Power conversion device and method for diagnosing abnormality in voltage sensor characteristics

A method for diagnosing an abnormality in voltage sensor characteristics implemented in an abnormality diagnosis controller of a power conversion device, the power conversion device comprising:

• a voltage boost converter which performs DC/DC conversion of a DC voltage supplied from a DC power source and outputs a boosted DC voltage by switching of a first power semiconductor element group;
• an inverter which is connected to a subsequent stage of the voltage boost converter, performs DC/AC conversion of the boosted DC voltage by switching of a second power semiconductor element group, and outputs an AC voltage;
• a primary smoothing capacitor which is connected between the DC power source and the voltage boost converter and smoothens the DC voltage supplied to the voltage boost converter;
• a secondary smoothing capacitor which is connected between the voltage boost converter and the inverter and smoothens the boosted DC voltage supplied to the inverter;
• an intermediate capacitor provided inside the voltage boost converter;
• a primary-side voltage sensor which measures the voltage of the primary smoothing capacitor;
• a secondary-side voltage sensor which measures the voltage of the secondary smoothing capacitor;
• an intermediate voltage sensor which measures the voltage of the intermediate capacitor;
• and
• an abnormality diagnosis controller which makes a diagnosis of the presence/absence of an abnormality in detection characteristics of the three voltage sensors, i.e. the primary-side voltage sensor, the secondary-side voltage sensor and the intermediate voltage sensor;
• wherein the method comprises:
• a first step of halting switching operations of the voltage boost converter and the inverter;
• a second step of disconnecting the DC power source which is supplied to the voltage boost converter;
• a third step of implementing a discharge operation based on control of the voltage boost converter and a discharge operation based on control of the inverter, and measuring a detected voltage value of each of the three voltage sensors, i.e. the primary-side voltage sensor, the secondary-side voltage sensor and the intermediate voltage sensor;
• a fourth step of successively sampling and gathering the detected voltage values of the three voltage sensors during the discharge operation based on control of the inverter, upon halting the discharge operation based on control of the voltage boost converter when the deviation in the detected voltage values of two voltage sensors selected from among the three voltage sensors becomes equal to or lower than a predetermined deviation threshold value, and selecting and successively storing, in a storage unit, the detected voltage values of the two voltage sensors which indicate a maximum value and a minimum value, among the three voltage sensors, for each successive sampling;
• a fifth step of halting the discharge operation based on control of the inverter, when all of the detected voltage values of the three voltage sensors which are successively gathered in the fourth step become less than a predetermined threshold value;
• and
• a sixth step of making a diagnosis of the presence/absence of an abnormality in the detection characteristics of the three voltage sensors, on the basis of comparison results between the deviation between the maximum value and the minimum value successively stored in the storage unit during implementation of the fourth step, and a predetermined determination threshold value.