A method and system for low voltage ride through control of a grid-forming variable speed pumped storage unit

Abstract

The application discloses a kind of network type variable-speed pumped storage unit low voltage ride through control method and system, when grid drop fault occurs, grid-side converter maintains transient power angle stability by improving virtual synchronous control (VSG) active power ring, and introduces PI control in reactive power ring to improve response speed, according to low voltage ride through standard calculation and output power instruction;At the same time, based on synchronous rotating coordinate system, current positive and negative sequence separation control is implemented to ensure three-phase current balance under asymmetric fault, and virtual impedance is introduced to suppress transient overcurrent, to prevent converter lockout.Machine-side converter utilizes the adjustable characteristics of unit speed, so that the active power of machine-side follows the power of grid-side, and the transient unbalanced energy is converted into rotor kinetic energy storage by increasing rotor speed, so as to suppress the power fluctuation of DC bus and maintain the stability of DC voltage.The application improves the transient stability and grid-connected safety of the unit during low voltage ride through.

Description

Technical Field

[0001] This invention relates to a low-voltage ride-through control method and system for grid-connected variable-speed pumped storage units, belonging to the field of power system control technology. Background Technology

[0002] Full-power variable-speed pumped-storage units utilize grid-side converter-based grid control technology to exhibit voltage source-external characteristics, providing crucial virtual inertia and damping support. However, during grid voltage dips, grid-based control faces the dual challenges of overcurrent protection and transient energy imbalance.

[0003] Existing technologies typically employ grid-side switching control, switching the grid-side converter to current-limiting mode during faults and relying on the DC-side Crowbar circuit for hard switching to dissipate unbalanced power. The drawbacks are: the converter is forced to switch from voltage source to current source characteristics, losing its reactive power support capability to the grid; the control mode switching process during fault recovery is complex and easily triggers secondary disturbances; and the forced reliance on the DC-side Crowbar energy-dissipating hardware circuit not only increases system cost and size, but frequent operation can also lead to converter lockout or even loss of control.

[0004] Existing technologies often overlook the fact that the source of transient energy during a fault is the kinetic energy of the turbine-side rotor, failing to effectively utilize the kinetic energy absorption potential of the unit's large-inertia rotor, resulting in overly passive control measures. Summary of the Invention

[0005] Objective: To overcome the shortcomings of existing technologies, such as overcurrent problems in grid-type converters and DC bus voltage overvoltage problems during grid voltage dips, this invention provides a low-voltage ride-through control method and system for grid-type variable-speed pumped storage units, comprehensively improving the transient stability and low-voltage ride-through capability of full-power variable-speed pumped storage units.

[0006] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] Firstly, a low-voltage ride-through control method for a grid-connected variable-speed pumped storage unit specifically includes:

[0008] Construct an equivalent model of a full-power variable speed pumped storage unit based on VSG.

[0009] When a grid fault voltage drop occurs, the power angle value, output active power, and output reactive power of the grid-side converter after the fault are obtained based on the equivalent model of the full-power variable speed pumped storage unit based on VSG. Based on the power angle value and output active power of the grid-side converter after the fault, an improved active-frequency control equation is constructed. Based on the output reactive power of the grid-side converter after the fault, an improved reactive-voltage control equation is constructed.

[0010] The instantaneous current and fault current of the grid-side converter are obtained based on the equivalent model of the full-power variable speed pumped storage unit based on VSG. According to the constraint equation of the instantaneous fault current of the grid-side converter, a virtual impedance is set to suppress the instantaneous fault current. The d-axis and q-axis voltage components of the grid-side converter are calculated based on the positive and negative sequence currents of the instantaneous current of the grid-side converter and the virtual impedance. The d-axis and q-axis voltage components are input into the positive sequence current control loop to control the grid-side converter.

[0011] The reference values ​​of active and reactive power of the grid-side converter during a fault are obtained based on the equivalent model of the full-power variable speed pumped storage unit based on VSG. The reference values ​​of active and reactive power are then input into the modified active-frequency control equation and reactive-voltage control equation to control the grid-side converter.

[0012] When the active power on the grid side changes, the corrected turbine angular velocity reference value is calculated based on the equivalent model of the full-power variable speed pumped storage unit based on VSG, and the turbine speed regulation system is controlled based on the corrected turbine angular velocity reference value.

[0013] In a second aspect, a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements a low-voltage ride-through control method for a grid-type variable-speed pumped storage unit as described in any of the first aspects.

[0014] Thirdly, a computer device comprising:

[0015] Memory is used to store instructions.

[0016] A processor is configured to execute the instructions, causing the computer device to perform operations of a low-voltage ride-through control method for a grid-type variable-speed pumped storage unit as described in any of the first aspects.

[0017] Beneficial Effects: This invention provides a low-voltage ride-through control method and system for grid-connected variable-speed pumped storage units. The invention is based on a unit model that combines generator-side constant DC voltage control with grid-side virtual synchronous generator (VSG) control. When a grid fault occurs, the grid-side converter maintains transient power angle stability by improving the VSG active power loop and introducing PI control in the reactive power loop to enhance response speed. It calculates and outputs power commands based on low-voltage ride-through standards. Simultaneously, it implements current positive and negative sequence separation control based on a synchronous rotating coordinate system to ensure three-phase current balance under asymmetrical faults and introduces virtual impedance to suppress transient overcurrents and prevent converter blockage. The generator-side converter utilizes the unit's adjustable speed characteristic to actively track grid-side power. By increasing rotor speed, it converts transient unbalanced energy into stored rotor kinetic energy, thereby smoothing DC bus power fluctuations and maintaining DC voltage stability. This invention comprehensively improves the transient stability and grid connection safety of the unit during low-voltage ride-through through the coordinated operation of generator-side active energy storage and grid-side current limiting support. Compared with the prior art, the advantages of the present invention are as follows:

[0018] 1. This invention overcomes the limitations of traditional low-throughput circuits by actively increasing the rotor speed through the machine-side converter, converting the transient unbalanced energy during a fault into rotor kinetic energy for storage, effectively suppressing DC bus power fluctuations and maintaining DC voltage stability.

[0019] 2. The present invention introduces a virtual impedance link in the grid-side converter, which significantly suppresses transient overcurrent during faults and prevents converter blockage; combined with positive and negative sequence separation control, it ensures the balance of three-phase current during asymmetrical faults.

[0020] 3. By improving the active and reactive power control loops of the grid-side VSG, this invention not only maintains the synchronous stability of the transient power angle, but also responds quickly to the grid dip depth and injects reactive current to support the recovery of the grid connection point voltage, thus comprehensively improving the unit's low-voltage protection capability and grid-friendliness. Attached Figure Description

[0021] Figure 1 This is an overall flowchart of a low-voltage ride-through control method for a grid-type variable-speed pumped storage unit according to the present invention.

[0022] Figure 2 The diagram shows the structure of the equivalent model of the full-power variable speed pumped storage unit based on VSG provided by this invention.

[0023] Figure 3 This is a structural diagram of the current sequence control loop after adding virtual impedance in an embodiment of the present invention.

[0024] Figure 4 This is a diagram of the improved VSG active power loop and reactive power loop control structure in an embodiment of the present invention.

[0025] Figure 5 The voltage and current waveforms at the grid connection point for the low-voltage ride-through control of the grid-connected unit of the present invention are shown.

[0026] Figure 6 This is a power waveform diagram of the low voltage crossing control grid side of the grid-type variable speed pumped storage unit of the present invention.

[0027] Figure 7 The waveform diagram of the DC bus voltage for the low-voltage ride-through control of the grid-type variable speed pumped storage unit of the present invention is shown.

[0028] Figure 8 The waveform diagram of the low voltage ride-through control speed of the grid-type variable speed pumped storage unit of the present invention is shown. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0030] The present invention will be further described below with reference to specific embodiments.

[0031] Example 1:

[0032] This embodiment introduces a low-voltage ride-through control method for a grid-type variable-speed pumped storage unit, such as... Figure 1 As shown, it includes:

[0033] Step 1: Construct an equivalent model of a full-power variable-speed pumped storage unit based on VSG (Virtual Synchronous Generator).

[0034] Step 2: When a voltage drop occurs in the power grid due to a fault, the power angle value, output active power, and output reactive power of the grid-side converter after the fault are obtained based on the equivalent model of the full-power variable-speed pumped storage unit based on VSG. Based on the power angle value and output active power of the grid-side converter after the fault, an improved active-frequency control equation is constructed. Based on the output reactive power of the grid-side converter after the fault, an improved reactive-voltage control equation is constructed to control the output active and reactive power of the VSG.

[0035] Step 3: Obtain the instantaneous current and fault current of the grid-side converter based on the equivalent model of the full-power variable speed pumped storage unit based on VSG. According to the constraint equation of the instantaneous fault current of the grid-side converter, set the virtual impedance to suppress the instantaneous fault current. Calculate the d-axis and q-axis voltage components of the grid-side converter based on the positive and negative sequence currents of the instantaneous current and the virtual impedance. Input the d-axis and q-axis voltage components into the positive sequence current control loop to control the grid-side converter.

[0036] Step 4: Obtain the reference values ​​of active and reactive power of the grid-side converter during a fault based on the equivalent model of the full-power variable speed pumped storage unit based on VSG. Input the reference values ​​of active and reactive power into the modified active-frequency control equation and reactive-voltage control equation respectively to control the grid-side converter.

[0037] Step 5: When the active power on the grid side changes, calculate the corrected turbine angular velocity reference value based on the equivalent model of the full-power variable speed pumped storage unit based on VSG, and control the turbine speed regulation system based on the corrected turbine angular velocity reference value.

[0038] Step 6: Once the grid connection point voltage returns to normal, exit the low voltage ride-through control and resume normal control.

[0039] Furthermore, the equivalent model of the full-power variable-speed pumped storage unit based on VSG, such as... Figure 2 As shown, it includes: a turbine system, a turbine speed control system, a permanent magnet synchronous generator, a turbine-side converter, and a grid-side converter.

[0040] The turbine speed control system is connected to the turbine system to control the turbine speed. The turbine system is connected to the permanent magnet synchronous generator to convert mechanical energy into electrical energy. The turbine-side converter controls the DC bus voltage to stabilize, and the grid-side converter is connected to the power grid to control the output active and reactive power.

[0041] Furthermore, the turbine system includes: the transfer function of the turbine system.

[0042] Wherein, the transfer function of the water turbine system for:

[0043] ,

[0044] in, is the water hammer inertial time constant, which represents the time required for the water flow rate in the water intake pipeline to increase from 0 to the rated value, and s is the Laplace operator.

[0045] Furthermore, the turbine speed control system includes: a transfer function for the turbine speed control system and a guide vane opening transfer function.

[0046] Among them, the transfer function of the turbine speed regulation system for:

[0047] ,

[0048] Among them, K p It is the proportional gain of the speed controller; K i It is the integral gain of the speed controller; K d It is the differential gain of the speed controller.

[0049] The guide vane opening transfer function is:

[0050] ,

[0051] in, Let be the inertial time constant of the relay.

[0052] Furthermore, the permanent magnet synchronous generator includes: the swing equation of the permanent magnet synchronous generator, the transfer function of the permanent magnet synchronous generator, the three-phase voltage equation of the permanent magnet synchronous generator, the stator voltage equation of the permanent magnet synchronous generator, and the electromagnetic torque equation of the permanent magnet synchronous generator.

[0053] The permanent magnet synchronous generator connects the turbine to the turbine-side converter. The swing equation of the permanent magnet synchronous generator is as follows:

[0054] ,

[0055] in: The inertial time constant of the unit, The mechanical torque input to the generator. For the electromagnetic torque on the stator side, Given the rotor angular velocity, the transfer function of the permanent magnet synchronous generator is obtained. for:

[0056] ,

[0057] Three-phase voltage equations of a permanent magnet synchronous generator in the abc coordinate system:

[0058] ,

[0059] in, , , These are the stator voltages of phases A, B, and C of the permanent magnet synchronous generator, respectively. , , These are the stator currents of phases A, B, and C of the permanent magnet synchronous generator, respectively. , , These represent the total magnetic flux of the A-phase, B-phase, and C-phase windings, respectively. This is the stator resistance.

[0060] The expression for the stator voltage in the d-axis and q-axis coordinate system is:

[0061] ,

[0062] in, and These are the d-axis and q-axis components of the stator voltage of the permanent magnet synchronous generator, respectively. and These are the d-axis and q-axis components of the stator current of a permanent magnet synchronous generator, respectively. and These are the d-axis and q-axis components of the stator winding inductance, respectively. The rotor's electric angular velocity, It is a permanent magnet flux linkage. This is the stator resistance.

[0063] The expression for the electromagnetic torque of a permanent magnet synchronous generator (with a stator current d-axis component reference value of 0 and isdref=0) is as follows:

[0064] ,

[0065] in, This represents the number of pole pairs of the motor. This refers to the electromagnetic torque of the motor.

[0066] Furthermore, the machine-side converter includes: an inner loop for torque current control and an outer loop for DC voltage control.

[0067] The machine-side converter stabilizes the DC-side voltage and adjusts the electromagnetic torque according to changes in the DC voltage.

[0068] The machine-side converter uses a PI controller to achieve rapid current and power tracking. The expressions for the reference values ​​of the inner current loop and the outer DC voltage loop are as follows:

[0069] ,

[0070] ,

[0071] in, and These represent the d-axis and q-axis reference values ​​for the stator voltage of the permanent magnet synchronous generator, respectively. and These represent the reference values ​​for the d-axis and q-axis components of the stator current in a permanent magnet synchronous generator. and These are the reference and actual values ​​of the DC bus voltage, respectively. and The control coefficient for the inner current loop. and These are the control coefficients for the outer voltage loop. The rotor's electric angular velocity, It is a permanent magnet flux linkage.

[0072] The inner current loop uses a feedforward decoupling method to compensate for the coupling terms. and .

[0073] Furthermore, the grid-side converter includes: a virtual synchronous generator strategy, active power-frequency control equations, and reactive power-voltage control equations.

[0074] The grid-side converter uses a virtual synchronous generator strategy to simulate the rotor motion equation of a synchronous generator, the expression of which is:

[0075] ,

[0076] The active-frequency control equation can be expressed as:

[0077] ,

[0078] The reactive power-voltage control equation can be expressed as:

[0079] ,

[0080] in, and These are active power (W) and reactive power commands (var), respectively. This is the active power droop coefficient. and The active power (W) and reactive power (var) output by the VSG. The effective value of the virtual back electromotive force of VSG (V). For voltage command (V). The effective value (V) of the voltage output by VSG. ω is the angular frequency (rad / s). The rated angular frequency (rad / s). The damping coefficient is... This is the reactive power-voltage droop factor. Virtual moment of inertia (kg· ), This is the voltage regulation coefficient. The phase angle is the electromotive force.

[0081] Furthermore, the power angle characteristic equation before the fault is:

[0082]

[0083] The power angle characteristic equation after a fault is: After a fault occurs in the power grid, the increased disturbance power angle is... The characteristic equation for the work angle at this time is:

[0084]

[0085] in, The output active power (W) of the VSG after the fault.

[0086] Subtracting the power angle characteristic equations before and after the fault and further simplifying them, we obtain:

[0087]

[0088] in, The angular frequency of the power grid (rad / s) ω is the angular frequency (rad / s). This is the reactive power-voltage droop factor. Virtual moment of inertia (kg· ), The active power (W) output by the VSG.

[0089] Furthermore, the improved active-frequency control equation is obtained as follows:

[0090]

[0091] Since the VSG reactive power loop only has an integral component, its response speed is slow. The improved reactive power loop adds a proportional component to the integral component to speed up the response speed. At the same time, the voltage droop component is removed, and only the given reactive power portion is retained. The improved reactive-voltage control equation is as follows:

[0092]

[0093] When a short-circuit fault occurs in the power grid, an inrush current is generated, which is the instantaneous current between the grid-side converter and the power grid. for:

[0094]

[0095] in, Line resistance (Ω); The grid voltage (V) during the fault; The mains voltage is (V). For grid reactance; For line inductance, The imaginary unit, Let t be a natural constant and t be a time constant. The effective value of the virtual back electromotive force of VSG (V).

[0096] Ignoring transient components, the instantaneous fault current between the grid-side converter and the grid for:

[0097]

[0098] Furthermore, by increasing the virtual impedance, the virtual impedance limits the instantaneous value of the fault current. for:

[0099]

[0100] in, and These are the resistance (Ω) and reactance (Ω) of the virtual impedance, respectively.

[0101] like Figure 3 As shown, after the virtual impedance is introduced into the grid-side converter, the line impedance is relatively small compared to the virtual impedance. Therefore, the simplified instantaneous fault current value is:

[0102]

[0103] The fault current is set to not exceed the rated current I. r By multiplying it by 1.25, we obtain the constraint equations:

[0104]

[0105] Adding virtual impedance generates positive-sequence voltage components on the d-axis and q-axis. and The calculation expression is:

[0106]

[0107] in, , These represent the positive sequence components of the current along the d-axis and q-axis, respectively.

[0108] Furthermore, according to national standards, during the grid voltage drop to 0.2-0.9 pu, the reactive current injected into the grid by the generating unit is... The active current is calculated based on the reactive current and the maximum current. .

[0109]

[0110]

[0111] in, This is the per-unit value of the grid voltage; The maximum current (A) that the pumped storage unit can provide to the power grid. This is the fault current.

[0112] When a short-circuit fault occurs, the output power of the grid-side converter is:

[0113]

[0114] In the formula, The grid voltage is the positive sequence voltage (V) along the d-axis. The positive sequence current (A) of the d-axis of the grid-side converter. The grid voltage is the q-axis positive sequence voltage (V). This is the q-axis positive sequence current (A) of the grid-side converter.

[0115] The reactive power output of the grid-side converter during a fault is obtained based on the injected reactive current. for:

[0116]

[0117] in, The VSG output voltage (V) during a fault. This is the reactive power command (var).

[0118] The reference value of active power output by VSG during a fault is calculated based on the active current. for:

[0119]

[0120] The modified VSG active power loop and reactive power loop are obtained as follows: Figure 4 As shown.

[0121] The modified active-frequency control equation is as follows:

[0122] ,

[0123] The revised reactive power-voltage control equation is as follows:

[0124]

[0125] Furthermore, the power flowing through the DC-side bus capacitor is:

[0126]

[0127] in, For DC-side capacitor (F); The electromagnetic power (W) of the machine-side converter; The active power (W) output by the grid-side converter.

[0128] The relationship between the DC side voltage and the rotor speed of the permanent magnet synchronous generator is obtained as follows:

[0129]

[0130] in, and These represent the angular velocities before and after the integration time interval.

[0131] The corrected reference value of the turbine angular velocity was obtained. for:

[0132]

[0133] Furthermore, once the grid connection voltage returns to normal, the low-voltage ride-through improvement control is discontinued, and normal control is resumed.

[0134] Example 2:

[0135] This embodiment describes a computer-readable storage medium storing a computer program that, when executed by a processor, implements a low-voltage ride-through control method for a grid-type variable-speed pumped storage unit as described in any of Embodiment 1.

[0136] Example 3:

[0137] This embodiment describes a computer device, including:

[0138] Memory is used to store instructions.

[0139] A processor is configured to execute the instructions, causing the computer device to perform the operation of a low-voltage ride-through control method for a grid-type variable-speed pumped storage unit as described in any of Embodiment 1.

[0140] Example 4:

[0141] This embodiment takes a 500kW grid-connected variable-speed pumped storage power station as an example, with the unit's rotational inertia J. T 1800 kg·m 2 The water hammer inertia time constant Tw is 0.5, Kp, Ki, and Kd are 3.2, 0.6, and 0.56 respectively, the relay time constant Ty is 0.2s, the stator resistance Rs is 0.0067Ω, the d-axis armature reaction inductance is 0.0068H, the q-axis armature reaction inductance is 0.0047H, the permanent magnet flux linkage is 9.3Wb, and the rotor pole pairs n p The DC bus voltage U is 3. dc The voltage is 800V, and the inertia J of the grid-side active ring rotor is 0.5 kg·m. 2 Damping coefficient Dp The reactive power regulation coefficient K is 25. q The voltage regulation coefficient D is 10. q The parameters are: 1000, filter inductance: 3mH, filter capacitor: 50μF, grid voltage RMS: 380V, rated frequency: 50Hz, corresponding synchronous angular velocity: 314rad / s, maximum injected reactive current i. max It is 500A.

[0142] The grid-connected full-power variable-speed pumped storage unit operates in steady state, employing DC voltage outer loop control and torque current inner loop control on the unit side, and VSG control on the grid side. During the 0-0.4s interval, the grid voltage is normal, and the virtual synchronous generator is functioning normally.

[0143] A short-circuit fault occurs in the power grid during the 0.4-1.2s period, causing a voltage drop at the grid connection point. The method of this invention is used for control, and the fault is cleared in 1.2s, restoring the normal control strategy.

[0144] Simulation results of the control process: such as Figure 5 As shown, the grid voltage drops by 50% in 0.4 seconds and returns to normal in 1.2 seconds; from Figure 6 It can be seen that the VSG not only increases its reactive power to support the recovery of its output voltage, but also reduces its active power output; from Figure 7 It can be seen that the DC bus voltage fluctuates slightly at 0.4s and 1.2s. This is because the active power on the generator side cannot completely track the active power on the grid side at the moment of the fault and after the fault is cleared. During the fault, the active power on the generator side completely tracks the active power on the grid side, and the DC bus voltage remains basically stable. Figure 8 It can be seen that during the fault, the rotor speed increased due to the imbalance between the mechanical power of the turbine and the electromagnetic power of the generator. After the fault ended, the rotor speed returned to the rated speed, which verified the effectiveness of the control method.

[0145] In summary, this invention proposes a low-voltage ride-through control method for grid-connected variable-speed pumped storage units. Addressing the issues of grid disconnection and overcurrent during symmetrical or asymmetrical voltage dip faults in the power grid, this invention actively increases the rotor speed via the generator-side converter, converting the transient imbalance energy during the fault into stored rotor kinetic energy. This effectively smooths DC bus power fluctuations and maintains DC voltage stability. Simultaneously, a virtual impedance element is introduced into the grid-side converter to suppress transient overcurrents during faults, preventing converter blockage. Combined with positive and negative sequence separation control in a synchronous rotating coordinate system, the balance of the three-phase output current is ensured during asymmetrical faults. Furthermore, by improving the active and reactive power control loops of the grid-side VSG, not only is transient power angle synchronization stability maintained, but reactive current can also be rapidly injected based on the grid dip depth to support voltage recovery at the grid connection point. This invention achieves coordinated operation between active energy storage on the generator side and current-limiting support on the grid side, comprehensively improving the transient stability and low-voltage ride-through capability of grid-connected full-power variable-speed pumped storage units. It has important guiding significance and engineering application value for grid-friendly connection of pumped storage units in the context of high proportion of new energy power grids.

[0146] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0147] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0148] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1The function specified in one or more boxes.

[0149] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0150] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-voltage ride-through control method for a grid-type variable-speed pumped storage unit, characterized in that: Specifically, it includes: Construct an equivalent model of a full-power variable-speed pumped storage unit based on VSG; When a voltage drop occurs in the power grid due to a fault, the power angle value, output active power, and output reactive power of the grid-side converter after the fault are obtained based on the equivalent model of the full-power variable speed pumped storage unit based on VSG. Based on the power angle value and output active power of the grid-side converter after the fault, an improved active-frequency control equation is constructed. Based on the output reactive power of the grid-side converter after the fault, an improved reactive-voltage control equation is constructed. The instantaneous current and fault current of the grid-side converter are obtained based on the equivalent model of the full-power variable speed pumped storage unit based on VSG. According to the constraint equation of the instantaneous fault current of the grid-side converter, virtual impedance is set to suppress the instantaneous fault current. The d-axis and q-axis voltage components of the grid-side converter are calculated based on the positive and negative sequence currents of the instantaneous current of the grid-side converter and the virtual impedance. The d-axis and q-axis voltage components are input into the positive sequence current control loop to control the grid-side converter. The reference values ​​of active and reactive power of the grid-side converter during a fault are obtained based on the equivalent model of the full-power variable speed pumped storage unit based on VSG. The reference values ​​of active and reactive power are then input into the modified active-frequency control equation and reactive-voltage control equation to control the grid-side converter. When the active power on the grid side changes, the corrected turbine angular velocity reference value is calculated based on the equivalent model of the full-power variable speed pumped storage unit based on VSG, and the turbine speed regulation system is controlled based on the corrected turbine angular velocity reference value.

2. The low-voltage ride-through control method for a grid-type variable-speed pumped storage unit according to claim 1, characterized in that: The equivalent model of the full-power variable speed pumped storage unit based on VSG includes: turbine system, turbine speed regulation system, permanent magnet synchronous generator, generator-side converter, and grid-side converter; The turbine speed control system is connected to the turbine system to control the turbine speed. The turbine system is connected to the permanent magnet synchronous generator to convert mechanical energy into electrical energy. The turbine-side converter controls the DC bus voltage to stabilize, and the grid-side converter is connected to the power grid to control the output active and reactive power.

3. The low-voltage ride-through control method for a grid-type variable-speed pumped storage unit according to claim 2, characterized in that: The turbine system includes: a transfer function of the turbine system; the turbine speed control system includes: a transfer function of the turbine speed control system and a guide vane opening transfer function; the permanent magnet synchronous generator includes: the swing equation of the permanent magnet synchronous generator, the transfer function of the permanent magnet synchronous generator, the three-phase voltage equation of the permanent magnet synchronous generator, the stator voltage equation of the permanent magnet synchronous generator, and the electromagnetic torque equation of the permanent magnet synchronous generator; the generator-side converter includes: an inner loop control for torque current and an outer loop control for DC voltage; the grid-side converter includes: a virtual synchronous generator strategy, an active power-frequency control equation, and a reactive power-voltage control equation.

4. The low-voltage ride-through control method for a grid-type variable-speed pumped storage unit according to claim 1, characterized in that: The expression for the improved active-frequency control equation is as follows: ； The expression for the improved reactive power-voltage control equation is as follows: ； in, and These are active power and reactive power commands, respectively. and The active and reactive power output by the VSG. The damping coefficient is... This is the reactive power-voltage droop factor. Angular frequency, The rated angular frequency, The angular frequency of the power grid. Here, s represents the virtual moment of inertia, t represents the Laplace operator, and t represents the unit of time. This is the voltage regulation coefficient. This represents the effective value of the VSG virtual back electromotive force.

5. The low-voltage ride-through control method for a grid-type variable-speed pumped storage unit according to claim 1, characterized in that: The expressions for the d-axis and q-axis voltage components of the grid-side converter are as follows: ； in, and These represent the positive-sequence voltage components on the d-axis and q-axis after adding virtual impedance, respectively. , These represent the positive sequence components of the current along the d-axis and q-axis, respectively. and These are the resistance and reactance of the virtual impedance, respectively.

6. The low-voltage ride-through control method for a grid-type variable-speed pumped storage unit according to claim 1, characterized in that: The modified active-frequency control equation is expressed as follows: ； The modified reactive power-voltage control equation is expressed as follows: ； in, This is the reference value for the active power output by the VSG during a fault. This is the reference value for reactive power output by the VSG during a fault. and The active and reactive power output by the VSG. The damping coefficient is... This is the reactive power-voltage droop factor. Angular frequency, The rated angular frequency, The angular frequency of the power grid. Here, s represents the virtual moment of inertia, t represents the Laplace operator, and t represents the unit of time. This is the voltage regulation coefficient. The effective value of the virtual back electromotive force of VSG. This refers to the VSG output voltage during a fault. Reactive current injected into the power grid to power generating units.

7. The low-voltage ride-through control method for a grid-type variable-speed pumped storage unit according to claim 1, characterized in that: The expression for the corrected turbine angular velocity reference value is as follows: ； in, This is the corrected reference value for the turbine's angular velocity. The angular velocity before the integration time interval is... For DC side capacitors, and These are the reference and actual values ​​of the DC bus voltage, respectively. This represents the number of pole pairs of the motor. This is the inertial time constant of the unit.

8. The low-voltage ride-through control method for a grid-type variable-speed pumped storage unit according to claim 1, characterized in that: Also includes: Once the grid connection voltage returns to normal, exit low-voltage ride-through control and resume normal control.

9. A computer-readable storage medium, characterized in that: It stores a computer program, which, when executed by a processor, implements a low-voltage ride-through control method for a grid-type variable-speed pumped storage unit as described in any one of claims 1-8.

10. A computer device, characterized in that: include: Memory, used to store instructions; A processor is configured to execute the instructions, causing the computer device to perform the operation of a low-voltage ride-through control method for a grid-type variable-speed pumped storage unit as described in any one of claims 1-8.

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