A power supply system

Abstract

The application provides a power supply system applied to a photovoltaic power station and an energy storage power station collection system. The power supply system comprises a plurality of power conversion devices, a transformer and a power station controller. The power conversion devices are connected to a power grid through the transformer, and the connection of the transformer to the power grid is a grid connection point. The power station controller is configured to generate a first indication signal for indicating the equivalent impedance of the power supply system according to the device voltage of the plurality of power conversion devices and the voltage of the grid connection point, and send the first indication signal to the plurality of power conversion devices. The power conversion device is configured to determine the estimated voltage of the grid connection point according to the first indication signal, and adjust the reactive power output by the power conversion device according to the estimated voltage of the grid connection point when the estimated voltage of the grid connection point is out of a preset interval. According to the scheme, the impedance is used to realize the prediction control of the high-voltage side voltage of the grid connection point, the accuracy and response speed of the voltage regulation control are improved, and the stable operation of the power grid is ensured.

Description

Technical Field

[0001] This application relates to the field of power electronics, and more particularly to a power supply system. Background Technology

[0002] New energy, as a clean and renewable energy source, is widely used. New energy power supply systems generally consist of multiple power electronic devices that step up and merge voltages in stages. These power electronic devices form a point of common coupling (PCC) with the power grid. When operating in a grid-connected configuration, power electronic devices such as photovoltaic inverters and energy storage converters transmit electrical energy to the grid through this PCC. In practical applications, variations in load impedance or unstable power output in the new energy power supply system can cause voltage and frequency fluctuations at the PCC connection point. This increases power losses and can even jeopardize equipment safety. Typically, power electronic devices have primary voltage regulation capabilities, which can improve the stability of the PCC voltage to some extent. However, these devices can only detect the low-voltage side, resulting in significant voltage regulation control errors and affecting the system's voltage regulation control accuracy.

[0003] Therefore, improving the voltage regulation control accuracy of the system is a problem that needs to be solved. Summary of the Invention

[0004] This application provides a power supply system that collects the high-voltage side voltage at the grid connection point and the low-voltage side equipment voltage through a power station controller, monitors and estimates the equivalent impedance in real time, and sends the equivalent impedance to the power conversion equipment, thereby realizing predictive control of the high-voltage side voltage at the grid connection point and improving the accuracy and response speed of voltage regulation control.

[0005] In a first aspect, a power supply system is provided, comprising multiple power conversion devices, a transformer, and a power station controller. The power conversion devices are connected to the power grid via the transformer, and the connection point between the transformer and the power grid is the grid connection point. The power station controller generates a first indication signal indicating the equivalent impedance of the power supply system based on the device voltages of the multiple power conversion devices and the voltage of the grid connection point, and sends the first indication signal to the multiple power conversion devices. The power conversion devices determine the estimated voltage of the grid connection point based on the first indication signal. When the estimated voltage of the grid connection point exceeds a preset range, the power conversion devices adjust the reactive power output of the power conversion devices according to the estimated voltage of the grid connection point.

[0006] Power conversion equipment includes inverters and energy storage converters. Multiple power conversion devices are connected to the grid connection point via transformers. Therefore, the voltage at the grid connection point is affected by the voltages of multiple power conversion devices. When the power output of the power conversion devices changes, the voltage at the grid connection point also fluctuates, which can affect the stable operation of the power grid, increase energy loss, and even damage the equipment. Power conversion devices can adjust their output power in a timely manner by monitoring the voltage, thereby regulating the power output to stabilize the voltage at the grid connection point. However, since power conversion devices operate on the low-voltage side, they cannot detect the voltage at the high-voltage side of the grid connection point. When the power conversion devices perform voltage regulation control on the low-voltage side, they cannot detect changes in the voltage at the high-voltage side of the grid connection point. Therefore, there is a control error in the voltage regulation control, affecting the accuracy of the power supply system's voltage regulation control. Thus, it is necessary to improve the control efficiency of voltage regulation control.

[0007] In this application, the equivalent impedance of the power supply system refers to the equivalent impedance of the circuit composed of multiple power conversion devices and various electrical components in the power supply system connected to the grid connection point. Equivalent impedance simplifies system analysis and calculation. The power station controller comprehensively controls and manages the power conversion devices in each subarray of the power supply system. The power station controller can monitor the grid connection point voltage and collect the voltage of each power conversion device, thus obtaining the equivalent impedance of each subarray's internal external components. The power station controller sends the equivalent impedance to the power control device via a first indication signal. The power control device can then estimate the high-voltage side grid connection point voltage based on the equivalent impedance and adjust the output reactive power according to the estimated grid connection point voltage, achieving predictive control of the high-voltage side voltage at the grid connection point.

[0008] When the estimated voltage at the grid connection point exceeds the preset range, or when the voltage fluctuation at the grid connection point is large and the voltage change at the grid connection point exceeds the threshold, voltage regulation control is performed based on the indication signal, and then the power control equipment adjusts the reactive power to avoid erroneous adjustments.

[0009] According to the scheme of this application, the equivalent impedance is monitored and estimated in real time by the power station controller, and the equivalent impedance is sent to the power conversion equipment, thereby realizing predictive control of the voltage on the high-voltage side of the grid connection point and improving the accuracy and response speed of voltage regulation control.

[0010] In conjunction with the first aspect, in the various implementations of the first aspect, the equivalent impedance of the power supply system satisfies:

[0011]

[0012] Where P is the active power dispatch command, Q is the reactive power dispatch command, and U... grid U is the voltage at the grid connection point. emf The device voltage δ for each power conversion device pa For U grid and Uemf The phase difference between them, ω is the angular frequency of each power conversion device, and L real denoted as the equivalent impedance of the power supply system, and j is the imaginary unit.

[0013] Active power dispatch instructions refer to the active power adjustment instructions issued based on the real-time operating conditions and demand of the power system. These instructions are used to instruct the increase or decrease of power to maintain the stable operation of the power system, ensure supply and demand balance, and meet power load demands. Reactive power dispatch instructions are issued to the power supply system to adjust the reactive power output of equipment based on real-time grid operating conditions to maintain grid stability. These instructions are used to instruct adjustments to the excitation system, the capacity of reactive power compensation devices, and other operations to ensure that grid parameters such as voltage and frequency remain within a safe and stable range. The power plant controller monitors the voltage U at the grid connection point. grid Active power P and reactive power Q, and the device voltage U of the power conversion equipment reported by the digital acquisition equipment of the receiving subarray. emf Therefore, the equivalent impedance L of the power supply system can be obtained by solving the simultaneous equations using the above formulas. real .

[0014] According to the scheme in this application, the equivalent impedance of each subarray station to the outside can be accurately calculated using the above formula, which improves the accuracy of voltage regulation control of power conversion equipment and enhances the operational stability of the power grid.

[0015] In conjunction with the first aspect, in various implementations of the first aspect, the power plant controller is further configured to acquire the voltage at the grid connection point after a first time period following the transmission of the first indication signal. After a second time period following the transmission of the first indication signal, a second indication signal for indicating the equivalent impedance of the power supply system is generated and transmitted based on the device voltages of the multiple power conversion devices and the voltage at the grid connection point, wherein the length of the second time period is greater than the length of the first time period.

[0016] The power plant controller periodically acquires the voltage at the grid connection point, which is monitored by the power plant controller or other sensors. After acquiring the voltage, the power plant controller assesses it. When the voltage is relatively stable, the power plant controller may not send an indication signal to notify the power conversion equipment of the equivalent impedance. When the voltage at the grid connection point fluctuates significantly, after a second period following the transmission of the first indication signal, the power plant controller sends a second indication signal. This second indication signal indicates the equivalent impedance of the power supply system at this time. The period during which the power plant controller sends the indication signal is longer than the period during which it acquires the grid connection point voltage.

[0017] According to the scheme in this application, the power plant controller monitors the voltage at the high-voltage side grid connection point in real time and sends an indication signal when voltage regulation is required, thereby indicating the equivalent impedance to the power conversion equipment, which improves the response speed and accuracy of voltage regulation control and enhances the operational stability of the power grid.

[0018] In conjunction with the first aspect, in various implementations of the first aspect, the power station controller is also used to send a second indication signal to the power conversion device at a second moment after sending the first indication signal, when the change in the equivalent impedance of the power supply system is greater than a preset threshold, to indicate the changed equivalent impedance of the power supply system.

[0019] The power plant controller periodically acquires the voltage at the grid connection point, which is monitored by the power plant controller or other sensors. Based on the grid connection point voltage, the power plant controller calculates the equivalent impedance of the power supply system in real time and assesses it. When the change in the equivalent impedance of the power supply system exceeds a preset threshold, the voltage at the grid connection point usually also changes significantly, requiring voltage regulation. The power plant controller sends a second indication signal to the power conversion equipment, indicating the changed equivalent impedance. The power conversion equipment re-estimates the grid connection point voltage based on the newly indicated equivalent impedance and adjusts the output reactive power accordingly.

[0020] According to the scheme of this application, when the equivalent impedance changes significantly, the power station controller re-indicates the new equivalent impedance to the power conversion equipment, thereby adjusting the reactive power output of the power conversion equipment, improving the response speed and accuracy of voltage regulation control, and improving the operational stability of the power grid.

[0021] In conjunction with the first aspect, in various implementations of the first aspect, when sending a first indication signal to multiple power conversion devices, the first indication signal sent to at least two power conversion devices indicates different equivalent impedances of the power supply system.

[0022] Due to the differences between the various power conversion devices, the equivalent impedance is not the same for each power conversion device. The power station controller sends different indication signals to each power conversion device to indicate its own equivalent impedance.

[0023] According to the scheme of this application, by sending different indication signals to different power conversion devices, precise and differentiated control of all power conversion devices can be achieved, thereby improving the accuracy of voltage regulation control of power conversion devices and improving the operational stability of the power grid.

[0024] In conjunction with the first aspect, in various implementations of the first aspect, during the process of determining the estimated voltage of the grid connection point according to the first indication signal, the power conversion device is specifically used to determine the estimated voltage of the grid connection point according to the device voltage of the power conversion device and the equivalent impedance of the power supply system, and the estimated voltage of the grid connection point decreases as the equivalent impedance of the power supply system increases.

[0025] In a power supply system, when a power conversion device is connected to the grid connection point, the voltage at the connection point decreases due to the presence of equivalent impedance. The greater the equivalent impedance of the system, the greater the voltage drop at the connection point. The power conversion device can estimate the voltage at the high-voltage side grid connection point based on the equivalent impedance provided by the power station controller. Instead of directly indicating the grid connection point voltage, the power station controller instructs the power conversion device to provide the equivalent impedance. The power conversion device can then estimate the grid connection point voltage based on the equivalent impedance. Since the grid connection point voltage changes constantly, real-time indication of the grid connection point voltage or reactive power would result in a significant delay in voltage regulation control due to communication bandwidth and latency, limiting its response speed. In contrast, the equivalent impedance is relatively fixed and changes slowly. After the power station controller instructs the power conversion device to provide the equivalent impedance, the power conversion device can calculate the required reactive power adjustment based on the equivalent impedance, resulting in a faster response and less susceptibility to communication bandwidth limitations.

[0026] In conjunction with the first aspect, among the various implementations of the first aspect, the estimated voltage at the grid connection point satisfies:

[0027]

[0028] in, For the estimated voltage at the grid connection point, U emf The device voltage for each power conversion device, Let L be the current at the grid connection point, ω be the angular frequency of each power conversion device, and L be the current at the grid connection point. real This is the equivalent impedance of the power supply system.

[0029] In a power supply system, when power conversion equipment is connected to the grid, the voltage at the grid connection point decreases due to the presence of equivalent impedance. The greater the equivalent impedance of the system, the greater the voltage drop at the grid connection point. This voltage drop is calculated by subtracting the voltage of each power conversion device from the voltage caused by the equivalent impedance. The voltage at the grid connection point can then be obtained.

[0030] According to the scheme in this application, the grid connection point voltage is estimated based on the equivalent impedance, which improves the accuracy and response speed of voltage regulation control of power conversion equipment and enhances the operational stability of the power grid.

[0031] In conjunction with the first aspect, in the various implementations of the first aspect, during the process of adjusting the reactive power output of the power conversion device according to the estimated voltage of the grid connection point, each power conversion device is specifically used to determine the reactive power reference value of the grid connection point according to the estimated voltage of the grid connection point, and the change value of the reactive power reference value of the grid connection point is proportional to the difference between the estimated voltage of the grid connection point and the preset range.

[0032] The power conversion equipment can calculate the reactive power reference value of the grid connection point based on the estimated voltage of the grid connection point and the preset excitation voltage regulation method. The change value of the reactive power reference value changes with the change of the estimated voltage. The larger the estimated voltage is from the preset range, the larger the change value of the reactive power reference value.

[0033] In conjunction with the first aspect, in various implementations of the first aspect, during the process of adjusting the reactive power output of the power conversion device according to the first indication signal, each power conversion device is also used to determine the reactive power consumed by the equivalent impedance of the power supply system based on the equivalent impedance of the power supply system. The reactive power output of the power conversion device is adjusted based on the reactive power reference value at the grid connection point and the reactive power consumed by the equivalent impedance of the power supply system.

[0034] The power conversion equipment first needs to estimate the reactive power reference value and the grid connection point current. Then, based on the equivalent impedance and the grid connection point current, it estimates the grid connection point voltage and the reactive power consumed by the impedance. Next, it updates the reactive power reference value based on the grid connection point voltage. Finally, the target value is the sum of the reactive power consumed by the impedance and the reactive power reference value.

[0035] In conjunction with the first aspect, among the various implementations of the first aspect, the reactive power output by the power conversion device satisfies:

[0036] Q emf = ref +L real |I grid | 2 ,

[0037] Among them, Q emf Q represents the target output power of the power conversion device. ref Let L be the reactive power reference value at the grid connection point, ω be the angular frequency of each power conversion device, and L be the reactive power reference value at the grid connection point. real This is the equivalent impedance of the power supply system.

[0038] According to the scheme of this application, the final reactive power of the power conversion equipment can be accurately calculated using the above formula, which improves the accuracy of voltage regulation control of the power conversion equipment and enhances the operational stability of the power grid. Attached Figure Description

[0039] Figure 1This is a schematic diagram of a new energy and energy storage power station provided in this application;

[0040] Figure 2 This is a schematic diagram of an application scenario provided in this application;

[0041] Figure 3 This is a schematic diagram of the process for adjusting reactive power in a power conversion device provided in this application. Detailed Implementation

[0042] The technical solutions in this application will now be described with reference to the accompanying drawings.

[0043] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0044] The power supply system provided in this application can be applied to various fields, including new energy smart microgrids, power transmission and distribution, new energy fields (such as photovoltaic grid-connected fields, thermal power grid-connected fields, or wind power grid-connected fields), photovoltaic power generation, wind power generation, thermal power generation, or high-power converter fields (such as converting DC power to high-power high-voltage AC power), etc. The specific application scenario can be determined accordingly, and no limitations are imposed here. The power supply system provided in this application can be applied to power supply systems with different power generation devices, such as photovoltaic power supply systems, wind power supply systems, thermal power supply systems, nuclear power supply systems, chemical power supply systems, or biomass power supply systems. The specific application scenario can be determined accordingly, and no limitations are imposed here. The power supply system provided in this application can be adapted to different application scenarios, such as applications supplying power to loads in photovoltaic-storage power supply environments, applications supplying power to loads in wind-storage power supply environments, applications supplying power to loads in pure energy storage power supply environments, or other application scenarios.

[0045] Figure 1 This is a schematic diagram illustrating the convergence of new energy and energy storage power stations. (For example...) Figure 1 As shown, current new energy and energy storage power stations are generally composed of multiple power electronic devices that step up and merge voltages. The voltage stability of a new energy power station will affect the stable operation of the station itself, as well as the stable operation of the entire system. Figure 1The grid-connected system in this context comprises multiple power conversion devices operating in parallel. The AC output of each power conversion device is connected to the point of common coupling (PCC). The grid-connected system is connected to the AC power grid. Since the AC grid connected to multiple power conversion devices is not an ideal grid, it is generally assumed that the inverter is connected to the AC grid through an equivalent impedance. Each power conversion device outputs a specific power. During grid-connected operation, the power conversion devices perform primary voltage regulation control by detecting the low-voltage side voltage, which can improve the stability of the PCC voltage to some extent. However, because the power conversion devices generally operate on the low-voltage side and cannot detect the high-voltage side PCC voltage, the voltage regulation control of the power conversion devices has a control error relative to the PCC voltage, affecting the system's voltage regulation control accuracy.

[0046] To address the aforementioned issues, this application provides a power supply system that collects the high-voltage side voltage at the grid connection point and the low-voltage side equipment voltage through a power station controller, monitors and estimates the equivalent impedance in real time, and sends the equivalent impedance to the power conversion equipment. This enables predictive control of the high-voltage side voltage at the grid connection point, improving the accuracy and response speed of voltage regulation control.

[0047] Figure 2 This is a schematic diagram of the application scenario of the power supply system provided in this application.

[0048] In one application scenario, the power supply system is a photovoltaic power supply system, and the power conversion device 20 is an inverter 21 used to convert direct current (DC) to alternating current (AC). The inverter 21 includes an inverter circuit, a control unit, a sampling unit, and a computing unit. The AC output terminal of the inverter circuit is the output port of the inverter 21, which is connected to a transformer 30 via a cable or directly to a single-phase or three-phase AC power grid 60, and is connected to the AC output terminals of other inverters 21 to form a parallel system. The DC output terminal of the inverter unit is the input port of the inverter 21, and is connected to the DC output terminals of other inverters 21 to form a series or parallel system. The inverter 21 is also connected in parallel with one or more photovoltaic strings 11 through the DC conversion unit; a photovoltaic string 11 can be obtained by connecting one or more photovoltaic modules in series. The photovoltaic string 11 is connected to the AC grid 60 through the inverter 21. The photovoltaic string 11 converts light energy into DC electrical energy. The inverter 21 converts the DC power generated by the photovoltaic string 11 into AC power, which is then transmitted to the AC grid 60.

[0049] In another application scenario, the power supply system is an energy storage power supply system, and the power conversion device 20 is an energy storage converter 22 (power control system, PCS). The energy storage converter 22 is used to connect the energy storage battery 12 to the AC power grid 60 to realize charging and discharging power conversion. The energy storage battery 12 can be a high-capacity, high-power battery. The energy storage battery 12 can be a secondary battery. Secondary batteries include, but are not limited to, lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, magnesium-ion batteries, calcium-ion batteries, air batteries, lead-acid batteries, and nickel-cadmium batteries. This application does not limit the specific type of secondary battery; any battery capable of charging and discharging is acceptable. The energy storage battery 12 can realize the storage and release of electrical energy.

[0050] In another application scenario, the power supply system is a photovoltaic-storage system, and the power conversion device 20 includes an inverter 21 and an energy storage converter 22. The photovoltaic-storage system includes a photovoltaic string 11, an inverter 21, and an energy storage battery 12. The photovoltaic-storage system may also include an AC grid 60 and a load (not shown). The inverter 21 can convert DC power from the photovoltaic string 11 into AC power and supply the AC power to the AC grid 60 or the load. Alternatively, the inverter 21 can supply DC power from the photovoltaic string 11 to the energy storage battery 12 to charge it. The energy storage battery 12 in the photovoltaic-storage system can store and release electrical energy. The energy storage battery 12 can store DC power from the photovoltaic string 11, and it can also supply power to the AC grid 60 or the load through the inverter 21. The inverter 21 may include two DC ports and one AC port, with the two DC ports used to connect the photovoltaic string 11 and the energy storage battery 12, respectively. The AC port can be used to output AC power, which can be distributed through a distribution box. The photovoltaic string 11 can supply power to the AC grid 60 and the load via the DC port. The energy storage battery 12 can supply power to the load via the DC port. The AC grid 60 can supply power to the load via the AC port.

[0051] See also Figure 2 The power supply system includes multiple power conversion devices 20, transformers 30, and a power station controller 40. The power conversion devices 20 are connected to the power grid through the transformers 30. The connection point between the transformers 30 and the power grid is the grid connection point 50. The power station controller 40 is used to generate a first indication signal for indicating the equivalent impedance of the power supply system based on the device voltages of the multiple power conversion devices 20 and the voltage of the grid connection point 50, and sends the first indication signal to the multiple power conversion devices 20.

[0052] Multiple power conversion devices 20 are connected to the grid connection point 50 via a transformer 30. Therefore, the voltage at the grid connection point 50 is affected by the voltages of these multiple power conversion devices 20. When the power output of the power conversion devices 20 changes, the voltage at the grid connection point 50 also fluctuates, which can affect the stable operation of the power grid, increase energy loss, and even damage the equipment. The power conversion devices 20 can adjust their output power in a timely manner by monitoring the voltage, thereby regulating the power output to stabilize the voltage at the grid connection point 50. However, since the power conversion devices 20 operate on the low-voltage side, they cannot detect the voltage at the high-voltage side of the grid connection point 50. When the power conversion devices 20 perform voltage regulation control on the low-voltage side, they cannot detect changes in the voltage at the high-voltage side of the grid connection point 50. Therefore, there is a control error in the voltage regulation control, affecting the accuracy of the power supply system's voltage regulation control. Thus, it is necessary to improve the control efficiency of the voltage regulation control.

[0053] In practical applications, the power conversion device 20 and the AC power grid 60 are mainly connected by a grid-connected transformer 30 and transmission lines, all of which are inductive loads. Generally, the components between the AC power grid 60 and the power conversion device 20 can be considered as an inductive impedance. When the output power of the power conversion device 20 increases, since the output voltage of the power conversion device 20 remains constant, the current flowing through the inductive impedance increases, and the voltage drop across the inductive impedance increases accordingly. This leads to a drop in voltage at the grid connection point 50, affecting the stable operation of the power grid.

[0054] In this application, the equivalent impedance of the power supply system refers to the equivalent impedance of the circuit composed of multiple power conversion devices 20 connected to the grid connection point 50 and various electrical components in the power supply system, which is equivalently transformed into the equivalent impedance. The equivalent impedance simplifies system analysis and calculation. The power station controller 40 performs comprehensive control and management of the power conversion devices 20 in each subarray of the power supply system. The power station controller 40 can monitor the voltage of the grid connection point 50 and collect the voltage of each power conversion device 20, thereby obtaining the equivalent impedance of each subarray's internal external components. The power station controller 40 sends the equivalent impedance to the power control device through a first indication signal, so that the power control device can estimate the voltage of the high-voltage side grid connection point 50 based on the equivalent impedance. The power control device adjusts the output reactive power according to the estimated voltage of the grid connection point 50, thereby realizing predictive control of the high-voltage side voltage of the grid connection point 50.

[0055] According to the scheme of this application, the equivalent impedance is monitored and estimated in real time by the power station controller 40, and the equivalent impedance is sent to the power conversion equipment 20, thereby realizing the predictive control of the high voltage side voltage of the grid connection point 50, and improving the accuracy and response speed of voltage regulation control.

[0056] In one embodiment, the equivalent impedance of the power supply system satisfies:

[0057]

[0058] Where P is the active power dispatch command, Q is the reactive power dispatch command, and U... grid For the voltage at grid connection point 50, U emf The device voltage, δ, for each power conversion device 20 pa For U grid and U emf The phase difference between them, ω, is the angular frequency of each power conversion device 20, L real denoted as the equivalent impedance of the power supply system, and j is the imaginary unit.

[0059] Active power dispatch instructions refer to active power adjustment instructions issued based on the real-time operating conditions and demand of the power system. These instructions are used to instruct the increase or decrease of power to maintain the stable operation of the power system, ensure supply and demand balance, and meet power load demands. Reactive power dispatch instructions are issued to the power supply system to adjust the reactive power output of equipment based on real-time grid operating conditions to maintain grid stability. These instructions are used to instruct adjustments to the excitation system, the capacity of reactive power compensation devices, and other operations to ensure that grid parameters such as voltage and frequency remain within a safe and stable range. The power station controller 40 monitors the voltage U at the grid connection point 50. grid Active power P and reactive power Q, and the device voltage U of the power conversion device 20 reported by the digital acquisition device of the subarray. emf Therefore, the equivalent impedance L of the power supply system can be obtained by solving the simultaneous equations using the above formulas. real .

[0060] In one embodiment, the power station controller 40 is further configured to acquire the voltage of the grid connection point 50 after a first time period following the transmission of the first indication signal. After a second time period following the transmission of the first indication signal, a second indication signal for indicating the equivalent impedance of the power supply system is generated and transmitted based on the device voltages of the plurality of power conversion devices 20 and the voltage of the grid connection point 50, wherein the length of the second time period is greater than the length of the first time period.

[0061] The power plant controller 40 periodically acquires the voltage at grid connection point 50, which is monitored by the power plant controller 40 or other sensors. After acquiring the voltage at grid connection point 50, the power plant controller 40 assesses the voltage. When the voltage at grid connection point 50 is relatively stable, the power plant controller 40 may not send an indication signal to notify the power conversion device 20 of the equivalent impedance. When the voltage at grid connection point 50 fluctuates significantly, after a second period following the transmission of the first indication signal, the power plant controller 40 sends a second indication signal, which indicates the equivalent impedance of the power supply system at that time. The period during which the power plant controller 40 sends the indication signal is longer than the period during which the power plant controller 40 acquires the voltage at grid connection point 50.

[0062] In one embodiment, the power station controller 40 is further configured to send a second indication signal to the power conversion device 20 at a second moment after sending the first indication signal, when the change in the equivalent impedance of the power supply system is greater than a preset threshold, to indicate the changed equivalent impedance of the power supply system.

[0063] The power plant controller 40 periodically acquires the voltage at grid connection point 50, which is monitored by the power plant controller 40 or other sensors. Based on the voltage at grid connection point 50, the power plant controller 40 calculates the equivalent impedance of the power supply system in real time and makes a judgment on the equivalent impedance. When the change in the equivalent impedance of the power supply system exceeds a preset threshold, the voltage at grid connection point 50 usually also changes significantly, requiring voltage regulation. The power plant controller 40 sends a second indication signal to the power conversion device 20, indicating the changed equivalent impedance. The power conversion device 20 re-estimates the voltage at grid connection point 50 based on the newly indicated equivalent impedance and adjusts the output reactive power accordingly.

[0064] In one embodiment, when a first indication signal is sent to a plurality of power conversion devices 20, the first indication signal sent to at least two power conversion devices 20 indicates that the equivalent impedance of the power supply system is different.

[0065] Because of the differences between the power conversion devices 20, the equivalent impedance is not the same for each power conversion device 20. The power station controller 40 sends different indication signals to each power conversion device 20 to indicate its own equivalent impedance.

[0066] Figure 3 This is a schematic diagram of the process of adjusting reactive power in the power conversion device 20 provided in the embodiment of this application.

[0067] The power conversion device 20 is used to determine the estimated voltage of the grid connection point 50 according to the first indication signal. When the estimated voltage of the grid connection point 50 exceeds the preset range, the reactive power output of the power conversion device 20 is adjusted according to the estimated voltage of the grid connection point 50.

[0068] When the estimated voltage of grid connection point 50 exceeds the preset range, the voltage fluctuation of grid connection point 50 is large, and the voltage change of grid connection point 50 exceeds the threshold, voltage regulation control is performed according to the indication signal, and the power control equipment adjusts the reactive power to avoid erroneous adjustment.

[0069] like Figure 3 As shown in S110, the power conversion device 20 first calculates the reactive reference power Q1 based on the power device side voltage and the preset excitation voltage regulation method.

[0070] S120, the power conversion device 20 then estimates the grid-connected current vector based on the active power command P and the reactive power command Q.

[0071] S130, the power conversion device 20 estimates the voltage at the high-voltage side grid connection point 50 based on the equivalent impedance value issued by the power station controller 40.

[0072] In one embodiment, during the process of determining the estimated voltage of the grid connection point 50 according to the first indication signal, the power conversion device 20 is specifically used to determine the estimated voltage of the grid connection point 50 according to the device voltage of the power conversion device 20 and the equivalent impedance of the power supply system. The estimated voltage of the grid connection point 50 decreases as the equivalent impedance of the power supply system increases.

[0073] In the power supply system, when the power conversion device 20 is connected to the grid connection point 50, the voltage at the grid connection point 50 will decrease due to the presence of equivalent impedance. The larger the equivalent impedance of the system, the greater the voltage drop at the grid connection point 50. The power conversion device 20 can estimate the voltage at the high-voltage side of the grid connection point 50 based on the equivalent impedance issued by the power station controller 40. The power station controller 40 indicates the equivalent impedance to the power conversion device 20 instead of directly indicating the voltage at the grid connection point 50. The power conversion device 20 can estimate the voltage at the grid connection point 50 based on the equivalent impedance. Since the voltage at the grid connection point 50 changes constantly, if the voltage or reactive power is indicated in real time, the voltage regulation control will have a large delay and limited response speed due to the influence of communication bandwidth and time delay. However, the equivalent impedance is relatively fixed and changes slowly. After the power station controller 40 indicates the equivalent impedance to the power conversion device 20, the power conversion device 20 can calculate the reactive power value that needs to be adjusted based on the equivalent impedance, which is more rapid and less affected by communication bandwidth.

[0074] In one embodiment, the estimated voltage at grid connection point 50 satisfies:

[0075]

[0076] in, For the estimated voltage at grid connection point 50, U emf The device voltage for each power conversion device 20, Let ω be the current at grid connection point 50, ω be the angular frequency of each power conversion device 20, and L be the current at grid connection point 50. real This is the equivalent impedance of the power supply system.

[0077] In a power supply system, when power conversion devices 20 are connected to grid connection point 50, the voltage at grid connection point 50 will decrease due to the presence of equivalent impedance. The greater the equivalent impedance of the system, the greater the voltage drop at grid connection point 50. This voltage drop is calculated by subtracting the voltage drop caused by the equivalent impedance from the device voltage of each power conversion device 20. The voltage at grid connection point 50 can then be obtained.

[0078] S140, the power conversion device 20 calculates the reactive power reference based on the voltage of the high-voltage side grid connection point 50 and the preset excitation voltage regulation method.

[0079] In one embodiment, during the process of adjusting the reactive power output of the power conversion device 20 according to the estimated voltage of the grid connection point 50, each power conversion device 20 is specifically used to determine the reactive power reference value of the grid connection point 50 according to the estimated voltage of the grid connection point 50, and the change value of the reactive power reference value of the grid connection point 50 is proportional to the difference between the estimated voltage of the grid connection point 50 and a preset range.

[0080] The power conversion device 20 can calculate the reactive power reference value of the grid connection point 50 based on the estimated voltage of the grid connection point 50 and the preset excitation voltage regulation method. The change value of the reactive power reference value changes with the change of the estimated voltage. The larger the estimated voltage is from the preset range, the larger the change value of the reactive power reference value.

[0081] S150, the power conversion device 20 estimates the reactive power compensation amount of the high-voltage side grid connection point 50 based on the equivalent impedance value issued by the power station controller 40.

[0082] S160, the power conversion device 20 performs the final reactive power command according to the power conversion device 20.

[0083] In one embodiment, during the process of adjusting the reactive power output of the power conversion device 20 according to the first indication signal, each power conversion device 20 is further configured to determine the reactive power consumed by the equivalent impedance of the power supply system based on the equivalent impedance of the power supply system. The reactive power output of the power conversion device 20 is adjusted based on the reactive power reference value at the grid connection point 50 and the reactive power consumed by the equivalent impedance of the power supply system.

[0084] The power conversion device 20 first needs to estimate the reactive power reference value and estimate the current at the grid connection point 50. Then, based on the equivalent impedance and the current at the grid connection point 50, it estimates the voltage at the grid connection point 50 and the reactive power consumed by the impedance. Next, it updates the reactive power reference value based on the voltage at the grid connection point 50. Finally, the target value is obtained as the sum of the reactive power consumed by the impedance and the reactive power reference value.

[0085] In one embodiment, the reactive power output by the power conversion device 20 satisfies:

[0086] Q emf = ref +L real |I grid | 2 ,

[0087] Among them, Q emf Q is the target output power of the power conversion device 20. refLet ω be the reactive power reference value at grid connection point 50, and L be the angular frequency of each power conversion device 20. real This is the equivalent impedance of the power supply system.

[0088] According to the scheme of this application, the final reactive power of the power conversion device 20 can be accurately calculated by the above formula, which improves the accuracy of voltage regulation control of the power conversion device 20 and improves the operational stability of the power grid.

[0089] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A power supply system, characterized in that, The power supply system includes multiple power conversion devices, transformers, and a power station controller. The power conversion devices are connected to the power grid through the transformers, and the connection point between the transformers and the power grid is the grid connection point. The power station controller is configured to: generate a first indication signal for indicating the equivalent impedance of the power supply system based on the device voltage of the plurality of power conversion devices and the voltage of the grid connection point, and send the first indication signal to the plurality of power conversion devices; The power conversion device is used for: The estimated voltage of the grid connection point is determined based on the first indication signal; When the estimated voltage of the grid connection point exceeds the preset range, the reactive power output of the power conversion device is adjusted according to the estimated voltage of the grid connection point.

2. The power supply system according to claim 1, characterized in that, The equivalent impedance of the power supply system satisfies: Wherein, P is the active power dispatch command of the power grid, Q is the reactive power dispatch command of the power grid, and U... grid U is the voltage at the grid connection point. emf For each of the power conversion devices, the device voltage, δ pa For U grid and U emf The phase difference between them, ω, is the angular frequency of each of the power conversion devices, L real is the equivalent impedance of the power supply system, and j is the imaginary unit.

3. The power supply system according to claim 1 or 2, characterized in that, The power station controller is also used for: After a first time period following the transmission of the first indication signal, the voltage at the grid connection point is acquired; After the second period of sending the first indication signal, a second indication signal for indicating the equivalent impedance of the power supply system is generated and sent based on the device voltage of the plurality of power conversion devices and the voltage of the grid connection point. The length of the second period is greater than the length of the first period.

4. The power supply system according to claim 1 or 2, characterized in that, The power station controller is also used for: At a second moment after sending the first indication signal, when the change in the equivalent impedance of the power supply system is greater than a preset threshold, a second indication signal is sent to the power conversion device to indicate the changed equivalent impedance of the power supply system.

5. The power supply system according to any one of claims 1 to 4, characterized in that, When the first indication signal is sent to the plurality of power conversion devices, the first indication signal sent to at least two of the power conversion devices indicates that the equivalent impedance of the power supply system is different.

6. The power supply system according to any one of claims 1 to 5, characterized in that, In the process of determining the estimated voltage of the grid connection point based on the first indication signal, the power conversion device is specifically used for: The estimated voltage of the grid connection point is determined based on the device voltage of the power conversion equipment and the equivalent impedance of the power supply system. The estimated voltage of the grid connection point decreases as the equivalent impedance of the power supply system increases.

7. The power supply system according to claim 6, characterized in that, The estimated voltage at the grid connection point satisfies: in, U is the estimated voltage at the grid connection point. emf The device voltage for each of the power conversion devices, Let ω be the current at the grid connection point, and L be the angular frequency of each of the power conversion devices. real The equivalent impedance of the power supply system is given.

8. The power supply system according to any one of claims 1 to 7, characterized in that, In the process of adjusting the reactive power output of the power conversion equipment based on the estimated voltage of the grid connection point, each power conversion equipment is specifically used for: Based on the estimated voltage of the grid connection point, a reactive power reference value for the grid connection point is determined. The change in the reactive power reference value of the grid connection point is proportional to the difference between the estimated voltage of the grid connection point and the preset interval.

9. The power supply system according to claim 8, characterized in that, During the process of adjusting the reactive power output of the power conversion device according to the first indication signal, each power conversion device is further configured to: Based on the equivalent impedance of the power supply system, determine the reactive power consumed by the equivalent impedance of the power supply system. The reactive power output of the power conversion device is adjusted based on the reactive power reference value of the grid connection point and the reactive power consumed by the equivalent impedance of the power supply system.

10. The power supply system according to claim 9, characterized in that, The reactive power output of the power conversion device satisfies: Q emf =Q ref +ωL real |I grid | 2 Among them, Q emf Q represents the target output power of the power conversion device. ref Let ω be the reactive power reference value at the grid connection point, and L be the angular frequency of each of the power conversion devices. real The equivalent impedance of the power supply system is given.

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