Method for estimating a torque of a three-phase drive motor for a vehicle

A drive apparatus for a vehicle comprising:

• a converter;
• a three-phase drive motor;
• three phase lines, each said phase lines leading from the converter to the drive motor, and supplying said drive motor with power,
• a current measuring unit for measuring a respective current strength in at least two of the three phase lines;
• a voltage measuring unit for measuring a respective voltage at each of the three phase lines;
• a calculation unit for determining a rotating field frequency as a function of the respective current strengths measured by the current measuring unit or the respective voltages measured by the voltage measuring unit;
• an estimation unit for determining an estimated value for a torque as a function of the respective measured current strengths, the respective measured voltages and the determined rotating field frequency by calculating a power value as a sum of a first and of a second partial power value, wherein the first partial power value corresponds to the product of the current strength in the first phase line and a first line-to-line voltage between the first phase line and a third one of the three phase lines, and wherein the second partial power value corresponds to the product of the current strength in the second phase line and a second line-to line voltage between the second phase line and the third phase line;
• a low-pass filter configured to filter the power value for obtaining an average electrical active power of the converter;
• and
• a power loss model configured to determine a power loss in a drive motor;
• wherein a rotating field power is determined by subtracting the power loss from the average electrical active power of the converter and the torque is estimated as a function of the rotating field power.