Resonant inverter control system

A resonant inverter apparatus comprising an inverter circuit in which a direct current output by a power source is converted to a three phase alternating current and supplied to a three phase motor, a resonant circuit that is connected to the output terminal of the inverter circuit, and a control circuit that control the resonant circuit and the inverter circuit, wherein:

• said inverter circuit comprises a three phase main circuit in which three circuits, one for each phase, connected in parallel, wherein a main switching element that is connected to the plus terminal of said power source and the main switching elements that are connected to the minus terminal of the power source are connected in series, and connected in parallel to diodes respectively connected to these two main switching elements;
• capacitors that are connected in parallel to the main switching elements in each of the circuits for each phase;
• load current sensors that detect a load current flowing across main connection points, at which two main switching elements in each of the circuits for each phase are connected together, and said motor;
• and cross-terminal voltage sensors that detect the cross-terminal voltage of the main switching elements in the each of the circuits for each phase;
• said resonant circuit comprises auxiliary connection points in which three auxiliary circuits, one for each phase, connected serially to two auxiliary switching elements that allow a current to pass only in one direction are connected in parallel, and two auxiliary switching elements in each of the auxiliary circuits for each phase are connected together;
• three phase auxiliary circuits connected to the main connection points of said inverter circuit;
• resonant inductors connected between the auxiliary connection points in said auxiliary circuits for each phase and said terminals on the opposite side;
• and a resonant current sensor that detects a resonant current flowing to the inductor;
• said control circuit comprises a zero voltage detecting device that detects whether or not the cross-terminal voltage detected by each of the cross-terminal voltage sensors is zero and outputs a zero voltage detection signals that corresponds to each of the cross-terminal voltages in the case that they are zero;
• a resonant current arrival determining device that determines whether or not the resonant current detected by said resonant current sensors is larger than the load current detected by said load current sensors and in the case that they are larger outputs an arrival determination signal;
• a drive signal generating device that generates a main drive signal that turns OFF the main switching elements to a non-conducting state when the resonant current arrival determination device has output an arrival determination signal, generates a main drive signal that turns ON the main switching elements to a conducting state when said zero voltage detecting device has output a zero voltage detection signal corresponding to each cross-terminal voltage, generates an auxiliary drive signal that turn ON the auxiliary switching elements at a predefined switching timing, and turns OFF an auxiliary switching element that is in a conducting state after a predetermined on continuation time has passed from the predefined switching timing;
• and current conducting device determining devices that determine whether or not a current is flowing in any of the main switching elements or diodes in each of the circuits for each phase in said inverter circuit;
• and
• said drive signal generating device comprises a resonant action prohibiting device that prohibits the generation of an auxiliary drive signal that turns ON a corresponding auxiliary switching element in said resonant circuit during the turn-OFF of the main switching element in the case that said current conducting device determination device has determined that a current is flowing in a main switching element.