Adaptive additional damping control method for virtual synchronous generator based on frequency deviation

Abstract

The present invention discloses a method for adaptive additional damping control of a virtual synchronous generator based on frequency deviation, comprising the following steps: S1, using a pole configuration method to design SDC parameters; S2, based on the designed SDC parameters, introducing SDC into a VSG system; S3, using an adaptive strategy of SDC to control the gain coefficient of SDC, and completing adaptive additional damping control of the virtual synchronous generator. SDC is introduced into the VSG system, and a pair of zero poles are introduced into the system, so that the dominant pole moves, increasing the damping ratio of the system; the damping torque is deflected, and the negative damping caused by reactive coupling is reduced. When the system frequency is disturbed, the oscillation of frequency and active power becomes weaker, and the steady state is reached faster, thereby enhancing the stability of the system. The adaptive parameters can be automatically adjusted according to the disturbance situation to prevent excessive adaptive parameters from weakening the stability of the system, and take into account the stability and adjustment time of the system under disturbances of different sizes.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic power, and in particular relates to a method for adaptively controlling additional damping of a virtual synchronous generator based on frequency deviation. Background Art

[0002] In order to cope with the growing demand for electricity and environmental pressure, the power system is forming a development trend of high proportion of new energy and high proportion of power electronic equipment. The grid-connected inverter is the energy conversion interface between the renewable energy power generation system and the power grid. The virtual synchronous generator (VSG) is a control method in which the inverter simulates the characteristics of the synchronous generator. It has the inertia and damping operation characteristics of the synchronous generator, and automatically adjusts its output active power and reactive power according to the changes in the grid voltage frequency and amplitude, providing necessary support for the grid. Unlike synchronous generators, the synchronization characteristics between VSG and the grid are not dominated by the physically rotating rotor, but are determined by the corresponding control strategy.

[0003] When the control parameters are unreasonable and the line resistance is relatively large, the various control loops of the VSG will introduce negative damping to the VSG system, causing the system damping to decrease. Among them, the negative damping effect caused by reactive coupling caused by line parameters is particularly prominent. When the system damping decreases, low-frequency oscillations are more likely to occur, which brings new challenges to the safe and stable operation of the VSG.

[0004] In response to this challenge, there are related articles that have been studied. The paper "Analysis and Control of Low-Frequency Oscillation Damping of Virtual Synchronous Generator Considering the Influence of Voltage Loop" considers that the introduction of voltage loop provides additional negative damping components to the VSG system, thereby deteriorating the VSG low-frequency oscillation damping characteristics and increasing the risk of low-frequency oscillation instability in the system. A voltage loop phase compensation method is proposed to reduce the negative damping components introduced by the voltage loop and improve the VSG damping characteristics. However, the negative damping problem introduced by the voltage loop can be solved by modifying the voltage loop control parameters. The negative damping problem introduced by reactive loop coupling is caused by line parameters and cannot be solved by modifying the control parameters.

[0005] The document “Additional damping control based on VSG and its application in photovoltaic energy storage grid-connected system” introduces additional damping control into the frequency-active power loop, which can adjust the active power input and output of VSG according to the system frequency change, increase the damping of VSG system, and suppress the low-frequency oscillation of the system when the load changes suddenly. However, its additional damping control is composed of only proportional parameters, which is only sensitive to frequency deviation and cannot obtain the frequency change rate of the system; and additional damping control is only introduced into the frequency and active power loops, without solving the negative damping problem caused by reactive coupling; and its proportional parameters are fixed and cannot be automatically adjusted according to the disturbance situation, and cannot take into account the stability of the system under disturbances of different sizes. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the frequency deviation-based virtual synchronous generator adaptive additional damping control method provided by the present invention solves the problem of negative damping caused by reactive coupling in the prior art.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a virtual synchronous generator adaptive additional damping control method based on frequency deviation, comprising the following steps:

[0008] S1. Use pole placement method to design SDC parameters;

[0009] S2, based on the designed SDC parameters, introduce SDC into the VSG system;

[0010] S3, adopting the adaptive strategy of SDC to control the gain coefficient of SDC, and completing the adaptive additional damping control of the virtual synchronous generator.

[0011] Further: In S1, the SDC parameter is specifically the additional damping control , its specific expression is:

[0012]

[0013] In the formula, is the proportional gain, is the differential gain and filter time constant, is the gain coefficient of SDC, and s is the Laplace operator.

[0014] The beneficial effect of the above further scheme is: the method of designing SDC parameters of the present invention is specifically to introduce additional damping control to cause it to deflect, thereby reducing the negative damping it generates, and even providing positive damping, thereby reducing the negative damping problem caused by reactive coupling and improving system stability.

[0015] Further: In S2, after the SDC is introduced into the VSG system, the open-loop transfer function of the VSG system is The specific expression is:

[0016]

[0017] Where G(s) is the voltage compensation signal of the VSG system. As input, the frequency deviation signal is the output transfer function.

[0018] Further: In S3, the SDC gain coefficient is controlled by using the SDC adaptive strategy The specific expression is:

[0019]

[0020] In the formula, is the gain reference value, is the gain adjustment coefficient, is the threshold parameter.

[0021] The beneficial effect of the above further solution is that the adaptive parameters can be automatically adjusted according to the disturbance situation, and the suppression effect can be enhanced as needed.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention provides an adaptive additional damping control method for a virtual synchronous generator based on frequency deviation. The SDC is introduced into the VSG system, and a pair of zero poles is introduced into the system, so that the dominant pole moves and the damping ratio of the system is increased; the damping torque is deflected, and the negative damping caused by reactive coupling is reduced. When the system frequency is disturbed, the oscillation of frequency and active power becomes weaker, and the steady state is reached faster, thereby enhancing the stability of the system.

[0024] (2) The present invention adopts an adaptive strategy, and the SDC adaptive parameters are automatically adjusted according to the change of disturbance. When the VSG system is subjected to a large disturbance, the adaptive parameters are automatically increased, so that the system can quickly restore stability and further improve the system's ability to suppress disturbances; when the disturbance is very small, the adaptive parameters are not adjusted to prevent excessive adaptive parameters from weakening the stability of the system, taking into account the stability and adjustment time of the system under disturbances of different sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the adaptive additional damping control method for virtual synchronous generator based on frequency deviation.

[0026] Figure 2 This is the VSG control structure diagram.

[0027] Figure 3 Control block diagram considering power coupling for VSG.

[0028] Figure 4 Schematic diagram of damping torque change.

[0029] Figure 5 This is the SDC control block diagram.

[0030] Figure 6 It is the root locus diagram of VSG system.

[0031] Figure 7 This is the pole-zero diagram of the VSG system after the introduction of SDC.

[0032] Figure 8 for Root locus plot of the system as it changes.

[0033] Fig. 9 For parameters Configuration diagram.

[0034] Fig.10 This is the ASDC control block diagram.

[0035] Fig.11 It is the simulation parameter diagram.

[0036] Fig.12 This is a comparison chart of VSG output power under small signal model and simulation circuit model.

[0037] Fig.13 P ref Comparison of active power, output frequency, and frequency change rate of VSG under the conditions of no SDC, SDC, and ASDC when a 0.02pu step occurs.

[0038] Fig.14 for P ref Comparison of active power, output frequency, and frequency change rate of VSG when a 0.1pu step occurs, without SDC, with SDC, and with ASDC. DETAILED DESCRIPTION

[0039] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0040] Embodiment 1:

[0041] like Figure 1 As shown, in one embodiment of the present invention, a method for adaptive additional damping control of a virtual synchronous generator based on frequency deviation comprises the following steps:

[0042] S1. Use pole placement method to design SDC parameters;

[0043] S2, based on the designed SDC parameters, introduce SDC into the VSG system;

[0044] S3, adopting the adaptive strategy of SDC to control the gain coefficient of SDC, and completing the adaptive additional damping control of the virtual synchronous generator.

[0045] In this embodiment, the method of designing SDC parameters of the present invention is specifically to introduce additional damping control to make it deflect, thereby reducing the negative damping generated by it, and even providing positive damping. The specific principle is:

[0046] Figure 2 The schematic diagram of the VSG grid-connected system is shown below, with its control module, which mainly includes the current-voltage loop and the active-reactive loop. The current-voltage loop is a current-voltage dual closed-loop synchronous control, which realizes the feedback control of the VSG output voltage and current. The active loop, namely the active-frequency (Pf) control link, simulates the rotor characteristics of the synchronous generator; the reactive loop, namely the reactive-voltage (QU) control link, simulates the voltage regulation characteristics of the synchronous generator. The coupling of the power control link will introduce negative damping to the VSG system.

[0047] When the line resistance cannot be ignored, the expressions for active and reactive power of VSG are as follows:

[0048]

[0049]

[0050] In the formula, , is the line impedance angle, is the power angle, that is, the VSG output voltage phase angle and PCC voltage phase angle difference, . is the VSG output voltage amplitude, is the PCC voltage amplitude, is the total line resistance, is the total line reactance.

[0051] Because the line impedance , eliminating the intermediate variable , the active and reactive power expressions of VSG can be rewritten as:

[0052]

[0053]

[0054] The small signal linearization model of the above formula is:

[0055]

[0056]

[0057] In the above formula, the coefficients of the small signal linearization model are specifically:

[0058]

[0059]

[0060]

[0061]

[0062] Wherein, the subscript “0” represents the initial steady-state operating point.

[0063] The control loop considering power coupling is obtained as follows, where D and J are the damping coefficient and virtual moment of inertia of VSG, , , and are the coefficients of the small signal linearization model, for arrive The transfer function of .

[0064] Depend on Figure 3 Can get Δδ arrive ΔP The transfer function is T Q , its specific expression is:

[0065]

[0066] According to the expression of the coefficients of the small signal linearization model, G QE =k q / s , H PE >0, H QE >0. When the system is in steady state operation δ 0 When the resistance is large, - H Qδ can be negative, resulting in a negative damping torque in the power coupling. Δδ and Δ ω Torque on the phase plane T Q Analyze as Figure 4 shown.

[0067] from Figure 5 It can be seen that when- H Qδ When the value is negative, the resultant torque T Q Located in the fourth quadrant of the vector diagram, at this time, the damping torque of the vertical axis If the negative damping torque is a negative number, the introduction of negative damping torque will reduce the stability of the system. Therefore, the additional damping control H(s) can be set to make it deflect, thereby reducing the negative damping it produces, or even providing positive damping.

[0068] In S1, the SDC parameter is specifically the additional damping control , its specific expression is:

[0069]

[0070] In the formula, is the proportional gain, is the differential gain and filter time constant, is the gain coefficient of SDC, and s is the Laplace operator.

[0071] In this embodiment, considering that the frequency deviation and change rate are two important characteristics of the frequency, H(s) is composed of a proportional link and a high-pass filter to obtain the frequency deviation and change rate. The specific structure is as follows: Figure 5 shown.

[0072] The frequency deviation signal Used as the input signal of SDC. After calculating the proportional link and the differential link, the SDC method converts the voltage compensation signal Introduce reactive power control loop. is the proportional gain, is the differential gain and filter time constant, is the gain coefficient of SDC, and for The upper and lower limits of .

[0073] In S2, after the SDC is introduced into the VSG system, the open-loop transfer function of the VSG system is The specific expression is:

[0074]

[0075] Where G(s) is the voltage compensation signal of the VSG system. As input, the frequency deviation signal is the output transfer function.

[0076] In this embodiment, SDC introduces a pair of zero poles into the system. When the parameters of SDC change, the root locus of the system can be expressed by Figure 6 According to the root locus law, the root locus of the system starts from the pole of the open-loop transfer function and ends at the zero point or infinity. After introducing a pair of zero poles, the dominant pole of the system will change from Figure 6 It can be seen that as long as the parameters are selected appropriately, the root locus of the system will pass through the desired dominant pole. , so that the position of the dominant pole of the system changes from Shift to new dominant pole position According to control theory, the farther the system pole is from the imaginary axis, the smaller the adjustment time is and the faster it reaches steady state. The smaller the angle, the lower the damping ratio. The larger the value, the smaller the adjustment time and overshoot of the system, and the higher the system stability. After the introduction of SDC, the dominant pole moves away from the imaginary axis, and the corresponding The angle becomes smaller, making the system damping ratio As the value increases, the rise time and adjustment time become faster, the overshoot becomes smaller, and the system stability increases. At the same time, a closed-loop zero point is introduced to speed up the system response.

[0077] Embodiment 2:

[0078] This embodiment provides a specific SDC parameter configuration example for Embodiment 1.

[0079] When the system does not have SDC, find the poles and transfer function of the system. Construct the state space small signal model of the system and use the voltage compensation signal ∆V n As input, the frequency deviation signal ∆ω As the output, the transfer function of the system is obtained. Since the transfer function has a high order, in order to facilitate analysis and research, it can be reduced by solving the dominant transient response component of the system. G (s), only the closed-loop poles that dominate the time response are retained, and the reduced-order transfer function is recorded as G'(s). The dominant poles of the system are obtained as =-3.977+19.462j, =-3.977-19.462j.

[0080] Expand G'(s) by partial fractions:

[0081]

[0082] After the introduction of SDC, the closed-loop transfer function of the system is:

[0083]

[0084] The characteristic equation is:

[0085]

[0086] The dominant pole of the system moves on the root locus, always satisfying The characteristic equation of , so the desired dominant pole , Satisfy the following formula:

[0087]

[0088] Will and Expressed in terms of magnitude and phase angle, we obtain the magnitude equation and phase angle equation:

[0089]

[0090] Set the real part of the desired dominant pole to twice the original dominant pole, and the imaginary part to the imaginary part of the original dominant pole to obtain the desired dominant pole position , .set up and for , ,Will , Substitution and You can get the model , Phase Angle , The simultaneous mode equation and phase angle equation are solved to obtain a differential gain of 0.2559 and a filter time constant of 0.0701.

[0091] verify: Figure 7 The figure shows the comparison of the pole positions of the system before and after the introduction of SDC. The red circle is the original pole, the blue cross is the pole when SDC is connected, and the green five-pointed star is the desired pole. Figure 7 It can be seen that after the introduction of the SDC method, the dominant pole of the system is Move to the Pole of Hope Nearby, the damping ratio is increased from 0.2 to 0.38, the new dominant pole is very close to the desired dominant pole position, and the error is This is caused by the reduction of the order of . Therefore, the design result is reasonable.

[0092] In S3, the SDC adaptive strategy is used to control the gain coefficient of the SDC The specific expression is:

[0093]

[0094] In the formula, is the gain reference value, is the gain adjustment coefficient, is the threshold parameter.

[0095] like Figure 8 As shown, in this embodiment, the gain coefficient of SDC The larger the control, the greater the damping of the system. It can effectively improve the stability of the system, but It cannot be enlarged all the time, because too large This may lead to an intensification of periodic oscillations, and it can also be seen from the root locus diagram that When it increases, the other pair of poles will move closer to the imaginary axis, weakening the stability of the system. Therefore, when the oscillation of the system is more serious, increase , and when the system oscillation is not serious, Therefore, the present invention proposes an adaptive strategy for SDC.

[0096] The frequency fluctuation of the general system is about 0.1rad / s. At least it can be doubled when the fluctuation is the largest, so you can set is 1000. It is a threshold parameter, because when the actual power system is in operation, there will often be some small disturbances due to the environment or other factors. In order to prevent unnecessary changes in the SDC during steady-state operation, thereby affecting the stable operation of the system, a threshold needs to be set. How to obtain Fig. 9 As shown, and are the thresholds of angular frequency deviation and change rate respectively. Only when both the frequency deviation and the frequency change rate exceed the threshold, It is 1 only when it is 1, and 0 at other times, and the adaptive supplementary damping control (ASDC) is obtained. Fig.10 shown.

[0097] In order to better verify the correctness of the above analysis and the effectiveness of the proposed control strategy for suppressing the low-frequency oscillation of the system, a VSG control system simulation model was built on the MATLAB / Simulink platform, and simulation experiments were carried out. The simulation parameters are as follows: Fig.11 shown.

[0098] Small Signal Model Verification:

[0099] like Fig.12 As shown, in t =10s, a sinusoidal disturbance with an amplitude of 0.8MW and a frequency of 7.5Hz is applied to the active reference command of the VSG. Taking the output active power of the VSG as the observed quantity, it can be observed that when the same disturbance is applied, the active power curve of the VSG output in the small signal model completely coincides with the time domain simulation curve of the actual circuit model in MATLAB / Simulink.

[0100] To verify the effectiveness of the proposed SDC and adaptive SDC strategies, active power command disturbances are applied to the VSG without SDC, with SDC, and with adaptive SDC, and the response curves of active power, frequency, and frequency change rate are observed. Fig.13 As shown, when the disturbance is small: the active power instruction of the VSG undergoes a 0.02pu step.

[0101] Fig.13 The response curves of active power, frequency and frequency change rate of the VSG system when there is no SDC, SDC connected, and adaptive SDC connected, when the active power reference jumps from 1.0pu to 1.02pu in 10s are shown. It can be seen from the figure that the VSG control system using SDC can reach steady state faster than the traditional VSG control system, the fluctuation amplitude of the active power and output frequency of the VSG is smaller, the overshoot is smaller, the frequency change rate of the VSG is smaller, the response is smoother, and the system damping is greater; at the same time, due to the small disturbance, the adaptive strategy does not make the gain coefficient Therefore, the inhibitory effects of ASDC and SDC are similar.

[0102] Depend on Fig.14 It can be seen that the VSG control system using SDC can reach steady state faster than the traditional VSG control system, with shorter adjustment time, smaller overshoot, and greater system damping; while the VSG control system using ASDC is faster than the one using SDC, and the active power and output frequency of VSG respond to disturbances faster, with smaller overshoot, smoother response, and faster recovery to steady state. This is because the disturbance is large at this time, and the adaptive strategy will make the gain coefficient It increases significantly when the frequency deviation is large, so ASDC is better than SDC in suppressing disturbances.

[0103] In summary, the introduction of SDC into the VSG system can effectively improve the negative damping problem introduced by reactive coupling, increase system damping, and suppress low-frequency oscillation of the system. When the disturbance is large, ASDC can also further improve stability.

[0104] The beneficial effects of the present invention are as follows: the present invention provides a virtual synchronous generator adaptive additional damping control method based on frequency deviation, introduces SDC into the VSG system, introduces a pair of zero poles into the system, moves the dominant pole, and increases the damping ratio of the system; deflects the damping torque, reduces the negative damping caused by reactive coupling, and when the system frequency is disturbed, the oscillation of frequency and active power becomes weaker, reaches a steady state faster, and enhances the stability of the system.

[0105] The present invention adopts an adaptive strategy, and the SDC adaptive parameters are automatically adjusted according to the change of disturbance. When the VSG system is subjected to a large disturbance, the adaptive parameters are automatically increased, so that the system can quickly restore stability and further improve the system's ability to suppress interference; when the disturbance is very small, the adaptive parameters are not adjusted to prevent excessive adaptive parameters from weakening the stability of the system, taking into account the stability and adjustment time of the system under disturbances of different sizes.

[0106] In the description of the present invention, it is necessary to understand that the orientation or positional relationship indicated by the terms "center", "thickness", "upper", "lower", "horizontal", "top", "bottom", "inner", "outer", "radial", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", and "third" are used only for descriptive purposes, and cannot be understood as indicating or implying the relative importance or the number of implicitly specified technical features. Therefore, the features defined by "first", "second", and "third" may explicitly or implicitly include one or more of the features.

Claims

1. A virtual synchronous generator adaptive additional damping control method based on frequency deviation, characterized in that: The following steps are involved: S1. Use pole placement method to design SDC parameters; S2, based on the designed SDC parameters, introduce SDC into the VSG system; S3, using the adaptive strategy of SDC to control the gain coefficient of SDC, and completing the adaptive additional damping control of the virtual synchronous generator; In S1, the SDC parameter is specifically the additional damping control , its specific expression is: In the formula, is the proportional gain, is the differential gain and filter time constant, is the gain coefficient of SDC, s is the Laplace operator; In S3, the SDC adaptive strategy is used to control the gain coefficient of the SDC The specific expression is: In the formula, is the gain reference value, is the gain adjustment coefficient, is the threshold parameter.

2. The method for adaptive additional damping control of a virtual synchronous generator based on frequency deviation according to claim 1 is characterized in that: In S2, after the SDC is introduced into the VSG system, the open-loop transfer function of the VSG system is The specific expression is: Where G(s) is the voltage compensation signal of the VSG system. As input, the frequency deviation signal is the output transfer function.

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