RESEARCH

 

Fault Tolerant Converter for Multiple Inverter based Photovoltaic (PV) System 

In order to provide sustainable energy solutions, grid connected PV systems are increasingly utilized worldwide due to their inherent advantages. They help in reducing greenhouse gas emissions and provide clean and green energy. The reduction in the PV installation and maintenance cost along with the advanced and innovative Power Electronics technology has taken the grid connected PV systems to a higher level. The grid connected PV systems utilize power electronics converters for efficient power conversion. The inverters act as an interface between PV and the grid, ensuring an efficient power conversion from DC (Direct Current) to AC (Alternating Current). Inverters provide the desired AC voltage at the required frequency following the grid standard code. They also maintain the efficient operation of the grid connected PV system by providing ancillary services like Reactive power support, Low Voltage Ride-Through (LVRT), Fault-ride Through (FRT) etc. Grid-connected inverters often operate in parallel to scale up the generation and expand power capacity. Parallel inverter operation is highly desirable and is a promising method to achieve reliability since it introduces modularity and redundancy in the system. The load is shared among each parallel module, so the current stress on a single power switch is reduced greatly. However, the circulating current may exist between parallel modules due to improper load sharing and may damage power semiconductors in the inverters. In order to reduce the effect of circulation current, the output voltage of all paralleled inverters must be strictly consistent in frequency, phase and amplitude to guarantee the optimum output power sharing.

Grid-connected PV systems are highly susceptible to abnormal events or faults due to the presence of switching devices. Fault occurrence in any part of the system may severely affect the operation leading to the instability at the grid side. Fault analysis is a fundamental task to eliminate any kind of dangerous and undesirable situations that might occur in the system. The researchers have invested considerable efforts to devise intelligent and human error free fault diagnostic techniques. The reliability of any system is the probability of survival over a period of time. Higher reliability suggests that the system is able to perform the desired operation without any disruption for longer periods. In order to improve the system reliability and minimize the O&M cost, it is essential to have a mechanism in place that is able to handle the failure conditions such that the power quality and the stability of the system is maintained. Such a mechanism is called fault tolerant mechanism. Fault tolerant operation is based on devising a strategy such that the system is able to maintain continuous supply even in the event of fault. 

Research Objectives

With the inverters operating in parallel, it is expected that if one inverter fails, remaining inverters ensure that the system does not shut down. This is where the converter level redundancy gains significance. While converter level redundancy has the capability to handle these kindly of failures and make the system effectively more reliable, this domain has not been explored to its depth. This research aims to explore converter level redundancy as the fault tolerant mechanism for grid connected inverters operating in parallel.

The long-term aim of this research is to develop fault tolerant converter for grid connected PV system. The system consists of two inverters (3-phase) of capacity 2kW each operating in parallel. The major objective of this research is to make the system fault tolerant such that with any fault occurrence, the system is able to continuously operate feeding the required loads. The faulty part is isolated and then repaired; once it is repaired, it can be connected back to the system. Following are the sub-objectives of this research-