Abstract

The two most common methods to measure insulation are AC current injection and resistive bridge. In general, the AC current injection method is flexible for various operating conditions and is widely used in DC charging but has higher complexity and cost compared to the resistive bridge method. Regardless of the method, the approach has to meet the standard requirements such as accuracy, response time, and operating voltage limits. One of the key challenges associated with the resistive bridge method is dealing with a large RC time constant. Some systems such as megawatt chargers require very large Y-capacitances (for example, 4µF). This application note discusses the design considerations for a resistive-bridge approach that is specially designed to deal with large Y-capacitances by employing a novel predictive algorithm to shorten the measurement time without requiring heavy computation such as floating-point operations.