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ANALYSIS OF THE CONTROL BEHAVIOR OF A BIDIRECTIONAL THREE-PHASE PWM RECTIFIER SYSTEM
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| Author(s) |
Johann W. Kolar; Hans Ertl; Karl Edelmoser; Franz C. Zach |
| Abstract |
This paper treats the analysis of the control-oriented system structure and the dynamic quality of a three-phase PWM rectifier system. Based on the application of the space vector calculus one can give a clear and simple mathematical description of the power electronic system. The transformation into a (rotating) d,q-coordinate system oriented with respect to the mains voltage space vector leads to a split of the mains current into two parts. One part determines the contribution which gives the required power flow into the DC bus, the other part defines the instantaneous reactive power condition in the mains. Furthermore the system equations show directly the possibility of the control of both current components in a decoupled manner. This makes a realization of the system control in form of a cascade structure reasonable. Thereby also the possibility of a simple realization of current limitation and a feedforward control of the load behavior is possible. As more detailed research shows one has to pay special attention to the voltage control loop which is superimposed on the current control loop. The small-signal transfer function of the system to be controlled by the voltage controller shows (for energy flow from the mains into the DC voltage bus) a zero located in the right s-half-plane. This is equivalent to allpass behavior. This behavior can be interpreted in a physical sense via the then given system function as step-up (boost) converter: Fora power flow from the DC link into the mains the system acts as a buck-converter. Accordingly, the system zero then lies in the left s-half-plane. Besides the dependency of the location of the poles and zeros on the system load condition the following aspects of the system are investigated: (1) the influence of the dimensioning of the mains-side inductances and of the capacitor buffering the DC voltage on the dynamic behavior, (2) possibilities of feedforward control based on the load and mains voltage conditions and (3) the design of a DC link current controller for prediction of the system response to a change in the controller output signal by a SMITH-predictor. |
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| Filesize: | 3.092 MB |
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| Type |
Members Only |
| Date |
Last modified 2019-08-02 by System |
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