Method and apparatus for instability compensation of V/Hz pulse width modulation inverter-fed induction motor drives
AssigneeBaldor Electric Company
InventorYouqing Xiang
Life of this patent
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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.
Claims18
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 .DELTA..omega. in angular speed change in the system;
- and
- (c) identifying instability in said motor drive system based upon values of ##EQU28## and .DELTA..omega..
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 .DELTA..omega. in angular speed change in the system;
- (c) computing a change .DELTA..nu..sub.s in a voltage vector .nu..sub.s derived from said change ##EQU35## in the magnitude of stator current and said change .DELTA..omega. in angular speed change in said system;
- and
- (d) adjusting said system's output based on said change .DELTA..nu..sub.s in said voltage vector .nu..sub.s .
An apparatus for identifying instability in 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 ##EQU45## in the magnitude of stator current in the system and for detecting a change .DELTA..omega. in angular speed change in the system;
- and
- compensator circuitry coupled to said instability detection circuitry for identifying instability based on values of ##EQU46## and .DELTA..omega..
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 .DELTA..omega. in angular speed change in the system;
- processing circuitry for computing a change .DELTA..nu..sub.s in a voltage vector .nu..sub.s derived from said change ##EQU52## in the magnitude of stator current and said change .DELTA..omega. in angular speed change in said system;
- and
- control circuitry, responsive to said change .nu..sub.s in said voltage vector .nu..sub.s to adjust said system's output.
Dependencies are inferred from the claim text.