Abstract: An improvement of control for prevention of a short circuit between controllable elements used as switching elements in a pulse-width modulation type inverter apparatus which outputs a variable amplitude or variable frequency a.c. voltage. The pulse-width modulation type inverter apparatus is of a type wherein, a selecting means selects an output from a processing means within a period during which the result of detection by a current detector falls within a region of substantially zero level and also selects only a signal corresponding to each switching element which effectively acts on the generation of the output current, out of signals generated by a PWM signal generating means during a period other than the above-described period, thereby to output the same as a drive signal for the switching element.

Abstract: A wave generation circuit for a pulse width modulation inverter generates a plurality of differently phased waves which are modulated to form driving signals for switching elements in the inverter. This circuit has a single memory element having waveform data stored therein and also has an operation circuit for providing phase address signals which indicate the address of the waveform data corresponding to each phase. The data at the indicated addresses are read out of the memory element and latched by a phase latch circuit for each phase. When all of the stored data corresponding to each phase have been latched, the operation circuit transmits an output timing signal to cause the phase latch circuits to simultaneously provide the latched data which form driving signals for the switching elements.

Abstract: An inverter control apparatus contrived for improving the torque characteristic of an induction motor, wherein a current inputted to the induction motor is continuously detected, and the output voltage of the inverter is corrected by a voltage corresponding to a variation in the detected current.

Abstract: An inverter control apparatus comprises a first current level setting unit 5 which sets a protection level for switching elements included in an inverter 1, and a second current level setting unit 7 which sets a current level that prevents a stall torque/slip point from being exceeded and which is determined in association with the load characteristic of an induction motor and the voltage/frequency ratio being delivered by the inverter. The smaller of the two current levels is selected to control the frequency to lower or stop its rise to prevent the slip frequency from being exceeded. Thus, stable operation without stalling or damage to the inverter elements is achieved regardless of the voltage/frequency ratio set to drive the motor or the particular induction motor used.