An equivalent power test scheme for modular multilevel converters (MMCs)

A Viable Mission Profile Emulator for Power Modules in Modular Multilevel Converters

“…It can be observed that the capacitor voltage is controlled to increase gradually from 0 V to 300 V in the start-up process. It consumes about 2.5 seconds in total in order to reach the steady state, which is pretty close to 2.7 seconds predicted by (8)- (11). From the zoom-in Fig.…”

“…Together with other main system parameters shown in Table III, the carrier frequency used for the capacitor voltage control can be determined. In the experiment, the voltage control should be able to effectively charge and discharge the capacitor by 5 V increase/decrease within 0.1 s or 5 fundamental cycles (which is adjustable) to stabilize its voltage at 300 V. According to (8)- (11), the minimum carrier frequency of the voltage stabilizer calculated is 1.5 kHz for the high switching frequency mission profile applications. When it comes to the low switching frequency mission profile, considering the existence of ineffective additional switching actions (such as for NLM) as mentioned in Section II-C, longer time will be taken to charge or discharge the capacitor in this case.…”

“…However, owing to inherent characteristics of the resonant circuit, it is impossible to inject a DC bias current into the SM, which consequently cannot emulate the practical operation condition of the MMC. In order to implement the DC component, a halfbridge converter is utilized as the current source [11], where its system parameters (e.g., power supply voltage, coupling inductor and SM capacitor) are easy to be scaled according to a practical MMC system. Nonetheless, it is not able to cope with the low switching frequency mission profiles, where plenty of undesirable harmonics may be introduced into the arm current.…”

A Minimum Viable Mission Profile Emulator for IGBT Modules in Modular Multilevel Converters

“…In the prior-art studies, sub-module (SM) based test setups focus mainly on the electrical behavior emulation. An equivalent test scheme in [6] utilizes two SMs to emulate the electrical features of SMs (e.g., the SM capacitor voltage and the arm current). Based on the resonant test circuit proposed in [7] and control of the MMC can be conducted.…”

“…For the test bench in [10], series-connected IGBTs have to be used when applying the testing to Device Under test (DUT) rated at higher than 2 kV to fulfill the highvoltage requirement. The test bench in [6] has to increase the switching frequency in order to achieve a smooth arm current, but scarifies its thermal performance of the MMC with a low switching frequency in the field. The resonant test circuit in…”