Direct black-start method and system for grid-forming type permanent magnet direct-drive wind turbine generator

Abstract

The invention discloses a direct black-start method and system for a grid-forming type permanent magnet direct-drive wind turbine generator, and the method comprises the steps: starting a rotor-side converter, accelerating a permanent magnet direct-drive fan to a given rotating speed, continuously charging a direct current side when the rotating speed rises until a rated voltage is reached, and maintaining the capacitor voltage of the direct current side through machine-side control; a grid-side converter is started, and inertia support is provided for the system through control of the virtual synchronous machine; a load is accessed, and a virtual synchronous machine and a linear active-disturbance-rejection technology are combined to improve the stability of a network construction type system. According to the method, the autonomous frequency and voltage supporting capacity of the direct-driven wind turbine generator are improved, the direct-driven wind turbine generator can independently serve as a black-start power supply to participate in power grid black-start, and the black-start process can be effectively achieved for a regional power grid lacking a conventional black-start power supply.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy black start control, and in particular relates to a direct black start method and system for a grid-type permanent magnet direct-drive wind turbine set. Background Art

[0002] Deserts, grasslands, mountains and other places have rich wind energy resources, but these areas are often remote. If the public power grid is used for power supply, not only will the transmission lines be long, which will increase the economic cost, but it will also be difficult to implement. Usually, renewable energy generation in an isolated off-grid environment is used to distribute electricity. Therefore, how to start wind turbines and what control strategy to use for black start are of great significance to the construction of a new power system. At present, the black start mode of wind turbines mostly adopts energy storage inverters, diesel generators and various energy storage devices. This black start mode must consider the economy of additional equipment, and when the wind turbine requires large-capacity starting support equipment, it not only increases the footprint of on-site equipment, but also poses a great safety hazard to operators. At present, the grid-type control technology is more commonly used for the control of wind turbines in isolated island environments. This type of control technology has better performance in weak and low-inertia power grids, and can provide frequency support and inertia support for the system. However, the grid-type control technology usually adopts power synchronization control, so power fluctuations will directly affect the stability of the entire system. In addition, at this stage, the black start of wind turbines must consider economy and safety. At present, the black start mode of wind turbines that does not require additional equipment and the joint operation method that can suppress power fluctuations and improve the stability of the grid system have not been reported. Summary of the invention

[0003] In view of the technical problems existing in the prior art, the present invention provides a direct black start method and system for a grid-forming permanent magnet direct-drive wind turbine group, which can improve the frequency and voltage supporting capabilities of the direct-drive wind turbine group, enable it to independently participate in the black start of the power grid as a black start power supply, and enable the system to have better frequency and voltage regulation capabilities during the black start process.

[0004] In order to achieve the above object, the present invention adopts the following technical scheme: In one aspect, the present invention provides a direct black start method for a grid-type permanent magnet direct-drive wind turbine generator set, the method comprising the following steps: Step 1: Start the direct-drive wind turbine pitch system and adjust the pitch angle. When the direct-drive wind turbine pitch system and yaw system reach working conditions, drive the wind turbine to accelerate to the rated speed. Step 2: Start the machine-side converter, and charge the DC side capacitor to a preset voltage value, while maintaining the DC capacitor voltage through the machine-side converter control; Step 3: Start the grid-side converter to establish the grid-side AC voltage; Step 4: After the grid-side AC voltage is established, the AC load is put into operation, and the grid-side converter control is used to provide support for the system. The linear anti-disturbance technology is combined to suppress system fluctuations, improve system stability, and start the unit.

[0005] On the other hand, the present invention provides a direct black start system for a grid-type permanent magnet direct-drive wind turbine generator set, the system comprising: The first module is used to start the direct-drive fan and accelerate the fan speed to the rated speed; The second module is used to start the machine-side converter, and the machine side charges the DC side capacitor to a preset voltage value, while maintaining the DC capacitor voltage through the machine-side converter; The third module is used to start the grid-side converter and establish the grid-side AC voltage; The fourth module is used to realize that after the AC voltage on the grid side is established, the AC load is put into use, the grid-side converter control provides support for the system, and the linear anti-disturbance technology is combined to suppress system fluctuations, improve system stability, and start the unit.

[0006] Compared with the prior art, the present invention has the following beneficial effects: 1) The grid-side converter control model based on virtual synchronous machine control in the present invention can realize the use of the grid-connected direct-drive wind power system as an independent black start power supply to provide inertia support without the need for an external auxiliary power supply, which can significantly reduce the black start cost.

[0007] 2) The present invention combines linear anti-disturbance technology to suppress voltage fluctuations and thus power fluctuations, which can effectively improve the stability of the grid-type system. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a flow chart of the direct black start method of the grid-type permanent magnet direct-drive wind turbine set of the present invention; Figure 2 It is a schematic diagram of a grid-forming permanent magnet direct-drive wind turbine generator set with a direct black start function according to the present invention; Figure 3 is a control block diagram of the present invention; Figure 4 It is a schematic diagram of starting the wind turbine generator set of the present invention under off-grid conditions. DETAILED DESCRIPTION

[0009] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention 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 invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0010] In one embodiment, Figure 1 As shown, a direct black start method for a grid-type permanent magnet direct-drive wind turbine generator set is provided, comprising the following steps: Step 1: Start the direct-drive wind turbine pitch system and adjust the pitch angle. When the direct-drive wind turbine pitch system and yaw system reach working conditions, drive the wind turbine to accelerate to the rated speed, including: First, the direct-drive wind turbine pitch control system is started to resume the rotation of the wind turbine. The direct-drive wind turbine pitch control system of the present invention adjusts the speed of the wind turbine with the goal of maintaining a constant speed of the wind turbine. The pitch angle control can accelerate the wind turbine to the rated speed. The mathematical model is as follows: ; in, is the pitch angle of the wind turbine; , They are the proportional coefficient and integral coefficient in pitch control respectively; , They are respectively the rated speed and actual speed of the fan; Represents the integral transformation sign.

[0011] Step 2: Start the machine-side converter, and the machine-side charges the DC side capacitor until the preset voltage value is reached. At the same time, the DC capacitor voltage is maintained by controlling the machine-side converter. The model is as follows: ; in, is the dq axis reference current; , They are the actual value of capacitor side voltage and the reference value of capacitor side voltage respectively; , They are the proportional coefficient and integral coefficient in the voltage outer loop respectively; Represents the integral transformation sign.

[0012] like Figure 3 As shown in the above formula, the machine-side converter is controlled according to the capacitor-side voltage. , The actual value and reference value of the capacitor voltage are obtained by sampling the real-time voltage on the capacitor side and comparing it with the reference value, and then the reference current is obtained through proportional-integral control. , They are the proportional coefficient and integral coefficient in the voltage outer loop respectively.

[0013] Step 3: The grid-side converter is started to establish the grid-side AC voltage, including: like Figure 3 As shown, the left converter is the machine-side converter, and its control method is to collect the three-phase current on the rotor side, and then decompose the three-phase current on the rotor side into two-phase static coordinates through Clark coordinate transformation, and then transform the two-phase static coordinates into two-phase rotating coordinates through Park coordinate transformation, and participate in the machine-side current inner loop together with the output value of the DC side capacitor voltage through the DC side voltage outer loop, and perform inverse Park coordinate transformation on the output value of the machine-side current inner loop, transform the two-phase rotating coordinates into two-phase static coordinates, and then transform them into three-phase output values ​​through inverse Clark transformation, and complete the control of the machine-side converter through pulse width modulation (PWM); the right converter is the grid-side converter, and its control method is to collect the grid-side AC voltage and the grid-side After the alternating current, the three-phase current on the rotor side is decomposed into two-phase stationary coordinates through Clark coordinate transformation, and then the two-phase stationary coordinates are transformed into two-phase rotating coordinates through Park coordinate transformation. The active power and reactive power of the system are calculated through the values ​​of the two-phase rotating coordinate transformation. The calculated power value is controlled by the virtual synchronous machine to obtain the reference value of the voltage outer loop, and the reference value of the current inner loop using the linear active interference rejection technology is obtained through the voltage outer loop. The output value of the current inner loop using the linear active interference rejection technology is subjected to inverse Park coordinate transformation, and the two-phase rotating coordinates are transformed into two-phase stationary coordinates, and then transformed into three-phase output values ​​through inverse Clark transformation, and the control of the grid-side converter is completed through pulse width modulation (PWM).

[0014] Virtual synchronous machine control can provide frequency and phase for wind turbines, so the system no longer needs a phase-locked loop to synchronize frequency and phase. The frequency and phase in the subsequent startup process are provided by the virtual synchronous machine. The following are the specific steps of virtual synchronous machine control: (1) Construct the second-order characteristic equation of the virtual rotor of the virtual synchronous machine: ; The rotor motion equation model is mainly constructed based on the rotor mechanical equation of the synchronous generator. is the virtual moment of inertia; is the rotor angular velocity, system angular velocity, and rated speed; is the mechanical torque, the electromagnetic torque; is mechanical power, electromagnetic power; is the damping coefficient, power angle, and t is the time.

[0015] (2) Constructing a virtual excitation model: ; in, is the reactive power-droop coefficient; is the voltage deviation value; is the reactive power deviation value; , are the rated voltage value of the grid connection point, the voltage amplitude of the grid connection point, , are the reactive power command value and the actual reactive power output of the system respectively.

[0016] Step 4: After the AC voltage on the grid side is established, the AC load is put into operation, and the grid-side converter control provides support for the system. The linear anti-disturbance technology is combined to suppress system fluctuations and improve system stability. The unit is started, including: The use of linear active disturbance rejection can improve system stability. The following is the linear active disturbance rejection controller model: (1) Construct a third-order linear observer as: ; in, ; ; To control the gain; ; is the state empty variable of the third-order linear observer; , , are the controller output value, the differential of the output value, and the total disturbance of the system respectively; is the differential of the total disturbance; is the input quantity; is an estimate of the system state; is the state observation gain of the linear observer; is the observer bandwidth; Output for the system.

[0017] (2) The linear error feedback control law is constructed as: ; in, , They are proportional control gain and differential control gain respectively; , are the controller output value and the differential of the output value respectively; To be the target of the charge; The output of the linear error feedback law.

[0018] Figure 4The schematic diagram of wind turbine startup in an isolated and off-grid environment is shown, including the first wind turbine, the second wind turbine, the third wind turbine...the nth wind turbine, and corresponding circuit breakers S1, S2, S3...Sn are arranged behind the corresponding wind turbines, and each wind turbine is equipped with a 0.69Kv / 35kV step-up transformer. In addition, there are switches Br1, Br2, Br3...Brn in the AC load on the right, which are used to connect and disconnect the load to the system.

[0019] The present invention only describes the starting method and control strategy of the first wind turbine with a capacity of 2MW without connecting to other power sources, and the other wind turbines are not described. First, start the direct-drive wind turbine pitch system of the first wind turbine and adjust the pitch angle. When the direct-drive wind turbine pitch system and the yaw system reach the working conditions, drive the wind turbine to accelerate to the rated speed; secondly, start the machine-side converter, and the machine side charges the DC side capacitor until the preset voltage value, and at the same time, the DC capacitor voltage is maintained at 1100V through the machine-side converter control; again, start the grid-side converter to establish an AC voltage of 690V; then, the voltage is increased to 35kV through the step-up transformer and then merged into the AC bus, completing the process of establishing the AC bus, and finally, the circuit breakers S2, S3...Sn and switches Br1, Br2, Br3...Brn can be closed in sequence to connect to the other wind turbines and loads, so that the entire system can operate.

[0020] like Figure 2 As shown, the present invention also provides a direct black start system for a grid-type permanent magnet direct-drive wind turbine set, the system comprising: The first module is used to start the direct-drive fan and accelerate the fan speed to the rated speed; The second module is used to start the machine-side converter, and the machine side charges the DC side capacitor to a preset voltage value, while maintaining the DC capacitor voltage through the machine-side converter; The third module is used to start the grid-side converter and establish the grid-side AC voltage; The fourth module is used to realize that after the AC voltage on the grid side is established, the AC load is put into use, the grid-side converter control provides support for the system, and the linear anti-disturbance technology is combined to suppress system fluctuations, improve system stability, and start the unit.

Claims

1. A direct black start method for a grid-type permanent magnet direct-drive wind turbine generator set, characterized in that: The following steps are involved: Step 1: Start the direct-drive wind turbine pitch system and adjust the pitch angle. When the direct-drive wind turbine pitch system and yaw system reach working conditions, drive the wind turbine to accelerate to the rated speed. Step 2: Start the machine-side converter, and charge the DC side capacitor to a preset voltage value, while maintaining the DC capacitor voltage through the machine-side converter control; Step 3: Start the grid-side converter to establish the grid-side AC voltage; Step 4: After the grid-side AC voltage is established, the AC load is put into operation, and the grid-side converter control is used to provide support for the system. The linear anti-disturbance technology is combined to suppress system fluctuations, improve system stability, and start the unit.

2. A direct black start method for a grid-type permanent magnet direct-drive wind turbine according to claim 1, characterized in that: The step 1 includes: starting the direct-drive wind turbine pitch control system and waiting for the wind turbine speed to rise to the rated speed. The specific mathematical model is as follows: ； in, is the pitch angle of the wind turbine; , They are the proportional coefficient and integral coefficient in pitch control respectively; , They are respectively the rated speed and actual speed of the fan; Represents the integral transformation sign.

3. The direct black start method of a grid-type permanent magnet direct-drive wind turbine set according to claim 1, characterized in that: Start the machine-side converter and maintain the DC bus-side capacitor voltage stable in step 2. The specific mathematical model is as follows: ； in, , is the dq axis reference current; , They are the actual value of capacitor side voltage and the reference value of capacitor side voltage respectively; , They are the proportional coefficient and integral coefficient in the voltage outer loop respectively; Represents the integral transformation sign.

4. The direct black start method of a grid-type permanent magnet direct-drive wind turbine set according to claim 1, characterized in that: The step 3 includes network-side virtual synchronous machine control; The virtual synchronous machine control specifically includes: (1) Construct the second-order characteristic equation of the virtual rotor of the virtual synchronous machine: ； in, is the virtual moment of inertia; is the rotor angular velocity, system angular velocity, and rated speed; is the mechanical torque, the electromagnetic torque; is mechanical power, electromagnetic power; is the damping coefficient, power angle, and t is the time; (2) Constructing a virtual excitation model: ； in, is the reactive power-droop coefficient; is the voltage deviation value; is the reactive power deviation value; , are the rated voltage value of the grid connection point, the voltage amplitude of the grid connection point, , are the reactive power command value and the actual reactive power output of the system respectively.

5. The direct black start method of a grid-type permanent magnet direct-drive wind turbine set according to claim 1, characterized in that: The step 4 includes suppressing voltage fluctuations and thus power fluctuations by using a linear auto-disturbance rejection technique. The specific model of the linear auto-disturbance rejection technique is: (1) Construct a third-order linear observer as: ； in, ; ; To control the gain; ; is the state empty variable of the third-order linear observer; , , are the controller output value, the differential of the output value, and the total disturbance of the system respectively; is the differential of the total disturbance; is the input quantity; is an estimate of the system state; is the state observation gain of the linear observer; is the observer bandwidth; Output for the system; (2) The linear error feedback control law is constructed as: ； in, , They are proportional control gain and differential control gain respectively; , are the controller output value and the differential of the output value respectively; To be the target of the charge; The output of the linear error feedback law.

6. A direct black start system based on a direct black start method of a grid-type permanent magnet direct-drive wind turbine set according to any one of claims 1 to 4, characterized in that: include: The first module is used to start the direct-drive wind turbine pitch system and adjust the pitch angle. When the direct-drive wind turbine pitch system and yaw system reach working conditions, the wind turbine is driven to accelerate to the rated speed. The second module is used to start the machine-side converter, and the machine side charges the DC side capacitor to a preset voltage value, while maintaining the DC capacitor voltage through the machine-side converter; The third module is used to start the grid-side converter and establish the grid-side AC voltage; The fourth module is used to realize that after the AC voltage on the grid side is established, the AC load is put into use, the grid-side converter control provides support for the system, and the linear anti-disturbance technology is combined to suppress system fluctuations, improve system stability, and start the unit.

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