Patent ID: 7577007

Claim:
A power converting apparatus comprising: a single-phase multiplex converter connected to a load via a reactor to provide electric power to the load, said single-phase multiplex converter including a first single-phase inverter to which a maximum DC source voltage is supplied and at least one second single-phase inverter, said first single-phase inverter outputting voltage pulses at a rate of one pulse per half period of a reference AC voltage, said first and at least one second single-phase inverters being connected in series at AC output sides of said single-phase inverters, wherein said first and at least one second single-phase inverters convert DC power fed from a DC power supply into AC power; and a control unit for controlling said single-phase multiplex converter to produce an output voltage having a quasi-sinusoidal waveform simulated by the sum of output voltages of respective single-phase inverters, said control unit including a current controller for regulating an output current of said single-phase multiplex converter to follow a target current which is determined in accordance with the load, wherein said current controller drives said at least one second single-phase inverter such that the output current of said single-phase multiplex converter follows the target current, said control unit includes a central processing unit having a mathematical processing capability, and a control circuit including a digital signal processing circuit and an analog circuit including a hysteresis comparator circuit having an ordinary range of hysteresis, said central processing unit outputs a current signal corresponding to the target current, said current controller regulates the output current using said control circuit, said current controller generates a control signal which is supplied to said at least one second single-phase inverter so that the output current of said single-phase multiplex converter increases and decreases within the ordinary range of hysteresis, and said hysteresis comparator circuit has a marginal range of hysteresis encompassing the ordinary range of hysteresis and, if the output current of said single-phase multiplex converter goes out of the ordinary range of hysteresis, said control unit makes a correction so that output current of said single-phase multiplex converter varies within the ordinary range of hysteresis.