Spectral characteristics of resonant-link inverters

The limitations on the operating frequency of hard switched and resonant link inverters are studied. The maximum operating frequency of a hard switched inverter is found to be well defined by the allowed power dissipation due to on-state and switching losses. For resonant link inverters the upper limit is not as well defined and depends upon a trade-off between a number of different factors. For a system using high power bipolar transistors, it is seen that a resonant line system may achieve switching frequencies approximately ten times greater than those possible with a comparable hard switched inverter. The frequency spectrum of the resonant line configuration was compared with PWM (pulse width modulation). It was shown that the improvement in harmonic distortion associated with a delta modulated resonant link inverter is not as great as may be expected from the increase in link frequency that may be obtained. This is a result of constraints placed on switching instants and the need to use integral pulse modulation