A feedback control switching unit of an inverter control unit selects, based on a magnitude relationship between a predetermined switching determination amount and at least one switching threshold, at least one of feedback control units to thereby execute switching among feedback control modes, such as a current feedback control mode and a torque feedback control mode, of the respective feedback control units for driving of the AC motor. A switching command generating unit generates a switching command for an inverter based on a manipulated variable calculated by the selected feedback control unit. When a torque response request determining unit determines that a required torque responsiveness is high, the feedback control switching unit reduces the number of executions of switching among the feedback control modes.

A feedback control switching unit of an inverter control unit selects, based on a magnitude relationship between a predetermined switching determination amount and at least one switching threshold, at least one of feedback control units to thereby execute switching among feedback control modes, such as a current feedback control mode and a torque feedback control mode, of the respective feedback control units for driving of the AC motor. A switching command generating unit generates a switching command for an inverter based on a manipulated variable calculated by the selected feedback control unit. When a torque response request determining unit determines that a required torque responsiveness is high, the feedback control switching unit reduces the number of executions of switching among the feedback control modes.

A power regenerative converter, includes: a power module configured to include rectifiers and regenerative switches; a smoothing capacitor connected to direct-current power supply terminals, and that accumulates direct-current power during an alternating-current to direct-current conversion; a bus current detector that detects a bus current flowing between either of the direct-current power supply terminals and the smoothing capacitor; a power supply phase detector that detects a phase of an input power supply; a base drive signal generator that generates base drive signals that perform ON/OFF control of the regenerative switching elements based on a power supply phase detected by the power supply phase detection unit; a regeneration controller that performs a start and stop process of a power regenerative operation based on a detection result of the bus current detector and the base drive signals; and an overload detector that detects overload of a power regenerative converter based on the detection result of the bus current detector.

A power regenerative converter, includes: a power module configured to include rectifiers and regenerative switches; a smoothing capacitor connected to direct-current power supply terminals, and that accumulates direct-current power during an alternating-current to direct-current conversion; a bus current detector that detects a bus current flowing between either of the direct-current power supply terminals and the smoothing capacitor; a power supply phase detector that detects a phase of an input power supply; a base drive signal generator that generates base drive signals that perform ON/OFF control of the regenerative switching elements based on a power supply phase detected by the power supply phase detection unit; a regeneration controller that performs a start and stop process of a power regenerative operation based on a detection result of the bus current detector and the base drive signals; and an overload detector that detects overload of a power regenerative converter based on the detection result of the bus current detector.

A motor system provided with one motor and two inverters includes a first inverter control unit which changes a frequency of a first carrier wave (first carrier frequency) used for producing a switching signal fora first inverter according to an operating point of the motor; and a second inverter control unit which changes a frequency of a second carrier wave (second carrier frequency) used for producing a switching signal for a second inverter according to an operating point of the motor. The first carrier frequency has a changing characteristic depending on the first inverter control unit and the second carrier frequency has a changing characteristic depending on the second inverter control unit, and the changing characteristics are different from each other to make the first carrier frequency and the second carrier frequency differ from each other at an identical operating point.

A motor system provided with one motor and two inverters includes a first inverter control unit which changes a frequency of a first carrier wave (first carrier frequency) used for producing a switching signal fora first inverter according to an operating point of the motor; and a second inverter control unit which changes a frequency of a second carrier wave (second carrier frequency) used for producing a switching signal for a second inverter according to an operating point of the motor. The first carrier frequency has a changing characteristic depending on the first inverter control unit and the second carrier frequency has a changing characteristic depending on the second inverter control unit, and the changing characteristics are different from each other to make the first carrier frequency and the second carrier frequency differ from each other at an identical operating point.

The invention includes an inverter to convert a direct-current voltage from a direct-current power supply into an alternating-current voltage and apply the alternating-current voltage to a motor that, a direct-current-voltage detecting unit to detect a voltage in the direct-current power supply, a current detecting unit to detect an electric current flowing to the inverter, and an inverter control unit to generate PWM signals for driving switching elements of the inverter based on the detected voltage the detected electric current, to set a specific phase difference between a phase of a carrier signal used for generation of the PWM signals and a phase of the alternating-current voltage, and to control the inverter such that a frequency of the PWM signals are synchronized with a frequency of the alternating-current voltage, the frequency of the PWM signals being an integer multiple of three times the frequency of the alternating-current voltage.

The invention includes an inverter to convert a direct-current voltage from a direct-current power supply into an alternating-current voltage and apply the alternating-current voltage to a motor that, a direct-current-voltage detecting unit to detect a voltage in the direct-current power supply, a current detecting unit to detect an electric current flowing to the inverter, and an inverter control unit to generate PWM signals for driving switching elements of the inverter based on the detected voltage the detected electric current, to set a specific phase difference between a phase of a carrier signal used for generation of the PWM signals and a phase of the alternating-current voltage, and to control the inverter such that a frequency of the PWM signals are synchronized with a frequency of the alternating-current voltage, the frequency of the PWM signals being an integer multiple of three times the frequency of the alternating-current voltage.

Exhaust gases from an engine, input to turbo-compounder, drive a bladed turbine rotor therein, which drives a multi-phase AC generator, the output of which is used to electrically drive a multi-phase induction motor, the rotor of which is mechanically coupled to the engine, so as to provide for recovering power to the engine. The multi-phase AC generator may be coupled to the engine either by closure of a contactor, engagement of an electrically-controlled clutch, or by control of either a solid-state switching or control system or an AC excitation signal, when the frequency (f.sub.GENERATOR) of the multi-phase AC generator meets or exceeds that (f.sub.MOTOR) of the multi-phase induction motor.

The invention discloses a method for MGP new energy grid-connected control, wherein, the synchronous motor is connected to a synchronous generator; the new energy module drives the synchronous motor to rotate through a frequency converter; the frequency converter controls the power transmission; and the synchronous motor drives the synchronous generator for grid connection. The present invention has the beneficial effects that: the control method and system provided by the invention can improve the stability and reliability of the grid.