Power conversion apparatus

A power conversion apparatus comprising:

• a converter that receives a three-phase AC power supply and outputs a DC voltage;
• an inverter connected to the output of the converter and drives an AC motor via an output switch;
• a power switch for directly driving the AC motor with the AC power supply;
• a first current detector for detecting an output current of the inverter;
• a voltage detector and a second current detector for detecting the voltage and current of the power supply system on the input side of the converter, respectively, and
• a control unit for controlling the three-phase output voltage of the inverter based on a first three-phase voltage command, the control unit involves:
• a speed controller that outputs a first Q-axis current reference by controlling so that a deviation between a given speed reference and a speed feedback obtained directly or indirectly of the AC motor is minimized;
• a first 3-phase to 2-phase converter for converting a three-phase current detected by the first current detector into a first Q-axis current feedback and a first D-axis current feedback based on a first reference phase;
• a first Q-axis current controller that outputs a first Q-axis voltage reference by controlling so that the deviation between the first Q-axis current reference via the first switch and the first Q-axis current feedback is minimized;
• a first D-axis current controller that outputs a D-axis voltage reference by controlling so that the deviation between a first D-axis current reference corresponding to a given magnetic flux reference via a second switch, and the first D-axis current feedback is minimized;
• a first 2-phase to 3-phase converter that converts the first Q-axis voltage reference and the first D-axis voltage reference into the first three-phase voltage command based on the first reference phase;
• an operation circuit for obtaining an output frequency of the inverter by computation from the speed feedback, the first Q-axis current reference, and the magnetic flux reference, and integrates the obtained output frequency to obtain the first reference phase;
• a phase synchronization circuit for obtaining a second reference phase by using the output of the voltage detector as an input;
• a third switch for switching between the first reference phase and the second reference phase;
• a reactive power detection circuit for detecting reactive power of the power supply system from the voltage detector and the second current detector;
• a reactive power controller that outputs a second D-axis current reference by controlling so that the deviation between the reactive power and a predetermined reactive power reference is minimized, and
• a synchronous incorporation controller for switching the AC motor from driving by the inverter to driving by the AC power supply,
• wherein, the synchronous incorporation controller adjusts the speed of the AC motor and the output voltage of the inverter to match the voltage, output frequency and phase of the AC power supply and the inverter, and turns on the power switch to make the synchronous incorporation, and then the first to third switches are switched to perform reactive power control of the power system including the drive system of the AC motor by the inverter.