Virtual Synchronous Machine Control Method and System Based on Active Disturbance Rejection Current Control

Abstract

This invention discloses a virtual synchronous machine control method and system based on active disturbance rejection current control, which uses the current controller command value i dref 、i qref and the actual value of inverter output current i d 、i q By introducing a linear active disturbance rejection current controller, the modulated wave signal c of the dq axis is obtained. d c q The modulated wave signal c along the dq axis d c q A reverse coordinate transformation is performed, and then the output of the grid voltage feedforward stage is superimposed to obtain the PWM modulated wave signal. For the PWM modulated wave signal m... a PWM modulation is performed to obtain the duty cycle signal of the inverter switching transistors. This signal is then used by the drive protection circuit of the three-phase grid-connected inverter to control the switching transistors' on / off states. This invention, by applying active disturbance rejection control (ADRC) to the virtual synchronous machine current loop, effectively improves the system's anti-interference capability, reduces the impact of grid strength and power variations on system stability, and enhances overall system stability.

Description

Technical Field

[0001] This invention relates to the field of inverter grid-connected control, and in particular to a virtual synchronous machine control method and system based on active disturbance rejection current control. Background Technology

[0002] With the increasing demand for electricity, and in order to achieve sustainable energy utilization, the proportion of renewable energy sources such as solar and wind power connected to the grid is growing. As a key interface for renewable energy power generation systems, grid-connected inverters must ensure reliable energy transmission while simultaneously providing voltage and frequency support. However, with the increasing penetration rate of renewable energy, traditional inverter control methods, due to their low rotational inertia and poor stability under weak grid conditions, cannot meet current technological requirements. Therefore, to mimic the inertia characteristics of synchronous motors, the concept of virtual synchronous machines was proposed and has been extensively studied by researchers. Depending on the control method, virtual synchronous machines can be divided into voltage-controlled and current-controlled types, both capable of providing voltage and frequency support to the grid. Current-controlled virtual synchronous machines, due to the fast response capability of the PQ dual-loop controller, allow the inverter output power to be quickly adjusted to the reference value. To address some issues in grid-connected operation of voltage-controlled virtual synchronous machines, numerous studies have been conducted. However, research on current-controlled virtual synchronous machines is relatively limited. Furthermore, existing control methods for current-controlled virtual synchronous machines (such as CN108649615A) exhibit poor adaptability under weak grid conditions and varying output power, which restricts the widespread application of current-controlled virtual synchronous machines. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a virtual synchronous machine control method and system based on self-disruption current control to address the shortcomings of the existing technology, thereby improving the adaptability of the traditional virtual synchronous machine under weak grid and power variation conditions and enhancing the anti-disturbance performance of the grid-connected inverter.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a virtual synchronous machine control method based on self-disruption current control, comprising the following steps:

[0005] S1. Calculate the modulation signal c along the dq axis using the following formula. d c q Its frequency domain expression is: Among them, B0 and K p ω is the controller gain; ω0 is the bandwidth of the linearly extended state observer; i dref (s), i qref (s) represent the actual voltage reference value. Compared with the actual angular frequency reference value The current controller command values ​​obtained by performing active power and reactive power control respectively; i d (s), i q (s) represent the output current values ​​of the virtual synchronous machine inverter;

[0006] S2, the modulation signal c on the dq axis d (s), c q (s) Perform an inverse coordinate transformation, and then compare the result of the inverse coordinate transformation with the three-phase voltage u at the common point PCC on the AC side of the inverter. a u b u c The outputs of the grid voltage feedforward circuit are superimposed to obtain the PWM modulated wave signal;

[0007] S3. The PWM modulation wave signal is modulated by PWM to obtain the duty cycle signal of the inverter switching transistor. The inverter's drive protection circuit controls the switching transistor to turn on and off.

[0008] This invention applies active disturbance rejection control to calculate the modulated wave signal in the current loop of a virtual synchronous machine, which effectively improves the system's anti-interference capability and reduces the impact of grid strength and power variations on system stability. Compared with traditional current-controlled virtual synchronous machines, the stability under weak grid conditions is improved, enhancing system stability and ensuring the power supply reliability of renewable energy power generation systems.

[0009] i dref (s), i qref The specific process of obtaining (s) includes:

[0010] 1) At the beginning of each sampling period, the voltage u at the PCC point on the AC side of the inverter is... abc Perform sampling;

[0011] 2) The sampled PCC point voltage u abc Input to the phase-locked loop controller to obtain the actual value of the d-axis grid voltage u. d Actual value of grid voltage angular frequency ω g Grid voltage phase angle θ PLL Inverter output current value i d i q ;

[0012] 3) Transfer the d-axis grid voltage command signal V m The actual value of the grid voltage u along the d-axis d By subtracting the values, we obtain the actual voltage reference value. The grid voltage angular frequency command signal ω n The actual value of the grid voltage angular frequency ω g By subtracting the values, we obtain the actual angular frequency reference value.

[0013] 4) For actual voltage reference value Compared with the actual angular frequency reference value Reactive power control and active power control are performed separately to obtain the current controller command value i. dref (s) and i qref (s).

[0014] The transfer function G of the phase-locked loop controller PLL (s) is: Where, k p_PLL For proportional gain, k i_PLL This is the integral gain.

[0015] In step 4) above, the active power control and reactive power control in the virtual synchronous machine control are implemented using the following formulas respectively:

[0016] P e =(Jω n s+D p ω n (ω) n -ω g )+P set ;

[0017] Q e ≈(Ks+D q (V) m -u d )+Q set ;

[0018] Where P set and Q set These are the reference values ​​for active power and reactive power, respectively, P. e and Q e These are the instantaneous values ​​of the output active power and reactive power, respectively; J is the virtual moment of inertia; and D... p and D q These are the active damping coefficient and the passive damping coefficient, respectively; K is the reactive inertia coefficient; V m This represents the peak value of the phase voltage.

[0019] The state-space expression of the differential equation in the time domain of the linear extended state observer is as follows: in, x is the state variable of the active disturbance rejection system, y is the output of the controlled object in the active disturbance rejection system, and u is the input of the controlled object in the active disturbance rejection system.

[0020] In this invention, B0 = 1 / L f L f This is the output filter inductor.

[0021] As an inventive concept, the present invention also provides a virtual synchronous machine control system based on self-disruption current control, which includes a computer device; the computer device is configured or programmed to perform the steps of the method described above.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: by applying active disturbance rejection control to the virtual synchronous machine current loop, the present invention effectively improves the anti-interference capability of the system, reduces the impact of grid strength and power changes on system stability, enhances system stability, and ensures the power supply reliability of the renewable energy power generation system. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the main circuit structure of the virtual synchronous machine control based on the self-rejection current controller according to an embodiment of the present invention;

[0024] Figure 2 This is a control block diagram of the linear active disturbance rejection current controller implemented in this invention;

[0025] Figure 3(a) and Figure 3(b) show the experimental results of virtual synchronizers with different current control when the SCR changes; Figure 3(a) shows the virtual synchronizer with active disturbance rejection current control according to the embodiment of the present invention; Figure 3(b) shows the virtual synchronizer with conventional current control.

[0026] Figure 4(a) and Figure 4(b) show the experimental results of virtual synchronizers with different current control when the output power changes; Figure 4(a) is the virtual synchronizer with self-disruption current control according to the embodiment of the present invention; Figure 4(b) is the virtual synchronizer with conventional current control. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] like Figure 1 and Figure 2 As shown, the virtual synchronous machine control system structure diagram based on the self-disruption current controller in this embodiment of the invention includes two parts: the main circuit structure and the control system. The main circuit mainly includes a DC voltage source, a three-phase three-bridge converter (grid-connected inverter, i.e., the inverter mentioned above), and the AC side filter inductor L of the three-phase three-bridge converter. f (i.e., output filter inductor), filter capacitor C f and parasitic resistance R f Connected to the AC power grid, L gand R g The equivalent inductance and equivalent resistance of the power grid are given. The control system includes a sampling module for sampling the AC voltage and current on the inverter output side, which is directly connected to the phase-locked loop. The coordinate transformation module is connected to the input of the linear active disturbance rejection current control, and the output of the PWM drive module is connected to the grid-connected inverter. abc (u a u b u c ) represents the three-phase output phase voltage, i abc (i a i b i c ) represents the output phase current on the inverter side.

[0029] Figure 2 This is a control block diagram of an embodiment of the present invention. At the beginning of each sampling period, the three-phase output phase voltage u is... abc Output phase current i abc Sampling is performed separately. The control system includes phase-locked loop control, feedforward control, power outer loop control, current inner loop control, and carrier-layered PWM control to obtain the trigger pulses of each switch in the inverter circuit, controlling the on and off of the inverter circuit switches. abc (m a m b m c ) represents the PWM modulated wave signal, i dref and i qref For the inner current loop reference command, K f This is the voltage feedforward coefficient.

[0030] The data converted by the AD converter is sent to the DSP controller for processing; the sampled three-phase voltage u abc (u a u b u c The introduction of a phase-locked loop controller yields the actual d-axis grid voltage value u. d Actual value of grid voltage angular frequency ω g Grid voltage phase angle θ PLL Actual value of inverter output current i d i q The transfer function G of the phase-locked loop controller PLL (s) is:

[0031]

[0032] Where, k p_PLL For proportional gain, k i_PLL This is the integral gain.

[0033] The d-axis grid voltage command signal V mCompared with the actual value u d By subtracting the values, we obtain the actual voltage reference value. The grid voltage angular frequency command signal ω n Compared with the actual value ω g By subtracting the values, we obtain the actual angular frequency reference value. Actual voltage reference value Compared with the actual angular frequency reference value Reactive power control and active power control are performed separately to obtain the current controller command value i. dref and i qref The virtual synchronous machine control includes active power control and reactive power control, and the specific implementation methods are as follows:

[0034]

[0035]

[0036] P e =(Jω n s+D p ω n (ω) n -ω g )+P set ;

[0037] Q e ≈(Ks+D q (V) m -u d )+Q set ;

[0038] Where P set and Q set These are the reference values ​​for active power and reactive power, respectively, P. e and Q e These are the instantaneous values ​​of the output active power and reactive power, respectively; J is the virtual moment of inertia; and D... p and D q These are the active damping coefficient and the passive damping coefficient, respectively; K is the reactive inertia coefficient; V m This represents the peak value of the phase voltage.

[0039] In this embodiment of the invention, the state-space expression of the differential equation in the time domain of the linear extended state observer is: in, Let x be the state variable of the active disturbance rejection system, y be the output of the controlled object in the active disturbance rejection system, and u be the input of the controlled object in the active disturbance rejection system. The first derivative of x; in d-axis control, the input is the actual value of the d-axis output current i. d and d-axis modulation signal c d The corresponding output quantities y are respectively and In q-axis control, the input quantity is the actual value of the q-axis output current, i. q and q-axis modulation signal c q The corresponding output quantities y are respectively and In this embodiment of the invention, the output quantity is an intermediate variable.

[0040] The current controller command value i dref i qref and the actual value of inverter output current i d i q By introducing a linear active disturbance rejection current controller, the modulated wave signals c on the d and q axes are obtained. d c q The modulated wave signal c along the d and q axes d c q Perform an inverse coordinate transformation to obtain the inverse coordinate transformation result c. a c b c c Then, the output of the grid voltage feedforward stage (u) is superimposed. a *K f u b *K f u c *K f ), thus obtaining the PWM modulated wave signal m a m b m c That is, m a =c a +u a *K f m b =u b *K f m c =u c *K f .

[0041] d, q-axis modulation wave signal c d c q With the current inner loop input signal i d i q i dref and i qref The following relationship exists:

[0042]

[0043] Among them, B0 and K p ω is the controller gain; ω0 is the bandwidth of the linearly extended state observer. ω0 = MK p M takes values ​​from 1 to 3. B0 = 1 / L fL f This is the output filter inductor.

[0044] For PWM modulated wave signal m a m b m c PWM modulation is performed to obtain the duty cycle signal of the inverter switching transistor, which is then controlled by the drive protection circuit of the three-phase grid-connected inverter to turn the inverter circuit switching transistor on and off.

[0045] To observe the advantages of the self-disruption current control virtual synchronous machine (IDCMM) in weak grid conditions compared to the traditional current control virtual synchronous machine under varying grid strength, this embodiment of the invention demonstrates its superior performance. Grid strength is represented by SCR (Signal Limiting Rate). Generally, an SCR < 6 indicates a weak grid, with a smaller SCR indicating a weaker grid. Setting SCR = 5 and SCR = 2, with a phase-locked loop bandwidth BW = 20Hz and an output power P = 1.0 pu, Figure 3(a) shows the grid-connected current waveform of the proposed IDCMM, and Figure 3(b) shows the grid-connected current waveform of the traditional current control virtual synchronous machine. As shown in Figures 3(a) and 3(b), when the SCR decreases from 5 to 2, the proposed IDCMM still operates stably, while the traditional current control virtual synchronous machine exhibits oscillation and instability. Compared to the traditional current control virtual synchronous machine, the IDCMM proposed in this embodiment demonstrates stronger stability under weak grid conditions.

[0046] To observe the advantages of the self-disturbance rejection current-controlled virtual synchronizer of this invention compared to the traditional current-controlled virtual synchronizer under weak power grid conditions when the output power changes, with a phase-locked loop bandwidth BW = 40Hz and SCR = 2.5, the output power was varied, and the changes in the output current waveform of the virtual synchronizer were observed, as shown in Figures 4(a) and 4(b). As can be seen from Figures 4(a) and 4(b), when the output power increases from 0.4 pu to 0.6 pu, the self-disturbance rejection current-controlled virtual synchronizer of this invention can still maintain stable operation, while the traditional current-controlled virtual synchronizer will exhibit oscillation. Compared to the traditional current-controlled virtual synchronizer, the self-disturbance rejection current-controlled virtual synchronizer of this invention can improve the system's stability under varying output power conditions.

[0047] In summary, by employing the self-rejecting current control virtual synchronous machine proposed in this embodiment of the invention, the system achieves higher stability under weak power grid conditions, taking into account changes in grid strength and system output power.

Claims

1. A virtual synchronous machine control method based on active disturbance rejection current control, characterized in that, Includes the following steps: S1. Determine the modulation wave signal c of the inverter's d and q axes. d c q The frequency domain expression c d (s), c q (s): Among them, B0 and K p All are controller gains; ω0 is the bandwidth of the linearly extended state observer, i dref (s) represents the reference value for the actual voltage. The d-axis current command value obtained from active power control, i qref (s) represents the reference value for the actual angular frequency. The q-axis current command value obtained from reactive power control, i d (s), i q (s) represent the actual values ​​of the inverter's d-axis and q-axis output currents, respectively; S2, for c d (s), c q (s) Perform an inverse coordinate transformation, and then compare the result of the inverse coordinate transformation with the three-phase voltage u at the common point PCC on the AC side of the inverter. a u b u c The outputs of the grid voltage feedforward circuit are superimposed to obtain the PWM modulated wave signal; S3. The PWM modulation wave signal is modulated by PWM to obtain the duty cycle signal of the inverter switching transistor. The inverter's drive protection circuit controls the switching transistor to turn on and off. i dref (s), i qref The specific process of obtaining (s) includes: 1) At the beginning of each sampling period, the three-phase voltage u at the inverter AC side common point PCC is... a u b u c Perform sampling; 2) The sampled three-phase voltage u at point PCC a 、u b 、u c Input to the phase-locked loop controller to obtain the actual value of the d-axis grid voltage u. d Actual value of grid voltage angular frequency ω g Grid voltage phase angle θ PLL ; 3) Transfer the d-axis grid voltage command signal V m The actual value of the grid voltage u along the d-axis d By subtracting the values, we obtain the actual voltage reference value. The grid voltage angular frequency command signal ω n The actual value of the grid voltage angular frequency ω g By subtracting the values, we obtain the actual angular frequency reference value. 4) For actual voltage reference value Compared with the actual angular frequency reference value Reactive power control and active power control are performed separately to obtain the current controller command value i. dref (s) and i qref (s); The state-space expression of the differential equation in the time domain of the linear extended state observer is as follows: in, Let x be the state variable of the active disturbance rejection system, y be the output of the controlled object in the active disturbance rejection system, and u be the input of the controlled object in the active disturbance rejection system. The first derivative of x; in d-axis control, the input is the actual value of the d-axis output current i. d and d-axis modulation signal c d The corresponding output quantities y are respectively and In q-axis control, the input quantity is the actual value of the q-axis output current, i. q and q-axis modulation signal c q The corresponding output quantities y are respectively and 2. The virtual synchronous machine control method based on active disturbance rejection current control according to claim 1, characterized in that, The transfer function G of the phase-locked loop controller PLL (s) is: Among them, k p_PLL For proportional gain, k i_PLL This is the integral gain.

3. The virtual synchronous machine control method based on active disturbance rejection current control according to claim 1, characterized in that, In step 4), the following formulas are used to implement active power control and reactive power control in the virtual synchronous machine control, respectively: P e =(Jω n s+D p ω n )(ω n -ω g )+P set ; Q e ≈(Ks+D q )(V m -u d )+Q set ; Where P set and Q set These are the active power reference value and the reactive power reference value, respectively. e and Q e These are the instantaneous values ​​of the output active power and reactive power, respectively; J is the virtual moment of inertia; and D... p and D q These are the active damping coefficient and the passive damping coefficient, respectively; K is the reactive inertia coefficient; V m This represents the peak value of the phase voltage.

4. The virtual synchronous machine control method based on active disturbance rejection current control according to claim 1, characterized in that, Actual values ​​of inverter d-axis and q-axis output current i d i q The acquisition process includes: sampling the three-phase voltage u at point PCC. a 、u b 、u c Input to the phase-locked loop controller to obtain the grid voltage phase angle θ PLL Based on the grid voltage phase angle and the sampled three-phase current i at point PCC a i b i c The actual values ​​of the inverter's d-axis and q-axis output current i are obtained. d i q .

5. The virtual synchronous machine control method based on active disturbance rejection current control according to claim 1, characterized in that, ω0=MK p M takes values ​​from 1 to 3.

6. The virtual synchronous machine control method based on active disturbance rejection current control according to claim 1, characterized in that, B0 = 1 / L f L f This is the output filter inductor.

7. A virtual synchronous machine control system based on active disturbance rejection current control, characterized in that, It includes a computer device; said computer device is configured or programmed to perform the steps of the method according to any one of claims 1 to 6.

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