A method for controlling harmonics in vehicle-to-grid interaction

Abstract

This invention provides a method for controlling harmonics in vehicle-to-grid (V2G) interaction. The method includes: when an electric vehicle connects to a charging pile, a primary filtering is performed using a pile-level power filter; a waveform recorder acquires the filtered voltage and current waveforms; a cloud-based master station calculates the harmonic quantities of the received voltage and current waveforms; a charging station-level control terminal generates a station-level power filter control strategy based on the received harmonic quantities and distributes the strategy to the station-level power filter; and the station-level power filter performs secondary filtering based on the received control strategy, reducing the harmonic content of V2G interaction. This invention achieves secondary filtering by determining the corresponding station-level power filter control strategy based on real-time waveforms and controlling power in real-time during the filtering process. It determines a suitable control strategy during V2G interaction to suppress harmonics and reduce power quality problems caused by V2G interaction.

Description

Technical Field

[0001] This invention relates to the field of vehicle-to-grid interaction harmonic control technology, and in particular to a method for controlling vehicle-to-grid interaction harmonics. Background Technology

[0002] Under the development strategy of energy conservation and emission reduction, electric vehicles have become one of the green and energy-saving means of transportation. They use electricity as their driving force and batteries as their energy storage devices, effectively solving problems such as energy waste and environmental pollution. Charging facilities are a crucial prerequisite for ensuring the promotion and widespread adoption of electric vehicles. However, with the number of electric vehicles increasing year by year, the large number of electric vehicle charging operations inevitably increases the load on the power grid, leading to problems such as transformer overload and power distribution line faults, potentially causing power quality deterioration and generating power grid harmonics. This is mainly manifested in the following ways: the operation of multiple chargers in a charging station will inevitably inject a large amount of harmonic current into the power grid; and because the front-stage rectifiers of high-power DC chargers often use high-frequency switching devices, ultra-high order harmonics in the range of 2–150kHz will also be introduced into the power grid during operation.

[0003] Furthermore, the massive integration of electric vehicles (EVs) enables vehicle-to-grid (V2G) interaction with the power grid. In the design and implementation of this V2G system, on the one hand, EVs act as loads, and the charging and discharging devices of their power batteries utilize numerous switching devices, which themselves are sources of harmonic pollution. On the other hand, EVs act as energy storage micro-sources, and the diverse types of loads on the power system's load side, along with the increasing penetration of nonlinear components such as power electronic devices, inevitably pose challenges to the power quality of the V2G system. When EVs connect to the grid with local loads, it is desirable for them to simultaneously provide standard three-phase sinusoidal voltage to both the load and the grid, injecting clean current into the grid, reducing grid losses, and improving grid efficiency. Therefore, it is crucial to address the power quality issues caused by EVs acting as both power sources and loads, and to improve the reliability of power supply.

[0004] In conclusion, appropriate control strategies are needed during vehicle-to-grid (V2G) interaction to suppress harmonics and reduce power quality issues caused by V2G interaction. Summary of the Invention

[0005] The purpose of this invention is to propose a method for controlling harmonics in vehicle-to-grid (V2G) interaction, addressing the technical problem of suppressing harmonics and reducing power quality issues caused by V2G interaction.

[0006] On the one hand, a method for controlling harmonics in vehicle-to-grid (V2G) interaction is provided, applied to a V2G system connected to the power grid. The V2G system includes at least a cloud-based master station, a charging station-level control terminal connected to the cloud-based master station, and a charging pile connected to the charging station-level control terminal. The charging station-level control terminal also includes a waveform recorder and a station-level power filter, and the charging pile also includes a pile-level power filter.

[0007] When an electric vehicle connects to the charging pile, it completes a filtering process through the pile-level power filter.

[0008] The waveform recorder acquires the filtered voltage and current waveforms and transmits the acquired voltage and current waveforms to the cloud main station;

[0009] The cloud-based main station responds to the corresponding calculation requests, calculates the received voltage and current waveforms, obtains the harmonic quantities of each waveform, and sends them to the charging station-level control terminal.

[0010] The charging station-level control terminal generates a station-level power filter control strategy based on the received waveform harmonic quantities and sends the station-level power filter control strategy to the station-level power filter.

[0011] The station-level power filter performs secondary filtering according to the received station-level power filter control strategy, reducing the harmonic content of vehicle-to-grid interaction to a preset acceptable value.

[0012] Preferably, it further includes:

[0013] When the pile-level power filter completes one filtering cycle, it connects the electric vehicle to the vehicle-to-grid interaction system.

[0014] Preferably, it further includes:

[0015] After acquiring the filtered voltage and current waveforms, the waveform recorder transmits the acquired voltage and current waveforms to the charging station-level control terminal.

[0016] The charging station-level control terminal transmits the acquired waveform to the cloud master station and outputs a calculation request to the cloud master station.

[0017] Preferably, the harmonic order that the pile-level power filter can suppress is determined according to the following formula:

[0018]

[0019] Where n represents the harmonic order that can be suppressed, L represents the capacitance value of the pile-level power filter, C represents the value of the pile-level power filter, and f is the voltage and current frequency of the power grid.

[0020] Preferably, the station-level power filter consists of a compensation device, a current-source inverter, and a constant current source. Based on the received station-level power filter control strategy, it outputs a corresponding harmonic compensation current through the compensation device, the current-source inverter, and the constant current source to suppress harmonics.

[0021] Preferably, it further includes:

[0022] When executing the station-level power filter control strategy, the station-level power filter monitors its own power adjustment range in real time.

[0023] When the adjustable range reaches the preset limit, an adjustment signal is generated and sent to the charging station-level control terminal.

[0024] Preferably, it further includes:

[0025] After receiving the signal from the station-level power filter, the charging station-level control terminal obtains the power adjustable parameters of each charging pile in the station, and determines the power adjustment strategy of each charging pile based on the obtained power adjustable parameters.

[0026] The charging station-level control terminal sends corresponding power adjustment strategies to each charging pile within the station.

[0027] Preferably, it further includes:

[0028] The charging piles adjust the power of each charging pile according to the received power adjustment strategy to adjust the interaction power of the vehicle network.

[0029] The charging station-level control terminal monitors the adjusted harmonic content in real time and adjusts the power adjustment strategy of each charging pile according to the real-time harmonic content to control the corresponding harmonic content within an acceptable range.

[0030] In summary, implementing the embodiments of the present invention has the following beneficial effects:

[0031] The present invention provides a method for controlling harmonics in vehicle-to-grid interaction. Charging piles are connected to corresponding pile-level power filters to complete primary filtering; a waveform recorder records the waveform and connects to a charging station-level control terminal for information exchange; the charging station-level control terminal is connected to a station-level power filter for control; the station-level power filter is connected to the power grid to complete secondary filtering. Secondary filtering is achieved by determining the real-time waveform and the corresponding station-level power filter control strategy, and power is controlled in real-time during the filtering process. A suitable control strategy is determined during vehicle-to-grid interaction to suppress harmonics and reduce power quality problems caused by vehicle-to-grid interaction. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0033] Figure 1 This is a schematic diagram of a vehicle-to-everything (V2X) interactive system according to an embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of the main flow of a vehicle-to-grid interactive harmonic control method according to an embodiment of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0036] like Figure 1 The diagram shows the architecture of the vehicle-to-grid (V2G) interaction system connected to the power grid in this application. The V2G interaction system includes at least a cloud-based master station, a charging station-level control terminal connected to the cloud-based master station, and charging piles connected to the charging station-level control terminal. The charging station-level control terminal also includes a waveform recorder and a station-level power filter. Each charging pile also includes a pile-level power filter. Each of the n charging piles in the station is connected to its corresponding pile-level power filter to complete primary filtering. All pile-level power filters are connected together and connected to the power grid and the waveform recorder. The waveform recorder records waveforms and is connected to the charging station-level control terminal for information exchange. The charging station-level control terminal is connected to the cloud-based master station for information exchange and is also connected to the station-level power filter for control. Furthermore, the charging station-level control terminal is also connected to each charging pile to control each charging pile. The station-level power filter is connected to the power grid to complete secondary filtering.

[0037] like Figure 2 The diagram shown is a schematic representation of an embodiment of a vehicle-to-grid (V2G) harmonic control method provided by the present invention. In this embodiment, the method includes the following steps:

[0038] Step S1: When the electric vehicle is connected to the charging pile, a filtering process is completed through the pile-level power filter.

[0039] Step S2: The waveform recorder acquires the filtered voltage waveform and current waveform, and transmits the acquired voltage waveform and current waveform to the cloud main station;

[0040] Step S3: The cloud master station responds to the corresponding calculation request to calculate the received voltage waveform and current waveform, obtain the harmonic quantities of each waveform, and send them to the charging station-level control terminal.

[0041] Step S4: The charging station-level control terminal generates a station-level power filter control strategy based on the received waveform harmonic quantities and sends the station-level power filter control strategy to the station-level power filter.

[0042] In step S5, the station-level power filter performs secondary filtering according to the received station-level power filter control strategy to reduce the harmonic content of vehicle-to-grid interaction to a preset acceptable value.

[0043] In other words, after an electric vehicle connects to a charging pile and undergoes primary filtering by a pile-level power filter, it interacts with the power grid. A waveform recorder acquires the voltage and current waveforms after primary filtering and sends them to the charging station-level control terminal. The charging station-level control terminal then sends the acquired waveforms to the cloud master station and requests calculation. The cloud master station performs FFT calculations on the received waveforms, generating harmonic quantities and sending them to the charging station-level control terminal. Based on the received FFT results, the charging station-level control terminal calculates and generates a station-level power filter control strategy and sends the strategy to the station-level power filter. The station-level power filter executes the received control strategy to complete secondary filtering, reducing the harmonic content of the vehicle-grid interaction to an acceptable value. Here, FFT refers to the Fast Fourier Transform; the details of FFT are not elaborated upon here.

[0044] In a specific embodiment, when the pile-level power filter completes its first filtering step, it connects the electric vehicle to the vehicle-to-grid (V2G) system. The first filtering step can only remove harmonics of a fixed order. However, in the actual process of V2G interaction, various harmonics exist, necessitating a second filtering step to further reduce the harmonic content.

[0045] Specifically, after acquiring the filtered voltage and current waveforms, the waveform recorder transmits the acquired voltage and current waveforms to the charging station-level control terminal.

[0046] The charging station-level control terminal transmits the acquired waveform to the cloud master station and outputs a calculation request signal to the cloud master station.

[0047] In this embodiment, each charging pile of a charging station is equipped with a pile-level power filter. The pile-level power filter is a passive power filter, that is, it uses a combination of inductors and capacitors to filter fixed high-order harmonics. The harmonic order that the pile-level power filter can suppress is determined according to the following formula:

[0048]

[0049] Where n represents the harmonic order that can be suppressed, L represents the capacitance value of the pile-level power filter, C represents the value of the pile-level power filter, and f is the voltage and current frequency of the power grid, typically 50Hz. Under these conditions, harmonics of the corresponding order will flow into the passive filter instead of flowing into the power grid, thus achieving primary filtering of harmonics.

[0050] In this embodiment, the station-level power filter consists of a compensation device, a current-source inverter, and a constant current source. Based on the received station-level power filter control strategy, it outputs a corresponding harmonic compensation current through the compensation device, the current-source inverter, and the constant current source to suppress harmonics. The station-level power filter is an active power filter, which consists of a compensation device, a current-source inverter, and a constant current source. It can output a corresponding harmonic compensation current according to the received control strategy, thereby suppressing harmonics.

[0051] In this embodiment, multiple charging piles are typically available at a single charging station. Since the adjustable range of the active power filter is limited, a power control strategy is needed to further ensure that harmonic suppression remains within acceptable limits. The power control strategy is as follows:

[0052] When executing the station-level power filter control strategy, the station-level power filter monitors its own power adjustment range in real time.

[0053] When the adjustable range reaches the preset limit, an adjustment signal is generated and sent to the charging station-level control terminal.

[0054] After receiving the signal from the station-level power filter, the charging station-level control terminal obtains the power adjustable parameters of each charging pile in the station, and determines the power adjustment strategy of each charging pile based on the obtained power adjustable parameters.

[0055] The charging station-level control terminal sends the corresponding power adjustment strategy to each charging pile in the station.

[0056] The charging piles adjust the power of each charging pile according to the received power adjustment strategy to adjust the interaction power of the vehicle network.

[0057] The charging station-level control terminal monitors the adjusted harmonic content in real time and adjusts the power adjustment strategy of each charging pile according to the real-time harmonic content to control the corresponding harmonic content within an acceptable range.

[0058] In other words, the station-level power filter monitors its adjustable range in real time during the execution of the control strategy. When the adjustable range reaches the limit, it sends a signal to the charging station-level control terminal. The charging station-level control terminal receives the signal from the station-level power filter and calculates the adjustable power range of each charging pile in the station. The charging station-level control terminal sends the power adjustment strategy to each charging pile in the station. The charging pile receives the power adjustment strategy from the charging station-level control terminal and adjusts the vehicle-to-grid interaction power. The charging station-level control terminal monitors the harmonic content after adjustment in real time to ensure that it is within an acceptable range.

[0059] In summary, implementing the embodiments of the present invention has the following beneficial effects:

[0060] The present invention provides a method for controlling harmonics in vehicle-to-grid interaction. Charging piles are connected to corresponding pile-level power filters to complete primary filtering; a waveform recorder records the waveform and connects to a charging station-level control terminal for information exchange; the charging station-level control terminal is connected to a station-level power filter for control; the station-level power filter is connected to the power grid to complete secondary filtering. Secondary filtering is achieved by determining the real-time waveform and the corresponding station-level power filter control strategy, and power is controlled in real-time during the filtering process. A suitable control strategy is determined during vehicle-to-grid interaction to suppress harmonics and reduce power quality problems caused by vehicle-to-grid interaction.

[0061] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for controlling harmonics in vehicle-to-grid (V2G) interaction, applied to a V2G system connected to a power grid, wherein the V2G system includes at least a cloud-based master station, a charging station-level control terminal connected to the cloud-based master station, and a charging pile connected to the charging station-level control terminal, wherein the charging station-level control terminal further includes a waveform recorder and a station-level power filter, and the charging pile further includes a pile-level power filter, characterized in that... The method comprises the following steps: When the electric vehicle accesses the charging pile, the first filtering is completed by the pile-level power filter; The waveform recorder acquires the filtered voltage waveform and current waveform, and transmits the acquired voltage waveform and current waveform to the cloud host station; The cloud host station performs FFT calculation on the received voltage waveform and current waveform in response to the corresponding calculation request, obtains the harmonic content of the waveform, and issues the harmonic content to the charging station-level control terminal; The charging station-level control terminal generates a station-level power filter control strategy according to the received harmonic content of the waveform, and issues the station-level power filter control strategy to the station-level power filter; The station-level power filter performs the second filtering according to the received station-level power filter control strategy, and reduces the harmonic content of the vehicle-to-grid interaction to a preset acceptable value.

2. The method of claim 1, wherein, Further comprising: When the pile-level power filter completes the first filtering, the electric vehicle is connected to the vehicle-to-grid interaction system.

3. The method of claim 2, wherein, Further comprising: After the waveform recorder acquires the filtered voltage waveform and current waveform, the acquired voltage waveform and current waveform are transmitted to the charging station-level control terminal; The charging station-level control terminal transmits the acquired waveform to the cloud host station and outputs a calculation request signal to the cloud host station.

4. The method of claim 3, wherein, The pile-level power filter determines the suppressible harmonic order according to the following formula: Wherein, n represents the suppressible harmonic order, L represents the value of the capacitance of the pile-level power filter, C represents the value of the pile-level power filter, and f is the voltage and current frequency of the power grid.

5. The method of claim 4, wherein, The station-level power filter is composed of a compensation device, a current-type inverter and a constant current source, which outputs the corresponding harmonic compensation current through the compensation device, the current-type inverter and the constant current source according to the received station-level power filter control strategy, to realize the suppression of harmonics.

6. The method of claim 5, wherein, Further comprising: When the station-level power filter executes the station-level power filter control strategy, it real-time monitors the adjustable range of its power; When the adjustable range reaches the preset limit, an adjustment signal is generated and sent to the charging station-level control terminal.

7. The method of claim 6, wherein, Further comprising: After the charging station-level control terminal receives the signal of the station-level power filter, it acquires the power adjustable parameters of each charging pile in the station, and determines the power adjustment strategy of each charging pile according to the acquired power adjustable parameters; The charging station-level control terminal sends the corresponding power adjustment strategy to each charging pile in the station.

8. The method of claim 7, wherein, Further comprising: The charging pile adjusts the interaction power of the vehicle-to-grid according to the received power adjustment strategy by adjusting the power of each charging pile; The charging station-level control terminal real-time monitors the adjusted harmonic content, and adjusts the power adjustment strategy of each charging pile according to the real-time harmonic content to control the corresponding harmonic content within the acceptable range.

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