考虑谐波的电动汽车充电策略及对配电网电缆载流能力和热寿命的影响

为避免电动汽车充电引起配网电缆过载,合理确定配电网电缆载流量,建立数学模型定量分析了两种充电功率模式在高峰和避峰充电时对配电网电缆温度和热寿命的影响。该模型考虑了电动汽车充电的时间特性和谐波特性,以渗透率和谐波含量为参数构建了电动汽车充电功率和配电网电缆电流的数学方程,基于IEC 60287定量分析了谐波电流含量对电缆交流电阻、钢带屏蔽层磁滞和涡流损耗导致的电缆温升影响,最后基于Arrhenius模型建立了电缆温度和热寿命间的数学关系。该模型选取一典型城市配电网,针对高峰和避峰时间段各采用高功率和低功率共4种充电模式进行了仿真分析,设置居民负荷电流峰值为70%电缆额定电流,结果表明,在30%渗透率下,电动汽车充电行为提升了配网电缆温度26.19℃,若不计谐波影响,温升为20.89℃,电动汽车谐波对电动汽车充电行为引起的配电网电缆温升的贡献为20.17%;夏季高峰高功率模式在30%渗透率下会引起配网电缆过载;低功率避峰充电策略下配电网电缆温度最低,电缆寿命损失最小,用户充电费用最少。

Impact of EV Charging Strategies on Ampacity and Thermal Life of Distribution Cables with Consideration of Harmonic Distortions

In order to avoid overloading of distribution cables dues to electric vehicles(EVs) charging and determine suitable ampacity, this paper presents a methodology for modeling and analyzing the cable temperature and thermal life when EVs are charged using four strategies, e.g. low/high power uncontrolled domestic charging and off-peak domestic charging. The model is formulated to predict the current of distribution cable by taking into account the stochastic nature of the charging power, start time of individual charging, and harmonic wave characteristic. Then, analytical solution of the cable temperature is deduced based on IEC 60287 equations, and the influences of harmonic waves on additional AC resistance of conductors, hysteresis loss and eddy current loss of armor layer are analyzed. Finally, thermal life of distribution cable is predicted by Arrhenius model(AM). A typical distribution system with residential load ratio of 0.7 is adopted as an example of simulation. The results of a 30% penetration of EVs in the simulation show that the temperature of distribution cable will increase by 26.19 ℃, and will increase by 20.89 ℃ if the harmonic wave is not taken into consideration. The contribution of harmonic waves to the temperature increment is 20.17%. High power uncontrolled domestic charging will result in overloading of distribution cable at a 30% penetration level in summer. Low power off-peak domestic charging is the recommended as a charging strategy with the lowest cable temperature, thermal life loss, and charging expenses.