Coordination control method of offshore wind power system and wind power converter

Abstract

The invention discloses a coordination control method of an offshore wind power system and a wind power converter. The coordination control method comprises the following steps: acquiring a direct current side voltage reference value and a direct current side voltage acquisition value of a grid side converter; adjusting the direct current side voltage reference value and the direct current side voltage acquisition value of the grid-side converter through a direct current voltage loop to obtain an alternating current voltage amplitude reference value; and generating a modulation signal based on the AC voltage amplitude reference value to control the grid-side converter. According to the method, the grid-side converter in the offshore wind power alternating current system is controlled in a grid construction mode, so that the alternating current voltage amplitude and the direct current voltage amplitude of the grid-side converter are cooperatively controlled, and relatively stable voltage is provided for the offshore wind power alternating current system.

Description

Technical Field

[0001] The present application relates to the technical field of offshore wind power, and in particular to a coordinated control method and a wind power converter for an offshore wind power system. Background Art

[0002] In order to improve the environment, build a low-carbon, environmentally friendly, energy-saving and emission-reducing energy system, improve my country's energy structure, reduce fossil energy consumption and greenhouse gas emissions, and promote the sustainable development of the national economy and society, vigorously developing new energy has become an inevitable choice.

[0003] my country has an extremely long continental coastline and abundant offshore wind resources. The research conclusion of the China Meteorological Administration shows that the technical development of wind energy resources in the sea area with a water depth of 5 to 50 meters using 6MW offshore wind turbines is 400 million kW. The deep sea area is larger and is less restricted by the planning of marine functional areas such as marine military, shipping routes, ports, and aquaculture, as well as the ecological red line areas designated by marine nature reserves. The potential for development is much higher than that of the near sea.

[0004] However, how to transmit offshore wind power to the land at low cost and high efficiency is a research hotspot, among which frequency division transmission and DC transmission are the current mainstream methods. In order to reduce the construction cost of DC transmission and improve the efficiency of DC transmission, some experts and scholars have proposed the use of diode rectification on the rectifier side of DC transmission. Diode rectification shows the characteristics of AC active power being positively correlated with AC voltage on the AC side, while active power is not related to AC frequency, which is very different from the characteristics of active power being related to frequency in traditional AC power grids. In addition, when dealing with micro AC power grids composed of multiple converters, traditional AC systems often use master-slave control or distributed control to control frequency. Due to the characteristics of diode rectification circuits, frequency distributed control methods cannot be applied, and frequency master-slave control has very high requirements on the power regulation capability of the main converter. Due to the randomness of wind power, it is obvious that wind power converters are not competent for the main converter tasks of master-slave control.

[0005] Therefore, for offshore wind power projects using diode rectification solutions, coordinated control of active power and frequency is a relatively large challenge. Summary of the invention

[0006] In view of this, the purpose of the present application is to provide a coordinated control method and wind power converter for an offshore wind power system, so as to adopt grid-type control for the grid-side converter in the offshore wind power AC system, so that its AC voltage amplitude and DC voltage amplitude are coordinated controlled to provide a relatively stable voltage for the offshore wind power AC system.

[0007] On one hand, the present application provides a coordinated control method for an offshore wind power system, the coordinated control method comprising:

[0008] Obtaining a DC side voltage reference value and a DC side voltage acquisition value of a grid-side converter;

[0009] The DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter are adjusted through a DC voltage loop to obtain an AC voltage amplitude reference value;

[0010] A modulation signal is generated based on an AC voltage amplitude reference value to control the grid-side converter.

[0011] In one embodiment, the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter are adjusted through a DC voltage loop to obtain an AC voltage amplitude reference value, including:

[0012] Based on the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter, a DC side voltage deviation value is obtained;

[0013] The DC side voltage deviation value is adjusted by the dead zone controller, the regulator and the limiter in sequence to obtain the AC voltage amplitude adjustment value;

[0014] After the AC voltage amplitude setting value and the AC voltage amplitude adjustment value are superimposed, the AC voltage amplitude reference value is obtained.

[0015] In one embodiment, the DC side voltage deviation value is obtained based on the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter, including:

[0016] The DC side voltage acquisition value of the grid-side converter is filtered and then subtracted from the DC side voltage reference value of the grid-side converter to obtain the DC side voltage deviation value.

[0017] In one embodiment, the DC side voltage deviation value is adjusted by the dead zone controller, the regulator and the limiter in sequence to obtain the AC voltage amplitude adjustment value, including:

[0018] After the DC side voltage deviation value is adjusted by the dead zone controller, a non-zero value to be adjusted is output;

[0019] After the value to be adjusted is adjusted by the regulator and the limiter in sequence, the AC voltage amplitude adjustment value is obtained.

[0020] In one embodiment, after the DC side voltage deviation value is adjusted by the dead zone controller, a non-zero value to be adjusted is output, including:

[0021] When the DC side voltage deviation value exceeds a preset threshold in the dead zone controller, a non-zero value to be adjusted is output.

[0022] In one embodiment, the preset threshold includes one or more groups of thresholds, and each group of thresholds includes a first threshold greater than zero and a second threshold less than zero.

[0023] In one embodiment, when the DC side voltage deviation value exceeds a preset threshold in the dead zone controller, a non-zero value to be adjusted is output, including:

[0024] When the DC side voltage deviation exceeds the preset threshold in the dead zone controller:

[0025] The portion of the DC side voltage deviation value exceeding the preset threshold is used as a non-zero value to be adjusted; or, the portion of the DC side voltage deviation value exceeding the preset threshold is multiplied by a preset coefficient and used as a non-zero value to be adjusted.

[0026] In one embodiment, generating a modulation signal based on an AC voltage amplitude reference value includes:

[0027] After the AC voltage amplitude reference value, the AC voltage acquisition value of the grid-side converter and the AC current acquisition value of the grid-side converter are passed through the voltage and current control link, a modulation voltage reference value is obtained;

[0028] A modulation signal is generated based on a modulation voltage reference value and a synchronization phase of the grid-side converter.

[0029] In one embodiment, before generating the modulation signal based on the modulation voltage reference value and the synchronous phase of the grid-side converter, the coordinated control method further includes:

[0030] The synchronous phase of the grid-side converter is obtained based on the reactive power reference value of the grid-side converter, the reactive power measured value of the grid-side converter and the frequency rated value of the grid-side converter.

[0031] On the other hand, the present application provides a wind power converter, which includes a machine-side converter, a grid-side converter and a controller. The controller includes a memory and a processor. The memory is configured to store a computer program. When the processor executes the computer program, it implements the coordinated control method of the offshore wind power system.

[0032] The coordinated control method and wind power converter of the offshore wind power system provided in the embodiment of the present application adopts grid-type control on the grid-side converter in the offshore wind power AC system, so that the AC voltage amplitude and the DC voltage amplitude are coordinated controlled, thereby providing a relatively stable voltage for the offshore wind power AC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of an offshore wind power system provided in an embodiment of the present application;

[0034] Figure 2 A schematic diagram of a coordinated control method for an offshore wind power system provided in an embodiment of the present application;

[0035] Figure 3A schematic diagram of a DC voltage loop control provided in an embodiment of the present application;

[0036] Figure 4 A schematic diagram of a voltage and current control link provided in an embodiment of the present application;

[0037] Figure 5 A control schematic diagram of a machine-side converter provided in an embodiment of the present application.

[0038] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer and more understandable, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0040] Definition of relevant variables involved in this application:

[0041] P MPPT : Maximum power tracking value

[0042] P m_e : Measured value of electromagnetic power of machine-side converter

[0043] θ vsc : Synchronous phase of DC transmission inverter

[0044] θ m_vsc : Synchronous phase of the machine-side converter

[0045] θ g_vsc : Synchronous phase of the grid-side converter

[0046] ω0: Rated operating angular frequency

[0047] ω g : Angular frequency of the grid-side converter

[0048] u abc : AC measurement grid-connected voltage of inverter

[0049] V g_dc_ref 、V g_dc : DC side voltage reference value and DC side voltage acquisition value of the grid-side converter

[0050] V dc_ref 、V dc : DC side voltage reference value and acquisition value of the inverter

[0051] Q g_ref , Q g: Reactive power reference value of grid-side converter and reactive power measured value of grid-side converter

[0052] U g_ref : AC voltage amplitude reference value of grid-side converter

[0053] U m_ref , U m : Voltage amplitude reference value and acquisition value of the machine-side converter

[0054] i m_dref 、i m_qref : Reference values ​​of d-axis and q-axis currents of the machine-side converter

[0055] i g_dref 、i g_qref : Reference values ​​of d-axis and q-axis currents of the grid-side converter

[0056] i dref 、i qref : Current reference values ​​of the d-axis and q-axis of the inverter

[0057] e m_dref 、e m_qref : D-axis and q-axis modulation voltage reference values ​​of the machine-side converter

[0058] e g_dref 、e g_qref : Reference values ​​of d-axis and q-axis modulation voltages of the grid-side converter

[0059] e dref 、e qref : D-axis and q-axis modulation voltage reference values ​​of the electric inverter

[0060] e m_a 、e m_b 、e m_c : Modulation voltage values ​​of the a-axis, b-axis and c-axis of the machine-side converter

[0061] e g_a 、e g_b 、e g_c : Modulation voltage values ​​of the grid-side converter a-axis, b-axis and c-axis

[0062] e a 、e b 、e c : Modulation voltage values ​​of inverter a-axis, b-axis and c-axis

[0063] like Figure 1As shown, the offshore wind power system provided in the embodiment of the present application includes a wind turbine set, a wind power converter, a transformer and a DC transmission converter connected in sequence, the wind power converter includes a machine-side converter and a grid-side converter, and the DC transmission converter includes a diode rectifier and an inverter connected to the diode rectifier through a DC transmission line.

[0064] Specifically, the offshore wind farm includes multiple wind turbines (such as wind turbines 1 to wind turbines n in the figure), each wind turbine is connected to a wind turbine transformer (not shown in the figure) through a corresponding wind power converter, and then connected to the AC system of offshore wind power. Each wind turbine includes a machine-side converter Q1 and a grid-side converter Q2 through a corresponding wind power converter. After the wind turbines are collected by the offshore wind power AC system, the voltage is increased again by transformer T1 and then connected to diode rectifier Q3. The DC power rectified by diode rectifier Q3 is transmitted to inverter Q4 through an offshore DC cable, and then inverted into AC power by inverter Q4 and transmitted to the onshore AC system.

[0065] In one embodiment, the offshore wind power system further comprises a controller, which may be integrated in the wind power converter or may be independent of the wind power converter. The controller may be configured to execute a coordinated control method for the offshore wind power system.

[0066] like Figure 2 As shown, in one embodiment, the coordinated control method of an offshore wind power system includes the following steps:

[0067] S11, obtaining a DC side voltage reference value and a DC side voltage acquisition value of the grid-side converter;

[0068] S12, adjusting the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter through a DC voltage loop to obtain an AC voltage amplitude reference value;

[0069] S13. Generate a modulation signal based on the AC voltage amplitude reference value to control the grid-side converter.

[0070] In one embodiment, the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter are adjusted through a DC voltage loop to obtain an AC voltage amplitude reference value, including:

[0071] Based on the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter, a DC side voltage deviation value is obtained;

[0072] The DC side voltage deviation value is adjusted by the dead zone controller, the regulator and the limiter in sequence to obtain an AC voltage amplitude adjustment value;

[0073] The AC voltage amplitude reference value is obtained by superimposing the AC voltage amplitude setting value and the AC voltage amplitude adjustment value.

[0074] The step of obtaining the DC side voltage deviation value based on the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter includes:

[0075] The DC side voltage collection value of the grid-side converter is filtered and then subtracted from the DC side voltage reference value of the grid-side converter to determine the DC side voltage deviation value.

[0076] The DC side voltage deviation value is adjusted by the dead zone controller, the regulator and the limiter in sequence to obtain the AC voltage amplitude adjustment value, including:

[0077] After the DC side voltage deviation value is adjusted by the dead zone controller, a non-zero value to be adjusted is output;

[0078] The AC voltage amplitude adjustment value is obtained by adjusting the value to be adjusted by the regulator and the limiter in sequence.

[0079] Specifically, when the DC side voltage deviation value exceeds the preset threshold value in the dead zone controller, a non-zero value to be adjusted is output. The preset threshold value includes a set of threshold values ​​or multiple sets of threshold values, and each set of threshold values ​​includes a first threshold value greater than zero and a second threshold value less than zero. In a specific implementation, the portion of the DC side voltage deviation value exceeding the preset threshold value is used as the non-zero value to be adjusted; or, the portion of the DC side voltage deviation value exceeding the preset threshold value is multiplied by a preset coefficient and used as the non-zero value to be adjusted.

[0080] The following combination Figure 3 Explanation of the DC voltage loop:

[0081] like Figure 3 As shown, the DC voltage loop input is the DC side voltage reference value V of the grid-side converter g_dc_ref And the DC side voltage acquisition value V of the grid-side converter g_dc .

[0082] The DC side voltage acquisition value V of the grid-side converter g_dc After passing through the low-pass filter LPF, it is compared with the DC side voltage reference value V g_dc_ref The output DC side voltage deviation value is △V g_dc .

[0083] DC side voltage deviation value △V g_dc Through the dead zone controller, regulator G V After the limiter Limit, the AC voltage amplitude adjustment value △U is obtained g .

[0084] AC voltage amplitude adjustment value △U g and AC voltage amplitude setting value U g_set Superposition, get the AC voltage amplitude reference value U g_ref .

[0085] Among them, the dead zone controller acts on the DC side voltage deviation value △V g_dc , when the DC side voltage deviation value △V g_dc After exceeding the preset threshold, a non-zero value to be adjusted will be output. The preset threshold can be a set of two values, one greater than zero and the other less than zero. g_dc After exceeding the preset threshold, the excess portion is used as the value to be adjusted. The preset threshold can also be multiple groups. When the DC side voltage deviation value △V g_dc After exceeding each set of thresholds, the excess portion is multiplied by a coefficient and added to the value to be adjusted.

[0086] In one embodiment, generating a modulation signal based on the AC voltage amplitude reference value includes:

[0087] The AC voltage amplitude reference value, the AC voltage collection value of the grid-side converter, and the AC current collection value of the grid-side converter are subjected to a voltage and current control link to obtain a modulation voltage reference value;

[0088] The modulation signal is generated based on the modulation voltage reference value and the synchronization phase of the grid-side converter.

[0089] The synchronous phase of the grid-side converter is obtained based on a reactive power reference value of the grid-side converter, an actual reactive power value of the grid-side converter, and a frequency rating value of the grid-side converter.

[0090] The following combination Figure 4 Explain the voltage and current control link:

[0091] like Figure 4 As shown, the voltage and current control link includes a voltage control outer loop and a current control inner loop.

[0092] The input of the voltage control outer loop includes the AC voltage amplitude reference value U output by the DC voltage loop g_ref And the AC voltage acquisition value U of the grid-side converter g_dq The AC voltage amplitude reference value U output by the DC voltage loop g_ref And the AC voltage acquisition value U of the grid-side converter g_dq , after the voltage control outer loop, the current reference value i of the grid-side converter is output g_dqref .

[0093] The input of the current control inner loop includes the current reference value i of the grid-side converter output by the voltage control outer loop g_dqref And the AC current collection value i of the grid-side converter g_dq The current reference value i of the grid-side converter g_dqref and the AC current collection value i of the grid-side converter g_dq , after passing through the current control inner loop, the modulation voltage reference value is output, that is, the d-axis and q-axis modulation voltage reference value e g_dref 、e g_qref .

[0094] The reactive power reference value Q of the grid-side converter is g_ref and the measured reactive power value Q of the grid-side converter g As input, through the reactive power-frequency controller G Q After that, the output frequency deviation value △ω of the grid-side converter is obtained g ; Output frequency deviation value △ω of the grid-side converter g Then add it to the rated frequency value ω0 of the grid-side converter to get the frequency output value ω of the grid-side converter. g ; Frequency output value of the grid-side converter ω g After the integration link, the synchronous phase θ of the grid-side converter is obtained g_vsc .

[0095] Combined d-axis and q-axis modulation voltage reference value e g_dref 、e g_qref The synchronous phase θ of the grid-side converter g_vsc After Park transformation, the modulation voltage values ​​of the grid-side converter a-axis, b-axis and c-axis are obtained. g_a 、e g_b 、e g_c , and then after modulation by the PWM modulation module, the PWM wave of the wind turbine grid-side converter, that is, the modulation signal, is generated.

[0096] Figure 5 This is the control diagram of the machine-side converter. Figure 5 As shown in the figure, the input of the machine-side converter is the maximum power tracking value P of the offshore wind turbine MPPT The measured value of electromagnetic power P of the machine-side converter m_e , maximum power tracking value P MPPT The measured value of electromagnetic power P of the machine-side converter m_e Power deviation value △P m Through control link After that, the d-axis current reference value i of the machine-side converter is obtained. m_dref .

[0097] Terminal voltage reference value U of the machine-side converter g_ref The collected value U of the machine-side converter gVoltage deviation value △U g Through the control link GU g After that, the q-axis current reference value i of the machine-side converter is obtained. m_qref .

[0098] The d-axis current reference value i of the machine-side converter m_dref and the q-axis current reference value i of the machine-side converter m_qref After the current control loop, the d-axis and q-axis modulation voltage reference values ​​e of the machine-side converter are obtained. m_dref 、e m_qref .

[0099] Combined with the d-axis and q-axis modulation voltage reference values ​​e of the machine-side converter m_dref 、e m_qref The synchronous phase θ of the generator-side converter m_vsc After Park transformation, the modulation voltage values ​​of the a-axis, b-axis and c-axis of the machine-side converter are obtained. m_a 、e m_b 、e m_c , and then after modulation by the PWM modulation module, the PWM wave of the wind turbine side converter is generated, that is, the modulation signal.

[0100] The above-mentioned DC transmission converter adopts constant DC voltage control. Among them, the AC frequency and voltage of the wind farm adopt distributed control, that is, all wind turbine converters jointly coordinate and control the AC frequency and voltage of the wind farm, each wind turbine adopts the same control strategy, the machine-side converter adopts wind turbine power tracking control, the grid-side converter adopts grid-type control, its AC voltage amplitude and DC voltage amplitude are coordinated and controlled, and its frequency adopts reactive power and frequency coordinated control, thereby providing relatively stable frequency and voltage for the offshore wind power AC system.

[0101] The embodiment of the present application controls the grid-side converter of the wind turbine to adjust the frequency of reactive power and the control mode of adjusting the AC voltage by DC voltage based on the positive correlation characteristic of active power and AC voltage presented by diode rectification on the AC side. Different from the traditional grid-type control mode, this grid-type converter uses DC voltage to control the AC voltage amplitude. Due to the dynamic process, the DC side voltage amplitude of the converter is strongly correlated with the transmission power. At the same time, the offshore AC voltage amplitude in this application is strongly correlated with the active transmission amount. Therefore, the control mode of this scheme coordinates the balance between the input and output of wind power well, and provides a stable AC voltage for the offshore wind power AC system.

[0102] An embodiment of the present application also provides a wind power converter, which includes a controller, the controller includes a memory and a processor, the memory is configured to store a computer program, and when the processor executes the computer program, it implements the above-mentioned coordinated control method of the offshore wind power system.

[0103] The preferred embodiments of the present application are described above with reference to the accompanying drawings, but the scope of the present application is not limited thereby. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present application shall be within the scope of the present application.

Claims

1. A coordinated control method for an offshore wind power system, characterized in that: The coordinated control method comprises: Obtaining a DC side voltage reference value and a DC side voltage acquisition value of a grid-side converter; The DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter are adjusted through a DC voltage loop to obtain an AC voltage amplitude reference value; A modulation signal is generated based on the AC voltage amplitude reference value to control the grid-side converter.

2. The coordinated control method for an offshore wind power system according to claim 1, characterized in that: The step of adjusting the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter through a DC voltage loop to obtain an AC voltage amplitude reference value includes: Based on the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter, a DC side voltage deviation value is obtained; The DC side voltage deviation value is adjusted by the dead zone controller, the regulator and the limiter in sequence to obtain an AC voltage amplitude adjustment value; The AC voltage amplitude reference value is obtained by superimposing the AC voltage amplitude setting value and the AC voltage amplitude adjustment value.

3. The coordinated control method for an offshore wind power system according to claim 2, characterized in that: The obtaining of the DC side voltage deviation value based on the DC side voltage reference value and the DC side voltage acquisition value of the grid-side converter includes: The DC side voltage deviation value is obtained by subtracting the DC side voltage collection value of the grid-side converter from the DC side voltage reference value of the grid-side converter after passing through a filter.

4. The coordinated control method for an offshore wind power system according to claim 2, characterized in that: The DC side voltage deviation value is adjusted by the dead zone controller, the regulator and the limiter in sequence to obtain the AC voltage amplitude adjustment value, including: After the DC side voltage deviation value is adjusted by the dead zone controller, a non-zero value to be adjusted is output; The AC voltage amplitude adjustment value is obtained by adjusting the value to be adjusted by the regulator and the limiter in sequence.

5. The coordinated control method for an offshore wind power system according to claim 4, characterized in that: After the DC side voltage deviation value is adjusted by the dead zone controller, a non-zero value to be adjusted is output, including: When the DC side voltage deviation value exceeds a preset threshold in the dead zone controller, a non-zero value to be adjusted is output.

6. The coordinated control method for an offshore wind power system according to claim 5, characterized in that: The preset threshold includes one set of thresholds or multiple sets of thresholds, and each set of thresholds includes a first threshold greater than zero and a second threshold less than zero.

7. The coordinated control method for an offshore wind power system according to claim 5, characterized in that: When the DC side voltage deviation value exceeds a preset threshold value in the dead zone controller, a non-zero value to be adjusted is output, including: When the DC side voltage deviation value exceeds a preset threshold value in the dead zone controller: The portion of the DC side voltage deviation value exceeding the preset threshold is used as the non-zero value to be adjusted; or, the portion of the DC side voltage deviation value exceeding the preset threshold is multiplied by a preset coefficient and used as the non-zero value to be adjusted.

8. The coordinated control method for an offshore wind power system according to claim 1, characterized in that: The generating a modulation signal based on the AC voltage amplitude reference value comprises: The AC voltage amplitude reference value, the AC voltage collection value of the grid-side converter, and the AC current collection value of the grid-side converter are subjected to a voltage and current control link to obtain a modulation voltage reference value; The modulation signal is generated based on the modulation voltage reference value and the synchronization phase of the grid-side converter.

9. The coordinated control method for an offshore wind power system according to claim 8, characterized in that: Before generating the modulation signal based on the modulation voltage reference value and the synchronous phase of the grid-side converter, the coordinated control method further includes: The synchronous phase of the grid-side converter is obtained based on the reactive power reference value of the grid-side converter, the reactive power measured value of the grid-side converter and the frequency rated value of the grid-side converter.

10. A wind power converter, characterized in that: The wind power converter includes a machine-side converter, a grid-side converter and a controller. The controller includes a memory and a processor. The memory is configured to store a computer program. When the processor executes the computer program, it implements the coordinated control method of the offshore wind power system according to any one of claims 1 to 9.

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