Feedforward Proportional Carrier-Based PWM for Cascaded H-Bridge PV Inverter

In this paper, a feedforward proportional carrier-based pulsewidth modulation (PWM) is proposed for the dc link control of the single-phase cascaded H-bridge multilevel photovoltaic inverter. The conventional carrier-based PWM techniques, such as the phase-shifted PWM and the level-shifted PWM, require multiple individual dc voltage controllers for the individual maximum power point tracking (MPPT). Thus, the control structure and the controllers' designs are quite complex. Several noncarrier-based PWM techniques, such as the feedforward space vector modulation, the sorting-algorithm-based modulation, and the lookup table-based modulation, have the capability of individual dc voltage regulation. Although these noncarrier-based PWM techniques require only one total dc voltage controller in the outer voltage loop, the implementations of them are much more complicated than those of the carrier-based PWM techniques. In this paper, with the proposed feedforward proportional carrier-based PWM, each individual modulation signal is directly generated by multiplying the current loop controller's output and the modulation signal's feedforward proportional factor. With the feedforward PWM and the total dc voltage control, the individual dc voltage regulation is achieved. This carrier-based PWM combines the strengths of both the traditional carrier-based PWM and the noncarrier-based PWM. It is not only easy for implementation, but also requires only one total dc voltage controller in the outer voltage loop. The detailed description, derivation, and analysis of this modulation are included in this paper. In addition, the simulations and experiments demonstrate the performance of the dc link control and the individual MPPT using the proposed PWM and the control strategy.