Each test condition includes ten IMD measurements for statistical analysis (mean and standard deviation). Fixed-point math error is significant in some cases. Overall, the measurement errors and response time are well below the UL 2231-2 requirements (±15%, 10 seconds).

In Figure 3-6, for asymmetric faults, the error displayed is the Riso in the fault condition. The "1MΩ-1MΩ" case requires a 3s cycle to resolve due to a very large time constant.

Figure 3-6 IMD Riso Measurement Error, 1000VDC, 2s Cycle

Figure 3-7 IMD Ciso Error, 1MΩ to 100kΩ, 2s Cycle

In Figure 3-8, the relatively short time constant means that prediction for the final steady-state voltages is not necessary.

Figure 3-8 Switching Waveform Capture for 800VDC, 0.1µF, 1MΩ Symmetrical Condition

In Figure 3-9, the relatively long time constant means that prediction for the final steady-state voltages is necessary.

Figure 3-9 Switching Waveform Capture for 800VDC, 1µF, 1MΩ Symmetrical Condition

Figure 3-10 shows the switching timing diagram. Note that each switch state stays on for about 980ms. The ADC sampling period is about 1ms. The computation time after the ADC acquisition period is about 1.98ms.

Figure 3-10 Switching Timing Diagram

Figure 3-11 shows a computation time of about 2ms, which includes all of the math computations such as prediction and solving for the unknowns.

Figure 3-11 Zoomed-in Timing Diagram