A New Converter Topology to Increase Energy Harvesting of Large Scale PV Power Plants

Abstract

A new voltage and current balancing topology is introduced to enable a better energy yield from central inverters for large-scale solar power plants. The proposed balancing topology is characterized by its fractional power rating, high efficiency, scalability and low cost. The approach uniquely locates the maximum power point (MPP) for the system using a new developed algorithm such that it will increase the overall system efficiency. The proposed approach would be using a two staged differential power converter where the PV voltage and current are measured during each period of operation and the power converter will keep adjusting itself to maintain operation at the maximum power point. The two stages differential power converter is not a substitute for the central inverter; a central inverter would still be required to achieve maximum power point by matching the maximum available current and voltage seen by the inverter. The proposed two stages differential power converter is a new concept which addresses various needs of the present and future power generation units in the grid. The main advantages for the multistage differential power converter are: 1- The MPP is efficiently distributed on system level and each stage will match both voltage and current to reduce circulating power and maximize harvested power. 2- The controls are less complex than other existing solutions. 3- Less number of blocks, passive components, and switches used to run the new system for full integration with the grid. 4- Commercially practical solution since it requires simple control techniques and optimizes overall system efficiency. The first stage of the power differential converter is called the power sharing converter (PSC), and the second stage is voltage balancing converter (VBC). The PSC is a half H-Bridge circuit that has two PV groups are connected to it as an input to the converter; the PSC will adjust the total current between the two PV groups such that the current difference will be created between them equal to the maximum current available by one group subtracted from the other PV group by using passive element such as inductor between the two groups. VBC is also in the form of half H-bridges connected in parallel. Therefore, it would see all the available voltages by the connected strings such that each of the VBC would balance the voltages between the different strings. The voltage balancing is done by adjusting the switching duty ratio of the half H-Bridge switches. The proposed design gave an extra degree of freedom in creating better power matching conditions within each PV group as well as on the system level. The modeling equations for the proposed system was derived and proved the robustness of the proposed system. The simulation results showed the effectiveness of the proposed circuitry along with the newly proposed MPPT design, and it showed the system energy harvesting efficiency was 98% in comparison to the traditional method with 63% efficiency designed for a PV power plant with capacity of 160 KW. The circuit would be implemented in hardware design using Gallium Nitride (GaN) switches with switching frequency of 100 KHz which can endure high voltage rating and moderate current levels.