DC to AC inverter with neutral having a resonant circuit

DETAILED DESCRIPTION The present invention provides an improved inverter for converting a DC voltage into three phase AC with a neutral and also for converting a DC voltage into single phase AC with a neutral.
The invention has the advantages of having minimal switching losses, low stresses on the switching devices, high efficiency, small energy storage components, and does not require DC bus modulation.
An inverter for producing an output signal with a neutral at a fundamental frequency for connection to a load with a load neutral in accordance with the invention includes a DC power source having a DC potential, an LC circuit, coupled to the DC power source, having a resonant frequency and resonating at the resonant frequency when the DC potential is applied to the LC circuit to cause current flow between the DC power source and the LC circuit, preferably having high Q; a switching circuit coupled to the LC circuit, the switching circuit having a first state permitting current to flow from the LC circuit to the load, and load neutral and a second stat permitting current to flow from the load neutral and load to LC circuit; a zero voltage detector for detecting when a voltage across the switching circuit is zero for producing an output pulse synchronized with each zero voltage point of the resonant frequency and a controller for switching the first and second states at the fundamental frequency to produce an output applied to the load at the fundamental frequency, the fundamental frequency being preferably much lower than the resonant frequency and short circuiting the flow of current from application to the load during the pulses to cause energy to be fed into the LC circuit during the short circuiting of the load.
The switching circuit is comprised of first and second switches each having an on state permitting current to flow between two terminals when a control signal is applied to a control terminal, each control signal having a frequency equal to the fundamental frequency and an on interval one-half the period of the fundamental frequency