Computationally Efficient Distributed Predictive Controller for Cascaded Multilevel Impedance Source Inverter With LVRT Capability

Abstract

This paper presents a decoupled active and reactive power control scheme for grid-tied quasi-impedance source cascaded multilevel inverter (qZS-CMI). For photovoltaic (PV) applications, the proposed control scheme is based on an enhanced finite-set model predictive control (MPC) to harvest the desired active power from the PV modules with the ability to provide the ancillary services for the grid. The proposed control scheme has two modes of operation: normal grid mode and low voltage ride through (LVRT) mode. In normal grid mode, the controller commands the qZS-CMI to operate at the global maximum power point (MPP). The proposed technique regulates the impedance network's current and voltage according to the MPP of PV strings and grid current/voltage requirements. In LVRT mode, the controller commands the qZS-CMI to provide the required reactive power to the grid during voltage sags as an ancillary service from the inverter as imposed by the grid codes. The main features of the proposed system include the global MPP operation during normal grid condition, LVRT capability during a grid voltage sag, mitigation of the PV modules mismatch effect on overall energy harvesting, seamless transition between a normal grid and LVRT modes of operation, and an efficient predictive controller that exploits the model redundancies in the control objectives. Several real-time experiments are conducted to verify the system performance with transients in both the solar irradiance and the grid voltage.

A New Predictive Control Strategy for Multilevel Current-Source Inverter Grid-Connected

“…In general, predictive-type control strategies, use a mathematical model to predict the effect of the control action of the system. Traditional PC is computationally burdensome, especially for cascaded multilevel inverter topologies and other schemes with large sets of switching states and thus may not achieve feasible sampling frequencies [30]. There are several approaches to dealing with the computational burden problem.…”

A Grid-tied PV Inverter with Sag-severity- independent Low-voltage Ride Through, Reactive Power Support, and Islanding Protection

“…Conventional low-voltage ride through (LVRT) methods limit the output current and disable the MPPT during the fault to compensate for the energy surplus [10]. An LVRT technique for 20% sag can be found in [4]. During the sag, the MPPT is disabled while the first-stage boost converter works with a fixed duty cycle.…”

Computationally-Efficient Optimal Control of Cascaded Multilevel Inverters With Power Balance for Energy Storage Systems

“…For OSV MPC, this is done by considering only adjacent voltage vectors in αß frame, referred to as the nearest neighbor method [12]. A similar idea is proposed for OSS MPC of multilevel inverters by applying a voltage window [13] which is essentially the nearest neighbor method applied to a one-dimensional control set. However, both techniques reduce the control set, which can negatively effect dynamic performance.…”