Self tuning method and apparatus for permanent magnet sensorless control

A method of measuring a plurality of parameters of a Permanent Magnet Synchronous Motor (PMSM) by a motor controller to differentiate between a plurality of PMSMs, the method comprising the steps of:

• performing a first stage by
• applying regulated DC motor currents at a commanded fixed rotor angle, parking the PMSM at standstill, whereby a quadrature voltage applied across the PMSM windings is proportional to a stator resistance and to an applied park current, and
• selecting an initial set of controller parameters;
• performing a second stage by
• applying the quadrature voltage equal to zero,
• accelerating the PMSM with a constant torque up to a preset target speed in accordance with a time constant corresponding to an exponential decay of a quadrature current, and
• regulating a stator current at 0 value using a total acceleration time to the preset target speed, which the stator current is at 0 value when regulated DC motor currents are at zero value;
• and
• performing a third stage by calculating
• an electrical constant of the PMSM based on the values of the applied quadrature voltage and a free motor speed immediately after applying the 0 stator current,
• a load inertia based on the previously measured total acceleration time, and
• a set of parameters for the controller based on the determined motor parameters.

A controller for performing a Pulse Width Modulation (PWM) drive of a Permanent Magnet Synchronous Motor (PMSM) and for determining PMSM parameters to differentiate between a plurality of PMSMs, the controller comprising:

• an outer speed loop for setting the desired speed of the PMSM;
• a first inner current loop for regulating a quadrature component iq of the motor current;
• a second inner current loop for regulating a direct component id of the motor current, the motor current id being the equivalent motor stator current projected onto a d-axis aligned with a rotor field, and the motor current iq being the equivalent motor stator current projected on a q-axis, which is perpendicular to the rotor field;
• and
• a speed observer circuit having an input of voltages vα and vβ and currents iα and iβ and outputting an angular position of a rotor θr and an observed rotor speed ωobs,
• wherein each of the loops includes a compensator, whose parameters can be adjusted based on measured motor parameters, further comprising a processor for measuring the motor parameters that implements the steps of
• determining a plurality of parameters of a Permanent Magnet Synchronous Motor (PMSM) by a motor controller to differentiate between a plurality of PMSMs, the method comprising the steps of:
• applying regulated DC motor currents at a commanded fixed rotor angle;
• measuring a quadrature voltage vq after an initial transient has elapsed, the quadrature voltage being applied across the PMSM windings;
• parking the PMSM at standstill, whereby the quadrature voltage is proportional to a stator resistance and to the applied park current Ipark;
• selecting an initial set of controller parameters;
• applying the quadrature voltage equal to zero;
• measuring a time constant Ts corresponding to an exponential decay of a quadrature current iq;
• accelerating the PMSM with a constant torque up to a preset target speed;
• measuring a total acceleration time taccelerate until the preset target speed ωtarget is reached;
• regulating a stator current at 0 value, whereby the stator current is at 0 value when currents iq(ref) and id(ref) are both at zero value;
• measuring the quadrature voltage and a freewheeling motor speed ωfreewheel immediately after applying the 0 stator current;
• calculating an electrical constant KE of the PMSM based on the measured values of the applied quadrature voltage and the freewheeling motor speed;
• calculating a load inertia J based on the previously measured total acceleration time;
• and
• calculating a set of parameters for the controller based on the determined motor parameters.