A method for suppressing power oscillation of grid-connected converters based on hysteresis correction

Abstract

The present invention discloses a method for suppressing power oscillation of a grid-type converter based on hysteresis correction, including reactive power control, virtual inductance control, voltage and current closed-loop control, and improved active power control. In the improved active power control, mechanical power is first obtained through an active power controller, and then the mechanical power is respectively passed through a frequency controller and a hysteresis correction controller to obtain an initial phase value and a phase correction value, and finally the initial phase value and the phase correction value are superimposed to obtain a corrected output phase. The present invention can effectively suppress the dynamic oscillation of the system while realizing the simulation and control of the system inertia and damping, and obtain a more stable system output performance.

Description

Technical Field

[0001] The invention relates to the field of novel power systems, and in particular to a method for suppressing power oscillation of a grid-type converter based on hysteresis correction. Background Art

[0002] Against the backdrop of the global energy crisis and with the support of the "dual carbon" policy, new power systems have been vigorously developed. Converters, as a bridge between distributed power sources and power grids and loads, play an important role in new power systems. The intermittency and uncertainty of distributed power sources such as photovoltaics and wind power will reduce system inertia and affect the frequency stability of new power systems. Therefore, compared with grid-following converters, grid-forming converters that can actively provide voltage and frequency support have become an important research object. Due to the diversity of power sources and loads in new power systems, the system is susceptible to external conditions, power oscillations occur, and the stability of the system is threatened. It is urgent to propose an effective method to suppress the power oscillation problem of grid-forming converters. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method for suppressing power oscillation of a grid-type converter based on hysteresis correction.

[0004] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0005] A method for suppressing power oscillation of a grid-type converter based on hysteresis correction comprises the following steps:

[0006] 1) In the main circuit, the DC power supply U dc Provide energy, the output DC is converted into three-phase AC through the grid-type converter, and the three-phase electricity is filtered by the inductor L f And filter capacitor C f After that, it passes through the line inductance L line The grid and load can be connected, and the system can be switched between grid-connected and island operation modes by controlling the switch status of S1 and S2;

[0007] 2) Measure the grid-connected voltage u of the grid-connected converter at the grid-connected point abc and grid current i abc , the output electromagnetic power P is obtained by power calculation e And output reactive power Q e ;

[0008] 3) In the improved active power control, the active power controller is used to output electromagnetic power P e , output active reference value P ref , output angular frequency ω, and power frequency angular frequency ω0 are input signals. The four input signals are passed through the active power controller to obtain the output signal mechanical power Pm ; Active power controller corresponding model G P (P e ,P ref ,ω,ω0) is:

[0009]

[0010] In formula (1), k1 is the proportionality coefficient, k f is the frequency modulation coefficient, τ1 is the time constant, and s is the Laplace operator;

[0011] 4) In the improved active power control, for the frequency controller, the mechanical power P m The power frequency angular frequency ω0 is used as the input signal of the frequency controller. After passing through the frequency controller, the initial phase value θ can be obtained. i ; Frequency controller corresponding model G f (P m ,ω0) is:

[0012]

[0013] In formula (2), J P is the inertia coefficient, D P is the damping coefficient;

[0014] 5) In order to suppress power oscillation in the improved active power control, a hysteresis correction controller G is introduced. com (s), the mechanical power P m Through the lag correction controller G com (s) Output the phase correction value θ com , and then the phase correction value θ com With the initial phase θ i By adding, the oscillation part in the initial phase can be eliminated, thus obtaining the output phase θ; the lag correction controller G com (s) is expressed as:

[0015]

[0016] In formula (3), k2 is the correction coefficient, τ2 is the correction time constant;

[0017] 6) In reactive power control, the output reactive power Q e , output reactive power reference value Q ref , after reactive power control, the rated electromotive force E0 is obtained as output electromotive force E;

[0018] 7) In virtual inductance control, the output electromotive force E and the grid current i abcThe output phase θ obtained by the improved active power control is used as the input signal of the virtual inductance control. After the virtual inductance control, the output control voltage dq axis component u dref and u qref ;

[0019] 8) In the voltage and current closed-loop control and PWM control, the control voltage dq axis component u obtained by virtual inductance control is dref and u qref The output phase θ obtained by the improved active power control is input into the voltage and current closed-loop control, and a modulation signal is output. The modulation signal is controlled by PWM to realize the switch control of the grid-type converter.

[0020] Furthermore, in step 3), k1 is a proportionality coefficient, and its value range is 1.5≤k1≤2.5; k f is the frequency modulation coefficient, and its value range is 25≤k f ≤35; τ1 is the time constant, and its value range is 0≤τ1≤0.1.

[0021] Furthermore, in step 5), k2 is a correction coefficient, and its value range is 0≤k2≤0.1; τ2 is a correction time constant, and its value range is 300≤τ2≤350.

[0022] Compared with the prior art, the principles and advantages of this solution are as follows:

[0023] The present invention discloses a method for suppressing power oscillation of a grid-type converter based on hysteresis correction, including reactive power control, virtual inductance control, voltage and current closed-loop control, and improved active power control. In the improved active power control, mechanical power is first obtained through an active power controller, and then the mechanical power is respectively passed through a frequency controller and a hysteresis correction controller to obtain an initial phase value and a phase correction value, and finally the initial phase value and the phase correction value are superimposed to obtain a corrected output phase. The present invention can effectively suppress the dynamic oscillation of the system while realizing the simulation and control of the system inertia and damping, and obtain a more stable system output performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The topological structure and control block diagram of the power oscillation suppression method of the grid-type converter based on hysteresis correction in the embodiment of the present invention;

[0025] Figure 2 It is a comparison diagram of active power response under active power setting value step of the system before and after applying the proposed oscillation suppression method in an embodiment of the present invention;

[0026] Figure 3 A frequency response comparison diagram of a system under a step of active power setting value before and after applying the proposed oscillation suppression method in an embodiment of the present invention;

[0027] Figure 4 This is a comparison diagram of active power response under system frequency drop before and after applying the proposed oscillation suppression method in an embodiment of the present invention;

[0028] Figure 5 It is a frequency response comparison diagram of the system under frequency drop before and after applying the proposed oscillation suppression method in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments:

[0030] Figure 1 The topology structure and control block diagram of the power oscillation suppression method of the grid-type converter based on hysteresis correction are shown, which includes the following steps:

[0031] A method for suppressing power oscillation of a grid-type converter based on hysteresis correction comprises the following steps:

[0032] 1) In the main circuit, the DC power supply U dc Provide energy, the output DC is converted into three-phase AC through the grid-type converter, and the three-phase electricity is filtered by the inductor L f And filter capacitor C f After that, it passes through the line inductance L line The grid and load can be connected, and the system can be switched between grid-connected and island operation modes by controlling the switch status of S1 and S2;

[0033] 2) Measure the grid-connected voltage u of the grid-connected converter at the grid-connected point abc and grid current i abc , the output electromagnetic power P is obtained by power calculation e And output reactive power Q e ;

[0034] 3) In the improved active power control, the active power controller is used to output electromagnetic power P e , output active reference value P ref , output angular frequency ω, and power frequency angular frequency ω0 are input signals. The four input signals are passed through the active power controller to obtain the output signal mechanical power P m ; Active power controller corresponding model G P (P e ,P ref ,ω,ω0) is:

[0035]

[0036] In formula (4), k1 is the proportionality coefficient, k f is the frequency modulation coefficient, τ1 is the time constant, and s is the Laplace operator;

[0037] 4) In the improved active power control, for the frequency controller, the mechanical power P m The power frequency angular frequency ω0 is used as the input signal of the frequency controller. After passing through the frequency controller, the initial phase value θ can be obtained. i ; Frequency controller corresponding model G f (P m ,ω0) is:

[0038]

[0039] In formula (5), J P is the inertia coefficient, D P is the damping coefficient;

[0040] 5) In order to suppress power oscillation in the improved active power control, a hysteresis correction controller G is introduced. com (s), the mechanical power P m Through the lag correction controller G com (s) Output the phase correction value θ com , and then the phase correction value θ com With the initial phase θ i By adding, the oscillation part in the initial phase can be eliminated, thus obtaining the output phase θ; the lag correction controller G com (s) is expressed as:

[0041]

[0042] In formula (6), k2 is the correction coefficient, τ2 is the correction time constant;

[0043] 6) In reactive power control, the output reactive power Q e , output reactive power reference value Q ref , after reactive power control, the rated electromotive force E0 is obtained as output electromotive force E;

[0044] 7) In virtual inductance control, the output electromotive force E and the grid current i abc The output phase θ obtained by the improved active power control is used as the input signal of the virtual inductance control. After the virtual inductance control, the output control voltage dq axis component u dref and u qref ;

[0045] 8) In the voltage and current closed-loop control and PWM control, the control voltage dq axis component u obtained by virtual inductance control is dref and u qrefThe output phase θ obtained by the improved active power control is input into the voltage and current closed-loop control, and a modulation signal is output. The modulation signal is controlled by PWM to realize the switch control of the grid-type converter.

[0046] Furthermore, in step 3), k1 is a proportionality coefficient, and its value range is 1.5≤k1≤2.5; k f is the frequency modulation coefficient, and its value range is 25≤k f ≤35; τ1 is the time constant, and its value range is 0≤τ1≤0.1.

[0047] Furthermore, in step 5), k2 is a correction coefficient, and its value range is 0≤k2≤0.1; τ2 is a correction time constant, and its value range is 300≤τ2≤350.

[0048] Figure 2 and Figure 3 The following are the comparison diagrams of active power response and frequency response under the active setting value step of the system before and after applying the proposed oscillation suppression method. At this time, the working condition is to set the active power command of the grid-forming converter to change from 50kW to 100kW at 3s. When the active setting value changes, the comparison Figure 2 and Figure 3 It can be seen that before the proposed oscillation suppression method is adopted, the oscillation amplitude of active power and frequency is large, and the adjustment time is long; after the proposed oscillation suppression method is adopted, the oscillation amplitude of active power and frequency is reduced, and the adjustment time is significantly shortened, which improves the dynamic characteristics of the system.

[0049] Figure 4 and Figure 5 The following are the comparison diagrams of active power response and frequency response under system frequency drop before and after applying the proposed oscillation suppression method. At this time, the working condition is to set the grid frequency to drop from 50Hz to 49.5Hz at 3s. When the grid frequency drops, the comparison Figure 4 and Figure 5 It can be seen that before the proposed oscillation suppression method is adopted, the system active overshoot is large and the adjustment is slow. Affected by the grid frequency, the lowest frequency point drops to a smaller value, and it is easy to exceed the specified frequency change range under disturbance. After the proposed oscillation suppression method is adopted, the system frequency changes with the grid frequency, without oscillation and overshoot, and the dynamic characteristics of the system are significantly improved.

[0050] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, all changes made according to the shape and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for suppressing power oscillation of a grid-connected converter based on hysteresis correction, characterized in that: The steps include: 1) In the main circuit, the DC power supply U dc Provide energy, the output DC is converted into three-phase AC through the grid-type converter, and the three-phase electricity is filtered by the inductor L f And filter capacitor C f After that, it passes through the line inductance L line The grid and load can be connected, and the system can be switched between grid-connected and islanded operation modes by controlling the switch status of S1 and S2; 2) Measure the grid-connected voltage u of the grid-connected converter at the grid-connected point abc and grid current i abc , the output electromagnetic power P is obtained by power calculation e And output reactive power Q e ; 3) In the improved active power control, the active power controller is used to output electromagnetic power P e , output active reference value P ref , output angular frequency ω, and power frequency angular frequency ω0 are input signals. The four input signals are passed through the active power controller to obtain the output signal mechanical power P m ; Active power controller corresponding model G P (P e ,P ref ,ω,ω0) is: In formula (1), k1 is the proportionality coefficient, k f is the frequency modulation coefficient, τ1 is the time constant, and s is the Laplace operator; 4) In the improved active power control, for the frequency controller, the mechanical power P m The power frequency angular frequency ω0 is used as the input signal of the frequency controller. After passing through the frequency controller, the initial phase value θ can be obtained. i ; Frequency controller corresponding model G f (P m ,ω0) is: In formula (2), J P is the inertia coefficient, D P is the damping coefficient; 5) In order to suppress power oscillation in the improved active power control, a hysteresis correction controller G is introduced. com (s), the mechanical power P m Through the lag correction controller G com (s) Output the phase correction value θ com , and then the phase correction value θ com With the initial phase θ i By adding, the oscillation part in the initial phase can be eliminated, thus obtaining the output phase θ; the lag correction controller G com (s) is expressed as: In formula (3), k2 is the correction coefficient, τ2 is the correction time constant; 6) In reactive power control, the output reactive power Q e , output reactive power reference value Q ref , after reactive power control, the rated electromotive force E0 is obtained as output electromotive force E; 7) In virtual inductance control, the output electromotive force E and the grid current i abc The output phase θ obtained by the improved active power control is used as the input signal of the virtual inductance control. After the virtual inductance control, the output control voltage dq axis component u dref and u qref ; 8) In the voltage and current closed-loop control and PWM control, the control voltage dq axis component u obtained by virtual inductance control is dref and u qref The output phase θ obtained by the improved active power control is input into the voltage and current closed-loop control, and a modulation signal is output. The modulation signal is controlled by PWM to realize the switch control of the grid-type converter.

2. The method for suppressing power oscillation of a grid-connected converter based on hysteresis correction according to claim 1, characterized in that: In step 3), k1 is a proportionality coefficient, and its value range is 1.5≤k1≤2.5; k f is the frequency modulation coefficient, and its value range is 25≤k f ≤35; τ1 is the time constant, and its value range is 0≤τ1≤0.

1.

3. The method for suppressing power oscillation of a grid-connected converter based on hysteresis correction according to claim 1, characterized in that: In step 5), k2 is a correction coefficient, and its value range is 0≤k2≤0.1; τ2 is a correction time constant, and its value range is 300≤τ2≤350.

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