Full-power converter system for variable-speed pumped storage unit and control method

Abstract

The invention relates to the technical field of unit converters, in particular to a full-power converter system for a variable-speed pumped storage unit and a control method. The M3C circuit topological structure adopts a modular matrix type converter framework and comprises a plurality of sub-converter units; the operation control strategy module is integrated with a double-closed-loop decoupling control framework, comprises an outer-loop control unit and an inner-loop control unit, and coordinates regulation and control of current, voltage and power. Three sub-converters in star connection are adopted to form a nine-bridge-arm matrix structure, each bridge arm is formed by cascading H-bridge sub-modules and connecting the H-bridge sub-modules with inductors in series, and flexible interconnection of a primary-side three-phase system and a secondary-side three-phase system is achieved; a double-closed-loop decoupling framework is integrated in control, and power, direct-current capacitor voltage and alternating-current voltage amplitude are accurately regulated and controlled through combination of outer-loop fuzzy PI online setting and inner-loop model predictive control.

Description

Technical Field

[0001] This invention relates to the field of generator converter technology, and in particular to a full-power converter system and control method for variable speed pumped storage units. Background Technology

[0002] Existing domestically produced small-capacity variable-speed generator units mostly adopt a pole-changing dual-speed method, which has inherent defects such as low material utilization, severe magnetic field distortion, large harmonic losses, and poor voltage waveform. In the field of full-power converters, there are problems such as the control platform relying on imported chips and operating systems, insufficient robustness of key control strategies (such as circulating current suppression and capacitor voltage balancing), large steady-state errors under complex operating conditions, and long system integration verification cycles. As a result, the units have poor operational stability in grid peak shaving, frequency regulation, reactive power support, and fault ride-through scenarios, making it difficult to meet the independent and controllable requirements of large-scale seawater pumped storage power stations.

[0003] Therefore, there is a need for a full-power converter system and control method for variable-speed pumped storage units that improves system tracking accuracy and disturbance rejection capability through dual closed-loop decoupling and model predictive control, effectively reduces steady-state error and harmonic loss through circulating current suppression and voltage balancing strategies, supports flexible submodule cascading, has high power density and small footprint, facilitates engineering modification and capacity expansion, and whose control strategy has four-quadrant operation and arbitrary amplitude and frequency output capability, significantly enhancing grid support, fault ride-through and new energy grid connection regulation performance to meet the needs of the current environment. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is: severe cavitation and material deterioration, significant decrease in material strength and hardness, rubber seals on the guide vane end face, frequent erosion and loss by water flow, resulting in displacement of the double arm spacing, stiffness of the water guide mechanism, excessive leakage of the main shaft seal, frequent start of the top cover drainage pump, and overall leakage of the guide vane.

[0005] The above-mentioned technical problems are solved by the following technical solution: This invention proposes a full-power converter system for variable-speed pumped storage units, which includes, M3C circuit topology and operation control strategy module, The M3C circuit topology adopts a modular matrix converter framework, which includes several sub-converter units; The operation control strategy module integrates a dual closed-loop decoupled control framework, which includes an outer loop control unit and an inner loop control unit to coordinate the regulation of current, voltage and power.

[0006] In a preferred embodiment of the full-power converter system for a variable-speed pumped storage unit described in this invention: The dual-closed-loop decoupled control framework of the operation control strategy module adopts a PI-based control strategy; The inner loop control is designed based on the dq component of the bridge arm voltage.

[0007] In a preferred embodiment of the full-power converter system for a variable-speed pumped storage unit described in this invention: The outer loop control unit adjusts the constant active power, constant reactive power, constant DC capacitor voltage, and constant AC voltage amplitude, and the parameters are tuned online through the fuzzy PI controller to adapt to dynamic changes; The inner loop control unit directly regulates the input and output currents and circulating current.

[0008] In a preferred embodiment of the full-power converter system for a variable-speed pumped storage unit described in this invention: The sub-converter units in the M3C circuit topology are designed in a star connection form, with each sub-converter unit independently handling a set of bridge arm branches. Each bridge arm branch is cascaded with multiple H-bridge sub-modules and connected in series with an inductor to achieve interconnection of the primary side three-phase u, v, w and the secondary side three-phase a, b, c.

[0009] In a preferred embodiment of the full-power converter system for a variable-speed pumped storage unit described in this invention: The input-side PI inner-loop control framework of the operation control strategy module includes a current measurement comparator, a PI controller, and a feedforward superposition unit; The error between the measured current value and the outer loop reference value is calculated, and after PI regulation, it is combined with the feedforward term to generate a reference voltage. The frame is embedded in the dq component expression for precise control of the bridge arm voltage.

[0010] In a preferred embodiment of the full-power converter system for a variable-speed pumped storage unit described in this invention: The operation control strategy module is connected to the circulating control unit, which adjusts the bridge arm circulating current to minimize steady-state error; The circulating control unit incorporates a dual closed-loop decoupling control framework to suppress internal circulating current and improve overall decoupling efficiency.

[0011] A control method comprising the aforementioned full-power converter system for a variable-speed pumped storage unit, and, The control is performed using a dual-closed-loop decoupling control framework, including the following steps: By adjusting parameters online using a fuzzy PI controller, constant active power, constant reactive power, constant DC capacitor voltage, and constant AC voltage amplitude can be achieved, and an inner loop reference value can be generated. In the inner loop control, a PI control strategy is used to handle current decoupling based on the expression of the dq component of the bridge arm voltage. In the circulation control stage, a proportional control mechanism is used to regulate the bridge arm circulation; In the capacitor voltage equalization control stage, the capacitor voltage of the submodule is dynamically equalized using the reference value expression of the input frequency circulating current component.

[0012] In a preferred embodiment of the control method described in this invention: The outer loop control loop is further divided into outer loop input side and outer loop output side sub-processes. The outer loop input side subprocess adopts a constant active power and constant AC voltage amplitude control method; The outer loop output subprocess adopts a constant DC capacitor voltage and constant reactive power control method. By combining online tuning of fuzzy controller parameters with inner loop model prediction, the power factor and voltage amplitude are optimized and controlled, and a stable reference current value is provided for the inner loop control.

[0013] In a preferred embodiment of the control method described in this invention: The inner loop control loop is further divided into inner loop input side and inner loop output side sub-processes. The inner loop input side subprocess compares the current measurement value with the outer loop reference value, generates a reference voltage through PI regulation and feedforward superposition, and embeds it into the dq component expression to achieve precise control of the bridge arm voltage; The inner loop output side subprocess adopts process coordination to ensure rapid current response and decoupling, and reduce the impact of cross-coupling.

[0014] The beneficial effects of this invention are as follows: It employs three star-connected sub-converters to form a nine-arm matrix structure, with each arm consisting of cascaded H-bridge sub-modules and series-connected inductors, achieving flexible interconnection between the primary and secondary three-phase systems; it integrates a dual-closed-loop decoupling framework for control, combining online tuning of the outer-loop fuzzy PI control with inner-loop model predictive control to precisely regulate active / reactive power, DC capacitor voltage, and AC voltage amplitude; the input / output side uses PI + feedforward inner-loop control, with proportional control introduced in the circulating current stage to suppress steady-state error, and capacitor voltage balancing dynamically adjusted using the reference value of the circulating current component at the input frequency. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0016] Figure 1 The circuit architecture diagram of the M3C circuit topology of the present invention is shown.

[0017] Figure 2 The circuit architecture diagram of the operation control strategy module of the present invention is shown.

[0018] Figure 3 This is a schematic diagram of the inner loop control unit in this invention.

[0019] Figure 4 This is a flowchart of the corresponding control method of the system in this invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0021] The terminology used in this invention refers to those general terms currently widely used in the art in consideration of the functionality of the invention; however, these terms may vary according to the intent of those skilled in the art, precedent, or new techniques. Furthermore, specific terms may be chosen independently, and in such cases, their detailed meanings will be described in the detailed description of the invention. Therefore, the terminology used in this specification should not be construed as simple names, but rather based on the meaning of the terms and the overall description of the invention.

[0022] Reference Figures 1-2 This embodiment provides a full-power converter system for variable-speed pumped storage units.

[0023] The M3C circuit topology 1 adopts a modular matrix converter framework, consisting of three star-connected sub-converter units 11. Each sub-converter unit 11 includes three bridge arm branches, forming a total of nine bridge arm branches with the same structure. Each bridge arm branch is connected in series with multiple H-bridge sub-modules and in series with an inductor to realize the interconnection of the primary side three phases u, v, w and the secondary side three phases a, b, c.

[0024] The entire framework supports bidirectional power flow, four-quadrant operation, and adaptation to any voltage level. The three phases on the primary and secondary sides are interconnected via bridge arm branches. Each sub-converter unit 11 independently handles a set of bridge arm branches, supporting flexible adjustment of the number of cascaded submodules to optimize power density and minimize footprint in medium-voltage, high-power applications. The bridge arm branches utilize fully controlled IGBT power devices, allowing for selective adjustment of the number of H-bridge submodules to adapt to different voltage levels and achieve bidirectional power conversion.

[0025] The operation control strategy module 2 integrates a dual closed-loop decoupled control framework, including an outer loop control unit 21 and an inner loop control unit 22, which is used to coordinate the regulation of current, voltage and power through decoupling, thereby improving the stability, tracking performance and robustness of the system under complex operating conditions.

[0026] The outer loop control unit 21 is responsible for regulating the constant active power, constant reactive power, constant DC capacitor voltage, and constant AC voltage amplitude. It uses a fuzzy PI controller to tune parameters online to adapt to dynamic changes and provides a reference current value to the inner loop control unit 22. The inner loop control unit 22 handles the direct regulation of the input and output currents. It adopts a PI control strategy based on the expression of the bridge arm voltage dq component. The input side compares the current measurement value with the outer loop reference value, and after PI regulation, it combines with the feedforward term to generate a reference voltage. It works in conjunction with a similar structure on the output side to achieve current decoupling and stable tracking.

[0027] The dual-loop decoupled control framework can use model predictive control to discretize the continuous-time model and add feedback correction to enhance tracking accuracy and robustness. Furthermore, it integrates a repetitive control parameter self-correction unit embedded in the bridge arm branch to achieve zero steady-state error tracking of the output to the command signal, enhances harmonic current suppression capability, and supports output adjustment of arbitrary amplitude and frequency.

[0028] As one embodiment provided, such as Figures 1-3 , The dual-loop decoupling control framework of the operation control strategy module 2 adopts a PI-based control strategy, where the inner loop control is designed based on the dq component of the bridge arm voltage. Based on the control principle of a voltage source converter, the bridge arm voltage is decomposed into d-axis and q-axis components, and independent decoupling control of the current is achieved through a mathematical model in the dq coordinate system. This method allows the system to process active and reactive components separately on the input and output sides, avoiding cross-coupling interference. It also supports harmonic suppression, reducing system losses by filtering out higher-order harmonic components and achieving dynamic adjustment of the power factor.

[0029] The cascaded inner and outer loops of the dual closed-loop decoupled control framework ensure that the inner loop focuses on fast current tracking, while the outer loop maintains overall power balance, thereby maintaining stable system operation under conditions of frequency fluctuations or amplitude changes, such as quickly responding to load demands during grid peak shaving.

[0030] The outer loop control unit 21 is responsible for adjusting the constant active power, constant reactive power, constant DC capacitor voltage, and constant AC voltage amplitude. The parameters are tuned online via a fuzzy PI controller to adapt to dynamic changes. The outer loop control unit 21 first acquires the system's real-time power and voltage signals and compares them with set reference values. Then, the fuzzy PI controller automatically adjusts the proportional and integral parameters based on the error magnitude and rate of change, achieving adaptive parameter optimization. This involves increasing the proportional gain to accelerate response during sudden load changes or enhancing the integral action to eliminate residuals during steady-state operation.

[0031] The outer loop control unit 21 provides the inner loop control unit 22 with a precise reference current value, ensuring coordination between the inner and outer loops. Simultaneously, the inner loop control unit 22 directly regulates the input and output currents and circulating current. It discretizes the continuous-time model of the M3C using model predictive control, derives a predictive model for the arm current, and introduces a feedback correction term to compensate for model errors. This enhances tracking accuracy and robustness under load disturbances or grid faults, such as maintaining current continuity in fault ride-through scenarios.

[0032] The sub-converter units 11 of the M3C circuit topology 1 are designed in a star connection configuration, where each sub-converter unit 11 independently handles a set of bridge arm branches. The star connection connects the three sub-converter units 11 into a matrix frame. The three phases u, v, w on the primary side and the three phases a, b, c on the secondary side are interconnected through bridge arm branches. Each bridge arm branch is cascaded with multiple H-bridge submodules and connected in series with an inductor to suppress current surges.

[0033] The overall design allows for flexible adjustment of the number of cascaded H-bridge submodules according to application requirements. For example, in medium-voltage, high-power scenarios, the number of modules can be increased to improve voltage level adaptability, while optimizing power density and minimizing footprint. Through integration with a dual-closed-loop decoupled control framework, sub-converter unit 11 can achieve unified control of the bridge arm branches, supporting bidirectional power flow and four-quadrant operation, such as seamless switching between power generation and pumping modes in pumped storage units.

[0034] The input-side PI inner-loop control framework of the operation control strategy module 2 includes a current measurement comparator, a PI controller, and a feedforward superposition unit. First, the current measurement comparator acquires the input-side current signal and calculates the error with the reference value provided by the outer-loop control unit 21. Then, the PI controller adjusts this error signal, and the compensation term introduced by the feedforward superposition unit generates a reference voltage output. This framework is embedded in the dq component expression for precise control of the bridge arm voltage and works in conjunction with a similar structure on the output side to achieve overall current decoupling and stable tracking.

[0035] When handling grid-side current on the input side, the framework can respond quickly to voltage fluctuations, ensuring decoupled control reduces cross-effects. As a core component of the dual-closed-loop decoupled control framework, the input-side framework ensures shortened current response time and reduced system oscillations under complex operating conditions.

[0036] The operation control strategy module 2 is connected to the circulating control unit 23, which adjusts the bridge arm circulating current to minimize steady-state error. The circulating control unit 23 adopts a proportional control mechanism, which directly acts on the bridge arm circulating current path, avoiding the error amplification caused by integral accumulation in the circulating current stage of traditional PI control.

[0037] The circulating current control unit 23 is also integrated with the capacitor voltage equalization control framework. It calculates and applies an equalization signal using the reference value expression of the circulating current component at the input frequency to dynamically adjust the capacitor voltage of the submodule, ensuring voltage balance is maintained when the load changes. The circulating current control unit 23 is embedded in the dual closed-loop decoupling control framework to suppress internal circulating current and improve overall decoupling efficiency. In multi-bridge arm parallel operation, it reduces uneven energy distribution and improves system reliability.

[0038] The operation control strategy module 2 is based on PI dual closed-loop decoupling optimization, dynamic regulation mechanism of inner and outer loop units, star connection design of M3C sub-converter unit 11, and precise integration of input-side PI framework and circulating current control unit 23, to achieve fine coordination of current, circulating current and voltage.

[0039] As one embodiment provided, such as Figures 1-4 , The entire control method adopts a dual closed-loop decoupled control framework for regulation. First, the input and output current and voltage signals are collected as the basic data for subsequent regulation. Then, in the outer loop control link, the parameters are tuned online through a fuzzy PI controller to achieve regulation of constant active power, constant reactive power, constant DC capacitor voltage and constant AC voltage amplitude, and generate inner loop reference values.

[0040] The entire process compares the acquired signal with a preset reference value and uses fuzzy logic to dynamically adjust the PI parameters based on the error and rate of change, ensuring power balance under dynamic changes and outputting a stable inner-loop reference current value. In the inner-loop control stage, a PI control strategy is used to handle current decoupling based on the dq component expression of the bridge arm voltage. The bridge arm voltage is decomposed in the dq coordinate system, enabling independent control of the input and output currents and avoiding cross-coupling. In the circulating current control stage, a proportional control mechanism is used to adjust the bridge arm circulating current. Direct proportional adjustment intervenes in the circulating current path to minimize steady-state error and suppress internal energy unevenness. In the capacitor voltage equalization control stage, the capacitor voltage of the submodules is dynamically equalized using the reference value expression of the circulating current component at the input frequency. This expression calculates the circulating current compensation signal based on the system frequency and applies it to each submodule to achieve uniform voltage distribution. Through these steps, current, voltage, power, and circulating current are coordinated to achieve stable system operation under complex conditions, four-quadrant power conversion, and harmonic suppression.

[0041] The outer loop control is further divided into outer loop input side and outer loop output side sub-processes. The outer loop input side sub-process adopts a constant active power and constant AC voltage amplitude control method, focusing on active power transmission and voltage amplitude stability on the input side. It captures dynamic changes on the input side through online tuning of fuzzy controller parameters. The outer loop output side sub-process adopts a constant DC capacitor voltage and constant reactive power control method, which focuses on capacitor voltage maintenance and reactive power compensation on the output side. It achieves optimized regulation of power factor and voltage amplitude through a combination of online tuning of fuzzy controller parameters and prediction of inner loop model.

[0042] The entire integration process involves generating initial reference values ​​in the outer loop, which are then fed into the inner loop model prediction stage. The continuous-time model is discretized and feedback correction is added to compensate for prediction deviations. This process also provides a stable reference current value for the inner loop control stage, ensuring the overall balance of the decoupled control.

[0043] The inner loop control loop is further divided into inner loop input side and inner loop output side sub-processes. The inner loop input side sub-process compares the current measurement value with the outer loop reference value, generates a reference voltage through PI regulation and feedforward superposition, and embeds it into the dq component expression to achieve precise control of the bridge arm voltage. The entire sub-process processes the error signal through PI regulation, introduces compensation through feedforward superposition to accelerate the response, and uses dq transformation to simplify the control calculation. The inner loop output-side subprocess uses a similar process to work together, which ensures fast current response and decoupling, reduces the impact of cross-coupling on the output-side subprocess mirroring the input-side mechanism, and coordinates the processing of the output current signal to achieve unified decoupling of the inner and outer currents.

[0044] Finally, it should be noted that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways as long as they do not depart from the scope of the present invention.

Claims

1. A full-power converter system for a variable-speed pumped storage unit, characterized in that: include, M3C circuit topology (1) and operation control strategy module (2). The M3C circuit topology (1) adopts a modular matrix converter framework, including several sub-converter units (11). The operation control strategy module (2) integrates a dual closed-loop decoupled control framework, including an outer loop control unit (21) and an inner loop control unit (22), which coordinates the regulation of current, voltage and power.

2. The full-power converter system for a variable-speed pumped storage unit according to claim 1, characterized in that: The dual closed-loop decoupling control framework of the operation control strategy module (2) adopts a PI-based control strategy; The inner loop control is designed based on the dq component of the bridge arm voltage.

3. The full-power converter system for variable-speed pumped storage units according to claim 1, characterized in that: The outer loop control unit (21) adjusts the constant active power, constant reactive power, constant DC capacitor voltage and constant AC voltage amplitude, and adjusts the parameters online through the fuzzy PI controller to adapt to dynamic changes; The inner loop control unit (22) directly regulates the input and output currents and circulating current.

4. The full-power converter system for variable-speed pumped storage units according to claim 1, characterized in that: The sub-converter unit (11) of the M3C circuit topology (1) is designed in a star connection form, and the sub-converter unit (11) independently handles a group of bridge arm branches. Each bridge arm branch is cascaded with multiple H-bridge sub-modules and connected in series with an inductor to achieve interconnection of the primary side three-phase u, v, w and the secondary side three-phase a, b, c.

5. The full-power converter system for variable-speed pumped storage units according to any one of claims 1 to 4, characterized in that: The input-side PI inner loop control framework of the operation control strategy module (2) includes a current measurement comparator, a PI controller, and a feedforward superposition unit; The error between the measured current value and the outer loop reference value is calculated, and after PI regulation, it is combined with the feedforward term to generate a reference voltage. The frame is embedded in the dq component expression for precise control of the bridge arm voltage.

6. The full-power converter system for a variable-speed pumped storage unit according to claim 5, characterized in that: The operation control strategy module (2) is connected to the circulation control unit (23), which adjusts the bridge arm circulation to minimize steady-state error; The circulating control unit (23) is embedded in a dual closed-loop decoupling control framework to suppress internal circulating flow and improve overall decoupling efficiency.

7. A control method, characterized in that, Including the full-power converter system for variable-speed pumped storage units as described in claim 6, and, The control is performed using a dual-closed-loop decoupling control framework, including the following steps: By adjusting parameters online using a fuzzy PI controller, constant active power, constant reactive power, constant DC capacitor voltage, and constant AC voltage amplitude can be achieved, and an inner loop reference value can be generated. In the inner loop control, a PI control strategy is used to handle current decoupling based on the expression of the dq component of the bridge arm voltage. In the circulation control stage, a proportional control mechanism is used to regulate the bridge arm circulation; In the capacitor voltage equalization control stage, the capacitor voltage of the submodule is dynamically equalized using the reference value expression of the input frequency circulating current component.

8. The control method according to claim 7, characterized in that: The outer loop control loop is further divided into outer loop input side and outer loop output side sub-processes. The outer loop input side subprocess adopts a constant active power and constant AC voltage amplitude control method; The outer loop output subprocess adopts a constant DC capacitor voltage and constant reactive power control method. By combining online tuning of fuzzy controller parameters with inner loop model prediction, the power factor and voltage amplitude are optimized and controlled, and a stable reference current value is provided for the inner loop control.

9. The control method according to claim 8, characterized in that: The inner loop control loop is further divided into inner loop input side and inner loop output side sub-processes. The inner loop input side subprocess compares the current measurement value with the outer loop reference value, generates a reference voltage through PI regulation and feedforward superposition, and embeds it into the dq component expression to achieve precise control of the bridge arm voltage; The inner loop output side subprocess adopts process coordination to ensure rapid current response and decoupling, and reduce the impact of cross-coupling.

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