Accurate Condition Monitoring of Semiconductor Devices in Cascaded H-Bridge Modular Multilevel Converters

Abstract

This paper presents an online condition monitoring (CM) scheme for semiconductors used in modular multilevel converters (MMCs) that comprise cascaded H-bridge submodules. The CM algorithm is based on detecting changes in the ONstate resistance of the semiconductors over time. The proposed method is shown to successfully perform a curve-tracing of semiconductors in MMCs while the semiconductor junction remains at a temperature that is readily measurable and undergoes minute changes during the measurement process. The ON-state resistance value is estimated from the measured ON-state voltage drop of the semiconductors and the measured arm current. Measuring the ON-state resistance at known temperatures allows for separating temperature-dependent variations of the ONstate resistance from age-dependent variations of this parameter. Suitable methods for reducing the effect of noise on the curvetraced data are proposed, and a recursive least square (RLS) estimator is used to extract the optimum ON-state resistance from the traced vCE − iC curve. Simulation results show that the proposed scheme can accurately determine the ON-state resistance of semiconductors at a known temperature and under various levels of measurement noise. Moreover, experimental results on a low-power prototype show that the proposed scheme is applicable in practice, and provides similar online curves to what a commercial curve tracer can produce offline. The experimental verification has been conducted under constant load conditions; however, the proposed methods can be used under any variable load condition as well.

A Novel ON-State Resistance Estimation Technique for Online Condition Monitoring of Semiconductor Devices Under Noisy Conditions

“…Moreover, an online measurement system must be able to withstand the high voltages of the semiconductor device while it is in OFF state. Several semiconductor ONstate voltage measurement circuits have been introduced in the literature that provide both protection against high voltages, and accurate voltage measurement while the semiconductor is ON [18], [21]- [23]. In this article, the isolation circuit based on self-triggering depletion-mode MOSFETs is used.…”

“…In this paper, a single-position design is considered for the DM-MOSFETs, however, scalability of this circuit design for higher voltages has been demonstrated in [31]. A detailed explanation of the selected isolation circuit is presented in [23]. The main components used in the PCB of Fig.…”

“…Although the measurement circuit based on DM-MOSFET is superior to the double-diode system in maintaining low measurement errors, it is shown in this paper that measurement noise can cause large errors in the estimated ON-state resistance [23], [24]. Therefore, it is important to devise post-processing algorithms that allow accurate estimation of the ON-state resistance in noisy environments.…”

“…In [16], [21]- [23], depletion mode MOSFETs (DM-MOSFETs) are used for protecting the measurement circuit from the OFF-state voltage. This design is shown to also have a high bandwidth when a small resistance is placed between the gate-source terminals of the DM-MOSFETs [16].…”

“…In [8], estimation errors of ±3% are reported, however, the comparison is made with datasheet information, rather than offline measurements with curve tracers. A unique method of accurate ON-state resistance estimation is proposed in [23], where the effect of noise and offsets are considered. This method is only applicable to modular multilevel converters, where the existing redundancies are leveraged for achieving a high estimation accuracy.…”