A method and system for regulating grid voltage feedforward regulator of grid-connected inverter

Abstract

The present invention discloses a method and system for regulating a grid voltage feedforward regulator of a grid-connected inverter. The regulating method comprises the following steps: step S10: using an RP algorithm and a PCM algorithm to measure the voltage at a common coupling point of a grid voltage feedforward regulator of a grid-connected inverter respectively. If the difference between the two is greater than a first threshold, step S20 is performed, otherwise step S10 is continued; step S20: parameter adjustment is performed on the grid voltage feedforward regulator of the grid-connected inverter; step S30: using an RP algorithm and a PCM algorithm to measure the voltage at a common coupling point of the grid voltage feedforward regulator of the grid-connected inverter after parameter adjustment respectively. If the difference between the two is less than a second threshold, the grid voltage feedforward regulator is successfully adjusted, otherwise step S20 is continued.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected inverter stability control, and in particular to a method and system for regulating a grid voltage feedforward regulator of a grid-connected inverter. Background Art

[0002] In order to solve the global energy crisis and environmental pollution problems, power systems that rely on renewable energy have become an emerging force. As various energy conversion interfaces, grid-connected inverters not only play an important role in delivering energy to the power grid, but their operating characteristics under weak power grids also directly determine the stability of renewable energy distributed power generation systems. However, as the proportion of distributed power generation systems in the power grid increases, their impact on the power grid is becoming increasingly important. Due to long-distance transmission lines, a large number of nonlinear devices and other reasons, the power grid exhibits weak grid characteristics. Under weak power grids, the voltage at the common coupling point contains rich harmonics, voltage distortion affects the current injected into the power grid, and the wide range of grid impedance changes will reduce the system phase margin, and the system is at risk of instability.

[0003] There are currently two main suppression methods for the impact of grid voltage distortion on grid-connected current: one is to increase the loop gain at the fundamental and background harmonic frequencies, and the other is to adopt a grid voltage feedforward strategy. Some are based on capacitor current feedforward for compensation, some are based on the MR phase of the leading link for compensation, some use the active suppression method of the external power compensation circuit to suppress, and some use the detected grid impedance value and the positive feedback of the grid current introduced by the feedforward control to offset, but the above methods cannot adapt to the situation where the grid impedance changes over a wide range.

[0004] In summary, as the power grid gradually presents the characteristics of a weak grid, when a large number of power electronic devices and new energy sources are connected, unfavorable factors such as harmonic components will be introduced at the same time. In order to improve the ability of the grid-connected inverter to adapt to the wide range of grid impedance changes under weak grids, it is necessary to improve the existing grid voltage feedforward for the grid-connected inverter. Summary of the invention

[0005] In response to the problems and needs raised above, this solution proposes a method and system for adjusting the grid voltage feedforward regulator of a grid-connected inverter. Due to the adoption of the following technical features, the above technical objectives can be achieved and many other technical effects can be brought about.

[0006] An object of the present invention is to provide a method for adjusting a grid voltage feedforward regulator of a grid-connected inverter, comprising the following steps:

[0007] Step S10: using the RP algorithm and the PCM algorithm to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter respectively, if the difference between the two is greater than the first threshold, proceed to step S20, otherwise continue to step S10;

[0008] Step S20: adjusting parameters of the grid voltage feedforward regulator of the grid-connected inverter;

[0009] Step S30: Use the RP algorithm and the PCM algorithm to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter after parameter adjustment. If the difference between the two is less than the second threshold, the grid voltage feedforward regulator is adjusted successfully, otherwise continue to step S20.

[0010] In addition, the grid voltage feedforward regulation method for a grid-connected inverter according to the present invention may also have the following technical features:

[0011] In one example of the present invention, the grid voltage feedforward regulator of the grid-connected inverter is composed of a proportional link, a primary differential link, and a secondary differential link, and its transfer function is:

[0012]

[0013] In the formula, M, N, and K are the proportional term coefficient, the first differential term coefficient, and the second differential term coefficient, respectively. PWM is the grid-connected inverter bridge transfer function, C is the grid-connected inverter filter capacitor, H ad is the active damping filter capacitor voltage sampling coefficient, L 1 is the inverter side inductance of the grid-connected inverter, s is the primary differential link, s 2 It is the second differential link.

[0014] In an example of the present invention, step S20 includes the following steps:

[0015] S21: According to the output impedance of the grid-connected inverter, the expression of the phase margin Υ is obtained as follows:

[0016]

[0017] Where, τ is the power grid digital control delay, ω g is the angular frequency corresponding to the intersection of the grid-connected inverter impedance and the grid impedance under weak grid conditions, L 2 is the grid-side inductance of the grid-connected inverter, A 11 , A 22 , A 12 , A 21 The resonant coefficient of the current controller including the cosine link, the proportional coefficient of the current controller including the cosine link, the resonant coefficient of the current controller including the sine link, and the proportional coefficient of the current controller including the sine link;

[0018] S22: Determine the maximum value γ of Y according to the transfer function of the grid voltage feedforward regulator of the grid-connected inverter max The value of the proportional term coefficient M when ;

[0019] S23: According to the relevant margin γ max Determine the first differential term coefficient N and the second differential term coefficient K, the expression is:

[0020]

[0021]

[0022]

[0023] In the formula, ω N ,ω K are the frequencies corresponding to the intersection of the inverter output impedance and the grid impedance when N=0 and K=0, and ω is the system angular frequency.

[0024] In one example of the present invention, in step S22, the transfer function determines that Y obtains a maximum value γ max The expression of the value of the proportional term coefficient M is:

[0025]

[0026] In the formula, ω M is the frequency corresponding to the intersection of the inverter output impedance and the grid impedance after M=0, T s is the sampling time.

[0027] Another object of the present invention is to provide a grid voltage feedforward regulator regulation system for a grid-connected inverter, comprising:

[0028] A first measuring unit is configured to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter by using the RP algorithm and the PCM algorithm respectively;

[0029] a first judging unit configured to judge the difference between the RP algorithm and the PCM algorithm, and if the difference is less than or equal to a first threshold, the first measuring unit continues to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter until the difference is greater than the first threshold;

[0030] A parameter adjustment unit configured to adjust parameters of a grid voltage feedforward regulator of a grid-connected inverter;

[0031] A second measuring unit is configured to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter after the parameters are adjusted by the parameter adjustment unit by using the RP algorithm and the PCM algorithm respectively;

[0032] The second judgment unit is configured to judge the difference between the RP algorithm and the PCM algorithm. If the difference is greater than or equal to the second threshold, the second measurement unit continues to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter until the difference is greater than or equal to the second threshold.

[0033] In one example of the present invention, the grid voltage feedforward regulator of the grid-connected inverter is composed of a proportional link, a primary differential link, and a secondary differential link, and its transfer function is:

[0034]

[0035] In the formula, M, N, and K are the proportional term coefficient, the first differential term coefficient, and the second differential term coefficient, respectively. PWM is the grid-connected inverter bridge transfer function, C is the grid-connected inverter filter capacitor, H ad is the active damping filter capacitor voltage sampling coefficient, L 1 is the inverter side inductance of the grid-connected inverter, s is the primary differential link, s 2 It is the second differential link.

[0036] In one example of the present invention, the second measuring unit includes:

[0037] The phase margin calculation module is configured to obtain the expression of the phase margin Y according to the output impedance of the grid-connected inverter:

[0038]

[0039] Where, τ is the power grid digital control delay, ω g is the angular frequency corresponding to the intersection of the grid-connected inverter impedance and the grid impedance under weak grid conditions, L 2 is the grid-side inductance of the grid-connected inverter, A 11 , A 22 , A 12 , A 21 The resonant coefficient of the current controller including the cosine link, the proportional coefficient of the current controller including the cosine link, the resonant coefficient of the current controller including the sine link, and the proportional coefficient of the current controller including the sine link;

[0040] The proportional term coefficient calculation module is configured to determine the maximum value γ of Y according to the transfer function of the grid voltage feedforward regulator of the grid-connected inverter. max The value of the proportional term coefficient M when ;

[0041] The differential coefficient calculation module is configured to be used according to the relevant margin γ max Determine the first differential term coefficient N and the second differential term coefficient K, the expression is:

[0042]

[0043]

[0044]

[0045] In the formula, ω N ,ω K are the frequencies corresponding to the intersection of the inverter output impedance and the grid impedance when N=0 and K=0, and ω is the system angular frequency.

[0046] In one example of the present invention, the transfer function determines that Y takes a maximum value γ max The expression of the value of the proportional term coefficient M is:

[0047]

[0048] In the formula, ω M is the frequency corresponding to the intersection of the inverter output impedance and the grid impedance after M=0, T s is the sampling time.

[0049] The best embodiment for carrying out the present invention will be described in more detail below with reference to the accompanying drawings so that the features and advantages of the present invention can be easily understood. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention, wherein the drawings are only used to illustrate some embodiments of the present invention, but not to limit all embodiments of the present invention thereto.

[0051] Figure 1 A structural block diagram of a grid-connected inverter system including a grid voltage feedforward regulator according to an embodiment of the present invention;

[0052] Figure 2 4 is a control block diagram of a grid-connected inverter based on a grid voltage feedforward regulator according to an embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the technical solution of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in conjunction with the drawings of specific embodiments of the present invention. The same figure marks in the drawings represent the same parts. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described 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.

[0054] According to the first aspect of the present invention, a method for adjusting a grid voltage feedforward regulator of a grid-connected inverter comprises the following steps:

[0055] Step S10: using the RP algorithm and the PCM algorithm to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter respectively, if the difference between the two is greater than the first threshold, proceed to step S20, otherwise continue to step S10;

[0056] It should be noted that:

[0057] The RP algorithm transfer function is:

[0058]

[0059] Among them, the grid voltage u g is the predicted value, A represents the low-pass filter, which is 0.98; the switching frequency is 18kHz, then the number of switching cycles in the grid cycle is N 0 is 360; k represents the predicted value of the sampling period and is taken as 2; m generally represents a gain coefficient less than 1 and is taken as 0.96.

[0060] The transfer function of the PCM algorithm is:

[0061]

[0062] Among them, it means that T s is the sampling time, α and β represent the control coefficients.

[0063] Step S20: adjusting parameters of the grid voltage feedforward regulator of the grid-connected inverter;

[0064] Step S30: Use the RP algorithm and the PCM algorithm to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter after parameter adjustment. If the difference between the two is less than the second threshold, the grid voltage feedforward regulator is adjusted successfully, otherwise continue to step S20.

[0065] This regulation method can ensure that when the grid impedance changes over a wide range under a weak grid, by measuring the voltage at the common coupling point, the parameters of the grid voltage feedforward regulator can be adjusted in time, thereby maintaining the system with sufficient phase margin and improving the robustness of the grid-connected inverter.

[0066] In one example of the present invention, the grid voltage feedforward regulator of the grid-connected inverter is composed of a proportional link, a primary differential link, and a secondary differential link, and its transfer function is:

[0067]

[0068] In the formula, M, N, and K are the proportional term coefficient, the first differential term coefficient, and the second differential term coefficient, respectively. PWM is the grid-connected inverter bridge transfer function, C is the grid-connected inverter filter capacitor, H ad is the active damping filter capacitor voltage sampling coefficient, L 1 is the inverter side inductance of the grid-connected inverter, s is the primary differential link, s 2 It is the second differential link.

[0069] In an example of the present invention, step S20 includes the following steps:

[0070] S21: Figure 1 and Figure 2 As shown in Figure 2, according to the output impedance of the grid-connected inverter, the expression of the phase margin Υ is:

[0071]

[0072] Where, τ is the power grid digital control delay, ω g is the angular frequency corresponding to the intersection of the grid-connected inverter impedance and the grid impedance under weak grid conditions, L 2 is the grid-side inductance of the grid-connected inverter, A 11 , A 22 , A 12 , A 21 The resonant coefficient of the current controller including the cosine link, the proportional coefficient of the current controller including the cosine link, the resonant coefficient of the current controller including the sine link, and the proportional coefficient of the current controller including the sine link;

[0073] S22: Determine the maximum value γ of Y according to the transfer function of the grid voltage feedforward regulator of the grid-connected inverter max The value of the proportional term coefficient M when ;

[0074] S23: According to the relevant margin γ max Determine the first differential term coefficient N and the second differential term coefficient K, the expression is:

[0075]

[0076]

[0077]

[0078] In the formula, ω N ,ω K are the frequencies corresponding to the intersection of the inverter output impedance and the grid impedance when N=0 and K=0, and ω is the system angular frequency.

[0079] It should be noted that since the expression of the first differential term coefficient N is too long and not conducive to calculation, D is used to replace a part of the expression N, thereby reducing the length and calculation amount of the first differential term coefficient N.

[0080] In one example of the present invention, in step S22, the transfer function determines that Y obtains a maximum value γ max The expression of the value of the proportional term coefficient M is:

[0081]

[0082] In the formula, ω M is the frequency corresponding to the intersection of the inverter output impedance and the grid impedance after M=0, T s is the sampling time.

[0083] According to the second aspect of the present invention, a grid voltage feedforward regulator regulation system for a grid-connected inverter comprises:

[0084] A first measuring unit is configured to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter by using the RP algorithm and the PCM algorithm respectively;

[0085] a first judging unit configured to judge the difference between the RP algorithm and the PCM algorithm, and if the difference is less than or equal to a first threshold, the first measuring unit continues to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter until the difference is greater than the first threshold;

[0086] A parameter adjustment unit configured to adjust parameters of a grid voltage feedforward regulator of a grid-connected inverter;

[0087] A second measuring unit is configured to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter after the parameters are adjusted by the parameter adjustment unit by using the RP algorithm and the PCM algorithm respectively;

[0088] The second judgment unit is configured to judge the difference between the RP algorithm and the PCM algorithm. If the difference is greater than or equal to the second threshold, the second measurement unit continues to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter until the difference is greater than or equal to the second threshold.

[0089] This regulation system can ensure that when the grid impedance changes over a wide range under weak power grid conditions, by measuring the voltage at the common coupling point, the parameters of the grid voltage feedforward regulator can be adjusted in time, thereby maintaining the system with sufficient phase margin and improving the robustness of the grid-connected inverter.

[0090] In one example of the present invention, the grid voltage feedforward regulator of the grid-connected inverter is composed of a proportional link, a primary differential link, and a secondary differential link, and its transfer function is:

[0091]

[0092] In the formula, M, N, and K are the proportional term coefficient, the first differential term coefficient, and the second differential term coefficient, respectively. PWM is the grid-connected inverter bridge transfer function, C is the grid-connected inverter filter capacitor, H ad is the active damping filter capacitor voltage sampling coefficient, L 1 is the inverter side inductance of the grid-connected inverter, s is the primary differential link, s 2 It is the second differential link.

[0093] In one example of the present invention, Figure 1 and Figure 2 As shown, the second measuring unit includes:

[0094] The phase margin calculation module is configured to obtain the expression of the phase margin Y according to the output impedance of the grid-connected inverter:

[0095]

[0096] Where, τ is the power grid digital control delay, ω g is the angular frequency corresponding to the intersection of the grid-connected inverter impedance and the grid impedance under weak grid conditions, L 2 is the grid-side inductance of the grid-connected inverter, A 11 , A 22 , A 12 , A 21 The resonant coefficient of the current controller including the cosine link, the proportional coefficient of the current controller including the cosine link, the resonant coefficient of the current controller including the sine link, and the proportional coefficient of the current controller including the sine link;

[0097] The proportional term coefficient calculation module is configured to determine the maximum value γ of Y according to the transfer function of the grid voltage feedforward regulator of the grid-connected inverter. max The value of the proportional term coefficient M when ;

[0098] The differential coefficient calculation module is configured to be used according to the relevant margin γ max Determine the first differential term coefficient N and the second differential term coefficient K, the expression is:

[0099]

[0100]

[0101]

[0102] In the formula, ω N ,ω K are the frequencies corresponding to the intersection of the inverter output impedance and the grid impedance when N=0 and K=0, and ω is the system angular frequency.

[0103] In one example of the present invention, the transfer function determines that Y takes a maximum value γ max The expression of the value of the proportional term coefficient M is:

[0104]

[0105] In the formula, ω M is the frequency corresponding to the intersection of the inverter output impedance and the grid impedance after M=0, T s is the sampling time.

[0106] The exemplary implementation scheme of the grid voltage feedforward regulation method and regulation system for a grid-connected inverter proposed in the present invention is described in detail with reference to the preferred embodiments. However, it can be understood by those skilled in the art that, without departing from the concept of the present invention, various modifications and variations can be made to the above-mentioned specific embodiments, and various technical features and structures proposed in the present invention can be combined in various ways without exceeding the protection scope of the present invention, which is determined by the attached claims.

Claims

1. A method for adjusting a grid voltage feedforward regulator of a grid-connected inverter, characterized in that: The steps include: Step S10: using the RP algorithm and the PCM algorithm to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter respectively, if the difference between the two is greater than the first threshold, proceed to step S20, otherwise continue to step S10; Step S20: Parameter adjustment is performed on the grid voltage feedforward regulator of the grid-connected inverter; wherein the grid voltage feedforward regulator of the grid-connected inverter is composed of a proportional link, a primary differential link, and a secondary differential link, and its transfer function is: In the formula, M, N, and K are the proportional term coefficient, the first differential term coefficient, and the second differential term coefficient, respectively. PWM is the grid-connected inverter bridge transfer function, C is the grid-connected inverter filter capacitor, H ad is the voltage sampling coefficient of the active damping filter capacitor, L1 is the inverter side inductance of the grid-connected inverter, s is the primary differential link, s 2 is the second differential link; Step S30: using the RP algorithm and the PCM algorithm to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter after parameter adjustment respectively, if the difference between the two is less than the second threshold, the grid voltage feedforward regulator is adjusted successfully, otherwise, continue to step S20; Wherein, the step S20 includes the following steps: S21: According to the output impedance of the grid-connected inverter, the expression of the phase margin Υ is obtained as follows: Where, τ is the power grid digital control delay, ω g is the angular frequency corresponding to the intersection of the grid-connected inverter impedance and the grid impedance under weak power grid, L2 is the grid-side inductance of the grid-connected inverter, A 11 , A 22 , A 12 , A 21 The resonant coefficient of the current controller including the cosine link, the proportional coefficient of the current controller including the cosine link, the resonant coefficient of the current controller including the sine link, and the proportional coefficient of the current controller including the sine link; S22: Determine the maximum value γ of Y according to the transfer function of the grid voltage feedforward regulator of the grid-connected inverter max The value of the proportional term coefficient M when ; wherein the transfer function determines that Y obtains the maximum value γ max The expression of the value of the proportional term coefficient M is: In the formula, ω M is the frequency corresponding to the intersection of the inverter output impedance and the grid impedance after M=0, T s is the sampling time; S23: According to the relevant margin γ max Determine the first differential term coefficient N and the second differential term coefficient K, the expression is: In the formula, ω N ,ω K are the frequencies corresponding to the intersection of the inverter output impedance and the grid impedance when N=0 and K=0, and ω is the system angular frequency.

2. A grid voltage feedforward regulator regulation system for a grid-connected inverter, characterized in that: include: A first measuring unit is configured to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter by using the RP algorithm and the PCM algorithm respectively; a first judging unit configured to judge the difference between the RP algorithm and the PCM algorithm, and if the difference is less than or equal to a first threshold, the first measuring unit continues to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter until the difference is greater than the first threshold; The parameter adjustment unit is configured to adjust the parameters of the grid voltage feedforward regulator of the grid-connected inverter; wherein the grid voltage feedforward regulator of the grid-connected inverter is composed of a proportional link, a primary differential link, and a secondary differential link, and its transfer function is: In the formula, M, N, and K are the proportional term coefficient, the first differential term coefficient, and the second differential term coefficient, respectively. PWM is the grid-connected inverter bridge transfer function, C is the grid-connected inverter filter capacitor, H ad is the voltage sampling coefficient of the active damping filter capacitor, L1 is the inverter side inductance of the grid-connected inverter, s is the primary differential link, s 2 is the second differential link; A second measuring unit is configured to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter after the parameters are adjusted by the parameter adjustment unit by using the RP algorithm and the PCM algorithm respectively; Wherein, the second measuring unit comprises: The phase margin calculation module is configured to obtain the expression of the phase margin Y according to the output impedance of the grid-connected inverter: Where, τ is the power grid digital control delay, ω g is the angular frequency corresponding to the intersection of the grid-connected inverter impedance and the grid impedance under weak power grid, L2 is the grid-side inductance of the grid-connected inverter, A 11 , A 22 , A 12 , A 21 The resonant coefficient of the current controller including the cosine link, the proportional coefficient of the current controller including the cosine link, the resonant coefficient of the current controller including the sine link, and the proportional coefficient of the current controller including the sine link; The proportional term coefficient calculation module is configured to determine the maximum value γ of Y according to the transfer function of the grid voltage feedforward regulator of the grid-connected inverter. max The value of the proportional term coefficient M when ; wherein the transfer function determines that Y obtains the maximum value γ max The expression of the value of the proportional term coefficient M is: In the formula, ω M is the frequency corresponding to the intersection of the inverter output impedance and the grid impedance after M=0, T s is the sampling time; The differential coefficient calculation module is configured to be used according to the relevant margin γ max Determine the first differential term coefficient N and the second differential term coefficient K, the expression is: In the formula, ω N ,ω K are the frequencies corresponding to the intersection of the inverter output impedance and the grid impedance when N=0 and K=0, and ω is the system angular frequency; The second judgment unit is configured to judge the difference between the RP algorithm and the PCM algorithm. If the difference is greater than or equal to the second threshold, the second measurement unit continues to measure the voltage at the common coupling point of the grid voltage feedforward regulator of the grid-connected inverter until the difference is greater than or equal to the second threshold.

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