Multilevel Current Source Inverter Research Articles

Natural Current Balancing of Multicell Current Source Converters

This paper explores the issue of balancing the intermediate inductor currents of a multilevel current source inverter (CSI). The paper begins by identifying that single-phase multicell CSIs and flying capacitor voltage source inverters (FCVSIs) form a topological dual pair. This allows the established understanding of the natural balance process of the FCVSI intermediate capacitor voltages to suggest that the intermediate inductor currents of the CSI should also settle to their target balance values when phase-shifted carrier (PSC) pulse width modulation (PWM) is used. This concept is confirmed by full switched simulations. Next, an analytic model is developed to explore the dynamic response and robustness of the balancing process, using a double Fourier series representation of the converter switching signals to linearise a nonlinear transient circuit model. The model is verified against simulations, and predicts that the resistance of the intermediate inductors can perturb the steady state balancing point. The model further predicts that the resistance of the inductance must be small compared to the load resistance to minimize this effect. Results obtained on a five-level experimental CSI precisely match the theoretical model and hence support these conclusions.

Multilevel Converter Topology Using Two Types of Current-Source Inverters

A multilevel power-converter topology based on two types of current-source inverters (CSIs) has been proposed for large induction motor drives. The topology utilizes the combination of the load-commutated inverter (LCI) using thyristors and the CSI using gate turn-off thyristors (GTOs). As a result, the multilevel-inverter operation takes advantage of a soft switching of the LCI and hard switching of the CSI. The output capacitor is required to generate the leading power factor for load commutation of the LCI. It is shown that the proposed multilevel operation contributes to the leading-power-factor generation by providing the effective phase shift. Thus, the leading power factor required for the load commutation of the LCI is obtained with significantly smaller capacitors at the inverter's output terminals. As a result, the proposed approach can employ the LCI and utilize its soft-switching operation, yielding a cost-effective solution compared with the conventional multilevel CSI using two GTO CSIs. The switching losses are curtailed due to the natural commutation of the LCI and the six-step operation of the GTO CSI. Therefore, the proposed multilevel inverter can both increase the output power level and decrease the output capacitor size for LCI. The simulation and experimental results have been shown to verify the feasibility of the proposed multilevel topology and its operation

Novel Current-Source Multi-Level Inverter Driven by Single Gate Drive Power Supply

This paper proposes a novel current-source multi-level inverter, which is based on a current-source half bridge topology. Multi-level inverters are effective to reduce harmonic distortion of the output voltage and the output current. However, the multi-level inverters require many gate drive power supplies to drive switching devices. The gate drive circuits using a bootstrap circuit and a pulse transformer can reduce the number of the gate drive power supplies, but a pulse width of the output PWM waveform is limited. Furthermore, high-speed power switching devices are indispensable to compose a high-frequency power converter but various problems of high frequency noise arise due to high dv/dt rate, especially in high-side switching devices.The proposed current-source multi-level inverter is composed with a common emitter topology of all switching devices. Therefore, it is possible to operate with a single power supply of gate drive circuit, which allows stabilizing a potential level of all the drive circuits.In this paper, effectiveness of the proposed circuit is verified with experimental results.