Discrete domain STATCOM current controller design method and system

Abstract

The invention provides a discrete domain STATCOM current controller design method and system. The method comprises the steps that a discrete domain model of a controlled object is established based on design factors; constructing a closed-loop transfer function of current closed-loop system minimum beat control by considering the zero static error control performance of the current closed-loop system; and obtaining a transfer function of the STATCOM current controller in a discrete domain according to the discrete domain model of the controlled object and the closed-loop transfer function, converting the transfer function into a difference recursion equation, and programming in a digital processor. According to the design method of the STATCOM current digital controller, continuous frequency domain design is avoided, design is directly carried out in the discrete frequency domain, parameters of the digital controller can be directly obtained according to system parameters and design requirements, implementation is easy, and good current control performance can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a discrete domain STATCOM current controller design method and system. Background Art

[0002] With the increase in the penetration rate of renewable energy generation, traditional power systems face more challenges, such as voltage instability, low power factor, increased line loss and other problems. STATCOM (Static Synchronous Compensator) is a power electronic device used in power systems to improve power quality and enhance system stability. STATCOM is connected to the power grid in parallel through a power electronic converter, and can quickly and continuously adjust reactive current and reactive power, thereby improving the stability and power quality of the power system and meeting the needs of modern power systems. In addition to the main circuit design and modulation method of STATCOM, the design of the current controller of STATCOM is the key to achieving reactive regulation capability. The control goal is to make the STATCOM output current quickly and accurately track the command current signal. The steady-state tracking accuracy, dynamic response speed and compensation bandwidth of the control method directly affect the reactive compensation performance of the device.

[0003] At present, the main methods of current control in STATCOM include: proportional integral control, proportional resonant control, and repetitive control. These control methods are to design the controller in the continuous frequency domain, and then obtain the discrete transfer function of the controller by frequency discretization, and then convert it into a differential recursive formula and implement it on the digital controller. Due to the processing overhead of the program, the control output of the digital controller adopts a one-beat lag method. When the frequency is low (usually the switching frequency of the chain STATCOM is within 1kHZ), the control lag has a great negative impact on the stability of the control, and even leads to the failure of the control. To deal with this problem, a unit lag link is added during the continuous frequency domain analysis. Its frequency domain characteristics are relatively complex (belonging to transcendental functions), and are generally processed by the mathematical means of Pade approximation. The approximate processing is related to the control bandwidth and depends on the designer's theoretical knowledge and design experience, making it difficult to achieve good control performance. In addition, the controller designed in the continuous frequency domain needs to be discretized before it can be implemented in the DSP controller. The discretization methods of the continuous domain controller include: backward difference method, bilinear transformation method, zero-pole correspondence method, etc. According to the digital signal processing theory, each discretization method will change the frequency characteristics of the controller, causing the actual system transfer function to deviate from the designed transfer function, resulting in the inability to achieve good design performance.

[0004] In high-power and low-switching control frequency applications such as STATCOM, conventional design methods require designers to have rich theoretical knowledge and engineering experience, otherwise it is difficult to design an ideal STATCOM digital controller. Summary of the invention

[0005] The object of the present invention is to provide a discrete domain STATCOM current controller design method and system, aiming to solve the above-mentioned problems in the prior art.

[0006] An embodiment of the present invention provides a discrete domain STATCOM current controller design method, comprising:

[0007] Establish a discrete domain model of the controlled object based on design factors;

[0008] Considering the zero-static-error control performance of the current closed-loop system, a closed-loop transfer function for minimum-beat control of the current closed-loop system is constructed;

[0009] The transfer function of the STATCOM current controller in the discrete domain is obtained according to the discrete domain model of the controlled object and the closed-loop transfer function, which is converted into a differential recursive equation and implemented in a digital processor through programming.

[0010] An embodiment of the present invention provides a discrete domain STATCOM current controller design system, comprising:

[0011] A first design module is used to establish a discrete domain model of the controlled object based on design factors;

[0012] The second design module is used to consider the zero-static-error control performance of the current closed-loop system and construct a closed-loop transfer function of the minimum-beat control of the current closed-loop system;

[0013] The third design module is used to obtain the transfer function of the STATCOM current controller in the discrete domain according to the discrete domain model of the controlled object and the closed-loop transfer function, convert it into a differential recursive equation, and implement it in a digital processor through programming.

[0014] An embodiment of the present invention also provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program implements the steps of the above-mentioned discrete domain STATCOM current controller design method when executed by the processor.

[0015] An embodiment of the present invention further provides a computer-readable storage medium, on which a program for implementing information transmission is stored, and when the program is executed by a processor, the steps of the above-mentioned discrete domain STATCOM current controller design method are implemented.

[0016] The use of the embodiments of the present invention can include the following beneficial effects: In order to solve the design problem of the current controller of STATCOM, the embodiments of the present invention propose a design method for a STATCOM digital controller that avoids continuous frequency domain design and is directly designed and implemented in the discrete frequency domain. This method can directly obtain the parameters of the digital controller based on system parameters and design requirements, is easy to implement, and can obtain better current control performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate one or more embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 is a flow chart of a discrete domain STATCOM current controller design method according to an embodiment of the present invention;

[0019] Figure 2 1 is a STATCOM control structure diagram of state decoupling and voltage feedforward according to an embodiment of the present invention;

[0020] Figure 3 is a block diagram of active and reactive current equivalent control according to an embodiment of the present invention;

[0021] Figure 4 is a current digital control block diagram of an embodiment of the present invention;

[0022] Figure 5 It is a schematic diagram of a discrete domain STATCOM current controller design system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solutions in one or more embodiments of this specification, the following will be combined with the drawings in one or more embodiments of this specification to clearly and completely describe the technical solutions in one or more embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on one or more embodiments of this specification, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this document.

[0024] Method Embodiment

[0025] According to an embodiment of the present invention, a discrete domain STATCOM current controller design method is provided. Figure 1: is a flow chart of a discrete domain STATCOM current controller design method according to an embodiment of the present invention. Figure 1 As shown, the discrete domain STATCOM current controller design method according to an embodiment of the present invention specifically includes:

[0026] Step S101, establishing a discrete domain model of the controlled object based on design factors, specifically includes:

[0027] Considering the sampling, one-beat control lag and zero-order hold of digital control, the discrete domain transfer function of the controlled object is established as shown in Formula 1;

[0028]

[0029] Wherein, G(z) represents the controlled object model in the discrete domain, z represents a discrete frequency domain complex variable, Z[.] represents Z-transformation of the continuous domain model, e represents a natural constant, s represents a continuous frequency domain complex variable, T represents the sampling time, L represents the filter inductance of STATCOM, and r represents the equivalent resistance of the filter inductance;

[0030] The controlled object includes a one-beat lag link, a sample-and-hold device and a first-order controlled object;

[0031] Step S102, considering the zero-static-error control performance of the current closed-loop system, constructing a closed-loop transfer function for minimum-beat control of the current closed-loop system, specifically including:

[0032] The mathematical relationship between the transfer function of the STATCOM current controller, the transfer function of the current closed-loop system and the transfer function of the controlled object is established as shown in Formula 2;

[0033]

[0034] Where D(z) represents the transfer function of the current controller, G(z) represents the transfer function of the controlled object, and Φ(z) represents the transfer function of the current closed-loop system;

[0035] Considering the zero-static-error control performance of the current closed-loop system, the transfer function and error transfer function of the current closed-loop system are obtained as shown in Formula 3. The mathematical relationship between the transfer function and the error transfer function of the current closed-loop system is shown in Formula 4. Combining Formula 3 and Formula 4, the closed-loop transfer function of the minimum-beat control of the current closed-loop system is obtained as shown in Formula 5.

[0036]

[0037] Φ e (z) = 1 - Φ(z) Formula 4;

[0038] Φ(z)=z -2 Formula 5;

[0039] Among them, Φ e (z) represents the error transfer function of the current closed-loop system, f 11 、f 21 They represent monomials about z respectively;

[0040] Step S103, obtaining the transfer function of the STATCOM current controller in the discrete domain according to the discrete domain model of the controlled object and the closed-loop transfer function, converting it into a differential recursive equation, and implementing it in a digital processor by programming, specifically includes:

[0041] According to the discrete domain model of the controlled object and the closed-loop transfer function and based on Formula 2, a transfer function of the STATCOM current controller in the discrete domain as shown in Formula 6 is obtained, and according to the transfer function of the current controller in the discrete domain and the input and output of the current controller, a mathematical relationship as shown in Formula 7 is obtained, which is converted into a differential recursive equation as shown in Formula 8 through Z inverse transformation, and implemented in a digital processor through programming;

[0042]

[0043] u(n)=u(n-2)+k·e(n)-k·b·e(n-1) Formula 8;

[0044] in, E(z) represents the current error signal in the control system, U(z) represents the control signal, u(n) is the current control output, u(n-2) is the control output two beats ago, e(n) is the current current error signal, e(n-1) is the current error signal of the previous beat, and n represents a discrete time variable.

[0045] The above technical solution of the embodiment of the present invention is described in detail below in combination with the specific situation of the discrete domain STATCOM current controller design method of the embodiment of the present invention.

[0046] The embodiment of the present invention proposes a design processing method in discrete frequency domain for a STATCOM current controller. The control structure of a STATCOM system is as follows: Figure 2 As shown, the dashed box on the left is the controller part, and the solid box on the right is the STATCOM model under the synchronous rotating coordinate (dq coordinate). dref and I qref is the current reference for the d-axis and q-axis, I ca ,I cb and I cc It is the three-phase compensation current output by STATCOM. After three-phase to two-phase rotation transformation, the corresponding dq coordinate compensation current I is obtained. cd and Icq , through the action of current regulator, state decoupling and voltage feedforward, the control quantity of dq axis is generated, and then through inverse transformation to control the operation of the main circuit of STATCOM.

[0047] exist Figure 2 In the control structure, the modulation and coordinate transformation process is regarded as a unit ratio link, and the control structure can be simplified to an equivalent control block diagram of the active and reactive current control loops, such as Figure 3 As shown, G id (s) and G iq (s) is a controller for active and reactive current loops. Conventional designs are performed in the continuous frequency domain. The embodiment of the present invention proposes a method for completing the design in the discrete frequency domain, which can obtain control performance superior to conventional methods and is easy to implement. The control structure of active current and reactive current is the same, and the design of the controller is also the same.

[0048] Considering the sampling, one-beat control lag and zero-order hold in the digital implementation process, the block diagram of active and reactive current digital control can be used. Figure 4 Description, G id (s) and G iq The (s) continuous domain controller is also transformed into a discrete z-domain controller D(z). The s in the controller represents a continuous frequency domain complex variable, and the z represents a discrete frequency domain complex variable.

[0049] In the discrete frequency domain, Figure 4 The controlled objects in the include: the one-beat delay link z -1 , sample-and-hold ZOH and first-order controlled object The discrete domain model can be expressed as follows (to avoid cumbersomeness, the transfer functions appearing below refer to the discrete domain transfer functions unless otherwise specified):

[0050]

[0051] Where G(z) represents the controlled object model in the discrete domain, Z[.] represents the Z-transformation of the continuous domain model, e represents the natural constant, T represents the sampling time, L represents the filter inductance of STATCOM, and r represents the equivalent resistance of the filter inductance.

[0052] The current closed-loop transfer function Φ(z) is:

[0053]

[0054] Where D(z) represents the transfer function of the controller.

[0055] According to the principle of automatic control, the lag link contained in the controlled object cannot be offset and must exist in the designed closed-loop transfer function, so the transfer function of the current closed-loop system has the following form:

[0056] Φ(z)=z -1 F1(z) (3);

[0057] Among them, F1(z) is the unknown polynomial with respect to z.

[0058] According to formula (2), the expression of the controller can be written as:

[0059]

[0060] That is, the transfer function of the controller can be expressed by the current closed-loop transfer function and the transfer function of the controlled object.

[0061] The error transfer function of the system Φ e (z) is:

[0062]

[0063] Where R(z) is the z-domain expression of the input signal, and Y(z) is the output signal expression.

[0064] The error E(z) is:

[0065] E(z)=R(z)Φ e (z) (6);

[0066] Assuming the input is a step signal, its transfer function is:

[0067]

[0068] According to the final value theorem of Z transform, the steady-state error of the system is:

[0069]

[0070] According to formula (8), in order to achieve zero-error tracking, e(∞) tends to zero, Φ e (z) must have the following form:

[0071] Φ e (z) = (1-z -1 )F2(z) (9);

[0072] Among them, F2(z) is also an undetermined polynomial about z. Combined with equation (3), in order to make the system have a faster response performance, the system transfer function Φ(z) should have a finite word length response characteristic, that is, the characteristic of the FIR filter; in order to make the system obtain zero static error characteristics, the system closed-loop error transfer function Φ e (z) has the mode of formula (9). By setting the fastest response time, Φ(z) and Φ e (z) have the same order, and the corresponding transfer function of the current controller of STATCOM can be obtained by applying the method of undetermined coefficients. This discrete frequency domain transfer function is then converted into a discrete time domain expression, that is, a differential recursive formula, and implemented in a digital signal processor.

[0073] Specifically, Figure 4 The current control closed-loop transfer function and error transfer function are in the form of:

[0074]

[0075] In the formula, m and n are the orders of the unknown polynomials F1(z) and F2(z). For the rapidity of control, let: m = 1, n = 1, thus:

[0076]

[0077] The relationship between the closed-loop transfer function and the closed-loop error transfer function is:

[0078] Φ e (z) = 1 - Φ(z) (12);

[0079] According to formula (11) and formula (12), we can get: 11 =f 21 =1, the closed-loop transfer function of the current loop minimum beat control is:

[0080] Φ(z)=z -2 (13);

[0081] That is, the current closed loop has a two-beat lag and zero-static-error control performance.

[0082] According to formula (4), the expression of the current controller is:

[0083]

[0084] in, These two coefficients are related to the filter inductance and inductor equivalent resistance of STATCOM, as well as the sampling time. k and b are related to circuit parameters and sampling time.

[0085] The input of the current controller is the current error signal, and the output is the control signal, namely:

[0086]

[0087] After the inverse z-transform, the time domain difference recursive equation of the controller can be obtained:

[0088] u(n)=u(n-2)+k·e(n)-k·b·e(n-1) (16);

[0089] Among them, u(n) is the current control output, u(n-2) is the control output two beats ago, e(n) is the current error signal, e(n-1) is the current error signal of the previous beat, and n represents a discrete time variable.

[0090] The entire design process is to substitute the filter inductance and inductor equivalent resistance of STATCOM and the sampling time into formula (14) to obtain the discrete domain expression of the digital controller, and then obtain the differential recursive formula of the digital controller through inverse z-transformation. The entire design process is very concise and clear.

[0091] System Example

[0092] According to an embodiment of the present invention, a discrete domain STATCOM current controller design system is provided. Figure 5 Schematic diagram of a discrete domain STATCOM current controller design system according to an embodiment of the present invention. Figure 5 As shown, the discrete domain STATCOM current controller design system according to an embodiment of the present invention specifically includes:

[0093] The first design module 50 is used to establish a discrete domain model of the controlled object based on design factors, specifically for:

[0094] Considering the sampling, one-beat control lag and zero-order hold of digital control, the discrete domain transfer function of the controlled object is established as shown in Formula 1;

[0095]

[0096] Wherein, G(z) represents the controlled object model in the discrete domain, z represents a discrete frequency domain complex variable, Z[.] represents Z-transformation of the continuous domain model, e represents a natural constant, s represents a continuous frequency domain complex variable, T represents the sampling time, L represents the filter inductance of STATCOM, and r represents the equivalent resistance of the filter inductance;

[0097] The controlled object includes a one-beat lag link, a sample-and-hold device and a first-order controlled object;

[0098] The second design module 52 is used to consider the zero-static-error control performance of the current closed-loop system and construct a closed-loop transfer function of the minimum-beat control of the current closed-loop system, specifically for:

[0099] The mathematical relationship between the transfer function of the STATCOM current controller, the transfer function of the current closed-loop system and the transfer function of the controlled object is established as shown in Formula 2;

[0100]

[0101] Where D(z) represents the transfer function of the current controller, G(z) represents the transfer function of the controlled object, and Φ(z) represents the transfer function of the current closed-loop system;

[0102] Considering the zero-static-error control performance of the current closed-loop system, the transfer function and error transfer function of the current closed-loop system are obtained as shown in Formula 3. The mathematical relationship between the transfer function and the error transfer function of the current closed-loop system is shown in Formula 4. Combining Formula 3 and Formula 4, the closed-loop transfer function of the minimum-beat control of the current closed-loop system is obtained as shown in Formula 5.

[0103]

[0104] Φ e (z) = 1 - Φ(z) Formula 4;

[0105] Φ(z)=z -2 Formula 5;

[0106] Among them, Φ e (z) represents the error transfer function of the current closed-loop system, f 11 、f 21 They represent monomials about z respectively;

[0107] The third design module 54 is used to obtain the transfer function of the STATCOM current controller in the discrete domain according to the discrete domain model of the controlled object and the closed-loop transfer function, convert it into a differential recursive equation, and implement it in a digital processor through programming, specifically for:

[0108] According to the discrete domain model of the controlled object and the closed-loop transfer function and based on Formula 2, a transfer function of the STATCOM current controller in the discrete domain as shown in Formula 6 is obtained, and according to the transfer function of the current controller in the discrete domain and the input and output of the current controller, a mathematical relationship as shown in Formula 7 is obtained, which is converted into a differential recursive equation as shown in Formula 8 through Z inverse transformation, and implemented in a digital processor through programming;

[0109]

[0110]

[0111] u(n)=u(n-2)+k·e(n)-k·b·e(n-1) Formula 8;

[0112] in, E(z) represents the current error signal in the control system, U(z) represents the control signal, u(n) is the current control output, u(n-2) is the control output two beats ago, e(n) is the current current error signal, e(n-1) is the current error signal of the previous beat, and n represents a discrete time variable.

[0113] The embodiment of the present invention is a system embodiment corresponding to the above-mentioned method embodiment. The specific operations of each module can be understood by referring to the description of the method embodiment, which will not be repeated here.

[0114] In summary, compared with the conventional continuous frequency domain STATCOM current controller prior art, the embodiments of the present invention have the following advantages:

[0115] (1) The design of the current controller of STATCOM is completed in the discrete frequency domain. The design process is simple. According to the input system parameters required by formula (10), the discrete domain transfer function of the controller can be obtained. Then, the discrete frequency domain is converted to the discrete time domain to obtain the differential recursive formula, which avoids the conversion process from the continuous frequency domain to the discrete domain in the traditional processing method. There is no distortion problem of control information, and it is easy to program and implement in the digital signal processor;

[0116] (2) The design of the STATCOM current controller can be completed fully digitally, which reduces the requirements for theoretical knowledge and engineering experience of designers. The entire design process can be easily programmed to avoid the influence of human factors;

[0117] (3) The current controller control method of the STATCOM can achieve better control performance, which can not only realize the tracking of fast current instructions without static error, but also make corresponding optimization processing according to the requirements of rapidity and stability.

[0118] Device Example 1

[0119] An embodiment of the present invention provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program implements the steps described in the method embodiment when executed by the processor.

[0120] Device Example 2

[0121] An embodiment of the present invention provides a computer-readable storage medium, on which a program for implementing information transmission is stored. When the program is executed by a processor, the steps described in the method embodiment are implemented.

[0122] The computer-readable storage medium in this embodiment includes, but is not limited to, ROM, RAM, magnetic disk or optical disk, etc.

[0123] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A discrete domain STATCOM current controller design method, characterized in that include: Establish a discrete domain model of the controlled object based on design factors; Considering the zero-static-error control performance of the current closed-loop system, a closed-loop transfer function for minimum-beat control of the current closed-loop system is constructed; The transfer function of the STATCOM current controller in the discrete domain is obtained according to the discrete domain model of the controlled object and the closed-loop transfer function, which is converted into a differential recursive equation and implemented in a digital processor through programming.

2. The method according to claim 1, characterized in that Establishing the discrete domain model of the controlled object based on design factors specifically includes: Considering the sampling, one-beat control lag and zero-order hold of digital control, the discrete domain transfer function of the controlled object is established as shown in Formula 1; Wherein, G(z) represents the controlled object model in the discrete domain, z represents a discrete frequency domain complex variable, Z[.] represents Z-transformation of the continuous domain model, e represents a natural constant, s represents a continuous frequency domain complex variable, T represents the sampling time, L represents the filter inductance of STATCOM, and r represents the equivalent resistance of the filter inductance; The controlled object includes a one-beat-delay link, a sample-and-hold device and a first-order controlled object.

3. The method according to claim 1, characterized in that Considering the zero-static-error control performance of the current closed-loop system, the closed-loop transfer function for minimum-beat control of the current closed-loop system is constructed, which specifically includes: The mathematical relationship between the transfer function of the STATCOM current controller, the transfer function of the current closed-loop system and the transfer function of the controlled object is established as shown in Formula 2; Where D(z) represents the transfer function of the current controller, G(z) represents the transfer function of the controlled object, and Φ(z) represents the transfer function of the current closed-loop system; Considering the zero-static-error control performance of the current closed-loop system, the transfer function and error transfer function of the current closed-loop system are obtained as shown in Formula 3. The mathematical relationship between the transfer function and the error transfer function of the current closed-loop system is shown in Formula 4. Combining Formula 3 and Formula 4, the closed-loop transfer function of the minimum-beat control of the current closed-loop system is obtained as shown in Formula 5. Φ e Ψ(z) = 1 - Φ(z), Equation 4; Φ(z) = z -2 Equation 5; Among them, Φ e (z) represents the error transfer function of the current closed-loop system, f 11 、f 21 denote monomials about z respectively.

4. The method according to claim 3, characterized in that The transfer function of the STATCOM current controller in the discrete domain is obtained according to the discrete domain model of the controlled object and the closed-loop transfer function, converted into a differential recursive equation, and implemented in a digital processor by programming, specifically including: According to the discrete domain model of the controlled object and the closed-loop transfer function and based on Formula 2, a transfer function of the STATCOM current controller in the discrete domain as shown in Formula 6 is obtained, and according to the transfer function of the current controller in the discrete domain and the input and output of the current controller, a mathematical relationship as shown in Formula 7 is obtained, which is converted into a differential recursive equation as shown in Formula 8 through Z inverse transformation, and implemented in a digital processor through programming; u(n)=u(n-2)+k·e(n)-k·b·e(n-1) Formula 8; in, E(z) represents the current error signal in the control system, U(z) represents the control signal, u(n) is the current control output, u(n-2) is the control output two beats ago, e(n) is the current current error signal, e(n-1) is the current error signal of the previous beat, and n represents a discrete time variable.

5. A discrete domain STATCOM current controller design system, characterized in that include: A first design module is used to establish a discrete domain model of the controlled object based on design factors; The second design module is used to consider the zero-static-error control performance of the current closed-loop system and construct a closed-loop transfer function of the minimum-beat control of the current closed-loop system; The third design module is used to obtain the transfer function of the STATCOM current controller in the discrete domain according to the discrete domain model of the controlled object and the closed-loop transfer function, convert it into a differential recursive equation, and implement it in a digital processor through programming.

6. The system according to claim 5, characterized in that The first design module is specifically used for: Considering the sampling, one-beat control lag and zero-order hold of digital control, the discrete domain transfer function of the controlled object is established as shown in Formula 1; Wherein, G(z) represents the controlled object model in the discrete domain, z represents a discrete frequency domain complex variable, Z[.] represents Z-transformation of the continuous domain model, e represents a natural constant, s represents a continuous frequency domain complex variable, T represents the sampling time, L represents the filter inductance of STATCOM, and r represents the equivalent resistance of the filter inductance; The controlled object includes a one-beat-delay link, a sample-and-hold device and a first-order controlled object.

7. The system according to claim 5, characterized in that The second design module is specifically used for: The mathematical relationship between the transfer function of the STATCOM current controller, the transfer function of the current closed-loop system and the transfer function of the controlled object is established as shown in Formula 2; Where D(z) represents the transfer function of the current controller, G(z) represents the transfer function of the controlled object, and Φ(z) represents the transfer function of the current closed-loop system; Considering the zero-static-error control performance of the current closed-loop system, the transfer function and error transfer function of the current closed-loop system are obtained as shown in Formula 3. The mathematical relationship between the transfer function and the error transfer function of the current closed-loop system is shown in Formula 4. Combining Formula 3 and Formula 4, the closed-loop transfer function of the minimum-beat control of the current closed-loop system is obtained as shown in Formula 5. Φ e Φ(z) = 1 - Φ(z), Equation 4; Φ(z) = z -2 Equation 5; Among them, Φ e (z) represents the error transfer function of the current closed-loop system, f 11 、f 21 denote monomials about z respectively.

8. The system according to claim 7, characterized in that The third design module is specifically used for: According to the discrete domain model of the controlled object and the closed-loop transfer function and based on Formula 2, a transfer function of the STATCOM current controller in the discrete domain as shown in Formula 6 is obtained, and according to the transfer function of the current controller in the discrete domain and the input and output of the current controller, a mathematical relationship as shown in Formula 7 is obtained, which is converted into a differential recursive equation as shown in Formula 8 through Z inverse transformation, and implemented in a digital processor through programming; u(n)=u(n-2)+k·e(n)-k·b·e(n-1) Formula 8; in, E(z) represents the current error signal in the control system, U(z) represents the control signal, u(n) is the current control output, u(n-2) is the control output two beats ago, e(n) is the current current error signal, e(n-1) is the current error signal of the previous beat, and n represents a discrete time variable.

9. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, the steps of the discrete domain STATCOM current controller design method as described in any one of claims 1 to 4 are implemented.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores an implementation program for information transmission, and when the program is executed by a processor, the steps of the discrete domain STATCOM current controller design method according to any one of claims 1 to 4 are implemented.

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