Converter control method and device based on virtual synchronous machine, and computer readable storage medium

Abstract

The invention belongs to the technical field of flexible direct current transmission, and particularly relates to a converter control method and device based on a virtual synchronous machine and a computer readable storage medium. The method aims at a multi-converter parallel connection scene in a sending-end converter station or a receiving-end converter station. Calculating the reactive power difference adjusting quantity of the current converter when the reactive power in the current converter station is balanced based on the reactive power actual value difference between the current converter and other current converters of which the same pole is connected in parallel and the reactive power actual value difference between two poles in the current converter station where the current converter is located; when the virtual excitation control part generates the control voltage of the current converter, besides an alternating current bus voltage instruction value, an alternating current bus voltage actual value and a current converter reference voltage, calculation parameters are superposed with a reactive power difference regulating variable, so that reactive power dynamic balance of each current converter is realized, the phenomenon of reactive circulation of the current converter is avoided, and the service life of the current converter is prolonged. And the stability of the system in a multi-converter parallel connection scene is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible direct current transmission, and in particular relates to a converter control method and device based on a virtual synchronous machine, and a computer-readable storage medium. Background Art

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

[0003] For the scenario of multiple converters in parallel, the document "Control Strategy of Bipolar Flexible DC Converter Station Accessed to Isolated New Energy Power Field" proposes a method of coordinated control of AC voltage and frequency droop of bipolar converter units (referred to as dual U / f droop control). Both dual converters adopt reactive power / AC voltage (Q / U) droop control to adjust the amplitude balance of the AC bus voltage of the dual converters. Both dual converters adopt active power / AC frequency (P / f) droop control to adjust the phase synchronization of the AC bus voltage of the dual converters. However, since the primary and secondary devices involved in the control loops of each converter have certain differences, the control device of each converter independently controls the reactive power, the reactive power command value Qref of each converter remains consistent, and the sum of the reactive powers of the converters is constant, resulting in inconsistent reactive power of each converter. The deviation between the reactive power of one converter and the reactive power command value is greater than zero, and the deviation between the reactive power of the other converter and the reactive power command value is less than zero, which leads to a large reactive power circulation between the two converters, making it impossible to achieve reactive power balance of multiple converters, which may cause the reactive power of the converter to exceed the limit and affect the stable operation of the system. Summary of the invention

[0004] The purpose of the present invention is to provide a converter control method, device and computer-readable storage medium based on a virtual synchronous machine, so as to solve the problem that the existing converter control method in a multi-converter parallel scenario causes reactive power circulation between converters, affecting the stable operation of the system.

[0005] In order to solve the above technical problems, the present invention provides a converter control method based on a virtual synchronous machine, which adopts virtual synchronous machine control to obtain the voltage command value of the converter; the virtual synchronous machine control includes a virtual mechanical control part, a reactive power differential adjustment part, a virtual excitation control part and a converter voltage control part; the virtual mechanical control part is used to calculate the phase angle; the reactive power differential adjustment part is used to calculate the reactive power differential adjustment amount of the converter according to the difference in actual reactive power values ​​between the converter and other converters connected in parallel with the same pole, and the difference in actual reactive power values ​​between the two poles in the converter station where the converter is located; the virtual excitation control part is used to calculate the converter control voltage according to the AC bus voltage command value, the actual value of the AC bus voltage, the reactive power differential adjustment amount of the converter and the converter reference voltage; the converter voltage control part is used to calculate the voltage command value of the converter according to the phase angle and the converter control voltage.

[0006] Furthermore, the calculation process of the reactive power differential regulation amount of the converter is as follows: the first regulation amount allocated to the converter is calculated according to the difference in actual reactive power values ​​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 differences in actual reactive power values ​​between the converter and other converters connected in parallel to the same pole is calculated as the second regulation amount, the first regulation amount and the second regulation amount are superimposed to obtain the reactive power difference of the converter, and the reactive power differential regulation amount of the converter is obtained according to the reactive power difference of the converter and the reactive power differential regulation coefficient.

[0007] Furthermore, the calculation formula of the reactive power differential regulation amount of the converter is:

[0008]

[0009] Among them, 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, n is the number of converters in another pole, Q i is the actual reactive power value of the ith converter in the pole where the converter is located, Q opj is the actual reactive power value of the jth converter in the other pole, q i is the difference in actual reactive power between this converter and the other i-th converter connected in parallel with the same pole.

[0010] Furthermore, the calculation process of the converter control voltage is: PI control is performed on the difference between the AC bus voltage command value and the actual value of the AC bus voltage, and the value after PI control is superimposed on the converter's reactive power differential adjustment amount and the converter reference voltage to obtain the converter control voltage.

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

[0012] Furthermore, the calculation formula of the phase angle is as follows:

[0013]

[0014] Among them, T J is the inertia time constant of the virtual synchronous machine; ω is the angular velocity of the virtual synchronous machine, t is time, ω0 is the reference angular velocity of the AC power grid; P ref is the active power command value of the converter, P is the actual value of the AC active power 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: the present invention is a pioneering invention, which aims at the scenario of multiple converters in parallel in the sending-end converter station or the receiving-end converter station. The reactive power differential adjustment amount of the converter is calculated when the reactive power in the converter station is balanced based on the difference in actual reactive power values ​​between the converter and other converters in parallel with the same pole, and the difference in actual reactive power values ​​between the two poles in the converter station where the converter is located. When the virtual excitation control part generates the control voltage of the converter, in addition to the AC bus voltage command value, the actual value of the AC bus voltage and the reference voltage of each converter, the reactive power differential adjustment amount is also superimposed on the calculated parameters, thereby realizing the dynamic balance of reactive power of each converter, avoiding the occurrence of reactive circulating current of the converter, and improving the stability of the system in the scenario of multiple converters in parallel.

[0016] To solve the above technical problems, the present invention further provides a converter control device based on a virtual synchronous machine, comprising a processor, wherein the processor is used to execute computer instructions to implement the above-mentioned converter control method based on a virtual synchronous machine.

[0017] Furthermore, the converter control devices use optical fiber communication to transmit the actual value of the reactive power of the converter to each other.

[0018] The beneficial effects of the above technical solution are as follows: the present invention is a pioneering invention, and for the scenario of multiple converters in parallel in a sending-end converter station or a receiving-end converter station, the control device of each converter calculates the reactive power differential adjustment amount of the converter when the reactive power in the converter station is balanced based on the difference in actual reactive power values ​​between the converter and other converters in parallel with the same pole, and the difference in actual reactive power values ​​between the two poles in the converter station where the converter is located. When the virtual excitation control part generates the control voltage of the converter, in addition to the AC bus voltage command value, the actual value of the AC bus voltage and the reference voltage of each converter, the reactive power differential adjustment amount is also superimposed on the calculated parameters, thereby achieving dynamic reactive power balance of each converter, avoiding the occurrence of reactive circulating current of the converter, and improving the stability of the system in the scenario of multiple converters in parallel.

[0019] In order to solve the above technical problems, the present invention further provides a computer-readable storage medium, in which computer-executable instructions are stored. The computer-executable instructions are used to implement the above-mentioned converter control method based on virtual synchronous machine when executed.

[0020] The beneficial effects of the above technical solution are as follows: the present invention is a pioneering invention, which aims at the scenario of multiple converters in parallel in the sending-end converter station or the receiving-end converter station. The reactive power differential adjustment amount of the converter is calculated when the reactive power in the converter station is balanced based on the difference in actual reactive power values ​​between the converter and other converters in parallel with the same pole, and the difference in actual reactive power values ​​between the two poles in the converter station where the converter is located. When the virtual excitation control part generates the control voltage of the converter, in addition to the AC bus voltage command value, the actual value of the AC bus voltage and the reference voltage of each converter, the reactive power differential adjustment amount is also superimposed on the calculated parameters, thereby realizing the dynamic balance of reactive power of each converter, avoiding the occurrence of reactive circulating current of the converter, and improving the stability of the system in the scenario of multiple converters in parallel. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0023] Figure 3 It is a waveform diagram of reactive power balance control of multiple converters in an embodiment of the method of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clear, the specific implementation methods of the present invention are further described below in conjunction with the accompanying drawings.

[0025] The present invention calculates the reactive power differential adjustment amount of the converter when the reactive power in the converter station is balanced based on the difference in the actual value of reactive power between the converter and other converters connected in parallel with the same pole, and the difference in the actual value of reactive power between the two poles in the converter station where the converter is located. When the virtual excitation control part generates the control voltage of the converter, the calculation parameters are not only the AC bus voltage command value, the AC bus voltage actual value and the reference voltage of each converter, but also the reactive power differential adjustment amount is superimposed, so as to realize the dynamic balance of reactive power of each converter, avoid the phenomenon of reactive circulating current of the converter, meet the stable control requirements of AC voltage, reactive power, active power and frequency of multiple converters, and improve the stability of the system in the scenario of multiple converters in parallel. At the same time, in the converter voltage control part, the inner loop current control link of the traditional virtual synchronous machine control logic is no longer used, so that the VSC converter presents the characteristics of a voltage source, effectively suppresses the high-frequency resonance phenomenon that may occur in the AC system, and improves the power quality and operation safety of the AC power grid.

[0026] Method Embodiment

[0027] A converter control method based on a virtual synchronous machine of the present invention is as follows: Figure 2 As shown, the voltage command value of each converter is obtained by virtual synchronous machine control, and the virtual synchronous machine control includes a virtual mechanical control part, a reactive power differential adjustment part, a virtual excitation control part and a converter voltage control part; the virtual mechanical control part is used to calculate the phase angle; the reactive power differential adjustment part is used to calculate the reactive power differential adjustment amount of the converter according to the difference in actual reactive power values ​​between the converter and other converters connected in parallel with the same pole, and the difference in actual reactive power values ​​between the two poles in the converter station where the converter is located; the virtual excitation control part is used to calculate the converter control voltage according to the AC bus voltage command value, the actual value of the AC bus voltage, the reactive power differential adjustment amount of the converter and the reference voltage of each converter; the converter voltage control part is used to calculate the voltage command value of the converter according to the phase angle and the control voltage of each converter, which is described in detail below.

[0028] 1. Virtual mechanical control part

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

[0030]

[0031] Among them, T Jrepresents the inertia time constant of the virtual synchronous machine, in seconds; ω represents the angular velocity of the virtual synchronous machine, ω0 represents the reference angular velocity of the AC power grid, in rad / s; t represents time; P ref represents the active power command value of the converter, P represents the actual value of the AC active power of the converter, in MW; D represents the damping of the virtual synchronous machine, dimensionless; θ represents the phase angle of the virtual synchronous machine, in rad. J ,ω0,P ref , D and other parameters remain consistent.

[0032] 2. Reactive power differential regulation part

[0033] The calculation method of the reactive power differential regulation amount of the converter is as follows: the first regulation amount allocated to the converter is calculated according to the difference in the actual 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 differences in the actual reactive power between the converter and other converters connected in parallel with the same pole is calculated as the second regulation amount, the reactive power difference of the converter is obtained by superimposing the first regulation amount and the second regulation amount, and the reactive power differential regulation amount of the converter is obtained according to the reactive power difference of the converter and the reactive power differential regulation coefficient. The calculation formula is as follows:

[0034] The first adjustment amount QA1 evenly distributed by the 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 the converter is located, and n is the number of converters in the other pole; Q i It represents the actual reactive power value of the ith converter in the pole where the converter is located, Q opj Represents the actual value of reactive power of the jth converter in the other pole, in Mvar; q i is the difference in actual reactive power between this converter and the other i-th converter connected in parallel with the same pole; k0 represents the reactive power differential adjustment coefficient, in units of kV / Mvar, and the k0 parameters of each converter remain consistent.

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

[0042] △Q=k0(Q op -Q)

[0043] When the positive pole of the converter station is connected to two converters in parallel and the negative pole is connected to two converters in parallel, that is, the converter station is a four-converter parallel scenario, the actual reactive power values ​​of the two converters at the same pole are Q1 and Q2, and the actual reactive power values ​​of the two converters at the opposite pole are Q op1 , Q op2 At this time, the first adjustment amount QA1 evenly distributed by the converter at this level is:

[0044]

[0045] The reactive power difference regulation of the first converter in this pole is:

[0046] ΔQ=k0*(QA1+q1)

[0047] q1=Q2-Q1

[0048] The reactive power difference regulation of the second converter in this pole is:

[0049] ΔQ=k0*(QA1+q2)

[0050] q2=Q1-Q2

[0051] 3. Virtual excitation control part

[0052] Virtual excitation control adopts AC voltage mode, performs PI control on the difference between the AC bus voltage command value and the actual value of the AC bus voltage, and superimposes the value after PI control on the reactive power difference adjustment amount of the converter and the converter reference voltage to obtain the converter control voltage. The specific calculation formula is:

[0053]

[0054] Among them, E q represents the converter control voltage, E0 represents the converter reference voltage, U sref Indicates the AC bus voltage command value, U s Indicates the actual value of the AC bus voltage, in kV; kp indicates the proportional coefficient of the PI control link, and ki indicates the integral coefficient of the PI control link, dimensionless. Among them, the parameters such as E0, kp, and ki of each converter remain consistent.

[0055] 4. Converter voltage control part

[0056] The converter voltage control uses the phase angle θ determined by the virtual mechanical control and the converter control voltage Eq determined by the 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 They represent the voltage command values ​​of converter phase a, phase b, and phase c respectively, in kV.

[0059] Device Embodiment

[0060] A converter control device based on a virtual synchronous machine of the present invention, one converter control device is provided for each converter, and includes a processor, and the processor is used to execute computer instructions to control the converter according to the converter control method based on a virtual synchronous machine introduced in the above method embodiment. The specific implementation process of the method has been described in detail in the method embodiment, and will not be repeated here. As a preferred embodiment, the converter control devices use optical fiber communication to transmit the actual value of the reactive power of the converter to each other, and the communication protocol can adopt IEC 60044-8, IEEE 802.31000Base, Aurora, etc., and the transmission rate is at least 20Mbps.

[0061] Computer Readable Storage Medium Embodiments

[0062] A computer-readable storage medium of the present invention stores computer executable instructions in the storage medium. The computer executable instructions are used to implement a converter control method based on a virtual synchronous machine when executed. The specific implementation process of the method has been described in detail in the method embodiment and will not be repeated here.

[0063] The reactive power balance control waveform obtained by controlling multiple converters based on the control method of the present invention 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 powers of converter 1 and converter 2 respectively; Q1 and Q2 are the AC reactive powers 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, avoids the phenomenon of reactive power circulation of multiple converters, and realizes 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 by using virtual synchronous machine control; the virtual synchronous machine control includes a virtual mechanical control part, a reactive power differential regulation part, a virtual excitation control part and a converter voltage control part; the virtual mechanical control part is used to calculate the phase angle; the reactive power differential regulation part is used to calculate the reactive power differential regulation amount of the converter according to the difference in actual reactive power values ​​between the converter and other converters connected in parallel with the same pole, and the difference in actual reactive power values ​​between the two poles in the converter station where the converter is located; the virtual excitation control part is used to calculate the converter control voltage according to the AC bus voltage command value, the actual value of the AC bus voltage, the reactive power differential regulation amount of the converter and the converter reference voltage; the converter voltage control part is used to calculate the voltage command value of the converter according to the phase angle and the converter control voltage.

2. The converter control method based on virtual synchronous machine according to claim 1, characterized in that: The calculation process of the reactive power differential regulation amount of the converter is as follows: the first regulation amount allocated to the converter is calculated according to the difference in actual reactive power values ​​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 differences in actual reactive power values ​​between the converter and other converters connected in parallel to the same pole is calculated as the second regulation amount, the first regulation amount and the second regulation amount are superimposed to obtain the reactive power difference of the converter, and the reactive power differential regulation amount of the converter is obtained according to the reactive power difference of the converter and the reactive power differential regulation coefficient.

3. The converter control method based on virtual synchronous machine according to claim 2, characterized in that: The calculation formula of the reactive power differential regulation of this converter is: Among them, 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, n is the number of converters in another pole, Q i is the actual reactive power value of the ith converter in the pole where the converter is located, Q opj is the actual reactive power value of the jth converter in the other pole, q i is the difference in actual reactive power between this converter and the other i-th converter connected in parallel with the same pole.

4. The converter control method based on a virtual synchronous machine according to any one of claims 1 to 3, characterized in that: The calculation process of the converter control voltage is as follows: PI control is performed on the difference between the AC bus voltage command value and the actual value of the AC bus voltage, and the value after PI control is superimposed on the converter's reactive power differential adjustment amount and the converter reference voltage to obtain the converter control voltage.

5. The converter control method based on a virtual synchronous machine according to any one of claims 1 to 3, characterized in that: The phase angle is determined based on the converter active power command value, the converter active power actual value, the reference angular velocity of the AC power grid, the inertia time constant of the virtual synchronous machine, and the damping of the virtual synchronous machine.

6. The converter control method based on virtual synchronous machine according to claim 5, characterized in that: The calculation formula of the phase angle is as follows: Among them, T J is the inertia time constant of the virtual synchronous machine; ω is the angular velocity of the virtual synchronous machine, t is time, ω0 is the reference angular velocity of the AC power grid; P ref is the active power command value of the converter, P is the actual value of the AC active power of the converter; D is the damping of the virtual synchronous machine; θ is the phase angle of the virtual synchronous machine.

7. 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 the virtual synchronous machine according to any one of claims 1-6.

8. The converter control device based on virtual synchronous machine according to claim 7, characterized in that: The converter control devices use optical fiber communication to transmit the actual value of the converter's reactive power to each other.

9. A computer-readable storage medium storing computer-executable instructions, characterized in that: The computer executable instructions are used to implement the converter control method based on the virtual synchronous machine as described in any one of claims 1 to 6 when being executed.

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