Virtual synchronous machine active power control method based on angular frequency error proportion feedforward

Abstract

The invention discloses a virtual synchronous machine active power control method based on angular frequency error proportional feedforward, which is characterized in that an angular frequency error output by a virtual synchronous machine is used for correcting an angle output by the virtual synchronous machine after being subjected to a proportional link, so that transient damping of a system is improved, and the stability of the system is improved. And therefore, active power dynamic oscillation suppression can be realized on the premise that the virtual damping is zero. Due to the fact that the virtual damping can be zero, the active power deviation generated when the power grid frequency deviates can be eliminated, and the active power control precision is improved. Therefore, the method can be applied to the field of virtual synchronous machine control so as to solve the contradiction problem between dynamic oscillation and steady-state deviation existing in conventional virtual synchronous machine active power control, and the active power control precision is improved.

Description

Technical Field

[0001] The invention relates to the technical field of new energy grid-connected power generation, and in particular to a virtual synchronous machine active power control method based on angular frequency error proportional feedforward. Background Art

[0002] Virtual synchronous machine technology can improve the inertia and damping of the grid-connected inverter of new energy sources and enhance its support capacity for the power grid. Therefore, in recent years, virtual synchronous machine technology has received extensive attention and research. However, the introduction of virtual inertia turns the active frequency closed-loop control system into a typical second-order oscillation system. Under the two disturbances of the grid-connected active reference command and the grid frequency, dynamic power oscillation, overshoot and static error will inevitably occur. Although the increase of virtual damping can suppress the oscillation and overshoot of active power, virtual damping will also introduce damping power, which will cause a large active power steady-state error when the grid frequency changes. Therefore, the active power control of conventional virtual synchronous machines has the problem of difficulty in balancing dynamic performance and steady-state performance.

[0003] The document "Ji Xiaotong, Li Zhe, Liu Dan, et al. Active power control method and device for virtual synchronous generator of grid-connected converter [P]. Hubei Province: CN202410032817.0, 2024-03-26." proposes an active power control method for a virtual synchronous generator based on damping power proportional integral adjustment, which realizes the dynamic oscillation suppression of active power and the elimination of steady-state errors. However, this method requires the design of two parameters, the proportional coefficient and the integral coefficient, and the parameter debugging process is relatively complicated.

[0004] The document "Ji Xiaotong, Li Zhe, Liu Dan, et al. Active power control method and related device of virtual synchronous machine of grid-connected converter [P]. Hubei Province: CN202410079019.3, 2024-04-02." proposed a virtual synchronous machine power angle correction method based on active power and first-order lag link, which realized the dynamic oscillation suppression of active power and the elimination of steady-state error. However, this method requires the design of two parameters: the cutoff frequency and gain of the first-order lag link, and the parameter debugging process is also complicated.

[0005] The literature "Shi Rongliang, Yang Guihua, Wang Guobin, et al. Active response strategy of VSG grid-connected energy storage based on active fractional-order differential correction [J]. Electric Power Automation Equipment, 2024, 44(02): 204-210." proposed an improved transient damping control strategy for virtual synchronous machine based on active fractional-order differential correction. This method also achieves active power dynamic oscillation suppression and steady-state error elimination when the virtual damping is zero. However, the fractional-order differential operation required by this method is difficult to implement.

[0006] From the above analysis, it can be seen that although the existing technology can solve the problems of dynamic power oscillation, overshoot and static error that will inevitably occur in traditional virtual synchronous machines under the two disturbances of grid-connected active reference instructions and grid frequency, most algorithms have problems such as complex parameter debugging and difficult implementation. Summary of the invention

[0007] In order to solve the contradiction between dynamic oscillation and steady-state power deviation in active power control of conventional virtual synchronous machines, the present invention discloses an active power control method for virtual synchronous machines based on angular frequency error proportional feedforward.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A virtual synchronous machine active power control method based on angular frequency error proportional feedforward comprises the following steps:

[0010] Step 1: Difference the set grid rated angular frequency ω0 and the angular frequency ω output by the virtual synchronous machine, and multiply it by the droop coefficient k ω The first power deviation ΔP1 is obtained, which satisfies:

[0011] ΔP1=(ω0-ω)*k ω

[0012] Among them, the rated angular frequency ω0 of the power grid is 100πrad / s;

[0013] Step 2: Set the virtual synchronous machine active power reference value P ref Add the first power deviation ΔP1 obtained in step 1 and subtract the active power P output by the virtual synchronous machine e , and obtain the second power deviation ΔP2, which satisfies:

[0014] ΔP2=P ref +ΔP1-P e

[0015] Step 3: Integrate the second power deviation ΔP2 obtained in step 2 according to the following formula to obtain an angular frequency error Δω, which satisfies:

[0016]

[0017] Where, s represents the Laplace operator, J represents the virtual inertia of the virtual synchronous machine;

[0018] Step 4: Add the angular frequency error Δω obtained in step 3 to the set grid rated angular frequency ω0 to obtain the angular frequency ω output by the virtual synchronous machine, satisfying:

[0019] ω=ω0+Δω

[0020] Step 5: Integrate the angular frequency ω of the virtual synchronous machine output obtained in step 4 to obtain the first angle θ1 of the virtual synchronous machine output, which satisfies:

[0021]

[0022] Step 6: The angular frequency error Δω obtained in step 3 is passed through a proportional link to obtain the feedforward angle deviation Δθ, which satisfies:

[0023] Δθ=kΔω

[0024] Where k is the feedforward proportional coefficient of the angular frequency error Δω, and Δθ is the feedforward angle deviation;

[0025] Step 7: Add the first angle θ1 of the virtual synchronous machine output obtained in step 5 to the feedforward angle deviation Δθ obtained in step 6 to obtain the second angle θ2 of the virtual synchronous machine output, which satisfies:

[0026] θ2=θ1+Δθ

[0027] Step 8: Based on the second angle θ2 of the virtual synchronous machine output obtained in step 7 and the voltage amplitude E of the virtual synchronous machine output obtained based on the reactive power control of the virtual synchronous machine, a voltage reference value u is generated according to the following formula: αref 、u βref ,satisfy:

[0028]

[0029] Among them, u αref is the voltage reference α component in the stationary αβ coordinate system, u βref is the voltage reference value β component in the stationary αβ coordinate system;

[0030] Step 9: Substitute the voltage reference value u obtained in step 8 αref 、u βref The input voltage and current dual closed-loop control system finally outputs a PWM signal to realize the control of the virtual synchronous machine.

[0031] Furthermore, the active power P output by the virtual synchronous machine in step 2 is e The calculation steps are as follows:

[0032] Step 2-1: Sample the grid-connected voltage u of phase a output by the virtual synchronous machine a and c-phase grid-connected voltage u c , and transform it to the stationary αβ coordinate system to obtain the α component u of the grid-connected voltage output by the virtual synchronous machine in the stationary αβ coordinate system α and the β component u β ,satisfy:

[0033]

[0034] Step 2-2: Sample the grid-connected current i of phase a output by the virtual synchronous machine a and c-phase grid-connected current i c , and transform it to the stationary αβ coordinate system to obtain the α component i of the grid-connected current output by the virtual synchronous machine in the stationary αβ coordinate system α and β component i β ,satisfy:

[0035]

[0036] Step 2-3: The voltage α component u obtained according to step 2-1 α and the β component u β 、The current α component i obtained in step 2-2 α and β component i β , calculate the active power P according to the following formula e ,satisfy:

[0037] P e =1.5(u α i α +u β i β ).

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention discloses a virtual synchronous machine active power control method based on angular frequency error proportional feedforward. Different from conventional methods, the present invention introduces a virtual synchronous machine output angle correction method based on angular frequency error proportional feedforward. The method corrects the angle of the virtual synchronous machine output after passing the angular frequency error Δω output by the virtual synchronous machine through a proportional link k, thereby increasing the transient damping of the system, realizing the suppression of the dynamic oscillation and overshoot of the active power of the virtual synchronous machine, and eliminating the steady-state deviation of the active power, thereby making the virtual synchronous machine have both good dynamic characteristics and good steady-state characteristics. Compared with conventional methods, the method of the present invention does not need to design multiple controller parameters, but only needs to design a proportional coefficient, so that the virtual synchronous machine can have both good dynamic characteristics and steady-state characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a conventional virtual synchronous machine active power control block diagram;

[0041] Figure 2 It is a control block diagram of the virtual synchronous machine active power control method based on angular frequency error proportional feedforward proposed by the present invention;

[0042] Figure 3This is the main circuit and power calculation block diagram of the virtual synchronous machine;

[0043] Figure 4 The figure shows the comparative simulation results of the conventional virtual synchronous machine and the method proposed in the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Figure 2 The present invention provides a virtual synchronous machine active power control method based on angular frequency error proportional feedforward. Figure 3 The main circuit of the virtual synchronous machine and the power calculation method thereof are provided.

[0046] See also Figure 2 and Figure 3 It can be seen that the embodiment of the present invention provides a virtual synchronous machine active power control method based on angular frequency error proportional feedforward, comprising the following steps:

[0047] Step 1: Difference the set grid rated angular frequency ω0 and the angular frequency ω output by the virtual synchronous machine, and multiply it by the droop coefficient k ω The first power deviation ΔP1 is obtained, which satisfies:

[0048] ΔP1=(ω0-ω)*k ω

[0049] Among them, the rated angular frequency ω0 of the power grid is 100πrad / s;

[0050] Step 2: Set the virtual synchronous machine active power reference value P ref Add the first power deviation ΔP1 obtained in step 1 and subtract the active power P output by the virtual synchronous machine e , and obtain the second power deviation ΔP2, which satisfies:

[0051] ΔP2=P ref +ΔP1-P e

[0052] Step 3: Integrate the second power deviation ΔP2 obtained in step 2 according to the following formula to obtain an angular frequency error Δω, which satisfies:

[0053]

[0054] Where, s represents the Laplace operator, J represents the virtual inertia of the virtual synchronous machine;

[0055] Step 4: Add the angular frequency error Δω obtained in step 3 to the set grid rated angular frequency ω0 to obtain the angular frequency ω output by the virtual synchronous machine, satisfying:

[0056] ω=ω0+Δω

[0057] Step 5: Integrate the angular frequency ω of the virtual synchronous machine output obtained in step 4 to obtain the first angle θ1 of the virtual synchronous machine output, which satisfies:

[0058]

[0059] Step 6: The angular frequency error Δω obtained in step 3 is passed through a proportional link to obtain the feedforward angle deviation Δθ, which satisfies:

[0060] Δθ=kΔω

[0061] Wherein, k is the feedforward proportional coefficient of the angular frequency error Δω, and Δθ is the feedforward angle deviation.

[0062] Step 7: Add the first angle θ1 of the virtual synchronous machine output obtained in step 5 to the feedforward angle deviation Δθ obtained in step 6 to obtain the second angle θ2 of the virtual synchronous machine output, which satisfies:

[0063] θ2=θ1+Δθ

[0064] Step 8: Based on the second angle θ2 of the virtual synchronous machine output obtained in step 7 and the voltage amplitude E of the virtual synchronous machine output obtained based on the reactive power control of the virtual synchronous machine, a voltage reference value u is generated according to the following formula: αref 、u βref ,satisfy:

[0065]

[0066] Among them, u αref is the voltage reference α component in the stationary αβ coordinate system, u βref is the voltage reference value β component in the stationary αβ coordinate system;

[0067] Step 9: Substitute the voltage reference value u obtained in step 8 αref 、u βref The input voltage and current dual closed-loop control system finally outputs a PWM signal to realize the control of the virtual synchronous machine.

[0068] Furthermore, the active power P output by the virtual synchronous machine in step 2 is e The calculation steps are as follows:

[0069] Step 2-1: Sample the grid-connected voltage u of phase a output by the virtual synchronous machine a and c-phase grid-connected voltage u c , and transform it to the stationary αβ coordinate system to obtain the α component u of the grid-connected voltage output by the virtual synchronous machine in the stationary αβ coordinate system α and the β component u β ,satisfy:

[0070]

[0071] Step 2-2: Sample the grid-connected current i of phase a output by the virtual synchronous machine a and c-phase grid-connected current i c , and transform it to the stationary αβ coordinate system to obtain the α component i of the grid-connected current output by the virtual synchronous machine in the stationary αβ coordinate system α and β component i β ,satisfy:

[0072]

[0073] Step 2-3: The voltage α component u obtained according to step 2-1 α and the β component u β 、The current α component i obtained in step 2-2 α and β component i β , calculate the active power P according to the following formula e ,satisfy:

[0074] P e =1.5(u α i α +u β i β ).

[0075] In order to verify the effectiveness of the method proposed in this invention, the active power control strategy of the virtual synchronous machine ( Figure 1 During the simulation, the active power reference value P ref 5kW before 4s, P at 4s ref The actual angular frequency of the power grid increases from 5kW to 10kW at 7s. g It suddenly decreases from 100πrad / s (50Hz) to 99.6πrad / s (49.8Hz). The virtual inertia J is 1kg / m 2 , the grid rated angular frequency ω0 is 100πrad / s, the droop coefficient k ω The voltage peak of the grid phase is 311V, and the peak voltage of the virtual synchronous machine output is 311. The grid line resistance is 2Ω, and the line inductance is 3mH.

[0076] Figure 4 The comparative simulation results of the conventional virtual synchronous machine active power control and the virtual synchronous machine active power control proposed in the present invention are given. During the simulation, the virtual damping coefficient D of the conventional method is taken as 0, 5Ws / rad and 10Ws / rad respectively. The method of the present invention takes k as 0.1.

[0077] Depend on Figure 4 It can be seen that when the virtual damping coefficient D is 0, the active power output of the conventional virtual synchronous machine control strategy has obvious oscillation and overshoot. When the virtual damping coefficient D increases to 5, the active power oscillation is reduced. Figure 4 It can be seen that the increase of virtual damping coefficient will also cause the grid frequency to deviate (after 7s), and the active power steady-state deviation will also increase significantly. When the virtual damping coefficient D continues to increase to 10, Figure 4 It can be seen that the active power oscillation is significantly suppressed, however, the active power deviation (after 7s) further increases. It can be seen that the conventional virtual synchronous machine active power control strategy cannot achieve active power dynamic oscillation suppression and steady-state static error elimination by adjusting the virtual damping coefficient at the same time.

[0078] At the same time, by Figure 4 It can be seen that when the method proposed in the present invention is used, not only the active power oscillation is suppressed, but also when the grid frequency deviates (after 7s), the active power steady-state deviation also approaches zero (that is, the active power of the method proposed in the present invention is equal to the active power of the conventional method when D=0). It can be seen that the method proposed in the present invention can simultaneously achieve active power dynamic oscillation suppression and steady-state static error elimination, and the simulation results prove the effectiveness of the method proposed in the present invention.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A virtual synchronous machine active power control method based on angular frequency error proportional feedforward, characterized in that: The steps include: Step 1: Difference the set grid rated angular frequency ω0 and the angular frequency ω output by the virtual synchronous machine, and multiply it by the droop coefficient k ω The first power deviation ΔP1 is obtained, which satisfies: ΔP1=(ω0-ω)*k ω Among them, the rated angular frequency ω0 of the power grid is 100πrad / s; Step 2: Set the virtual synchronous machine active power reference value P ref Add the first power deviation ΔP1 obtained in step 1 and subtract the active power P output by the virtual synchronous machine e , and obtain the second power deviation ΔP2, which satisfies: ΔP2=P ref +ΔP1-P e Step 3: Integrate the second power deviation ΔP2 obtained in step 2 according to the following formula to obtain an angular frequency error Δω, which satisfies: Where, s represents the Laplace operator, J represents the virtual inertia of the virtual synchronous machine; Step 4: Add the angular frequency error Δω obtained in step 3 to the set grid rated angular frequency ω0 to obtain the angular frequency ω output by the virtual synchronous machine, satisfying: ω=ω0+Δω Step 5: Integrate the angular frequency ω of the virtual synchronous machine output obtained in step 4 to obtain the first angle θ1 of the virtual synchronous machine output, which satisfies: Step 6: The angular frequency error Δω obtained in step 3 is passed through a proportional link to obtain the feedforward angle deviation Δθ, which satisfies: Δθ=kΔω Where k is the feedforward proportional coefficient of the angular frequency error Δω, and Δθ is the feedforward angle deviation; Step 7: Add the first angle θ1 of the virtual synchronous machine output obtained in step 5 to the feedforward angle deviation Δθ obtained in step 6 to obtain the second angle θ2 of the virtual synchronous machine output, which satisfies: θ2=θ1+Δθ Step 8: Based on the second angle θ2 of the virtual synchronous machine output obtained in step 7 and the voltage amplitude E of the virtual synchronous machine output obtained based on the reactive power control of the virtual synchronous machine, a voltage reference value u is generated according to the following formula: αref 、u βref ,satisfy: Among them, u αref is the voltage reference α component in the stationary αβ coordinate system, u βref is the voltage reference value β component in the stationary αβ coordinate system; Step 9: Substitute the voltage reference value u obtained in step 8 αref 、u βref The input voltage and current dual closed-loop control system finally outputs a PWM signal to realize the control of the virtual synchronous machine.

2. The method for controlling active power of a virtual synchronous machine based on angular frequency error proportional feedforward according to claim 1, characterized in that: The active power P output by the virtual synchronous machine in step 2 e The calculation steps are as follows: Step 2-1: Sample the grid-connected voltage u of phase a output by the virtual synchronous machine a and c-phase grid-connected voltage u c , and transform it to the stationary αβ coordinate system to obtain the α component u of the grid-connected voltage output by the virtual synchronous machine in the stationary αβ coordinate system α and the β component u β ,satisfy: Step 2-2: Sample the grid-connected current i of phase a output by the virtual synchronous machine a and c-phase grid-connected current i c , and transform it to the stationary αβ coordinate system to obtain the α component i of the grid-connected current output by the virtual synchronous machine in the stationary αβ coordinate system α and β component i β ,satisfy: Step 2-3: The voltage α component u obtained according to step 2-1 α and the β component u β 、The current α component i obtained in step 2-2 α and β component i β , calculate the active power P according to the following formula e ,satisfy: P e =1.5(in α and α +in β and β )。

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