Method for identifying a malfunction in an inverter-motor assembly

A method for identifying a malfunction in a multiphase inverter-motor assembly comprising an electric motor and an inverter having power switches distributed across branches, each phase of the electric motor being connected to a branch of the inverter by a phase switch, the method comprising a plurality of sequential diagnostic procedures each comprising:

• initially configuring the inverter in which a control choice is made for each branch of the inverter, this choice being made from among the group consisting of:
• open-mode fixed control of the power switches;
• pulse-width modulation control according to a predetermined diagnostic duty cycle of the power switches;
• initially configuring the phase switches in which a choice of state is made for each phase switch, this choice being made between a closed state and an open state;
• biasing the phases in which a predetermined diagnostic voltage is applied to each of the branches of the inverter;
• a voltage measurement step in which the voltage of each phase is measured;
• a comparison step in which the voltage measurement of each phase is compared with an expected resultant value, and
• identifying a malfunction when the voltage measurement of a phase differs from the expected resultant value, and said method further comprising:
• a first sequential diagnostic procedure in which:
• all of the power switches are open-mode controlled in the step of initially configuring the inverter;
• all of the phase switches are positioned in the open state in the step of initially configuring the phase switches;
• in the step of biasing the phases the predetermined diagnostic voltage is substantially 50% of the supply voltage of the inverter;
• in the comparison step, the expected resultant value for each phase is substantially equal to the predetermined diagnostic voltage;
• in the step of identifying a malfunction, when the voltage measurement of a phase is substantially equal to the supply voltage of the inverter, a short circuit is identified on the power switch on the high side of the corresponding phase,
• a second sequential diagnostic procedure in which:
• in the step of initially configuring the inverter, all of the power switches are open-mode controlled with the exception of the power switches corresponding to a phase being tested which are pulse-width modulation controlled according to a predetermined diagnostic duty cycle;
• all of the phase switches are positioned in the open state in the step of initially configuring the phase switches;
• in the step of biasing the phases, the predetermined diagnostic voltage is substantially 50% of the supply voltage of the inverter;
• in the comparison step, the expected resultant value for the phase being tested is a value substantially equal to the supply voltage of the inverter multiplied by the predetermined diagnostic duty cycle, and the expected resultant value for the other phases is substantially equal to the predetermined diagnostic voltage,
• a third sequential diagnostic procedure in which:
• in the step of initially configuring the inverter, all of the power switches are open-mode controlled;
• all of the phase switches are positioned in the closed state in the step of initially configuring the phase switches;
• in the step of biasing the phases, the predetermined diagnostic voltage is substantially 50% of the supply voltage of the inverter;
• in the voltage measurement step, the average of the voltages of all of the phases is determined;
• in the comparison step, the expected resultant value for the average of the voltages of all of the phases is substantially equal to the predetermined diagnostic voltage;
• in the step of identifying a malfunction, when the average of the voltages of all of the phases is lower than the predetermined diagnostic voltage, a short circuit is identified between at least one phase and ground, this short circuit being located between the phase switches and the motor.