Single-Phase Grid-Connected Photovoltaic H-Bridge N-Level Inverter Control Strategy

In this chapter, we present a novel control strategy for a single-phase cascaded H-bridge multilevel inverter in a grid-connected solar PV system. Unlike the known grid-connected inverters controls using a DC/DC converter for the MPPT pursuit, our control technique offers an MPPT algorithm for each PV module by handling its corresponding inverter only. The inverter connection of the grid is made through an LCL filter due to its ability to reduce harmonics instead of a simple inductance filter. To relieve the resonance phenomenon through the capacitors and inductors, a passive damping resistor is connected in series with the capacitor. We have used both controllers PI and PR, respectively, on the synchronous reference frame dq and the stationary reference frame αβ. The main purpose is to eliminate significant harmonics (3rd, 5th, and 7th) using our novel controller in order to improve the quality of the injected energy into the grid. By controlling the active and reactive power, we have proved that the PI controllers cannot track the sinusoidal references without a steady error in the synchronous reference frame dq. Furthermore, the PR controller has better performances and is more interesting for controlling the DC/AC converters. Indeed, in the stationary reference frame αβ, the PR controller gives a static error near zero for sinusoidal currents. Moreover, injected current quality improvement due to the most dominant odd harmonics elimination (3rd, 5th, and 7th) is insured by the HC. The adequate drive pulses are generated by a proportional modulator algorithm.