Low-voltage ride through control method and system for doubly-fed variable-speed pumped storage unit

Abstract

The invention discloses a low-voltage ride-through control method and system for a doubly-fed variable-speed pumped storage unit, and belongs to the field of doubly-fed variable-speed pumped storage unit control. The method comprises the steps of collecting stator current Is when the doubly-fed variable-speed pumped storage unit normally operates, converting the stator current Is into stator dq-axis current Isd and Isq through coordinate transformation, converting active power reference values and reactive power reference values of a stator side into stator dq-axis current reference values # imgabs0 # and # imgabs1 #, and making differences between the stator dq-axis current Isd and Isq and the stator dq-axis current reference values # imgabs2 # and # imgabs3 #, rotor current loop input reference values # imgabs4 # and # imgabs5 # are obtained through PI adjustment, low-voltage ride-through control is switched when a voltage drop fault occurs, a virtual inductor L1 is added into a rotor side current loop, and a stator current compensation coefficient k is introduced according to the voltage drop degree; k times of stator dq axis current Isd and Isq are added into rotor current loop input reference values # imgabs6 # and # imgabs7 #; and after the fault is recovered, the doubly-fed variable-speed pumped storage unit is switched to normal operation control.

Description

Technical Field

[0001] The invention belongs to the field of control of doubly-fed variable-speed pumped-storage units, and particularly relates to a low-voltage ride-through control method and system for doubly-fed variable-speed pumped-storage units. Background Art

[0002] With the grid connection and operation of a large number of intermittent and random renewable energy power generations, energy storage technologies are required to absorb new energy power generations. A pumped-storage power station has functions of peak shaving, valley filling, frequency modulation, phase modulation and emergency standby, and is an effective large-capacity energy storage method.

[0003] A doubly-fed variable-speed pumped-storage unit adopts a doubly-fed induction motor. The stator winding is directly connected to the grid, and the rotor winding is connected to the grid through a partial power converter for excitation. It can support variable-speed constant-frequency operation, P / Q decoupling control and maximum power point tracking, and has excellent regulation characteristics. The variation range of the rotational speed is related to the capacity of the converter. Generally, the size of the converter applied to this type of unit is about 30% of the rated power. However, since the stator is directly connected to the grid, the doubly-fed motor is extremely sensitive to grid faults. The high-amplitude electromotive force (EMF) generated by the grid voltage dip may damage the small-capacity converter. Therefore, relevant low-voltage ride-through control strategies need to be studied.

[0004] There are few existing studies on doubly-fed variable-speed pumped-storage units. The low-voltage ride-through control strategies mainly include two aspects: a hardware protection circuit and a software control strategy. The most common hardware protection circuit is to connect a crowbar circuit on the rotor side. When a grid fault is detected, the crowbar is switched on, and at the same time, the rotor-side converter is blocked, and the fault current is released through the crowbar circuit. The disadvantage of this method is that once the rotor-side converter is blocked, the unit will no longer be controllable and lose its own flexible regulation advantage. The software control strategy improves the low-voltage ride-through ability of the unit by improving the control loop without adding any hardware circuits. It mainly includes three types of control strategies: improving the controlled object, improving the rotor-side current controller, and improving the rotor current command. The method of improving the controlled object improves the suppression ability of the post-fault EMF by changing the controlled object of the current loop, but the converter often needs to output a higher voltage; the method of improving the rotor-side current controller replaces the PI controller with a high-performance controller such as a robust, resonant, hysteresis, nonlinear, or sliding-mode controller to improve the dynamic response and anti-interference ability of the current loop, but this type of method cannot suppress overvoltage; the method of improving the rotor current command allows free classification and negative-sequence components in the rotor current, but it often requires flux linkage observation and relatively complex calculations, and has low accuracy when the voltage dip is large, and will increase the complexity of the system.

[0005] For this reason, the present invention proposes a low voltage ride-through control method for a doubly-fed variable-speed pumped storage unit. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a low voltage ride-through control method and system for a doubly-fed variable-speed pumped storage unit, solving the problems in the prior art.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] The low voltage ride-through control method for a doubly-fed variable-speed pumped storage unit includes the following steps:

[0009] Collect the stator current I when the doubly-fed variable-speed pumped storage unit is operating normally s , and convert it into the stator dq-axis currents I sd and I sq through coordinate transformation, and convert the reference values of the active power and reactive power on the stator side into the reference values of the stator dq-axis currents and

[0010] Subtract the stator dq-axis currents I sd and I sq from the reference values of the stator dq-axis currents and , and obtain the input reference values of the rotor current loop through PI regulation and

[0011] When a voltage dip fault occurs, the doubly-fed variable-speed pumped storage unit switches to low voltage ride-through control, and a virtual inductor L1 is added to the rotor side current loop

[0012] According to the degree of voltage dip, introduce a stator current compensation coefficient k;

[0013] Add k times the stator dq-axis currents I and to the input reference values of the rotor current loop sd and I sq ;

[0014] After the fault is restored, the doubly-fed variable-speed pumped storage unit switches to normal operation control.

[0015] Furthermore, the doubly-fed variable-speed pumped storage unit includes: a doubly-fed motor, a rotor side converter, and a grid side converter; the stator winding of the doubly-fed motor is directly connected to the power grid, and the rotor winding of the doubly-fed motor is connected to the power grid for excitation through a partial power converter; when the doubly-fed variable-speed pumped storage unit is operating normally, the rotor side converter controls the active power and reactive power on the stator side, and the grid side converter controls the stability of the DC bus voltage.

[0016] Furthermore, when performing low-voltage ride-through control, the virtual inductor is L1, and the rotor current at this time is the port voltage output by the rotor-side converter which is the equivalent inductor voltage drop; at this time, the rotor circuit satisfies the following relationship:

[0017]

[0018] where ω r is the rotor electrical angular velocity, L1 is the equivalent virtual inductor, R r is the resistance of the rotor winding, is the rotor open-circuit voltage in the rotor coordinate system, σL r is the rotor leakage inductance, and j is the imaginary part identifier in the complex number field.

[0019] Furthermore, the constraint of the virtual inductor L1 is:

[0020]

[0021] where I and U are the maximum current and voltage allowed by the rotor-side converter respectively.

[0022] Furthermore, the range of the stator current compensation coefficient k is: 0 < k < L s / L m where L s is the self-inductance of the rotor winding, and L m is the mutual inductance between the stator and rotor windings.

[0023] Furthermore, in a doubly-fed variable-speed pumped-storage unit, in the rotor coordinate system, the expressions of the rotor voltage and current are:

[0024]

[0025] where u ro is the rotor open-circuit voltage, R r is the resistance of the rotor winding, ω r is the rotor electrical angular velocity; ir r and ur r are the rotor current and voltage in the rotor coordinate system respectively, σL r is the rotor leakage inductance; ψ s is the stator flux linkage; L s is the self-inductance of the rotor winding, and L m is the mutual inductance between the stator and rotor windings, and j is the imaginary part identifier in the complex number field.

[0026] The low-voltage ride-through control system of a doubly-fed variable-speed pumped-storage unit includes:

[0027] A stator current acquisition module: acquires the stator current I when the doubly-fed variable-speed pumped-storage unit is operating normally s, which is converted into the stator dq-axis currents \(I_{d}\) sd and \(I_{q}\) sq , and the reference values of the active power and reactive power on the stator side are converted into the reference values of the stator dq-axis currents and

[0028] Rotor current calculation module: The stator dq-axis currents \(I_{d}\) sd and \(I_{q}\) sq are subtracted from the reference values of the stator dq-axis currents and , and the input reference values of the rotor current loop are obtained through PI regulation and

[0029] Low voltage ride-through control module: When a voltage dip fault occurs, the doubly-fed variable-speed pumped storage unit switches to low voltage ride-through control, and a virtual inductor \(L_{1}\) is added to the rotor side current loop

[0030] Compensation calculation module: According to the degree of voltage dip, a stator current compensation coefficient \(k\) is introduced;

[0031] Compensation module: \(k\) times the stator dq-axis currents \(I_{d}\) and are added to the input reference values of the rotor current loop sd and \(I_{q}\) sq ;

[0032] And, fault recovery module: After the fault is recovered, the doubly-fed variable-speed pumped storage unit switches to normal operation control;

[0033] The doubly-fed variable-speed pumped storage unit includes a doubly-fed motor, a rotor side converter, and a grid side converter; the stator winding of the doubly-fed motor is directly connected to the grid, and the rotor winding of the doubly-fed motor is connected to the grid through a partial power converter for excitation; when the doubly-fed variable-speed pumped storage unit operates normally, the rotor side converter controls the active power and reactive power on the stator side, and the grid side converter controls the stability of the DC bus voltage.

[0034] A computer storage medium stores a readable program, which can execute the above-mentioned low voltage ride-through control method of the doubly-fed variable-speed pumped storage unit when the program runs.

[0035] An electronic device includes: a processor, a memory, a communication interface, and a communication bus, and the processor, the memory, and the communication interface complete communication with each other through the communication bus;

[0036] The memory is used to store at least one executable instruction, and the executable instruction causes the processor to execute the operations corresponding to the above-mentioned low voltage ride-through control method of the doubly-fed variable-speed pumped storage unit.

[0037] A computer program product includes computer instructions that direct a computing device to perform operations corresponding to the above-mentioned low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit.

[0038] Advantages of the present invention:

[0039] 1. The low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit provided by the present invention does not require flux linkage observation, greatly reducing the complexity of the control system, improving the control accuracy, and making the control more reliable.

[0040] 2. The present invention effectively suppresses overvoltage and overcurrent on the rotor side through virtual inductor control and stator current compensation, without the need for additional hardware devices, reducing the system cost and enhancing the low-voltage ride-through ability of the unit.

[0041] 3. The low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit provided by the present invention takes into account the constraints of the voltage output capacity of the rotor-side converter during the grid fault transient period, can effectively utilize the converter capacity, and maintain the controllability of the unit without overvoltage and overcurrent.

[0042] 4. The low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit provided by the present invention utilizes the inherent characteristics of the doubly-fed motor. By controlling the quantitative relationship between the stator current and the rotor current, rather than directly controlling the stator current or the rotor current to generate the rotor current command, it is easier to implement in control. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0044] Figure 1 is a schematic structural diagram of a doubly-fed variable-speed pumped-storage unit;

[0045] Figure 2 is a schematic diagram of the change during the transient process of the stator flux linkage;

[0046] Figure 3 is an equivalent circuit model of the rotor side under virtual inductor control;

[0047] Figure 4 is the low-voltage ride-through control block diagram of the present invention;

[0048] Figure 5 is the rotor current diagram obtained by controlling with the control method proposed by the present invention and the control method without using the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] Embodiment 1

[0051] As Figure 1 shown, the doubly-fed variable-speed pumped-storage unit includes: a doubly-fed motor, a reversible pump-turbine, a rotor-side converter, and a grid-side converter;

[0052] Among them, the stator winding of the doubly-fed motor is directly connected to the power grid, and the rotor winding of the doubly-fed motor is connected to the power grid through a partial power converter for excitation; when the doubly-fed variable-speed pumped-storage unit operates normally, the rotor-side converter controls the active power and reactive power on the stator side, and the grid-side converter controls the stability of the DC bus voltage and maintains unity power factor operation. In the power generation mode, the reversible pump-turbine provides torque to maintain the rotation of the motor, and in the pumping mode, the pump consumes power.

[0053] According to the relevant principles of the doubly-fed motor, the space vector form of the dynamic mathematical model in the stationary coordinate system is:

[0054]

[0055]

[0056] ψ s = L s i s + L m i r (3)

[0057] ψ r = L m i s + L r i r (4)

[0058] In the formula, u, i, and ψ respectively represent the voltage, current, and magnetic flux space vectors; the subscripts "s" and "r" respectively represent the stator and the rotor; L s and L r are respectively the self-inductances of the stator and rotor windings; L m is the mutual inductance between the stator and rotor windings; R s and R r are respectively the resistances of the stator winding and the rotor winding; ω r is the rotor electrical angular velocity.

[0059] The expressions of the rotor voltage and current can be obtained using Equations (1) to (4):

[0060]

[0061] The rotor voltage in Equation (5) can be divided into two parts. The first part is the induced electromotive force caused by the stator flux linkage. At the same time, when the rotor current is 0, i.e., the rotor is open-circuited, this term is also the rotor open-circuit voltage, so it is denoted as u ro ; The second part is the voltage drop across the rotor impedance. Transforming Equation (5) into the rotor coordinate system gives:

[0062]

[0063] where the superscript "r" represents the rotor coordinate system, and σL r is the rotor leakage inductance.

[0064] The rotor open-circuit voltage u ro reflects the electromagnetic coupling relationship between the stator and the rotor. During a grid voltage fault, the rotor current, DC bus voltage, and electromagnetic torque of the doubly-fed variable-speed pumped-storage unit are mainly affected by it. Assume that a three-phase symmetrical fault occurs in the grid voltage at t = 0. Since the stator of the doubly-fed variable-speed pumped-storage unit is directly connected to the grid, the stator voltage u s in vector form can be expressed as:

[0065]

[0066] where U s is the amplitude of the stator voltage, ω s is the stator electrical angular velocity, and h represents the degree of the grid voltage fault.

[0067] According to Equations (3), (4), and (7), neglecting the smaller stator resistance, the analytical expressions of the stator flux linkage ψ s before and after the fault are obtained:

[0068]

[0069] where ψ sf and ψ sn are the forced component and natural component of the stator flux linkage respectively. Since the flux linkage is a continuously varying quantity and cannot change suddenly, a transient natural component that decays with the stator time constant τ s = L s / R s is generated after the fault. According to the characteristic that the flux linkage cannot change suddenly, the analytical expression of the stator flux linkage ψ s after the fault is solved:

[0070]

[0071] According to Equation (9), the stator flux linkage can be obtained as consisting of a rotating AC component ψ sf and a decaying DC component ψ sn . During the transient process, the change of the stator flux linkage is as Figure 2 shown. Among them, Figure 2 (a)-(c) in it respectively represent: the stator flux linkage during normal operation, the stator flux linkage at the moment of voltage dip, and the stator flux linkage during the transient process.

[0072] Embodiment 2

[0073] In this embodiment, as Figure 4 shown, the low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit includes the following steps:

[0074] S1. Collect the stator current I s of the doubly-fed variable-speed pumped-storage unit during normal operation, and convert it into the stator dq-axis currents I sd and I sq through coordinate transformation (dq transformation), and convert the reference values of the active power and reactive power on the stator side into the reference values of the stator dq-axis currents and

[0075] S2. Subtract the stator dq-axis currents I sd and I sq from the reference values of the stator dq-axis currents and , and obtain the input reference values of the rotor current loop through PI regulation (proportional-integral regulation) and

[0076] The process of PI regulation is as follows:

[0077] 1) Proportional control (P): According to the current error, adjust the control quantity proportionally. The larger the proportional gain K p , the faster the response.

[0078] 2) Integral control (I): Eliminate the steady-state error by accumulating the historical error. The larger the integral gain K i , the faster the error is eliminated.

[0079] 3) Comprehensive action: The PI regulator combines proportional and integral controls, and the output control quantity is the sum of the two.

[0080] S3. When a voltage dip fault occurs, the doubly-fed variable-speed pumped-storage unit switches to low-voltage ride-through control, and a virtual inductor L1 is added to the rotor-side current loop;

[0081] The variation of the stator flux affects the variation of the open-circuit voltage and rotor current on the rotor side. During the low-voltage ride-through process of the doubly-fed motor, the biggest obstacle lies in that the stator flux can induce an induced electromotive force (EMF) fault component on the rotor side that is much higher than the DC bus voltage. According to Equation (5), at this time, the limited voltage output capacity of the rotor-side converter is not sufficient to cancel out this EMF, thus the fault current cannot be completely eliminated. At this time, the fundamental requirement to maintain system controllability to suppress overvoltage and overcurrent is to reduce the excitation voltage demand on the rotor side. Since the EMF acts on the rotor transient impedance and the rotor-side converter, this requires a large EMF voltage drop to be shared on the rotor transient inductance and resistance. Therefore, a virtual inductor L1 can be added to the rotor current loop. Through a certain control algorithm, making the rotor current loop act as the virtual inductor L1 for this transient current component can play a certain role in suppressing the rotor current.

[0082] When performing low-voltage ride-through control, assuming the value of the virtual inductor is L1, the equivalent circuit on the rotor side during the transient state is as Figure 3 shown. Assuming the rotor current at this time is The port voltage output by the rotor-side converter is the equivalent inductor voltage drop.

[0083] At this time, the following relationship is satisfied in the rotor circuit:

[0084]

[0085] According to Equations (10) and (11), the larger L1 is, the smaller is, and the larger

[0086] is. Therefore, increasing the value of the virtual inductor L1 has a stronger inhibitory effect on the rotor current, but the voltage that the converter needs to output is also larger. Since the capacity of the converter is limited, neither the voltage nor the current can exceed the limit, so the value of the virtual inductor needs to be restricted.

[0087]

[0088]

[0089] The rotor voltage satisfies:

[0090]

[0091] Among them, ω r is the rotor electrical angular velocity, L1 is the equivalent virtual inductor, ir'r is the rotor current, and R r is the resistance of the rotor winding. is the rotor open-circuit voltage in the rotor coordinate system, ur'r is the port voltage output by the converter, σL r is the rotor leakage inductance, j is the imaginary part identifier in the complex domain, and I and U are the maximum allowable current and voltage of the rotor-side converter, respectively.

[0092] Therefore, the virtual inductor L1 must satisfy the constraints of both Equation (13) and (15) simultaneously.

[0093] S4. According to the degree of voltage dip, introduce the stator current compensation coefficient k;

[0094] At the same time, according to the relevant principles of the doubly-fed motor, the essence that the stator magnetic flux cannot change suddenly is that the stator magnetization current I sm is a constant value, and its expression is:

[0095]

[0096] where I sm is the stator current, I s is the stator current, I r is the stator current, ψ s is the stator magnetic flux, L s is the stator inductance, L m is the mutual inductance between the stator and the rotor.

[0097] The fluctuation of the rotor current under the fault is opposite to that of the stator current. Therefore, introducing the stator current-related compensation amount in the rotor current loop can effectively suppress the voltage and current fluctuations. According to different degrees of voltage dip, the range of the stator current compensation coefficient k is 0 < k < L s / L m .

[0098] The stator current compensation coefficient k is determined by the degree of voltage dip. k = (1 - h)L s / L m , h is the degree of grid voltage dip, L s is the stator inductance, L m is the mutual inductance between the stator and the rotor. The higher the degree of voltage dip, the larger the rotor EMF after the fault and the larger the rotor current. At this time, in order to reduce the excitation voltage requirement on the rotor side, the compensation amount to be added is also larger.

[0099] S5. Add k times the stator dq-axis currents I and to the rotor current loop input reference values sd and I sq ;

[0100] S6. After the fault is restored, the doubly-fed variable-speed pumped-storage unit switches to normal operation control;

[0101] When the doubly-fed variable-speed pumped storage unit operates normally, the rotor-side converter controls the active power and reactive power of the stator side, and the grid-side converter controls the stability of the DC bus voltage and maintains unit power factor operation.

[0102] Based on a similar inventive concept, an embodiment of the present invention further provides a computer storage medium storing a readable program, which, when running, can execute the above-mentioned low-voltage ride-through control method for a doubly-fed variable-speed pumped storage unit.

[0103] Based on a similar inventive concept, an embodiment of the present invention provides an electronic device, including: a processor, a memory, a communication interface, and a communication bus, and the processor, the memory, and the communication interface complete communication with each other through the communication bus;

[0104] The memory is used to store at least one executable instruction, and the executable instruction causes the processor to execute the operations corresponding to the above-mentioned low-voltage ride-through control method for a doubly-fed variable-speed pumped storage unit.

[0105] Based on a similar inventive concept, an embodiment of the present invention further provides a computer program product, including computer instructions, and the computer instructions instruct a computing device to execute the operations corresponding to the above-mentioned low-voltage ride-through control method for a doubly-fed variable-speed pumped storage unit.

[0106] Embodiment 3

[0107] In this embodiment, taking a 300MW doubly-fed variable-speed pumped storage unit as an example, a simulation study is carried out to verify the superiority of the low-voltage ride-through control method of the present invention;

[0108] Before the fault occurs, the speed of the doubly-fed motor is 7% supersynchronous, and the unit stably outputs at 90% of the rated power. An 80% voltage dip fault occurs at t = 2s and recovers at t = 2.625s;

[0109] The controlled rotor current and rotor voltage are as Figure 5 shown; where Figure 5 (a) in represents that the proposed control method is not added, Figure 5 (b) in represents that the proposed control method is added; it can be seen that: when the proposed control method of the present invention is not added, at the moment of the grid voltage dip, that is, at t = 2s, the impact of the rotor current is about 3 times that in normal operation, and the magnitude of this current is very likely to exceed the capacity range of the converter, resulting in converter damage or unit tripping, further exacerbating the fault. After adding the proposed control method of the present invention, the rotor current at the moment of the fault is limited within a reasonable range, about 1.33 times that in normal operation. Therefore, the proposed control method can effectively suppress the overcurrent on the rotor side at the moment of the fault and maintain the normal operation of the unit.

[0110] Embodiment 4

[0111] Based on the low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit proposed in Embodiment 2, in this embodiment, a low-voltage ride-through control system for a doubly-fed variable-speed pumped-storage unit is proposed, specifically including:

[0112] Stator current acquisition module: Acquire the stator current I during the normal operation of the doubly-fed variable-speed pumped-storage unit s , and convert it into stator dq-axis currents I sd and I sq through coordinate transformation, and convert the reference values of active power and reactive power on the stator side into reference values of stator dq-axis currents and

[0113] Rotor current calculation module: Subtract the stator dq-axis currents I sd and I sq from the reference values of stator dq-axis currents and , and obtain the input reference values of the rotor current loop through PI regulation and

[0114] Low-voltage ride-through control module: When a voltage dip fault occurs, the doubly-fed variable-speed pumped-storage unit switches to low-voltage ride-through control, and a virtual inductor L1 is added to the rotor-side current loop

[0115] Compensation calculation module: According to the degree of voltage dip, introduce a stator current compensation coefficient k;

[0116] Compensation module: Add k times the stator dq-axis currents I and to the input reference values of the rotor current loop sd and I sq ;

[0117] And a fault recovery module: After the fault is recovered, the doubly-fed variable-speed pumped-storage unit switches to normal operation control.

[0118] The method of the present invention can be implemented in hardware, firmware, or be implemented as software or computer code that can be stored in a recording medium (such as a CDROM, RAM, floppy disk, hard disk, or magneto-optical disk), or be implemented as computer code originally stored in a remote recording medium or a non-transitory machine-readable medium and to be downloaded through a network and stored in a local recording medium, so that the method described herein can be stored in such software processing on a recording medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware (such as an ASIC or FPGA). It will be understood that a computer, a processor, a microprocessor controller, or programmable hardware includes a storage component (e.g., RAM, ROM, flash memory, etc.) that can store or receive software or computer code, and when the software or computer code is accessed and executed by the computer, the processor, or the hardware, the method described herein is implemented. Further, when a general-purpose computer accesses the code for implementing the method shown herein, the execution of the code converts the general-purpose computer into a dedicated computer for executing the method shown herein.

[0119] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and all these changes and improvements fall within the scope of the present invention claimed.

Claims

1. A low voltage ride-through control method for a doubly-fed variable speed pumped-storage unit, characterized in that, It includes the following steps: Collect the stator current I of the doubly-fed variable-speed pumped-storage unit during normal operation s , and convert it into the stator dq-axis currents I sd and I sq through coordinate transformation, and convert the reference values of the active power and reactive power on the stator side into the reference values of the stator dq-axis currents and Subtract the stator dq-axis currents I sd and I sq from the stator dq-axis current reference values and , and after PI regulation, obtain the rotor current loop input reference values and When a voltage dip fault occurs, the doubly-fed variable-speed pumped-storage unit switches to low-voltage ride-through control, and a virtual inductor L1 is added to the rotor-side current loop According to the degree of voltage dip, a stator current compensation coefficient k is introduced; At the input reference value of the rotor current loop and add k times the stator dq-axis currents I sd and I sq ; After the fault is restored, the doubly-fed variable-speed pumped-storage unit switches to normal operation control.

2. The low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit according to claim 1, wherein, The doubly-fed variable-speed pumped-storage unit includes: a doubly-fed motor, a rotor-side converter, and a grid-side converter; the stator winding of the doubly-fed motor is directly connected to the grid, and the rotor winding of the doubly-fed motor is connected to the grid through a partial power converter for excitation; when the doubly-fed variable-speed pumped-storage unit operates normally, the rotor-side converter controls the active power and reactive power on the stator side, and the grid-side converter controls the stability of the DC bus voltage.

3. The low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit according to claim 2, wherein When performing low-voltage ride-through control, the virtual inductor is L1, and the rotor current at this time is the port voltage output by the rotor-side converter which is the equivalent inductor voltage drop; at this time, the following relationship is satisfied in the rotor circuit: Among them, ω r is the electrical angular velocity of the rotor, L1 is the equivalent virtual inductance, R r is the resistance of the rotor winding, is the open-circuit voltage of the rotor in the rotor coordinate system, σL r is the leakage inductance of the rotor, and j is the imaginary part identifier in the complex domain.

4. The low voltage ride-through control method for a doubly-fed variable-speed pumped storage unit according to claim 3, wherein The constraint of the virtual inductor L1 is: Where I and U are the maximum current and voltage allowed by the rotor-side converter respectively.

5. The low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit according to claim 2, wherein, The range of the stator current compensation coefficient k is: 0 < k < L s / L m , where L s is the self-inductance of the rotor winding, and L m is the mutual inductance between the stator and rotor windings.

6. The low-voltage ride-through control method for a doubly-fed variable-speed pumped-storage unit according to claim 2, characterized in that, In the doubly-fed variable-speed pumped-storage unit, in the rotor coordinate system, the expressions of rotor voltage and current: where, u ro is the rotor open-circuit voltage, R r is the resistance of the rotor winding, ω r is the rotor electrical angular velocity; ir r and ur r are the rotor current and voltage in the rotor coordinate system, σL r is the rotor leakage inductance; ψ s is the stator flux linkage; L s is the self-inductance of the rotor winding, L m is the mutual inductance between the stator and rotor windings, and j is the imaginary part identifier in the complex number domain.

7. Double-fed variable-speed pumped-storage unit low voltage ride-through control system, characterized in that, It includes: Stator current acquisition module: Acquire the stator current I during the normal operation of the doubly-fed variable-speed pumped-storage unit s , and convert it into the stator dq-axis currents I sd and I sq , and convert the reference values of the active power and reactive power on the stator side into the reference values of the stator dq-axis currents and Rotor current calculation module: Subtract the stator dq-axis currents I sd and I sq from the stator dq-axis current reference values and , and after PI regulation, obtain the input reference values and Low-voltage ride-through control module: When a voltage dip fault occurs, the doubly-fed variable-speed pumped-storage unit switches to low-voltage ride-through control, and a virtual inductor L1 is added to the rotor-side current loop Compensation calculation module: According to the degree of voltage dip, a stator current compensation coefficient k is introduced; Compensation module: Add k times the stator dq-axis currents I and to the input reference values of the rotor current loop sd and I sq ; And a fault recovery module: After the fault is restored, the doubly-fed variable-speed pumped-storage unit switches to normal operation control; The doubly-fed variable-speed pumped-storage unit includes a doubly-fed motor, a rotor-side converter, and a grid-side converter; the stator winding of the doubly-fed motor is directly connected to the grid, and the rotor winding of the doubly-fed motor is connected to the grid through a partial power converter for excitation; when the doubly-fed variable-speed pumped-storage unit operates normally, the rotor-side converter controls the active power and reactive power on the stator side, and the grid-side converter controls the stability of the DC bus voltage.

8. A computer storage medium stores a readable program, characterized in that, When the program runs, it can execute the low-voltage ride-through control method of the doubly-fed variable-speed pumped-storage unit according to any one of claims 1-6.

9. An electronic device, characterized in that, It includes: A processor, a memory, a communication interface, and a communication bus. The processor, the memory, and the communication interface complete mutual communication through the communication bus; The memory is used to store at least one executable instruction, and the executable instruction causes the processor to execute the operations corresponding to the low-voltage ride-through control method of the doubly-fed variable-speed pumped-storage unit according to any one of claims 1-6.

10. A computer program product comprising computer instructions, characterized in that, The computer instruction instructs the computing device to execute the operations corresponding to the low-voltage ride-through control method of the doubly-fed variable-speed pumped-storage unit according to any one of claims 1-6.

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