Method and apparatus for stability control of open loop motor drive operation
Motor drives and control methods are presented for sensorless motor speed control in which inverter output currents are sampled from the inverter output, and a frequency modulation value is determined based on the current feedback and either one or more voltage commands or one or more voltage feedback signals. A speed or frequency setpoint is adjusted at least partially according to the frequency modulation value to provide an adjusted frequency or speed setpoint value that is then used in controlling the inverter to provide stability control to mitigate hunting or motor stoppage.
1. A method for sensorless motor speed control in a motor drive, the method comprising:
receiving a frequency or speed setpoint value representing a desired motor speed for a driven motor;
sampling at least one AC output current feedback signal or value from an output of an inverter of the motor drive;
computing a frequency modulation value based on the at least one AC output current feedback signal or value and on at least one voltage command or feedback signal or value, wherein computing the frequency modulation value comprises:
computing an estimated motor performance value based on the at least one AC output current feedback signal or value and on the at least one voltage command or feedback signal or value, and
computing the frequency modulation value based at least partially on the estimated motor performance value;
adjusting the frequency or speed setpoint value based at least partially on the frequency modulation value to provide an adjusted frequency or speed setpoint value; and
controlling the inverter according to the adjusted frequency or speed setpoint value.
2. The method of claim 1 , wherein adjusting the frequency or speed setpoint value comprises:
rate limiting the frequency or speed setpoint value to provide a rate limited frequency or speed setpoint value; and
subtracting the frequency modulation value from the rate limited frequency or speed setpoint value to provide the adjusted frequency or speed setpoint value.
3. The method of claim 1 , wherein adjusting the frequency or speed setpoint value comprises subtracting the frequency modulation value from the frequency or speed setpoint value to provide the adjusted frequency or speed setpoint value.
4. The method of claim 3 , wherein computing the frequency modulation value comprises:
high pass filtering the estimated motor performance value to provide a filtered estimated motor performance value; and
computing the frequency modulation value based at least partially on the filtered estimated motor performance value.
5. The method of claim 3 , wherein computing the estimated motor performance value comprises computing an estimated torque value, and wherein the frequency modulation value is computed at least partially according to the estimated torque value.
6. The method of claim 3 , wherein computing the estimated motor performance value comprises computing at least one of an estimated power factor value, an estimated power factor angle value, and an estimated power value, and wherein the frequency modulation value is computed at least partially according to the at least one estimated power factor value, power factor angle value, or power value.
7. The method of claim 1 , wherein computing the frequency modulation value comprises:
high pass filtering the estimated motor performance value to provide a filtered estimated motor performance value; and
computing the frequency modulation value based at least partially on the filtered estimated motor performance value.
8. The method of claim 1 , wherein computing the estimated motor performance value comprises computing an estimated torque value, and wherein the frequency modulation value is computed at least partially according to the estimated torque value.
9. The method of claim 8 , wherein computing the estimated torque value comprises:
computing at least one estimated stator or rotor flux value based on the at least one AC output current feedback signal or value, the at least one voltage command or feedback signal or value, and on at least one resistance value; and
computing the estimated torque value based on the at least one estimated flux value, the at least one AC output current feedback signal or value, and on a rated torque value.
10. The method of claim 1 , wherein computing the estimated motor performance value comprises computing at least one of an estimated power factor value, an estimated power factor angle value, and an estimated power value, and wherein the frequency modulation value is computed at least partially according to the at least one estimated power factor value, power factor angle value, or power value.
11. A non-transitory computer readable medium with computer executable instructions for sensorless motor speed control in a motor drive, the computer readable medium comprising computer executable instructions for:
receiving a frequency or speed setpoint value representing a desired motor speed for a driven motor;
sampling at least one AC output current feedback signal or value from an output of an inverter of the motor drive;
computing a frequency modulation value based on the at least one AC output current feedback signal or value and on at least one voltage command or feedback signal or value, wherein computing the frequency modulation value comprises:
computing an estimated motor performance value based on the at least one AC output current feedback signal or value and on the at least one voltage command or feedback signal or value, and
computing the frequency modulation value based at least partially on the estimated motor performance value;
adjusting the frequency or speed setpoint value based at least partially on the frequency modulation value to provide an adjusted frequency or speed setpoint value; and
controlling the inverter according to the adjusted frequency or speed setpoint value.
12. A motor drive, comprising:
an inverter including a plurality of switching devices operable according to switching control signals to provide AC output power to drive a motor load; and
a sensorless motor speed controller providing the switching control signals to the inverter to regulate the AC output power at least partially according to a frequency or speed setpoint value, the sensorless motor speed controller comprising:
a signal generator component operative to compute a frequency modulation value based on at least one AC output current feedback signal or value representing at least one AC output current of the inverter and on at least one voltage command or feedback signal or value used in controlling the inverter, wherein the signal generator component is operative to compute an estimated motor performance value based on the at least one AC output current feedback signal or value and on the at least one voltage command or feedback signal or value, and to compute the frequency modulation value based at least partially on the estimated motor performance value,
an adjustment component operative to adjust the frequency or speed setpoint value based at least partially on the frequency modulation value to provide an adjusted frequency or speed setpoint value, and
a command generator component operative to provide the switching control signals to the inverter at least partially according to the adjusted frequency or speed setpoint value.
13. The motor drive of claim 12 , wherein the sensorless motor speed controller comprises a high pass filter operative to high pass filter the estimated motor performance value to provide a filtered estimated motor performance value; and
signal generator component is operative to compute the frequency modulation value based at least partially on the filtered estimated motor performance value.
14. The motor drive of claim 12 , wherein the signal generator component is operative to compute the estimated motor performance value as an estimated torque value, and to compute the frequency modulation value based at least partially on the estimated torque value.
15. The motor drive of claim 12 , wherein the signal generator component is operative to compute the estimated motor performance value as at least one of an estimated power factor value, an estimated power factor angle value, and an estimated power value, and to compute the frequency modulation value based at least partially on the at least one estimated power factor value, power factor angle value, or power value.
16. The motor drive of claim 12 , wherein the sensorless motor speed controller comprises a rate limiter component operative to rate limit the frequency or speed setpoint value to provide a rate limited frequency or speed setpoint value; and
wherein the adjustment component is operative to subtract the frequency modulation value from the rate limited frequency or speed setpoint value to provide the adjusted frequency or speed setpoint value.
17. The motor drive of claim 12 , wherein the adjustment component is operative to subtract the frequency modulation value from the frequency or speed setpoint value to provide the adjusted frequency or speed setpoint value.