CN103208816A - Power collection and transmission system for wind power plant and voltage control method for alternating current generatrix of power collection and transmission system - Google Patents

Abstract

The invention discloses a power collection and transmission system of a wind farm, comprising: an AC bus, a wind power generating set, a rectification station and an inverter station; the rectification station includes a rectifier and a converter transformer; the DC side of the rectifier and the DC side of the inverter station The AC side of the rectifier is connected to one side of the converter transformer through the commutation inductor, and the other side of the converter transformer is connected to the AC bus and grounded through the capacitor. The invention also discloses the AC bus voltage control method of the above-mentioned system. By using the two control dimensions of the rectifier on the wind farm side, the AC bus voltage of the system is controlled as a whole, including the voltage amplitude and frequency, to ensure that the wind farm power collection system The stability of the AC voltage reduces the harmonic components of the AC system of the wind farm.

Description

A wind farm power collection and transmission system and its AC bus voltage control method

technical field

The invention belongs to the technical field of power system transmission and distribution, and in particular relates to a power collection and transmission system of a wind farm and an AC bus voltage control method thereof.

Background technique

With energy shortages and environmental changes, wind energy has received great attention. It is necessary to use science and technology to develop and utilize wind energy. Wind power is one of the good ways. The instability and uncertainty of wind energy, in order to ensure the safe and stable operation of the national grid, the safe and stable grid connection of wind farms has always been a technical bottleneck and problem restricting the development of wind power. question.

At present, there are mainly the following methods for wind farm grid connection at home and abroad: (1) The wind farm power collection system is directly connected to the grid through AC lines (cables or overhead lines); (2) The wind farm power collection system passes through rectifiers, DC lines (cable or overhead line), inverter, that is, flexible DC transmission technology connected to the AC grid. The second method, that is, the grid connection through flexible DC transmission has the following advantages over the first AC line direct grid connection: 1. It can realize long-distance power transmission; 2. It can be controlled by rectifiers and inverters. For AC systems Provide reactive power support, which is of great significance to maintain the voltage stability of the AC system; 3. The wind farm power collection system is relatively independent from the AC system, and AC faults will not be directly transmitted.

When a wind farm is connected to the grid using flexible DC transmission, it will encounter a problem, that is, the stability of the busbar voltage of the wind farm power collection system. The wind farm power collection system is relatively independent of the AC system. It is difficult to connect the voltage of the wind farm power collection system with the external power grid, and it is only connected with the internal wind turbine and the rectifier of the flexible direct current transmission system. The technology of controlling the voltage of the collector system by wind turbines is not perfect yet. In addition, the uncontrollability and uncertainty of wind energy itself make the output and electrical characteristics of wind turbines not very stable. Therefore, a flexible DC It is more appropriate and appropriate to use the rectifier in the transmission system to control the voltage of the wind farm power collection system.

Huang Chuan, Wang Zhixin, Wang Guoqiang et al. published a paper titled "Simulation Research on Offshore Wind Farm Three-level VSC-HVDC (Voltage Source Type Direct Current Transmission Technology) System (Power Electronics Technology, 2011, 45(8), 89-92) A method for the busbar voltage of the wind farm power collection system is proposed in the paper, which controls the AC voltage of the power collection system by controlling the output reactive power of the wind farm side rectifier. Although this method can control the AC voltage amplitude of the wind farm collector system to a certain extent, it cannot control the frequency of the AC voltage because it only uses one dimension of the wind farm rectifier to control the AC voltage. The AC voltage of the wind farm collector system is closely related to the safe and stable operation of the entire wind farm. The instability of the AC voltage frequency of the collector system will be transmitted in the AC line inside the wind farm, increasing the harmonic components of the AC system, and the harmonic components will be further transmitted to the wind farm. Inside the wind turbine, the internal winding of the wind motor generates heat, which affects the service life of electrical components and causes great damage to the wind motor. In addition, harmonics will also bring more losses, reduce the output energy efficiency of the wind farm, and also affect the wind farm. stable operation.

Contents of the invention

Aiming at the above-mentioned technical defects in the prior art, the present invention provides a wind farm power collection and transmission system and its AC bus voltage control method, which can keep the system AC voltage frequency stable and reduce wind farm harmonic components.

A power collection and transmission system for a wind farm, comprising: an AC bus, a wind power generator, a rectifier station and an inverter station; the wind power generator includes a plurality of wind generators, the wind generators are connected to the AC bus, and the The AC side is connected to the AC busbar, the DC side of the rectifier station is connected to the DC side of the inverter station, and the AC side of the inverter station is connected to the AC grid.

The rectifier station includes a rectifier and a converter transformer; the DC side of the rectifier is connected to the DC side of the inverter station, the AC side of the rectifier is connected to one side of the converter transformer through a commutation inductor, and the other side of the converter transformer is connected to the converter transformer. The AC bus is connected and connected to ground through a capacitor.

The rectifier adopts a three-phase six-leg structure, and each bridge arm is formed by cascading several IGBTs.

The AC bus voltage control method of the above-mentioned power collection and transmission system includes the following steps:

(1) Collect the three-phase input current I _a ~ I _c of the rectifier station, the three-phase branch current I _sa ~ I _sc flowing into the converter transformer, and the three-phase bus voltage U _a ~ U _c of the AC bus;

(2) Perform dq transformation on the three-phase branch currents I _sa to I _sc , three-phase input currents I _a to I _c and three-phase bus voltages U _a to U _c respectively to obtain the d-axis of the three-phase branch currents Component I _sd and q-axis component I _sq , d-axis component I _d and q-axis component I _q of three-phase input current, d-axis component U _d and q-axis component U _q of three-phase bus voltage;

(3) Subtract the d-axis component U d and the q-axis component U _q of the three-phase bus voltage from the given d-axis voltage control variable U _dref and _q -axis voltage control variable U _qref respectively to obtain the d-axis voltage error signal ΔU _d and q-axis voltage error signal ΔU _q ;

(4) Perform PI adjustment and feed-forward decoupling compensation on the d-axis voltage error signal ΔU _d and the q-axis voltage error signal ΔU _q respectively to obtain the d-axis current control amount I _dref and the q-axis current control amount I _qref ;

(5) The d-axis component I sd and the q-axis component I _sq of the three-phase branch current are respectively subtracted from the d-axis current control quantity I _dref and the _q -axis current control quantity I _qref to obtain the d-axis current error signal ΔI _d and q axis current error signal ΔI _q ;

(6) Perform PI adjustment and feed-forward decoupling compensation on the d-axis current error signal ΔI _d and the q-axis current error signal ΔI _q respectively, to obtain the d-axis modulation signal M _d and the q-axis modulation signal M _q ;

(7) Perform dq inverse transformation on the d-axis modulation signal M _d and the q-axis modulation signal M _q to obtain three-phase modulation signals M _a ~ M _c , and then according to the three-phase modulation signals Ma _~ M _c through SPWM (sine Wave pulse width modulation) technology generates a set of PWM signals to control the rectifier.

In the step (4), PI adjustment and feed-forward decoupling compensation are performed on the d-axis voltage error signal ΔU _d and the q-axis voltage error signal ΔU _q according to the following formula:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; dref</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; Ld</span>}}$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; qref</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="p"\; filenames="HDA00003018275100021.png"\; state="\{\{state\}\}">p</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}}$

Among them: s is the Laplacian operator, K _p1 and K _p2 are given proportional coefficients, K _i1 and K _i2 are given integral coefficients, I _Ld and I _Lq are d-axis current feedforward compensation amounts and the amount of q-axis current feed-forward compensation.

The d-axis current feed-forward compensation amount I _Ld and the q-axis current feed-forward compensation amount I _Lq are obtained according to the following formula:

I _Ld =ωCU _q

I _Lq ＝ _ωCUd

Where: ω is the angular frequency of the AC bus voltage and ω=2πf, f=50Hz, and C is the capacitance of the capacitor.

In the described step (6), PI regulation and feed-forward decoupling compensation are carried out to the d-axis current error signal ΔI _d and the q-axis current error signal ΔI _q according to the following formula:

${\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; Ld</span>}}<span\; class="notranslate">\; ]</span>}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}}$

${\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}}<span\; class="notranslate">\; ]</span>}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}}$

Among them: s is the Laplacian operator, K _p3 and K _p4 are given proportional coefficients, K _i3 and K _i4 are given integral coefficients, U _Ld and U _Lq are d-axis voltage feedforward compensation amounts and q-axis voltage feed-forward compensation, U _dc is the DC bus voltage of the rectifier station.

The d-axis voltage feed-forward compensation amount U _Ld and the q-axis voltage feed-forward compensation amount U _Lq are obtained according to the following formula:

U _Ld = ωLI _sq

U _Lq =ωLI _sd

Where: ω is the angular frequency of the AC bus voltage and ω=2πf, f=50Hz, L is the total inductance value of the commutation inductance and the leakage inductance of the commutation transformer.

When a wind farm is connected to the grid using flexible DC transmission, it is difficult to control the voltage of the AC bus of the wind farm's power collection system, and the frequency is also difficult to stabilize. important role. By adopting the AC bus voltage control method of the present invention, the two control dimensions of the wind farm side rectifier can be fully used to control the AC bus voltage of the system as a whole, including the voltage amplitude and frequency, so the beneficial technical effects of the present invention lie in:

(1) To ensure the stability of the AC voltage of the wind farm power collection system, it can reduce the harmonic components of the wind farm AC system, prevent the damage caused by the harmonic components to the inside of the wind farm and even the wind turbines, and reduce the damage caused by the harmonic components. Damage to the electrical components inside the wind turbine, including generators, transformers, transmission lines and corresponding electrical components, so as to ensure the life and normal operation of electrical equipment.

(2) Reducing the harmonic component of the AC system of the wind farm can further reduce the loss, reduce the additional loss of the generator, the transformer and the line due to the harmonic component, reduce the power loss of the harmonic component in the electrical components, and make full use of the equipment Capacity, ensure the utilization rate of equipment, and improve the output energy efficiency of wind farms.

(3) Since the wind power control system needs to collect the AC voltage of the wind power collection system as the input signal quantity, maintaining the stability of the voltage amplitude and frequency of the wind power collection system is also of great help to the smooth operation of the wind power control system. Thus ensuring the safe and stable operation of the wind farm and the entire wind power grid-connected system.

Description of drawings

Fig. 1 is a schematic structural diagram of the power collection and transmission system of the present invention.

Fig. 2 is a schematic flowchart of the principle flow of the system AC bus voltage control method of the present invention.

Fig. 3 is a schematic diagram of the waveform of the AC bus voltage of the system under the control method of the present invention.

Fig. 4 is a schematic diagram comparing the harmonic components of the AC bus voltage of the system under the prior art and the method of the present invention.

Detailed ways

In order to describe the present invention more specifically, the technical solution and its control method of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, a power collection and transmission system for a wind farm includes: an AC busbar, a wind turbine, a rectifier station, and an inverter station; A current collector, a collector inductor L _j and a collector transformer T _j with a connection mode of Δ/Y are connected to the AC bus;

The rectifier station includes a rectifier and a converter transformer T; the rectifier adopts a three-phase six-leg structure, and each bridge arm is formed by cascading several IGBTs; the DC side of the rectifier is connected to the DC side of the inverter station through a transmission line, and the rectifier The AC side of the transformer T is connected to one side of the converter transformer T with the connection mode Y/Δ through the commutation inductance L, and the other side of the converter transformer T is connected to the AC bus and grounded through the capacitor C.

The inverter station adopts an inverter with a three-phase six-leg structure, and each bridge arm is formed by cascading several IGBTs; the DC side of the rectifier and the DC side of the inverter are connected in parallel with a DC bus capacitor, and the DC side of the rectifier The voltage at both ends is the DC bus voltage U _dc of the rectifier station. The AC side of the inverter is connected to the AC grid through the transmission inductance L _s and the transmission transformer T _s with a connection mode of Δ/Y.

As shown in Figure 2, the AC bus voltage control method of the above-mentioned power collection and transmission system includes the following steps:

(1) Use the voltage and current Hall sensors to collect the three-phase input current I _a ~ I _c of the rectifier station, the three-phase branch current I _sa ~ I _sc flowing into the converter transformer T, and the three-phase bus voltage U _a ~ I sc of the AC bus U _c .

(2) Perform dq transformation on the three-phase branch currents I _sa ~ I _sc , three-phase input currents I _a ~ I _c and three-phase bus voltages U _a ~ U _c respectively to obtain the d-axis component I _sd of the three-phase branch currents and q-axis component I _sq , d-axis component I _d and q-axis component I _q of the three-phase input current, d-axis component U _d and q-axis component U _q of the three-phase bus voltage;

The dq transformation matrix is as follows:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; abc</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; dq</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\end{array}\right]$

Where: θ is the phase of the AC bus voltage and θ=ωt, ω is the angular frequency of the AC bus voltage and ω=2πf, f=50Hz, t is time.

(3) Subtract the d-axis component U d and the q-axis component U _q of the three-phase bus voltage from the given d-axis voltage control variable U _dref and _q -axis voltage control variable U _qref respectively to obtain the d-axis voltage error signal ΔU _d and the q-axis voltage error signal ΔU _q ; in this embodiment, U _qref =0,

(4) Perform PI adjustment and feed-forward decoupling compensation on the d-axis voltage error signal ΔU _d and q-axis voltage error signal ΔU _q respectively according to the following formula to obtain the d-axis current control value I _dref and the q-axis current control value I _qref ; $I_{\mathrm{dref}}=(K_{p1}+\frac{K_{i1}}{\mathrm{the\; s}})\mathrm{\&Delta;}{u}_d+I_d-I_{\mathrm{Ld}}$ I _Ld =ωCU _q $I_{\mathrm{qref}}=({\mathrm{<figure-callout\; id="2"\; label="K\; p"\; filenames="HDA00003018275100021.png"\; state="\{\{state\}\}">K</figure-callout>}}_p+\frac{{\mathrm{<figure-callout\; id="2"\; label="K\; i"\; filenames="HDA00003018275100021.png"\; state="\{\{state\}\}">K</figure-callout>}}_i}{\mathrm{the\; s}})\mathrm{\&Delta;}{u}_q+I_q+I_Q$ I _Lq ＝ _ωCUd

Among them: s is the Laplacian operator, K _p1 and K _p2 are given proportional coefficients, K _i1 and K _i2 are given integral coefficients, I _Ld and I _Lq are d-axis current feedforward compensation amounts and q-axis current feed-forward compensation, C is the capacitance of the capacitor; in this embodiment, K _p1 =K _p2 =0.8, K _i1 =20, K _i2 =100, C=2×10 ^-3 F.

(5) Subtract the d-axis component I sd and q-axis component I _sq of the three-phase branch current from the d-axis current control quantity I _dref and the q-axis current _control quantity I _qref respectively, and obtain the d-axis current error signals ΔI _d and q Shaft current error signal ΔI _q .

(6) Perform PI adjustment and feed-forward decoupling compensation on the d-axis current error signal ΔI _d and the q-axis current error signal ΔI _q according to the following formula, respectively, to obtain the d-axis modulation signal M _d and the q-axis modulation signal M _q ; $m_d=\frac{2[(K_{p3}+\frac{K_{i3}}{\mathrm{the\; s}})\mathrm{\&Delta;}{I}_d+u_d-u_{\mathrm{Ld}}]}{u_{\mathrm{dc}}}$ U _Ld = ωLI _sq $m_q=\frac{2[(K_{p4}+\frac{K_{i4}}{\mathrm{the\; s}})\mathrm{\&Delta;}{I}_q+u_q+u_Q]}{u_{\mathrm{dc}}}$ U _Lq =ωLI _sd

Among them: K _p3 and K _p4 are given proportional coefficients, K _i3 and K _i4 are given integral coefficients, U _Ld and U _Lq are d-axis voltage feedforward compensation amount and q-axis voltage feedforward compensation amount, L is the total inductance value of the converter inductance and the leakage inductance of the converter transformer, U _dc is the DC bus voltage of the rectifier station; in this embodiment, K _p3 =K _p4 =5.2, K _i3 =K _i4 =50, C=5.2 ×10 ^-3 F, U _dc = 100 kV.

(7) Perform dq inverse transformation on the d-axis modulation signal M _d and the q-axis modulation signal M _q to obtain three-phase modulation signals M _a ~ M _c , and then generate a set of PWM through SPWM technology according to the three-phase modulation signals M _a ~ M _c The signal is used to control the switching of each IGBT in the rectifier.

The dq inverse transformation matrix is as follows:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; dq</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; abc</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\\ \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\end{array}\right]$

In this embodiment, the wind farm is integrated into the power grid through the flexible DC transmission system. The wind farm power collection system is connected to the rectifier in the flexible DC transmission system, connected to the inverter through a 100km DC transmission cable, and then connected to the AC grid. The system rectifier controls the AC bus voltage amplitude and frequency of the wind farm collector system through two control dimensions, and the inverter controls the DC voltage and system output reactive power of the flexible direct current transmission system through two control dimensions. It is expected that the effective value of the AC bus line voltage is 35kV, and the transformation ratio of the converter transformer T is 35/110kV. The output active power P=100MW and the output reactive power Q=0Mvar of the entire wind farm power collection and transmission system.

Fig. 3 is a waveform diagram of the three-phase AC bus voltage of the wind farm power collection system after adopting the method for controlling the AC bus voltage of the flexible direct current transmission wind power grid-connected power collection system according to the present embodiment. It can be seen from Fig. 3 that after using the control method of this embodiment for the AC bus voltage of the flexible DC transmission wind power grid-connected collector system, the three-phase AC voltage amplitude and frequency are consistent with the expected values, and the voltage amplitude and frequency are effectively controlled , The three-phase sinusoidal waveform is clear, the phase difference is 120 degrees, and the AC bus voltage control of the wind power grid-connected collector system is stable.

Fig. 4 is a schematic diagram comparing the THD value of the harmonic component of the AC bus voltage of the power collecting system using the existing control method and the method for controlling the AC bus voltage of the power collecting system in this embodiment. The two curves in Fig. 4 respectively represent the THD values of the harmonic components of the AC busbar voltage for the grid-connected power collection system of the flexible direct current transmission wind farm using the existing control method and the present embodiment. It can be seen from Fig. 4 that the THD value of the harmonic component of the AC bus voltage of the collector system obtained by the existing control method is about 0.042 and fluctuates greatly, and the harmonic component of the AC bus voltage of the collector system obtained by this embodiment The component THD value is about 0.017 and is relatively stable around the average value. The harmonic components have been suppressed and reduced to a large extent, which reduces the influence of harmonics on the wind farm and the entire grid-connected system, reduces additional losses, and improves The energy efficiency of wind power grid-connected transmission ensures the safe and stable operation of the system.

Claims (7)

1. A collection and transmission system of a wind farm, comprising: an AC bus, a wind generator, a rectifier station and an inverter station; the wind generator includes a plurality of wind generators, and the wind generator is connected to the AC bus, rectified The AC side of the station is connected to the AC busbar, the DC side of the rectification station is connected to the DC side of the inverter station, and the AC side of the inverter station is connected to the AC grid; it is characterized in that: The rectifier station includes a rectifier and a converter transformer; the DC side of the rectifier is connected to the DC side of the inverter station, the AC side of the rectifier is connected to one side of the converter transformer through a commutation inductor, and the other side of the converter transformer is connected to the converter transformer. The AC bus is connected and connected to ground through a capacitor. 2. The power collection and transmission system according to claim 1, wherein the rectifier adopts a three-phase six-leg structure, and each bridge arm is formed by cascading several IGBTs. 3. A method for controlling the AC bus voltage of the power collection and transmission system as claimed in claim 1 or 2, comprising the steps of: (1) Collect the three-phase input current I _a ~ I _c of the rectifier station, the three-phase branch current I _sa ~ I _sc flowing into the converter transformer, and the three-phase bus voltage U _a ~ U _c of the AC bus; (2) Perform dq transformation on the three-phase branch currents I _sa to I _sc , three-phase input currents I _a to I _c and three-phase bus voltages U _a to U _c respectively to obtain the d-axis of the three-phase branch currents Component I _sd and q-axis component I _sq , d-axis component I _d and q-axis component I _q of three-phase input current, d-axis component U _d and q-axis component U _q of three-phase bus voltage; (3) Subtract the d-axis component U d and the q-axis component U _q of the three-phase bus voltage from the given d-axis voltage control variable U _dref and _q -axis voltage control variable U _qref respectively to obtain the d-axis voltage error signal ΔU _d and q-axis voltage error signal ΔU _q ; (4) Perform PI adjustment and feed-forward decoupling compensation on the d-axis voltage error signal ΔU _d and the q-axis voltage error signal ΔU _q respectively to obtain the d-axis current control amount I _dref and the q-axis current control amount I _qref ; (5) The d-axis component I sd and the q-axis component I _sq of the three-phase branch current are respectively subtracted from the d-axis current control quantity I _dref and the _q -axis current control quantity I _qref to obtain the d-axis current error signal ΔI _d and q axis current error signal ΔI _q ; (6) Perform PI adjustment and feed-forward decoupling compensation on the d-axis current error signal ΔI _d and the q-axis current error signal ΔI _q respectively, to obtain the d-axis modulation signal M _d and the q-axis modulation signal M _q ; (7) Perform dq inverse transformation on the d-axis modulation signal M _d and the q-axis modulation signal M _q to obtain the three-phase modulation signals M _a ~ M _c , and then generate the three-phase modulation signals Ma _~ M _c through SPWM technology A set of PWM signals to control the rectifier. 4. The AC bus voltage control method according to claim 3, characterized in that: in the step (4), the d-axis voltage error signal ΔU _d and _{the q-} axis voltage error signal ΔU _q are PI adjusted according to the following formula and feed-forward decoupling compensation: ${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; dref</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; Ld</span>}}$ ${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; qref</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}}$ Among them: s is the Laplacian operator, K _p1 and K _p2 are given proportional coefficients, K _i1 and K _i2 are given integral coefficients, I _Ld and I _Lq are d-axis current feedforward compensation amounts and the amount of q-axis current feed-forward compensation. 5. The AC bus voltage control method according to claim 4, characterized in that: the d-axis current feed-forward compensation amount I _Ld and the q-axis current feed-forward compensation amount I _Lq are obtained according to the following formula: I _Ld =ωCU _q I _Lq ＝ _ωCUd Where: ω is the angular frequency of the AC bus voltage and ω=2πf, f=50Hz, and C is the capacitance of the capacitor. 6. The AC bus voltage control method according to claim 3, characterized in that: in the described step (6), PI adjustment is carried out to the d-axis current error signal ΔI _d and the q-axis current error signal ΔI _q according to the following formula and feed-forward decoupling compensation: ${\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; Ld</span>}}<span\; class="notranslate">\; ]</span>}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}}$ ${\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}}<span\; class="notranslate">\; ]</span>}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}}$ Among them: s is the Laplacian operator, K _p3 and K _p4 are given proportional coefficients, K _i3 and K _i4 are given integral coefficients, U _Ld and U _Lq are d-axis voltage feedforward compensation amounts and q-axis voltage feed-forward compensation, U _dc is the DC bus voltage of the rectifier station. 7. The AC bus voltage control method according to claim 6, characterized in that: the d-axis voltage feed-forward compensation amount U _Ld and the q-axis voltage feed-forward compensation amount U _Lq are obtained according to the following formula: U _Ld = ωLI _sq U _Lq =ωLI _sd Where: ω is the angular frequency of the AC bus voltage and ω=2πf, f=50Hz, L is the total inductance value of the commutation inductance and the leakage inductance of the commutation transformer.

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