On lifetime evaluation of medium‐voltage drives based on modular multilevel converter

Abstract

Reliability is an important issue related to the modular multilevel converter (MMC)-based medium voltage (MV) drives. The design for reliability (DFR) approach has been discussed in many power electronic systems in recent years. MMC-based MV drives power losses and thermal cycling are strongly affected by start-up and low-speed operation, since zero-sequence current injection must be applied. In order to implement fast thermal simulations, the traditional DFR approach does not consider the heat sink thermal capacitance, which can significantly affect the MMC lifetime prediction. This article discusses how the heat sink realisations (material, thickness) affect the MMC-predicted lifetime and evaluates how the drive start-up time affects the damage in the power converter. The case study is based on a 1.4 MW slurry pump system driven by a three-phase induction motor. The lifetime evaluation of the MMC is realised through the Monte-Carlo simulation. The results show that the traditional approach results in an underestimation of up to 42.5% of the converter lifetime. In addition, long start-up times lead to a longer lifetime when compared to the shorter start-up times, due to the reduced thermal stresses in the semiconductors.

A Novel Method for Operation Monitoring of Thyristor Converter Based on Real‐Time Virtual Measurement of Valve Current in LCC‐HVDC

“…As for the power dissipation of high-power modules, voltage drop of the thyristor after it is conducted is related to both the current and the temperature. The power dissipation can be expressed by the exponential function as (11) represents: (11) where V f is the on-state voltage, I is the forward current, I s is the saturation current, V gT is the forbidden gap under different temperature, k is Boltzmann's constant, T is the absolute thyristor junction temperature, q is the electron charge, R s is the equivalent resistance in the conducting state of the thyristor, T ref is the reference temperature (usually 300 K), and k rs is the temperature exponential coefficient of the series-connected resistance.…”

“…In addition to determining a calculation for valve loss, an equivalent circuit model has to be constructed to bridge valve loss and valve temperature [7][8][9][10][11]. In Ref.…”

Two‐stage deadbeat‐based predictive torque control strategy for modular multilevel converter‐fed three‐phase induction motors

“…According to the discussion in section 2, the three-phase MMC with N = 2 can generate 5 distinct voltage levels at each of its output phases. As the MMC three phases independently synthesise their output voltage levels, the number of whole possible three-phase output voltage vectors would be 5 3 = 125. However, some of these vectors generate the same output line-to-line voltage.…”

“…The Modular Multilevel Converter (MMC), which was initially introduced to be utilised in HVDC systems [1], has recently attracted notable attention in medium-voltage electrical drive applications. This is due to its several advantages, such as modular topology, easy scalability to higher voltage levels, reduced switching frequency, improved output quality and transformerless configuration [2,3].…”