Abstract
The role of proportional-integral (PI) controller and proportional-integral-derivative (PID) controller as a speed controller for a Permanent Magnet Synchronous Motor (PMSM) in high performance drive system is still vital although new control techniques such as vector control theory that is more effective -but complex- is available. However, PI controller is slow in adapting to speed changes, load disturbances and parameters variations without continuous tuning of its gains. Conventional approach to these issues is to tune the gains manually by observing the output of the system. The tuning must be made on-line and automatic in order to avoid tedious task in manual control. Hence, an on-line self-tuning scheme using fuzzy logic controller (FLC) is proposed in this paper. The performance of the developed proposed controller is tested through a wide range of speeds as well as with load and parameters variations through simulation using MATLAB/SIMULINK. It is found that the proposed 25 rules FLC with adaptive input and output scaling factors enhances the performance of the system especially at high load inertia. The simulation results show that the developed controller can well adapt to speed changes as well as sudden speed reduction besides fast recovery from load torque and parameters variation and these show remarkable improvement compared to conventional PI controller performance.
Highlights
Fixed gains calculated is good when the system is running with rated speed and rated conditions
Fuzzy logic PI controller design can be classified into two major categories according to the way of their construction: Either the gains of the conventional PI controller are tuned on-line in according to the knowledge base and fuzzy inference, and the conventional PI controller generates the control signal or a typical fuzzy logic controller (FLC) is constructed as a set of heuristic control rules, or the control signal is directly deduced from the knowledge base and the fuzzy inference (Mudi & Pal., 1999)
The performance of the tuned-gain FLC performance against the performance of the fixed gains PI controller, and the performance of the fixed-gain FLC are presented
Summary
A typical control structure of a PMSM is shown in Figure 1 (Krishnan, 2001). As the current time constant is much smaller than the mechanical time constant, a change in current loop is very much faster compared to a change in speed loop. Current loop can be represented by a gain or constant. This can ease the design of speed controller as the control structure is reduced to second-order system and Figure 1 is simplified to Figure 2. Based on A 380W PMSM parameters given, satisfactory values for proportional gain (Kp) and integral gain (Ki) were determined using Ziegler-Nichols method (Kp = 0.2 and Ki = 2.1). These values were used as a starting point for the fuzzy-PI controller to update the gains based on the error and change of error. The starting points of gains are chosen to be at half rated speed to make the tuning of gains to be equivalent for lowest speed and highest speed
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