Transformer integrated static synchronous compensator system suitable for mountain wind power plant and control method

Abstract

The invention discloses a transformer integrated static synchronous compensator system suitable for a mountain wind power plant. The transformer integrated static synchronous compensator system comprises a magnetic integrated filter transformer module, a filter module and a cascade static synchronous compensator module, the magnetic integrated filter transformer module is connected between a wind power plant grid-connected point and a wind generating set of the wind power plant; the magnetic integrated filter transformer module is also connected with the cascade static synchronous compensator module through the filter module; the magnetic integrated filter transformer module is used for voltage conversion; the filtering module is matched with the magnetic integrated filtering transformer module for harmonic filtering; and the cascade static synchronous compensator module is used for realizing reactive compensation and wide-frequency-domain harmonic suppression. The invention further discloses a control method of the transformer integrated static synchronous compensator system suitable for the mountain wind power plant. The reactive power and harmonic wave comprehensive compensation of the wind power grid-connected system is achieved, the compensation system is small in occupied area, the working voltage needed by an active device is low, reliability is high, and the compensation effect is good.

Description

Technical Field

[0001] The present invention belongs to the field of electrical automation, and in particular relates to a transformer-integrated static synchronous compensator system and a control method suitable for mountain wind farms. Background Art

[0002] With the development of economy and technology and the improvement of people's living standards, electricity has become an indispensable secondary energy source in people's production and life, bringing endless convenience to people's production and life. Therefore, ensuring a stable and reliable supply of electricity has become one of the most important tasks of the power system.

[0003] Currently, with environmental concerns becoming increasingly severe, an increasing number of wind power systems are being integrated into the power grid. Due to the unique characteristics of wind power generation, most wind farms are located in remote mountainous areas with relatively weak grid infrastructure. This makes grid voltage distortion at the wind farm's connection point extremely likely. Furthermore, some wind farms are located in areas with a large number of high-energy-consuming nonlinear loads, such as electrified traction loads and industrial smelting loads. These loads cause the system's connection point voltage to remain low at a chronic level, with high current harmonic content. Furthermore, wind power generation is inherently characterized by high randomness and volatility, further exacerbating the deterioration of power quality at the connection point, severely impacting the overall stable operation of the power system and the output performance of wind turbines.

[0004] Currently, wind farm power quality management systems feature a diverse range of technologies. Mainstream equipment includes passive filters, active filters, hybrid filters, and static synchronous compensators (STATCOMs). However, each approach faces significant technical bottlenecks. While passive power filters offer a simple structure and manageable costs, their fixed compensation capacity and frequency selectivity lead to limited dynamic adaptability. Furthermore, their filtering characteristics are significantly affected by both their own and environmental parameters, making them susceptible to the risk of resonant amplification when grid impedance fluctuates. Active filters, while capable of full-band harmonic compensation, are limited by the voltage rating of their power devices and the cost of heat dissipation, making them uneconomical. Equipment costs increase exponentially with large-capacity applications. Hybrid filtering technology, through the coordinated optimization of active and passive elements, improves harmonic compensation depth while maintaining manageable costs. However, this solution still relies on independent reactive power compensation modules for grid connection point voltage support, failing to achieve coordinated harmonic and reactive power management. As a core reactive power compensation device, the static synchronous compensator, with its millisecond-level response speed and continuous regulation capabilities, is a critical device for maintaining voltage stability. However, its single function necessitates its integration into a comprehensive system with a harmonic control unit. Moreover, in medium and high voltage grid-connected scenarios, due to the insulation strength limitations of the switchgear, the static synchronous compensator needs to be connected to the grid through a dedicated step-down transformer. This increases the complexity of the system topology and the equipment footprint. In addition, the transformer no-load loss under low-load conditions cannot be ignored, resulting in significant hidden energy consumption. Summary of the Invention

[0005] One of the objectives of the present invention is to provide a transformer-integrated static synchronous compensator system suitable for mountain wind farms with high reliability and good effect.

[0006] A second object of the present invention is to provide a control method for the transformer-integrated static synchronous compensator system suitable for mountain wind farms.

[0007] The transformer-integrated static synchronous compensator system suitable for mountain wind farms provided by the present invention includes a magnetic integrated filter transformer module, a filter module and a cascaded static synchronous compensator module; the magnetic integrated filter transformer module is connected between the wind farm grid connection point and the wind turbine generator set of the wind farm; the magnetic integrated filter transformer module is also connected to the cascaded static synchronous compensator module through the filter module; the magnetic integrated filter transformer module is used for voltage conversion between the public power grid, the wind turbine generator set and the compensation device; the filter module cooperates with the magnetic integrated filter transformer module to achieve filtering of specific subharmonics at the system grid connection point; the cascaded static synchronous compensator module is used to achieve reactive power compensation and wide-band harmonic suppression in the wind farm.

[0008] The magnetic integrated filter transformer module includes a magnetic integrated filter transformer; the magnetic integrated filter transformer includes a grid-side winding, a load winding, a filter winding and an integrated reactance winding; the grid-side winding adopts a star connection method and is connected to the power grid through the wind farm's grid connection point to achieve power transmission; the load winding is connected to the wind farm's busbar to obtain the wind farm's electricity; the filter winding adopts a delta connection method and is connected to the integrated reactance winding; one end of the integrated reactance winding is connected to the filter winding, and the other end of the integrated reactance winding is connected to the filter module.

[0009] The filtering module includes a plurality of filter capacitors connected in series on each phase line and cooperating with the integrated reactance winding of the magnetic integrated filter transformer to form a harmonic path to filter the harmonics of each phase line.

[0010] The cascaded static synchronous compensator module adopts a three-phase cascade structure based on H-bridge modules; the three-phase H-bridge links adopt a star connection method, and each phase H-bridge link is composed of several H-bridge modules connected in series; the static synchronous compensator is used to achieve reactive power compensation and broadband harmonic suppression for the power grid.

[0011] The present invention also provides a control method for the transformer-integrated static synchronous compensator system applicable to a mountain wind farm, comprising the following steps:

[0012] S1. Obtain data information about the public power grid at the target wind farm connection point;

[0013] S2. Based on the obtained data information, calculate the active current command control to achieve control of the DC voltage of each phase H-bridge link of the cascaded static synchronous compensator;

[0014] S3. Based on the data information obtained, the reactive current command control calculation is performed to achieve dynamic compensation of reactive power at the grid point;

[0015] S4. Based on the obtained data information, the harmonic current command control calculation is performed to achieve two-way control of the grid and wind farm harmonics, thereby controlling the harmonic current of the grid connection point to the set value;

[0016] S5. Based on the obtained data information, the calculation of the phase voltage control command is performed to achieve voltage balance of each H-bridge module on each phase link of the cascaded static synchronous compensator;

[0017] S6. Based on the obtained data information, perform quasi-proportional resonant control of the command current to achieve zero static error tracking of the current inner loop control signal;

[0018] S7. Based on the obtained data information, a PWM control signal is generated to control the on and off of the switching devices of each H-bridge module in the static synchronous compensator to achieve control of the transformer integrated static synchronous compensator system.

[0019] The step S1 of obtaining the data information of the public power grid at the target wind farm grid connection point specifically includes the following steps:

[0020] Collect the public grid voltage signal V at the target wind farm grid connection point Sx ; Among them, the value of x is a, b or c, indicating the phase sequence; the voltage signal V Sx The grid fundamental angular frequency ω0 used for dq conversion and dq inverse conversion is obtained through the phase-locked loop PLL.

[0021] The calculation of active current command control based on the obtained data information in step S2 to achieve control of the DC voltage of each phase H-bridge link of the cascaded static synchronous compensator specifically includes the following steps:

[0022] Collect the capacitor voltage V of each phase link H bridge module of the cascaded static synchronous compensator module dc_x_n , n is the number of H-bridge modules in each phase link, n=1,2,...,12; for V dc_x_n The sum is performed to obtain the first intermediate voltage V dc , V dc and the first intermediate voltage reference value V dc_ref The PI controller is used to obtain the DC signal I used to ensure that the DC voltage of each phase link H bridge module is stable at the expected value. fd1_ref ; will I fd1_ref Perform the fundamental frequency dq inverse transformation to obtain the active current command control signal I fx1_ref_p .

[0023] The calculation of reactive current command control based on the obtained data information in step S3 to achieve dynamic compensation of reactive power at the grid connection point specifically includes the following steps:

[0024] Collect the public grid voltage signal V at the target wind farm grid connection point Sx and the current signal I Sx , perform phase detection to obtain the phase angle difference φ between the fundamental voltage and current at the grid connection point; compare φ with the phase angle difference reference value φ ref Through the PI controller, the DC signal I is obtained for reactive power compensation. fq1_ref ; will I fq1_ref Perform the fundamental frequency dq inverse transformation to obtain the reactive current command control signal I fx1_ref_q .

[0025] The calculation of harmonic current command control based on the obtained data information in step S4 is performed to achieve two-way control of grid and wind farm harmonics, thereby controlling the harmonic current of the grid connection point to a set value, which specifically includes the following steps:

[0026] Collect the public grid current signal I at the target wind farm grid connection point Sx , will I Sx Through the hth harmonic frequency dq transformation, the grid-side current d-axis component I is obtained based on the hth harmonic angular frequency. Sd and the q-axis component I Sq ; Among them, the following formula is used to perform the hth harmonic frequency dq conversion:

[0027]

[0028] Where k is a positive integer;

[0029] Will I Sd and I Sq The corresponding d-axis DC component I is obtained by low-pass filtering Sdh and the q-axis DC component I Sqh ; will I Sdh and I Sqh The harmonic current command control signal I for bidirectional suppression of grid-connected current harmonics is obtained by inverse transformation of the hth harmonic frequency dq. Sxh ; Among them, the following formula is used to perform the hth harmonic frequency dq inverse transformation:

[0030]

[0031] Where ω0 is the fundamental angular frequency.

[0032] The calculation of the intra-phase voltage balancing command control based on the obtained data information in step S5 to achieve voltage balancing of each H-bridge module on each phase link of the cascaded static synchronous compensator specifically includes the following steps:

[0033] According to the first intermediate voltage V dc The number n of H-bridge modules in each phase link of the cascaded static synchronous compensator is used to calculate the average value V of the capacitor voltage of each phase link H-bridge module. dc_ave_x for V dc_ave_x The collected capacitor voltage V of each phase link H bridge module of the cascade static synchronous compensator dc_x_n Make the difference and input the result into the P controller to obtain the first intermediate quantity; obtain the phase current I output by the cascaded static synchronous compensator invx And sum it with the first intermediate quantity to obtain the pure active regulation signal ΔV superimposed on the H-bridge module modulation signal dc_rx .

[0034] The step S6 of performing quasi-proportional resonant control of the command current based on the obtained data information to achieve zero-static-error tracking of the current inner-loop control signal specifically includes the following steps:

[0035] Under the fundamental frequency condition, Ifx1_ref_p with I fx1_ref_q Superposition, get the power flow control reference signal I fx_ref ; will I fx_ref with I invx Make a difference and input the difference into the quasi-proportional resonant controller to achieve I invx to I fx_ref Zero static error tracking;

[0036] Under the condition of harmonic frequency, I Sxh The harmonic current reference value I Sxh_ref Make a difference and input the difference into the quasi-proportional resonant controller to achieve I Sxh to I Sxh_ref Zero static error tracking;

[0037] The following formula is used as the transfer function of the quasi-proportional resonant controller:

[0038]

[0039] Where k p is the proportional gain coefficient; k r is the resonant gain coefficient; ω c is the cutoff frequency, and ω c Indicates the bandwidth of the gain at the resonant frequency; n' is the harmonic order, that is, the integer multiple relationship between the harmonic frequency and the fundamental frequency;

[0040] Finally, I fx_ref with I invx The difference and I Sxh with I Sxh_ref The difference is processed by the quasi-proportional resonant controller, and the processed signals are superimposed to obtain the current inner loop closed loop control signal V rx .

[0041] The step S7 of generating a PWM control signal based on the obtained data information and controlling the on and off of the switching devices of each H-bridge module in the STATCOM to achieve control of the transformer integrated STATCOM system specifically includes the following steps:

[0042] ΔV dc_rx With V rx Superposition, using PWM modulation scheme to obtain PWM modulation signal V rx_PWM ;

[0043] The obtained PWM modulation signal V rx_PWM The input is sent to the H-bridge module of each phase link of the cascaded static synchronous compensator to control the on-off state of the switching devices in the module, thereby realizing the control of the transformer integrated static synchronous compensator system.

[0044] The transformer-integrated static synchronous compensator system and control method provided by the present invention, suitable for mountain wind farms, adds a magnetic integrated filter transformer module, a filter module, and a cascaded static synchronous compensator module between the wind farm and the power grid, and controls the static synchronous compensator based on real-time data information from the wind farm and the power grid. This not only achieves comprehensive reactive power and harmonic compensation for the wind power grid-connected system, but also has a small footprint, low operating voltage required for active devices, high stability, and good compensation effect, providing a high-power-density, high-reliability solution to power quality problems in mountain wind farms. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the functional modules of the system of the present invention.

[0046] Figure 2 Schematic diagram of the circuit structure of the system of the present invention.

[0047] Figure 3 Schematic diagram of the grid-connected equivalent circuit model of the system of the present invention.

[0048] Figure 4 Schematic diagram of the control method of the present invention.

[0049] Figure 5 Schematic diagram of the control strategy of the control method of the present invention. DETAILED DESCRIPTION

[0050] like Figure 1 The figure shows a schematic diagram of the functional modules of the system of the present invention: the transformer-integrated static synchronous compensator system suitable for mountain wind farms disclosed in the present invention includes a magnetic integrated filter transformer module 1, a filter module 3 and a cascade static synchronous compensator module 4; the magnetic integrated filter transformer module is connected between the wind farm grid connection point and the wind turbine generator set of the wind farm; the magnetic integrated filter transformer module is also connected to the cascade static synchronous compensator module through the filter module; the magnetic integrated filter transformer module is used for voltage conversion between the public power grid, the wind turbine generator set and the compensation device; the filter module cooperates with the magnetic integrated filter transformer module to achieve filtering of specific subharmonics at the system grid connection point; the cascade static synchronous compensator module is used to achieve reactive power compensation and wide-band harmonic suppression in the wind farm.

[0051] like Figure 2 The circuit structure diagram of the system of the present invention is shown as follows: the magnetic integrated filter transformer module includes a magnetic integrated filter transformer; the magnetic integrated filter transformer includes a grid-side winding 5, a load winding 6, a filter winding 7 and an integrated reactance winding ( Figure 1 The middle mark is 2, Figure 2The grid-side winding is connected in a star configuration and is connected to the grid (generally a 110 kV public grid) through the wind farm's grid connection point to achieve power transmission. The load winding is connected to the wind farm's busbar to obtain electricity from the wind farm and can be connected in a delta or star configuration. The filter winding is connected in a delta configuration and is connected to the integrated reactor winding. One end of the integrated reactor winding is connected to the filter winding, and the other end of the integrated reactor winding is connected to the filter module. The integrated reactor winding adopts a mirrored two-section series structure.

[0052] In a specific implementation, the magnetic integrated filter transformer may adopt the inductive filtering transformers with integrated reactor described in the paper “A compact-design oriented shipboard power supply system with transformer integrated filtering method” by Qianyi Liu, Fang Liu, et al.

[0053] The filtering module includes a plurality of filter capacitors connected in series on each phase line and cooperating with the integrated reactance winding of the magnetic integrated filter transformer to form a harmonic path to filter the harmonics of each phase line.

[0054] The cascaded static synchronous compensator module adopts a three-phase cascade structure based on H-bridge modules; the three-phase H-bridge links adopt a star connection method, and each phase H-bridge link is composed of several H-bridge modules connected in series; the static synchronous compensator is used to achieve reactive power compensation and broadband harmonic suppression for the power grid.

[0055] The following describes the principle of the operating voltage that the transformer-integrated static synchronous compensator system of the present invention needs to withstand and the conditions for selecting the inductance and capacitance parameters of the LC filter.

[0056] Calculate the static synchronous compensator output voltage V invx Grid voltage V at the connection point with the compensation branch fx The relationship is:

[0057]

[0058] Where |V invx | is the output voltage amplitude of the static synchronous compensator; |V fx | is the amplitude of the grid voltage at the connection point of the compensation branch; P is the output active power of the compensation branch; Q is the output reactive power of the compensation branch; Z LC is the reactance of the LC filter; Lf is the inductance of the LC filter; C f is the capacitance of the LC filter; |Z LC | is the amplitude of the equivalent impedance of the LC filter; γ is the phase angle of the equivalent impedance of the LC filter; ω is the angular frequency;

[0059] The static synchronous compensator outputs the voltage V invx Grid voltage V at the connection point with the compensation branch fx It can be found from the relationship that: when the reactive power meter of the compensation branch output satisfies 0≤Q / S base When ≤2, there exists |V invx |≤|V fx This also means that when using a transformer-integrated static synchronous compensator system for reactive power compensation, the V can only be achieved when the reactive power Q output by the compensation branch is 0 to 2 times the rated power of the LC filter. invx | / |V fx |<1, thereby reducing the port voltage of the static synchronous compensator; therefore, when selecting the LC filter inductor and capacitor parameters, it is necessary to refer to the two constraints of the required output reactive power of the compensation branch and the specific tuning frequency of the LC filter branch.

[0060] The working mechanism of the transformer integrated static synchronous compensator system of the present invention is described below:

[0061] like Figure 3 The figure shows the grid-connected equivalent circuit model of the system of the present invention: V S and I S is the grid phase voltage and phase current, Z S is the system impedance, V PCC and I PCC is the phase voltage and phase current of the system grid connection point; V L and I L is the line voltage and line current of the wind power load, a represents the unit vector rotated counterclockwise by h·120°, a=e jh·120° , that is, the angle difference between the phase sequence components; h is the order of the harmonic frequency; N1, N2 and N3 are the number of turns of the grid-side winding, load winding and filter winding respectively; Z1, Z2 and Z3 are the equivalent impedance of the grid-side winding, load winding and filter winding respectively; Z LC is the equivalent impedance of the LC filter group; Z st It represents the equivalent impedance of the static synchronous compensator;

[0062] In the system, in addition to the impedance characteristic parameter Z st Except for Z, the other parameters are fixed values. stThere is a close relationship with the output voltage of the static synchronous compensator; based on this, the appropriate Z can be adjusted by accurately controlling the output voltage of the static synchronous compensator. st value, thereby achieving the goal of dynamic compensation of reactive power of the grid-connected system and bidirectional suppression of harmonics. Specifically:

[0063] Under fundamental wave conditions, the system grid connection point voltage and grid voltage, load current and phase difference angle The relationship between and θ is

[0064]

[0065] Where x is a, b or c, indicating the phase sequence; ω0 is the fundamental angular frequency; is the wind power load line voltage V Lx1 , line current I Lx1 Phase difference between them; θ is the system grid-connected point line current I PCCx1 , reverse line voltage -V PCCx1 The phase difference between

[0066] Under the condition of stable operation of the power grid, the variable V Sx1 ,ω0andL S are kept constant; similarly, when the load state reaches a stable state, I Lx1 , I 2x1 and Also remains constant; therefore, the grid voltage amplitude ||V PCCx1 | CCx1 |It changes with the phase difference angle θ; θ is related to the system grid-connected point line current I PCCx1 Related, in the case of grid-connected power generation Under this condition, tanθ is monotonically increasing; under this condition, V PCCx1 There is a one-to-one mapping relationship between the amplitude of and θ, so reactive dynamic compensation can be achieved by controlling θ; controlling θ = 0, so that |V PCCx1 |=|V Sx1 |, the equivalent output impedance Z of STATCOM can be calculated at this time st1 for

[0067]

[0068] Under harmonic conditions, the calculation considers only the influence of grid harmonic voltage on grid current and the harmonic current of the system grid connection point is:

[0069]

[0070] Where Z Sh 、Z 1h 、Z LCh and Z 3hIt is a constant value at a specific harmonic frequency, and the filter winding equivalent impedance Z 3h =0, so in order to eliminate the grid harmonic voltage V Sxh The impact on the grid-connected point current and suppressing the resonance between the harmonic voltage source and the LC filter branch, the equivalent impedance Z of the static synchronous compensator considering only the background harmonic voltage of the grid sth-V Must present infinite impedance Z sth-V =∞. When this condition is met, I PCCxh =0.

[0071] Calculation Considering that the grid-connected system harmonic current loop is only affected by the load current, the system grid-connected point harmonic current is:

[0072]

[0073] Ideally, if Z 3h +3Z sth +3Z LCh =0, then the load harmonic current I Lh All the current will flow through the hybrid branch instead of flowing into the grid through the grid connection point. PCCxh =0; at this time, only the static synchronous compensator equivalent output impedance Z under the influence of load harmonic current is considered sth-i for

[0074] Due to the special winding design of the magnetic integrated filter transformer, the filter winding equivalent impedance is equal to zero (i.e., Z 3h =0), so Z sth-i Only need to meet Z sth-i =-Z LCh ;

[0075] In summary, by controlling the output impedance of the static synchronous compensator, its equivalent impedance Z st Dynamic reactive power compensation and bidirectional harmonic suppression can be achieved for mountain wind power grid-connected systems when the following characteristic values ​​are present:

[0076]

[0077] Figure 4 Schematic diagram of the control method of the present invention: The control method of the transformer integrated static synchronous compensator system applicable to mountain wind farms disclosed in the present invention comprises the following steps:

[0078] S1. Obtaining data information about the public power grid at the target wind farm connection point; specifically, the steps include:

[0079] Collect the public grid voltage signal V at the target wind farm grid connection point Sx; Among them, the value of x is a, b or c, indicating the phase sequence; the voltage signal V Sx The grid fundamental angular frequency ω0 for dq conversion and dq inverse conversion is obtained through the phase-locked loop PLL;

[0080] S2. Based on the obtained data information, active current command control is calculated to achieve control of the DC voltage of each phase H-bridge link of the cascaded static synchronous compensator; specifically comprising the following steps:

[0081] Collect the capacitor voltage V of each phase link H bridge module of the cascaded static synchronous compensator module dc_x_n , n is the number of H-bridge modules in each phase link, n=1,2,...,12; for V dc_x_n The sum is performed to obtain the first intermediate voltage V dc , V dc and the first intermediate voltage reference value V dc_ref The PI controller is used to obtain the DC signal I used to ensure that the DC voltage of each phase link H bridge module is stable at the expected value. fd1_ref ; will I fd1_ref Perform the fundamental frequency dq inverse transformation to obtain the active current command control signal I fx1_ref_p ;

[0082] S3. Based on the obtained data information, the reactive current command control is calculated to achieve dynamic compensation of reactive power at the grid connection point; specifically comprising the following steps:

[0083] Collect the public grid voltage signal V at the target wind farm grid connection point Sx and the current signal I Sx , perform phase detection to obtain the phase angle difference φ between the fundamental voltage and current at the grid connection point; compare φ with the phase angle difference reference value φ ref Through the PI controller, the DC signal I is obtained for reactive power compensation. fq1_ref ; will I fq1_ref Perform the fundamental frequency dq inverse transformation to obtain the reactive current command control signal I fx1_ref_q ;

[0084] S4. Based on the obtained data information, calculate the harmonic current command control to achieve two-way control of the grid and wind farm harmonics, thereby controlling the harmonic current of the grid connection point to the set value; specifically, the following steps:

[0085] Due to bandwidth limitations and frequency response characteristics, the quasi-proportional resonant controller cannot accurately distinguish signals of multiple frequencies at the same time. Under the condition of wide-band harmonic compensation, in order to avoid the mutual coupling of compensation current signals between various harmonic frequencies, the present invention proposes a frequency division detection method for extracting specific order harmonic signals at the grid connection point of the wind power generation system. Figure 5As shown in the dotted box 11;

[0086] Collect the public grid current signal I at the target wind farm grid connection point Sx , will I Sx Through the hth harmonic frequency dq transformation, the grid-side current d-axis component I is obtained based on the hth harmonic angular frequency. Sd and the q-axis component I Sq ; Among them, the following formula is used to perform the hth harmonic frequency dq conversion:

[0087]

[0088] Where k is a positive integer;

[0089] Will I Sd and I Sq The corresponding d-axis DC component I is obtained by low-pass filtering Sdh and the q-axis DC component I Sqh ; will I Sdh and I Sqh The harmonic current command control signal I for bidirectional suppression of grid-connected current harmonics is obtained by inverse transformation of the hth harmonic frequency dq. Sxh ; Among them, the following formula is used to perform the hth harmonic frequency dq inverse transformation:

[0090]

[0091] Where ω0 is the fundamental angular frequency;

[0092] S5. Based on the obtained data information, the calculation of the phase voltage equalization command control is performed to achieve voltage balancing of each H-bridge module on each phase link of the cascaded static synchronous compensator; specifically, the steps include:

[0093] According to the first intermediate voltage V dc The number n of H-bridge modules in each phase link of the cascaded static synchronous compensator is used to calculate the average value V of the capacitor voltage of each phase link H-bridge module. dc_ave_x for V dc_ave_x The collected capacitor voltage V of each phase link H bridge module of the cascade static synchronous compensator dc_x_n Make the difference and input the result into the P controller to obtain the first intermediate quantity; obtain the phase current I output by the cascaded static synchronous compensator invx (This current is also the compensation branch phase current I fx ), and summed with the first intermediate quantity to obtain the pure active regulation signal ΔV superimposed on the H-bridge module modulation signal dc_rx ;

[0094] S6. Based on the obtained data information, perform quasi-proportional resonant control of the command current to achieve zero static error tracking of the current inner loop control signal; specifically, the steps include:

[0095] Under the fundamental frequency condition, I fx1_ref_p with I fx1_ref_q Superposition, get the power flow control reference signal I fx_ref ; will I fx_ref with I invx Make a difference and input the difference into the quasi-proportional resonant controller to achieve I invx to I fx_ref Zero static error tracking;

[0096] Under the condition of harmonic frequency, I Sxh The harmonic current reference value I Sxh_ref Make a difference and input the difference into the quasi-proportional resonant controller to achieve I Sxh to I Sxh_ref Zero static error tracking;

[0097] The quasi-proportional resonant controller has the ability to amplify signals at multiple resonant frequency points. Based on this characteristic, it can achieve comprehensive compensation for reactive power and harmonics under fundamental and harmonic conditions. Although signal coupling occurs when multiple frequency signals are simultaneously input into the quasi-proportional resonant controller, the frequency division detection scheme adopted in step S4 successfully filters out characteristic subharmonics, thereby ensuring accurate and error-free tracking of multiple frequency signals.

[0098] Specifically, the following formula is used as the transfer function of the quasi-proportional resonant controller:

[0099]

[0100] Where k p is the proportional gain coefficient; k r is the resonant gain coefficient; ω c is the cutoff frequency, and ω c Indicates the bandwidth of the gain at the resonant frequency; n' is the harmonic order, that is, the integer multiple relationship between the harmonic frequency and the fundamental frequency;

[0101] Finally, I fx_ref with I invx The difference and I Sxh with I Sxh_ref The difference is processed by the quasi-proportional resonant controller, and the processed signals are superimposed to obtain the current inner loop closed loop control signal V rx ;

[0102] S7. Based on the obtained data information, a PWM control signal is generated to control the switching devices of each H-bridge module in the static synchronous compensator to achieve control of the transformer integrated static synchronous compensator system; specifically, the steps include:

[0103] ΔV dc_rx With V rx Superposition, using PWM modulation scheme to obtain PWM modulation signal V rx_PWM ;

[0104] The obtained PWM modulation signal V rx_PWM The input is sent to the H-bridge module of each phase link of the cascaded static synchronous compensator to control the on-off state of the switching devices in the module, thereby realizing the control of the transformer integrated static synchronous compensator system.

[0105] When the system of the present invention performs reactive power compensation and the reactive power output by the compensation branch is within the range of 0 to 2 times the rated power of the LC filter, the system can make the voltage at the output port of the static synchronous compensator lower than the grid voltage at the connection point of the compensation system branch. Meeting this condition can effectively reduce the operating voltage required by active devices and improve the operating performance of the system.

[0106] Under fundamental frequency conditions, the present invention can eliminate the coupling between the fundamental active current and fundamental reactive current signals in the DQ0 framework, avoiding the complex feedforward cross-term calculation caused by using a second-order LC filter to connect the static synchronous compensator; in the application scenario of multi-frequency control, it can eliminate the mutual coupling between the compensation current signals of different frequencies obtained by quasi-proportional resonant control, further improving the control accuracy and stability of the system.

Claims

1. A transformer integrated static synchronous compensator system suitable for mountain wind farms, characterized by It includes a magnetic integrated filter transformer module, a filter module and a cascade static synchronous compensator module; the magnetic integrated filter transformer module is connected between the wind farm grid connection point and the wind turbine generator set in the wind farm; the magnetic integrated filter transformer module is also connected to the cascade static synchronous compensator module through the filter module; the magnetic integrated filter transformer module is used for voltage conversion between the public power grid, the wind turbine generator set and the compensation device; the filter module cooperates with the magnetic integrated filter transformer module to achieve filtering of specific subharmonics at the system grid connection point; the cascade static synchronous compensator module is used to achieve reactive power compensation and wide-band harmonic suppression in the wind farm.

2. The transformer integrated static synchronous compensator system suitable for mountain wind farms according to claim 1 is characterized in that The magnetic integrated filter transformer module includes a magnetic integrated filter transformer; the magnetic integrated filter transformer includes a grid-side winding, a load winding, a filter winding and an integrated reactance winding; the grid-side winding adopts a star connection method and is connected to the power grid through the wind farm's grid connection point to achieve power transmission; the load winding is connected to the wind farm's busbar to obtain the wind farm's electricity; the filter winding adopts a delta connection method and is connected to the integrated reactance winding; one end of the integrated reactance winding is connected to the filter winding, and the other end of the integrated reactance winding is connected to the filter module.

3. The transformer integrated static synchronous compensator system suitable for mountain wind farms according to claim 2 is characterized in that The filtering module includes a plurality of filter capacitors connected in series on each phase line and cooperating with the integrated reactance winding of the magnetic integrated filter transformer to form a harmonic path to filter the harmonics of each phase line.

4. The transformer integrated static synchronous compensator system suitable for mountain wind farms according to claim 3 is characterized in that The cascaded static synchronous compensator module adopts a three-phase cascade structure based on H-bridge modules; the three-phase H-bridge links adopt a star connection method, and each phase H-bridge link is composed of several H-bridge modules connected in series; the static synchronous compensator is used to achieve reactive power compensation and broadband harmonic suppression for the power grid.

5. A control method for a transformer integrated static synchronous compensator system suitable for a mountain wind farm according to any one of claims 1 to 4, characterized in that The steps include: S1. Obtain data information about the public power grid at the target wind farm connection point; S2. Based on the obtained data information, calculate the active current command control to achieve control of the DC voltage of each phase H-bridge link of the cascaded static synchronous compensator; S3. Based on the data information obtained, the reactive current command control calculation is performed to achieve dynamic compensation of reactive power at the grid point; S4. Based on the obtained data information, the harmonic current command control calculation is performed to achieve two-way control of the grid and wind farm harmonics, thereby controlling the harmonic current of the grid connection point to the set value; S5. Based on the obtained data information, the calculation of the phase voltage control command is performed to achieve voltage balance of each H-bridge module on each phase link of the cascaded static synchronous compensator; S6. Based on the obtained data information, perform quasi-proportional resonant control of the command current to achieve zero static error tracking of the current inner loop control signal; S7. Based on the obtained data information, a PWM control signal is generated to control the on and off of the switching devices of each H-bridge module in the static synchronous compensator to achieve control of the transformer integrated static synchronous compensator system.

6. The control method according to claim 5, characterized in that The step S1 of obtaining the data information of the public power grid at the target wind farm grid connection point specifically includes the following steps: Collect the public grid voltage signal V at the target wind farm grid connection point Sx ; Among them, the value of x is a, b or c, indicating the phase sequence; the voltage signal V Sx The grid fundamental angular frequency ω0 for dq conversion and dq inverse conversion is obtained through the phase-locked loop PLL; The calculation of active current command control based on the obtained data information in step S2 to achieve control of the DC voltage of each phase H-bridge link of the cascaded static synchronous compensator specifically includes the following steps: Collect the capacitor voltage V of each phase link H bridge module of the cascaded static synchronous compensator module dc_x_n , n is the number of H-bridge modules in each phase link, n=1,2,...,12; for V dc_x_n The sum is performed to obtain the first intermediate voltage V dc , V dc and the first intermediate voltage reference value V dc_ref The PI controller is used to obtain the DC signal I used to ensure that the DC voltage of each phase link H bridge module is stable at the expected value. fd1_ref ; will I fd1_ref Perform the fundamental frequency dq inverse transformation to obtain the active current command control signal I fx1_ref_p .

7. The control method according to claim 6, characterized in that The calculation of reactive current command control based on the obtained data information in step S3 to achieve dynamic compensation of reactive power at the grid connection point specifically includes the following steps: Collect the public grid voltage signal V at the target wind farm grid connection point Sx and the current signal I Sx , perform phase detection to obtain the phase angle difference φ between the fundamental voltage and current at the grid connection point; compare φ with the phase angle difference reference value φ ref Through the PI controller, the DC signal I is obtained for reactive power compensation. fq1_ref ; will I fq1_ref Perform the fundamental frequency dq inverse transformation to obtain the reactive current command control signal I fx1_ref_q .

8. The control method according to claim 7, characterized in that The calculation of harmonic current command control based on the obtained data information in step S4 is performed to achieve two-way control of grid and wind farm harmonics, thereby controlling the harmonic current of the grid connection point to a set value, which specifically includes the following steps: Collect the public grid current signal I at the target wind farm grid connection point Sx , will I Sx Through the hth harmonic frequency dq transformation, the grid-side current d-axis component I is obtained based on the hth harmonic angular frequency. Sd and the q-axis component I Sq ; Among them, the following formula is used to perform the hth harmonic frequency dq conversion: Where k is a positive integer; Will I Sd and I Sq The corresponding d-axis DC component I is obtained by low-pass filtering Sdh and the q-axis DC component I Sqh ; will I Sdh and I Sqh The harmonic current command control signal I for bidirectional suppression of grid-connected current harmonics is obtained by inverse transformation of the hth harmonic frequency dq. Sxh ; Among them, the following formula is used to perform the hth harmonic frequency dq inverse transformation: Where ω0 is the fundamental angular frequency.

9. The control method according to claim 8, characterized in that The calculation of the intra-phase voltage balancing command control based on the obtained data information in step S5 to achieve voltage balancing of each H-bridge module on each phase link of the cascaded static synchronous compensator specifically includes the following steps: According to the first intermediate voltage V dc The number n of H-bridge modules in each phase link of the cascaded static synchronous compensator is used to calculate the average value V of the capacitor voltage of each phase link H-bridge module. dc_ave_x for V dc_ave_x The collected capacitor voltage V of each phase link H bridge module of the cascade static synchronous compensator dc_x_n Make the difference and input the result into the P controller to obtain the first intermediate quantity; obtain the phase current I output by the cascaded static synchronous compensator invx And sum it with the first intermediate quantity to obtain the pure active regulation signal ΔV superimposed on the H-bridge module modulation signal dc_rx .

10. The control method according to claim 9, characterized in that The step S6 of performing quasi-proportional resonant control of the command current based on the obtained data information to achieve zero-static-error tracking of the current inner-loop control signal specifically includes the following steps: Under the fundamental frequency condition, I fx1_ref_p with I fx1_ref_q Superposition, get the power flow control reference signal I fx_ref ; will I fx_ref with I invx Make a difference and input the difference into the quasi-proportional resonant controller to achieve I invx to I fx_ref Zero static error tracking; Under the condition of harmonic frequency, I Sxh The harmonic current reference value I Sxh_ref Make a difference and input the difference into the quasi-proportional resonant controller to achieve I Sxh to I Sxh_ref Zero static error tracking; The following formula is used as the transfer function of the quasi-proportional resonant controller: Where k p is the proportional gain coefficient; k r is the resonant gain coefficient; ω c is the cutoff frequency, and ω c Indicates the bandwidth of the gain at the resonant frequency; n' is the harmonic number; Finally, I fx_ref with I invx The difference and I Sxh with I Sxh_ref The difference is processed by the quasi-proportional resonant controller, and the processed signals are superimposed to obtain the current inner loop closed loop control signal V rx ; The step S7 of generating a PWM control signal based on the obtained data information and controlling the on and off of the switching devices of each H-bridge module in the STATCOM to achieve control of the transformer integrated STATCOM system specifically includes the following steps: ΔV dc_rx With V rx Superposition, using PWM modulation scheme to obtain PWM modulation signal V rx_PWM ; The obtained PWM modulation signal V rx_PWM The input is sent to the H-bridge module of each phase link of the cascaded static synchronous compensator to control the on-off state of the switching devices in the module, thereby realizing the control of the transformer integrated static synchronous compensator system.

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