Practical limitations of embedded Z-source DC-DC converters in PV applications

Abstract

This paper presents a detailed mathematical model for embedded Z-source converters (EZSC) by using a state-space averaging technique. In addition, the steady-state operational limits are derived concerning the internal voltage drops and parasitic parameters. Z-source converters exhibit non-minimum phase behavior, which is due to the presence of right-hand plane (RHP) zero. Thus, control of such a converter is a challenge, that slowdowns the transient response of traditional linear controllers. The paper investigates the impedance matching, the position of maximum power point (MPP) in EZSC for both active and shoot-through operational modes, and the effect of RHP zero in the placement of MPP. The steady state solution is derived for dc-link voltage to analyze the impact of non-ideal passive components like capacitors, inductors, diode, and switches. The expression for critical shoot-through duty ratio (STDR) for which the dc-link voltage is maximal is derived. Through critical analysis, the paper provides a valuable insight into the behavior of the embedded topologies and its steady state operational limits under photovoltaic (PV) applications. The paper presents a detailed comparison between positive embedded Z-source converter (PEZSC) and negative embedded Z-source converter (NEZSC). Simulation results are obtained using Matlab/Simulink™ and compared with the experimental results obtained using a laboratory prototype.