Full-power pumped storage unit with multi-stage voltage architecture and control method

Abstract

The invention discloses a full-power pumped storage unit of a multi-stage voltage architecture and a control method. Relates to the technical field of power systems. The multi-winding transformer is used for converting high-voltage electric energy of a power grid into multiple independent low-voltage electric energy to be output; the modular converter is used for rectifying and inverting multiple low-voltage electric energy and then generating multi-phase independent medium-voltage energy supply in a cascade form; the modular converter is connected with the secondary side of the multi-winding transformer; the multi-phase open winding motor is used for receiving multi-phase independent medium-voltage energy supply; the multi-phase open winding motor is connected with the output end of the modular converter; according to the scheme, on the basis of a traditional full-power variable-frequency variable-speed pumped storage unit, unit structure composition and unit management methods are improved, and a full-power variable-frequency variable-speed pumped storage unit topology and control method based on a high-low-middle framework is provided. The defects that a traditional high-power variable-frequency variable-speed pumped storage unit is high in manufacturing cost, poor in operation reliability, small in efficient operation area and the like are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a full-power pumped storage unit with a multi-level voltage architecture and a control method. Background Art

[0002] As renewable energy generation represented by hydropower, wind power, photovoltaic power, etc. has received great attention, higher requirements have been put forward for the response characteristics of flexible grid adjustment measures for high proportion of new energy access; variable speed pumped storage power station, as a relatively mature energy storage technology, has become one of the important means to solve the problem of efficient use of new energy generation and improve the grid regulation capacity.

[0003] Traditional variable speed pumped storage technologies mainly include double-fed variable speed and full power variable speed solutions. The full power variable speed solution has gradually become the mainstream due to its large speed regulation range and high operating stability. However, the current full power variable speed pumped storage units have the following technical bottlenecks:

[0004] In terms of economy, traditional full-power variable-frequency variable-speed pumped-storage units mostly adopt a "high-medium-medium" architecture, and their core converter is a modular multilevel converter (MMC). This topology has a large demand for DC suspension capacitors, which significantly increases the converter manufacturing cost. In terms of stability, the traditional MMC topology is prone to circulating current problems due to the shared DC bus between modules. Current units generally use three-phase permanent magnet synchronous motors. When a phase failure or a converter module failure occurs, it is difficult for the system to achieve fault-tolerant operation. This leads to frequent system shutdowns and maintenance, and reduced operational reliability. In terms of operating efficiency, when existing units are operating at low power, all modules and motor windings usually still need to be fully put into operation, resulting in increased overall system power loss and low operating efficiency; this phenomenon is particularly significant during non-peak load periods. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the traditional full-power variable-frequency and variable-speed pumped-storage unit has a large demand for DC suspension capacitors, which leads to high manufacturing costs of the converter, easy circulation problems, difficulty in achieving fault-tolerant operation, and large unit losses during non-peak load periods. The purpose of the present invention is to provide a full-power pumped-storage unit and a control method with a multi-level voltage architecture. On the basis of the traditional full-power variable-frequency and variable-speed pumped-storage unit, improvements are made in the unit structure and unit management methods, and a full-power variable-frequency and variable-speed pumped-storage unit topology and control method based on the "high-low-medium" architecture is proposed to solve the defects of traditional high-power variable-frequency and variable-speed pumped-storage units, such as high manufacturing cost, poor operating reliability and small high-efficiency operating area.

[0006] The present invention is achieved through the following technical solutions:

[0007] This solution provides a full-power pumped storage unit with a multi-level voltage architecture, including:

[0008] A multi-winding transformer is used to convert the high-voltage electric energy of the power grid into multiple independent low-voltage electric energy outputs; the power grid is connected to the primary side of the multi-winding transformer;

[0009] A modular converter, used for rectifying and inverting low-voltage electric energy to generate multi-phase independent medium-voltage electric energy in a cascade form; the modular converter is connected to the secondary side of a multi-winding transformer;

[0010] A multi-phase open-winding motor is used to receive multi-phase independent medium-voltage energy supply; the multi-phase open-winding motor is connected to the output end of the modular converter.

[0011] Working principle of this scheme: Traditional full-power variable-frequency and variable-speed pumped-storage units have a large demand for DC suspension capacitors, which leads to high converter manufacturing costs, easy circulation problems, difficulty in achieving fault-tolerant operation, and large unit losses during non-peak load periods. The purpose of the present invention is to provide a full-power pumped-storage unit and a control method with a multi-level voltage architecture. On the basis of traditional full-power variable-frequency and variable-speed pumped-storage units, improvements are made to the unit structure and unit management methods, and a full-power variable-frequency and variable-speed pumped-storage unit topology and control method based on a "high-low-medium" architecture is proposed to solve the defects of traditional high-power variable-frequency and variable-speed pumped-storage units, such as high manufacturing cost, poor operating reliability and small high-efficiency operating area.

[0012] This solution reduces the demand for high-value DC capacitors and reduces the manufacturing cost of the converter through the design of modular converters. The independent multi-winding transformer enables voltage and current conversion to be performed at low voltage, effectively reducing the rated voltage level and design difficulty of the equipment. The multi-phase open-winding motor is based on single-phase or multi-phase fault tolerance, which facilitates system maintenance and rapid replacement of faulty modules, and improves the stability and redundancy of system operation.

[0013] A further optimization scheme is that the primary side of the multi-winding transformer is a three-phase winding connected in a Y shape, and the secondary side is an independently distributed single-phase winding.

[0014] A further optimized solution is that the modular converter is composed of a plurality of independent single-phase converters connected in cascade.

[0015] A further optimization scheme is that the single-phase converter is an H-bridge back-to-back converter.

[0016] A further optimization scheme is that the multi-phase open-winding motor is a distributed open-winding permanent magnet synchronous motor, and each phase open winding is connected to a group of independent cascaded single-phase converter groups; the number of phases of the multi-phase open-winding motor is 3n, n≥1.

[0017] A further optimization scheme is that the number of phases of the multi-phase open-winding motor and the number of independent single-phase converters in the modular H-bridge back-to-back converter are both determined by the rated output voltage and output power of the multi-phase open-winding motor.

[0018] This solution also provides a control method for controlling the full-power pumped storage unit with a multi-level voltage architecture as described above; the method comprises:

[0019] Sampling an operation signal of a multi-phase open-winding motor, wherein the operation signal includes a current signal of each phase open winding and a rotation speed of the multi-phase open-winding motor;

[0020] Performing coordinate transformation on the operation signal and mapping it into an orthogonal subspace;

[0021] The current signal is decoupled and controlled in the orthogonal subspace, and the active power and reactive power of the multi-phase open-winding motor are adjusted separately based on the speed-limited strategy.

[0022] A further optimization scheme is to control the output of the single-phase converter by using a phase-shifted PWM modulation technique after decoupling the current signal in the orthogonal subspace.

[0023] A further optimization scheme is that the current signal is subjected to coordinate transformation and projection to an orthogonal subspace, including the method:

[0024] According to the transformation matrix T, the coordinate transformation of the current signal of the m-phase open-winding motor is performed to project the m-phase open-winding current signal of the motor into the fundamental subspace α-β and the third harmonic subspace z 1 -z 2 and the 5th harmonic subspace o 1 -o 2 Three orthogonal subspaces:

[0025]

[0026] Where l represents the harmonic order, l = 2[m / 2]±1, when m is an even number, it is “-”, when m is an odd number, it is “+”; θ represents the phase difference between two adjacent phases,

[0027] A further optimization scheme is a control method for controlling the full-power pumped storage unit of the above-mentioned multi-level voltage architecture; the method comprises:

[0028] Get the current operation mode of the full-power variable-frequency variable-speed pumped storage unit;

[0029] If the current operating power is lower than a first preset power threshold, the open windings of some phases and their corresponding single-phase converters are disabled; if the current operating power is higher than a second preset power threshold, the open windings of all phases and their corresponding single-phase converters are used; wherein the first preset power threshold is less than the second preset power threshold;

[0030] If the current operation mode belongs to the fault mode, the power of the full-power variable-frequency variable-speed pumped-storage unit is reduced, and the non-faulty open windings and non-faulty single-phase converters are dynamically adjusted to keep the motor running stably.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] 1. The present invention provides a full-power pumped storage unit with a multi-level voltage architecture and a control method. Based on the traditional full-power variable-frequency and variable-speed pumped-storage unit, improvements are made in the unit structure and unit management method, and a full-power variable-frequency and variable-speed pumped-storage unit topology and control method based on a "high-low-medium" architecture is proposed to solve the defects of traditional high-power variable-frequency and variable-speed pumped-storage units, such as high manufacturing cost, poor operating reliability and small efficient operating area.

[0033] 2. The present invention provides a full-power pumped storage unit with a multi-level voltage architecture and a control method. The modular converter design reduces the need for high-value DC capacitors and reduces the converter manufacturing cost. The independent multi-winding transformer enables voltage and current conversion to be performed at low voltage, effectively reducing the rated voltage level and design difficulty of the equipment. The multi-phase open-winding motor is used to tolerate single-phase or multi-phase faults, which facilitates system maintenance and rapid replacement of faulty modules, thereby improving the stability and redundancy of system operation.

[0034] 3. The present invention provides a full-power pumped storage unit with a multi-level voltage architecture and a control method; in low-power mode, the non-full-phase operation strategy reduces the operating frequency and power consumption of the converter switch device, and expands the efficient operation area of ​​the unit. At the same time, the control decoupling speed regulation mode makes the energy transmission of the motor more accurate, reducing the impact of torque pulsation and harmonics on the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0036] Figure 1 It is a structural schematic diagram of a full-power variable-frequency variable-speed pumped storage unit;

[0037] Figure 2 It is a schematic diagram of the H-bridge back-to-back converter structure;

[0038] Figure 3 2 is a schematic diagram of the control principle of Example 2;

[0039] Figure 4 This is a schematic diagram of a non-full-phase operation strategy of a multi-phase motor in Example 3;

[0040] Figure 5 It is a schematic diagram of the operating state of a multi-phase open-winding motor under the pumping condition of Example 3;

[0041] Figure 6 This is a schematic diagram of a 20MW pumped storage unit example of Example 3. DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0043] The traditional full-power variable-frequency variable-speed pumped storage unit has a large demand for DC suspension capacitors, resulting in high converter manufacturing costs, easy circulation problems, difficulty in achieving fault-tolerant operation, and large unit losses during non-peak load periods. In view of this, this solution provides the following embodiments to solve the above technical problems:

[0044] Example 1

[0045] This embodiment provides a full-power pumped storage unit with a multi-level voltage architecture, such as Figure 1 As shown, including:

[0046] A multi-winding transformer is used to convert the high-voltage electric energy of the power grid into multiple independent low-voltage electric energy outputs; the power grid is connected to the primary side of the multi-winding transformer;

[0047] A modular converter, used for rectifying and inverting low-voltage electric energy to generate multi-phase independent medium-voltage electric energy in a cascade form; the modular converter is connected to the secondary side of a multi-winding transformer;

[0048] A multi-phase open-winding motor is used to receive multi-phase independent medium-voltage energy supply; the multi-phase open-winding motor is connected to the output end of the modular converter.

[0049] The primary side of the multi-winding transformer is a three-phase winding connected in a Y shape, and the secondary side is an independently distributed single-phase winding;

[0050] The modular converter is composed of a plurality of independent single-phase converters connected in cascade. Each core column of the multi-winding transformer includes a primary winding and a plurality of independent single-phase secondary windings, and the number of the secondary windings is consistent with the number of the single-phase converters in the modular converter.

[0051] The single-phase converter is an H-bridge back-to-back converter. Figure 2 As shown, the H-bridge back-to-back converter includes a rectifier unit for rectifying the AC power output by the multi-winding transformer into DC power; an inverter unit connected to the rectifier unit for inverting the DC power into the required medium-voltage AC power; an independent DC capacitor arranged between the rectifier unit and the inverter unit for voltage stabilization and energy storage, and effectively reducing the loop current.

[0052] The multi-phase open-winding motor is a distributed open-winding permanent magnet synchronous motor, each phase of the open winding is connected to a group of independent cascaded single-phase converter groups; the number of phases of the multi-phase open-winding motor is 3n, n≥1. Each phase of the open winding receives independent energy supply from each phase to achieve stable operation of the motor.

[0053] The number of phases of the multi-phase open-winding motor and the number of independent single-phase converters in the modular H-bridge back-to-back converter are determined by the rated output voltage and output power of the multi-phase open-winding motor; to reduce the voltage and power pressure of a single power unit; and to reduce the current flowing in the switching device to ensure normal operation of the device.

[0054] Example 2

[0055] This embodiment provides a control method for controlling a full-power pumped storage unit with a multi-level voltage architecture as described in Embodiment 1; the method comprises:

[0056] S1, sampling the operation signal of the multi-phase open-winding motor, wherein the operation signal includes the current signal of the open-winding multi-phase motor and the speed of the multi-phase open-winding motor;

[0057] S2, mapping the operation signal to an orthogonal subspace by coordinate transformation; this step specifically includes the following method:

[0058] According to the transformation matrix T, the coordinate transformation of the current signal of the m-phase open-winding motor is performed to project the m-phase open-winding current signal of the motor into the fundamental subspace α-β and the third harmonic subspace z 1 -z 2 and the 5th harmonic subspace o 1 -o 2 Three orthogonal subspaces:

[0059]

[0060] Where l represents the harmonic order, l = 2[m / 2]±1, when m is an even number, it is “-”, when m is an odd number, it is “+”; θ represents the phase difference between two adjacent phases,

[0061] S3, decouples and controls the current signal in the orthogonal subspace, and adjusts the active power and reactive power of the multi-phase open-winding motor separately based on the speed-limited strategy to achieve precise speed and torque control; also controls the output of the single-phase converter through the phase-shifted PWM modulation technology; ensures that the output voltage has a good sinusoidal waveform while reducing the harmonic content.

[0062] like Figure 3 As shown in the figure, by comparing the actual speed with the target speed command, the active power control of the motor is determined through PI adjustment. d =0, the motor reactive power command is 0. By changing the PMW carrier phase corresponding to the converters cascaded in the same phase, the modulation voltage output by the H-bridge converter is increased in the cascade process, and the output voltage of the converter output through the cascade has better sinusoidality and reduces the harmonic content.

[0063] This scheme simplifies the multi-variable multi-phase motor control problem into an equivalent single-phase system control through coordinate transformation, which is convenient for decoupling the motor's torque and excitation current, thereby achieving precise speed regulation.

[0064] Example 3

[0065] This embodiment provides a control method for controlling a full-power pumped storage unit with a multi-level voltage architecture as described in Embodiment 1; the method comprises:

[0066] Get the current operation mode of the full-power variable-frequency variable-speed pumped storage unit;

[0067] If the current operating power is lower than a first preset power threshold, the open windings of some phases and their corresponding single-phase converters are disabled; if the current operating power is higher than a second preset power threshold, the open windings of all phases and their corresponding single-phase converters are used; wherein the first preset power threshold is less than the second preset power threshold;

[0068] If the current operation mode belongs to the fault mode, the power of the full-power variable-frequency variable-speed pumped-storage unit is reduced, and the non-faulty open windings and non-faulty single-phase converters are dynamically adjusted to keep the motor running stably.

[0069] like Figure 4As shown in the figure, in low-power operation mode, non-full-phase operation is achieved by disabling some converters and phase windings to reduce system power loss; when a motor phase failure is detected, the operating power of the unit is reduced, and the remaining phase windings are dynamically adjusted to maintain stable system operation. When the multi-phase open-winding motor is running at low power, non-full-phase operation is achieved by disabling some three-phase windings, effectively reducing power loss. Under normal operating conditions, the simultaneous operation of multi-phase windings can significantly reduce torque pulsation and improve system efficiency and electromagnetic performance. Its multi-phase structure can also effectively suppress high-order harmonics in motor operation, thereby further improving the operating efficiency and stability of the unit.

[0070] Multi-phase open-winding motors can maintain stable operation in non-full-phase operation modes; when part of the motor windings or converters fail, the remaining open windings and converters that have not failed can continue to supply energy through dynamic adjustment, thereby achieving the unit's fault-tolerant operation capability.

[0071] Figure 5 As shown in the figure, under the pumping condition, it is assumed that the speed command of the multi-phase open-winding motor is 200rad / s and the torque command is 45kN·m in the initial stage, and it maintains a stable operating state before the command changes. At t=1s, the speed command suddenly increases from 200rad / s to 300rad / s, and the prime mover torque command gradually increases from 45kN to 50kN·m. Due to the increase in the speed of the prime mover, the torque of the prime mover will have a slight temporary drop at 1s.

[0072] It can be clearly observed that when the speed command shows an increasing trend, the active power absorbed by the full-power motor and its corresponding electromagnetic torque will experience an instantaneous increase, thereby causing the speed to increase rapidly. This phenomenon is attributed to the fact that the speed command adopts a step-like mutation form, which induces a significant peak effect of active power and electromagnetic torque. At the same time, due to the increase in the speed of the prime mover, the torque of the prime mover will have a slight temporary drop at 1s. Further, when the electromagnetic torque increases, the speed of the motor will be slightly lower than the speed command value at a certain stage. However, as the motor gradually enters steady-state operation, its speed will rise again to a level consistent with the command value.

[0073] Figure 6As shown, taking a 20MW pumped storage unit as an example, the unit of this embodiment adopts a six-phase permanent magnet synchronous motor, and 6 H bridges are cascaded per phase. When the operating power of the six-phase permanent magnet synchronous motor is less than 8MW, only the three-phase operation of the six-phase permanent magnet synchronous motor is required to meet the power demand of the unit. At this time, if the three-phase winding of the six-phase permanent magnet synchronous motor and its matching converter are disabled, the power loss caused by the switching devices of the six-phase permanent magnet synchronous motor can be effectively reduced. By detecting the active power of the unit, when P<8MW, the three-phase operation mode is adopted, and when P>8MW, the six-phase operation mode is adopted. The unit is flexible in adjustment and small in oscillation during non-full-phase operation and full-phase operation.

[0074] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A full-power pumped storage unit with a multi-level voltage architecture, characterized in that: include: Multi-winding transformers are used to convert high-voltage power from the grid into multiple independent low-voltage power outputs; The grid is connected to the primary side of a multi-winding transformer; A modular converter, used for rectifying and inverting low-voltage electric energy to generate multi-phase independent medium-voltage electric energy in a cascade form; the modular converter is connected to the secondary side of a multi-winding transformer; A multi-phase open-winding motor is used to receive multi-phase independent medium-voltage energy supply; the multi-phase open-winding motor is connected to the output end of the modular converter.

2. A full-power pumped storage unit with a multi-level voltage architecture according to claim 1, characterized in that: The primary side of the multi-winding transformer is a three-phase winding connected in a Y shape, and the secondary side is an independently distributed single-phase winding.

3. A full-power pumped storage unit with a multi-level voltage architecture according to claim 2, characterized in that: The modular converter is composed of multiple groups of independent cascaded single-phase converter groups.

4. A full-power pumped storage unit with a multi-level voltage architecture according to claim 3, characterized in that: The single-phase converter group is an H-bridge back-to-back converter.

5. A full-power pumped storage unit with a multi-level voltage architecture according to claim 3, characterized in that: The multi-phase open-winding motor is a distributed open-winding permanent magnet synchronous motor, and each phase of the open winding is correspondingly connected to a group of independent cascaded single-phase converter groups; the number of phases of the multi-phase open-winding motor is 3n, n≥1.

6. A full-power pumped storage unit with a multi-level voltage architecture according to claim 5, characterized in that: The number of phases of the multi-phase open-winding motor and the number of single-phase converters in the modular H-bridge back-to-back converter are both determined by the rated output voltage and output power of the multi-phase open-winding motor.

7. A control method, characterized in that: A method for controlling a full-power pumped storage unit with a multi-level voltage architecture according to any one of claims 1 to 6; the method comprising: Sampling an operation signal of a multi-phase open-winding motor, wherein the operation signal includes a current signal of each phase open winding and a rotation speed of the multi-phase open-winding motor; Performing coordinate transformation on the operation signal and mapping it into an orthogonal subspace; The current signal is decoupled and controlled in the orthogonal subspace, and the active power and reactive power of the multi-phase open-winding motor are adjusted separately based on the speed-limited strategy.

8. A control method according to claim 7, characterized in that: The coordinate transformation of the current signal is projected onto an orthogonal subspace, comprising: According to the transformation matrix T, the coordinate transformation of the current signal of the m-phase open-winding motor is performed to project the m-phase open-winding current signal of the motor into three orthogonal subspaces: the fundamental subspace α-β, the third harmonic subspace z1-z2, and the fifth harmonic subspace o1-o2: Where, l represents the harmonic order, l = 2[m / 2] ± 1, when m is an even number, it is "-", when m is an odd number, it is "+"; θ represents the phase difference between two adjacent phases, 9. A control method according to claim 8, characterized in that: After decoupling control is performed on the current signal in the orthogonal subspace, the output of the modular converter is controlled by a phase-shifted PWM modulation technique.

10. A control method, characterized in that: A method for controlling a full-power pumped storage unit with a multi-level voltage architecture according to any one of claims 1 to 6; the method comprising: Get the current operation mode of the full-power variable-frequency variable-speed pumped storage unit; If the current operating power is lower than a first preset power threshold, the open windings of some phases and their corresponding single-phase converters are disabled; if the current operating power is higher than a second preset power threshold, the open windings of all phases and their corresponding single-phase converters are used; wherein the first preset power threshold is less than the second preset power threshold; If the current operation mode belongs to the fault mode, the power of the full-power variable-frequency variable-speed pumped-storage unit is reduced, and the non-faulty open windings and non-faulty single-phase converters are dynamically adjusted to keep the motor running stably.

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