Modeling, control and analysis of cascaded inverter based grid-connected photovoltaic system

• Two novel control schemes are developed for equal and unequal dc link voltages of CTLI based grid connected PV systems.
• The simple SPWM, in place of SVPWM, modulation technique is utilizing CTLI.
• The CTLI works efficiently by maintaining active power flow with variable solar inputs and in absence of it.
• The controllers supply the reactive power flow for two power schemes successfully.
• The systems’ performances (especially THD and efficiency) to extract maximum power from the PV modules are satisfactory.

This paper proposes a vector controlled isolated source cascaded two-level inverter (CTLI), for grid connected photovoltaic (PV) system. The system is controlled to operate with variable solar irradiance, supplying different levels of active power. The PV systems are designed, modeled and tested with the proposed controller, to provide maximum power output. Additional operation as a reactive power supplier, in the absence of solar radiation, is also tested. A simple sinusoidal pulse width modulation (PWM) technique is used, instead of referred space vector PWM (SVPWM) technique, for the operation. Two different schemes have been considered to operate the inverter with equal and unequal DC-link voltages. The control scheme has been found working, for both active and reactive power supply in steady state and transient conditions. The power supplies of both the schemes are analyzed. The controller performance is found to be satisfactory for both the schemes to extract maximum power at the considered working conditions.