Method and apparatus for suppressing synchronous oscillation in power synchronous control converters

Abstract

This invention relates to a method and apparatus for suppressing synchronous oscillations in a power synchronous control converter. The method involves obtaining a first difference ΔP between a reference value of active power and a measured value of active power at the grid connection point of the power synchronous control converter; obtaining a first difference ΔQ between a reference value of reactive power and a measured value of reactive power at the grid connection point of the power synchronous control converter; limiting the synchronous frequency component of the first difference ΔP using a first band-stop filter to obtain a second difference ΔP; obtaining a reference phase of a modulation signal based on the second difference ΔP; limiting the synchronous frequency component of the first difference ΔQ using a second band-stop filter to obtain a second difference ΔQ; calculating a reference voltage amplitude of the modulation signal based on the second difference ΔQ; and generating a modulation signal for controlling the power synchronous control converter based on the reference phase and reference voltage amplitude of the modulation signal. This invention can effectively suppress synchronous oscillations during the operation of a power synchronous control converter.

Description

Technical Field

[0001] This invention relates to a method and apparatus for suppressing synchronous oscillations in a power synchronous control converter. Background Technology

[0002] Converters used in grid-connected renewable energy sources (such as wind turbines connected to the DC grid) are commonly classified into two types based on their synchronization methods: grid-following converters and grid-forming converters. Compared to earlier grid-following converters, grid-forming converters can provide both voltage and frequency support. As the proportion of renewable energy sources connected to the grid increases, traditional synchronous generators in the grid will be gradually phased out, and the voltage and frequency standards of the grid will no longer be able to be determined by them. Therefore, grid-forming converters, due to their ability to provide voltage and frequency support, have become a focus of research and have a very broad application prospect.

[0003] However, power synchronous control converters employing droop control lack damping characteristics in their power control, making them prone to synchronous oscillations during operation, which can lead to system instability and negatively impact the safe and stable operation of the power grid. Furthermore, the coupling effect between the active and reactive power loops in the power control loop exacerbates synchronous frequency oscillations, effectively introducing "negative damping" and further reducing system stability. Against this backdrop, suppressing synchronous oscillations in power synchronous control converters is a pressing issue that needs to be addressed, as it is crucial for ensuring the stable operation of the power grid as the proportion of renewable energy integration continues to rise. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for suppressing synchronous oscillations in a power synchronous control converter, which can effectively suppress synchronous oscillations during the operation of the power synchronous control converter.

[0005] Based on the same inventive concept, this invention has two independent technical solutions:

[0006] 1. A method for suppressing synchronous oscillations in a power synchronous control converter, comprising the following steps:

[0007] Step 1: Obtain the reference value of active power at the grid connection point of the power synchronous control converter. P ref and active power measurement value P out The first difference △P1;

[0008] Obtain the reactive power reference value at the grid connection point of the power synchronous control converter.Q ref and reactive power measurement values Q out The first difference △Q1;

[0009] Step 2: Limit the synchronization frequency component of the first difference ΔP1 through the first band-stop filter to obtain the second difference ΔP2; calculate the reference phase of the modulation signal based on the second difference ΔP2 using the active power control loop. d ref ;

[0010] The first difference ΔQ1 is passed through a second band-stop filter to limit its synchronization frequency component, thus obtaining a second difference ΔQ2. Based on the second difference ΔQ2, the reference voltage amplitude of the modulation signal is calculated using a reactive power control loop. V ref ;

[0011] Step 3: Based on the reference phase of the modulation signal d ref and reference voltage amplitude V ref The modulation signal for controlling the power synchronous control converter is generated; the modulation signal is transmitted to the PWM generator to generate the PWM signal for controlling the power synchronous control converter.

[0012] Furthermore, in step 2, the transfer functions of the first band-stop filter and the second band-stop filter are:

[0013]

[0014] In the formula, s For the Laplace operator, oh 0 represents the synchronization angular frequency of the power grid. x is the damping coefficient.

[0015] Furthermore, the damping coefficient x Determined by the following method,

[0016] Based on the spectral characteristics of power synchronous oscillation, a synchronization frequency is selected. f 0-symmetric upper limit frequency f 2 and lower limit frequency f 1, then the bandwidth Δ oh =2π ( f 2- f 1) Damping coefficient x =△ oh / oh 0.

[0017] Furthermore, in step 1, the active power measurement value P outand reactive power measurement values Q out The data was obtained directly from the grid connection point of the power synchronous control converter.

[0018] Furthermore, in step 2, the active power control loop calculates the reference phase of the modulation signal. O ref This can be achieved through the following method.

[0019] Based on the second difference △P2 、 Active sagging coefficient D p The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. oh The reference phase is obtained by adding the zeros together and then performing an integral transform. d ref .

[0020] Furthermore, in step 2, the reactive power control loop calculates the reference voltage amplitude of the modulation signal. V ref This can be achieved through the following method.

[0021] Based on the second difference △Q2 、 reactive power droop coefficient D q The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. oh The reference voltage amplitude is obtained by summing the zeros and then performing an integral transformation. V ref .

[0022] 2. A synchronous oscillation suppression device for a power synchronous control converter, comprising:

[0023] The active power control module includes a first band-stop filter. The first band-stop filter limits the synchronization frequency component of the first difference ΔP1 to obtain a second difference ΔP2. Based on the second difference ΔP2, the reference phase of the modulation signal is calculated by the active power control loop. d ref The first difference △P1 refers to the active power reference value at the grid connection point of the power synchronous control converter. P ref and active power measurement value P out The difference;

[0024] The reactive power control module includes a second band-stop filter. The second band-stop filter limits the synchronous frequency component of the first difference ΔQ1 to obtain a second difference ΔQ2. Based on the second difference ΔQ2, the reference voltage amplitude of the modulation signal is calculated by the reactive power control loop. Vref ;

[0025] Modulation signal generation module, the modulation signal generation module according to reference phase d ref Reference voltage amplitude V ref Generate the modulation signal for controlling the power synchronization control converter;

[0026] A PWM generator that generates a PWM signal from the modulation signal to control the power synchronization control converter.

[0027] Furthermore, the transfer functions of the first band-stop filter and the second band-stop filter are:

[0028]

[0029] In the formula, s For the Laplace operator, oh 0 represents the synchronization angular frequency of the power grid. x is the damping coefficient.

[0030] Furthermore, the active power control loop calculates the reference phase of the modulation signal. d ref This can be achieved through the following method.

[0031] Based on the second difference △P2 、 Active sagging coefficient D p The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. oh The reference phase is obtained by adding the zeros together and then performing an integral transform. d ref .

[0032] Furthermore, the reactive power control loop calculates the reference voltage amplitude of the modulation signal. V ref This can be achieved through the following method.

[0033] Based on the second difference △Q2 、 reactive power droop coefficient D q The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. oh The reference voltage amplitude is obtained by summing the zeros and then performing an integral transformation. V ref .

[0034] The beneficial effects of this invention are as follows:

[0035] This invention obtains the reference value of active power at the grid connection point of the power synchronous control converter. P refand active power measurement value P out The first difference △P1; obtain the reactive power reference value at the grid connection point of the power synchronous control converter. Q ref and reactive power measurement values Q out The first difference △Q1 is obtained; the first difference △P1 is passed through a first band-stop filter to limit its synchronization frequency component, thus obtaining a second difference △P2; based on the second difference △P2, the reference phase of the modulation signal is calculated through the active power control loop. d ref The first difference ΔQ1 is passed through a second band-stop filter to limit its synchronization frequency component, thus obtaining a second difference ΔQ2. Based on the second difference ΔQ2, the reference voltage amplitude of the modulation signal is calculated using a reactive power control loop. V ref According to the reference phase of the modulated signal d ref and reference voltage amplitude V ref The method generates a modulation signal to control the power synchronous control converter; the modulation signal is then transmitted to a PWM generator to generate a PWM signal to control the power synchronous control converter. This invention uses a band-stop filter to limit the synchronous harmonics of the power deviation signal in the input power control loop. The principle is simple, suppressing synchronous oscillations in the converter power control loop output voltage reference signal and eliminating synchronous propagation and amplification phenomena in subsequent stages such as modulation signal generation. Furthermore, this method does not affect the converter's balanced operating point.

[0036] The transfer functions of the first band-stop filter and the second band-stop filter of this invention are as follows:

[0037]

[0038] In the formula, s For the Laplace operator, oh 0 represents the synchronization angular frequency of the power grid. x This represents the damping coefficient. The present invention, through the transfer function of the aforementioned band-stop filter, further ensures the suppression of synchronous oscillations during the operation of the power synchronous control converter.

[0039] Damping coefficient of the present invention x Determined by the following method,

[0040] Based on the spectral characteristics of power synchronous oscillation, a synchronization frequency is selected. f 0-symmetric upper limit frequency f 2 and lower limit frequency f 1, then the bandwidth Δ oh =2π ( f 2- f1) Damping coefficient x =△ oh / oh 0. By setting the damping coefficient as described above, this invention can further ensure the suppression of oscillation signals within a certain bandwidth near the synchronization frequency.

[0041] After applying a band-stop filter, the bandwidth of power control increases, allowing the converter to operate stably with a higher droop factor compared to before applying the filter. Adding a band-stop filter does not affect the original stable operating point of power control and is applicable to power synchronous control converters operating in islanded or grid-connected configurations. Compared to existing converter synchronous oscillation suppression methods, the method of this invention is simpler in structure, easier to design parameters, can improve the synchronous oscillation problem of the system, is easier to apply in engineering, and exhibits good control performance under various operating conditions. Attached Figure Description

[0042] Figure 1 The diagram shows the power control principle of an existing power synchronous control converter.

[0043] Figure 2 This is a schematic diagram of the synchronous oscillation suppression method for power synchronous control converters based on band-stop filters according to the present invention.

[0044] Figure 3 Bode plots of the open-loop gain of the active and reactive loops before applying a band-stop filter;

[0045] Figure 4 Bode plots of the open-loop gain of the active and reactive loops after applying a band-stop filter according to this invention;

[0046] Figure 5 The waveforms of simulated voltage, current, and power before and after applying a band-stop filter are shown.

[0047] Figure 6 The voltage, current, and power waveforms obtained from the simulation of the band-stop filter cut-out midway are shown. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0049] Example 1:

[0050] Synchronous Oscillation Suppression Method for Power Synchronous Control Converters

[0051] like Figure 1As shown, based on the reference value of active power at the grid connection point P ref and active power measurement value P out 、 reactive power reference value Q ref and reactive power measurement values Q out ， The reference phase of the modulation signal is obtained through a power control loop. d ref and reference voltage amplitude V ref According to the reference phase of the modulated signal d ref and reference voltage amplitude V ref Generate control power synchronous control converter VSC The modulation signal is transmitted to the PWM generator to generate a control power synchronous control converter. VSC The PWM signal is existing technology.

[0052] like Figure 2 As shown, a first band-stop filter and a second band-stop filter are added to the power control loop. The transfer functions of the first band-stop filter and the second band-stop filter are:

[0053]

[0054] In the formula, s For the Laplace operator, oh 0 represents the synchronization angular frequency of the power grid. x This refers to the damping coefficient. x Determined by the following method,

[0055] Based on the spectral characteristics of power synchronous oscillation, a synchronization frequency is selected. f 0-symmetric upper limit frequency f 2 and lower limit frequency f 1, then the bandwidth Δ oh =2π ( f 2- f 1) Damping coefficient x =△ oh / oh 0.

[0056] like Figure 1 , Figure 2 As shown, the method for suppressing synchronous oscillation in a power synchronous control converter according to the present invention includes the following steps:

[0057] Step 1: Obtain the reference value of active power at the grid connection point of the power synchronous control converter.P ref and active power measurement value P out The first difference △P1; obtain the reactive power reference value at the grid connection point of the power synchronous control converter. Q ref and reactive power measurement values Q out The first difference △Q1.

[0058] Active power measurement value P out and reactive power measurement values Q out The data was obtained directly from the grid connection point of the power synchronous control converter.

[0059] Step 2: Limit the synchronization frequency component of the first difference ΔP1 through the first band-stop filter to obtain the second difference ΔP2; calculate the reference phase of the modulation signal based on the second difference ΔP2 using the active power control loop. d ref The first difference ΔQ1 is passed through a second band-stop filter to limit its synchronization frequency component, thus obtaining a second difference ΔQ2. Based on the second difference ΔQ2, the reference voltage amplitude of the modulation signal is calculated using a reactive power control loop. V ref .

[0060] The active power control loop calculates the reference phase of the modulation signal. d ref This is achieved through the following method, based on the second difference △P2. 、 Active sagging coefficient D p The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. oh The reference phase is obtained by adding the zeros together and then performing an integral transform. d ref .

[0061] The reactive power control loop calculates the reference voltage amplitude of the modulation signal. V ref This is achieved through the following method, based on the second difference △Q2. 、 reactive power droop coefficient D q The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. oh The reference voltage amplitude is obtained by summing the zeros and then performing an integral transformation. V ref .

[0062] Step 3: Based on the reference phase of the modulation signal d ref and reference voltage amplitudeV ref The modulated signal for controlling the power synchronous control converter VSC is generated; the modulated signal is transmitted to the PWM generator to generate the PWM signal for controlling the power synchronous control converter VSC.

[0063] As can be seen from the above, the active power control loop formula and the reactive power control loop formula of this invention are respectively:

[0064]

[0065]

[0066] like Figure 3 to Figure 6 As shown, Figure 3 (a) Bode plot of the open-loop gain of the active loop before applying the band-stop filter; Figure 3 (b) Bode plot of the open-loop gain of the reactive loop before applying the band-stop filter. Figure 4 (a) Bode plot of the open-loop gain of the active loop after applying the band-stop filter according to the present invention; Figure 4 (b) Bode plot of the open-loop gain of the reactive loop after applying the band-stop filter according to the present invention. Figure 3 , Figure 4 In the vertical axis: Mag represents the amplitude, in decibels (dB); Phase represents the phase, in degrees (deg).

[0067] Figure 5 (a) The voltage, current and power waveforms obtained from the simulation before applying the band-stop filter; Figure 5 (b) The voltage, current and power waveforms obtained by simulation after applying the band-stop filter according to the present invention. Figure 6 The present invention applies a band-stop filter at startup and cuts off the voltage, current and power waveforms obtained from the band-stop filter simulation at 5s. Figure 5 , Figure 6 In the ordinate: v a This refers to the voltage of phase a, in kilovolts (kV). i a The current in phase a is expressed in kiloamperes (kA). P Active power, measured in megawatts (MW). Q Reactive power, measured in megavars [Mvar].

[0068] Before and after using the band-stop filter in the embodiment, from Figure 3 , Figure 4 and Figure 5 The following conclusions can be drawn: Figure 3The Bode plot amplitude-frequency curve of the active loop open-loop gain is above the zero mark near the synchronization frequency, while the phase-frequency curve lags by 180° near the synchronization frequency. This indicates that before applying the band-stop filter, the system exhibits synchronous oscillations that lead to instability. After applying the band-stop filter of the embodiment, Figure 4 The Bode plots of the open-loop gains of the active and reactive power loops show that their amplitude-frequency curves are all less than 0 near the synchronization frequency, indicating that the system oscillations near the synchronization frequency are suppressed and the system is stable. Furthermore, based on the characteristics of the open-loop gain phase-frequency curves of the active and reactive power loops after adding the band-stop filter, it can be seen that the bandwidth of power control has increased. Compared to before adding the band-stop filter, the system can maintain stable operation with a larger droop factor. Figure 5 During the simulation, a sudden change in active power is caused, and the active power reference value is reset after 7 seconds. P ref It dropped to 0.8 PU, then recovered to 1.0 PU after 8 seconds. Figure 5 (a) It can be seen that before the band-stop filter is applied, the system becomes unstable due to synchronous frequency oscillations after being disturbed, and Figure 5 (b) It shows that after applying the band-stop filter, the system maintains stable operation and the power frequency oscillation is suppressed. Figure 6 A band-stop filter was applied when the system started up. The simulated waveform obtained by cutting off the band-stop filter at 5s showed that the system oscillated synchronously after the band-stop filter was removed and gradually lost stability, indicating that the applied band-stop filter can maintain the stable operation of the system.

[0069] Example 2:

[0070] A synchronous oscillation suppression device for power synchronous control converters

[0071] include:

[0072] The active power control module includes a first band-stop filter. The first band-stop filter limits the synchronization frequency component of the first difference ΔP1 to obtain a second difference ΔP2. Based on the second difference ΔP2, the reference phase of the modulation signal is calculated by the active power control loop. d ref The first difference △P1 refers to the active power reference value at the grid connection point of the power synchronous control converter. P ref and active power measurement value P out The difference;

[0073] The reactive power control module includes a second band-stop filter. The second band-stop filter limits the synchronous frequency component of the first difference ΔQ1 to obtain a second difference ΔQ2. Based on the second difference ΔQ2, the reference voltage amplitude of the modulation signal is calculated by the reactive power control loop.V ref ;

[0074] Modulation signal generation module, the modulation signal generation module according to reference phase d ref Reference voltage amplitude V ref Generate the modulation signal for controlling the power synchronization control converter;

[0075] A PWM generator that generates a PWM signal from the modulation signal to control the power synchronization control converter.

[0076] The transfer functions of the first band-stop filter and the second band-stop filter are:

[0077]

[0078] In the formula, s For the Laplace operator, oh 0 represents the synchronization angular frequency of the power grid. x is the damping coefficient.

[0079] The active power control loop calculates the reference phase of the modulation signal. d ref This is achieved through the following method, based on the second difference △P2. 、 Active sagging coefficient D p The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. oh The reference phase is obtained by adding the zeros together and then performing an integral transform. d ref .

[0080] The reactive power control loop calculates the reference voltage amplitude of the modulation signal. V ref This is achieved through the following method, based on the second difference △Q2. 、 reactive power droop coefficient D q The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. oh The reference voltage amplitude is obtained by summing the zeros and then performing an integral transformation. V ref .

[0081] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0082] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for suppressing synchronous oscillations in a power synchronous control converter, characterized in that, Includes the following steps: Step 1: Obtain the reference value of active power at the grid connection point of the power synchronous control converter. P ref and active power measurement value P out The first difference △P1; Obtain the reactive power reference value at the grid connection point of the power synchronous control converter. Q ref and reactive power measurement values Q out The first difference △Q1; Step 2: Limit the synchronization frequency component of the first difference ΔP1 through the first band-stop filter to obtain the second difference ΔP2; calculate the reference phase of the modulation signal based on the second difference ΔP2 using the active power control loop. δ ref ; The first difference ΔQ1 is passed through a second band-stop filter to limit its synchronization frequency component, thus obtaining a second difference ΔQ2. Based on the second difference ΔQ2, the reference voltage amplitude of the modulation signal is calculated using a reactive power control loop. V ref ; Step 3: Based on the reference phase of the modulation signal δ ref and reference voltage amplitude V ref The modulation signal for controlling the power synchronous control converter is generated; the modulation signal is transmitted to the PWM generator to generate the PWM signal for controlling the power synchronous control converter. In step 2, the active power control loop calculates the reference phase of the modulation signal. δ ref This can be achieved through the following method. Based on the second difference △P2 and the active droop coefficient D p The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. ω The reference phase is obtained by adding the zeros together and then performing an integral transform. δ ref； In step 2, the reactive power control loop calculates the reference voltage amplitude of the modulation signal. V ref This can be achieved through the following method. Based on the second difference △Q2 、 reactive power droop coefficient D q The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. ω The reference voltage amplitude is obtained by summing the zeros and then performing an integral transformation. V ref .

2. The synchronous oscillation suppression method according to claim 1, characterized in that: In step 2, the transfer functions of the first band-stop filter and the second band-stop filter are: In the formula, s For the Laplace operator, ω 0 represents the synchronization angular frequency of the power grid. ξ is the damping coefficient.

3. The method for suppressing synchronous oscillations according to claim 2, characterized in that: Damping coefficient ξ Determined by the following method, Based on the spectral characteristics of power synchronous oscillation, a synchronization frequency is selected. f 0-symmetric upper limit frequency f 2 and lower limit frequency f 1, then the bandwidth Δ ω =2π ( f 2- f 1) Damping coefficient ξ =△ ω / ω 0.

4. The method for suppressing synchronous oscillations according to claim 1, characterized in that: In step 1, the active power measurement value P out and reactive power measurement values Q out The data was obtained directly from the grid connection point of the power synchronous control converter.

5. A synchronous oscillation suppression device for a power synchronous control converter, characterized in that... ,include: The active power control module includes a first band-stop filter. The first band-stop filter limits the synchronization frequency component of the first difference ΔP1 to obtain a second difference ΔP2. Based on the second difference ΔP2, the reference phase of the modulation signal is calculated by the active power control loop. δ ref The first difference △P1 refers to the active power reference value at the grid connection point of the power synchronous control converter. P ref and active power measurement value P out The difference; The reactive power control module includes a second band-stop filter. The second band-stop filter limits the synchronous frequency component of the first difference ΔQ1 to obtain a second difference ΔQ2. Based on the second difference ΔQ2, the reference voltage amplitude of the modulation signal is calculated by the reactive power control loop. V ref The first difference △Q1 refers to the reactive power reference value at the grid connection point of the power synchronous control converter. Q ref and reactive power measurement values Q out The difference; Modulation signal generation module, the modulation signal generation module according to reference phase δ ref Reference voltage amplitude V ref Generate the modulation signal for controlling the power synchronization control converter; A PWM generator that generates a PWM signal from the modulation signal to control the power synchronization control converter; The active power control loop calculates the reference phase of the modulation signal. δ ref This can be achieved through the following method. Based on the second difference △P2 、 Active sagging coefficient D p The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. ω The reference phase is obtained by adding the zeros together and then performing an integral transform. δ ref ； The reactive power control loop calculates the reference voltage amplitude of the modulation signal. V ref This can be achieved through the following method. Based on the second difference △Q2 、 reactive power droop coefficient D q The frequency deviation is obtained, and then the frequency deviation is compared with the synchronization angular frequency of the power grid. ω The reference voltage amplitude is obtained by summing the zeros and then performing an integral transformation. V ref .

6. The synchronous oscillation suppression device according to claim 5, characterized in that: The transfer functions of the first band-stop filter and the second band-stop filter are: In the formula, s For the Laplace operator, ω 0 represents the synchronization angular frequency of the power grid. ξ is the damping coefficient.

Images