Controlling method of adjustable impedance series hybrid cascaded static synchronous compensator

Abstract

The application discloses a series-parallel hybrid cascaded static synchronous compensator with adjustable impedance and a control method thereof, and the method is as follows: obtaining grid-connected point voltage and load current information and performing positive and negative sequence component analysis on the information; calculating compensation line current components with the same size and opposite phase of positive and negative sequence components of the load current to realize compensation of reactive power and negative sequence current of the grid-connected point load; calculating zero sequence injection current for in-phase active power balance and obtaining reference operating currents of cascaded branches; calculating output reactive power of each phase based on cascaded branch voltages of each phase and the reference operating currents; calculating corresponding trigger angles of thyristors of each phase under the condition that the adjustable impedance bears all phase voltages and generates all reactive power, generating pulse control signals to realize control on the adjustable impedance; and each phase cascaded converter adopts quasi-proportional resonance control to track the reference operating current and generate corresponding PWM signals to control each phase cascaded converter.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and specifically to a control method for an adjustable impedance series hybrid cascaded static synchronous compensator. Background Technology

[0002] With the continuous expansion of the scale of medium and high voltage power grids and the increasing complexity of load types, problems such as three-phase imbalance, harmonic pollution, and reactive power fluctuations in the power grid are becoming increasingly prominent, seriously restricting the operating efficiency and power quality of the power grid.

[0003] To match the voltage levels of medium and high voltage power grids and address power quality issues in the grid, cascaded static synchronizing compensators (SSCs) have been proposed as a modular solution. Based on the different connection methods of the cascaded full-bridge branches, they can be further divided into star-connected and delta-connected cascaded SSCs. While star-connected cascaded SSCs have lower voltage withstand requirements for switching devices, they exhibit compensation singularities when outputting equal-amplitude positive-sequence and negative-sequence currents. This necessitates the injection of infinite zero-sequence current to balance the active power between cascaded branches, which can lead to system malfunctions and overvoltage issues in the switching devices, severely impacting the safe and stable operation of the system. Delta-connected cascaded SSCs, on the other hand, impose higher voltage withstand requirements on the switching devices and do not exhibit compensation singularities under any current output condition, making them more suitable for power quality compensation applications. Although research on cascaded SSCs is relatively complete, their high-capacity power electronic converters result in high costs and complex control, limiting their engineering application prospects in medium and high voltage power grids.

[0004] Therefore, developing a cascaded static synchronous compensator that can maintain the system's performance advantages while reducing compensator capacity and equipment investment costs is of great significance for promoting its large-scale application in medium and high voltage power grids and supporting the safe and efficient operation of the power grid. Summary of the Invention

[0005] In view of this, the present invention provides a control method for an adjustable impedance series hybrid cascaded static synchronous compensator, which at least solves the problems of high investment cost and limited application prospects of cascaded static synchronous compensators in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An adjustable impedance series hybrid cascaded static synchronous compensator includes: a three-phase delta-connected cascaded branch, wherein each cascaded branch includes an adjustable impedance and a cascaded converter, and the adjustable impedance and the cascaded converter on each cascaded branch are connected in series.

[0008] Each adjustable impedance includes a thyristor-controlled reactor, a fixed capacitor, and a filter inductor; the thyristor-controlled reactor is connected in parallel with the fixed capacitor and then in series with the filter inductor;

[0009] Each cascaded converter consists of n full-bridge modules; the full-bridge modules are connected in series.

[0010] A control method for an adjustable impedance series hybrid cascaded static synchronous compensator includes the following steps:

[0011] S1. Obtain grid connection point voltage and load current information and perform positive and negative sequence component analysis on them;

[0012] S2. Calculate the compensation line current component that is the same in magnitude but opposite in phase as the positive and negative sequence components of the load current, so as to compensate for the reactive power and negative sequence current of the load at the grid connection point.

[0013] S3. Calculate the zero-sequence injection current for active power balance within a phase and obtain the reference operating current for each level of branch circuit;

[0014] S4. Calculate the output reactive power of each phase based on the voltage of each cascaded branch and the reference operating current. Under the condition that the adjustable impedance can withstand all phase voltages and generate all reactive power, calculate the corresponding firing angle of each phase thyristor and generate a pulse control signal to realize the control of the adjustable impedance.

[0015] S5. Each phase cascaded converter uses quasi-proportional resonant control to track the reference operating current and generate corresponding PWM signals to control each phase cascaded converter.

[0016] Preferably, the specific content of S1 includes:

[0017] Collect the three-phase voltage at the grid connection point With load current ,in =a, b, or c indicates the phase sequence;

[0018] Obtained via phase-locked loop (PLL) phase ;

[0019] Extract the components of the three-phase voltage and load current of the power grid in the positive and negative sequence rotating coordinate system respectively.

[0020] Preferably, the specific content of S2 includes:

[0021] The positive sequence reactive components of the load current are respectively Negative-order active components and negative-order reactive components Taking the negative, we obtain the positive sequence reactive power compensation line current in sequence. Negative sequence active power compensation line current and negative sequence reactive power compensation line current Positive sequence active power compensation line current for:

[0022] Formula 1;

[0023] In the formula, , , and The components are, in order, the positive-sequence reactive component, the negative-sequence active component, the negative-sequence reactive component, and the positive-sequence active component of the three-phase voltage.

[0024] Preferably, the specific content of S3 includes:

[0025] Calculate the active and reactive components of the zero-sequence injected current in the dq coordinate system based on the current components of each compensation line:

[0026] Formula 2;

[0027] in:

[0028] ;

[0029] In the formula, and These are the active and reactive components of the zero-sequence injected current, respectively.

[0030] Transform the active and reactive components of the compensation line current and the zero-sequence injection current in the dq coordinate system to the abc coordinate system:

[0031] Formula 3;

[0032] Formula 4;

[0033] Formula 5;

[0034] In the formula, , and The compensation line currents on phase lines a, b, and c are, in order. The zero-sequence injection current is in the abc coordinate system. express The phase;

[0035] Based on the relationship between the line current, phase current, and zero-sequence injection current of the delta-connected cascaded converter, the reference operating currents of the cascaded branches of phases ab, bc, and ca are obtained. , as well as :

[0036] Formula 6.

[0037] Preferably, the specific content of S4 includes:

[0038] Constructed based on a generalized second-order integrator Cascaded branch voltage and reference operating current orthogonal components and ,in, =ab, bc, and ca represent the phase sequence of the cascaded branches. According to the instantaneous reactive power theory, the reactive power of the branches is:

[0039] Formula 7;

[0040] The adjustable impedance is then:

[0041] Formula 8;

[0042] In the formula, express Cascaded branch voltage Amplitude;

[0043] The adjustable impedance is obtained from the impedance-firing angle table. Corresponding trigger angle Simultaneously, detection is performed via a phase-locked loop. Cascaded branch voltage phase ;

[0044] Based on the trigger angle With phase The magnitude of the difference needs to be determined by triggering the thyristor, thereby generating a trigger pulse to achieve the alternating conduction control of the corresponding thyristor.

[0045] Preferably, the specific content of S5 includes:

[0046] Will Voltage of all full-bridge modules on the cascaded branch The sum of the given reference DC voltage The difference is calculated, and then fed into a PI controller and finally compared with the sinusoidal voltage signal of the cascaded branch. Multiply to obtain the DC voltage control reference operating current ;

[0047] Reference operating current and DC voltage control reference operating current The sum of and alternating current The difference is then used to obtain the reference modulation voltage via the QPR controller. ;

[0048] Average DC voltage of cascaded branches DC side voltage of each full-bridge module The amplitude of the modulation voltage adjustment component of each full-bridge module is obtained by subtraction and then proportionalization. , =1,2,3……n;

[0049] Further with and Multiplying the products by their signs yields the voltage balance component of the full-bridge module. ;

[0050] The modulation voltage of each full-bridge module in the cascaded branch is determined by... Plus and get;

[0051] Finally, the control pulse signals of each full-bridge module are obtained through the phase-shifted pulse width modulation strategy PS-PWM to realize the control of the cascaded converter.

[0052] Preferably, the DC voltage controls the reference operating current. Specifically:

[0053] Formula 9;

[0054] In the formula, and These represent the proportional and integral parameters of the PI controller, respectively.

[0055] The QPR controller transfer function is:

[0056] Formula 10;

[0057] In the formula, and These represent the proportional gain and the resonance control coefficient, respectively. and These represent the cutoff frequency and resonant frequency of the QPR, respectively.

[0058] Formula 11;

[0059] In the formula, This indicates a proportional parameter.

[0060] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a control method for an adjustable impedance series hybrid cascaded static synchronous compensator, which has the following beneficial effects:

[0061] Compared with existing technologies, the adjustable impedance series hybrid cascaded static synchronous compensator provided by this invention replaces the fixed inductor on the AC side of the traditional cascaded static synchronous compensator with an adjustable impedance based on a thyristor-controlled reactor. By adjusting the thyristor firing angle, the impedance can be adjusted under dynamic load compensation requirements, thereby generating a larger voltage drop across the adjustable impedance to reduce the voltage amplitude on the cascaded converter side. Due to the reduction in the AC side voltage amplitude of the cascaded converter, the operating DC voltage of the DC side capacitor of the cascaded full-bridge module can also be reduced accordingly, thereby reducing the voltage withstand capability and quantity requirements of the full-bridge module. Attached Figure Description

[0062] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0063] Figure 1 A schematic diagram of the topology of the adjustable impedance series hybrid cascaded static synchronous compensator provided by the present invention.

[0064] Figure 2 This is an equivalent working principle diagram of a single-phase cascaded branch provided in an embodiment of the present invention;

[0065] Figure 3 Adjustable impedance and firing angle provided in embodiments of the present invention Relationship diagram;

[0066] Figure 4 The adjustable impedance control principle diagram provided by the present invention;

[0067] Figure 5 The control principle diagram of the inverter provided by this invention. Detailed Implementation

[0068] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0069] This invention provides an adjustable impedance series hybrid cascaded static synchronous compensator, such as... Figure 1 As shown, it includes: a three-phase delta-connected cascaded branch, wherein each cascaded branch includes an adjustable impedance and a cascaded converter, and the adjustable impedance and the cascaded converter on each cascaded branch are connected in series.

[0070] Each adjustable impedance includes a thyristor-controlled reactor, a fixed capacitor, and a filter inductor; the thyristor-controlled reactor is connected in parallel with the fixed capacitor and then in series with the filter inductor; the thyristor-controlled reactor includes an anti-parallel thyristor. and , , indicating the phase number of the cascaded branch;

[0071] Each cascaded converter consists of n full-bridge modules; the full-bridge modules are connected in series.

[0072] It should be noted that:

[0073] Figure 2 This is the equivalent working principle diagram of a single-phase cascaded branch. , and They represent Cascaded branch voltage Adjustable impedance voltage and AC side voltage of cascaded converter In vector form. Satisfying the relation:

[0074] (a)

[0075] In the formula, express Adjustable impedance of cascaded branches; express Cascaded branch current The vector form; This indicates the thyristor firing angle. Thyristor-controlled reactor and fixed capacitor After being connected in parallel, it is then connected to the filter inductor. When connected in series, its impedance can be calculated as follows:

[0076] (b)

[0077] In the formula, and express and impedance; Indicates the impedance of the gate control reactor; It represents the angular frequency of the voltage at the grid connection point. Depend on Control, which can be calculated as:

[0078] (c)

[0079] Therefore, the adjustable impedance can ultimately be expressed as:

[0080] (d)

[0081] Figure 3 The adjustable impedance as a function of firing angle is given. The trend of change.

[0082] because From equation (a), we can see that in At a certain time, by adjusting the trigger angle Can make This can reduce Size, will It remains at a low level.

[0083] A control method for an adjustable impedance series hybrid cascaded static synchronous compensator includes the following steps:

[0084] S1. Obtain grid connection point voltage and load current information and perform positive and negative sequence component analysis on them;

[0085] S2. Calculate the compensation line current component that is the same in magnitude but opposite in phase as the positive and negative sequence components of the load current, so as to compensate for the reactive power and negative sequence current of the load at the grid connection point.

[0086] S3. Calculate the zero-sequence injection current for active power balance within a phase and obtain the reference operating current for each level of branch circuit;

[0087] S4. Calculate the output reactive power of each phase based on the voltage of each cascaded branch and the reference operating current. Under the condition that the adjustable impedance can withstand all phase voltages and generate all reactive power, calculate the corresponding firing angle of each phase thyristor and generate a pulse control signal to realize the control of the adjustable impedance.

[0088] S5. Each phase cascaded converter uses quasi-proportional resonant control to track the reference operating current and generate corresponding PWM signals to control each phase cascaded converter.

[0089] To further implement the above technical solution, the specific content of S1 includes:

[0090] Collect the three-phase voltage at the grid connection point With load current ,in =a, b, or c indicates the phase sequence;

[0091] Obtained via PLL phase ;

[0092] Extract the components of the three-phase voltage and load current of the power grid in the positive and negative sequence rotating coordinate system respectively.

[0093] To further implement the above technical solution, the specific content of S2 includes:

[0094] To compensate for the reactive power and negative sequence current of the load at the grid connection point, the static synchronous compensator needs to output a compensation component that is the same magnitude but opposite in phase as the corresponding load component. Therefore, the positive sequence reactive component of the load current is separately... Negative-order active components and negative-order reactive components Taking the negative, we obtain the positive sequence reactive power compensation line current in sequence. Negative sequence active power compensation line current and negative sequence reactive power compensation line current Simultaneously, in order to compensate for the offset of the system's active power output under unbalanced grid voltage, the system needs to output a positive-sequence active power compensation current component. If the total active power output of the static synchronous compensator is made zero, then the positive sequence active power compensation line current will be zero. for:

[0095] Formula 1;

[0096] In the formula, , , and The components are, in order, the positive-sequence reactive component, the negative-sequence active component, the negative-sequence reactive component, and the positive-sequence active component of the three-phase voltage.

[0097] To further implement the above technical solution, the specific content of S3 includes:

[0098] Due to the influence of unbalanced voltage and negative-sequence compensation current output, unbalanced active power is generated in the three-phase static synchronous coordinate system, affecting the DC voltage balance between the three-phase cascaded converters and the safe and stable operation of the system. Therefore, to balance the active power between the three-phase cascaded converters, the active and reactive components of the zero-sequence injected current in the dq coordinate system are calculated based on the current components of each compensation line:

[0099] Formula 2;

[0100] in:

[0101] ;

[0102] In the formula, and These are the active and reactive components of the zero-sequence injected current, respectively.

[0103] Transform the active and reactive components of the compensation line current and the zero-sequence injection current in the dq coordinate system to the abc coordinate system:

[0104] Formula 3;

[0105] Formula 4;

[0106] Formula 5;

[0107] In the formula, , and The compensation line currents on phase lines a, b, and c are, in order. The zero-sequence injection current is in the abc coordinate system. express The phase;

[0108] Based on the relationship between the line current, phase current, and zero-sequence injection current of the delta-connected cascaded converter, the reference operating currents of the cascaded branches of phases ab, bc, and ca are obtained. , as well as :

[0109] Formula 6.

[0110] To further implement the above technical solution, the specific content of S4 includes:

[0111] Adjustable impedance control structure such as Figure 4 The adjustable impedance branch is designed to handle all voltage drops and output all reactive power from that branch. The cascaded converter section is only responsible for improving system response speed and suppressing branch harmonic currents. To calculate the branch reactive power, a generalized second-order integrator is constructed. Cascaded branch voltage and reference operating current orthogonal components and ,in, =ab, bc, and ca represent the phase sequence of the cascaded branches. According to the instantaneous reactive power theory, the reactive power of the branches is:

[0112] Formula 7;

[0113] The adjustable impedance is then:

[0114] Formula 8;

[0115] In the formula, express Cascaded branch voltage Amplitude;

[0116] Since equation (d) is highly nonlinear and very difficult to solve in real time, a series of firing angles corresponding to reactive power can be obtained in advance using numerical methods. The magnitude is determined, and the reactive power-firing angle correspondence is obtained using interpolation. From this, a lookup table method can be used to generate trigger pulses in real time to achieve alternating conduction control of the thyristors. Specifically:

[0117] The adjustable impedance is obtained from the impedance-firing angle table. Corresponding trigger angle Simultaneously, detection is performed via a phase-locked loop. Cascaded branch voltage phase ;

[0118] According to the trigger angle With phase The magnitude determination between them requires triggering a thyristor, thereby generating a trigger pulse to achieve alternating conduction control of the corresponding thyristor. Specifically, when Greater than hour, Triggered, when Less than hour, trigger.

[0119] To further implement the above technical solution, the specific content of S5 includes:

[0120] Cascaded converter control structure such as Figure 5 The overall control structure adopts a dual closed-loop control structure consisting of a DC voltage outer loop and a current inner loop. The DC outer loop controls the DC voltage through... Voltage of all full-bridge modules on the cascaded branch The sum of the given reference DC voltage The difference is calculated, and then fed into a PI controller and finally compared with the sinusoidal voltage signal of the cascaded branch. Multiply to obtain the DC voltage control reference operating current ;

[0121] Reference operating current and DC voltage control reference operating current The sum of and alternating current The difference is then used to obtain the reference modulation voltage via the QPR controller. In order to achieve zero static error tracking of the sinusoidal signal, the current inner loop control loop adopts a quasi-proportional resonator (QPR).

[0122] To balance the voltage of the distributed capacitors in the branch, it is also necessary to adjust the modulation voltage of each cascaded full-bridge module. Average DC voltage of cascaded branches DC side voltage of each full-bridge module The amplitude of the modulation voltage adjustment component of each full-bridge module is obtained by subtraction and then proportionalization. , =1,2,3……n;

[0123] Further with and Multiplying the products by their signs yields the voltage balance component of the full-bridge module. ;

[0124] The modulation voltage of each full-bridge module in the cascaded branch is determined by... Plus and Received, among which As a feedforward voltage, it can improve the system's response speed.

[0125] Finally, the control pulse signals of each full-bridge module are obtained through the phase-shifted pulse width modulation strategy PS-PWM to realize the control of the cascaded converter.

[0126] To further implement the above technical solution, the DC voltage controls the reference operating current. Specifically:

[0127] Formula 9;

[0128] In the formula, and These represent the proportional and integral parameters of the PI controller, respectively.

[0129] The QPR controller transfer function is:

[0130] Formula 10;

[0131] In the formula, and These represent the proportional gain and the resonance control coefficient, respectively. and These represent the cutoff frequency and resonant frequency of the QPR, respectively.

[0132] Formula 11;

[0133] In the formula, This indicates a proportional parameter.

[0134] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A control method of a tunable impedance series hybrid cascaded static synchronous compensator, the tunable impedance series hybrid cascaded static synchronous compensator comprising: A three-phase delta-connected cascaded branch, wherein each cascaded branch includes an adjustable impedance and a cascaded converter, and the adjustable impedance and the cascaded converter on each cascaded branch are connected in series; each adjustable impedance includes a thyristor-controlled reactor, a fixed capacitor, and a filter inductor; wherein the thyristor-controlled reactor is connected in parallel with the fixed capacitor and then in series with the filter inductor; each cascaded converter includes n full-bridge modules; the full-bridge modules are connected in series; characterized by the following steps: S1. Obtain grid connection point voltage and load current information and perform positive and negative sequence component analysis on them; S2. Calculate the compensation line current component that is the same in magnitude but opposite in phase as the positive and negative sequence components of the load current, so as to compensate for the reactive power and negative sequence current of the load at the grid connection point. S3. Calculate the zero-sequence injection current for intra-phase active power balance and obtain the reference operating current for each stage of the cascaded branch: Calculate the active and reactive components of the zero-sequence injected current in the dq coordinate system based on the current components of each compensation line: Formula 1 ; in: ； wherein, and are the active and reactive components of the zero sequence injection current, respectively; and are the positive sequence reactive compensation line current and the positive sequence active compensation line current, respectively; and are the negative sequence active compensation line current and the negative sequence reactive compensation line current, respectively; , , and are the positive sequence reactive component, the negative sequence active component, the negative sequence reactive component and the positive sequence active component of the three-phase voltage, respectively. Transform the active and reactive components of the compensation line current and the zero-sequence injection current in the dq coordinate system to the abc coordinate system: Formula 2; Official 3; Official 4; wherein , and are the compensation line currents on phases a, b and c, respectively, is the zero sequence injection current in the abc coordinate system, denotes the phase of . Based on the relationship between the line current, phase current, and zero-sequence injection current of the delta-connected cascaded converter, the reference operating currents of the cascaded branches of phases ab, bc, and ca are obtained. , as well as : Official 5; S4. Calculate the output reactive power of each phase based on the voltage of each cascaded branch and the reference operating current. Under the condition that the adjustable impedance can withstand all phase voltages and generate all reactive power, calculate the corresponding firing angle of each phase thyristor and generate a pulse control signal to realize the control of the adjustable impedance. S5. Each phase cascaded converter uses quasi-proportional resonant control to track the reference operating current and generate corresponding PWM signals to control each phase cascaded converter.

2. The control method for the adjustable impedance series hybrid cascaded static synchronous compensator according to claim 1, characterized in that, The specific content of S1 includes: Collect the three-phase voltage at the grid connection point With load current ,in =a, b, or c indicates the phase sequence; Obtained via phase-locked loop (PLL) phase ; Extract the components of the three-phase voltage and load current of the power grid in the positive and negative sequence rotating coordinate system respectively.

3. The control method for the adjustable impedance series hybrid cascaded static synchronous compensator according to claim 1, characterized in that, The specific content of S2 includes: The positive sequence reactive components of the load current are respectively Negative-order active components and negative-order reactive components Taking the negative, we obtain the positive sequence reactive power compensation line current in sequence. Negative sequence active power compensation line current and negative sequence reactive power compensation line current Positive sequence active power compensation line current for: Official 6.

4. The control method for the adjustable impedance series hybrid cascaded static synchronous compensator according to claim 1, characterized in that, The specific content of S4 includes: Constructed based on a generalized second-order integrator Cascaded branch voltage and reference operating current orthogonal components and ,in, =ab, bc, and ca represent the phase sequence of the cascaded branches. According to the instantaneous reactive power theory, the reactive power of the branches is: Official 7; The adjustable impedance is then: Official 8; In the formula, express Cascaded branch voltage Amplitude; The adjustable impedance is obtained from the impedance-firing angle table. Corresponding trigger angle Simultaneously, detection is performed via a phase-locked loop. Cascaded branch voltage phase ; According to the trigger angle With phase The magnitude of the difference needs to be determined by triggering the thyristor, thereby generating a trigger pulse to achieve the alternating conduction control of the corresponding thyristor.

5. The control method for the adjustable impedance series hybrid cascaded static synchronous compensator according to claim 1, characterized in that, The specific content of S5 includes: Will Voltage of all full-bridge modules on the cascaded branch The sum of the given reference DC voltage The difference is calculated, and then fed into a PI controller and finally compared with the sinusoidal voltage signal of the cascaded branch. Multiply to obtain the DC voltage control reference operating current ; Reference operating current and DC voltage control reference operating current The sum of and alternating current The difference is then used to obtain the reference modulation voltage via the QPR controller. ; Average DC voltage of cascaded branches DC side voltage of each full-bridge module The amplitude of the modulation voltage adjustment component of each full-bridge module is obtained by subtraction and then proportionalization. , =1,2,3……n; Further with and Multiplying the negatives of the products yields the voltage balance component of the full-bridge module. ; The modulation voltage of each full-bridge module in the cascaded branch is determined by... Plus and Cascaded branch voltage get; Finally, the control pulse signals of each full-bridge module are obtained through the phase-shifted pulse width modulation strategy PS-PWM to realize the control of the cascaded converter.

6. The control method for the adjustable impedance series hybrid cascaded static synchronous compensator according to claim 5, characterized in that, DC voltage control reference operating current Specifically: Official 9; In the formula, and These represent the proportional and integral parameters of the PI controller, respectively. The QPR controller transfer function is: Official 10; In the formula, and These represent the proportional gain and the resonance control coefficient, respectively. and These represent the cutoff frequency and resonant frequency of the QPR, respectively. Official 11; In the formula, This indicates a proportional parameter.

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