Method for measuring electrical isolation of a vehicle chassis
View Patent ↗A method for measuring the isolation resistance between a chassis and a battery terminal in an electric vehicle. The method can include measuring an open voltage (VP(open)) of the positive terminal; measuring an open voltage (VN(open)) of the negative terminal; measuring a voltage (VN(S 1 closed)) between the negative terminal and the chassis with switch S 1 closed; measuring a voltage (VP(S 1 closed)) between the positive terminal and the chassis with switch S 1 closed; calculating the ratio (VP(open)/VN(closed)) of the voltages VP(open) and VN(closed); calculating the open ratio of the open voltages (VP(open)/VN(open)); calculating the difference between the ratio (VP(S 1 closed)/VN(S 1 closed)) and the open ratio (VP(open)/VN(open)); and multiplying the value of the test resistor (R 0 ) by the difference between the ratio (VP(S 1 closed)/(VN(S 1 closed)) and the open ratio (VP(S 2 open)/VN(S 1 open)) to obtain the isolation resistance.
1. A method of determining an isolation resistance between a chassis and a battery, the battery having a positive terminal and a negative terminal, the positive terminal connectable to the chassis via a switch S 2 , the negative terminal connectable to the chassis via a switch S 1 , the method comprising the steps of:
opening both switch S 1 and switch S 2 ;
measuring an open voltage (VP(open)) of the positive terminal when both switch S 1 and switch S 2 are open;
measuring an open voltage (VN(open)) of the negative terminal when both switch S 1 and switch S 2 are open;
closing switch S 1 while leaving switch S 2 open;
measuring a voltage (VN(S 1 closed)) between the negative terminal and the chassis with switch S 1 closed;
measuring a voltage (VP(S 1 closed)) between the positive terminal and the chassis with switch S 1 closed;
calculating the ratio (VP(S 1 closed)/VN(S 1 closed)) of the voltages VP(S 1 closed) and VN(S 1 closed);
calculating the open ratio of the open voltages (VP(open)/VN(open);
calculating the difference between the ratio (VP(S 1 closed)/VN(S 1 closed)) and the open ratio (VP(open)/VN(open)); and
multiplying the value of a test resistor by the difference between the ratio (VP(S 1 closed)/VN(S 1 closed)) and the open ratio (VP(open)/VN(open)) to obtain the isolation resistance.
2. The method of claim 1 wherein the voltage VN(S 1 closed) is measured across the test resistor.
3. The method of claim 2 wherein the test resistor is 4M Ohms to 10 M Ohms.
4. The method of claim 1 wherein switch S 1 is an isolated MOSFET switch.
5. The method of claim 1 wherein further comprising the step of isolating the battery if the isolation resistance is determined to be less than a specified value.
6. The method of claim 1 wherein the determination of isolation resistance is made while the battery is supplying power to a motor.
7. A method of determining an isolation resistance between a chassis and a battery, the battery having a positive terminal and a negative terminal, the positive terminal connectable to the chassis via a switch S 2 , the negative terminal connectable to the chassis via a switch S 1 , the method comprising the steps of:
opening both switch S 1 and switch S 2 ;
measuring an open voltage (VP(open)) of the positive terminal when both switch S 1 and switch S 2 are open;
measuring an open voltage (VN(open)) of the negative terminal when both switch S 1 and switch S 2 are open;
closing switch S 2 while leaving switch S 1 open;
measuring a voltage (VN(S 2 closed)) between the positive terminal and the chassis with switch S 2 closed;
measuring a voltage (VP(S 2 closed)) between the positive terminal and the chassis with switch S 2 closed;
calculating the ratio (VN(S 2 closed)/VP(S 2 closed)) of the voltages VP(S 2 closed) and VN(S 2 closed);
calculating the open ratio of the open voltages (VN(open)/VP(open));
calculating the difference between the ratio (VN(S 2 closed)/VP(S 2 closed)) and the open ratio (VN(open)/VP(open)); and
multiplying the value of a test resistor by the difference between the ratio (VN(S 2 closed)/VP(S 2 closed)) and the open ratio (VN(open)/VP(open)) to obtain the isolation resistance.
8. The method of claim 7 wherein the voltage VP(S 2 closed) is measured across the test resistor.
9. The method of claim 8 wherein the test resistor is 4M Ohms to 10 M Ohms.
10. The method of claim 7 wherein switch S 2 is an optoisolated MOSFET switch.
11. The method of claim 7 wherein further comprising the step of isolating the battery if the isolation resistance is determined to be less than a specified value.
12. The method of claim 7 wherein the determination of isolation resistance is made while the battery is supplying power to a motor.