A series type offshore wind power direct current power collection system voltage limiting control method

Abstract

This invention relates to a voltage limiting control method for a series-type offshore wind power DC collector system, comprising: superimposing a low-voltage DC link voltage control loop on the power control loop of the wind turbine generator-side converter, and obtaining a reference value for the d-axis component of the generator-side converter voltage. umsd_ref and q-axis component reference value umsq_ref The control signal for the generator-side converter is generated through sinusoidal pulse width modulation to maintain stable low-voltage DC link voltage while ensuring stable power output. The grid-side converter of the wind turbine adopts voltage / frequency control to obtain the d-axis reference value of the grid-side converter output voltage. uod _ ref and q-axis reference value uoq _ ref The grid-side converter control signal is generated by sinusoidal pulse width modulation. By setting the d-axis setpoint of the grid-side converter output voltage, the AC output voltage of the grid-side converter is limited, thereby controlling the DC output voltage of the wind turbine generator within the limit value.

Description

Technical Field

[0001] This invention relates to the field of offshore wind power technology, and in particular to a voltage limiting control method for a series-type offshore wind power DC collector system. Background Technology

[0002] Compared with AC aggregation, offshore wind power DC aggregation has a longer transmission distance, lower losses, no need for reactive power compensation, and no frequency stability issues, making it highly competitive in scenarios involving large-scale offshore wind power aggregation and long-distance transmission.

[0003] The topology of the series-type offshore wind power DC collector system is shown in the attached figure. Figure 1 As shown, several offshore DC wind turbines are connected in series to raise the voltage level to the high-voltage DC transmission voltage level. The voltage is then connected to an onshore converter station via a high-voltage DC transmission line and finally integrated into the onshore AC power grid. This topology eliminates the need for large-capacity, high-ratio DC converters and offshore platforms, significantly reducing cable length and lowering investment costs and construction difficulty. However, due to the series structure, current coupling exists between the offshore DC wind turbines. If the wind energy captured by each turbine differs significantly, without limitation, the DC voltage output at its ports will exceed the equipment's tolerance value, affecting the safe and stable operation of the system.

[0004] Therefore, voltage limiting control needs to be added to offshore DC wind turbines to ensure that the output DC voltage of the turbine is within a safe threshold. Traditional voltage limiting strategies set a voltage limit value. When the output DC voltage of the turbine exceeds this value, the turbine enters a voltage limiting mode, and an output DC voltage control loop is superimposed on the power control outer loop of the turbine's generator side converter. Summary of the Invention

[0005] The purpose of this invention is to propose a voltage limiting control method for a series-type offshore wind power DC collector system to solve the problems existing in the prior art. This invention has voltage limiting capability and, compared with traditional voltage limiting control strategies, output DC voltage fluctuation is smaller, thus achieving better control effect.

[0006] To achieve the above objectives, the present invention provides the following solution: A voltage limiting control method for a series-type offshore wind power DC collector system includes: The wind turbine generator-side converter adds a low-voltage DC link voltage control loop to the power control stage to obtain the reference value of the d-axis component of the generator-side converter voltage. umsd_ref Reference value of q-axis component of converter voltage on the machine side umsq_ref ,Will umsd_ref , umsq_ref The control signal for the machine-side converter is generated by sinusoidal pulse width modulation. The grid-side converter of the wind turbine adopts voltage / frequency control to obtain the d-axis reference value of the grid-side converter output voltage. uod _ ref q-axis reference value of grid-side converter output voltage uoq _ ref ,Will uod _ ref , uoq _ ref The grid-side converter control signal is generated by sinusoidal pulse width modulation.

[0007] Optionally, obtain the reference value of the d-axis component of the generator-side converter voltage. umsd_ref include: Based on the power control loop superimposed with a low-voltage DC voltage control loop, a reference value for the d-axis component of the inner loop current of the machine-side converter is generated. imsd_ref ; Reference value of the d-axis component of the inner loop current of the machine-side converter imsd_ref With the d-axis component of the machine-side converter current imsd The difference is then input to the PI controller, based on the inductive reactance of the machine-side converter. ωrLms q-axis component of the current in the machine-side converter imsq d-axis component of the converter voltage on the machine side umsd Obtain the reference value of the d-axis component of the converter voltage on the machine side. umsd_ref .

[0008] Optionally, the reference value of the d-axis component of the inner loop current of the machine-side converter. imsd_ref for: in, Kp _ d , Ti _ d These are the proportional and integral coefficients of the d-axis power control element of the machine-side converter, respectively. Kp_LV , Ti_ LV These are the proportional and integral coefficients of the d-axis low-voltage DC voltage control loop for the machine-side converter. VLV This refers to the low-voltage DC link voltage of the wind turbine generator. The active power output of the permanent magnet synchronous generator (PMSG) is... This is a reference value for the active power output of a permanent magnet synchronous generator (PMSG). This is a reference value for the low-voltage DC link voltage.

[0009] Optionally, obtain the reference value of the q-axis component of the generator-side converter voltage. umsq_ref include: The output AC voltage amplitude of the permanent magnet synchronous generator is Ums Given a reference value Ums _ ref ; Will Ums Compared with reference value Ums _ ref After subtraction, the PI controller generates a reference value for the q-axis component of the machine-side converter current. ; Reference value of q-axis component of machine-side converter current q-axis component of the current of the machine-side converter imsq The difference is then input to the PI controller, based on the inductive reactance of the machine-side converter. ωrLms d-axis component of the current in the machine-side converter imsd q-axis component of the machine-side converter voltage umsq Obtain the reference value of the q-axis component of the converter voltage on the machine side. umsq_ref .

[0010] Optionally, the reference value of the q-axis component of the machine-side converter current. for: in, K p_q , T i_q These are the proportional and integral coefficients of the outer loop of the q-axis voltage of the machine-side converter in the power transmission stage.

[0011] Optionally, obtain the d-axis reference value of the grid-side converter output voltage. uod _ ref include: Assume the DC voltage limit value of the offshore DC wind turbine output is VWT _ limit Then the given value of the AC voltage d-axis of the grid-side converter is ( VWT _ limit / VWT )· Uod _ ref ; Give the value ( V WT_limit / V WT )· U od_ref The difference between the d-axis component of the AC voltage of the grid-side converter and the input to the PI controller generates a reference value for the d-axis component of the inner loop current of the grid-side converter. ; Reference value of the d-axis component of the inner loop current of the grid-side converter d-axis component of grid-side converter output current i od The difference is then input to the PI controller, based on the inductive reactance of the grid-side converter. ω 0 L f dq-axis component of grid-side converter output voltageu od , u oq Obtain the d-axis reference value of the grid-side converter output voltage. u od_ref .

[0012] Optionally, the reference value of the d-axis component of the inner loop current of the grid-side converter. for: in, Kp _ od , Ti _ od These are the d-axis proportional and integral coefficients of the outer loop voltage of the grid-side converter, respectively.

[0013] Optionally, obtain the q-axis reference value of the grid-side converter output voltage. uoq _ ref include: q-axis component of grid-side converter output voltage uoq Given a reference value set to 0, and uoq After subtraction, the PI controller generates a reference value for the q-axis component of the inner loop current. ioq _ ref , ioq _ ref q-axis component of grid-side converter output current ioq The difference is then input to the PI controller, based on the inductive reactance of the grid-side converter. ω 0 Lf dq-axis component of grid-side converter output voltage uod , uoq Obtain the q-axis reference value of the grid-side converter output voltage. uoq _ ref .

[0014] The beneficial effects of this invention are as follows: This invention proposes a voltage limiting control method for a series-type offshore wind power DC collector system. While possessing voltage limiting capability, it also exhibits smaller output DC voltage fluctuations compared to traditional voltage limiting control strategies, thus achieving better control performance. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1This is a schematic diagram of the topology of a series-type offshore wind power DC collector system according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the control architecture of an offshore DC wind turbine according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the steady-state characteristics of a series-type offshore wind power DC collector system according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the machine-side converter control of the voltage limiting control strategy proposed in an embodiment of the present invention; Figure 5 This is a schematic diagram of the grid-side converter control for the voltage limiting control strategy proposed in this embodiment of the invention; Figure 6 The following is a schematic diagram of the simulation results of the voltage-limiting control strategy in an embodiment of the present invention; wherein, (a) is the wind power waveform diagram of wind turbine 1, 2 and 3 respectively, which is the wind power waveform diagram of the wind turbine 1, 2 and 3 respectively, (b) is the output power waveform diagram of the three wind turbine 1 and 2 respectively, considering the power loss of the wind turbine 1 and 2 respectively, (c) is the low voltage DC link voltage waveform diagram of each wind turbine 1 and 2 respectively, and (d) is the output DC voltage waveform diagram of the three wind turbine 1 and 2 respectively. Figure 7 The following is a schematic diagram of the simulation results of the conventional voltage limiting control strategy in an embodiment of the present invention; wherein, (a) is the wind power waveform diagram of wind turbine 1, 2 and 3 respectively, which is the wind power waveform diagram of the wind turbine 1, 2 and 3 respectively, (b) is the output power waveform diagram of the three wind turbine 1 and 3 considering the power loss of the wind turbine 1 and 3, (c) is the waveform diagram of the low voltage DC link voltage of each wind turbine 1 and 3 stable at the rated value, and (d) is the output DC voltage waveform diagram of the three wind turbine 1 and 3 respectively, which is the simulation result of the voltage limiting control strategy. Figure 8 The following is a schematic diagram of the simulation results of the voltage limiting control strategy proposed in the embodiment of the present invention; wherein, (a) is the wind power waveform diagram of wind turbine 1, 2 and 3 respectively, which is the wind power waveform diagram of the wind turbine 1, 2 and 3 respectively, (b) is the output power waveform diagram of the three wind turbine 1, 2 and 3 respectively, considering the power loss of the wind turbine 1, (c) is the low voltage DC link voltage waveform diagram of each wind turbine 1, and (d) is the output DC voltage waveform diagram of the three wind turbine 1. Figure 9 The waveform diagram shows a comparison between the DC output voltage of the wind turbine under the proposed strategy in this embodiment of the invention and the traditional strategy. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] As attached Figure 1 As shown, several offshore DC wind turbines are connected in series to form an offshore DC wind farm. The wind farm power is transmitted through a high-voltage DC transmission line and then connected to the onshore AC power grid via an onshore converter station.

[0020] The topology of offshore DC wind turbines in a series-type offshore wind power DC collector system is as follows: Figure 2 As shown, it mainly consists of an impeller, drive train, permanent magnet synchronous generator (PMSG), machine-side converter, grid-side converter, and twelve-pulse rectifier bridge. The grid-side converter and the twelve-pulse rectifier bridge together constitute a medium-voltage DC-DC converter. The impeller is connected to the PMSG via the drive train. β The pitch angle is the propeller angle. ω r The PMSG rotor speed is the value used to convert the wind power captured by the impeller into electrical energy, outputting an AC voltage. u ms Alternating current i ms The inductance of the machine-side converter is L ms The machine-side converter converts the AC power output from the PMSG into low-voltage DC power. V LV This refers to the low-voltage DC link voltage of the wind turbine generator. C LV For the low-voltage DC link bus capacitor, the grid-side converter will V LV Inverts the AC power into stable AC power and outputs a stable AC voltage. u o Alternating current i o , L f For filtering inductors, C f For filtering capacitors, i g The filtered current is ultimately output as a stable DC voltage via a twelve-pulse rectifier bridge. V WT .

[0021] As attached Figure 3 As shown, the output voltage of an offshore DC wind farm V HV Controlled by an onshore converter station, it can be equivalent to a DC voltage source during steady-state operation. The output current of an offshore DC wind farm is... I WF , No. iThe output voltage of the offshore DC wind turbine in Taiwan is V WTi ( i =1, 2… n The output current is I WTi ( i =1, 2… n Wind power is P wi When the wind turbine is operating in maximum power point tracking mode, this power can be considered equal to the output power of the permanent magnet synchronous generator (PMSG). P Mi Considering the power loss of the wind turbine, the actual output power of the wind turbine is P WTi .

[0022] Therefore, the steady-state operating characteristics of a series-type offshore wind power DC collector system can be expressed as: In this system, each offshore DC wind turbine is connected in series to raise the output voltage of the offshore DC wind farm to the high-voltage direct current (HVDC) transmission voltage level. The HVDC transmission voltage is equal to the sum of the output voltages of each offshore DC wind turbine. Due to the series structure, the output current of each wind turbine remains consistent and equal to the output current of the offshore DC wind farm. The output power of each wind turbine is equal to the product of its output voltage and output current. The sum of the power of each wind turbine is equal to the product of the HVDC transmission voltage and the output current of the offshore DC wind farm.

[0023] After the system reaches steady state, the output voltage of the offshore DC wind farm V HV When controlled at rated values ​​by the onshore converter station without voltage limiting control strategies, the offshore DC wind turbine operates in maximum power point tracking mode. Therefore, the output current of the offshore DC wind farm, i.e., the system steady-state current, can be obtained. I WF : Due to the series structure, the output current of each wind turbine is equal to the steady-state current of the system, therefore the steady-state output voltage of each wind turbine can be obtained: It can be seen that after the system reaches steady state, the output voltage of each wind turbine is proportional to its output power. n For example, if the value is 3, then: The above describes the steady-state operating characteristics of a series-type offshore wind power DC collector system. During steady-state operation, the output voltage of the offshore DC wind farm... V HVThe voltage is controlled at the rated value by the onshore converter station, and the output voltage of each offshore DC wind turbine is distributed according to its output power ratio, that is: Therefore, when the wind power captured by each offshore DC wind turbine is too different, the output voltage of the wind turbine with the larger wind energy captured may be too high, exceeding the withstand voltage value of the wind turbine equipment or components, thus affecting the safe and stable operation of the system. In order to ensure system safety, voltage limiting control of the wind turbine is required to prevent its output voltage from exceeding the safety threshold.

[0024] The control architecture of offshore DC wind turbines is shown in the attached figure. Figure 2 As shown, it mainly includes pitch angle control, turbine-side converter control, and grid-side converter control. The wind turbine drivetrain and pitch angle control are similar to those of traditional AC wind turbines. This is achieved by collecting the turbine-side converter voltage... u ms Machine-side converter current i ms Low-voltage DC link voltage V LV The synchronization angle is extracted from physical quantities such as phase-locked loop (PLL). θ m The system transforms the three-phase stationary coordinate system (abc coordinate system) to a two-phase rotating coordinate system (dq coordinate system), and then uses sinusoidal pulse width modulation (SPWM) to generate gate on / off signals for the switching devices of the generator-side converter to control the generator-side converter. Similarly, the AC voltage of the grid-side converter is acquired. u o AC current of grid-side converter i o Transform it from a three-phase stationary coordinate system (abc coordinate system) to a two-phase rotating coordinate system (dq coordinate system), and its synchronization angle θ 0 is determined by a given frequency f The signal is obtained by direct integration and then generated by sinusoidal pulse width modulation (SPWM) to control the gate on / off signals of the grid-side converter switching devices.

[0025] Traditional voltage limiting control strategies set a voltage limit value. When the output voltage of the wind turbine exceeds this threshold, the wind turbine enters a voltage limiting mode. An output DC voltage control loop is superimposed on the power control stage of the wind turbine's generator-side converter to control the output DC voltage of the unit within the limit value. The grid-side converter of the unit is responsible for maintaining the stability of the low-voltage DC link voltage of the wind turbine.

[0026] Based on this, the present invention proposes a novel voltage limiting control strategy for offshore DC wind turbines. The wind turbine's generator-side converter superimposes a low-voltage DC link voltage control loop on top of the power control stage, tracking the captured wind power while maintaining the stability of the low-voltage DC link voltage. The low-voltage DC control loop superimposed on the power control stage generates a reference value for the d-axis component of the inner loop current of the generator-side converter. ,in K p_d , T i_d These are the proportional and integral coefficients of the d-axis power control element of the machine-side converter, respectively. K p_LV , T i_LV These are the proportional and integral coefficients of the d-axis low-voltage DC voltage control loop of the machine-side converter, respectively. i msd_ref With the d-axis component of the machine-side converter current i msd The difference is then input to the PI controller, based on the inductive reactance of the machine-side converter. ω r L ms q-axis component of the current in the machine-side converter i msq d-axis component of the converter voltage on the machine side u msd Obtain the reference value of the d-axis component of the converter voltage on the machine side. u msd_ref ,Right now ,in K p_id , T i_id These are the proportional and integral coefficients of the inner loop of the d-axis current of the generator-side converter. The amplitude of the permanent magnet synchronous generator output AC voltage is... U ms Given a reference value U ms_ref The PI controller generates a reference value for the q-axis component of the current in the machine-side converter, i.e. q-axis component of the current from the machine-side converter i msq The difference is then input to the PI controller, based on the inductive reactance of the machine-side converter. ω r L ms d-axis component of the current in the machine-side converter i msd q-axis component of the machine-side converter voltage u msq Obtain the reference value of the q-axis component of the converter voltage on the machine side. u msq_ref ,Right now ,in K p_q , T i_q These represent the proportional and integral coefficients of the outer loop of the q-axis voltage of the machine-side converter during the power transmission stage. K p_iq , T i_iq These are the proportional and integral coefficients of the inner loop of the q-axis current of the machine-side converter during the power transmission stage. u msd_ref , u msq_ref The control signal for the machine-side converter is then generated via sinusoidal pulse width modulation (SPWM). (See attached image.) Figure 4 As shown.

[0027] The grid-side converter of the wind turbine adopts voltage / frequency control, that is... V / f For a single offshore DC wind turbine, the AC output voltage of its grid-side converter is rectified into DC voltage by a twelve-pulse rectifier bridge, and the two are directly proportional. Therefore, the DC output voltage of the wind turbine can be controlled by controlling the AC output voltage of the grid-side converter. Specifically, when the wind turbine enters voltage limiting mode, the d-axis setpoint of the grid-side converter AC voltage is set to a ratio equal to the DC voltage limiting value relative to the rated output DC voltage. Let the DC voltage limiting value of the offshore DC wind turbine be... VWT _ limit Then the given value of the AC voltage d-axis of the grid-side converter is ( VWT _ limit / VWT )· Uod _ ref The difference between this given value and the d-axis component of the grid-side converter AC voltage is input to the PI controller to generate a reference value for the d-axis component of the grid-side converter inner loop current. ,in Kp _ od , Ti _ od These are the proportional and integral coefficients of the outer loop voltage of the grid-side converter, respectively. Then, they are compared with the d-axis components of the grid-side converter output current. iod The difference is then input to the PI controller, based on the inductive reactance of the grid-side converter. ω 0 Lf dq-axis component of grid-side converter output voltage uod , uoq Obtain the d-axis reference value of the grid-side converter output voltage. uod _ ref ,Right now ,in, Kp _ iod , Ti _ iodThese represent the proportional and integral coefficients of the inner loop of the d-axis current of the grid-side converter. The q-axis component of the grid-side converter output voltage is also shown. uoq Given a reference value set to 0, and uoq After subtraction, the PI controller generates a reference value for the q-axis component of the inner loop current. ioq _ ref Then, it is compared with the q-axis component of the grid-side converter output current. ioq The difference is then input to the PI controller, based on the inductive reactance of the grid-side converter. ω 0 Lf dq-axis component of grid-side converter output voltage uod , uoq Obtain the q-axis reference value of the grid-side converter output voltage. uoq _ ref ,Right now ,in Kp _ ioq , Ti _ ioq These are the proportional and integral coefficients of the inner loop of the q-axis current of the grid-side converter, respectively. uod _ ref , uoq _ ref The grid-side converter control signal is then generated via sinusoidal pulse width modulation, as shown in the attached diagram. Figure 5 As shown.

[0028] The strategy proposed in this invention is compared with the strategy without voltage limiting and the traditional voltage limiting control strategy.

[0029] The setup in PSCAD / EMTDC is shown in the attached image. Figure 1 The series-type offshore wind power DC collector system shown in Table 1 has system parameters.

[0030] Table 1 System Parameters Three offshore DC wind turbines are connected in series to form an offshore DC wind farm. The wind turbines have a rated wind speed of 15 m / s, a rated power of 6 MW, and a rated output DC voltage of ±50 kV. The wind speed imbalance condition is set as follows: the wind speed of the first wind turbine is 15 m / s, the second wind turbine is 10 m / s, and the third wind turbine is 8 m / s. The voltage limit is set to 1.2 pu. V WT_limit =1.2 V WT The total simulation duration is 6 seconds.

[0031] Simulation results of the voltage-limiting control strategy are attached. Figure 6As shown, after the system reaches steady state, each wind turbine operates in maximum power point tracking (MPPT) mode, tracking the captured wind power. Wind turbine 1, due to its input rated wind speed, outputs a rated power of 6MW via the PMSG. Wind turbines 2 and 3 correspondingly track their captured wind power of 2.7MW and 1.5MW, respectively. (See attached diagram.) Figure 6 As shown in (a). Considering the power loss of the wind turbine units, the three wind turbine units output power of 4.02MW, 2.145MW, and 1.29MW respectively, as shown in the attached figure. Figure 6 As shown in (b), if the rated output DC voltage of the wind turbine is ±50kV, then the rated DC voltage of the offshore DC wind farm is ±150kV, or 300kV. In steady state, the output DC voltage of each wind turbine is distributed proportionally to its output power. V WT1 , V WT2 , V WT3 The theoretical values ​​are 161.17kV, 86.32kV, and 51.92kV, respectively. The simulation results are attached. Figure 6 As shown in (d), the simulated values ​​stabilized around 162kV, 86kV, and 51kV, respectively. The low-voltage DC link voltage of each wind turbine stabilized at its rated value, as shown in the attached figure. Figure 6 As shown in (c), the correctness of the steady-state characteristic analysis is verified.

[0032] Without voltage limiting control strategy, the DC output voltage of wind turbine 1 reaches about 1.6pu in steady state, which greatly exceeds the tolerance value of the device. In actual operation, it may cause the device to break down and affect the safe and stable operation of the system.

[0033] As attached Figure 7 As shown in (d), after adopting the traditional voltage limiting control strategy, the output DC voltage of wind turbine 1 is limited to 120kV, i.e., 1.2pu. Due to the limited output voltage, the output power cannot reach the maximum power value and is limited to 1.96MW, as shown in the attached diagram. Figure 7 (b) Other wind turbines' output DC voltage did not exceed the limit and they operated in maximum power point tracking mode, tracking the captured wind power, as shown in the attached figure. Figure 7 As shown in (a) and (b), the low-voltage DC link voltage of each wind turbine unit is stable at the rated value, as shown in the attached diagram. Figure 7 As shown in (c).

[0034] As attached Figure 8 As shown in (d), using the proposed voltage limiting control strategy, the output DC voltage of wind turbine 1 is limited to 120kV, i.e., 1.2pu. Due to the limited output voltage, the output power cannot reach the maximum power value and is limited to 1.94MW, as shown in the attached diagram. Figure 8(b) Other wind turbines' output DC voltage did not exceed the limit and they operated in maximum power point tracking mode, tracking the captured wind power, as shown in the attached figure. Figure 8 As shown in (a) and (b), the low-voltage DC link voltage of each wind turbine unit is stable at the rated value, as shown in the attached diagram. Figure 8 As shown in (c), the effectiveness of the proposed strategy has been verified.

[0035] The proposed voltage limiting control strategy achieves voltage limiting while maintaining a DC voltage fluctuation rate of 2.4% for the limited wind turbine output, compared to 4.2% for the traditional voltage limiting strategy. (See attached diagram) Figure 9 As shown, the DC voltage fluctuation is smaller, resulting in better control.

[0036] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A voltage limiting control method for a series-type offshore wind power DC collector system, characterized in that, including: The wind turbine generator-side converter adds a low-voltage DC link voltage control loop to the power control stage to obtain the reference value of the d-axis component of the generator-side converter voltage. umsd_ref Reference value of q-axis component of converter voltage on the machine side umsq_ref ,Will umsd_ref , umsq_ref The control signal for the machine-side converter is generated by sinusoidal pulse width modulation. The grid-side converter of the wind turbine adopts voltage / frequency control to obtain the d-axis reference value of the grid-side converter output voltage. you _ ref q-axis reference value of grid-side converter output voltage what _ ref ,Will you _ ref , what _ ref The grid-side converter control signal is generated by sinusoidal pulse width modulation.

2. The voltage limiting control method for a series-type offshore wind power DC collector system according to claim 1, characterized in that, Obtain the reference value of the d-axis component of the converter voltage on the machine side. umsd_ref include: Based on the power control loop superimposed with a low-voltage DC voltage control loop, a reference value for the d-axis component of the inner loop current of the machine-side converter is generated. imsd_ref ; Reference value of the d-axis component of the inner loop current of the machine-side converter imsd_ref With the d-axis component of the machine-side converter current imsd The difference is then input to the PI controller, based on the inductive reactance of the machine-side converter. ωrLms q-axis component of the current in the machine-side converter imsq d-axis component of the converter voltage on the machine side umsd Obtain the reference value of the d-axis component of the converter voltage on the machine side. umsd_ref .

3. The voltage limiting control method for a series-type offshore wind power DC collector system according to claim 2, characterized in that, Reference value of the d-axis component of the inner loop current of the machine-side converter imsd_ref for: in, Kp _ d , You _ d These are the proportional and integral coefficients of the d-axis power control element of the machine-side converter, respectively. Kp_LV , Ti_LV These are the proportional and integral coefficients of the d-axis low-voltage DC voltage control loop for the machine-side converter. 55 This refers to the low-voltage DC link voltage of the wind turbine generator. The active power output of the permanent magnet synchronous generator (PMSG) is... This is a reference value for the active power output of a permanent magnet synchronous generator (PMSG). This is a reference value for the low-voltage DC link voltage.

4. The voltage limiting control method for a series-type offshore wind power DC collector system according to claim 1, characterized in that, Obtain the reference value of the q-axis component of the generator-side converter voltage. umsq_ref include: The output AC voltage amplitude of the permanent magnet synchronous generator is Ums Given a reference value Ums _ ref ; Will Ums Compared with reference value Ums _ ref After subtraction, the PI controller generates a reference value for the q-axis component of the machine-side converter current. ; Reference value of q-axis component of machine-side converter current q-axis component of the current of the machine-side converter imsq The difference is then input to the PI controller, based on the inductive reactance of the machine-side converter. ωrLms d-axis component of the current in the machine-side converter imsd q-axis component of the machine-side converter voltage whatever Obtain the reference value of the q-axis component of the converter voltage on the machine side. umsq_ref .

5. The voltage limiting control method for a series-type offshore wind power DC collector system according to claim 4, characterized in that, Reference value of the q-axis component of the machine-side converter current for: in, K p_q , T i_q These are the proportional and integral coefficients of the outer loop of the q-axis voltage of the machine-side converter in the power transmission stage.

6. The voltage limiting control method for a series-type offshore wind power DC collector system according to claim 1, characterized in that, Obtain the d-axis reference value of the grid-side converter output voltage. you _ ref include: Assume the DC voltage limit value of the offshore DC wind turbine output is VWT _ limit Then the given value of the AC voltage d-axis of the grid-side converter is ( VWT _ limit / VWT )· You _ ref ; Give the value ( V WT_limit / V WT )· U od_ref The difference between the d-axis component of the AC voltage of the grid-side converter and the input to the PI controller generates a reference value for the d-axis component of the inner loop current of the grid-side converter. ; Reference value of the d-axis component of the inner loop current of the grid-side converter d-axis component of grid-side converter output current i od The difference is then input to the PI controller, based on the inductive reactance of the grid-side converter. ω 0 L f dq-axis component of grid-side converter output voltage u od , u oq Obtain the d-axis reference value of the grid-side converter output voltage. u od_ref .

7. The voltage limiting control method for a series-type offshore wind power DC collector system according to claim 6, characterized in that, Reference value of the d-axis component of the inner loop current of the grid-side converter for: in, Kp _ from , You _ from These are the d-axis proportional and integral coefficients of the outer loop voltage of the grid-side converter, respectively.

8. The voltage limiting control method for a series-type offshore wind power DC collector system according to claim 1, characterized in that, Obtain the q-axis reference value of the grid-side converter output voltage. u oq_ref include: q-axis component of grid-side converter output voltage what Given a reference value set to 0, and what After subtraction, the PI controller generates a reference value for the q-axis component of the inner loop current. something _ ref , something _ ref q-axis component of grid-side converter output current something The difference is then input to the PI controller, based on the inductive reactance of the grid-side converter. ω 0 Lf dq-axis component of grid-side converter output voltage you , what Obtain the q-axis reference value of the grid-side converter output voltage. what _ ref .

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