This letter proposes a new implementation of phase-disposition pulse-width modulation (PD-PWM) for multilevel flying capacitor (FC) converters using a single triangular carrier. The proposed implementation is much simpler than conventional PD-PWM techniques based on multiple trapezoidal shaped carriers, generates the same results as far as natural capacitor voltage balance is concerned and offers better quality line-to-line voltages when compared to phase-shifted PWM. The proposed algorithm is based on re-shaping the reference signal to fit within the range of a single carrier and assigning each crossing of the reference signal with the carrier to a particular pair of switches at any time. The proposed algorithm is suitable for digital implementation taking maximum benefit from the PWM units available in the processor. Simulation and experimental results are presented from the five-level FC Converter to verify the proposed PD-PWM implementation.

Discontinuous modulation applied to modular multilevel converters is an effective method for reducing the capacitor voltage ripples. In this paper, the discontinuous modulation is adapted and used in a motor drive application. For proper operation of the converter, a new energy controller is presented, which is suitable for operation with non-sinusoidal reference signals. Experimental results comparing the discontinuous modulation with other techniques operating at low motor speeds are shown. The results demonstrate the effectiveness of the discontinuous modulation on reducing capacitor voltage ripples and power losses.

Abstract-Connecting legs in parallel in a voltage source inverter is a way to increase the output current and thus, its rated power. The connection can be made using either coupled or uncoupled inductors and achieving an even contribution to the output current from all the legs is a crucial issue. Circulating currents produce additional losses and stress to the power devices of the converter. Therefore, they should be controlled and minimized. An efficient technique to attain such a balance when coupled inductors are used is presented in this paper. The proposed technique can also be used when the inductors are uncoupled, since it is a particular case where the coupling coefficients are zero. This technique does not include proportionalintegral controllers and does not require any parameter tuning either. The exact control action needed to reach current balance is straightforwardly calculated and applied. Experimental results are shown in this paper to verify the efficiency of the proposed balancing method.

No abstract

Abstract-Connecting legs of modular multilevel converters (MMCs) in parallel can assist an MMC-based high-voltage direct current (HVDC) to increase its current ratings and hence overall power handling capability. Consequently, each phase of the MMC would be integrated by several legs or sets of upper and lower arms (ULAs). This paper proposes a current control strategy for each ULA in order to ensure balanced current sharing among them. In addition, each ULA has its own circulating current control that follows a reference obtained from the instantaneous magnitudes of the output current and the modulation signal. All the proposed control actuations do not distort the phase output voltage of the MMC which follows the reference voltage. The performance of the proposed control strategies is evaluated by simulation studies in the PLECS Blockset under MATLAB/Simulink software platform.