Power enhancement of single‐phase transformer‐less grid‐connected cascaded half‐bridge diode clamped inverter under partial shaded photovoltaic

Abstract

This study presents a power-enhanced cascaded half-bridge (HB) diode clamped transformer-less multilevel inverter for grid-connected large-scale photovoltaic (PV) system addressing the problem of unequal power in isolated diode clamped (DC)-link due to partial shading. The HB diode clamped has the feasibility of increasing double times the DC-link voltage compared with the conventional cascaded h-bridge to enhance the inverter's power rating without compromising the count and peak inverse voltage of switching devices. Under partial shading conditions, the DC-link of individual HB suffers from different voltages and leads to unbalanced capacitor voltages. The proposed control scheme stabilizes the DC-link voltage of individual HB, extracts maximum active power from PV, and injects the same into the grid. The injected grid current total harmonic distortion satisfies the IEC 61727 and IEEE 1547 standards. PV parasitic capacitance in the transformer-less gridconnected system leads to leakage current. In the present work, LC-filters are placed among the power cells to bring these currents below 30 mA as per German standards VDE V 0126-1-1. For the planned inverter, a mathematical model using the switching function theory has been derived. The inverter's performance has been tested under partial shading conditions by using the MatLab/Simulink platform and experimentally verified with the software-inthe-loop real-time digital simulator OPAL-RT 5700. List of symbols and abbreviations: C a1 = C a2 = C a3 = C a , Filter capacitor; L a1 = La2 = L a3 = L a , Filter inductor; c, Number of HB's; n, Number of voltage levels; V dc , DC-link voltage of a capacitor; I dc , DC-link current of a HB; V HBc , AC output voltage of a HB; f x , Switching function; V x , Phase voltage; l, 1 (upper capacitor), 2 (lower capacitor); R s , Series resistance in PV cell; R sh , Parallel resistance in PV cell; I p , PV cell current; V p , PV cell voltage; I 0 , Saturation current; I 0r , Reverse saturation current; I sh , Shunt resistor current; I sc , Short circuit current; I ph , Photo current; λ, Solar irradiance; q, electron charge; k, Boltzmanns constant; T, Temperature; k i , Short circuit thermal coefficient; T 0 , Reference temperature; E, Bandgap energy; a, Number of parallel PV modules; b, Number of series PV modules; P mpp , Rated peak power; V oc , Open-circuit voltage; I sc , Short circuit current; V mpp , Rated voltage; I mpp , Rated current; δ, Duty cycle; T on , On time; T t , Switching period; i a , Grid current; v a , Grid current; L a , Filter inductance; R, Filter resistance; T s , Sampling time; m c *, Modulating signal; V cm , Commom-mode voltage; V tcm , Total common mode voltage; V dm , Differential-mode voltage; i cm , Common-mode current; C PV ,

Laguerre polynomial function‐based inverter control with low‐voltage ride‐through capabilities

“…As a result of reduced module pricing, photovoltaic (PV) technology has become popular among other renewable energy sources. 1,2 This is needed to meet the ever-increasing energy demand of industrial consumers and household consumers. This widespread use of single-phase grid-connected PV systems and the emergence of large-scale distributed generation (DG) systems have raised concerns about grid reliability, quality, and availability.…”

“…In recent years, the penetration of renewable energy sources (RES) into the electrical grid has risen significantly, thereby reducing the negative consequences of fossil fuel‐based power plants. As a result of reduced module pricing, photovoltaic (PV) technology has become popular among other renewable energy sources 1,2 . This is needed to meet the ever‐increasing energy demand of industrial consumers and household consumers.…”