Control device and power conversion device for detecting failure of an AC capacitor

A control device of a power conversion device including:

• at least one alternating-current capacitor which is positioned in a capacitor circuit branching from an alternating-current circuit on an output side of an inverter and which is disconnected from the capacitor circuit in an event of a fault;
• and
• a current sensor which is positioned in series with an alternating-current reactor between the inverter and a branch point to the capacitor circuit in the alternating-current circuit on the output side of the inverter and which obtains each of current values of alternating currents of respective phases that flow through the alternating-current circuit,
• the control device comprising:
• an amplitude calculating circuit which, during synchronous control for synchronizing an output voltage of the inverter and a system voltage of a system side which is performed during start-up of the power conversion device in a state where an alternating-current switch on the system side has been opened, obtains each of the current values of the alternating currents of the respective phases that flow through the alternating-current capacitor from the current sensor and which calculates each of values of amplitudes of fundamental wave components of the alternating currents of the respective phases based on the obtained current values of the alternating currents of the respective phases;
• a fault determining circuit which performs a magnitude comparison between each of the values of the amplitudes of the fundamental wave components of the alternating currents of the respective phases calculated by the amplitude calculating circuit and a predetermined determination value and which determines a fault of the alternating-current capacitor when the value of the amplitude of at least any phase among the values of the amplitudes of the fundamental wave components of the alternating currents of the respective phases is smaller than the predetermined determination value;
• and
• a fault information reporting circuit which, when a fault of the alternating-current capacitor is determined by the fault determining circuit during the synchronous control, reports fault information of the alternating-current capacitor, wherein
• the amplitude calculating circuit calculates each of the values of the amplitudes of the fundamental wave components of the alternating currents of the respective phases based on a predetermined current component of the alternating current of each phase calculated by multiplying each of the current values of the alternating currents of the respective phases by a value based on a phase angle adjusted based on the system voltage on the system side.