Method and apparatus for instability compensation of V/Hz pulse width modulation inverter-fed induction motor drives
First Claim
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1. A method of identifying instability in a three-phase induction motor drive system, comprising:
- (a) detecting, in an instability detector circuit coupled to at least two of three phases of said motor drive system, a change ##EQU27## in the magnitude of stator current in the system; and
(b) detecting, in an instability detector circuit coupled to at least two of three phases of said motor drive system, a change Δ
ω
in angular speed change in the system; and
(c) identifying instability in said motor drive system based upon values of ##EQU28## and Δ
ω
.
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Abstract
Index signals which represent the degree of instability in a three-phase induction motor system is derived by using phase current signals which are usually already available in V/Hz PWM inverters for other purposes. Proportional integration compensators, which may be implemented in software, process these index signals and generate frequency and/or voltage adjustments to the V/Hz controller in order to compensate for speed instability in the system. The compensation algorithm is robust to system changes and is also effective to improve acceleration and deceleration performance.
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Citations
18 Claims
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1. A method of identifying instability in a three-phase induction motor drive system, comprising:
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(a) detecting, in an instability detector circuit coupled to at least two of three phases of said motor drive system, a change ##EQU27## in the magnitude of stator current in the system; and
(b) detecting, in an instability detector circuit coupled to at least two of three phases of said motor drive system, a change Δ
ω
in angular speed change in the system; and(c) identifying instability in said motor drive system based upon values of ##EQU28## and Δ
ω
. - View Dependent Claims (2, 3)
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4. A method of controlling a three-phase induction motor drive system, comprising:
- (a) detecting a change ##EQU34## in the magnitude of stator current in the system;
(b) detecting a change Δ
ω
in angular speed change in the system;(c) computing a change Δ
ν
s in a voltage vector ν
s derived from said change ##EQU35## in the magnitude of stator current and said change Δ
ω
in angular speed change in said system; and(d) adjusting said system'"'"'s output based on said change Δ
ν
s in said voltage vector ν
s . - View Dependent Claims (5, 6, 7, 8, 9)
- (a) detecting a change ##EQU34## in the magnitude of stator current in the system;
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10. An apparatus for identifying instability in a three-phase induction motor drive system, comprising:
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instability detector circuitry coupled to at least two of said three phases of said motor drive, for detecting a change ##EQU45## in the magnitude of stator current in the system and for detecting a change Δ
ω
in angular speed change in the system; andcompensator circuitry coupled to said instability detection circuitry for identifying instability based on values of ##EQU46## and Δ
ω
. - View Dependent Claims (11, 12)
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13. An apparatus for controlling a three-phase induction motor drive system, comprising:
- instability detector circuitry, coupled to at least two of said three phases of said motor drive, for detecting a change ##EQU51## in the magnitude of stator current in the system and for detecting a change Δ
ω
in angular speed change in the system;processing circuitry for computing a change Δ
ν
s in a voltage vector ν
s derived from said change ##EQU52## in the magnitude of stator current and said change Δ
ω
in angular speed change in said system; andcontrol circuitry, responsive to said change ν
s in said voltage vector ν
s to adjust said system'"'"'s output. - View Dependent Claims (14, 15, 16, 17, 18)
- instability detector circuitry, coupled to at least two of said three phases of said motor drive, for detecting a change ##EQU51## in the magnitude of stator current in the system and for detecting a change Δ
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