A converter cluster system network construction method based on power grid nonlinear oscillation

Abstract

The application provides a grid nonlinear oscillation-based converter aggregation system network construction method, and belongs to the field of energy. First, a radial feeder aggregation system is based, a power capacitor is installed on the low-voltage side of a step-up transformer, a power oscillator combined with a feeder inductance and the power capacitor is constructed, a voltage-current nonlinear controller is further constructed, a network topology structure is formed, and finally, a nonlinear oscillator equation representing the dynamic characteristics of the converter aggregation system network construction is proposed. The application can reduce the electrical distance between synchronous machines in a large power grid, construct the electromagnetic induction coupling strength of the large power grid, and enhance the synchronous stability of the power grid.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of energy, and particularly relates to a converter collection system network construction method based on nonlinear oscillation of a power grid. BACKGROUND

[0002] With high proportion of power electronic devices and new energy access to power systems, the voltage and frequency parameters of the power grid are "stable", and the instantaneous "balance" of power generation and power consumption of new power systems is also challenged. In the traditional power system, when subjected to disturbances, the rotor kinetic energy of the synchronous generator, the thermal standby and the governor, the excitation regulation system and the power system stabilizer can maximize the stability of the voltage and frequency of the power grid.

[0003] At present, the network construction technology adopts devices such as energy storage and its converter, static var generator (SVG), wind turbine and photovoltaic and its converter, so that it can actively respond, support and enhance the inertia, frequency, voltage and short-circuit current of the power grid, and ultimately become a more friendly independent power source for the power grid.

[0004] On the other hand, new energy generation is widely distributed and has a large number of single units, which generally adopts a low-voltage access and a medium-voltage collection method to access the power grid, and has multiple operation control levels, large-scale security and control system and complex strategy. The photovoltaic and other new energy generation is stepped up to access the power grid, and the electrical distance from the main grid is 2-3 times that of conventional thermal power and hydroelectric generating units, which reduces the strength of the AC synchronous power grid and weakens the synchronous coupling capability. Generally, the new energy collection system needs to be structured and regularized, and various energy storage technologies are used to solve the problems of new energy uncertainty output and weak power grid strength of high proportion of new energy AC system. SUMMARY

[0005] To solve the above technical problems, the application provides a converter collection system network construction method based on nonlinear oscillation of a power grid, a collection system based on a radial feeder, an electric power capacitor installed on the low-voltage side of a step-up transformer, a construction of a power oscillator combined with a feeder inductance and an electric power capacitor, a further construction of a voltage-current nonlinear controller, a formation of a network topology structure, and finally a nonlinear oscillator equation representing the dynamic characteristics of the converter collection system network construction, a nonlinear oscillation operation and control of the converter, and a formation of a converter collection system network topology structure.

[0006] To achieve the above purpose, the application adopts the following technical solutions:

[0007] A converter collection system network construction method based on nonlinear oscillation of a power grid, comprising the following steps:

[0008] Step 1, based on the radial feeder collection system, install power capacitors on the low-voltage side of the step-up transformer, and construct a power oscillator combined with feeder inductance-power capacitors;

[0009] Step 2, construct a voltage-current nonlinear oscillation controller;

[0010] Step 3, design a nonlinear oscillation network modeling method for the converter collection system, and form a network topology structure;

[0011] Step 4, characterize the nonlinear oscillator equation of the converter collection system network dynamic characteristics, and design a voltage-current nonlinear controller control method.

[0012] Advantages:

[0013] The present application helps to optimize the layout and access mode of the converter, thereby improving the overall performance and response speed of the system, and can realize real-time adjustment of the grid frequency and power flow, thereby improving the flexibility and adaptability of new energy access, and promoting the efficient use of renewable energy, that is, the beneficial effects of the present application mainly include the following aspects:

[0014] 1) With the increasing proportion of new energy such as photovoltaic and wind power connected to the grid, the converter collection system of the feeder type power oscillator is proposed, which can effectively integrate new energy resources, support stable grid operation, and promote the use of clean energy.

[0015] 2) The power oscillator and converter collection system network topology can improve the power quality of the power grid, reduce harmonic distortion by adjusting voltage and frequency, and ensure that the power quality of the power system meets the standard requirements, protecting the safe operation of electrical equipment.

[0016] 3) The new energy collection system is equivalent to an oscillator synchronous network power supply, which can reduce the electrical distance between the synchronous machine and the large power grid, enhance the grid synchronization stability, and optimize the transmission network design through the synchronous network power supply, further improve the transmission capacity, reduce transmission loss, and enhance the economy and reliability of the power grid. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the structure diagram of the converter collection system network provided by the present application.

[0018] Figure 2 is the principle diagram of the nonlinear oscillation network modeling of the converter collection system provided by the present application.

[0019] Figure 3 is the voltage-current nonlinear controller schematic diagram for the phase-shifting transformer side converter and the parallel transformer side converter provided by the present application.

[0020] In the figure, reference numerals are: high-voltage AC power grid 101, step-up transformer 102, large-capacity power capacitor 201, step-up transformer low-voltage side bus 202, 1st phase-shift series transformer 203, nth phase-shift series transformer 204, Nth phase-shift series transformer 205, 1st voltage source converter 206, nth voltage source converter 207, Nth voltage source converter 208, DC power source 209, DC microgrid 210, shunt transformer 211, shunt transformer side converter 212, first PWM generator 213, voltage-current inner loop control 214, non-linear voltage controller 215, second PWM generator 216, current inner loop control 217, non-linear current controller 218, each feeder voltage 219, step-up transformer low-voltage side bus voltage 220, 1st feeder 301, nth feeder 302, Nth feeder 303, 1st step-up transformer 304, nth step-up transformer 305, Nth step-up transformer 306, 1st collection converter 307, nth collection converter 308, Nth collection converter 309. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the present application clearer, the following further describes the present application with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as there is no conflict. The technical solutions of the present application will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application and not all embodiments.

[0022] The components of the embodiments of the present application generally described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application.

[0023] Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0024] In order to make the objects, technical solutions and advantages of the present application clearer, the following further describes the present application with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as there is no conflict. The technical solutions of the present application will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application and not all embodiments.

[0025] The application provides a converter collection system network construction method based on power grid nonlinear oscillation, comprising the following steps:

[0026] Step 1: design a power oscillator composed of a power capacitor and a feeder equivalent reactance, comprising:

[0027] As shown in Figure 1 , the converter collection system network topology provided by the application equivalently forms a new power plant from a photovoltaic and wind power new energy base to realize various functions equivalent to or even exceeding those of a traditional thermal power plant. The new power plant mainly faces a 110kV, 220kV or 500kV high-voltage AC power grid 101 and is generally boosted by a step-up transformer 102. A large-capacity power capacitor 201 is installed at a low-voltage side bus 202 of the step-up transformer, and the capacitance of the capacitor is . The large-capacity power capacitor 201 has the functions of resisting high voltage, overvoltage and overcurrent protection after a certain period, and is subjected to overvoltage periodic tests to meet the needs of the large-capacity power capacitor 201 as the power oscillator of the application in resisting overvoltage and overcurrent. The low-voltage side bus 202 of the step-up transformer is a collection point of each branch feeder, and each branch contains a first feeder 301, an nth feeder 302 and an Nth feeder 303, a first step-up transformer 304, an nth step-up transformer 305 and an Nth step-up transformer 306 of 10 / 35kV or 1.0 / 35kV, and a first collection converter 307, an nth collection converter 308 and an Nth collection converter 309. The first collection converter 307 is connected to the first step-up transformer 304 of 10 / 35kV or 1.0 / 35kV through the first feeder 301; the nth collection converter 308 is connected to the nth step-up transformer 305 of 10 / 35kV or 1.0 / 35kV through the nth step-up transformer 305; and the Nth collection converter 309 is connected to the Nth step-up transformer 306 of 10 / 35kV or 1.0 / 35kV through the Nth step-up transformer 306. Figure 1 are AC voltages of AC ports of the first collection converter 307, the nth collection converter 308 and the Nth collection converter 309, respectively.

[0028] The collection converter in the application can refer to a high-power converter or an equivalent model of a small-power converter in each branch. The nth feeder is selected, and the single-phase feeder impedance is assumed to be , and the transformer reactance is , wherein , are the feeder resistance and inductance, respectively, is the power frequency, is an imaginary number, and n is a counting variable. ​​​Therefore, it can be inferred that the inductance of each single-phase feeder bus cluster converter to the step-up transformer 102 is . Figure 1 In the formula, N is the total number of feeder branches, T1, Tn, TN represent the 1st step-up transformer 304, the nth step-up transformer 305, and the Nth step-up transformer 306, respectively.

[0029] Based on the above description of the power capacitor and the equivalent reactance of the feeder, it is assumed that the equivalent inductance of each feeder is equal, i.e. , That is, the equivalent inductance of each feeder branch is is the number of feeder buses in the cluster system, the equivalent oscillation frequency of the cluster system power oscillator can be derived as and the characteristic impedance are respectively:

[0030] (1)

[0031] where, in the case of equal equivalent inductance of each feeder, is the equivalent oscillation frequency, is the equivalent characteristic impedance, is the capacitance of the large-capacity power capacitor 201.

[0032] In the new energy base sending-end power grid, the "double high" is a high proportion of new energy and a high proportion of power electronic equipment system. There are many devices in the system, and the system parameters are prone to large fluctuations. Assuming that the equivalent inductance of each feeder is not equal, i.e. all are not equal, the equivalent oscillation frequency and characteristic impedance of each feeder are defined as:

[0033] (2)

[0034] (3)

[0035] where, is the equivalent oscillation frequency of the 1st feeder 301 of the cluster system, is the equivalent characteristic impedance of the 1st feeder 301 of the cluster system; is the equivalent oscillation frequency of the nth feeder 302, is the equivalent characteristic impedance of the nth feeder 302; is the equivalent oscillation frequency of the Nth feeder 303, is the equivalent characteristic impedance of the Nth feeder 303; , , are the inductances of each feeder, respectively.

[0036] When taking the average value, the equivalent oscillation frequency and characteristic impedance of the cluster system are respectively:

[0037] (4)

[0038] wherein, for convenience of calculation, is the equivalent average characteristic impedance, is the equivalent average oscillation frequency.

[0039] Further, define variables:

[0040] (5)

[0041] (6)

[0042] (7)

[0043] wherein, , , are the a-phase currents flowing through the 1st feeder 301, the nth feeder 302, and the Nth feeder 303 of the collection system, respectively, , , are the b-phase currents flowing through the 1st feeder 301, the nth feeder 302, and the Nth feeder 303 of the collection system, respectively, , , are the c-phase currents flowing through the 1st feeder 301, the nth feeder 302, and the Nth feeder 303 of the collection system, respectively; , , are the a-phase equivalent voltages of the 1st feeder 301, the nth feeder 302, and the Nth feeder 303, respectively, , , are the b-phase equivalent voltages of the 1st feeder 301, the nth feeder 302, and the Nth feeder 303, respectively, , , are the c-phase equivalent voltages of the 1st feeder 301, the nth feeder 302, and the Nth feeder 303, respectively.

[0044] Step 2: Design a voltage-current nonlinear controller, including:

[0045] As Figure 1As shown, the application proposes a voltage-current nonlinear controller, which is mainly composed of the 1st phase-shifting series transformer 203, the nth phase-shifting series transformer 204, the Nth phase-shifting series transformer 205, the parallel transformer 211, the voltage source converter, the direct current power supply 209 and the direct current micro-grid 210. The 1st phase-shifting series transformer 203 is connected with the 1st voltage source converter 206, the nth phase-shifting series transformer 204 is connected with the nth voltage source converter 207, and the Nth phase-shifting series transformer 205 is connected with the Nth voltage source converter 208; the direct current power supply 209, the Nth voltage source converter 208, the nth voltage source converter 207, the 1st voltage source converter 206 and the parallel transformer side converter 212 together constitute the direct current micro-grid 210.

[0046] For the voltage source formed by the phase-shifting series transformer, the 1st phase-shifting series transformer 203 target voltage in series with the feeder side can be expressed as:

[0047] (8)

[0048] Wherein, , , are the a, b, c three-phase target voltages of the 1st phase-shifting series transformer 203 in series with the feeder side, is a controllable small parameter, is the equivalent oscillation frequency of the 1st feeder of the collection system, is the input equivalent excitation voltage, , , are the a, b, c three-phase voltages of the large-capacity power capacitor 201.

[0049] The nth phase-shifting series transformer 204 target voltage can be expressed as:

[0050] (9)

[0051] Wherein, , , are the a, b, c three-phase target voltages of the nth phase-shifting series transformer 204 in series with the feeder side, is a controllable small parameter, is the equivalent oscillation frequency of the nth feeder of the collection system, is the input equivalent excitation voltage, , , are the a, b, c three-phase voltages of the large-capacity power capacitor 201.

[0052] The Nth phase-shifting series transformer 205 target voltage can be expressed as:

[0053] (10)

[0054] wherein, , , are the target voltages of the a, b, c three phases of the Nth shunt series transformer 205 respectively, is the controllable small parameter quantity, is the equivalent oscillation frequency of the Nth feeder of the aggregation system, is the input equivalent excitation voltage, , , are the a, b, c three phase voltages of the large-capacity power capacitor 201 respectively.

[0055] The target current flowing through the shunt transformer 211 can be expressed as:

[0056] (11)

[0057] wherein, , , are the a, b, c three phase target currents of the shunt transformer 211 respectively, is the controllable small parameter quantity, and are the equivalent average characteristic impedance and the equivalent average oscillation frequency of the aggregation system respectively, is the input equivalent excitation voltage, , , are the a, b, c three phase voltages of the large-capacity power capacitor 201 respectively.

[0058] Step 3: Nonlinear oscillation network modeling of the converter aggregation system is performed, including:

[0059] Assuming that the feeder aggregation system behaves in three-phase balance, the three phases can be completely decoupled into a-phase, b-phase, and c-phase equivalent circuits, as shown in Figure 2 , that is, by Figure 1 further equivalent to Figure 2 circuit diagram, TP1, TPn, and TPN represent the 1st phase-shifting series transformer 203, the nth phase-shifting series transformer 204, and the Nth phase-shifting series transformer 205 respectively. This step builds a nonlinear oscillation network model of the converter aggregation system. Taking the a-phase as an example, the voltage-current differential equation can be established as follows:

[0060] (12)

[0061] , (13)

[0062] wherein, is the large-capacity power capacitor capacity, is the a-phase voltage of the large-capacity power capacitor 201, is the current value flowing into the external power grid, is the voltage of the AC side of the converter connected to the low-voltage end of the gathering network, is the transformation ratio of the transformer connected to the low-voltage end of the gathering network. Formula (13) takes the nth feeder as an example.

[0063] Multiply the same on both ends of formula (13) by , is the equivalent characteristic impedance of the nth feeder 302, and the following can be obtained:

[0064] , (14)

[0065] Further, considering , is the a-phase voltage of the large-capacity power capacitor 201, respectively, substitute in formula (11) into formula (12), substitute in formula (9) into formula (14), and after arrangement, the following can be obtained:

[0066] (15)

[0067] , (16)

[0068] Similarly, the derivation process of the oscillation differential equation of the b-phase and c-phase is similar to formula (12)-formula (16). If the oscillation differential equation of the b-phase and c-phase needs to be derived, i.e., for the b-phase: all the letters a in formula (12)-formula (16) are replaced by b; and for the c-phase: all the letters a in formula (12)-formula (16) are replaced by c.

[0069] Step 4: Perform voltage-current nonlinear controller control, including:

[0070] For the series phase-shifting transformer, the first voltage source converter 206, the nth voltage source converter 207, and the Nth voltage source converter 208 are used to control the output voltage. The present application sets the instruction of the Nth phase-shifting series transformer 205, which needs to collect the bus voltage signal of the low-voltage side bus 202 of the step-up transformer, i.e., , and also needs to generate The signals are further collected and compared with the instruction of the Nth phase-shifting series transformer 205, and the carrier signal is obtained through the voltage-current inner loop control, and then the PWM wave is generated to drive the Nth voltage source converter 208.

[0071] For the parallel transformer, the parallel transformer side converter 212 is used to control the output current. The instruction of the nonlinear current controller 218 is set by the application, and the instruction is formed by collecting the bus voltage signal of the low-voltage side bus 202 of the step-up transformer, that is , and the instruction is formed by collecting the bus voltage signal of the low-voltage side bus 202 of the step-up transformer, that is The signals are further collected and compared with the instruction of the Nth phase-shifting series transformer 205, and the carrier signal is obtained through the voltage-current inner loop control, and then the PWM wave is generated to drive the Nth voltage source converter 208.

[0072] Figure 3 The application provides a voltage-current nonlinear controller for a phase-shifting transformer side converter and a parallel transformer side converter. For the nonlinear voltage control, the application collects the feeder voltage and current, and implements the voltage-current inner loop control 214 through the nonlinear voltage controller 215, and further drives the phase-shifting transformer side converter through the first PWM generator 213. For the nonlinear current control, the application collects the feeder voltage 219 and the low-voltage side bus voltage 220 of the step-up transformer, and implements the current inner loop control 217 through the nonlinear current controller 218, and further drives the parallel transformer side converter 212 through the second PWM generator 216.

Claims

1. A method for configuring a grid-forming system based on nonlinear oscillation of a converter cluster, characterized in that, It comprises the following steps: Step 1, based on the radial feeder collection system, install power capacitors on the low-voltage side of the booster transformer, and build a power oscillator combined with feeder inductance-power capacitors; Install large-capacity power capacitors on the low-voltage side of the booster transformer bus; The low-voltage side of the booster transformer bus is the collection point of each branch feeder, and each branch contains the first feeder, the nth feeder, the Nth feeder, the first booster transformer, the nth booster transformer, the Nth booster transformer, the first collection converter, the nth collection converter, and the Nth collection converter; the first collection converter is connected to the first booster transformer through the first feeder; the nth collection converter is connected to the nth booster transformer through the nth booster transformer; the Nth collection converter is connected to the Nth booster transformer through the Nth booster transformer; Select the nth feeder, assuming single-phase feeder impedance is , transformer reactance is , where , are feeder resistance, inductance, is power frequency angular frequency, is imaginary number, n is a counting variable, ; it is assumed that the inductance of each single-phase feeder from the converter to the step-up transformer is ; Based on the above description of the power oscillator consisting of power capacitors and feeder equivalent reactances, assuming that each feeder equivalent inductance is equal, i.e. , is the equivalent inductance of each feeder branch, is the number of system feeder branches, the equivalent oscillation frequency and characteristic impedance of the power oscillator are respectively: （1） wherein, in the case of equal equivalent inductances of the respective feed lines, is the equivalent characteristic impedance, is the equivalent characteristic impedance, is the capacitance of the large-capacity power capacitor; Assume that the equivalent inductances of the feed lines are not equal, i.e. all not equal, the equivalent oscillation frequency and characteristic impedance of each feed line are defined as follows, respectively: （2） （3） wherein, is the equivalent resonant frequency of the first feeder of the collection system, is the equivalent characteristic impedance of the first feeder of the collection system; is the equivalent resonant frequency of the nth feeder, is the equivalent characteristic impedance of the nth feeder; is the equivalent resonant frequency of the Nth feeder, is the equivalent characteristic impedance of the Nth feeder; , , are the inductances of the respective feeders; When taking the average value, the equivalent oscillation frequency and characteristic impedance of the collection system are respectively: （4） wherein, is an equivalent average characteristic impedance, is an equivalent average oscillation frequency; Step 2, build a voltage-current nonlinear oscillation controller; Step 3, design a nonlinear oscillation network modeling method for the converter collection system, and form a network topology structure; Step 4, characterize the nonlinear oscillator equation of the converter collection system network dynamic characteristics, and design a voltage-current nonlinear controller control method.

2. The method of claim 1, wherein the grid nonlinear oscillation-based converter aggregation system network construction method is characterized by, Step 1 includes designing a network topology structure of the converter collection system, and equivalent new power plants such as photovoltaic and wind power new energy bases; the new power plants face 110kV, 220kV, and 500kV high-voltage alternating current networks and are boosted through booster transformers.

3. The method of claim 1, wherein the method is based on nonlinear oscillation of the power grid. Step 2 includes building a voltage-current nonlinear controller, which includes a first phase-shifting series transformer, an nth phase-shifting series transformer, an Nth phase-shifting series transformer, a parallel transformer, a voltage source converter, a direct current power supply, and a direct current microgrid; the first phase-shifting series transformer is connected to the first voltage source converter, the nth phase-shifting series transformer is connected to the nth voltage source converter, and the Nth phase-shifting series transformer is connected to the Nth voltage source converter; the direct current power supply and the Nth voltage source converter, the nth voltage source converter, the first voltage source converter, and the parallel transformer side converter together form a direct current microgrid.

4. The method of claim 3, wherein the grid nonlinear oscillation-based converter aggregation system networking method is characterized by, Step 2 includes: For the voltage source formed by the phase-shifting series transformer, the target voltage of the first phase-shifting series transformer in series with the feeder side is expressed as: （8） wherein, , , are the first phase-shifting series transformer series feeder side a, b, c three-phase target voltage, is a controllable small parameter quantity, is the equivalent oscillation frequency of the first feeder of the power grid, is the input equivalent excitation voltage, , , are a, b, c three-phase voltages of large-capacity power capacitors; The target voltage of the nth phase-shifting series transformer is expressed as: （9） wherein, , , are the nth phase-shifted series transformer series feeder side a, b, c three-phase target voltage, is the equivalent oscillation frequency of the nth feeder of the collection system, is the input equivalent excitation voltage; The target voltage of the Nth phase-shifting series transformer is expressed as: （10） wherein, , , are the target voltages of the three-phase a, b, c on the series feeder side of the Nth series-connected transformer, is the equivalent oscillation frequency of the Nth feeder of the collection system, is the input equivalent excitation voltage; The target current flowing through the parallel transformer is expressed as: （11） wherein, , , are the a, b, c three-phase target currents with parallel transformer access respectively, and are the equivalent average characteristic impedance and the equivalent average oscillation frequency of the collection system respectively, is the input equivalent excitation voltage; , , are the a-phase equivalent voltages of the 1st feeder, the nth feeder, the Nth feeder respectively, , , are the b-phase equivalent voltages of the 1st feeder, the nth feeder, the Nth feeder respectively, , , are the c-phase equivalent voltages of the 1st feeder, the nth feeder, the Nth feeder respectively.

5. The method of claim 4, wherein, Step 3 includes: Assuming that the feeder collection system behaves as a three-phase balance, the three-phase can be completely decoupled into a-phase, b-phase, and c-phase equivalent circuits; build a nonlinear oscillation network model of the converter collection system; for a-phase, the voltage-current differential equation is established as follows: （12） ， （13） wherein, is a large-capacity power capacitor capacity, is a phase a voltage of a large-capacity power capacitor, is a current value flowing into an external power grid, is a voltage of an AC side of an access converter at a low-voltage end of a gathering network, is a transformation ratio of a transformer at a low-voltage end of a gathering network; formula (13) represents a formula for the nth feeder line; Multiplying both sides of equation (13) by , is the equivalent characteristic impedance of the nth feeder, which gives ， （14） Further, consider , is the a-phase voltage of the large-capacity power capacitor, respectively, substituting in formula (12) and substituting in formula (14) and arranging to obtain: （15） ， （16）。 6. The method of claim 5, wherein the method further comprises: When deriving the oscillation differential equation of b-phase, all letters a in equations (12)-(16) are replaced by b; when deriving the oscillation differential equation of c-phase, all letters a in equations (12)-(16) are replaced by c.

7. The method of claim 5, wherein the grid nonlinear oscillation-based converter aggregation system networking method is characterized by, The step 4 comprises: for the series phase-shifting transformer, using the 1st voltage source converter, the nth voltage source converter and the Nth voltage source converter to control the output voltage; setting the instruction of the Nth phase-shifting series transformer, the instruction is formed by collecting the bus voltage signal of the bus on the low-voltage side of the booster transformer, i.e. also generating a signal; further, collecting the power filter voltage and current signals of the converter on the side of the parallel transformer, comparing the instruction of the Nth phase-shifting series transformer, obtaining the carrier signal through the voltage-current inner loop control, and then generating the PWM wave to drive the Nth voltage source converter.

8. The method of claim 7, wherein the grid nonlinear oscillation-based converter aggregation system networking method is characterized by, The step 4 comprises: for the parallel transformer, using the parallel transformer side converter to control the output current; setting the instruction of the nonlinear current controller, the formation of the instruction needs to collect the bus voltage signal of the low voltage side bus of the step-up transformer, that is also needs to generate the signal; further, collecting the current signal of the parallel transformer side converter port, comparing the instruction of the nonlinear current controller, obtaining the carrier signal through the current inner loop control, and then generating the PWM wave to drive the parallel transformer side converter.

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