Abstract
This paper presents a single chip FPGA (Altera Cyclone II) controlled single phase inverter, programmed for the reduction of harmonics in the output voltage. Separate composite digital observers have been designed for extracting the fundamental and harmonic components of the voltage and the highly distorted current signals, particularly when the inverter supplies nonlinear loads. These observers have been embedded into the FPGA along with the controllers and I/O interfaces. The multiple observers yield very pure in-phase and quadrature voltage signals for use in the outer loop and similar signals for stabilizing the inner current loop. The Inverter could be modeled as a feed back control system with the fundamental component of the voltage as the desired output while the voltage harmonics take the role of noise creeping into the output. To obtain a very low total harmonic distortion in the voltage waveform, the well-known control strategy of using a very large feed back around the noise signal has been employed.
Highlights
Stand-alone inverters are commonly used in the case of power failure, to deliver power for critical loads, which demand purely sinusoidal voltage at the specified magnitude, frequency, and low total harmonic distortion (THDv)
The load voltage and current corresponding to a nonlinear load, with a harmonic feedback gain in the range 0 < h < 20, were recorded, for validating the simulations
The reduction of distortion in the voltage waveform in single phase Inverters, caused by the currents drawn by nonlinear loads, can be done by feeding back the instantaneous harmonic content of the voltage signal
Summary
Stand-alone inverters are commonly used in the case of power failure, to deliver power for critical loads, which demand purely sinusoidal voltage at the specified magnitude, frequency, and low total harmonic distortion (THDv). The inner loop is used for current control and the outer loop is used for voltage control Many of these methods have not considered the reduction in distortion due to nonlinear loads. A Luenberger observer (simple observer) can be used for obtaining the filtered fundamental component from the periodic output voltage and current waveforms, which leads to the indirect estimation of the total harmonics in the output voltage due to the nonlinear loads [12]. The composite observer has a repetitive parallel structure, which can be implemented in an FPGA
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