Magnet temperature estimation in surface PM machines during six-step operation

This paper presents a method for estimating the magnet temperature in surface permanent magnet synchronous machines (SPMSM´s) during six-step operation. Six-step operation allows the maximum available DC bus voltage to be applied to a machine, which maximizes its torque and speed range. Six-step operation produces currents harmonics that induces additional losses in the permanent magnets and can therefore increase their temperature. Increase of magnet temperature can result in a reduced torque capability and eventually in a risk of demagnetization if excessive values are reached, with real-time rotor magnet temperature monitoring being, therefore, advisable. Six-step operation provides opportunities for rotor temperature monitoring from the electrical terminal variables (voltages and currents) of the motor. To achieve this goal, the rotor high frequency resistance is measured using the harmonic voltages and currents due to six-step operation, from which the magnet temperature can be estimated.