in the converter voltage control section, the inner-loop current control link of the traditional virtual synchronous machine control logic is no longer used, causing the VSC converter to exhibit voltage source characteristics, effectively suppressing the high-frequency resonance phenomenon that may occur in the AC system, and improving the power quality and operational safety of the AC grid.

[0026] Method Implementation Examples

[0027] This invention provides a converter control method based on a virtual synchronous machine, such as... Figure 2 As shown, the voltage command values ​​of each converter are obtained using virtual synchronous machine control. The virtual synchronous machine control includes a virtual mechanical control section, a reactive power differential regulation section, a virtual excitation control section, and a converter voltage control section. The virtual mechanical control section is used to calculate the phase angle. The reactive power differential regulation section is used to calculate the reactive power differential regulation amount of this converter based on the actual reactive power difference between this converter and other converters connected in parallel with the same pole, and the actual reactive power difference between the two poles within the converter station where this converter is located. The virtual excitation control section is used to calculate the converter control voltage based on the AC bus voltage command value, the actual AC bus voltage value, the converter's reactive power differential regulation amount, and the reference voltage of each converter. The converter voltage control section is used to calculate the converter voltage command value based on the phase angle and the control voltage of each converter. These are explained in detail below.

[0028] 1. Virtual mechanical control section

[0029] The virtual mechanical control adopts an active power control mode. Based on the converter's active power command value, the actual active power value of the converter, the reference angular velocity of the AC grid, the inertia time constant of the virtual synchronous machine, and the damping of the virtual synchronous machine, the phase angle required for the virtual control of the converter is calculated. The formula used to calculate the phase angle is as follows:

[0030]

[0031] Among them, T Jω represents the inertia time constant of the virtual synchronizer, in seconds; ω represents the angular velocity of the virtual synchronizer, ω0 represents the reference angular velocity of the AC power grid, in rad / s; t represents time; P ref The active power command value of the converter is represented by P, where P represents the actual AC active power of the converter in MW; D represents the damping of the virtual synchronous machine, dimensionless; and θ represents the phase angle of the virtual synchronous machine in rad. T for each converter... J , ω0, P ref Parameters such as D should be kept consistent.

[0032] 2. Reactive power differential adjustment section

[0033] The calculation method for the reactive power differential regulation of this converter is as follows: The first regulation is calculated based on the actual reactive power difference between the two poles within the converter station and the number of converters within the pole where this converter is located. The second regulation is calculated as the sum of the actual reactive power differences between this converter and other converters connected in parallel with the same pole. The first and second regulation are then added together to obtain the reactive power difference of this converter. The reactive power differential regulation is then obtained based on the reactive power difference and the reactive power differential regulation coefficient. The calculation formula is as follows:

[0034] The first regulation value QA1, which is allocated on average to this converter, is:

[0035]

[0036] The reactive power difference Δq of this converter is:

[0037]

[0038] The reactive power differential regulation ΔQ of this converter is:

[0039]

[0040] Where m is the number of converters in the pole where this converter is located, and n is the number of converters in the other pole; Q i Q represents the actual reactive power value of the i-th converter within the pole of this converter. opj q represents the actual reactive power of the j-th converter in the other pole, in Mvar; i This represents the difference in actual reactive power between this converter and the i-th converter connected in parallel with the same pole; k0 represents the reactive power difference adjustment coefficient, with units of kV / Mvar, and the k0 parameter of each converter remains consistent.

[0041] For example, when only one converter is installed at both the positive and negative poles of the converter station, i.e., when the converter station is a dual-converter parallel scenario, the reactive power differential regulation of this converter is:

[0042] △Q=k0(Q op -Q)

[0043] When a converter station has two converters connected in parallel on the positive pole and two converters connected in parallel on the negative pole, i.e., a four-converter parallel scenario, the actual reactive power values ​​of the two converters on the local pole are Q1 and Q2, and the actual reactive power value of the two converters on the opposite pole is Q. op1 Q op2 At this time, the first adjustment amount QA1, which is allocated on average to the converter in this stage, is:

[0044]

[0045] The reactive power differential adjustment of the first converter in this pole is:

[0046] ΔQ=k0*(QA1+q1)

[0047] q1 = Q2 - Q1

[0048] The reactive power differential adjustment of the second converter in this pole is:

[0049] ΔQ=k0*(QA1+q2)

[0050] q2 = Q1 - Q2

[0051] 3. Virtual excitation control section

[0052] The virtual excitation control adopts AC voltage mode, and performs PI control on the difference between the commanded AC bus voltage value and the actual AC bus voltage value. The PI-controlled value is then superimposed with the converter's reactive power differential regulation and the converter reference voltage to obtain the converter control voltage. The specific calculation formula is as follows:

[0053]

[0054] Among them, E q E0 represents the converter control voltage, and U represents the converter reference voltage. sref U represents the AC bus voltage command value. s E0 represents the actual value of the AC bus voltage, in kV; kp represents the proportional coefficient of the PI control loop, and ki represents the integral coefficient of the PI control loop, both dimensionless. The parameters E0, kp, and ki are kept consistent across all converters.

[0055] 4. Converter voltage control section

[0056] The converter voltage control utilizes the phase angle θ determined by virtual mechanical control and the converter control voltage Eq determined by virtual excitation control to calculate the converter voltage command value. The calculation formula is as follows:

[0057]

[0058] Among them, v a_ref v b_ref v c_ref These represent the voltage command values ​​for phases a, b, and c of the converter, respectively, in kV.

[0059] Device Examples

[0060] This invention discloses a converter control device based on a virtual synchronous machine. Each converter is equipped with a corresponding converter control device, including a processor. The processor executes computer instructions to control the converter according to the converter control method based on the virtual synchronous machine described in the above-described method embodiments. The specific implementation process of this method has been described in detail in the method embodiments and will not be repeated here. As a preferred embodiment, the converter control devices communicate with each other via optical fiber to transmit the actual reactive power values ​​of the converters. The communication protocol can adopt IEC 60044-8, IEEE 802.31000Base, Aurora, etc., with a transmission rate of at least 20 Mbps.

[0061] Computer-readable storage medium embodiments

[0062] The present invention provides a computer-readable storage medium storing computer-executable instructions. When executed, the computer-executable instructions implement a converter control method based on a virtual synchronous machine. The specific implementation process of the method has been described in detail in the method embodiments and will not be repeated here.

[0063] Based on the control method of this invention, multiple converters are controlled, and the resulting reactive power balance control waveform is as follows: Figure 3 As shown, Uac1 and Uac2 are the AC bus voltages of converter 1 and converter 2, respectively; Freq1 and Freq2 are the AC voltage frequencies of converter 1 and converter 2, respectively; P1 and P2 are the AC active power of converter 1 and converter 2, respectively; and Q1 and Q2 are the AC reactive power of converter 1 and converter 2, respectively. It can be seen that the control method of the present invention can meet the stable control requirements of AC voltage, reactive power, active power and frequency of multiple converters in the scenario of multiple converters in parallel, avoid the phenomenon of reactive power circulation of multiple converters, and realize the dynamic balance of reactive power of each converter.

Claims

1. A converter control method based on a virtual synchronous machine, characterized in that, The voltage command value of the converter is obtained using virtual synchronous machine control. The virtual synchronous machine control includes a virtual mechanical control section, a reactive power differential regulation section, a virtual excitation control section, and a converter voltage control section. The virtual mechanical control section is used to calculate the phase angle. The reactive power differential regulation section is used to calculate the reactive power differential regulation amount of the converter based on the actual reactive power difference between this converter and other converters connected in parallel with the same pole, and the actual reactive power difference between the two poles within the converter station where this converter is located. The virtual excitation control section is used to calculate the converter control voltage based on the AC bus voltage command value, the actual AC bus voltage value, the converter reactive power differential regulation amount, and the converter reference voltage. The converter voltage control section is used to calculate the converter voltage command value based on the phase angle and the converter control voltage. The calculation process of the reactive power differential adjustment amount of this converter is as follows: the first adjustment amount allocated to this converter is calculated based on the actual difference in reactive power between the two poles in the converter station where this converter is located and the number of converters in the pole where this converter is located. The sum of the actual differences in reactive power between this converter and other converters connected in parallel with the same pole is calculated as the second adjustment amount. The first adjustment amount and the second adjustment amount are superimposed to obtain the reactive power difference of this converter. The reactive power differential adjustment amount of this converter is obtained based on the reactive power difference of this converter and the reactive power differential adjustment coefficient.

2. The converter control method based on a virtual synchronous machine according to claim 1, characterized in that, The formula for calculating the reactive power differential regulation of this converter is: ； in, Here, k0 represents the reactive power differential regulation of this converter, m represents the number of converters in the pole containing this converter, and n represents the number of converters in the other pole. This represents the actual reactive power value of the i-th converter within the pole where this converter is located. This represents the actual reactive power value of the j-th converter within the other pole. This represents the difference in actual reactive power between this converter and the i-th converter connected in parallel with the same pole.

3. The converter control method based on a virtual synchronous machine according to claim 1 or 2, characterized in that, The calculation process of the converter control voltage is as follows: the difference between the AC bus voltage command value and the actual AC bus voltage value is subjected to PI control, and the value after PI control is superimposed with the reactive power differential adjustment of the converter and the converter reference voltage to obtain the converter control voltage.

4. The converter control method based on a virtual synchronous machine according to claim 1 or 2, characterized in that, The phase angle is determined based on the converter active power command value, the actual converter active power value, the reference angular velocity of the AC grid, the inertia time constant of the virtual synchronous machine, and the damping of the virtual synchronous machine.

5. The converter control method based on a virtual synchronous machine according to claim 4, characterized in that, The formula for calculating the phase angle is as follows: ； Among them, T J The inertia time constant of the virtual synchronizer; Let t be the angular velocity of the virtual synchronizer, and t be time. The reference angular velocity of the AC power grid; P ref θ is the active power command value of the converter, P is the actual AC active power value of the converter; D is the damping of the virtual synchronous machine; θ is the phase angle of the virtual synchronous machine.

6. A converter control device based on a virtual synchronous machine, comprising a processor, characterized in that, The processor is used to execute computer instructions to implement the converter control method based on a virtual synchronous machine as described in any one of claims 1-5.

7. The converter control device based on a virtual synchronous machine according to claim 6, characterized in that, The actual reactive power values ​​of the converters are transmitted between the converter control devices via optical fiber communication.

8. A computer-readable storage medium storing computer-executable instructions, characterized in that, The computer-executable instructions are used, when executed, to implement the converter control method based on a virtual synchronous machine as described in any one of claims 1-5.

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