Generalized Optimum Pwm Technique: Analysis and Application to Battery Charging (Pulse Harmonics).

The basic variables that characterize the classes of waveforms considered for optimization of PWM waveforms are evaluated. Using the Fourier coefficients of the waveform it is concluded that these classes of waveforms are best described by the amplitudes of the jump discontinuities that characterize them. This characterization of the waveforms greatly simplifies the evaluation of the Fourier coefficients when the harmonic components are desired. Through use of this characterization it is evident that contrary to what is widely reported in the literature the degrees of freedom, or the independent variables of the system, are twice the number of the jump discontinuities in the fundamental period of the waveform. This finding may enable the designer to reap the benefits of the PWM techniques with fewer number of switching operations. It also enables the comprehensive analysis of these waveforms. A new form of the optimization objective function is proposed. The new objective function is based on the total harmonic distortion factor (TDF). The TDF is chosen as it includes the entire harmonic spectrum instead of neglecting the higher harmonics. The justification is that the total elimination of the higher harmonic components from the TDF definition may lead to serious errors in some applications, e.g. variable speed AC motor drives. To alleviate computational problems a shift to the time domain is found quite attractive. This shift greatly reduces the computational effort and time and will bring the applications of optimum PWM waveforms techniques closer to the real time application. Another advantage of the change to the time domain is the ease of applying the proposed method of weighting functions. This provides a more systematic way of h and ling the problem and allows the designer more freedom in choosing the weighting function that suits his application. Two classes of these weighting functions were considered in this dissertation although many others can be treated in a similar manner. The application of the method to battery charging is discussed. Voltage or current waveforms at the input terminals of the rectifier are varied in such a way to approximate a sinusoidal waveform. These may be voltage or current waveforms. The waveforms are obtained by the suggested optimization technique. It is shown that by optimizing the voltage (or current) at the terminals of the battery pack the charger input current is optimized as well. Simulation results are presented to verify the operation of these chargers and to demonstrate the effects of such parameters as battery voltage to AC input voltage ratio and the circuit inductance.PhDElectrical engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160300/1/8502802.pd