Power Electronics for Renewable Energy Systems.

Power Electronics will play a key role for electrical energy pattern to shift to more renewable electrical energy and higher energy efficiency in various applications .Electrical energy is shifting towards the renewable energy sources as there are few challenges in Electrical energy Generation.

Small renewable energy power systems are trying to become the long-term power solution for various application like portable, transportation and stationary system. Power systems are can have limitless in possibilities for setups and configurations which can be used to produce the desired power for a application specific system. A small renewable system includes few like solar panels, wind power, fuel cells, batteries, capacitors, and other types of power devices. This systems can be integrate with power electronics to handle low, high, and variable power requirements. Example, solar panels can be used to convert solar energy into electrical energy when sunlight is directly hitting the PV (photo-voltaic)panels to get maximum efficiency, and then power from wind turbines can be used when wind speed and direction is ideal. The energy generated from these devices can be stored in batteries and it also used for electrolysis to produce hydrogen. The hydrogen can used to fed to fuel cells to provide power for long periods of time and also can be used for transportation applications. Power electronics is a key element to stabilize ,boost and manage power for a hybrid system.

The electrical output of devices varies , some system may need the output less than applied to the system. There are different application like , grid or residential power which requires the AC power. Also few devices like as cell phones require DC power. But output of fuel cells and batteries, is DC voltage which depends on the number of cells connected in series. An inverter can be used to change the output from DC to AC output when required. Also some renewable system have low on time so it is difficult for such devices to handle large amount of power from supply voltage. Because of this ,systems are usually designed to compensate for high power requirements. Power converters is used to regulate the power flowing through a circuit.

Fig1. Power Electronics as a Key element in renewable sources. Image Source-” Designing and Building Fuel Cells’ (McGraw-Hill, 2007)”

In present situation renewable energy technologies only give a certain voltage and current density (which is depends upon the load )to the power converter. The power converter is adjusted according to the voltage available from the fuel cell to a voltage high enough to operate the load. In Figure 2 it is shown that DC-DC boost converter is required to boost the voltage level for the inverter. This boost converter, not only boost the fuel cell voltage but , also regulates the inverter input voltage and isolates the low and high voltage circuits.

Fig2.FuelCell Interface Diagram ,Image Source-” Designing and Building Fuel Cells’ (McGraw-Hill, 2007)”

Impact of Power Electronics on Energy Systems

The saving of energy gives financial benefit, particularly where the energy cost is high. Power electronic control is more efficient because of the switching mode operation of power semiconductor devices. The national electric grid(An electrical grid is an interconnected) in India has a capacity of 382.15 GW as of 31 March 2021.The Renewable power plants, which also include large hydroelectric plants, constitute 36.8% of India’s total electric grid capacity. If we take a look on an example of United States According to EPRI(Electric Power Research Institute) , nearly 60–65% of grid-generated energy in the United States is consumed by motor drives and of that motor drivers 75% of these are pumps, fans and compressor-type of drives for industrial applications. Industrial applications, the conventional method of flow control is by throttle, where a coupled induction motor runs at a constant speed. This method causes a lot of energy wastage. In such applications, a power electronics-based variable-frequency motor speed control with fully open throttle can save around 20% of energy under a light load. In addition, a converter-fed machine’s efficiency can be improved further by flux(flux produced by the coils, generating. an induction of current on the rotor to generate a rotational. torque) programming control at light load. Power electronics-based load-proportional speed control of air conditioner/heat pump can save energy by up to 20%. For example, the cost of electricity is high in Japan. For this reason, most Japanese homes use variable-speed air-conditioning to save energy. One popular application of power electronics in recent years is variable-frequency multi-megawatt drives in diesel–electric ship propulsion, which can save a considerable amount of fuel compared with that of the traditional diesel–turbine drive.

References-

1. A book-”Spiegel, Colleen. Designing and Building Fuel Cells. US: McGraw-Hill Professional, 2007.”
2. A book-”Power Electronics for Renewable Energy Systems, Transportation and Industrial Applications (Wiley — IEEE) Hardcover — Illustrated, 25 July 2014”