Apparatus and method for determining mechanical parameters of an electric motor and load

1. A system for determining mechanical characteristics of an electric motor and mechanical load, comprising:

a speed signal modulation circuit comprising:

a first proportional integral (PI) controller configured to control a q-axis AC reference current based on a requested maximum AC rotor speed and an estimated maximum AC rotor speed, and

a second PI controller configured to control a q-axis DC reference current based on a requested DC rotor speed and an estimated DC rotor speed;

a field-oriented control (FOC) current loop circuit configured to generate AC and DC reference voltages in response to the q-axis AC reference current and q-axis DC reference current under control of an estimated electrical rotor position and measured feedback currents detected at the electric motor, wherein a d-axis reference current is set to zero;

a sensor-less rotor speed estimator circuit configured to generate an estimated rotor position angle, estimated rotor speed, and torque constant in response to the AC and DC reference voltages and measured feedback currents detected at the electric motor;

a speed signal demodulation circuit comprising:

an AC rotor speed estimation circuit configured to generate the estimated maximum AC rotor speed from the estimated rotor speed,

a DC rotor speed estimation circuit configured to generate the estimated DC rotor speed from the estimated rotor speed, and

a phase angle detection circuit configured to generate a phase angle measure of the AC rotor speed; and

a mechanical characteristics estimation circuit configured to determine a plurality of load torque parameters for the electric motor and mechanical load based on the q-axis AC reference current, q-axis DC reference current, a maximum AC rotor speed component, a DC rotor speed component, phase angle measure of the AC rotor speed, and torque constant, where the plurality of load torque parameters comprises a combined moment of inertia parameter, a combined static friction parameter A, a combined viscous friction parameter B, and one or more mechanical parameters representing one or more load characteristics.

2. The system of claim 1 , where the one or more mechanical parameters representing one or more load characteristics comprise a mechanical parameter C representing a fan characteristic load that is proportional to a square of a fan rotational speed and/or a mechanical parameter D representing a pump characteristic load that is proportional to a cube of a pump rotational speed.

3. The system of claim 1 , further comprising a voltage supply inverter circuit configured to receive the AC and DC reference voltages from the FOC current loop circuit and provide real AC and DC voltages to the electric motor which comprises a 3-phase permanent magnet motor.

4. The system of claim 3 , where the 3-phase permanent magnet motor is connected to provide the measured feedback currents to the FOC current loop circuit and sensor-less rotor speed estimator circuit.

5. The system of claim 1 , where the FOC current loop circuit comprises a direct-current (d-current) control block, a quadrature-current (q-current) control block, an inverse Park transformation block, a space vector modulation block, a voltage supply inverter (VSI) block, a Clarke transformation block, and a Park transformation block connected to controlling magnetizing and torque-producing components of the stator current in the electric motor.

6. The system of claim 1 , where sensor-less rotor speed estimator circuit comprises a rotor flux estimator block and angle tracking observer block which are connected to receive the measured feedback currents and the reference voltages and to generate the estimated rotor angle position, estimated rotor speed, and torque constant.

7. The system of claim 1 , where the mechanical characteristics estimation circuit is configured to determine the combined moment of inertia parameter based on the torque constant provided by the sensor-less rotor speed estimator circuit, the phase angle measure of the AC rotor speed, and the estimated maximum AC rotor speed provided by the speed signal demodulation circuit, and the amplitude of the AC q-axis current provided by speed signal modulator circuit i qACmax_req .

8. The system of claim 1 , where the mechanical load is selected from a group consisting of a gearbox load, a fan load, and a pump/compressor load.

9. The system of claim 2 , where the mechanical characteristics estimation circuit is configured to determine the combined static friction parameter A, the combined viscous friction parameter B, the mechanical parameter C, and the mechanical parameter D in a parameter matrix X by solving a matrix equation X=W rDC −1 ·K T ·I qDC_req , where W rDC −1 is a precalculated inverted speed matrix comprising a plurality of rotor speed values, where i q DC req is a precalculated q-axis current demand matrix comprising a plurality of q-axis DC reference current values, and where K T is the torque constant.

10. A method for determining mechanical parameters of an electric motor and mechanical load, the method comprising:

starting the electric motor in an open loop by providing reference voltages to the electric motor that are sufficient to generate a predetermined minimum rotor speed at the electric motor;

activating a speed modulator unit, FOC current loop unit, rotor flux estimator unit, angle tracking observer unit, and speed demodulator unit to initiate a mechanical parameter estimation process in a closed loop;

generating an estimated rotor position, estimated rotor speed, and estimated torque constant with the rotor flux estimator unit and the angle tracking observer unit based on the reference voltages and current feedback measurements from the electric motor;

demodulating the estimated rotor speed into estimated AC and DC rotor speed components at the speed demodulator unit;

modulating AC and DC current reference values to excite the electric motor and mechanical load by corresponding AC and DC torque components at the speed modulator unit based on demanded AC and DC rotor speed components and estimated AC and DC rotor speed components; and

estimating a plurality of load torque parameters for the electric motor and mechanical load based on the demanded AC and DC current values, phase angle of the AC current value, estimated AC and DC rotor speed components, and estimated torque constant,

where the plurality of load torque parameters comprises a combined moment of inertia parameter J, a combined static friction parameter A, a combined viscous friction parameter B, a mechanical parameter C representing a fan characteristic load that is proportional to a square of a fan rotational speed, and mechanical parameter D representing a pump characteristic load that is proportional to a cube of a pump rotational speed.

11. The method of claim 10 , where the electric motor comprises a 3-phase permanent magnet motor or a DC permanent magnet motor.

12. The method of claim 10 , further comprising generating, by the FOC current loop unit, reference voltages for a voltage supply inverter based on the estimated rotor position, AC and DC current reference values, and current feedback measurements.

13. The method of claim 10 , where estimating the plurality of load torque parameters comprises:

constructing a parameter matrix X including matrix values for the combined static friction parameter A, the combined viscous friction parameter B, the mechanical parameter C, and the mechanical parameter D; and

solving a matrix equation X=W rDC_req − ·K T ·I qDC_req , where W rDC_req −1 is a precalculated inverted speed demand matrix comprising a plurality of rotor speed demand values, where I qDC_req is a precalculated q-axis current demand matrix comprising a plurality of q-axis DC reference current values, and where K T is the torque constant.

14. The method of claim 10 , where estimating the plurality of load torque parameters comprises:

determining the combined moment of inertia parameter J based on the estimated torque constant, along with a phase angle measure of the AC rotor speed and estimated maximum AC rotor speed provided by the speed demodulator unit and an amplitude of the AC q-axis current provided by the speed modulator unit.

15. The method of claim 10 , where the mechanical load is selected from a group consisting of a gearbox load, a fan load, and a pump load.

16. An apparatus for determining mechanical parameters of a combined electric motor and mechanical load, comprising:

a speed modulator arranged to receive a nominal speed n N and to produce a q-axis AC reference current i qAC_req , a q-axis DC reference current i qDC_req , a maximum q-axis AC current value i qACmax_req , and a phase angle of the modulated AC voltage phase signal θ iqAC under control of an estimated maximum AC rotor speed ω rACmax_est and an estimated DC rotor speed ω rDC_req ;

a field-oriented control current loop having an input d-axis reference current I dreq set to zero and arranged to receive the q-axis AC reference current i qDC_req and q-axis DC reference current i qACmax_req and to produce reference voltages for a voltage supply inverter under control of an estimated electrical rotor position θ el_est and measured feedback currents detected at the electric motor;

a rotor speed and angle estimator arranged to receive the reference voltages and measured feedback currents detected at the electric motor and to produce an estimated rotor speed ω r_est a, a torque constant K T , and the estimated electrical rotor position θ el_est ;

a speed demodulator arranged to receive the estimated rotor speed ω r_est and to produce the estimated maximum AC rotor speed ω rACmax_est , the estimated DC rotor speed ω rDC_est , and a phase angle measure of the AC rotor speed θ ωrAC_est ; and

a mechanical parameters estimator arranged to receive the q-axis DC reference current i qDC_req , maximum q-axis AC current value i qACmax_req , phase angle of the modulated AC voltage phase signal θ iqAC , estimated maximum AC rotor speed ω rACmax_est , estimated DC rotor speed ω rDC_est , phase angle of the AC rotor speed θ ωrAC_est , and torque constant K T , and to determine a plurality of load torque parameters for the electric motor and mechanical load comprising a combined moment of inertia parameter J, a combined static friction parameter A, a combined viscous friction parameter B, a mechanical parameter C representing a fan characteristic load that is proportional to a square of a fan rotational speed, and mechanical parameter D representing a pump characteristic load that is proportional to a cube of a pump rotational speed.

17. The apparatus of claim 16 , where the electric motor comprises a 3-phase permanent magnet motor or a DC permanent magnet motor.

18. The apparatus of claim 16 , where the mechanical load is selected from a group consisting of a gearbox load, a fan load, and a pump load.

19. The apparatus of claim 16 , where the mechanical parameters estimator is configured to determine the combined static friction parameter A, the combined viscous friction parameter B, the mechanical parameter C, and the mechanical parameter D in a parameter matrix X by solving a matrix equation X=W rDC_req − ·K T ·I qDC_req , where W rDC_req −1 is a precalculated inverted speed demand matrix comprising a plurality of rotor speed demand values, where i qDC_req is a precalculated q-axis current demand matrix comprising a plurality of q-axis DC reference current values, and where K T is the torque constant.

20. The apparatus of claim 16 , where the mechanical parameters estimator is configured to determine the combined moment of inertia parameter J based on the torque constant K T , the phase angle measure of the AC rotor speed θ ωrAC_est , the estimated maximum AC rotor speed provided by the speed signal demodulation circuit, and the maximum q-axis AC current value i qACmax_req .