Control strategy of PV‐fed, grid‐interfaced, seven‐level T‐type MLI for distributed power generation

Abstract

The major concern with renewable sources of energy, feeding the distributed power generation system, is the power quality, reliability and efficiency of the system. This study proposes a novel topology comprising single-phase, seven-level, gridconnected photovoltaic-fed (PV) inverters in parallel. An important expediency of connecting multilevel inverters (MLIs) in parallel is that the failure of any source or the MLI module itself will never stop the overall generation, leading to improved efficiency and reliability of the system. This study also incorporates a novel controller comprising of two DC and an AC controller that independently controls the DC-link voltage of PV system and AC-side voltage so as to inject a pure sinusoidal current at unity power factor into the grid. Also, the AC controller discussed here is self-synchronising, i.e. aloof of phase-locked loop. The power mismatch problem that basically arises due to partial shading conditions in PV system has also been discussed. The MATLAB/Simulink-based proposed two seven-level grid-connected inverters in parallel are modelled and simulation results are presented. An experimental prototype of the PV-fed grid-connected system comprising two seven-level inverters in parallel is developed and tested to validate the simulation results.

Comprehensive review on control strategies of parallel‐interfaced voltage source inverters for distributed power generation system

“…Consequently, a suitable control strategy is required to make certain, the equal current sharing among the inverters. The controller, therefore, needs to fulfil the following objectives [22–26]: Module synchronisation. Improved load sharing. Obtain the desired output voltage. The controller should be able to employ proper current sharing amongst the parallel inverters, to protect any particular inverter from overheating. Minimum communication lines between the inverters to ensure better reliability. The performance of the controller should not differ with an increase or decrease in the number of inverters connected in parallel. The current/power‐sharing control topologies of parallel‐connected inverters are broadly classified as wired [27–53] or wireless controllers [25, 37, 54–133]. Although the wired controllers ensure efficient power‐sharing between the parallel‐connected inverters, yet, the presence of inter‐communication link between them makes the operation less reliable.…”

“…To accomplish high power requirement, reliability and redundancy of DPGS, better heat dissipation, and current sharing, the low power inverter modules need to be connected in parallel [26]. Fig.…”

“…Consequently, a suitable control strategy is required to make certain, the equal current sharing among the inverters. The controller, therefore, needs to fulfil the following objectives [22][23][24][25][26]:…”

“…Nevertheless, the connection of any two inverter modules in parallel is not a trivial task, as they are very sensitive even towards a minute change in operating conditions [25]. Several design objectives such as module synchronisation, equal current sharing between modules, minimal intercommunication lines, redundant operation, and so on should be fulfilled to connect the inverters in parallel [26]. To ensure equal power-sharing between the parallel inverter modules, several wired (non-modular) and wireless controller (droop/modular) [25,37, structures have been proposed.…”

Multi‐functional commercial solar photovoltaic plant integrated to three‐phase low voltage AC network

“…Various improved power converter topologies [13][14][15] and improved control methods [16][17][18][19][20][21][22] are discussed in the literature to limit the harmonics currents in the AC network due to the generation of the SPVP and the load characteristic, respectively. In [13], the transformer integrated filtering method, in [14], a 7-level T type multilevel inverter (MLI) based power converter topology and in [15], interleaved MLI based topology are presented to reduce the harmonics currents injected by the SPVP at the PCC. These discussed topologies have not considered the effect of the load behaviour on the system performance.…”