Doubly-fed wind turbine ride-through system and method based on energy storage device and converter reconstruction

Abstract

The present invention discloses a double-fed wind turbine ride-through system and method based on energy storage device and converter reconstruction, wherein the system comprises a double-fed induction wind turbine, a rotor-side converter, a capacitor digital converter, a grid-side converter, an inductor L g , inductor L, switch S 1 , switch S 2 , switch S 3 , coupling transformer, series transformer, power grid and superconducting magnetic energy storage device. During the fault period, the grid-side converter switches from the parallel operation mode to the series operation mode, with the goal of maintaining the stator terminal voltage unchanged, and controls the rotor-side converter to adaptively emit dynamic inductive / capacitive reactive current according to the grid connection point voltage. This method can not only maintain the terminal voltage of the doubly fed induction wind turbine, but also provide reactive support for the power grid, effectively realizing the low-high voltage continuous fault ride-through of the doubly fed induction wind turbine.

Description

Technical Field

[0001] The present invention belongs to the technical field of doubly-fed wind turbine ride-through, and in particular relates to a doubly-fed wind turbine ride-through system and method based on energy storage device and converter reconstruction. Background Art

[0002] Due to the flexible operation of doubly-fed induction generators, they have been widely used around the world. However, when a commutation failure occurs on the inverter side of the HVDC transmission system, the control strategy and reactive power compensation mechanism of the HVDC transmission system will cause a continuous fault of "first low and then high" on the busbar of the wind farm at the sending end. Compared with a single voltage fault, the doubly-fed induction generator will produce more severe transient shocks under this new type of fault and face a greater risk of disconnection from the grid. The continuous low and high voltage fault characteristics of the busbar of the wind farm at the sending end caused by the commutation failure of the HVDC transmission system will produce more severe transient shocks on the doubly-fed induction generator. The existing single low-through / high-through wind turbine protection scheme is difficult to fully adapt to the requirements of such continuous fault ride-through. Summary of the invention

[0003] The purpose of the present invention is to solve the problem that the existing single low-through / high-through wind turbine protection scheme is difficult to fully adapt to continuous fault ride-through, and a doubly-fed wind turbine ride-through system and method based on energy storage device and converter reconstruction is proposed.

[0004] The technical solution of the present invention is: a doubly-fed wind turbine ride-through system based on energy storage device and converter reconstruction comprises a doubly-fed induction wind turbine, a rotor-side converter, a capacitor digital converter, a grid-side converter, an inductor L g , inductor L, switch S1, switch S2, switch S3, coupling transformer, series transformer, power grid and superconducting magnetic energy storage device;

[0005] The stator end of the double-fed induction fan is connected to the inductor L g One end of is connected to the first coil of the coupling transformer, and the first coil of the coupling transformer is connected to the grid through the series transformer; the rotor side of the doubly fed induction wind turbine is connected to the rotor side converter, the capacitor digital converter and one end of the grid side converter in sequence; the other end of the grid side converter is connected to one end of the switch S2 and one end of the switch S3 respectively; the other end of the switch S2 is connected to the inductor L g The other end of the switch S3 is connected to one end of the inductor L; the other end of the inductor L is connected to the second coil of the coupling transformer; the two ends of the switch S1 are connected to the first coil of the coupling transformer; the connection point between the capacitor digital converter and the grid-side transformer is connected to the superconducting magnetic energy storage device.

[0006] The beneficial effects of the present invention are as follows: when a fault is detected, the control switch connects the grid-side converter to the series transformer, the grid-side converter with a transient control strategy and the superconducting magnetic energy storage device jointly achieve the goal of stabilizing the machine-end voltage, and the doubly-fed induction wind turbine can maintain stable operation and output power to the grid.

[0007] Based on the above system, the present invention also proposes a doubly-fed wind turbine ride-through method based on energy storage device and converter reconstruction, comprising the following steps:

[0008] S1: When the voltage at the common connection point between the series transformer and the grid is less than 0.9pu or greater than 1.1pu, the switches S1 and S2 are opened, the switch S3 is closed, and according to the transient control strategy of the rotor-side converter, the dynamic reactive current that meets the grid-connected requirements of the doubly-fed induction wind turbine is output;

[0009] S2: outputting corresponding compensation voltages according to the control strategy of the grid-side converter and the control strategy of the superconducting magnetic energy storage device;

[0010] S3: Use dynamic reactive current to stabilize the current of the doubly-fed induction wind turbine, and use the compensation voltage output by the grid-side converter and the superconducting magnetic energy storage device to stabilize the voltage of the doubly-fed induction wind turbine, so that the doubly-fed induction wind turbine can complete continuous fault ride-through.

[0011] Furthermore, in step S1, the transient control strategy of the rotor-side converter is specifically: adjusting the dynamic reactive current of the rotor-side converter according to the magnitude of the increase or decrease of the grid voltage.

[0012] Furthermore, in step S1, the grid connection requirements of the doubly-fed induction wind turbine are as follows: when the voltage at the common connection point is less than 0.9pu, the doubly-fed induction wind turbine outputs a dynamic reactive current I sq1 , and its calculation formula is:

[0013]

[0014] Among them, V pcc Indicates the voltage deviation per unit value of the common connection point;

[0015] When the voltage at the common connection point is greater than 1.1pu, the double-fed induction wind turbine outputs a dynamic reactive current I sq2 , and its calculation formula is:

[0016] I sq2 ≥-2ΔV pcc , ΔV pcc ≥0.1.

[0017] Further, in step S2, the control strategy of the grid-side converter is specifically as follows: the voltage reference value V at the busbar at the outlet side of the double-fed induction wind turbine is set to refThe difference between the actual voltage value V at the busbar on the outlet side of the doubly fed induction fan is used as the compensation voltage.

[0018] Furthermore, in step S2, the control strategy of the superconducting magnetic energy storage device is specifically as follows: the DC voltage reference value V of the voltage converter in the superconducting magnetic energy storage device is set to sc_dcref The actual value of the DC voltage V of the voltage converter sc_dc The difference is used as the compensation voltage.

[0019] The beneficial effect of the present invention is that during a fault, the grid-side converter switches from the parallel operation mode to the series operation mode, with the goal of maintaining the stator terminal voltage unchanged, and controls the rotor-side converter to adaptively emit dynamic inductive / capacitive reactive current according to the grid connection point voltage. This method can not only maintain the terminal voltage of the doubly-fed induction wind turbine, but also provide reactive support for the power grid, effectively realizing the low-high voltage continuous fault ride-through of the doubly-fed induction wind turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the structural diagram of the doubly-fed wind turbine ride-through system based on energy storage device and converter reconstruction;

[0021] Figure 2 A flow chart of a doubly-fed wind turbine ride-through method based on energy storage device and converter reconstruction;

[0022] Figure 3 is the control block diagram of the rotor-side converter control strategy;

[0023] Figure 4 It is the control block diagram of the grid-side converter control strategy;

[0024] Figure 5 This is the control block diagram of the DC / DC converter control strategy. DETAILED DESCRIPTION

[0025] The embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0026] like Figure 1 As shown, the present invention provides a doubly-fed wind turbine ride-through system based on energy storage device and converter reconstruction, comprising a doubly-fed induction wind turbine, a rotor-side converter, a capacitor-digital converter, a grid-side converter, an inductor L g , inductor L, switch S1, switch S2, switch S3, coupling transformer, series transformer, power grid and superconducting magnetic energy storage device;

[0027] The stator end of the double-fed induction fan is connected to the inductor L gOne end of is connected to the first coil of the coupling transformer, and the first coil of the coupling transformer is connected to the grid through the series transformer; the rotor side of the doubly fed induction wind turbine is connected to the rotor side converter, the capacitor digital converter and one end of the grid side converter in sequence; the other end of the grid side converter is connected to one end of the switch S2 and one end of the switch S3 respectively; the other end of the switch S2 is connected to the inductor L g The other end of the switch S3 is connected to one end of the inductor L; the other end of the inductor L is connected to the second coil of the coupling transformer; the two ends of the switch S1 are connected to the first coil of the coupling transformer; the connection point between the capacitor digital converter and the grid-side transformer is connected to the superconducting magnetic energy storage device.

[0028] Based on the above system, the present invention also proposes a doubly-fed wind turbine ride-through method based on energy storage device and converter reconstruction, such as Figure 2 As shown, the following steps are included:

[0029] S1: When the voltage at the common connection point between the series transformer and the grid is less than 0.9pu or greater than 1.1pu, the switches S1 and S2 are opened, the switch S3 is closed, and according to the transient control strategy of the rotor-side converter, the dynamic reactive current that meets the grid-connected requirements of the doubly-fed induction wind turbine is output;

[0030] S2: outputting corresponding compensation voltages according to the control strategy of the grid-side converter and the control strategy of the superconducting magnetic energy storage device;

[0031] S3: Use dynamic reactive current to stabilize the current of the doubly-fed induction wind turbine, and use the compensation voltage output by the grid-side converter and the superconducting magnetic energy storage device to stabilize the voltage of the doubly-fed induction wind turbine, so that the doubly-fed induction wind turbine can complete continuous fault ride-through.

[0032] In the embodiment of the present invention, in step S1, the transient control strategy of the rotor-side converter is specifically: adjusting the dynamic reactive current of the rotor-side converter according to the magnitude of the increase or decrease of the grid voltage.

[0033] In the embodiment of the present invention, in step S1, the grid connection requirements of the doubly-fed induction wind turbine are as follows: when the voltage at the common connection point is less than 0.9 pu, the doubly-fed induction wind turbine outputs a dynamic reactive current I sq1 , and its calculation formula is:

[0034]

[0035] Among them, V pcc Indicates the voltage deviation per unit value of the common connection point;

[0036] When the voltage at the common connection point is greater than 1.1pu, the double-fed induction wind turbine outputs a dynamic reactive current I sq2 , and its calculation formula is:

[0037] I sq2 ≥-2ΔV pcc , ΔV pcc ≥0.1.

[0038] In the embodiment of the present invention, in step S2, the control strategy of the grid-side converter is specifically: set the bus voltage reference value V at the outlet side of the double-fed induction wind turbine to ref The difference between the actual voltage value V at the busbar on the outlet side of the doubly fed induction fan is used as the compensation voltage.

[0039] In the embodiment of the present invention, in step S2, the control strategy of the superconducting magnetic energy storage device is specifically: the DC voltage reference value V of the voltage converter in the superconducting magnetic energy storage device is set to sc_dcref The actual value of the DC voltage of the voltage converter V sc_dc The difference is used as the compensation voltage.

[0040] In the embodiment of the present invention, the directions of the stator and rotor currents are based on the motor convention, and the voltage and flux equations of the doubly fed induction fan in the stationary stator coordinate system can be expressed as:

[0041]

[0042]

[0043]

[0044]

[0045] Where v, i and ψ are the voltage / current and flux space vectors respectively. The subscripts s and r denote the stator and rotor respectively. s , L r and L m They are stator, rotor and excitation inductance respectively. r is the rotor angular frequency.

[0046] Combined with the above equation, the rotor voltage can be re-expressed as:

[0047]

[0048] In the formula, the first term on the right side is the induced potential, which is expressed as It can be seen that the induced potential is related to the stator flux. The rotor voltage is composed of the induced potential and the voltage drop on the rotor transient impedance. Under severe faults, the large induced potential is the main cause of the rotor overvoltage. The stator flux expression during the fault is:

[0049]

[0050] In the formula, τ is the stator free flux decay time constant, k1 and k2 are the voltage amplitude change rates at t0-t1 and t2-t3 respectively. C represents the initial value of the free flux at each stage, which can be expressed as

[0051]

[0052] It can be seen from the above formula that compared with a single low voltage fault, the transient flux component under continuous fault has a cumulative effect, that is, the transient flux component that has not been fully decayed in the previous stage will be superimposed on the transient flux component in the next stage. At the same time, it can be seen from formula (5) that a larger transient flux component will lead to a larger rotor induced potential. In addition, since the maximum allowable voltage of RSC is limited by the DC voltage value and the modulation ratio, the difference between the rotor voltage and the induced potential will produce a larger overcurrent on the rotor transient impedance.

[0053] In the embodiment of the present invention, the structure and working principle of the DFIG system based on superconducting magnetic energy storage and grid-side converter reconstruction are as follows: the double-fed induction wind turbine topology structure integrated with superconducting magnetic energy storage is as follows: Figure 1 As shown. The superconducting magnetic energy storage device is connected in parallel with the DC bus of the doubly fed induction wind turbine through a DC / DC converter. The series transformer is connected between the machine end of the doubly fed induction wind turbine and the grid, and is bypassed by the power electronic switch S1 under normal operation. Under normal circumstances, the grid-side converter is connected in parallel with the stator. When a voltage fault is detected, the control switch connects the grid-side converter to the series transformer, and the grid-side converter with a transient control strategy and the superconducting magnetic energy storage device jointly achieve the goal of stabilizing the machine-end voltage.

[0054] Under normal operation, the series transformer is bypassed by switch S1. When a voltage fault is detected, switches S1 and S2 are opened, and switch S3 is closed. The grid-side converter controller switches to compensation control and injects compensation voltage to keep the DFIG terminal voltage at the value before the fault. Therefore, the DFIG can maintain stable operation and output power to the grid. The stator voltage is:

[0055]

[0056] In the formula, is the stator terminal voltage vector, is the grid voltage vector, It is the compensation voltage vector generated by GSC through the series transformer.

[0057] By compensating the stator voltage, the amplitude of the stator transient flux component can be effectively reduced, avoiding the transient flux that has not been completely attenuated in the previous fault stage from affecting the transient flux in the next fault stage, and curbing the DFIG rotor overvoltage and overcurrent caused by continuous faults. At the same time, the rotor-side converter can be kept flexible and controllable to provide reactive power support to the power grid.

[0058] In the embodiment of the present invention, the rotor-side converter control strategy takes the reference value to achieve the dynamic reactive current output required by the wind turbine grid connection standard. Figure 3 As shown in Figure 1, under normal circumstances, the rotor-side converter control scheme adopts a dual-loop vector control based on a PI controller. sref , Q sref Respectively with the actual value P s , Q s The inner ring rotor current command value I is obtained through the PI controller. rdref ,I rqref I rdref ,I rqref The actual value of the rotor current I rd ,I ra The deviation between the input value PI controller, plus the respective compensation terms, is the rotor voltage command value U rdref , U rqref However, during the fault period, the dynamic reactive power support of the doubly fed induction wind turbine to the grid needs to be additionally considered. Since the bandwidth of the inner current loop is designed to be significantly larger than the bandwidth of the outer power loop, the response speed of the inner current loop is significantly faster than that of the outer power loop. When a fault occurs, in order to improve the control performance of the rotor-side converter, the outer power loop is disconnected and the inner current loop control is used. The rotor current command value is converted into the three-phase rotor current I raref ,I rbref and I rcref , and respectively with the actual value of the three-phase rotor current I ra ,I rb and I rc The difference is input into the current hysteresis comparator to obtain the switching signal.

[0059] During a fault, the rotor reactive current changes its magnitude and direction in real time as the grid voltage drops or rises to support grid voltage recovery. According to the E.ON standard, the doubly-fed induction wind turbine needs to provide reactive support to the grid during low / high voltage faults. The additional reactive current that the doubly-fed induction wind turbine needs to output during low voltage is:

[0060]

[0061] According to the standard, the output reactive current of the double-fed induction wind turbine during high voltage should be:

[0062] I sq2 ≥-2ΔV pcc , ΔV pcc ≥0.1

[0063] According to the relationship between the stator and rotor currents, the q-axis rotor current reference value can be set as:

[0064]

[0065] The rotor active current decreases proportionally according to the positive sequence voltage deviation value of the common connection point. The rotor active current reference value is

[0066] I rd_ref =(1-|ΔV PCC |I rq_prefault )

[0067] At this time, the upper limit of the rotor active current is

[0068]

[0069] In the formula, I rm It is the safety threshold for DFIG to continue working.

[0070] The parameters of the PI controller are all set for normal operating conditions, and the robustness of the PI controller is poor. During a fault, the proposed scheme will cause the motor equivalent parameters to change in the stator series circuit, and the active current and reactive current reference values ​​will change rapidly. If the PI controller is still used, it will lead to a large tracking error. Therefore, a hysteresis comparator with a simple structure and good tracking performance is selected during a fault.

[0071] The grid-side converter control strategy is specifically as follows: During normal operation, the grid-side converter control strategy still adopts dual-loop control of the DC voltage outer loop and the current inner loop to stabilize the DC voltage. During a fault, the grid-side converter is connected in series with the stator side, and the series compensation mode of the grid-side converter is activated, which injects a compensation voltage into the stator circuit to maintain the stator voltage. Compared with symmetrical faults, asymmetrical faults are more common in power systems. Although the present invention is aimed at symmetrical continuous faults, the proposed control strategy is also applicable to single asymmetrical faults. In order to speed up the response speed, the present invention adopts a single voltage loop control strategy based on a hysteresis comparator.

[0072] like Figure 4 As shown, the voltage reference value V at the outlet of the doubly fed induction fan is ref The difference between the actual value V is the series compensation voltage reference value V cref . V cref And the actual value of the voltage on the filter capacitor V c The difference is sent to the hysteresis comparator to obtain the six trigger signals of the grid-side converter.

[0073] In the embodiment of the present invention, the DC / DC converter control strategy is used to stabilize the DC voltage. As a power type energy storage unit, the superconducting magnetic energy storage can quickly absorb or release energy through the DC / DC converter to keep the DC bus voltage constant. The control block diagram of the DC / DC converter is shown in FIG. Figure 5 As shown. DC voltage reference value V dcrefWith the actual value V dc The deviation between the basic value 0.5 and the adjustable duty cycle is input to the PI controller to generate an adjustable duty cycle ∈ [-0.5, +0.5]. The sum of the basic value 0.5 and the adjustable duty cycle is the duty cycle D of the IGBT.

[0074] The working principle and process of the present invention are as follows: The present invention proposes a DFIG continuous fault ride-through scheme based on superconducting magnetic energy storage system and grid-side converter reconstruction. First, the transient model of the doubly-fed induction wind turbine under continuous faults caused by commutation failure of the high-voltage direct current transmission system is analyzed. When a voltage fault is detected, the grid-side converter switches to the series compensation loop, and the grid-side converter and the superconducting magnetic energy storage system jointly achieve the goal of stabilizing the machine-end voltage, reducing the use length of the superconducting tape and reducing costs. In addition, a transient control strategy for the rotor-side converter is designed to achieve the dynamic reactive current output required by the wind turbine grid-connected standard.

[0075] The beneficial effects of the present invention are:

[0076] (1) When a fault is detected, the control switch connects the grid-side converter to the series transformer. The grid-side converter with transient control strategy and the superconducting magnetic energy storage device jointly achieve the goal of stabilizing the terminal voltage. The doubly-fed induction wind turbine can maintain stable operation and output power to the grid.

[0077] (2) During the fault period, the grid-side converter switches from the parallel operation mode to the series operation mode, with the goal of maintaining the stator terminal voltage unchanged, and controls the rotor-side converter to adaptively emit dynamic inductive / capacitive reactive current according to the grid connection point voltage. This method can not only maintain the terminal voltage of the doubly-fed induction wind turbine, but also provide reactive support for the grid, effectively realizing the low-high voltage continuous fault ride-through of the doubly-fed induction wind turbine.

[0078] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A doubly-fed wind turbine ride-through method based on energy storage device and converter reconstruction, characterized in that: The system for realizing the cross-over of the doubly-fed wind turbine includes a doubly-fed induction wind turbine, a rotor-side converter, a capacitor-digital converter, a grid-side converter, an inductor L g , inductor L, switch S1, switch S2, switch S3, coupling transformer, series transformer, power grid and superconducting magnetic energy storage device; The stator ends of the double-fed induction fan are respectively connected to the inductor L g One end of is connected to the first coil of the coupling transformer, and the first coil of the coupling transformer is connected to the power grid through a series transformer; the rotor side of the doubly fed induction wind turbine is connected to the rotor side converter, the capacitor digital converter and one end of the grid side converter in sequence; the other end of the grid side converter is respectively connected to one end of the switch S2 and one end of the switch S3; the other end of the switch S2 is connected to the inductor L g The other end of the switch S3 is connected to one end of the inductor L; the other end of the inductor L is connected to the second coil of the coupling transformer; the two ends of the switch S1 are connected to the first coil of the coupling transformer; the connection point between the capacitance digital converter and the grid-side transformer is connected to the superconducting magnetic energy storage device; The doubly-fed wind turbine ride-through method comprises the following steps: S1: When the voltage at the common connection point between the series transformer and the grid is less than 0.9pu or greater than 1.1pu, the switches S1 and S2 are opened, the switch S3 is closed, and according to the transient control strategy of the rotor-side converter, the dynamic reactive current that meets the grid-connected requirements of the doubly-fed induction wind turbine is output; S2: outputting corresponding compensation voltages according to the control strategy of the grid-side converter and the control strategy of the superconducting magnetic energy storage device; S3: Use dynamic reactive current to stabilize the current of the doubly-fed induction wind turbine, and use the compensation voltage output by the grid-side converter and the superconducting magnetic energy storage device to stabilize the voltage of the doubly-fed induction wind turbine, so that the doubly-fed induction wind turbine can complete continuous fault ride-through; In step S1, the grid connection requirements of the doubly-fed induction wind turbine are as follows: when the voltage at the common connection point is less than 0.9 pu, the doubly-fed induction wind turbine outputs a dynamic reactive current I sq1 , and its calculation formula is: Among them, V pcc Indicates the voltage deviation per unit value of the common connection point; When the voltage at the common connection point is greater than 1.1pu, the double-fed induction wind turbine outputs a dynamic reactive current I sq2 , and its calculation formula is: I sq2 ≥-2ΔV pcc ,ΔV pcc ≥0.1。 2. The method for doubly-fed wind turbine ride-through based on energy storage device and converter reconstruction according to claim 1 is characterized in that: In the step S1, the transient control strategy of the rotor-side converter is specifically: adjusting the dynamic reactive current of the rotor-side converter according to the magnitude of the increase or decrease of the grid voltage.

3. The method for doubly-fed wind turbine ride-through based on energy storage device and converter reconstruction according to claim 1, characterized in that: In step S2, the control strategy of the grid-side converter is specifically as follows: the voltage reference value V at the busbar at the outlet side of the double-fed induction wind turbine is set to ref The difference between the actual voltage value V at the busbar on the outlet side of the doubly fed induction fan is used as the compensation voltage.

4. The method for doubly-fed wind turbine ride-through based on energy storage device and converter reconstruction according to claim 1, characterized in that: In step S2, the control strategy of the superconducting magnetic energy storage device is specifically as follows: the DC voltage reference value V of the voltage converter in the superconducting magnetic energy storage device is set to sc_dcref The actual value of the DC voltage V of the voltage converter sc_dc The difference is used as the compensation voltage.

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