VSG damping enhancement control method based on active lead-lag compensation

Abstract

The invention discloses a VSG damping enhancement control method based on active lead-lag compensation, and belongs to the field of new energy converter technology control. The method comprises the steps of firstly sampling output voltage and current of a new energy converter, calculating output instantaneous active power and reactive power of a virtual synchronous generator through the sampled voltage and current, and then obtaining an output phase instruction value and a voltage control instruction value through an optimized active-frequency loop and an optimized reactive-voltage loop; and finally, through voltage and current double-closed-loop control, the control of the new energy converter is realized. According to the method, the system damping ratio is increased in the transient process through the control method that the active power is fed back to the forward channel after lead-lag compensation, overshoot and oscillation generated when the active power output by the system changes are effectively restrained, tiny overshoot which cannot be restrained cannot be generated, and when the power grid angular frequency breaks away from the rated value, the system damping ratio is increased. And the steady-state characteristics of the system are not influenced.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy converter control, and in particular to a VSG damping enhancement control method based on active power lead-lag compensation. Background Art

[0002] With the rapid development of renewable energy generation technologies, their penetration rate in the power grid continues to rise, posing unprecedented challenges to the stable operation of traditional power systems. Renewable energy generation equipment is typically connected to the grid using power electronic converters, which lack sufficient inertia and damping characteristics compared to traditional synchronous generators. This is especially true in weak grid environments, where the grid's short-circuit ratio is low and inertia is insufficient, making the grid susceptible to system stability issues. To improve the stability of renewable energy grid integration, virtual synchronous generator (VSG) technology has emerged. However, existing virtual synchronous generator control strategies still have many shortcomings. Increasing the virtual damping coefficient can effectively suppress overshoot and oscillations caused by changes in output active power. However, because the primary frequency modulation coefficient and the virtual damping coefficient jointly affect the difference between the system's angular frequency and the grid's angular frequency, when the grid's angular frequency deviates from the rated value, an excessively large virtual damping coefficient can cause steady-state errors in the output active power of the virtual synchronous generator during stable grid operation.

[0003] At present, many papers and patents have proposed solutions to the problem that the fixed virtual damping coefficient of the virtual synchronous generator cannot take into account both the dynamic and steady-state characteristics of the system. These solutions can be roughly divided into two categories: one is to dynamically adjust the virtual damping coefficient and virtual inertia coefficient of the system by combining adaptive algorithms, and the other is to suppress overshoot and oscillation by increasing the equivalent damping ratio during the transient process of the system. For example:

[0004] Titled "Cooperative Adaptive Control Strategy of Virtual Synchronous Generator Moment of Inertia and Damping Coefficient," Yang Yun, Mei Fei, Zhang Chenyu, Miao Huiyu, Chen Hongfei, and Zheng Jianyong published in Electric Power Automation Equipment, Vol. 39, No. 3, 2019, pp. 125-131. The article proposes a control method for the coordinated adaptation of the moment of inertia and damping coefficient, in which the change in virtual inertia is related to the angular frequency deviation and the rate of change of the angular frequency, while the change in the damping coefficient is related only to the angular frequency deviation. However, the article does not specify how to select the thresholds for the relevant adjustment parameters.

[0005] The article "VSG Control Strategy Based on Angular Frequency Transient Feedforward" by Wang Su'e, Liu Yufan, Hao Pengfei, and Chen Jingwen, Advanced Electrical Engineering and Power Technology, Vol. 43, No. 5, 2024, pp. 38-49, and the article "Virtual Synchronous Generator Transient Power Oscillation Suppression Strategy Considering Overshoot," by Lan Zheng, Long Yang, Zeng Jinhui, Tu Chunming, Xiao Fan, and Guo Qi, Automation of Electric Power Systems, Vol. 46, No. 11, 2022, pp. 131-141, respectively, achieve the effect of increasing the equivalent damping ratio during transient processes by using angular frequency transient feedforward and transient feedforward of the difference between the output active power and the active power command value. However, the compensation coefficients of both methods can cause the zero point to be too close to the imaginary axis, resulting in uncontrollable small overshoot in the system.

[0006] An article titled "Improved VSG Control Strategy Based on Transient Damping Enhancement" by Jiang Shiming and Tang Jie, published in Power System Protection and Control, Vol. 51, No. 19, 2023, pp. 144-154, and an article titled "VSG Control Strategy Based on Improved Inertia Damping Characteristics" by Li Zhijun, Jia Xueyan, Wang Lijuan, Zhang Yinan, and Zhang Yawen, published in Acta Energiae Solaris Sinica, Vol. 42, No. 7, 2021, pp. 78-85, respectively, achieves the effect of increasing the equivalent damping ratio during transients by introducing high-frequency components of the output active power and angular frequency, and by adding differential correction links to the forward channel and damping feedback channel. However, both methods increase the order of the active power-frequency link transfer function to 4th order, and the former method introduces too many adjustment parameters, making parameter design more difficult and unfavorable for engineering application. Summary of the Invention

[0007] The technical problem to be solved by the present invention is that the fixed virtual damping coefficient of the virtual synchronous generator cannot take into account both the dynamic and steady-state characteristics of the system, and the method of increasing the equivalent damping ratio during transient processes has the problem of uncontrollable small overshoot. Specifically, the present invention proposes a VSG damping enhancement control method based on active lead-lag compensation. The output active power is fed back to the active system forward channel after lead-lag compensation, achieving the effect of improving the system equivalent damping ratio during transient processes, effectively suppressing the overshoot and oscillation generated by changes in the system output active power, and preventing uncontrollable small overshoot. Moreover, when the grid angular frequency deviates from the rated value, it will not affect the system steady-state characteristics.

[0008] To achieve the above objectives, the present invention proposes a VSG damping enhancement control method based on active lead-lag compensation. The control method is used for a virtual synchronous generator, which includes a new energy converter. The control method includes the following steps:

[0009] Step 1: Sample the three-phase voltage u at the output side of the new energy converter a ,u b ,uc and three-phase current i a ,i b ,i c And the dq axis voltage component u in the synchronous rotating coordinate system is obtained by synchronous rotating coordinate transformation d ,u q and dq axis current components i d ,i q ;

[0010] Step 2: According to the dq axis voltage component u obtained in step 1 d ,u q and dq axis current components i d ,i q , calculate the instantaneous active power P of the virtual synchronous generator e and instantaneous reactive power Q e ;

[0011] Step 3: After active power lead and lag compensation through active power-frequency control algorithm, the output angular frequency command value ω is obtained. ref , then the output angular frequency command value ω ref The output voltage phase angle reference value δ is obtained by integration ref ;

[0012] Step 4: The instantaneous reactive power Q obtained in step 2 e , calculate the voltage control command value E ref , E ref =E0+m(Q ref -Q e ), where E0 is the rated output phase voltage amplitude of the virtual synchronous generator, m is the reactive-voltage droop coefficient, Q ref is the reactive power command value;

[0013] Step 5: The phase angle reference value δ of the output voltage obtained in step 3 ref And step 4 to obtain the voltage control command value E ref Perform voltage and current dual closed-loop control to generate pulse width modulation PWM signal;

[0014] Step 6: modulate the inverter according to the pulse width modulation (PWM) signal obtained in step 5, and output a drive signal for the converter power switch to achieve active power optimization control of the virtual synchronous generator.

[0015] Preferably, the instantaneous active power P in step 2 is e and instantaneous reactive power Q e The calculation formula is:

[0016]

[0017] Preferably, the phase angle reference value δ of the output voltage in step 3 is ref The calculation process is as follows:

[0018] First, according to the instantaneous active power P e , set active power command value P ref And the power P required for primary frequency modulation n , the angular frequency deviation compensation ω is calculated through the virtual inertia link, and its calculation formula is:

[0019]

[0020] Where n is the primary frequency modulation coefficient, ω′ is the angular frequency deviation compensation calculated by the virtual inertia link in the previous control cycle, ω0 is the rated angular frequency of the virtual synchronous generator, J ω is the virtual inertia, s is the Laplace operator;

[0021] Secondly, the instantaneous active power P e The transient compensation amount P obtained after lead-lag compensation e ′, its expression is:

[0022]

[0023] Where K c is the compensation coefficient, T c is the time coefficient of the first-order lag link;

[0024] Then, according to the angular frequency deviation compensation ω, transient compensation P e ′ and the rated angular frequency ω0 to obtain the output angular frequency instruction ω ref ,ω ref =ω-P e ′+ω0;

[0025] Finally, the output angular frequency instruction ω ref The output voltage phase angle reference value δ is obtained by integration ref , δ ref =∫ω ref .

[0026] The VSG damping enhancement control method based on active lead-lag compensation disclosed in the present invention has the following advantages compared with the control method combining dynamic adjustment with adaptive algorithm and the control method increasing the equivalent damping ratio in transient process:

[0027] 1. This control method achieves the effect of increasing the system equivalent damping ratio during transient processes by feeding the instantaneous active power back to the forward channel of the active system after lead-lag compensation. Only two adjustment parameters are introduced in the method, and the active-frequency link transfer function will not be excessively increased. The parameter design process is simple, which is conducive to engineering applications.

[0028] 2. This control method reasonably sets the adjustment parameters so that the added zero point in the transfer function is far away from the imaginary axis, which will not produce uncontrollable small overshoot and is more in line with the actual engineering application needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a control block diagram of the virtual synchronous generator involved in the present invention.

[0030] Figure 2 This is a block diagram of the active power-frequency loop control after active power lead-lag compensation of the present invention.

[0031] Figure 3 is the active power command value P ref When the time is 2 seconds, it suddenly increases from 50KW to 70KW. Under different virtual damping coefficients and different adjustment parameters, the instantaneous active power P of the virtual synchronous generator is e changes in the situation.

[0032] Figure 4 The instantaneous active power P of the virtual synchronous generator is obtained when the grid frequency drops by 0.1 Hz in 2 seconds and different virtual damping coefficients and different adjustment parameters are used. e changes in the situation.

[0033] Figure 5 is the active power command value P ref When the time is 2 seconds, it suddenly increases from 50KW to 70KW. Under different adjustment parameters, the instantaneous active power P of the virtual synchronous generator is e changes in the situation.

[0034] Figure 6 The instantaneous active power P of the virtual synchronous generator is when the grid frequency drops by 0.1Hz in 2 seconds and different adjustment parameters are used. e changes in the situation. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0036] Figure 1 This is a control block diagram of the virtual synchronous generator involved in the present invention. Figure 2 This is the active power-frequency loop control block diagram after active power lead-lag compensation of the present invention. Figure 1As can be seen, the virtual synchronous generator includes a new energy converter and an LC filter, which includes a filter inductor and a filter capacitor. The DC side of the new energy converter is connected to a new energy DC power source (PVDC) provided by photovoltaic, wind power, or energy storage, and the AC side is connected to the three-phase power grid after the filter inductor and line impedance are connected in series. In addition, one end of the filter capacitor is connected between the filter inductor and the line impedance, and the other end is grounded.

[0037] exist Figure 1 In the figure, Lf is the inductance of the filter inductor, ZL is the resistance of the line impedance, and C f is the capacitance of the filter capacitor. In this implementation case, the rated capacity of the new energy converter is S rate =70KVA, DC side voltage is 750V, AC side output three-phase voltage rated phase voltage is 220V / 50Hz, L f =0.005H, C f =le-5F, Z L =0.002H.

[0038] Depend on Figure 1 and Figure 2 It can be seen that the VSG damping enhancement control method based on active lead-lag compensation provided by the present invention includes the following steps:

[0039] Step 1: Sample the three-phase voltage u at the output side of the new energy converter a ,u b ,u c and three-phase current i a ,i b ,i c And the dq axis voltage component u in the synchronous rotating coordinate system is obtained by synchronous rotating coordinate transformation d ,u q and dq axis current components i d ,i q .

[0040] Step 2: According to the dq axis voltage component u obtained in step 1 d ,u q and dq axis current components i d ,i q , calculate the instantaneous active power P of the virtual synchronous generator e and instantaneous reactive power Q e .

[0041] In this embodiment, the instantaneous active power P e and instantaneous reactive power Q e The calculation formula is:

[0042]

[0043] Step 3: After active power lead and lag compensation through active power-frequency control algorithm, the output angular frequency command value ω is obtained. ref , then the output angular frequency command value ω ref The output voltage phase angle reference value δ is obtained by integration ref .

[0044] In this embodiment, the phase angle reference value δ of the output voltage ref The calculation process is as follows:

[0045] First, according to the instantaneous active power P e , set active power command value P ref And the power P required for primary frequency modulation n , the angular frequency deviation compensation ω is calculated through the virtual inertia link, and its calculation formula is:

[0046]

[0047] Where n is the primary frequency modulation coefficient, ω′ is the angular frequency deviation compensation calculated by the virtual inertia link in the previous control cycle, ω0 is the rated angular frequency of the virtual synchronous generator, J ω is the virtual inertia, s is the Laplace operator;

[0048] Secondly, the instantaneous active power P e The transient compensation amount P obtained after lead-lag compensation e ′, its expression is:

[0049]

[0050] Where K c is the compensation coefficient, T c is the time coefficient of the first-order lag link;

[0051] Then, according to the angular frequency deviation compensation ω, transient compensation P e ′ and the rated angular frequency ω0 to obtain the output angular frequency instruction ω ref ,ω ref =ω-P e ′+ω0;

[0052] Finally, the output angular frequency instruction ω ref The output voltage phase angle reference value δ is obtained by integration ref , δ ref =∫ω ref .

[0053] In this embodiment, ω0=2πf=100π=314.159rad / s, J ω =1.5kg ·m 2 , P ref =50KW. m=22292.993W·s / rad. K c =380, T c =1e-7.

[0054] Step 4: The instantaneous reactive power Q obtained in step 2 e , calculate the voltage control command value E ref , E ref =E0+m(Q ref -Q e ), where E0 is the rated output phase voltage amplitude of the virtual synchronous generator, m is the reactive-voltage droop coefficient, Q ref is the reactive power command value.

[0055] In this embodiment, E0=310V, Q ref =0, m=4.44e-3V / Var.

[0056] Step 5: The phase angle reference value δ of the output voltage obtained in step 3 ref And step 4 to obtain the voltage control command value E ref Perform voltage and current dual closed-loop control to generate pulse width modulation PWM signal.

[0057] Step 6: modulate the inverter according to the pulse width modulation (PWM) signal obtained in step 5, and output a drive signal for the converter power switch to achieve active power optimization control of the virtual synchronous generator.

[0058] To verify the technical effects of this invention, a simulation was conducted on a grid-connected system with a 70kW new energy converter. To eliminate the impact of the virtual damping coefficient D on the steady-state error of the virtual synchronous generator's output active power, D = 0 in this implementation case under lead-lag compensation. Figure 3 Given the active power command value P ref When the time is 2 seconds, it suddenly increases from 50KW to 70KW. Under different virtual damping coefficients and different adjustment parameters, the instantaneous active power P of the virtual synchronous generator is e changes in Figure 4 The instantaneous active power P of the virtual synchronous generator is given when the grid frequency drops by 0.1Hz for 2 seconds, with different virtual damping coefficients and different adjustment parameters. e changes in the situation. Figure 5 is the active power command value P ref When the time is 2 seconds, it suddenly increases from 50KW to 70KW. Under different adjustment parameters, the instantaneous active power P of the virtual synchronous generator is e changes in Figure 6 The instantaneous active power P of the virtual synchronous generator is when the grid frequency drops by 0.1Hz in 2 seconds and different adjustment parameters are used. e When K c =0, T c =0, it can be regarded as that no compensation link is added. It can be seen that when the compensation link is not added, as the fixed damping coefficient continues to increase, the system output active power has a better suppression effect on overshoot and oscillation. However, as the fixed damping coefficient continues to increase, when the grid frequency deviates from the rated frequency, the steady-state error of the system output active power also continues to increase. With the addition of the lead-lag link, the output active power is fed back to the forward channel after lead-lag compensation, and different suppression effects are shown under different adjustment coefficients. c =380, T c =1e-7, the system output active power will not produce steady-state error when the active power command value changes and the grid frequency deviates from the rated value, and overshoot and oscillation are effectively suppressed.

Claims

1. A VSG damping enhancement control method based on active lead-lag compensation, the control method is used for a virtual synchronous generator, the virtual synchronous generator includes a new energy converter, characterized in that: The control method comprises the following steps: Step 1: Sample the three-phase voltage u at the output side of the new energy converter a ,u b ,u c and three-phase current i a ,i b ,i c And the dq axis voltage component u in the synchronous rotating coordinate system is obtained by synchronous rotating coordinate transformation d ,u q and dq axis current components i d ,i q ; Step 2: According to the dq axis voltage component u obtained in step 1 d ,u q and dq axis current components i d ,i q , calculate the instantaneous active power P of the virtual synchronous generator e and instantaneous reactive power Q e ; Step 3: After active power lead and lag compensation through active power-frequency control algorithm, the output angular frequency command value ω is obtained. ref , then the output angular frequency command value ω ref The phase angle reference value δ of the output voltage is obtained by integration ref ; Step 4: The instantaneous reactive power Q obtained in step 2 e , calculate the voltage control command value E ref , E ref =E0+m(Q ref -Q e ), where E0 is the rated output phase voltage amplitude of the virtual synchronous generator, m is the reactive-voltage droop coefficient, Q ref is the reactive power command value; Step 5: The phase angle reference value δ of the output voltage obtained in step 3 ref And step 4 to obtain the voltage control command value E ref Perform voltage and current dual closed-loop control to generate pulse width modulation PWM signal; Step 6: modulate the inverter according to the pulse width modulation (PWM) signal obtained in step 5, and output a drive signal for the converter power switch to achieve active power optimization control of the virtual synchronous generator.

2. The VSG damping enhancement control method based on active power lead-lag compensation according to claim 1 is characterized in that: The instantaneous active power P in step 2 e and instantaneous reactive power Q e The calculation formula is:

3. The VSG damping enhancement control method based on active lead-lag compensation according to claim 1 is characterized in that: The phase angle reference value δ of the output voltage in step 3 ref The calculation process is as follows: First, according to the instantaneous active power P e , set active power command value P ref And the power P required for primary frequency modulation n , the angular frequency deviation compensation ω is calculated through the virtual inertia link, and its calculation formula is: Where n is the primary frequency modulation coefficient, ω′ is the angular frequency deviation compensation calculated by the virtual inertia link in the previous control cycle, ω0 is the rated angular frequency of the virtual synchronous generator, J ω is the virtual inertia, s is the Laplace operator; Secondly, the instantaneous active power P e The transient compensation amount P obtained after lead-lag compensation e ′, its expression is: Where K c is the compensation coefficient, T c is the time coefficient of the first-order lag link; Then, according to the angular frequency deviation compensation ω, transient compensation P e ′ and the rated angular frequency ω0 to obtain the output angular frequency instruction ω ref ,ω ref =ω-P e ′+ω0; Finally, the output angular frequency instruction ω ref The output voltage phase angle reference value δ is obtained by integration ref , δ ref =∫ω ref .

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