A method and system for evaluating time-varying harmonic current during electric vehicle charging

Abstract

The invention provides an electric vehicle charging process time-varying harmonic current evaluation method and system. The evaluation method comprises the following steps: respectively carrying out Fourier analysis on actually measured voltage and current data of each stage in the charging process of the electric vehicle to obtain each harmonic vector value of the voltage and the current, and obtaining prior distribution of the voltage through Fourier function fitting; calculating reference harmonic cross-symmetric component model parameters of each stage according to the condition that the product of the reference harmonic cross-symmetric component model parameters of each stage and the reference voltage points of the corresponding stage is equal to the reference current of the corresponding stage; calculating the equivalent resistance of the charging process of the electric vehicle according to the actually measured voltage and current data of each stage of the charging process of the electric vehicle, and fitting a change curve of the equivalent resistance of the charging process of the electric vehicle; according to the change of equivalent resistance in the charging process of the electric vehicle, adjusting reference harmonic cross-symmetric component model parameters of each stage, and then calculating real-time current evaluation values of each time in the charging process of the electric vehicle.

Description

technical field [0001] The disclosure belongs to the field of electric vehicle charging, and in particular relates to a time-varying harmonic current evaluation method and system during the charging process of an electric vehicle. Background technique [0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art. [0003] With the increasing shortage of energy and environmental pollution, electric vehicles emerged as a new type of transportation with low pollution and zero fuel consumption. The world attaches great importance to the exploration and development of electric vehicles. The main equipment used in the charging station is a power electronic device charger with nonlinear load characteristics. Under normal operating conditions, the charging station will generate harmonic currents of different frequencies, which will be generated through the grid-connected port connected to t...

AI Technical Summary

Problems solved by technology

The main equipment used in the charging station is a power electronic device charger with nonlinear load characteristics. Under normal operating conditions, the charging station will generate harmonic currents of different frequencies, which will be generated through the grid-connected port connected to the charging station. Connecting to the distribution network, in order to achieve fast charging, the charging power of electric vehicles is usually large, resulting in a high value of harmonic current injected into the distribution network by each electric vehicle. Neglected effects, such as: reducing the power quality of the system, reducing the power factor of the power system, and causing voltage loss and system three-phase imbalance, causing overload problems such as lines and transformers, and increasing the peak-to-valley difference of the system again. The operating efficiency is low, and it is prone to power supply shortage in some areas of the power grid

[0004] At present, there have been some studies on the harmonic modeling of electric vehicles. The common method is to build an uncontrolled rectification bridge circuit, establish a harmonic coupling admittance matrix model of the circuit, and use nonlinear time-varying resistance to approximate the rectification circuit part of the charging device. Equivalent input impedance, the inventor found that large-scale electric vehicle charging stations have added certain reactive power compensation and passive filter devices, and it is difficult to accurately determine their circuit topology

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