Quasi variable frequency motor controller

Patent metadata

Field	Value
Publication number	US-9350275-B2
Application number	US-201414321330-A
Country	US
Kind code	B2
Filing date	Jul 1, 2014
Priority date	May 19, 2014
Publication date	May 24, 2016
Grant date	May 24, 2016

Abstract

An apparatus for a quasi variable frequency motor controller is includes a DFC module that applies a first frequency to a motor as part of a discrete frequency control (“DFC”) method for motor starting. The first frequency includes a discrete frequency in a plurality of discrete frequencies of the DFC method and each discrete frequency includes a frequency lower than a fundamental frequency of an alternating current (“AC”) voltage source providing power to the motor. The apparatus includes a torque module that determines when motor torque generated by the motor reaches a negative torque threshold and a next frequency module that applies a second frequency to the motor in response to the torque module determining that the motor torque has reached the negative torque threshold. The second frequency is a next frequency in the DFC method.

First claim

What is claimed is:

1. An apparatus comprising:
a DFC module that applies a first frequency to a motor as part of a discrete frequency control (“DFC”) method for motor starting, the first frequency comprising a discrete frequency in a plurality of discrete frequencies of the DFC method and wherein each discrete frequency comprises a frequency lower than a fundamental frequency of an alternating current (“AC”) voltage source providing power to the motor;
a torque module that determines, from data received from motor sensors, when motor torque generated by the motor reaches a negative torque threshold; and
a next frequency module that applies a second frequency to the motor in response to the torque module determining that the motor torque has reached the negative torque threshold, the second frequency comprising a next frequency in the DFC method,
wherein at least a portion of the DFC module, the torque module, and the next frequency module comprise one or more of hardware and executable code, the executable code stored on one or more non-transitory computer readable storage media.

2. The apparatus of claim 1 , further comprising a switch module that selectively connects each input power conductor to the motor in a sequence, wherein the DFC module connects the power conductors to the motor based on a discrete frequency of the plurality of discrete frequencies.

3. The apparatus of claim 2 , wherein the switch module comprises one or more thyristors and wherein each thyristor is controlled using the DFC method by adjusting a phase angle for turning on each thyristor.

4. The apparatus of claim 2 , further comprising a step start module that executes one or more starting steps, each starting step initiated after the next frequency module advances the discrete frequency to a last discrete frequency of the DFC method, each step comprising one or more of:
setting, for a fixed period of time, an on time of a switch of the switching module to a fixed value; and
ramping an on time of a switch of the switching module.

5. The apparatus of claim 4 , further comprising a contactor module that applies full input voltage to the motor after one or more of a last step of the step start module and a last discrete frequency of the DFC module, the contactor module applying the full input voltage by closing a contactor in parallel with each thyristor.

6. The apparatus of claim 1 , wherein the DFC module applies a discrete frequency by varying a phase angle for turning on a thyristor to generate positive current pulses of varying amplitudes for a positive half cycle of the discrete frequency and then varying a phase angle for turning on a thyristor to generate negative current pulses of varying amplitudes for a negative half cycle of the discrete frequency, wherein each current pulse is generated at a rate consistent with the fundamental frequency of the AC voltage source.

7. The apparatus of claim 1 , wherein the torque module determines motor torque by calculating motor torque from input voltage and current information, the input voltage and current information from conductors connected to the motor to provide power to the motor.

8. The apparatus of claim 7 , wherein the torque module determines motor torque using the following equation:

T
est

=

3
2

⁢

P
⁡

[

I
β

·

∫

(

V
α

-

I
α

⁢

R
s

)

⁢

ⅆ
t

-

I
α

·

∫

(

V
β

-

I
β

⁢

R
s

)

⁢

ⅆ
t

]

wherein:
T est is calculated motor torque;
P is the number of motor poles;
R s is resistance of stator winding;
V α , V β are stator voltage in a stationary reference frame; and
I α , I β are stator current in the stationary reference frame,
wherein the voltage and current for each phase of the motor are transformed to the stationary reference frame using an alpha-beta transformation.

9. The apparatus of claim 1 , wherein the torque module determines motor torque by measuring motor torque.

10. The apparatus of claim 1 , wherein the torque module determines motor torque based on a phase of input power in relation to a phase of rotor current.

11. The apparatus of claim 1 , wherein the next frequency module applies a next frequency of the DFC method each time the torque module determines that the motor torque reaches the negative torque threshold until reaching a final frequency of the DFC method.

12. The apparatus of claim 1 , wherein a last discrete frequency in the DFC method comprises a frequency that is between 25 percent and 50 percent of the fundamental frequency of the AC voltage source.

13. The apparatus of claim 1 , wherein the motor comprises one of a three-phase AC squirrel cage motor and a three-phase AC synchronous motor.

14. A metho

Assignees

• Rockwell Automation Tech Inc

Inventors

• Wei Kun
• Lu Haihui
• Jaap Andrew
• Messersmith David
• Langer Randall
• Lee Ping

Classifications

• H02P1/04 Primary

  Means for controlling progress of starting sequence in dependence upon time or upon current, speed, or other motor parameter · CPC title

• H02P1/40

  in either direction of rotation · CPC title

• H02P1/16

  for starting dynamo-electric motors or dynamo-electric converters · CPC title

• H02P21/28 Primary

  Stator flux based control · CPC title

• H02P27/16

  using AC to AC converters without intermediate conversion to DC (H02P27/05 takes precedence) · CPC title