电动汽车绝缘电阻测量方法研究

Research on the Measurement Method of Insulation Resistance of Electric Vehicle

GB/T 18384.1—2015[1]给出了电动汽车有源电路绝缘电阻测量方法,该方法的绝缘电阻计算公式中包含有电压参数。然而如果用电压表直接测量电路电压,其测量值往往不能反映被测电路的真实电压,因此也不会得出正确的计算结果。为此,文章通过分析电压表内阻对电路的影响,推导出测量值与理论值接近程度的表达式,并据此提出了一种新的绝缘电阻测量方法,其核心做法就是在电路中并入一对至少小于电压表内阻2个数量级的等值电阻,这样,电压表对该电路的测量值就可以代表该电路的被测电压值,其计算结果是绝缘电阻与并入电阻的并联值,再通过电阻并联公式就可以得出正确的绝缘电阻值。最后,文章对GB 18384—2020[2]的绝缘电阻测量方法从理论和实践两个维度上提出了思考。

GB/T 18384.1—2015[1]gives a method for measuring the insulation resistance of the active circuit of electric vehicles.The calculation formula of the insulation resistance of this method includes voltage parameters.However,if a voltmeter is used to measure the circuit voltage directly,the measured value will often not reflect the true voltage of the circuit under test,therefore the calculation results will not be right.To solve such problems,this paper analyzes the influence of the internal resistance of the voltmeter on the circuit,and derives the expression of the degree of closeness between the measured value and the theoretical value.Based on analysis above,a new method of insulation resistance measurement is proposed.The core is to incorporate a pair of equivalent resistances that are at least two orders of magnitude smaller than the internal resistance of the voltmeter in the circuit,so that the measured voltage of the voltmeter can represent the circuit voltage,and the calculated result is the parallel value of the insulation resistance and the incorporated resistance.And then the correct insulation resistance value can be obtained through the resistance parallel formula.Finally,this paper puts forward thinking from the two dimensions of theory and practice to the insulation resistance measurement method of GB 18384—2020[2].