Control Intelligence Improves Renewable Energy Efficiency

Sep 1, 2007 12:00 PM
By Arefeen Mohammed, C2000 Applications Engineer, Texas Instruments, Dallas

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Throughout the world there is an increasing demand for renewable energy, yet system manufacturers continue to face the same issues that have always slowed the growth of this technology: They're required to increase the total amount of power gathered, while decreasing the cost per watt. One important way to help achieve these goals is by adding greater intelligence to the control of the inverter, which converts the variable voltage output of the energy collector into a steady voltage that is used for running applications or charging batteries. Intelligent inverters maximize power transfer from the gathering source, synchronize power output with the electrical utility and protect the local system from potentially damaging changes in the grid.

While sun- and wind-powered systems are the obvious applications, intelligent inverters also can benefit other sources of power, such as fuel cells, to maximize output. For all such applications, highly effective inverter control is available from digital signal controllers (DSCs), which have been shown to cut conversion-efficiency losses in half while significantly reducing costs. DSCs combine the high performance of digital signal processors (DSPs) with the programming ease and integration of microcontroller units (MCUs). In addition, DSCs with floating-point capabilities are now available, enhancing performance and making the job of programming complex algorithms easier.

The Inverter's Role

The main function of the inverter is to convert variable dc voltage input from the source into a clean sinusoidal 50-Hz or 60-Hz output for use by appliances and feeding back into the grid. Different applications may require single or multiple phases. In addition to dc-ac conversion, inverters perform such functions as disconnecting the circuit to protect it from power surges, charging the battery, logging data on usage and performance, and maximum power point (MPP) tracking (MPPT) to keep power generation as efficient as possible. Nominal power ranges between one and several hundred kilowatts peak (kWPK), allowing inverters to be designed around sophisticated source topologies, either with or without transformers, and with the integration of multiple control processors.

Fig. 1 shows where the inverter fits into an all-inclusive photovoltaic (PV) system that not only charges a battery and drives local ac loads, but also ties to the grid and has an alternate power source in the form of an ac generator. Similar configurations apply to wind turbines and other sources.

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