Harmonic suppression simulation modeling method for distributed power flow controller in offshore wind power collection scene

Abstract

The invention discloses a distributed power flow controller harmonic suppression simulation modeling method in an offshore wind power collection scene. The method comprises the following steps: S1, constructing an offshore wind turbine generator main circuit simulation model containing voltage source characteristic harmonic waves; s2, constructing an offshore wind turbine generator control circuit simulation model containing voltage source characteristic harmonic waves; s3, constructing a land power grid main circuit simulation model containing current source characteristic harmonic waves; s4, constructing a land power grid control circuit simulation model containing current source characteristic harmonic waves; s5, constructing a distributed power flow controller main circuit simulation model with a harmonic suppression function; and S6, constructing a distributed power flow controller control circuit simulation model with a harmonic suppression function. The invention provides a distributed power flow controller harmonic suppression simulation modeling method in an offshore wind power collection scene. Simulation modeling is performed on a distributed power flow controller with a harmonic suppression function, an offshore wind turbine generator containing voltage source characteristic harmonic waves and a land power grid containing current source characteristic harmonic waves.

Description

Technical Field

[0001] The present invention relates to the field of power system operation and control technology, and in particular to a harmonic control simulation modeling method for a distributed power flow controller in an offshore wind power collection scenario. Background Art

[0002] my country has abundant offshore wind power reserves, which are widely distributed from north to south. However, harmonics have exceeded the standard in the offshore wind farm projects that have been put into operation. When offshore wind power is connected to the onshore power grid via long-distance AC submarine cables, it is very likely that the inherent background harmonics of the onshore power grid will resonate and amplify. At the same time, offshore wind turbines are connected to the grid through converters, and voltage source characteristic harmonics are inevitably generated during the grid connection process. In recent years, many offshore wind power systems along the coast of my country have recorded 5th and 7th harmonic voltages and harmonic currents exceeding the standard, affecting the power quality at the grid connection point. The 5th harmonic current was amplified to more than 200A under low wind speed conditions, causing equipment damage and having a significant impact on the absorption of offshore wind energy. Suppressing harmonics and improving system operation reliability are the primary issues to be solved by offshore wind power systems.

[0003] Currently, existing harmonic control devices are mainly divided into passive filtering devices and active filtering devices. Passive filtering devices are filtering devices composed of harmonic capacitors and reactors, which are usually connected in parallel near the harmonic source. This can not only absorb harmonic currents, but also compensate for reactive power, and is simple to operate and maintain. Active filtering devices use power electronic switches to achieve dynamic control, and can quickly respond to changes in the frequency and size of harmonics while avoiding resonance with system impedance. Distributed power flow controllers are composed of single-phase voltage source converters, which are directly connected in series to the controlled line and applied to offshore wind power systems. They can compensate for harmonic voltages, reduce the harmonic content of offshore wind power system grid connection points, and give full play to the effect of active filtering devices.

[0004] The existing control solution is to install passive filtering devices at the connection point between the onshore switch station and the grid to suppress harmonics and meet the grid connection requirements, but it does not consider the impact of harmonics on the entire power generation system. Passive filters are usually a series-parallel combination of reactance and capacitance, which uses the LC series resonance effect to make the specified harmonic present a low impedance in the LC path, thereby filtering out this harmonic. However, a set of LC filters can only be designed for a certain frequency harmonic, and when the grid operating parameters change, the LC filter is prone to cause resonance of the system, which not only fails to filter out harmonics, but also increases harmonics. The parallel active filter device blocks the propagation of nonlinear loads into the grid by reversely compensating for harmonic currents, but it cannot solve the problem of harmonic amplification at the end bus of long transmission lines. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a simulation modeling method for harmonic control of a distributed power flow controller in an offshore wind power collection scenario. By simulating and modeling a distributed power flow controller with harmonic control function, an offshore wind turbine with voltage source characteristic harmonics, and an onshore power grid with current source characteristic harmonics, an electromagnetic transient modeling and simulation basis is provided for the distributed power flow controller for offshore wind power harmonic control, thereby providing support for the subsequent engineering implementation of the distributed power flow controller.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a simulation modeling method for harmonic control of a distributed power flow controller in an offshore wind power collection scenario, comprising the following steps: S1: Construct a simulation model of the main circuit of an offshore wind turbine with voltage source characteristic harmonics; S2: Construct a simulation model of offshore wind turbine control circuits containing voltage source characteristic harmonics; S3: Construct a simulation model of the main circuit of the onshore power grid containing harmonics of current source characteristics; S4: Construct a simulation model of the onshore power grid control circuit containing current source characteristic harmonics; S5: Construct a main circuit simulation model of a distributed power flow controller with harmonic control function; S6: Construct a simulation model of the control circuit of a distributed power flow controller with harmonic control function.

[0007] Preferably, in step S1, the offshore wind turbine generator system includes a plurality of wind power system units, cables, a collection network and a station main transformer; The main circuit of a single wind power system consists of a controlled voltage source, a step-up transformer, a filter inductor, a filter capacitor and a damping resistor.

[0008] Preferably, in step S2, the controlled voltage source control module samples the grid connection point voltage in the main circuit of a single unit of the wind power system and the outflow current of the controlled voltage source, outputs each single-phase voltage VA, VB and VC of the controlled voltage source, and outputs the grid connection point active power of the single unit of the wind power system and the amplitude and phase angle of the 7th harmonic voltage; The controlled voltage source control circuit performs Fourier transformation on the grid-connected point single-phase voltage in the main circuit of the single-machine wind power system and the single-phase current flowing out of the controlled voltage source to obtain the 7th single-phase harmonic voltage amplitude and the 7th single-phase harmonic voltage phase angle, obtain the grid-connected point single-phase voltage effective value and the grid-connected point single-phase voltage phase angle, obtain the controlled voltage source single-phase outflow current effective value and the controlled voltage source single-phase outflow current phase angle; then the active power is calculated according to the grid-connected point single-phase voltage and current, that is, the grid-connected point single-phase voltage effective value is multiplied by the controlled voltage source single-phase outflow current effective value, and then multiplied by the cosine value of the phase angle difference between the 7th single-phase harmonic voltage phase angle and the controlled voltage source single-phase outflow current phase, and finally multiplied by 3 to obtain the active power flowing out of the grid; Construct a sinusoidal voltage source simulation model, multiply Π by 100 and then by L to get ωL, then multiply by 1 / 3 of the apparent power of the wind power system transformer, divide by the effective value of the single-phase voltage at the grid connection point (it will switch to a constant of 0.4 at 0.1s), and then perform a rectangular coordinate transformation with the effective value of the single-phase voltage at the grid connection point. The output effective value is multiplied by The peak value of the sinusoidal voltage source is obtained, and the output phase angle is added to the single-phase voltage phase angle of the grid connection point to obtain the initial phase angle of the sinusoidal voltage source, and then the three-phase sinusoidal voltage source is calculated by a three-phase sinusoidal generator; Construct the 5th and 7th harmonic simulation models of voltage source characteristics, and multiply the effective value of the 5th harmonic voltage by The 5th harmonic voltage peak value is obtained, and then the 5th harmonic voltage source is calculated by the three-phase sine generator with the phase angle and frequency; the 7th harmonic voltage effective value is multiplied by The 7th harmonic voltage peak value is obtained, and then the 7th harmonic voltage source is obtained by calculating the phase angle and frequency through a three-phase sine generator; The sinusoidal voltage source is vector-added with the fifth and seventh voltage source characteristic harmonics to obtain the power source equivalent model of the offshore wind turbine with voltage source characteristic harmonics.

[0009] Preferably, in step S3, the main circuit simulation model of the onshore power grid includes a three-phase three-winding transformer, a load, a controllable current source and an induction motor.

[0010] Preferably, the step S4 constructs an onshore power grid control circuit simulation model containing current source characteristic harmonics, specifically as follows: multiplying the initial given value of the 5th harmonic current peak by a ramp transfer function (increasing from an initial value of 0 to 1 with a fixed slope within 0.05s) to simulate the continuous increase and step of the harmonic current, and performing a three-phase sine calculation on the current peak with 5 times the frequency and an initial phase angle of 0° to obtain the 5th harmonic current source; multiplying the initial given value of the 7th harmonic current peak by a ramp transfer function (increasing from an initial value of 0 to 1 with a fixed slope within 0.05s) to simulate the continuous increase and step of the harmonic current, and performing a three-phase sine calculation on the current peak with 7 times the frequency and an initial phase angle of 0° to obtain the 7th harmonic current source; The fifth harmonic current and the seventh harmonic current are added together to obtain an onshore power grid simulation model containing current source characteristic harmonics.

[0011] Preferably, the circuit simulation model of step S5 includes two groups of DPFCs connected in series, one group controls the seventh harmonic and the other group controls the fifth harmonic, each group of DPFC is provided with a bypass switch to perform the DPFC on / off operation; one group of DPFC includes three single-phase DPFC sub-modules, each DPFC sub-module includes an IGBT, a diode, a DC capacitor, a filter inductor, a filter capacitor and a single-phase dual-winding coupling transformer.

[0012] Preferably, in step S6, the distributed power flow controller control circuit simulation model includes a control module and a PWM modulation module; S61, the control module samples the DC capacitor voltage Vdcse, the current IL flowing through the filter inductor and the output voltage Vse in the main circuit of the single-phase DPFC submodule; performs Fourier transformation on the output voltage Vse and the current IL flowing through the filter inductor to obtain the output voltage effective value Vse_Mag, the output voltage phase angle Vse_Phase, the effective value IL_Mag of the current flowing through the filter inductor and the phase angle IL_Phase of the current flowing through the filter inductor; performs Fourier transformation on the current ILine flowing into the DPFC to obtain the effective value ILineMag of the current flowing into the DPFC and the phase angle ILinePhase of the current flowing into the DPFC; calculates the sine value of the difference between the fundamental component of the output voltage phase angle Vse_Phase and the phase angle ILinePhase of the current flowing into the DPFC, and multiplies it with the fundamental component of the output voltage effective value Vse_Mag to obtain the fundamental component Vseq_1th of the q-axis component of the output voltage; Calculate the fundamental component angle and the 7th harmonic component phase angle. The time TIME multiplied by Π and then multiplied by 100 is ωt. ωt is multiplied by 1 and 7 respectively to get theta1 and theta7. The initial phase angle of the current flowing into the DPFC is added to theta1 to get the phase angle of the fundamental current flowing into the DPFC. Theta7 is the phase angle of the 7th harmonic current flowing into the DPFC. In the d-axis control loop, the DC voltage command value 1 is subtracted from the DC capacitor voltage Vdcse to obtain the difference between the DC capacitor voltage command value and the actual value, and the difference is multiplied by the charging time, and PI control is performed. Then, the difference is subtracted from the fundamental component of the d-axis component of the output voltage to obtain the difference between the d-axis component command value of the output voltage and the actual value, and the difference is multiplied by the charging time to perform PI control. Then, the difference is subtracted from the sum of the fundamental component of the d-axis component of the current flowing into the DPFC and the fundamental component of the q-axis component of the output voltage and the product of the angular velocity and the filter capacitor multiplication value ωC, and then the fundamental component of the d-axis component of the current flowing through the filter inductor is subtracted to obtain the difference between the fundamental component command value of the d-axis component of the current flowing through the filter inductor and the actual value, and then multiplied by the charging time, and the difference between the fundamental component command value of the d-axis component of the current flowing through the filter inductor and the actual value is performed PI control. Then, the difference is subtracted from the sum of the fundamental component of the d-axis component of the output voltage and the product of the fundamental component of the q-axis component of the current flowing through the filter inductor and the product of the angular velocity and the filter inductance multiplication value ωL, and then divided by 1 to obtain the component Vd of the reference voltage on the d-axis; In the q-axis control loop, ZeroTime is the control amount of 0.1s after the charging time, that is, the q-axis command value before 0.6s is the fundamental component of the q-axis component of the output voltage, and the q-axis command value after 0.6s is 0. The difference between the fundamental component command value of the q-axis component of the output voltage and the actual value is obtained by subtracting the difference between the fundamental component command value of the q-axis component of the output voltage and the actual value and multiplying it with the charging time, and performing PI control; the fundamental component of the q-axis component of the current flowing into the DPFC minus the difference between the fundamental component command value of the q-axis component of the output voltage controlled by PI and the actual value is subtracted Remove the fundamental component of the d-axis component of the output voltage and the product of the angular velocity and the filter capacitor multiplication value ωC, then subtract the fundamental component of the q-axis component of the current flowing through the filter inductor to obtain the difference between the command value and the actual value of the fundamental component of the q-axis component of the current flowing through the filter inductor, then multiply it by the charging time, and perform PI control; then subtract the difference between the fundamental component of the q-axis component of the output voltage Vseq_1th and the fundamental component of the d-axis component of the current flowing through the filter inductor ILd_1th and the product of the angular velocity and the filter inductance multiplication value ωL, and then divide it by a constant 1 to obtain the reference voltage component Vq on the q-axis; The reference voltage component Vd on the d-axis and the reference voltage component Vq on the q-axis are subjected to inverse DQ transformation and multiplied by the charging time to obtain the fundamental component of the reference voltage, and the fundamental component of the reference voltage and the 7th harmonic component of the reference voltage are added to obtain the reference voltage VREF; S62, the PWM modulation module simulation model compares the modulation voltage Vref generated by the control module with the 7000 Hz triangular carrier to generate g1, g2, g3 and g4 trigger conduction signals, which trigger the IGBT in the main circuit of the single-phase DPFC sub-module to turn on or off.

[0013] The present invention provides a simulation modeling method for harmonic control of a distributed power flow controller in an offshore wind power collection scenario. The harmonic source of the voltage source characteristic of the wind farm is represented by a controlled voltage source, which can simplify the operation of the simulation system, highlight the research on the harmonics of the voltage source characteristic of the wind turbine, and can achieve the generation of harmonic voltage after simulation verification. The present invention proposes a simulation modeling method for an onshore power grid containing harmonics of current source characteristics. By adding a controlled current source to equate the harmonics of the current source characteristics, the harmonic problem of the onshore power grid is accurately simulated, and the generation of harmonic current can be achieved after simulation verification. The present invention proposes a simulation modeling method for harmonic control of a distributed power flow controller in an offshore wind power collection scenario. The simulation modeling method can significantly suppress the harmonic voltage amplitude of the grid connection point, and has high flexibility and adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 This is a simulation model diagram of the offshore wind farm structure of the present invention; Figure 2 This is a simulation model diagram of a single-machine main circuit of a wind power system according to the present invention; Figure 3 It is the structural parameter diagram of the 35kV cable of the present invention; Figure 4 This is a simulation model diagram of a controlled voltage source control module of the present invention; Figure 5 This is a simulation model diagram of a controlled voltage source control circuit of the present invention; Figure 6 This is a simulation model diagram of the main circuit of the onshore power grid of the present invention; Figure 7 This is a simulation model diagram of a controlled current source control circuit of the present invention; Figure 8 This is a simulation model diagram of DPFC in the system of the present invention; Fig. 9 A DPFC unit diagram in each group of DPFCs of the present invention; Fig.10 This is a simulation model diagram of a single-phase DPFC submodule of the present invention; Fig.11 This is a simulation model diagram of the main circuit of the single-phase DPFC submodule of the present invention; Fig.12 This is a simulation model diagram of the main circuit of the single-phase DPFC submodule of the present invention; Fig.13 This is a simulation model diagram of the DPFC control circuit of the present invention; Fig.14 It is a simulation model diagram of the method for calculating the fundamental wave and the seventh harmonic components of the present invention; Fig.15 It is a simulation model diagram of the method for calculating the phase angle of the fundamental wave and the seventh harmonic component of the present invention; Fig.16 This is a simulation model diagram of the fundamental component control loop of the present invention; Fig.17 This is a simulation model diagram of the seventh harmonic component control loop of the present invention; Fig.18 This is a simulation model diagram for reference voltage calculation of the present invention; Fig.19 This is a simulation model diagram of the PWM modulation module of the present invention; Fig. 20 It is a simulation waveform diagram of the harmonic source under the condition of sudden change in amplitude of the harmonic source of the present invention. DETAILED DESCRIPTION

[0015] A simulation modeling method for harmonic control of a distributed power flow controller in an offshore wind power collection scenario includes the following steps: S1: Construct a simulation model of the main circuit of an offshore wind turbine with voltage source characteristic harmonics; S2: Construct a simulation model of offshore wind turbine control circuits containing voltage source characteristic harmonics; S3: Construct a simulation model of the main circuit of the onshore power grid containing harmonics of current source characteristics; S4: Construct a simulation model of the onshore power grid control circuit containing current source characteristic harmonics; S5: Construct a main circuit simulation model of a distributed power flow controller with harmonic control function; S6: Construct a simulation model of the control circuit of a distributed power flow controller with harmonic control function.

[0016] S1: Construct a simulation model of the main circuit of an offshore wind turbine with voltage source characteristic harmonics. The simulation model of the offshore wind farm structure is as follows: Figure 1 As shown, the wind farm consists of 16 wind power system units, 35kV cables, 35kV collection networks and station main transformers.

[0017] The simulation model of the main circuit of a single wind power system is as follows: Figure 2 The main circuit diagram of the wind power system consists of a controlled voltage source, a step-up transformer, a filter inductor, a filter capacitor and a damping resistor. The parameters of the wind power system are shown in Table 1. Table 1 Main parameter settings of single-machine simulation model of wind power system

[0018] The structural parameters of the 35kV cable simulation model are as follows: Figure 3 As shown in Figure 2, the length of the cable between the two wind power systems is 1 km. The electrical parameters of the 35kV cable simulation model are shown in Table 2.

[0019] Table 2 Electrical parameter settings for 35kV cable simulation model

[0020] The parameter settings of the main transformer of the wind power system are shown in Table 3.

[0021] Table 3 Main parameter settings of main transformer of wind power system

[0022] S2: Construct an offshore wind turbine control circuit simulation model containing voltage source characteristic harmonics. The controlled voltage source control module is as follows: Figure 4 As shown, the controlled voltage source control module samples the grid connection point voltage pccVoltage in the main circuit of the single-machine wind power system and the controlled voltage source outflow current IL, outputs the single-phase voltages VA, VB and VC of the controlled voltage source, and outputs the active power of the grid connection point of the single-machine wind power system and the amplitude and phase angle of the 7th harmonic voltage.

[0023] Controlled voltage source control circuit such as Figure 5As shown, the controlled voltage source control circuit performs Fourier transform on the grid-connected point single-phase voltage pcc_Voltage_A in the main circuit of a single machine of the wind power system and the single-phase current IL_A flowing out of the controlled voltage source to obtain the 7th single-phase harmonic voltage amplitude pcc_voltage_A_harm and the 7th single-phase harmonic voltage phase angle pcc_voltage_A_harm_Phase, and obtains the grid-connected point single-phase voltage effective value pcc_voltage_A_RMS and the grid-connected point single-phase voltage phase angle pcc_voltage_A_Phase, and obtains the controlled voltage The effective value of the single-phase outflow current IL_A_RMS of the source and the phase angle IL_A_Phase of the single-phase outflow current of the controlled voltage source; then the active power is calculated according to the single-phase voltage and current of the grid connection point, that is, the effective value of the single-phase voltage pcc_voltage_A_RMS of the grid connection point is multiplied by the effective value of the single-phase outflow current IL_A_RMS of the controlled voltage source, and then multiplied by the cosine value of the phase angle difference between the 7th single-phase harmonic voltage phase angle pcc_voltage_A_Phase and the single-phase outflow current phase IL_A_Phase of the controlled voltage source, and finally multiplied by 3 to obtain the active power flowing out of the grid connection point; Construct a sinusoidal voltage source simulation model, multiply Π by 100 and then by L to get ωL, then multiply it by 1 / 3 of the apparent power of the wind power system single-machine transformer 5MVA, divide it by the effective value of the single-phase voltage at the grid connection point pcc_voltage_A_RMS (it will switch to a constant of 0.4 at 0.1s), and then perform a rectangular coordinate transformation with the effective value of the single-phase voltage at the grid connection point pcc_voltage_A_RMS, where the output effective value is multiplied by The peak value of the sinusoidal voltage source is obtained, and the output phase angle is added to the single-phase voltage phase angle pcc_voltage_A_Phase at the grid connection point to obtain the initial phase angle of the sinusoidal voltage source, and then the three-phase sinusoidal voltage source is calculated by the three-phase sinusoidal generator; Construct the 5th and 7th harmonic simulation models of voltage source characteristics, and multiply the effective value of the 5th harmonic voltage by The 5th harmonic voltage peak value is obtained, and then the 5th harmonic voltage source is calculated by the three-phase sine generator with the phase angle and frequency; the 7th harmonic voltage effective value is multiplied by The 7th harmonic voltage peak value is obtained, and then the 7th harmonic voltage source is obtained by calculating the phase angle and frequency through a three-phase sine generator; The sinusoidal voltage source is vector-added with the fifth and seventh voltage source characteristic harmonics to obtain the power source equivalent model of the offshore wind turbine with voltage source characteristic harmonics.

[0024] S3: Construct a simulation model of the main circuit of the onshore power grid containing harmonics of the current source characteristics. The simulation model of the main circuit of the onshore power grid containing harmonics of the current source characteristics is as follows: Figure 6As shown in Figure 4, the onshore power grid simulation model mainly includes a three-phase three-winding transformer, load, controllable current source and induction motor, etc. The main parameter settings of the onshore power grid main circuit simulation model are shown in Table 4.

[0025] Table 4 Main parameter settings of onshore power grid simulation model

[0026] S4: Construct a simulation model of the onshore power grid control circuit containing current source characteristic harmonics. The simulation model of the controlled current source control circuit is as follows: Figure 7 As shown in the figure, the initial given value of the 5th harmonic current peak is 0.025kA (stepped to 0.035kA at 3.5s), and multiplied by the ramp transfer function (increasing from the initial value 0 to 1 at a fixed slope within 0.05s) to simulate the continuous increase and step of the harmonic current. The current peak value is calculated by three-phase sinusoidal calculation with 5 times the frequency and 0° initial phase angle to obtain the 5th harmonic current source. The 7th harmonic current source is the same.

[0027] The fifth harmonic current and the seventh harmonic current are added together to obtain an onshore power grid simulation model containing current source characteristic harmonics.

[0028] S5: Construct a simulation model of the main circuit of a distributed power flow controller with harmonic control function. Two groups of DPFC are connected in series in the system, such as Figure 8 As shown, DPFC7 treats the 7th harmonic and DPFC5 treats the 5th harmonic. Each DPFC group contains 6 DPFC units, such as Fig. 9 As shown, each DPFC group is provided with a bypass switch, which can be used to switch the DPFC on and off.

[0029] Each DPFC unit contains three single-phase DPFC sub-modules, such as Fig.10 As shown. Among them, the main circuit of the single-phase DPFC submodule is as follows Fig.11 As shown in Figure 5, the main circuit consists of IGBT, diode, DC capacitor, filter inductor, filter capacitor and single-phase dual-winding coupling transformer. The main circuit parameter settings of the single-phase DPFC submodule are shown in Table 5. The main circuit topology is a single-phase H-bridge converter composed of IGBTs connected in anti-parallel with diodes, and an LC filter is used for filtering.

[0030] Table 5 Single-phase DPFC submodule main circuit parameter settings

[0031] S6: Construct a distributed power flow controller control circuit simulation model with harmonic control function. Take the DPFC control circuit for harmonic control as an example. The DPFC control circuit simulation model is divided into a control module and a PWM modulation module, such as Fig.12 shown.

[0032] S6.1: Construct a simulation model of the distributed power flow controller control module with harmonic control function. The detailed control circuit of DPFC is as follows: Fig.13 As shown. Fig.11 It can be obtained that the control module samples the DC capacitor voltage Vdcse, the current IL flowing through the filter inductor and the output voltage Vse in the main circuit of the single-phase DPFC sub-module. The output voltage Vse and the current IL flowing through the filter inductor are Fourier transformed to obtain the output voltage effective value Vse_Mag, the output voltage phase angle Vse_Phase, the effective value IL_Mag of the current flowing through the filter inductor and the phase angle IL_Phase of the current flowing through the filter inductor. The current ILine flowing into the DPFC is Fourier transformed to obtain the effective value ILineMag of the current flowing into the DPFC and the phase angle ILinePhase of the current flowing into the DPFC. The sine value of the difference between the fundamental component of the output voltage phase angle Vse_Phase and the phase angle ILinePhase of the current flowing into the DPFC is calculated, and multiplied by the fundamental component of the output voltage effective value Vse_Mag to obtain the fundamental component Vseq_1th of the q-axis component of the output voltage. The calculation methods of the remaining physical quantities d, the fundamental component of the q-axis component, and the 7th harmonic component are similar, which can be referred to. Fig.14 .

[0033] The calculation method of the fundamental component angle and the 7th harmonic component phase angle is as follows: Fig.15 As shown. The time TIME multiplied by Π and then multiplied by 100 is ωt, and ωt is multiplied by 1 and 7 respectively to get theta1 and theta7. The initial phase angle of the current flowing into the DPFC ILinePhase is added to theta1 to get the phase angle of the fundamental current flowing into the DPFC ILine_theta1. Theta7 is the phase angle of the 7th harmonic current flowing into the DPFC ILine_theta7.

[0034] The simulation model of the control loop of the fundamental component is as follows Fig.16As shown. Taking the d-axis control loop as an example, the DC voltage command value 1 is subtracted from the DC capacitor voltage Vdcse to obtain the difference VdcseError between the DC capacitor voltage command value and the actual value, and multiplied by the charging time ChargeTime (i.e., charging is performed at 0.5s), and PI control is performed, and then the difference VsedError between the output voltage d-axis component command value and the actual value is obtained by subtracting it from the fundamental component Vsed_1th of the output voltage d-axis component, and then multiplied by the charging time ChargeTime to perform PI control. Then, the difference is made between the fundamental component ILined_1th of the d-axis component of the current flowing into the DPFC, the fundamental component Vseq_1th of the q-axis component of the output voltage, and the product of the angular velocity and the filter capacitor multiplication value ωC, and then the fundamental component ILd_1th of the d-axis component of the current flowing through the filter inductor is subtracted to obtain the difference ILdError between the fundamental component command value and the actual value of the d-axis component of the current flowing through the filter inductor, and then multiplied by the charging time ChargeTime, and the difference ILdError between the fundamental component command value and the actual value of the d-axis component of the current flowing through the filter inductor is subjected to PI control. Then, the difference is made between the fundamental component Vsed_1th of the d-axis component of the output voltage, the fundamental component ILq_1th of the q-axis component of the current flowing through the filter inductor, and the product of the angular velocity and the filter inductance multiplication value ωL, and then divided by 1 to obtain the reference voltage component Vd on the d-axis.

[0035] The q-axis control loop is similar, and ZeroTime is the control quantity that lags behind the charging moment ChargeTime by 0.1s, that is, the q-axis command value before 0.6s is the fundamental component Vseq_1th of the q-axis component of the output voltage, and the q-axis command value after 0.6s is 0. The difference between the command value and the actual value of the fundamental component Vseq_1th of the q-axis component of the output voltage is obtained by subtracting it from the command value, which is the fundamental component of the q-axis component of the output voltage, to obtain the difference VseqError between the command value and the actual value, and multiplying it by the charging moment ChargeTime, and performing PI control. The fundamental component ILineq_1th of the q-axis component of the current flowing into the DPFC is subtracted from the difference VseqError between the fundamental component command value and the actual value of the q-axis component of the output voltage after PI control, and then the fundamental component Vsed_1th of the d-axis component of the output voltage and the product of the angular velocity and the filter capacitor multiplication value ωC are subtracted, and then the fundamental component ILq_1th of the q-axis component of the current flowing through the filter inductor is subtracted to obtain the difference ILqError between the command value and the actual value of the fundamental component of the q-axis component of the current flowing through the filter inductor, and then multiplied by the charging time ChargeTime, and PI control is performed. Then, the difference is subtracted from the difference between the fundamental component Vseq_1th of the q-axis component of the output voltage and the fundamental component ILd_1th of the d-axis component of the current flowing through the filter inductor and the product of the angular velocity and the filter inductance multiplication value ωL, and then divided by a constant 1 to obtain the reference voltage component Vq on the q-axis.

[0036] The reference voltage component Vd on the d-axis and the reference voltage component Vq on the q-axis are subjected to inverse DQ transformation and multiplied by the charging time ChargeTime to obtain the fundamental component Vr_1th of the reference voltage. The seventh harmonic component Vr_7th of the reference voltage is generated in the same way. Fig.17 The reference voltage VREF is obtained by adding the fundamental component Vr_1th of the reference voltage and the 7th harmonic component Vr_7th of the reference voltage, as shown in Fig.18 shown.

[0037] S6.2: Construct a simulation model of the PWM modulation module of a distributed power flow controller with harmonic control function. The simulation model of the PWM modulation module is as follows: Fig.19 The modulation voltage Vref generated by the control module is compared with the 7000 Hz triangular carrier to generate g1, g2, g3 and g4 triggering conduction signals, which trigger the IGBT in the main circuit of the single-phase DPFC submodule to turn on or off.

[0038] For DPFC with 7th harmonic control function: after the DPFC access system is put into operation at 1.0s, DPFC can quickly reduce the 7th harmonic voltage generated by the onshore power grid to near zero, and after the controlled current source amplitude changes at 2.5s and 3.5s, it can also restore the harmonic voltage amplitude at the grid connection point to near zero.

[0039] For DPFC with 5th harmonic control function: after DPFC is connected to the system and put into operation at 1.5s, DPFC can quickly reduce the 5th harmonic voltage generated by the offshore wind power system to zero, and after the amplitude of the controlled voltage source changes at 2.5s and 3.5s, it can also quickly recover to near zero.

[0040] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A simulation modeling method for harmonic control of distributed power flow controller in offshore wind power collection scenario, characterized in that: The following steps are involved: S1: Construct a simulation model of the main circuit of an offshore wind turbine with voltage source characteristic harmonics; S2: Construct a simulation model of offshore wind turbine control circuits containing voltage source characteristic harmonics; S3: Construct a simulation model of the main circuit of the onshore power grid containing harmonics of current source characteristics; S4: Construct a simulation model of the onshore power grid control circuit containing current source characteristic harmonics; S5: Construct a main circuit simulation model of a distributed power flow controller with harmonic control function; S6: Construct a simulation model of the control circuit of a distributed power flow controller with harmonic control function.

2. According to the method for simulation modeling of harmonic control of distributed power flow controller in offshore wind power collection scenario of claim 1, it is characterized in that: In step S1, the offshore wind turbine generator system includes multiple wind power system units, cables, a collection network and a station main transformer; The main circuit of a single wind power system consists of a controlled voltage source, a step-up transformer, a filter inductor, a filter capacitor and a damping resistor.

3. According to the method for simulation modeling of harmonic control of distributed power flow controller in offshore wind power collection scenario of claim 1, it is characterized in that: In the step S2, the controlled voltage source control module samples the grid connection point voltage in the main circuit of the single machine of the wind power system and the outflow current of the controlled voltage source, outputs the single-phase voltages VA, VB and VC of the controlled voltage source, and outputs the grid connection point active power of the single machine of the wind power system and the amplitude and phase angle of the 7th harmonic voltage; The controlled voltage source control circuit performs Fourier transformation on the grid-connected point single-phase voltage in the main circuit of the single-machine wind power system and the single-phase current flowing out of the controlled voltage source to obtain the 7th single-phase harmonic voltage amplitude and the 7th single-phase harmonic voltage phase angle, obtain the grid-connected point single-phase voltage effective value and the grid-connected point single-phase voltage phase angle, obtain the controlled voltage source single-phase outflow current effective value and the controlled voltage source single-phase outflow current phase angle; then the active power is calculated according to the grid-connected point single-phase voltage and current, that is, the grid-connected point single-phase voltage effective value is multiplied by the controlled voltage source single-phase outflow current effective value, and then multiplied by the cosine value of the phase angle difference between the 7th single-phase harmonic voltage phase angle and the controlled voltage source single-phase outflow current phase, and finally multiplied by 3 to obtain the active power flowing out of the grid; Construct a sinusoidal voltage source simulation model, multiply Π by 100 and then by L to get ωL, then multiply it by 1 / 3 of the apparent power of the wind power system transformer, divide it by the effective value of the single-phase voltage at the grid connection point, and then perform a rectangular coordinate transformation with the effective value of the single-phase voltage at the grid connection point. The output effective value is multiplied by The peak value of the sinusoidal voltage source is obtained, and the output phase angle is added to the single-phase voltage phase angle of the grid connection point to obtain the initial phase angle of the sinusoidal voltage source, and then the three-phase sinusoidal voltage source is calculated by a three-phase sinusoidal generator; Construct the 5th and 7th harmonic simulation models of voltage source characteristics, and multiply the effective value of the 5th harmonic voltage by The 5th harmonic voltage peak value is obtained, and then the 5th harmonic voltage source is calculated by the three-phase sine generator with the phase angle and frequency; the 7th harmonic voltage effective value is multiplied by The 7th harmonic voltage peak value is obtained, and then the 7th harmonic voltage source is obtained by calculating the phase angle and frequency through a three-phase sine generator; The sinusoidal voltage source is vector-added with the fifth and seventh voltage source characteristic harmonics to obtain the power source equivalent model of the offshore wind turbine with voltage source characteristic harmonics.

4. According to the method for simulation modeling of harmonic control of distributed power flow controller in offshore wind power collection scenario of claim 1, it is characterized in that: In step S3, the main circuit simulation model of the onshore power grid includes a three-phase three-winding transformer, a load, a controllable current source and an induction motor.

5. According to the method for simulation modeling of harmonic control of distributed power flow controller in offshore wind power collection scenario of claim 1, it is characterized in that: The step S4 constructs an onshore power grid control circuit simulation model containing current source characteristic harmonics, specifically as follows: multiplying the initial given value of the 5th harmonic current peak by the ramp transfer function (increasing from the initial value 0 to 1 with a fixed slope within 0.05s) to simulate the continuous increase and step of the harmonic current, and performing a three-phase sine calculation on the current peak with 5 times the frequency and the initial phase angle of 0° to obtain the 5th harmonic current source; multiplying the initial given value of the 7th harmonic current peak by the ramp transfer function (increasing from the initial value 0 to 1 with a fixed slope within 0.05s) to simulate the continuous increase and step of the harmonic current, and performing a three-phase sine calculation on the current peak with 7 times the frequency and the initial phase angle of 0° to obtain the 7th harmonic current source; The fifth harmonic current and the seventh harmonic current are added together to obtain an onshore power grid simulation model containing current source characteristic harmonics.

6. According to the method for simulation modeling of harmonic control of distributed power flow controller in offshore wind power collection scenario of claim 1, it is characterized in that: The circuit simulation model of step S5 includes two groups of DPFCs connected in series, one group controls the seventh harmonic and the other group controls the fifth harmonic. A bypass switch is set for each group of DPFCs to perform the switching-on / off operation on the DPFCs. One group of DPFCs includes three single-phase DPFC submodules, and each DPFC submodule includes an IGBT, a diode, a DC capacitor, a filter inductor, a filter capacitor and a single-phase double-winding coupling transformer.

7. According to the method for simulation modeling of harmonic control of distributed power flow controller in offshore wind power collection scenario of claim 1, it is characterized in that: In the step S6, the distributed power flow controller control circuit simulation model includes a control module and a PWM modulation module; S61, the control module samples the DC capacitor voltage Vdcse, the current IL flowing through the filter inductor and the output voltage Vse in the main circuit of the single-phase DPFC submodule; performs Fourier transformation on the output voltage Vse and the current IL flowing through the filter inductor to obtain the output voltage effective value Vse_Mag, the output voltage phase angle Vse_Phase, the effective value IL_Mag of the current flowing through the filter inductor and the phase angle IL_Phase of the current flowing through the filter inductor; performs Fourier transformation on the current ILine flowing into the DPFC to obtain the effective value ILineMag of the current flowing into the DPFC and the phase angle ILinePhase of the current flowing into the DPFC; calculates the sine value of the difference between the fundamental component of the output voltage phase angle Vse_Phase and the phase angle ILinePhase of the current flowing into the DPFC, and multiplies it with the fundamental component of the output voltage effective value Vse_Mag to obtain the fundamental component Vseq_1th of the q-axis component of the output voltage; Calculate the fundamental component angle and the 7th harmonic component phase angle. The time TIME multiplied by Π and then multiplied by 100 is ωt. ωt is multiplied by 1 and 7 respectively to get theta1 and theta7. The initial phase angle of the current flowing into the DPFC is added to theta1 to get the phase angle of the fundamental current flowing into the DPFC. Theta7 is the phase angle of the 7th harmonic current flowing into the DPFC. In the d-axis control loop, the DC voltage command value 1 is subtracted from the DC capacitor voltage Vdcse to obtain the difference between the DC capacitor voltage command value and the actual value, and multiplied by the charging time (i.e., charging is performed at 0.5s), and PI control is performed. Then, the difference between the output voltage d-axis component and the fundamental component is subtracted to obtain the difference between the output voltage d-axis component command value and the actual value, and multiplied by the charging time, and PI control is performed. Then, the difference between the output voltage d-axis component and the fundamental component of the d-axis component of the current flowing into the DPFC and the fundamental component of the q-axis component of the output voltage and the angular velocity and the filter capacitor are multiplied. The difference between the fundamental component of the d-axis component of the current flowing through the filter inductor and the actual value is obtained by subtracting the fundamental component of the d-axis component of the current flowing through the filter inductor from the command value, and then multiplying it by the charging time. The difference between the fundamental component of the d-axis component of the current flowing through the filter inductor and the actual value is subjected to PI control; the difference is then taken from the sum of the fundamental component of the d-axis component of the output voltage and the fundamental component of the q-axis component of the current flowing through the filter inductor and the product of the angular velocity and the filter inductance multiplication value ωL, and then divided by 1 to obtain the component Vd of the reference voltage on the d-axis; In the q-axis control loop, ZeroTime is the control amount of 0.1s after the charging time, that is, the q-axis command value before 0.6s is the fundamental component of the q-axis component of the output voltage, and the q-axis command value after 0.6s is 0. The difference between the fundamental component command value of the q-axis component of the output voltage and the actual value is obtained by subtracting the difference between the fundamental component command value of the q-axis component of the output voltage and the actual value and multiplying it with the charging time, and performing PI control; the fundamental component of the q-axis component of the current flowing into the DPFC minus the difference between the fundamental component command value of the q-axis component of the output voltage controlled by PI and the actual value is subtracted Remove the fundamental component of the d-axis component of the output voltage and the product of the angular velocity and the filter capacitor multiplication value ωC, then subtract the fundamental component of the q-axis component of the current flowing through the filter inductor to obtain the difference between the command value and the actual value of the fundamental component of the q-axis component of the current flowing through the filter inductor, then multiply it by the charging time, and perform PI control; then subtract the difference between the fundamental component of the q-axis component of the output voltage Vseq_1th and the fundamental component of the d-axis component of the current flowing through the filter inductor ILd_1th and the product of the angular velocity and the filter inductance multiplication value ωL, and then divide it by a constant 1 to obtain the reference voltage component Vq on the q-axis; The reference voltage component Vd on the d-axis and the reference voltage component Vq on the q-axis are subjected to inverse DQ transformation and multiplied by the charging time to obtain the fundamental component of the reference voltage, and the fundamental component of the reference voltage and the 7th harmonic component of the reference voltage are added to obtain the reference voltage VREF; S62, the PWM modulation module simulation model compares the modulation voltage Vref generated by the control module with the 7000 Hz triangular carrier to generate g1, g2, g3 and g4 trigger conduction signals, which trigger the IGBT in the main circuit of the single-phase DPFC sub-module to turn on or off.

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