Robust Stability Analysis of Active Voltage Control for High-power IGBT Switching by Kharitonov's Theorem

Abstract

The main idea of Active Voltage Control (AVC) is to employ classic feedback-control methods forcing the IGBT collector voltage transient to follow a predefined trajectory. This feedback control of IGBTs has great advantages in guaranteeing that IGBTs remain in Safe Operating Area (SOA), restricting EMI, mitigating the voltage/current stress, minimizing/predicting their power losses and balancing voltages of IGBTs in series. Inevitably, however, AVC introduces stability issues. Based on the assumption that accurate IGBT small-signal model parameters are available, an analogue Proportional-Derivative (PD) and multi-loop feedback control was proposed to achieve stable performance in previous work. Due to nonlinearities and uncertainties in IGBT parameters, previous stability analysis methods have important limitations. This work uses Kharitonov's theorem during the IGBT controlled turn-off to assess the system's stability and guide the AVC design to account for model uncertainties and varying parameters. We conducted experiments to investigate the system's robust stability due to these uncertainties in the IGBT parameters, which confirm the validity of the proposed theoretical analysis. With the use of wide bandwidth op-amps it is shown that the feedback design may be simplified.

Sufficient Condition-Based Stability Analysis of a Power Converter Applied Switching Transient Waveform Modification Using Kharitonov’s Theorem

“…The DC voltage was set to be 30 V. The reference waveform was formed with an arbitrary waveform generator. It has been proposed in [11] that the stability of the closed-loop gate drive for switching transient modification can be accessed by the appearance of the gate-source voltage with the reference voltage as input. The switching waveforms during turn-off under Design I, Design II, Design III, and Design IV are shown in Figure 5.…”

“…The turn-off switching transient can be divided into five subintervals. The minimum and maximum values of V DS , C dg , and C ds in each subinterval can be calculated by (10), (11), and (12), as shown in Table 2. For different circuit designs, the ranges of the parameters c 0 , c 1 , c 2 , c 3 , c 4 , and c 5 in (8) can be obtained by substituting the parameters in Tables 1 and 2 into (7) and (9).…”

“…Furthermore, the corresponding small signal model parameters rely on the accuracy of the device model and would not be easily extracted. The work in [11] followed from [10] and made some improvements. To overcome the aforementioned limitations, different estimation ranges were attached to the corresponding parameters for each operating point.…”

“…This signal was used as the reference waveform for the closed-loop gate drive circuit in the following investigation. This paper follows from [11] by using Kharitonov's Theorem to achieve a sufficient condition-based stability analysis of the applied switching transient waveform modification of a power converter. In Section 2, a closed-loop gate drive prototype for switching transient waveform modification is presented.…”

Comprehensive Study on Gate Driver for SiC-MOSFETs with Gate Boost

“…This circuit works stably but it requires an additional inverting gate that introduces a time delay tdnot. The boost delay time tdbst for this circuit is calculated in (13).…”