CN114784859A - Offshore wind farm black start method based on diesel-storage combined system - Google Patents

Abstract

The invention discloses a black start method for an offshore wind farm based on a diesel-storage combined system, comprising: step S1, the energy storage device adopts a zero-voltage start-up control strategy to reduce the excitation inrush current; step S2, starts the diesel generator set, and uses an auxiliary load to assist Diesel generator sets are started; Step S3, put into the balanced load and supply power to the auxiliary machines of the wind turbines; Step S4, the wind turbines are started one by one and capture wind energy to generate electricity; Step S5, after the wind turbines suitable for conveying active power are started, put in to adjust the phase The wind turbine operating in the mode; step S6, reduce the adjustable load according to the rated power of the motor load to be put into operation, wait for the system to enter a steady state and put into the motor load to realize black start. The invention adopts a reasonable black-start operation method and control strategy of the wind farm, and the phase-modulation operation mode of the wind turbine enables the grid-side converter of the non-starting unit to participate in the reactive power support, improves the system voltage stability during the black-start process, and is beneficial to the black-start went well.

Description

A black-start method for offshore wind farms based on diesel-storage combined system

technical field

The invention relates to the technical field of power grid black start, in particular to a black start method for an offshore wind farm based on a diesel-storage combined system.

Background technique

At present, the black-start power source of the power system is mainly conventional power plants, but the cold start of traditional power plants is realized by starting auxiliary units with backup power. With the increase of the proportion of new energy, wind power has gradually become a new choice for starting auxiliary units. Wind farms connected to the grid via HVDC lines rely on a reference to obtain frequency and voltage from the grid during start-up. Therefore, when the HVDC transmission line fails or the power grid fails to obtain energy from the power grid, the auxiliary power source is required as the starting power source for the wind turbine and auxiliary equipment.

Wind turbines equipped with auxiliary power supply have the self-start function, and the start-up time is short, which enables the wind farm to have the ability to promote the recovery of the system grid. Using the auxiliary power supply, not only the self-starting of the wind turbine can be realized, but also the load power shortage can be supplemented by the energy storage device when the wind power fluctuates. Through reasonable operation steps and control strategies, the wind turbines can start the units in the wind farm in sequence, provide long-term stable power for the load and improve the system voltage quality. However, the robustness of the system during the black start process of the wind farm is low, and the voltage quality will affect the stable operation of the system and the smooth progress of the black start.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention proposes a reasonable black-start method for offshore wind farms based on the diesel-storage combined system. The present invention adopts a reasonable black-start operation method and control strategy for wind farms. The grid-side converter participates in reactive power support to improve the system voltage quality.

In order to achieve the above object, the present invention is achieved through the following technical solutions:

The present invention is a black start method for an offshore wind farm based on a diesel-storage combined system, comprising the following steps:

Step S1, close the energy storage line booster circuit breaker, the energy storage device starts at zero voltage to reduce the excitation inrush current, the energy storage system charges the high-voltage side bus of the wind farm through the step-up transformer and the submarine cable, and starts at zero voltage after reaching the rated voltage operation ends;

Step S2, start the diesel generator set, turn on the diesel generator starting load after the diesel generator outlet voltage reaches the rated value, and perform the synchronous grid connection operation after the diesel generator returns to the steady state again to close the port circuit breaker of the diesel generator set. The energy storage works together as the balanced power supply of the isolated grid system, gradually reducing the starting load of the diesel engine, so that the energy storage system is in a charging state;

Step S3, when the energy storage system charge meets the start-up requirements, the adjustable load is put in as a balance load, and then the auxiliary load breaker of the wind turbine is closed to supply power to the auxiliary machines of the wind turbine. When the wind speed meets the start-up conditions, the wind turbine starts to capture wind energy. , close the circuit breaker at the outlet port of the wind turbine, use the machine-side converter to control the speed of the permanent magnet synchronous generator and charge the DC side capacitor, and transmit power to the high-voltage side bus through the grid-side converter;

Step S4, start all wind turbines in turn according to step S3 to realize the expansion of the start-up scale, maintain the power balance of the isolated grid system, and increase the size of the adjustable load as the number of input fans increases;

In step S5, after the generator set that transmits active power is started, the wind turbine generator set running in the phase modulation mode is put into operation;

In step S6, the size of the adjustable load is reduced according to the rated power of the motor to be put into operation, and the load port circuit breaker is closed after the system enters a steady state, and the motor load is started to realize a black start.

A further improvement of the present invention is that: the zero-voltage startup of the energy storage system in the S1 is specifically: the zero-voltage startup control strategy makes the outer loop reference voltage _{udref integrate} according to the difference between the grid voltage _ug and the network reference voltage u _nref , until the energy storage The difference between the output voltage and the rated voltage enters the regulation dead zone, and the PI link is used to time the time of entering the dead zone. After continuously being within the dead zone range for longer than the set time, the PI timing link is set to a high level and no longer changes, and u is latched. _{The dref} signal determines the reference value of the voltage outer loop in the initial state, and the zero-voltage start-up process ends.

A further improvement of the present invention is: the specific operation of maintaining the power balance of the isolated grid system in the step S4 is: the power balance is specifically the balance of active power and reactive power. The power balance is as follows:

P _BESS +P _oil +P _w =P _load +P _loss (1)

In the formula: P _BESS is the active power of the energy storage system; P _w is the active power of the wind turbine; P _load is the load power; P _oil is the active power of the diesel generator; P _loss is the system power loss;

The reactive power balance formula of the system is as follows:

Q _BESS +Q _oil +Q _WSVG =Q _load +Q _loss (2)

In the formula: Q _BESS is the reactive power of the energy storage system; Q _WSVG is the reactive power compensation of the wind turbine; Q _load is the load reactive power; Q _oil is the reactive power of the diesel generator set; Q _loss is the system reactive power loss.

A further improvement of the present invention is that: the phase modulation operation mode of the wind turbine in step S5 is specifically divided into:

a. The voltage droop control method is adopted when the wind turbine is in normal operation mode;

b. Set the reactive power compensation mode when the wind turbine does not perform active power transmission.

The further improvement of the present invention is that: the specific operation of adopting the voltage droop control method is as follows: the grid-side controller will adopt the grid voltage directional vector control strategy, and introduce the grid-side voltage information into the q-axis, and pass the difference between the voltage reference value and the actual value through The proportional link obtains the reactive power reference value, and after making a difference with the actual reactive power output, the q-axis current reference value of the proportional and integral link is sent to the control link to realize the voltage droop control of the grid-side controller.

The further improvement of the present invention is that: the operation of setting the reactive power compensation mode is as follows: firstly, the controller module on the machine side is removed, then the size of the DC side capacitance is adjusted to an appropriate value, then the control loop is switched to the reactive power compensation control loop and connected to the grid, and finally the To suppress fluctuations, a 2.0uF capacitor can also be put into the high-voltage side of the transformer for filtering.

The further improvement of the present invention is: when running in the reactive power compensation mode, the voltage of the grid voltage v _g is compensated for the voltage drop according to the output reactive power Q _g , and then the PCC measurement point voltage is obtained, and then the difference with the reference value v _ref is obtained after the lead and lag compensation The trigger angle is calculated by the link and the PI link, and the trigger angle is used to phase-shift the grid-side voltage. When the grid voltage is higher than the reference voltage, the trigger angle is negative, the output voltage is ahead of the voltage at the acquisition point, the controller absorbs reactive power, and vice versa controls The device will emit reactive power.

The beneficial effects of the present invention are as follows: the present invention adopts a reasonable black-start operation method and control strategy of the wind farm, and the phase-modulation operation mode of the wind power unit enables the grid-side converter of the non-start unit to participate in the reactive power support, thereby improving the system voltage during the black-start process. Stability, reduce the scenario where the large reactive power demand in the starting phase of the rotating load reduces the voltage of the system node, which leads to the failure of the energy storage system and the wind turbine, and improves the load carrying capacity of the combined wind and diesel storage system as a black-start power source.

Description of drawings

Figure 1 is the wiring structure diagram of the offshore wind power system in the black start scenario;

Figure 2 is the simulation waveform of the PCC point voltage during the self-starting process of the wind farm;

Figure 3 is the simulation waveform of the PCC point voltage during the starting process of the motor load.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention, so that those skilled in the art can refer to the drawings. The description text can be implemented accordingly.

As shown in Fig. 1-Fig. 3, the present invention considers a black-start method for an offshore wind farm based on a diesel-storage combined system under an isolated grid, and the specific steps are as follows:

Step S1, close the energy storage line step-up circuit breakers KM1 and KM2, the energy storage device adopts the zero-voltage start-up control strategy to reduce the excitation inrush current, and the energy storage system charges the high-voltage side bus of the wind farm through the step-up transformer and the submarine cable to achieve The zero-voltage start operation ends after the rated voltage. After the start-up is completed, the energy storage system will serve as the main reference source during the black start process, providing stable voltage and frequency support for the isolated grid system;

Step S2, close the circuit breakers KM5 and KM3 to start the diesel generator set, close the circuit breaker KM4 after the diesel generator outlet voltage reaches the rated value and put it into the diesel generator starting load, after the diesel generator returns to the steady state again, perform the synchronous grid connection operation to close the diesel generator. The circuit breaker at the grid-connected port of the unit, together with the energy storage, acts as the balanced power supply of the isolated grid system after the grid-connection is completed. Gradually reduce the start-up load of diesel engines to keep the energy storage system in a state of charge;

In step S3, when the electric charge of the energy storage system meets the start-up requirement, the adjustable load is put in as a balance load. Then close the auxiliary load breaker of the wind turbine to supply power to the auxiliary equipment of about 100KW and 50KVar of the wind turbine. When the wind speed meets the starting conditions, the wind turbine starts to capture wind energy, close the breaker of the outlet port of the wind turbine, and use the machine-side converter to control the permanent magnet The speed of the synchronous generator is controlled and the DC side capacitor is charged, and the power is transmitted to the high-voltage side bus through the grid-side converter;

In step S4, other wind turbines are started in turn according to step S3 to realize the expansion of the startup scale. At this time, the system does not drive the black start load and the energy storage system is in the charging state. The power of the system is balanced to avoid overcharging of the energy storage system and the reverse transfer of the power of the diesel generator set and the overheating of the coils.

Step S5, when the wind turbines suitable for capturing wind energy are started up, the grid-side controller of the wind turbines that are not started adopts the phase modulation operation control strategy to perform reactive power compensation on the system to improve the system voltage quality;

In step S6, the size of the adjustable load is reduced according to the rated power of the motor to be put into operation, and the load port circuit breaker is closed after the system enters a steady state, and the motor load is started to realize a black start.

In step S1, the zero-voltage startup method of the energy storage system is as follows: the zero-voltage startup control strategy makes the outer loop reference voltage _{udref integrate} according to the difference between the grid voltage _ug and the network reference voltage u _nref , so as to realize the gradual increase of the control signal and the output voltage. When the difference between the output voltage of the energy storage and the rated voltage enters the regulation dead zone, the PI link is used to time the time of entering the dead zone. After being continuously within the dead zone range for longer than the set time, the PI timing link is set to a high level and will not change. Latch the _udref signal to determine the reference value of the voltage outer loop in the initial state, and the zero-voltage start-up process ends.

In step S4, the system power balance method is as follows: during the operation of the wind fuel storage system, the balance of active power and reactive power of the system needs to be maintained, and with the fluctuation of wind speed, the maximum output power and actual output power of the wind turbine also change accordingly. The power shortage caused by the power fluctuation of the wind turbine needs to be provided by the energy storage system. Assuming that the diesel generator sets in the system are running at the rated state, the main active support equipment in the system are diesel generator sets, energy storage systems and wind turbines. The active power balance formula is as follows:

P _BESS +P _oil +P _w =P _load +P _loss (1)

In the formula: P _BESS is the active power of the energy storage system; P _w is the active power of the wind turbine; P _load is the load power; P _oil is the active power of the diesel generator.

Under the traditional control strategy, the grid-side control loop of the wind turbine sets the reactive power reference value to zero, but the power electronic device conversion process and the step-up transformer will still consume a certain amount of reactive power; when the wind turbine is put into the voltage droop strategy, the wind turbine will When the voltage drops, it will provide a certain amount of reactive power support; the reactive power compensation mode of the wind turbine operates like a static reactive power compensator. The main devices that provide reactive power in the system are diesel generator sets, energy storage systems and control units. Therefore, the reactive power balance formula of the system is as follows:

Q _BESS +Q _oil +Q _WSVG =Q _load +Q _loss (2)

In the formula: Q _BESS is the reactive power of the energy storage system; Q _WSVG is the reactive power compensation of the wind turbine; Q _load is the load reactive power; Q _oil is the reactive power of the diesel generator set.

In step S5, the phase modulation operation mode of the wind turbine generator set is specifically: the voltage droop control method is adopted in the normal operation mode of the wind turbine generator set, the grid-side controller will adopt the grid voltage directional vector control strategy, and the grid-side voltage information will be introduced into the q-axis, and the voltage reference value The difference with the actual value is obtained through the proportional link to obtain the reactive power reference value, and after the difference with the actual reactive power output, the q-axis current reference value of the proportional and integral link is sent to the control link to realize the voltage droop control of the grid-side controller; the wind turbine does not carry out During active power transmission, the reactive power compensation mode can be set, so that the grid-side controller operates in a reactive power compensation mode similar to SVG, which is called WSVG mode. At this time, the following operations need to be performed: first cut off the machine side controller module, then adjust the DC side capacitor size to an appropriate value, then switch to the reactive power compensation control loop and connect it to the grid, and finally, to stabilize the fluctuations, it can also be put into the high voltage side of the transformer. 2.0uF capacitor filter. When running in the reactive power compensation mode, the voltage drop of the grid voltage v _g is compensated according to the output reactive power Q _g to obtain the PCC measurement point voltage, and then the difference is made with the reference value v _ref , and the trigger angle is calculated through the lead-lag compensation link and the PI link. . The trigger angle is used to phase-shift the grid-side voltage. When the grid voltage is higher than the reference voltage, the trigger angle is negative, the output voltage is ahead of the acquisition point voltage, and the controller absorbs reactive power, otherwise the controller will emit reactive power.

Finally it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention but not to limit it, although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand: still can Modifications or equivalent substitutions are made to the specific embodiments, and any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention shall all be included in the scope of the present claims.

Claims (7)

1. an offshore wind farm black start method based on diesel storage combined system, is characterized in that: comprise the steps: Step S1, close the energy storage line booster circuit breaker, the energy storage device starts at zero voltage to reduce the excitation inrush current, the energy storage system charges the high-voltage side bus of the wind farm through the step-up transformer and the submarine cable, and starts at zero voltage after reaching the rated voltage operation ends; Step S2, start the diesel generator set, turn on the diesel generator starting load after the diesel generator outlet voltage reaches the rated value, and after the diesel generator returns to the steady state again, perform the synchronous grid connection operation to close the diesel generator set port circuit breaker, and after the grid connection is completed Together with the energy storage, it acts as a balanced power supply for the isolated grid system, gradually reducing the starting load of the diesel engine, so that the energy storage system is in a charging state; Step S3, after the energy storage system charge meets the startup requirements, the adjustable load is put in as a balance load, and then the auxiliary load breaker of the wind turbine is closed to supply power to the auxiliary machines of the wind turbine. When the wind speed meets the startup conditions, the wind turbine starts to capture For wind energy, close the breaker at the outlet port of the wind turbine, use the machine-side converter to control the speed of the permanent magnet synchronous generator, charge the DC-side capacitor, and transmit power to the high-voltage side bus through the grid-side converter; Step S4, start all wind turbines in turn according to step S3 to realize the expansion of the start-up scale, maintain the power balance of the isolated grid system, and increase the size of the adjustable load as the number of input fans increases; In step S5, after the generator set that transmits active power is started, the wind turbine generator set running in the phase modulation mode is put into operation; In step S6, the size of the adjustable load is reduced according to the rated power of the motor to be put into operation, and the load port circuit breaker is closed after the system enters a steady state, and the motor load is started to realize a black start. 2 . The black start method of an offshore wind farm based on a diesel-storage combined system according to claim 1 , wherein the zero-voltage start-up of the energy storage system in the S1 is specifically: the zero-voltage start-up control strategy makes the outer loop reference voltage u _dref is integrated according to the difference between the grid voltage _ug and the network reference voltage u _nref , until the difference between the energy storage output voltage and the rated voltage enters the regulation dead zone, and the PI link is used to time the time of entering the dead zone, and it is continuously within the dead zone range greater than After the set time, the PI timing link is set to a high level and will not change, and the _udref signal is latched to determine the voltage outer loop reference value of the initial state, and the zero-voltage start-up process ends. 3. A black-start method for an offshore wind farm based on a diesel-storage combined system according to claim 1, characterized in that: the specific operation of maintaining the power balance of the isolated grid system in the step S4 is: the power balance is specifically active power and no power. When the diesel generator set in the system is running at the rated state, the active power balance formula of the system is as follows: P _BESS +P _oil +P _w =P _load +P _loss (1) In the formula: P _BESS is the active power of the energy storage system; P _w is the active power of the wind turbine; P _load is the load power; P _oil is the active power of the diesel generator; P _loss is the system power loss; The reactive power balance formula of the system is as follows: Q _BESS +Q _oil +Q _WSVG =Q _load +Q _loss (2) In the formula: Q _BESS is the reactive power of the energy storage system; Q _WSVG is the reactive power compensation of the wind turbine; Q _load is the load reactive power; Q _oil is the reactive power of the diesel generator set; Q _loss is the system reactive power loss. 4. A kind of black start method of offshore wind farm based on diesel storage combined system according to claim 1, it is characterized in that: described step S5 wind turbine phase modulation operation mode is specifically divided into: a. The voltage droop control method is adopted when the wind turbine is in normal operation mode; b. Set the reactive power compensation mode when the wind turbine does not perform active power transmission. 5. A black-start method for an offshore wind farm based on a diesel-storage combined system according to claim 4, characterized in that: the specific operation of adopting the voltage droop control method is: the grid-side controller will adopt the grid voltage directional vector control strategy, The grid-side voltage information is introduced into the q-axis, and the difference between the voltage reference value and the actual value is obtained through the proportional link to obtain the reactive power reference value. After the difference with the actual reactive power output, the q-axis current reference value through the proportional and integral link is sent to the control link. , to realize the voltage droop control of the grid-side controller. 6. A black-start method for an offshore wind farm based on a diesel-storage combined system according to claim 4, characterized in that: the operation of setting the reactive power compensation mode is as follows: first, the machine-side controller module is removed, and then the DC-side capacitance is adjusted. to an appropriate value, then switch to the reactive power compensation control loop and connect it to the grid. Finally, to smooth the fluctuations, a 2.0uF capacitor can be added to the high-voltage side of the transformer for filtering. 7. A black-start method for an offshore wind farm based on a diesel-storage combined system according to claim 6, characterized in that: when operating in a reactive power compensation mode, voltage drop compensation is performed on the grid voltage v _g according to the output reactive power Q _g Then, the voltage of the PCC measurement point is obtained, and then the difference is made with the reference value v _ref . The trigger angle is calculated through the lead-lag compensation link and the PI link, and the trigger angle is used to phase-shift the grid-side voltage. When the grid voltage is higher than the reference voltage, the trigger angle is Negative value, the output voltage is ahead of the acquisition point voltage, the controller absorbs reactive power, otherwise the controller will emit reactive power.

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