A control method for isolated network operation of a permanent magnet hydraulic power generation system

Abstract

The application provides a kind of permanent magnet hydraulic power generation system isolated network operation control method. The output power is adjusted by grid-side converter according to the current voltage value and the current frequency value of isolated network and target voltage value and target frequency value, so that the adjusted voltage value and the adjusted frequency value are target voltage value and target frequency value respectively. The electromagnetic torque of permanent magnet generator is adjusted by machine-side converter according to the current bus voltage value and target bus voltage value of DC bus, so that the adjusted bus voltage value is target bus voltage value. The guide vane opening of water turbine is adjusted by speed regulator according to the current speed value and optimal speed value of water turbine, so that the adjusted speed value is optimal speed value. By using the scheme of the application, in the isolated network operation state, the water turbine can maintain optimal speed operation according to the current water head while maintaining the rated voltage and rated frequency of isolated network, so as to balance the power supply stability and power generation efficiency of the system.

Description

Technical Field

[0001] This invention relates to the field of hydropower technology, and in particular to a method for controlling the isolated operation of a permanent magnet hydropower system. Background Technology

[0002] A permanent magnet hydropower system typically consists of a turbine, a permanent magnet synchronous generator, a full-power converter, and local loads. This system combines the stability of hydropower with the high efficiency of a permanent magnet motor, making it particularly suitable for remote areas, islands, or emergency power supply scenarios. The system features intelligent switching between grid-connected and islanded modes; when the main power grid fails, it can quickly switch to islanded operation mode to provide stable power to local loads.

[0003] In existing technologies, permanent magnet hydropower systems operating in isolated grids typically rely on the turbine governor to directly regulate the grid voltage and frequency. The full-power converter only performs power rectification and inversion, without actively regulating the grid voltage and frequency. This control method, where the governor regulates the grid voltage and frequency independently, suffers from slow response, low regulation accuracy, and underutilization of the full-power converter's capacity, resulting in weak system resilience to load disturbances. Another control method involves the full-power converter regulating the grid voltage and frequency independently, with the turbine operating at a fixed speed. Since the turbine cannot operate at its optimal speed based on the current head, this leads to low power generation efficiency and insufficient hydropower utilization. Furthermore, existing solutions often employ grid-connected power control architectures, where the grid-side converter lacks independent grid-connection capabilities and fails to consider multi-level dynamic coordination timing under load disturbances, thus failing to balance isolated grid power supply stability and transient immunity.

[0004] Therefore, how to provide a solution to the above-mentioned technical problems is a technical problem that needs to be solved by those in the relevant technical field. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a method for controlling the isolated operation of a permanent magnet hydropower system. In the isolated operation state, the method can maintain the rated voltage and rated frequency of the isolated grid while keeping the turbine running at the optimal speed at the current head, thereby taking into account both the power supply stability and power generation efficiency of the system.

[0006] This invention provides a method for controlling the isolated operation of a permanent magnet hydropower system. The method is applied to a permanent magnet hydropower system comprising a governor, a turbine, a permanent magnet generator, and a full-power converter. The governor is connected to the turbine, the input of the permanent magnet generator is connected to the turbine, and the output of the permanent magnet generator is connected to the isolated grid load through the turbine-side converter and the grid-side converter of the full-power converter. The control method includes: The grid-side converter obtains the current voltage and frequency values ​​of the islanded grid, and adjusts the output power according to the current voltage and frequency values, as well as the target voltage and frequency values ​​of the islanded grid, so that the adjusted voltage and frequency values ​​are respectively the target voltage and target frequency values; The generator-side converter obtains the current bus voltage value of the DC bus and adjusts the electromagnetic torque of the permanent magnet generator according to the current bus voltage value and the target bus voltage value of the DC bus, so that the adjusted bus voltage value is the target bus voltage value. The governor obtains the current head and speed of the turbine, determines the optimal speed based on the current head, and adjusts the guide vane opening based on the current speed and the optimal speed to make the adjusted speed the optimal speed.

[0007] Preferably, the grid-side converter adjusts its output power based on the current voltage and frequency values, as well as the target voltage and frequency values ​​of the isolated grid, including: The grid-side converter performs closed-loop adjustment of the output active and reactive power based on the current voltage and frequency values, as well as the target voltage and frequency values ​​of the isolated grid.

[0008] Preferably, the grid-side converter performs closed-loop adjustment of the output active and reactive power according to the following formula:

[0009]

[0010]

[0011] in, Representative grid-side converter d Shaft current setpoint, and These represent the proportional gain and integral gain of the outer frequency loop of the grid-side converter, respectively. The target angular velocity value represents the isolated network. This represents the current angular velocity value of the isolated network. Represents time, Representative grid-side converter q Shaft current setpoint, and These represent the proportional gain and integral gain of the outer voltage loop of the grid-side converter, respectively. This represents the target voltage value for the isolated grid. This represents the current voltage value of the isolated grid. Representative grid-side converter d The target voltage value of the shaft, and They represent grid-side converters respectively. d The proportional gain and integral gain of the shaft current loop, Representative grid-side converter d The current value of the shaft. Representative grid-side converter filter inductor q The equivalent inductance of the shaft, Representative grid-side converter q The current value of the shaft. The decomposed value of the current voltage of the isolated network d Shaft voltage feedforward decoupling. Representative grid-side converter q The target voltage value of the shaft, and These respectively represent the grid-side converters q The proportional gain and integral gain of the shaft current loop, Representative grid-side converter filter inductor d The equivalent inductance of the shaft, The decomposed value of the current voltage of the isolated network q Shaft voltage feedforward decoupling.

[0012] Preferably, after the grid-side converter adjusts its output power according to the current voltage and frequency values, as well as the target voltage and frequency values ​​of the isolated grid, the input power and output power of the DC bus are balanced through the charging and discharging of the DC bus capacitor and the rotational kinetic energy changes of the permanent magnet hydroelectric power generation system.

[0013] Preferably, the DC bus is charged and discharged according to the following formula:

[0014] in, This represents the total capacitance of the DC bus. The rate of change of the bus voltage at the DC bus. Representative machine-side converter d The switching function of the axis. Represents permanent magnet generator d The current value of the shaft. Representative machine-side converter q The switching function of the axis. Represents permanent magnet generator q The current value of the shaft. This represents the equivalent DC load current drawn by the grid-side converter from the DC bus.

[0015] Preferably, the expression for the rotational kinetic energy of the permanent magnet hydroelectric power generation system is:

[0016] in, Represents the rotational kinetic energy of a permanent magnet hydroelectric power generation system. This represents the total moment of inertia of the water turbine and the permanent magnet generator. This represents the electric angular velocity of the permanent magnet generator rotor.

[0017] Preferably, the generator-side converter adjusts the electromagnetic torque of the permanent magnet generator based on the current bus voltage value and the target bus voltage value of the DC bus, including: The generator-side converter is equipped with a DC bus voltage outer loop. The difference between the target DC bus voltage value and the current bus voltage value is calculated by the PID controller to generate an electromagnetic torque command. The electromagnetic torque of the permanent magnet generator is adjusted according to the electromagnetic torque command. Specifically, the electromagnetic torque is reduced when the difference is less than zero, and the electromagnetic torque is increased when the difference is greater than zero.

[0018] Preferably, the governor determines the optimal speed of the turbine based on the current head, including: The governor calculates the optimal turbine speed corresponding to the current head by interpolation based on the current head and the turbine's operating characteristic curve.

[0019] Preferably, the governor adjusts the guide vane opening of the turbine according to the current speed value and the optimal speed value, including: The governor performs PID calculations based on the difference between the current speed value and the optimal speed value to obtain the guide vane opening adjustment command, and adjusts the guide vane opening of the turbine according to the guide vane opening adjustment command.

[0020] Preferably, the permanent magnet hydropower generation system also includes a head detection unit, which is used to detect the current head of the turbine.

[0021] The present invention has at least the following beneficial effects: (1) High power supply stability: The grid-side converter adopts a voltage and frequency dual closed-loop independent grid structure, which can respond to load disturbances in milliseconds. The voltage and frequency of the isolated grid are maintained at the rated value, resulting in high power supply quality. (2) High power generation efficiency: The governor tracks the optimal speed according to the real-time head, and the turbine always runs in the highest efficiency zone, resulting in high water energy utilization. (3) Strong anti-disturbance capability: During the transient process of load disturbance, the power difference is buffered by the DC bus capacitor and the unit rotational kinetic energy, and with the hierarchical coordinated timing response, there is no oscillation and no power impact; (4) Smooth and reliable start-up: The graded start-up strategy is adopted, gradually transitioning from the pressure build-up speed to the optimal speed, and the start-up process is smooth and shock-free. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A schematic diagram of a permanent magnet hydroelectric power generation system provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating a method for controlling the isolated operation of a permanent magnet hydropower system, as provided in an embodiment of the present invention. Detailed Implementation

[0024] The core of this invention is to provide a method for controlling the isolated operation of a permanent magnet hydropower system. In the isolated operation state, it can maintain the rated voltage and rated frequency of the isolated grid while keeping the turbine running at the optimal speed at the current head, thereby taking into account both the power supply stability and power generation efficiency of the system.

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that the structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which this application can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size should still fall within the scope of the technical content disclosed in this application, provided that they do not affect the effects and purposes that this application can produce.

[0027] This invention provides a method for controlling the isolated operation of a permanent magnet hydropower system. To more clearly illustrate this solution, the permanent magnet hydropower system in this invention will first be described.

[0028] Please see Figure 1 , Figure 1This is a schematic diagram of a permanent magnet hydroelectric power generation system provided in an embodiment of the present invention. The system includes a governor 110, a turbine 120, a permanent magnet generator 130, and a full-power converter. The full-power converter includes a machine-side converter 140, a grid-side converter 150, and a DC bus 160 located between the machine-side converter 140 and the grid-side converter 150. The governor 110 is connected to the turbine 120. The input terminal of the permanent magnet generator 130 is connected to the turbine 120, and the output terminal of the permanent magnet generator 130 is connected to the isolated grid load through the machine-side converter 140 and the grid-side converter 150 of the full-power converter. In a specific implementation, the permanent magnet generator 130 is a permanent magnet synchronous generator, and a circuit breaker 170 can also be installed between the grid-side converter 150 and the isolated grid load.

[0029] Optionally, in the above embodiments, the permanent magnet hydroelectric power generation system further includes a head detection unit, which is used to detect the current head of the turbine 120. The head refers to the height difference between the inlet and outlet water flow of the turbine, and is a key parameter determining the turbine's output and optimal speed.

[0030] Based on this, embodiments of the present invention also provide a method for controlling the isolated operation of a permanent magnet hydropower system. Please refer to [link / reference]. Figure 2 , Figure 2 This is a flowchart illustrating the islanded operation control method for a permanent magnet hydropower system provided in this embodiment of the invention. As described above, the permanent magnet hydropower system includes a governor, a turbine, a permanent magnet generator, and a full-power converter. The governor is connected to the turbine, the input terminal of the permanent magnet generator is connected to the turbine, and the output terminal of the permanent magnet generator is connected to the islanded load through the turbine-side converter and the grid-side converter of the full-power converter. The control method may include the following steps: Step S210: The grid-side converter obtains the current voltage and frequency values ​​of the isolated grid, and adjusts the output power according to the current voltage and frequency values, as well as the target voltage and frequency values ​​of the isolated grid, so that the adjusted voltage and frequency values ​​are the target voltage and target frequency values, respectively.

[0031] It should be noted that islanded operation refers to the operating mode of a permanent magnet hydropower system disconnected from the public power grid and independently supplying power to local loads. In this embodiment of the invention, target voltage and frequency values ​​for the islanded grid are preset, and the grid-side converter adjusts the voltage and frequency values ​​of the islanded grid based on these target values. Specifically, the grid-side converter acquires the current voltage and frequency values ​​of the islanded grid in real time. When the islanded grid load changes, the current voltage and frequency values ​​will deviate from the target voltage and frequency values. The grid-side converter automatically adjusts its output power to quickly bring the voltage and frequency values ​​of the islanded grid back to the target values. It can be understood that controlling the voltage and frequency of the islanded grid by the grid-side converter offers fast response, high adjustment accuracy, and prevents significant deviations in voltage and frequency from rated values ​​when the islanded grid load fluctuates, resulting in higher power supply stability.

[0032] Optionally, in the above embodiments, the grid-side converter in step S210 adjusts its output power based on the current voltage and frequency values, as well as the target voltage and frequency values ​​of the islanded grid, including: The grid-side converter performs closed-loop adjustment of the output active and reactive power based on the current voltage and frequency values, as well as the target voltage and frequency values ​​of the isolated grid.

[0033] Specifically, the grid-side converter performs closed-loop adjustment of the output active and reactive power according to the following formula: Grid-side converter frequency outer loop (output active current given):

[0034] Grid-side converter voltage outer loop (output reactive current given):

[0035] Grid-side converter dq Shaft current inner loop (including voltage feedforward decoupling):

[0036] in, Representative grid-side converter d Shaft current setpoint, and These represent the proportional gain and integral gain of the outer frequency loop of the grid-side converter, respectively. The target angular velocity value represents the isolated network. This represents the current angular velocity value of the isolated network. Represents time, Representative grid-side converter q Shaft current setpoint, and These represent the proportional gain and integral gain of the outer voltage loop of the grid-side converter, respectively. This represents the target voltage value for the isolated grid. This represents the current voltage value of the isolated grid. Representative grid-side converter d The target voltage value of the shaft, and They represent grid-side converters respectively. d The proportional gain and integral gain of the shaft current loop, Representative grid-side converter d The current value of the shaft. Representative grid-side converter filter inductor q The equivalent inductance of the shaft, Representative grid-side converter q The current value of the shaft. The decomposed value of the current voltage of the isolated network d Shaft voltage feedforward decoupling. Representative grid-side converter q The target voltage value of the shaft, and They represent grid-side converters respectively. q The proportional gain and integral gain of the shaft current loop, Representative grid-side converter filter inductor d The equivalent inductance of the shaft, The decomposed value of the current voltage of the isolated network q Shaft voltage feedforward decoupling.

[0037] In this embodiment of the invention, the grid-side converter acquires the current voltage, angular velocity (proportional to frequency), and current of the isolated grid in real time. When the load of the isolated grid changes, the current voltage and frequency values ​​of the isolated grid will deviate from the target voltage and frequency values. The grid-side converter automatically performs closed-loop adjustment of the output active and reactive power to quickly pull the voltage and frequency values ​​of the isolated grid back to the target voltage and frequency values.

[0038] For example, when the islanded grid load increases, the DC current on the grid side increases, and the current voltage value of the islanded grid... and angular velocity value When the voltage decreases, the grid-side converter automatically performs closed-loop adjustment of the output active and reactive power, and the outer loop output active and reactive current setpoints are reduced. , Increase the power output of the grid-side converter to improve the voltage value of the isolated grid. and angular velocity value The voltage and frequency values ​​are rapidly increased to the target values. It's understandable that when the islanded load decreases, the signs of the increases and decreases of each variable are reversed, ensuring symmetrical adjustment logic.

[0039] Step S220: The generator-side converter obtains the current bus voltage value of the DC bus and adjusts the electromagnetic torque of the permanent magnet generator according to the current bus voltage value and the target bus voltage value of the DC bus, so that the adjusted bus voltage value is the target bus voltage value.

[0040] Optionally, in the above embodiments, the generator-side converter in step S220 adjusts the electromagnetic torque of the permanent magnet generator according to the current bus voltage value and the target bus voltage value of the DC bus, including: The generator-side converter is equipped with a DC bus voltage outer loop. The difference between the target DC bus voltage value and the current bus voltage value is calculated by the PID controller to generate an electromagnetic torque command. The electromagnetic torque of the permanent magnet generator is adjusted according to the electromagnetic torque command. Specifically, the electromagnetic torque is reduced when the difference is less than zero, and the electromagnetic torque is increased when the difference is greater than zero.

[0041] It should be noted that when the grid-side converter adjusts its output power, the input power of the generator-side converter has not yet changed synchronously, resulting in an imbalance between the input and output power of the DC bus, which can cause fluctuations in the DC bus voltage. In this embodiment of the invention, the generator-side converter aims to maintain a constant DC bus voltage. A target DC bus voltage value is preset, and the current DC bus voltage value is obtained in real time through a DC bus voltage control loop. The difference between this current DC bus voltage value and the target DC bus voltage value is calculated. After PID calculation, the voltage deviation signal outputs an electromagnetic torque adjustment command. The electromagnetic torque of the permanent magnet generator is adjusted according to the electromagnetic torque adjustment command to bring the DC bus voltage back to the target DC bus voltage value.

[0042] For example, when the islanded grid load increases, the grid-side converter automatically increases its power output, rapidly raising the voltage and frequency values ​​of the islanded grid to the target values. At this time, the DC bus voltage drops. The generator-side converter then increases the electromagnetic torque of the permanent magnet generator, increasing the generator-side input power to balance the input and output power of the DC bus, causing the DC bus voltage to return to the target value. It can be understood that when the islanded grid load decreases, the signs of the increases and decreases of the variables are reversed, resulting in symmetrical adjustment logic.

[0043] Optionally, in the above embodiments, after the grid-side converter adjusts the output power according to the current voltage value, the current frequency value, and the target voltage value and target frequency value of the isolated grid, the input power and output power of the DC bus are balanced through the charging and discharging of the DC bus capacitor and the rotational kinetic energy change of the permanent magnet hydropower generation system.

[0044] Specifically, the DC bus capacitor is charged and discharged according to the following formula:

[0045] in, This represents the total capacitance of the DC bus. The rate of change of the bus voltage at the DC bus. Representative machine-side converter d The switching function of the axis. Represents permanent magnet generator d The current value of the shaft. Representative machine-side converter q The switching function of the axis. Represents permanent magnet generator q The current value of the shaft. This represents the equivalent DC load current drawn by the grid-side converter from the DC bus.

[0046] Specifically, the expression for the rotational kinetic energy of a permanent magnet hydroelectric power generation system is:

[0047] in, Represents the rotational kinetic energy of a permanent magnet hydroelectric power generation system. This represents the total moment of inertia of the water turbine and the permanent magnet generator. This represents the electric angular velocity of the permanent magnet generator rotor.

[0048] In this embodiment of the invention, when the islanded grid load changes, the transient power difference is initially buffered by the charging and discharging of the DC bus capacitor and the rotational kinetic energy of the permanent magnet hydroelectric power generation system. Specifically, when the islanded grid load changes abruptly, the DC current output on the grid side changes rapidly, and the generator power output does not adjust synchronously. The charging and discharging of the DC bus capacitor buffers the power difference, directly causing fluctuations in the bus voltage, which serves as the trigger signal for the generator-side electromagnetic torque adjustment. Simultaneously, after the electromagnetic torque of the permanent magnet generator is adjusted, the permanent magnet hydroelectric power generation system provides transient power buffering by releasing or absorbing rotational kinetic energy, maintaining a short-term power balance between the generator output power and the islanded grid power. The rotational kinetic energy of the permanent magnet hydroelectric power generation system includes the rotational kinetic energy of the permanent magnet generator rotor, the rotational kinetic energy of the turbine runner, and the rotational kinetic energy of the main shaft. Since the rotational kinetic energy of the permanent magnet hydroelectric power generation system is proportional to the square of the electric angular velocity of the permanent magnet generator rotor, the change in kinetic energy directly changes the rotational speed of the permanent magnet generator, simultaneously causing the turbine speed to deviate from the optimal speed value corresponding to the current head, providing adjustment deviation for the subsequent speed governor.

[0049] Step S230: The governor obtains the current head and speed of the turbine, determines the optimal speed of the turbine based on the current head, and adjusts the guide vane opening of the turbine based on the current speed and the optimal speed so that the adjusted speed is the optimal speed.

[0050] Optionally, in the above embodiments, step S230, in which the speed governor determines the optimal speed value of the turbine based on the current head, includes: The governor calculates the optimal turbine speed corresponding to the current head by interpolation based on the current head and the turbine's operating characteristic curve.

[0051] In this embodiment of the invention, the optimal speed of the turbine refers to the speed at which the turbine operates with the highest efficiency under the current head conditions. Since the turbine is mechanically connected to the permanent magnet generator, the optimal speed of the turbine is also the optimal speed of the permanent magnet generator. After the governor obtains the current head of the turbine, it interpolates and calculates the optimal speed of the turbine corresponding to the current head based on the turbine's operating characteristic curve, and uses this as the target control value of the governor. In specific implementation, multiple experiments can be conducted to measure the head, speed, and power of the turbine under different operating conditions, and the hydraulic efficiency under different operating conditions corresponding to different heads and speeds can be calculated. A head-efficiency-speed operating characteristic curve representing the mapping relationship between speed and hydraulic efficiency under each operating condition can be established in advance.

[0052] Optionally, in the above embodiments, step S230, in which the speed governor adjusts the guide vane opening of the turbine according to the current speed value and the optimal speed value, includes: The governor performs PID calculations based on the difference between the current speed value and the optimal speed value to obtain the guide vane opening adjustment command, and adjusts the guide vane opening of the turbine according to the guide vane opening adjustment command.

[0053] It should be noted that when the generator-side converter adjusts the electromagnetic torque of the permanent magnet generator, it causes an imbalance between the electromagnetic torque of the permanent magnet generator and the mechanical torque of the turbine. In this case, it is necessary to release or absorb rotational kinetic energy through the generator set to rebalance the electromagnetic torque of the permanent magnet generator and the mechanical torque of the turbine. Since the rotational kinetic energy of the permanent magnet hydroelectric power generation system is proportional to the square of the electric angular velocity of the permanent magnet generator, changes in kinetic energy directly change the rotational speed of the permanent magnet generator, simultaneously causing changes in the rotational speed of the turbine, deviating it from the optimal rotational speed value corresponding to the current head. In this embodiment of the invention, the speed governor uses the optimal rotational speed value corresponding to the current turbine head as the control target, obtains the current rotational speed value of the turbine in real time, and calculates the difference between it and the optimal rotational speed value. After the rotational speed deviation signal is processed by PID control, a guide vane opening adjustment command is output. The turbine's guide vane opening is adjusted according to the guide vane opening adjustment command, changing the turbine's hydraulic torque and restoring the turbine's rotational speed to the optimal value. Understandably, during the entire process of islanded grid disturbance response, the grid-side converter continuously maintains the rated voltage and frequency of the islanded grid, ensuring the stability of the power supply on the grid side. At the same time, it also allows the turbine to operate at the optimal speed at the current head, thus balancing the system's power supply stability and power generation efficiency.

[0054] For example, when the islanded grid load increases, the grid-side converter automatically increases its power output. The turbine-side converter then increases the electromagnetic torque of the permanent magnet generator (PMG), causing an imbalance between the PMG's electromagnetic torque and the turbine's mechanical torque. This leads to a decrease in the PMG's speed, which in turn causes a decrease in the turbine's speed. At this point, the governor outputs a command to increase the guide vane opening, increasing the turbine's guide vane opening and increasing the turbine's mechanical torque. This rebalances the PMG's electromagnetic torque and the turbine's mechanical torque, restoring the turbine's speed to its optimal value. It can be understood that when the islanded grid load decreases, the signs of the increases and decreases of each variable are reversed, resulting in symmetrical adjustment logic.

[0055] To enable those skilled in the art to better understand this solution, the following describes the startup phase, stable operation phase, and islanded load disturbance process of the islanded operation control method for permanent magnet hydropower systems provided in the embodiments of the present invention.

[0056] Start-up phase: (1) The governor adjusts the opening of the turbine guide vanes to raise the turbine and permanent magnet generator to the pressure build-up speed, so that the output terminal voltage amplitude of the permanent magnet generator is within the allowable range of DC bus pressure build-up; (2) The AC voltage output from the permanent magnet generator is uncontrolled rectified by the generator-side converter to initially charge the DC bus capacitor and establish the initial bus voltage. (3) After the initial voltage of the DC bus reaches the operating threshold of the converter, the machine-side converter is put into controllable rectification mode to precisely adjust the DC bus voltage to the rated value and stabilize it in closed loop. (4) After the DC bus voltage stabilizes, the grid-side converter is put into voltage-frequency (V / f) control to actively establish the rated voltage and rated frequency of the isolated grid; (5) After the electrical parameters of the isolated network stabilize, the governor switches to the optimal speed closed-loop mode, calculates the optimal speed based on the real-time head, and adjusts the guide vane opening to gradually raise the turbine to the optimal operating condition.

[0057] Stable operation phase: (1) The grid-side converter is continuously closed-loop regulated to keep the voltage and frequency of the isolated grid at the rated value.

[0058] (2) The governor continuously tracks the optimal speed to keep the turbine running in the highest efficiency zone.

[0059] (3) The generator-side converter rectifies and inverts the output power of the permanent magnet generator to stably deliver power to the isolated grid.

[0060] In order to ensure that the turbine always operates in the highest efficiency range when the water head of the turbine changes, the governor will update the optimal speed value in real time, and the optimal speed will not change abruptly. The reasons are as follows: the water head is determined by the upstream and downstream water levels and water flow conditions, which is a slow change and will not change abruptly; the turbine generator is a large inertia device with smooth operation, and the frequency change caused by the change in water flow is controllable; the governor output will set limits on the guide vane opening rate change rate and the speed change rate, and the output will be smoothly transitioned to avoid abrupt changes in command; when using the PID algorithm, the target speed will be filtered, limited, and smoothly tracked, without step impact.

[0061] Isolated network load disturbance process: (1) When the load on the isolated grid increases, the load current on the grid side increases, and the voltage and frequency values ​​of the isolated grid decrease accordingly; (2) The active and reactive currents output from the outer loop of the grid-side converter increase; (3) The input power and output power of the DC bus are unbalanced, and the bus voltage of the DC bus decreases; (4) The deviation between the current DC bus voltage and the target bus voltage is greater than 0, and the machine side... q The shaft current setpoint is increased; (5) The increase in electromagnetic torque of the permanent magnet generator leads to an imbalance between the mechanical torque of the water turbine and the electromagnetic torque of the permanent magnet generator, and the speed of the permanent magnet generator and the water turbine decreases synchronously. (6) When the deviation between the current speed value of the turbine and the optimal speed value is greater than 0, the governor outputs a command to increase the guide vane opening, thereby increasing the guide vane opening of the turbine and increasing the mechanical torque of the turbine. (7) The mechanical torque of the turbine and the electromagnetic torque of the permanent magnet generator are rebalanced, the turbine speed is restored to the optimal speed value corresponding to the current head, and the bus voltage value of the DC bus, the voltage value and frequency value of the isolated network are restored to the target value.

[0062] When the load on the isolated network decreases, the adjustment links only have the signs of the increase and decrease of each variable reversed, and the adjustment logic is symmetrical.

[0063] As described above, the islanded operation control method for a permanent magnet hydropower system provided in this embodiment of the invention obtains the current voltage and frequency values ​​of the islanded grid through a grid-side converter, and adjusts the output power according to the current voltage and frequency values, as well as the target voltage and frequency values ​​of the islanded grid, so that the adjusted voltage and frequency values ​​are respectively the target voltage and frequency values; the generator-side converter obtains the current DC bus voltage value, and adjusts the electromagnetic torque of the permanent magnet generator according to the current bus voltage value and the target DC bus voltage value, so that the adjusted bus voltage value is the target bus voltage value; the speed governor obtains the current head and current speed values ​​of the turbine, determines the optimal speed value of the turbine according to the current head, and adjusts the guide vane opening of the turbine according to the current speed value and the optimal speed value, so that the adjusted speed value is the optimal speed value. Using the solution of this invention, in islanded operation, while maintaining the rated voltage and rated frequency of the islanded grid, the turbine can maintain the optimal speed at the current head, thereby balancing the power supply stability and power generation efficiency of the system.

[0064] The various embodiments described in this specification are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. It should also be noted that in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0065] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling the isolated operation of a permanent magnet hydropower system, characterized in that, An application is made in a permanent magnet hydropower system, which includes a governor, a turbine, a permanent magnet generator, and a full-power converter. The governor is connected to the turbine, the input of the permanent magnet generator is connected to the turbine, and the output of the permanent magnet generator is connected to an isolated grid load through the turbine-side converter and the grid-side converter of the full-power converter. The control method includes: The grid-side converter acquires the current voltage and frequency values ​​of the isolated grid, and adjusts the output power according to the current voltage and frequency values, as well as the target voltage and target frequency values ​​of the isolated grid, so that the adjusted voltage and frequency values ​​are respectively the target voltage and target frequency values. The generator-side converter acquires the current bus voltage value of the DC bus and adjusts the electromagnetic torque of the permanent magnet generator according to the current bus voltage value and the target bus voltage value of the DC bus, so that the adjusted bus voltage value is the target bus voltage value. The governor acquires the current head and the current speed of the turbine, determines the optimal speed of the turbine based on the current head, and adjusts the guide vane opening of the turbine based on the current speed and the optimal speed, so that the adjusted speed is the optimal speed.

2. The method for controlling the isolated operation of a permanent magnet hydropower system according to claim 1, characterized in that, The grid-side converter adjusts its output power based on the current voltage and frequency values, as well as the target voltage and frequency values ​​of the isolated grid, including: The grid-side converter performs closed-loop adjustment of the output active and reactive power based on the current voltage value, the current frequency value, and the target voltage and frequency values ​​of the isolated grid.

3. The method for controlling the isolated operation of a permanent magnet hydropower system according to claim 2, characterized in that, The grid-side converter performs closed-loop adjustment of the output active and reactive power according to the following formula: ； ； ； in, Represents the grid-side converter d Shaft current setpoint, and These represent the proportional gain and integral gain of the outer frequency loop of the grid-side converter, respectively. This represents the target angular velocity value of the isolated network. This represents the current angular velocity value of the isolated network. Represents time, Represents the grid-side converter q The current setpoint of the shaft, and These represent the proportional gain and integral gain of the outer voltage loop of the grid-side converter, respectively. This represents the target voltage value of the isolated network. This represents the current voltage value of the isolated network. Represents the grid-side converter d The target voltage value of the shaft, and These respectively represent the grid-side converters d The proportional gain and integral gain of the shaft current loop, Represents the grid-side converter d The current value of the shaft. Represents the filter inductor of the grid-side converter. q The equivalent inductance of the shaft, Represents the grid-side converter q The current value of the shaft. The decomposed value of the current voltage of the isolated network d Shaft voltage feedforward decoupling. Represents the grid-side converter q The target voltage value of the shaft, and These respectively represent the grid-side converters q The proportional gain and integral gain of the shaft current loop, Represents the filter inductor of the grid-side converter. d The equivalent inductance of the shaft, The decomposed value of the current voltage of the isolated network q Shaft voltage feedforward decoupling.

4. The method for controlling the isolated operation of a permanent magnet hydropower system according to claim 1, characterized in that, The grid-side converter adjusts its output power based on the current voltage and frequency values, as well as the target voltage and frequency values ​​of the isolated grid. Through the charging and discharging of the DC bus capacitor and the rotational kinetic energy changes of the permanent magnet hydroelectric power generation system, the input power and output power of the DC bus are balanced.

5. The islanded operation control method for a permanent magnet hydropower system according to claim 4, wherein the DC bus performs capacitor charging and discharging according to the following formula: ； in, This represents the total capacitance of the DC bus. The rate of change of the bus voltage of the DC bus represents the value of ... Represents the machine-side converter d The switching function of the axis. Represents the permanent magnet generator d The current value of the shaft. Represents the machine-side converter q The switching function of the axis. Represents the permanent magnet generator q The current value of the shaft. This represents the equivalent DC load current drawn by the grid-side converter from the DC bus.

6. The method for controlling the isolated operation of a permanent magnet hydropower system according to claim 4, characterized in that, The expression for the rotational kinetic energy of the permanent magnet hydroelectric power generation system is: ； in, This represents the rotational kinetic energy of the permanent magnet hydroelectric power generation system. This represents the total moment of inertia of the water turbine and the permanent magnet generator. This represents the electric angular velocity of the permanent magnet generator rotor.

7. The method for controlling the isolated operation of a permanent magnet hydropower system according to claim 1, characterized in that, The generator-side converter adjusts the electromagnetic torque of the permanent magnet generator based on the current bus voltage value and the target bus voltage value of the DC bus, including: The generator-side converter is equipped with a DC bus voltage outer loop. The difference between the target bus voltage value and the current bus voltage value is calculated by a PID controller to generate an electromagnetic torque command. The electromagnetic torque of the permanent magnet generator is adjusted according to the electromagnetic torque command. Specifically, when the difference is less than zero, the electromagnetic torque is reduced, and when the difference is greater than zero, the electromagnetic torque is increased.

8. The method for controlling the isolated operation of a permanent magnet hydropower system according to claim 1, characterized in that, The governor determines the optimal speed of the turbine based on the current head, including: The governor calculates the optimal speed of the turbine corresponding to the current head by interpolation based on the current head and the turbine's operating characteristic curve.

9. The method for controlling the isolated operation of a permanent magnet hydropower system according to claim 1, characterized in that, The governor adjusts the guide vane opening of the turbine based on the current speed value and the optimal speed value, including: The speed governor performs PID calculations based on the difference between the current speed value and the optimal speed value to obtain a guide vane opening adjustment command, and adjusts the guide vane opening of the turbine according to the guide vane opening adjustment command.

10. The method for controlling the isolated operation of a permanent magnet hydropower system according to claim 1, characterized in that, The permanent magnet hydropower generation system also includes a head detection unit, which is used to detect the current head of the turbine.

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