Control System and Control Method for Active Crowbar Circuit of Variable Speed ​​Pumped Storage Unit

Abstract

This invention relates to an active crowbar circuit control system and method for variable-speed pumped-storage hydroelectric power generation units, belonging to the field of variable-speed pumped-storage power generation-motor control technology. To improve the unit's low-voltage ride-through capability and enhance grid power quality, the present invention uses an RL filter circuit with a resistor connected to the crowbar-side converter and an inductor connected in parallel between the doubly-fed induction generator (DFIG) and the rotor-side converter. One end of the three-phase current detection module is connected to the CSC controller, and the other end is connected to the inductor. One end of the drive circuit is connected to the CSC controller, and the other end is connected to the crowbar-side converter. One end of the DC voltage detection module is connected to the CSC controller, and the other end is connected to a capacitor. One end of the three-phase voltage detection module is connected to the CSC controller, and the other end is connected to the three-phase power grid. This invention improves the unit's low-voltage ride-through capability.

Description

Technical Field

[0001] This invention belongs to the field of variable speed pumped storage power generation - motor control technology, specifically relating to the active crowbar circuit control system and control method for variable speed pumped storage units. Background Technology

[0002] Pumped storage power stations are an important means of solving grid peak-shaving problems, ensuring grid operation safety, and promoting the economical operation of various power sources. Doubly fed induction generator (DFIGM) pumped storage units use a stator connected to the grid, with symmetrically distributed three-phase excitation windings on the rotor, and excitation current supplied by a converter. By adjusting the amplitude, frequency, and phase of the rotor-side voltage or current through the converter, the active and reactive power of the unit can be quickly adjusted, enhancing system stability.

[0003] To fulfill the mission of ensuring the safety of the new power system, variable-speed pumped storage units need to possess fault ride-through capabilities, maintaining parallel operation with the grid and generating reactive power to help restore grid voltage during grid faults. Currently, control strategies based on low-voltage ride-through auxiliary devices (LVRADs) cannot simultaneously improve unit performance and grid power quality. A single LVRAD has the disadvantages of limited functionality and low cost-effectiveness, while using multiple LVRADs in combination increases system complexity and cost and hinders system stability. Summary of the Invention

[0004] The problem this invention aims to solve is to improve the low-voltage ride-through capability of the unit and improve the power quality of the power grid. It proposes an active crowbar circuit control system and its control method for variable-speed pumped storage units.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] An active crowbar circuit control system for a variable speed pumped storage unit includes an active crowbar circuit, a CSC (Crowbar side converter) controller, a three-phase current detection module, a drive circuit, a DC voltage detection module, and a three-phase voltage detection module.

[0007] The active crowbar circuit includes an RL filter circuit consisting of a resistor connected to an inductor, a crowbar-side converter, and a capacitor. The resistor of the RL filter circuit is connected to the crowbar-side converter, and the inductor of the RL filter circuit is connected in the circuit between the doubly fed motor and the rotor-side converter (RSC). The inductor and the crowbar-side converter are connected in parallel.

[0008] One end of the three-phase current detection module is connected to the CSC controller, and the other end of the three-phase current detection module is connected to an inductor;

[0009] One end of the drive circuit is connected to the CSC controller, and the other end of the drive circuit is connected to the crowbar-side converter.

[0010] One end of the DC voltage detection module is connected to the CSC controller, and the other end of the DC voltage detection module is connected to a capacitor;

[0011] One end of the three-phase voltage detection module is connected to the CSC controller, and the other end of the three-phase voltage detection module is connected to the three-phase power grid;

[0012] The doubly fed motor is connected to the gearbox and the three-phase power grid, respectively, and the gearbox is connected to the water pump turbine.

[0013] Furthermore, the crowbar-side converter consists of three sets of circuits connected in parallel. Each set of circuits includes a first switching transistor, a first freewheeling diode, a second switching transistor, and a second freewheeling diode. The first switching transistor is connected in anti-parallel to the first freewheeling diode, and the second switching transistor is connected in anti-parallel to the second freewheeling diode. The collector of the first switching transistor is connected to the positive terminal of the capacitor, the emitter of the first switching transistor is connected to the collector of the second switching transistor, and the emitter of the second switching transistor is connected to the negative terminal of the capacitor. The connection circuit of the first switching transistor and the second switching transistor is connected to the resistor of the RL filter circuit.

[0014] Furthermore, the CSC controller includes a rotation angle acquisition module, an asymmetric current detection module, a voltage regulation control module, and a PWM (Pulse width modulation) generation module. The rotation angle acquisition module and the voltage regulation control module are respectively connected to the asymmetric current detection module, and the asymmetric current detection module is connected to the PWM generation module.

[0015] Grid voltage u sabc The fluid flows into the rotation angle acquisition module, which consists of a positive and negative sequence separation module and a phase-locked loop (PLL).

[0016] Rotor-side current i rabc The current flows into the asymmetric current detection module, which consists of a positive and negative sequence separation module, a coordinate transformation module, and a low-pass filter (LPF).

[0017] DC side actual voltage U SC The current flows into the voltage regulation control module, which has a PI controller (proportional integral controller);

[0018] Asymmetrical current detection module output current The input flows into the PWM generation module, which has a PI controller, a PR controller, or a PIR controller.

[0019] Furthermore, the crowbar-side converter is replaced with an H-bridge cascaded or modular multilevel converter (MMC) or an MMC plus H-bridge multilevel topology.

[0020] An active crowbar circuit control method for a variable-speed pumped-storage unit, based on the aforementioned active crowbar circuit control system for a variable-speed pumped-storage unit, includes the following steps:

[0021] S1, grid voltage u sabc The input flows into the rotation angle acquisition module. The positive and negative sequence separation module first separates the grid voltage into two components, positive and negative sequence, using the delay method. The PLL obtains the phase angle ωt of the grid fundamental positive sequence by detecting the positive sequence signal of the grid voltage phase a.

[0022] S2. Input the phase angle ωt of the fundamental positive sequence of the power grid obtained in step S1 into the coordinate transformation module of the asymmetric current detection module;

[0023] S3, rotor side current i rabc The current flows into the asymmetrical current detection module. The positive and negative sequence separation module first separates the rotor-side current into three-phase positive and negative sequence components of the rotor-side active current. Then, the coordinate transformation module uses ωt to convert the three-phase positive and negative sequence components of the rotor-side active current into two-phase positive and negative sequence components of the rotor-side active current.

[0024] S4. The two-phase positive and negative sequence components of the rotor-side active current obtained in step S3 are filtered out by a low-pass filter (LPF) to remove high-frequency harmonics, thus obtaining the filtered two-phase positive and negative sequence components of the rotor-side active current.

[0025] S5, the voltage regulation control module adopts closed-loop control, which controls the DC side voltage command voltage U. SC-ref With DC side actual voltage U SC By performing PI regulation, the active current Δi that compensates for the DC side voltage is obtained. d , will Δi d The two-phase positive and negative sequence components of the filtered rotor-side active current obtained in step S4 are superimposed on the positive and negative sequence components, and then the positive sequence component of the three-phase current containing only the fundamental frequency is obtained through inverse coordinate transformation. Only the negative sequence component of the fundamental three-phase current Calculate the output current of the asymmetric current detection module

[0026] S6. The output current of the asymmetric current detection module obtained in step S5. The input signal is used as the command signal to the PWM generation module, and the three-phase current output from the CSC AC side is used as the actual signal i. svg The signal is adjusted by a PI controller, and then compared with a triangular carrier wave to generate PWM signals for the six switching transistors in the CSC. The CSC is then controlled by a drive circuit.

[0027] Furthermore, the transformation formula for converting the three-phase current to two-phase current in step S3 of the coordinate transformation module is as follows:

[0028] i dq =T abc-dq ·i abc

[0029] Among them, T abc-dq Let i be the transformation matrix. abc For three-phase current, i a Let i be the phase current. b Let i be the phase b current. c Let i be the phase c current. abc =[i a i b i c ] T i dq For two-phase currents, i d Let i be the d-phase current. q Let i be the phase q current. dq =[i d i q ] T ;

[0030]

[0031] Furthermore, in step S4, the low-pass filter LPF is a second-order low-pass filter with a transfer function G. LPF The formula for calculating (s) is as follows:

[0032]

[0033] Where, ω c Let ξ be the cutoff frequency of the LPF, ξ be the damping ratio, and ω be the damping ratio. c The value is taken as the fundamental frequency of the rotor-side current, and s is the current variable after Laplace transform.

[0034] Furthermore, in step S5, the active current Δi of the compensated DC-side voltage... d The calculation formula is:

[0035]

[0036] In the formula, K p1 K is the proportional gain of the PI controller in the voltage regulator module. i1 Here, t represents the integral coefficient of the PI controller in the voltage regulation control module, and t represents time.

[0037] Asymmetrical current detection module output current The calculation formula is:

[0038]

[0039] Furthermore, the specific implementation method of step S6 includes the following steps:

[0040] S6.1, Asymmetrical current detection module output current The input signal is used as the command signal to the PWM generation module, and the three-phase current output from the CSC AC side is used as the actual signal i. svg The calculation formula for adjustment via a PI controller is:

[0041]

[0042] Where, Δi pwm The output signal of the PI controller serves as the modulation wave for the comparator, K. p2 K represents the proportional gain of the PI controller in the PWM generation module. i2 The integral coefficients of the PI controller in the PWM generation module;

[0043] S6.2, The output signal Δi of the PI controller obtained in step S6.1 pwm It is compared with a triangular carrier wave, and the comparison method is: if Δi pwm If the carrier wave is less than or equal to the triangular carrier wave, the comparator outputs 1; otherwise, the comparator outputs 0. pwm The comparison result between phase a and the phase a triangular carrier wave is the PWM signal of the first switching transistor, and its inversion is the PWM signal of the second switching transistor; Δi pwm The comparison result between the b-phase portion and the b-phase triangular carrier wave is the PWM signal of the first switch in the second group; inverting it yields the PWM signal of the second switch in the second group. Δi pwm The c-phase part is compared with the c-phase triangular carrier to obtain the PWM signal of the first switch in the third group. Inverting it gives the PWM signal of the second switch in the third group. The three triangular carriers have equal amplitude, equal frequency, and phase difference of 120°.

[0044] S6.3. Based on the PWM signals of the six switching transistors in the CSC generated in step S6.2, the CSC is controlled by the drive circuit.

[0045] Furthermore, in step S6, a PR controller is used to replace the PI controller. The PR controller consists of a proportional element and a resonant element, and its expression is as follows:

[0046]

[0047] Where, ω n K is the resonant frequency of the PR controller. p K is the proportional coefficient of the PR controller. r Let ω be the resonant coefficient of the PR controller. c This is the cutoff frequency of the equivalent low-pass filter;

[0048] The PR controller consists of a proportional controller and multiple R-resonant controllers. The number of R-resonant controllers corresponds to the number of harmonics at a specific sub-frequency. This is achieved by setting K... r ω n and ω c To adjust the harmonics within a specific range at a specific sub-frequency, parameter K r The larger the value, the better the PR controller performs within ±ω. n ω at the location c The greater the gain within the range, the better it guarantees the resonant angular frequency ±ω. n It has good control characteristics.

[0049] The beneficial effects of this invention are as follows:

[0050] The active crowbar circuit control system for variable speed pumped storage units described in this invention, compared with conventional crowbar circuits, can improve the power quality of the grid by reducing the negative sequence component of the grid connection point current and reducing the THD of the grid connection point current. It can also improve the low voltage ride-through performance of the unit by making the DC bus voltage of the unit more stable and the recovery time shorter, the motor speed attenuation less, and the torque mutation smaller.

[0051] The present invention discloses an active crowbar circuit control system for a variable speed pumped storage unit. The active crowbar circuit breaks away from the traditional approach of using crowbar resistance to consume energy generated during faults. It is not only used during faults but also during normal periods. During faults, it absorbs excess energy generated by the fault and generates reactive power, thereby improving the reactive power support capacity of the unit. During normal periods, it coordinates with the unit to exchange energy with the grid to eliminate grid harmonics and improve energy utilization.

[0052] The active crowbar circuit control system for variable speed pumped storage units described in this invention has at least 6 switching transistors compared to traditional crowbar circuits. It uses capacitors instead of resistors to absorb energy, thus avoiding safety issues such as high voltage stress on the switching transistors, overcurrent breakdown of the switching transistors, and overheating of the crowbar circuit.

[0053] The active crowbar circuit control system for variable speed pumped storage units described in this invention, compared to the reactive power compensation device in conventional doubly-fed generator units, moves the conventional reactive power compensation device from the stator side to the rotor side, solving the problem that the reactive power compensation device in conventional doubly-fed generator units cannot suppress the short-circuit current generated during faults.

[0054] The active crowbar circuit control system for variable speed pumped storage units described in this invention integrates more functions compared to a single low voltage ride-through auxiliary device. It can effectively solve the problem of low cost-effectiveness of auxiliary devices that can only be used for low voltage ride-through, and can achieve the function of a single auxiliary device that meets or even exceeds the function of multiple devices used in combination. It has the advantages of simple control and low cost, while avoiding the problems of system complexity and instability caused by multiple auxiliary devices.

[0055] The present invention discloses an active crowbar circuit control method for variable speed pumped storage units. The asymmetric current detection module no longer only detects the active component of the rotor-side current. It is put into use when the system imbalance is severe. It not only compensates for reactive power, but also compensates for the grid-side negative sequence component, making it easier for the system to achieve the single power factor control target.

[0056] The present invention discloses an active crowbar circuit control method for a variable speed pumped storage unit. The voltage stabilizing module control block uses a ramp source to provide the command value. When the actual value of the DC side capacitor voltage is large compared with the expected command value, by setting the initial value and slope of the ramp source, the command signal can be slowly changed from the actual value to the expected value, which can reduce the deviation between the actual value and the command value, make the voltage stabilizing control module more stable, and make it easier to keep the DC side capacitor voltage of the improved crowbar branch constant.

[0057] The active crowbar circuit control method for variable speed pumped storage units described in this invention is simpler than conventional reactive power compensation devices and can achieve peak-valley regulation. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the active crowbar circuit control system for a variable-speed pumped storage unit as described in this invention.

[0059] Figure 2 This is a simplified structural diagram of the active crowbar circuit of the active crowbar circuit control system for a variable speed pumped storage unit as described in this invention.

[0060] Figure 3 This is a schematic diagram of the active crowbar circuit of the active crowbar circuit control system for a variable speed pumped storage unit according to the present invention.

[0061] Figure 4 This is a schematic diagram of the CSC controller of the active crowbar circuit control system for variable speed pumped storage units according to the present invention.

[0062] Figure 5 This is a schematic diagram of the positive and negative sequence separation principle of the delay method in the active crowbar circuit control method for variable speed pumped storage units described in this invention.

[0063] Figure 6 This invention describes the working principle of positive and negative sequence current detection under grid asymmetry in the active crowbar circuit control method for variable speed pumped storage units.

[0064] Figure 7 This is a schematic diagram of the modular multilevel converter (MMC) in the active crowbar circuit control system for variable speed pumped storage units according to the present invention.

[0065] Figure 8 This is a schematic diagram of the structure of a submodule of the modular multilevel converter (MMC) in the active crowbar circuit control system for variable speed pumped storage units according to the present invention. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0067] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0068] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 - Appendix Figure 8 Detailed explanation is as follows: Specific implementation method one:

[0070] An active crowbar circuit control system for a variable speed pumped storage unit includes an active crowbar circuit 1, a CSC controller 2, a three-phase current detection module 3, a drive circuit 4, a DC voltage detection module 5, and a three-phase voltage detection module 6.

[0071] The active crowbar circuit 1 includes an RL filter circuit consisting of a resistor 1-2 connected to an inductor 1-3, a crowbar-side converter 1-1, and a capacitor 1-4. The resistor 1-2 of the RL filter circuit is connected to the crowbar-side converter 1-1, and the inductor 1-3 of the RL filter circuit is connected to the circuit between the doubly fed motor 8 and the rotor-side converter 9. The inductor 1-3 and the crowbar-side converter 1-1 are connected in parallel.

[0072] One end of the three-phase current detection module 3 is connected to the CSC controller 2, and the other end of the three-phase current detection module 3 is connected to the inductor 1-3;

[0073] One end of the drive circuit 4 is connected to the CSC controller 2, and the other end of the drive circuit 4 is connected to the crowbar-side converter 1-1;

[0074] One end of the DC voltage detection module 5 is connected to the CSC controller 2, and the other end of the DC voltage detection module 5 is connected to capacitors 1-4;

[0075] One end of the three-phase voltage detection module 6 is connected to the CSC controller 2, and the other end of the three-phase voltage detection module 6 is connected to the three-phase power grid 7;

[0076] The doubly fed motor 8 is connected to the gearbox 10 and the three-phase power grid 7 respectively, and the gearbox 10 is connected to the water pump turbine 11.

[0077] Furthermore, the crowbar-side converter 1-1 is composed of three sets of circuits connected in parallel. Each set of circuits includes a first switching transistor 1-1-1, a first freewheeling diode 1-1-2, a second switching transistor 1-1-3, and a second freewheeling diode 1-1-4. The first switching transistor 1-1-1 is connected in anti-parallel to the first freewheeling diode 1-1-2, and the second switching transistor 1-1-3 is connected in anti-parallel to the second freewheeling diode 1-1-4. The collector of the first switching transistor 1-1-1 is connected to the positive terminal of the capacitor 1-4, the emitter of the first switching transistor 1-1-1 is connected to the collector of the second switching transistor 1-1-3, and the emitter of the second switching transistor 1-1-3 is connected to the negative terminal of the capacitor 1-4. The connection circuit of the first switching transistor 1-1-1 and the second switching transistor 1-1-3 is connected to the resistor 1-2 of the RL filter circuit.

[0078] Furthermore, the CSC controller 2 includes a rotation angle acquisition module 2-1, an asymmetric current detection module 2-2, a voltage regulation control module 2-3, and a PWM generation module 2-4. The rotation angle acquisition module 2-1 and the voltage regulation control module 2-3 are respectively connected to the asymmetric current detection module 2-2, and the asymmetric current detection module 2-2 is connected to the PWM generation module 2-4.

[0079] Grid voltage u sabc The flow is into the rotation angle acquisition module 2-1, which is composed of a positive and negative sequence separation module and a phase-locked loop (PLL).

[0080] Rotor-side current i rabc The current flows into the asymmetric current detection module 2-2, which is composed of a positive and negative sequence separation module, a coordinate transformation module, and a low-pass filter (LPF).

[0081] DC side actual voltage U SC The current flows into the voltage regulator control module 2-3, which has a PI controller;

[0082] Asymmetrical current detection module output current The input flows into the PWM generation module 2-4, which has a PI controller, a PR controller, or a PIR controller.

[0083] Preferably, the main control module of the CSC controller uses a DSP of model TMS320F28335 manufactured by TI, the three-phase current detection module uses an HC5FW300-S Hall current sensor, the three-phase voltage detection module and the DC voltage detection module both use CHV-25P Hall voltage sensors, and the drive circuit uses a drive circuit of model 2SP0115T2A0-12 manufactured by Infineon.

[0084] Furthermore, the asymmetrical current detection module is modified to detect the positive-sequence active and reactive components. and negative order active and reactive components The detection process employs two control loops, one for negative sequence and one for positive sequence, as follows: Figure 6 As shown, the asymmetrical current detection module no longer only detects the active component of the rotor-side current. When the system imbalance is severe, it is put into use to not only compensate for reactive power, but also to compensate for the grid-side negative sequence component, making it easier for the system to achieve the single power factor control target.

[0085] Furthermore, the voltage regulator control block uses a ramp source to provide the command value. To ensure that the active crowbar circuit has good compensation characteristics, the DC-side capacitor voltage must remain constant. When the actual value of the DC-side capacitor voltage is large compared to the desired command value, by setting the initial value and slope of the ramp source, the command signal can be gradually changed from the actual value to the desired value, which can reduce the deviation between the actual value and the command value, making the voltage regulator control module more stable and making it easier to keep the DC-side capacitor voltage of the improved crowbar branch constant.

[0086] Furthermore, the active crowbar circuit control system for a variable-speed pumped-storage hydroelectric unit employs a supercapacitor or a capacitor-in-parallel battery energy storage system on the DC side of the active crowbar circuit. The DC-side energy storage system exchanges energy with the unit's rotor side via the CSC, and the charging and discharging power of the energy storage system can be directly controlled by the CSC. Because the DC-side voltage is clamped by the energy storage system's voltage, when the active crowbar circuit operates only in reactive power mode, the control method is simpler than conventional reactive power compensation devices, and it can also achieve peak-valley regulation.

[0087] The active crowbar circuit control system for variable speed pumped storage units described in this embodiment can improve the reactive power support capability of the unit and improve the power quality of the power grid. Compared with the reactive power compensation device in conventional doubly fed units, it transfers the reactive power compensation device from the stator side to the rotor side, which can suppress the short-circuit current generated during faults. Compared with traditional low voltage ride-through auxiliary devices, it integrates the functions of low voltage ride-through and power quality improvement in a single auxiliary device, and has the advantages of high cost performance and simple control. Specific Implementation Method Two:

[0089] An active crowbar circuit control method for a variable-speed pumped-storage unit, based on the active crowbar circuit control system for a variable-speed pumped-storage unit described in Specific Embodiment 1, includes the following steps:

[0090] S1, grid voltage u sabc The input flows into the rotation angle acquisition module. The positive and negative sequence separation module first separates the grid voltage into two components, positive and negative sequence, using the delay method. The PLL obtains the phase angle ωt of the grid fundamental positive sequence by detecting the positive sequence signal of the grid voltage phase a.

[0091] S2. Input the phase angle ωt of the fundamental positive sequence of the power grid obtained in step S1 into the coordinate transformation module of the asymmetric current detection module;

[0092] S3, rotor side current i rabcThe current flows into the asymmetrical current detection module. The positive and negative sequence separation module first separates the rotor-side current into three-phase positive and negative sequence components of the rotor-side active current. Then, the coordinate transformation module uses ωt to convert the three-phase positive and negative sequence components of the rotor-side active current into two-phase positive and negative sequence components of the rotor-side active current.

[0093] Furthermore, the transformation formula for converting the three-phase current to two-phase current in step S3 of the coordinate transformation module is as follows:

[0094] i dq =T abc-dq ·i abc

[0095] Among them, T abc-dq Let i be the transformation matrix. abc For three-phase current, i a Let i be the phase current. b Let i be the phase b current. c Let i be the phase c current. abc =[i a i b i c ] T i dq For two-phase currents, i d Let i be the d-phase current. q Let i be the phase q current. dq =[i d i q ] T ;

[0096]

[0097] Furthermore, the coordinate transformation module employs the arctangent principle. It transforms the three-phase grid voltages from abc coordinates to dq coordinates using Clark transformation. α Let v be the voltage of phase α. β For the β-phase voltage, subtracting π / 2 from the reverse tangent gives the phase angle ωt of the fundamental positive sequence of the power grid.

[0098] S4. The two-phase positive and negative sequence components of the rotor-side active current obtained in step S3 are filtered out by a low-pass filter (LPF) to remove high-frequency harmonics, thus obtaining the filtered two-phase positive and negative sequence components of the rotor-side active current.

[0099] Furthermore, in step S4, the low-pass filter LPF is a second-order low-pass filter with a transfer function G. LPF The formula for calculating (s) is as follows:

[0100]

[0101] Where, ω cLet ξ be the cutoff frequency of the LPF, ξ be the damping ratio, and ω be the damping ratio. c The value is taken as the fundamental frequency of the rotor-side current, and s is the current variable after Laplace transform;

[0102] S5, the voltage regulation control module adopts closed-loop control, which controls the DC side voltage command voltage U. SC-ref With DC side actual voltage U SC By performing PI regulation, the active current Δi that compensates for the DC side voltage is obtained. d , will Δi d The two-phase positive and negative sequence components of the filtered rotor-side active current obtained in step S4 are superimposed on the positive and negative sequence components, and then the positive sequence component of the three-phase current containing only the fundamental frequency is obtained through inverse coordinate transformation. Only the negative sequence component of the fundamental three-phase current Calculate the output current of the asymmetric current detection module

[0103] Furthermore, in step S5, the active current Δi of the compensated DC-side voltage... d The calculation formula is:

[0104]

[0105] In the formula, K p1 K is the proportional gain of the PI controller in the voltage regulator module. i1 Here, t represents the integral coefficient of the PI controller in the voltage regulation control module, and t represents time.

[0106] Asymmetrical current detection module output current The calculation formula is:

[0107]

[0108] Furthermore, Δi d The two-phase positive and negative sequence components of the filtered rotor-side active current are superimposed onto the asymmetrical current detection module. A certain amount of compensation current from the DC-side capacitor C of the active crowbar circuit is applied to these components, resulting in a certain output current from the asymmetrical current detection module. It not only contains the rotor-side current conversion part, but also the DC-side current conversion part of the active crowbar circuit, thereby controlling the working state of the CSC switch tube to enable energy exchange between the AC side and DC side of the active crowbar circuit. The exchanged energy is used by the unit to compensate for the grid current.

[0109] S6. The output current of the asymmetric current detection module obtained in step S5. The input signal is used as the command signal to the PWM generation module, and the three-phase current output from the CSC AC side is used as the actual signal i. svgThe signal is adjusted by a PI controller, and then compared with a triangular carrier wave to generate PWM signals for the six switching transistors in the CSC. The CSC is then controlled by a drive circuit.

[0110] Furthermore, the specific implementation method of step S6 includes the following steps:

[0111] S6.1, Asymmetrical current detection module output current The input signal is used as the command signal to the PWM generation module, and the three-phase current output from the CSC AC side is used as the actual signal i. svg The calculation formula for adjustment via a PI controller is:

[0112]

[0113] Where, Δi pwm The output signal of the PI controller serves as the modulation wave for the comparator, K. p2 K represents the proportional gain of the PI controller in the PWM generation module. i2 The integral coefficients of the PI controller in the PWM generation module;

[0114] S6.2, The output signal Δi of the PI controller obtained in step S6.1 pwm It is compared with a triangular carrier wave, and the comparison method is: if Δi pwm If the carrier wave is less than or equal to the triangular carrier wave, the comparator outputs 1; otherwise, the comparator outputs 0. pwm The comparison result between phase a and the phase a triangular carrier wave is the PWM signal of the first switching transistor, and its inversion is the PWM signal of the second switching transistor; Δi pwm The comparison result between the b-phase portion and the b-phase triangular carrier wave is the PWM signal of the first switch in the second group; inverting it yields the PWM signal of the second switch in the second group. Δi pwm The c-phase part is compared with the c-phase triangular carrier to obtain the PWM signal of the first switch in the third group. Inverting it gives the PWM signal of the second switch in the third group. The three triangular carriers have equal amplitude, equal frequency, and phase difference of 120°.

[0115] S6.3. Based on the PWM signals of the six switching transistors in the CSC generated in step S6.2, the CSC is controlled by the drive circuit. Specific implementation method three:

[0117] The difference between this embodiment and specific embodiment two is that in step S6, a PR controller is used instead of a PI controller. The PR controller consists of a proportional element and a resonant element, and its expression is as follows:

[0118]

[0119] Where, ω n K is the resonant frequency of the PR controller. p K is the proportional coefficient of the PR controller. r Let ω be the resonant coefficient of the PR controller. c This is the cutoff frequency of the equivalent low-pass filter;

[0120] The PR controller consists of a proportional controller and multiple R-resonant controllers. The number of R-resonant controllers corresponds to the number of harmonics at a specific sub-frequency. This is achieved by setting K... r ω n and ω c To adjust the harmonics within a specific range at a specific sub-frequency, parameter K r The larger the value, the better the PR controller performs within ±ω. n ω at the location c The greater the gain within the range, the better it guarantees the resonant angular frequency ±ω. n It has good control characteristics.

[0121] The active crowbar circuit control system for variable-speed pumped storage units described in this embodiment employs hysteresis control or PR control in its PWM generation module. Addressing the difficulty in adjusting the PI parameters of the PI controller, this embodiment uses hysteresis control in its PWM generation module. The deviation between the CSC AC side current command signal and the actual signal is adjusted by setting the loop width of the hysteresis comparator: a wider loop width results in a lower switching frequency and a larger current tracking error; a narrower loop width results in a smaller current tracking error but a higher switching frequency and greater switching losses. When using PI control, PR control is employed to address the issue of still relatively high levels of certain harmonics in the rotor current and grid connection point current. Specific implementation method four:

[0123] The difference between this embodiment and specific embodiment one is that the crowbar-side converter 1-1 is replaced with an H-bridge cascaded or modular multilevel converter (MMC) or an MMC plus H-bridge multilevel topology.

[0124] The active crowbar circuit control system for variable speed pumped storage units described in this embodiment adopts a multilevel topology such as H-bridge cascade, modular multilevel converter (MMC), or MMC plus H-bridge.

[0125] The topology of a modular multilevel converter (MMC) is as follows: Figure 7 and Figure 8As shown, there are 6 bridge arms, each composed of n identical cascaded sub-modules. Each sub-module consists of an IGBT half-bridge and a DC capacitor. Each phase includes 2 bridge arms (upper and lower) and 2 reactors L. The reactors L act as buffers to suppress high-frequency circulating currents and can suppress inrush currents when a short circuit occurs on the DC side, thus providing protection. In the MMC, to ensure equal voltage distribution of energy, the sum of the voltages of the upper and lower bridge arms should equal the DC-side capacitor voltage. In extreme cases, if the upper bridge arm voltage is zero, then the lower bridge arm voltage is the DC bus-side capacitor voltage U. dc The voltage U dc The voltage is evenly distributed across n sub-modules, so the capacitor voltage of each sub-module is U. dc / n. Accordingly, the PWM generation module is modified while its input remains unchanged. The operating mode can be either carrier-layered PWM or carrier-phase-shifted PWM.

[0126] The active crowbar circuit control system for variable-speed pumped storage units described in this embodiment, if the PWM generation module adopts a carrier phase-shifted PWM method, its basic principle is that the drive signal of each sub-module is generated by comparing a sine wave and a triangular carrier wave. Sub-modules in the same bridge arm have the same sine reference wave, while the triangular carrier waves differ by a specific angle. For three phases, the triangular carrier waves have equal amplitude and the same frequency, while the sine modulation waves differ by 120° depending on the phase. The phase of each group of triangular carrier waves in all bridge arms is sequentially shifted laterally by 2π / n angles, and the number of MMC output voltage levels is n+1; the phase of each group of triangular carrier waves in all bridge arms is sequentially shifted laterally by π / n angles, and the number of MMC output voltage levels is 2n+1.

[0127] The active crowbar circuit control system for variable-speed pumped storage units described in this embodiment, if the PWM generation module adopts the carrier-layered PWM method, its principle is to superimpose multiple triangular carriers with the same amplitude, frequency, initial phase, and different initial values, compare them with a sinusoidal modulation wave, and generate a wave to control each group of power units. Depending on the arrangement of the phase relationships between the carriers, the triangular carrier layering method can be divided into three types: in-phase layering, positive-negative-opposite-phase layering, and alternating reverse layering. By setting the peak-to-peak value of the triangular carriers, the following two level modulation methods are possible: n carriers dividing the modulation wave amplitude into n equal parts can make the MMC output a 2n+1 level; n carriers dividing the modulation wave amplitude into n / 2 equal parts can make the MMC output an n+1 level.

[0128] The active crowbar circuit control system for variable speed pumped storage units described in this embodiment has an output voltage containing at least n+1 levels. The more levels the output voltage contains, the lower the harmonic content of the regulated system and the lower the voltage stress borne by the switching transistor in the active crowbar circuit.

[0129] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0130] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method of active crowbar circuit control for a variable speed pumped storage generating unit, characterized by, The active crowbar circuit (1), the CSC controller (2), the three-phase current detection module (3), the driving circuit (4), the direct current voltage detection module (5), and the three-phase voltage detection module (6) are connected in series. The active crowbar circuit (1) comprises an RL filter circuit composed of a resistor (1-2) and an inductor (1-3), a crowbar side converter (1-1), and a capacitor (1-4). One end of the three-phase current detection module (3) is connected to the CSC controller (2), and the other end of the three-phase current detection module (3) is connected to the inductor (1-3). One end of the driving circuit (4) is connected to the CSC controller (2), and the other end of the driving circuit (4) is connected to the crowbar side converter (1-1). One end of the direct current voltage detection module (5) is connected to the CSC controller (2), and the other end of the direct current voltage detection module (5) is connected to the capacitor (1-4). One end of the three-phase voltage detection module (6) is connected to the CSC controller (2), and the other end of the three-phase voltage detection module (6) is connected to the three-phase power grid (7). The double-fed motor (8) is connected to the gear box (10) and the three-phase power grid (7), respectively, and the gear box (10) is connected to the water pump water turbine (11). The method comprises the following steps: S1, grid voltage u sabc The in-flow rotation angle acquisition module and the positive and negative sequence separation module separate the grid voltage into positive and negative sequence components by using a delay method. The PLL acquires the phase angle ωt of the grid fundamental positive sequence by detecting the positive sequence signal of the phase a of the grid voltage. S2, inputting the phase angle ωt of the power grid fundamental positive sequence obtained in step S1 into the coordinate transformation module of the asymmetric current detection module; S3, rotor-side current i rabc The in-flow asymmetric current detection module and the positive and negative sequence separation module first separate the rotor-side current into three-phase positive and negative sequence components of the rotor-side active current, and then convert the three-phase positive and negative sequence components of the rotor-side active current into two-phase positive and negative sequence components of the rotor-side active current through the coordinate transformation module using ωt. S4, filtering the two-phase positive and negative sequence components of the rotor-side active current obtained in step S3 through a low-pass filter (LPF) to obtain the filtered two-phase positive and negative sequence components of the rotor-side active current; S5, the voltage regulation control module adopts closed-loop control, which controls the DC side voltage command voltage U. SC-ref With DC side actual voltage U SC By performing PI regulation, the active current Δi that compensates for the DC side voltage is obtained. d , will Δi d The two-phase positive and negative sequence components of the filtered rotor-side active current obtained in step S4 are superimposed on the positive and negative sequence components, and then the positive sequence component of the three-phase current containing only the fundamental frequency is obtained through inverse coordinate transformation. Only the negative sequence component of the three-phase current with fundamental frequency Calculate the output current of the asymmetrical current detection module. ; S6. The output current of the asymmetric current detection module obtained in step S5. The input signal is used as the command signal to the PWM generation module, and the three-phase current output from the CSC AC side is used as the actual signal i. svg The signal is adjusted by a PI controller, and then compared with a triangular carrier wave to generate PWM signals for the six switching transistors in the crowbar-side converter. The CSC is then controlled by a drive circuit.

2. A method of active crowbar circuit control for a variable speed pumped storage generator set as claimed in claim 1, wherein, The crowbar side converter (1-1) is composed of three groups of circuits connected in parallel, each group of circuits comprising a first switch tube (1-1-1), a first freewheeling diode (1-1-2), a second switch tube (1-1-3), and a second freewheeling diode (1-1-4), wherein the first switch tube (1-1-1) is connected in anti-parallel with the first freewheeling diode (1-1-2), wherein the second switch tube (1-1-3) is connected in anti-parallel with the second freewheeling diode (1-1-4), the collector of the first switch tube (1-1-1) is connected to the positive electrode of the capacitor (1-4), the emitter of the first switch tube (1-1-1) is connected to the collector of the second switch tube (1-1-3), the emitter of the second switch tube (1-1-3) is connected to the negative electrode of the capacitor (1-4), and the connection point of the first switch tube (1-1-1) and the second switch tube (1-1-3) is connected to one end of the resistor (1-2) of the RL filter circuit.

3. A method of controlling a forced crowbar circuit for a variable speed pumped storage generator set according to claim 1 or 2, wherein The CSC controller (2) comprises a rotation angle acquisition module (2-1), an asymmetric current detection module (2-2), a voltage stabilization control module (2-3) and a PWM generation module (2-4), wherein the rotation angle acquisition module (2-1) and the voltage stabilization control module (2-3) are connected to the asymmetric current detection module (2-2) respectively, and the asymmetric current detection module (2-2) is connected to the PWM generation module (2-4). Grid voltage u sabc An inflow rotation angle acquisition module (2-1) is composed of a positive and negative sequence separation module and a phase-locked loop (PLL). Rotor-side current i rabc An inflow asymmetric current detection module (2-2) is composed of a positive and negative sequence separation module, a coordinate transformation module and a low-pass filter (LPF). Actual voltage on DC side U SC flows into a voltage stabilization control module (2-3) which has a PI controller; Asymmetric current detection module output current flows into a PWM generation module (2-4) having a PI controller or a PR controller or a PIR controller.

4. A method of active crowbar circuit control for a variable speed pumped storage generator set as claimed in claim 3, wherein, The pry bar side converter (1-1) is replaced by an H-bridge cascade or a modular multilevel converter (MMC) or an MMC plus H-bridge multilevel topology structure.

5. A method of active crowbar circuit control for a variable speed pumped storage generator set as claimed in claim 4, wherein, The transformation formula of the three-phase current into the two-phase current in the coordinate transformation module in step S3 is as follows: ； where T abc-dq is the transformation matrix, i abc is the three-phase current, i a is the a-phase current, i b is the b-phase current, i c is the c-phase current, i abc = [i a , i b , i c ] T , i dq is the two-phase current, i d is the d-phase current, i q is the q-phase current, i dq = [i d , i q ] T ; 。 6. A method of active crowbar circuit control for a variable speed pumped storage generator set as claimed in claim 5, wherein, The low-pass filter LPF in step S4 employs a second-order low-pass filter, and the transfer function The calculation formula is as follows: ； where ω c is the cut-off frequency of the LPF, is the damping ratio, ω c is the fundamental frequency of the rotor-side current, and s is the Laplace-transformed current variable.

7. A method of active crowbar circuit control for a variable speed pumped storage generator set as claimed in claim 6, wherein, The active current Δi that compensates the DC side voltage in step S5 d The calculation formula is: ； In the formula, K p1 is the proportional coefficient of the PI controller in the voltage stabilization control module, K i1 is the integral coefficient of the PI controller in the voltage stabilization control module, and t is time. Asymmetric current detection module outputs current The calculation formula is: 。 8. A method of active crowbar circuit control for a variable speed pumped storage generator set as claimed in claim 7, wherein, The specific implementation method in step S6 comprises the following steps: S6.1, asymmetric current detection module output current The three-phase current output by the CSC AC side is input to the PWM generation module as an actual signal i svg The calculation formula for adjusting through the PI controller is: ； Wherein, Δi pwm is the output signal of the PI controller, as the modulation wave of the comparator, K p2 is the proportional coefficient of the PI controller in the PWM generation module, K i2 is the integral coefficient of the PI controller in the PWM generation module; S6.2, output signal Δi of the PI controller obtained in step S6.1 is compared with the triangular carrier pwm If Δi is less than or equal to the triangular carrier, the comparator outputs 1, otherwise the comparator outputs 0. pwm The comparison result of the a-phase part in Δi and the a-phase triangular carrier is the PWM signal of the first switch tube, and the inverse is the PWM signal of the second switch tube. pwm ​ Δi pwm The comparison result of the b-phase part in Δi pwm The comparison result of the c-phase part in Δi with the c-phase triangular carrier is the PWM signal of the first switch tube in the third group, and the inverse is the PWM signal of the second switch tube in the third group. The three triangular carriers have equal amplitude, equal frequency, and the phase difference is 120°. S6.3, controlling the CSC through a driving circuit according to the PWM signals of the six switching tubes in the CSC generated in step S6.

2.

9. A method of active crowbar circuit control for a variable speed pumped storage generator set as claimed in claim 8, wherein, In step S6, the PR controller is used to replace the PI controller, the PR controller is composed of a proportional link and a resonance link, and the expression is as follows: ； where ω n is the resonant frequency of the PR controller, K p is the proportional coefficient of the PR controller, K r is the resonant coefficient of the PR controller, ω c is the equivalent low-pass filter cutoff frequency; The PR controller is composed of a proportional controller and multiple R resonance controllers, the number of R resonance controllers is consistent with the number of specific frequency harmonics, and K r , ω n and ω c are set to adjust the harmonics within a specific range at a specific frequency, and the larger the value of K r , the greater the gain of the PR controller within the ω n range at ±ω c , so as to ensure better control characteristics at the resonance angular frequency ±ω n .

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