FLC-Based DTC Scheme to Improve the Dynamic Performance of an IM Drive

 

ABSTRACT:

This paper presents a fuzzy logic hysteresis comparator-based direct torque control (DTC) scheme of an induction motor (IM) under varying dynamic conditions. The fuzzy logic controller (FLC) is used to adjust the bandwidth of the torque hysteresis controller in order to reduce the torque and flux ripples and, hence, to improve motor dynamic response. The effects of torque hysteresis bandwidth on the amplitude of torque ripples of an IM are also discussed in this paper. Based on the slopes of motor-estimated torque and stator current, an FLC is designed to select the optimum bandwidth of the torque hysteresis controller. This paper also proposes a simpler algorithm than the conventional trigonometric function-based algorithm to evaluate the sector number (required for DTC scheme) of the stator flux-linkage space vector. The proposed algorithm reduces the computational burden on the microprocessor. In order to test the performance of the proposed FLC-based DTC scheme for IM drive, a complete simulation model is developed using MATLAB/ Simulink. The proposed FLC-based DTC scheme is also implemented in real time using DSP board DS1104 for a prototype 1/3 hp motor. The performance of the proposed drive is tested in both simulation and experiment.

KEYWORDS:

1          Direct torque control (DTC)

2          Field-oriented control(FOC)

3          Fuzzy logic controller (FLC)

4          Induction motor (IM)

5          Torque and flux hysteresis controllers

6          Torque ripples

SOFTWARE: MATLAB/SIMULINK

CONVENTIONAL BLOCK DIAGRAM:

 Fig. 1. Conventional DTC scheme for IM drive.

SIMULATION RESULTS:

Fig. 2. Steady-state speed responses of the IM drive for a step change in load from 0.3 to 0.8 N · m at 120 rad/s. (a) Conventional DTC. (b) FLC-based DTC.

Fig. 3. Developed torque responses of the IM drive for a step change in load from 0.3 to 0.8 N · m at speed of 120 rad/s. (a) Conventional DTC. (b) FLC-based DTC scheme.

Fig. 4. Developed torque of the IM drive at 40% of rated load. The step change in speed from 100 to 150 rad/s is applied at 0.15 s. (a) Conventional DTC. (b) FLC-based DTC scheme.

Fig. 5. Steady-state stator flux-linkage responses of the IM drive, at 40% rated load and speed of 120 rad/s. (a) Conventional DTC. (b) Proposed FLCbased DTC scheme.

Fig. 6. Steady-state stator current response of the IM drive at 40% rated load and speed of 120 rad/s. (a) Conventional DTC. (b) FLC-based DTC scheme.

CONCLUSION:

A novel FLC-based DTC scheme for IM drive has been presented in this paper. The proposed FLC-based IM drive has been successfully implemented in real time using DSP board DS1104 for a laboratory 1/3 hp IM. The FLC is used to adapt the bandwidth of the torque hysteresis controller in order to reduce the torque ripple of the motor. A performance comparison of the proposed FLC-based DTC scheme with a conventional DTC scheme has also been provided both in simulation and experiment. Comparative results show that the torque ripple of the proposed drive has considerably been reduced. The dynamic speed response of the proposed FLC-based DTC scheme has also been found better as compared to the conventional DTC scheme.

REFERENCES:

[1] I. Takahashi and T. Nouguchi, “A new quick response and high efficiency control strategy for an induction motor,” IEEE Trans. Ind. Appl., vol. IA- 22, no. 5, pp. 820–827, Sep. 1986.

[2] L. Tang, L. Zhong, M. F. Rahman, and Y. Hu, “A novel direct torque control for interior permanent-magnet synchronous machine drive with low ripple in torque and flux-a speed-sensorless approach,” IEEE Trans. Ind. Appl., vol. 39, no. 6, pp. 1748–1756, Sep./Oct. 2003.

[3] S. Kouro, R. Bernal, H. Miranda, C. A. Silva, and J. Rodriguez, “Highperformance torque and flux control for multilevel inverter fed induction motors,” IEEE Trans. Power Electron., vol. 22, no. 6, pp. 2116–2123, Nov. 2007.

[4] D. Casadei and T. Angelo, “Implementation of a direct torque control algorithm for induction motors based on discrete space vector modulation,” IEEE Trans. Power Electron., vol. 15, no. 4, pp. 769–777, July 2000.

[5] C.-T. Lin and C. S. G. Lee, Neural Fuzzy Systems: A Neuro-Fuzzy Synergism to Intelligent Systems. Upper Saddle River, NJ: Prentice-Hall, 1996.

Direct Torque Control of Permanent-Magnet Synchronous Machine Drives With a Simple Duty Ratio Regulator

ABSTRACT:

The conventional switching-table-based direct torque- controlled (DTC) ac machine drive is usually afflicted by large torque ripple, as well as steady-state error of torque. The existing methods, which optimize the duty ratio of the active vector, are usually complicated and parameter dependent. Based on the analysis of instantaneous variation rates of stator flux and torque of each converter output voltage vector, a simple and effective method considering the effect of machine angular velocity is proposed to obtain the duty ratio. The experimental results carried on a dSPACE platform with a laboratory prototype of the permanent-magnet machine verify that the proposed duty-based DTC method can achieve excellent transient response, less torque ripple, and less steady-state error, without resorting to the complicated control method over a wide range of operating regions.

KEYWORDS:
1. Direct torque control (DTC)
2. Duty ratio
3. Permanent-magnet synchronous machines (PMSMs)
4. Steady-state error
5. Torque ripple

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

image001Fig. 1. Control diagram of DTC of PMSM.

EXPECTED SIMULATION RESULTS:

image002

Fig. 2. Comparison of steady-state performance of various DTC methods (rated condition: 400 r/min, 5 N • m). (a) Conventional DTC method. (b) M1. (c) M2. (d) Proposed DTC method.

image003Fig. 3. Dynamic performances of torque response with inner torque loop control only and without outer speed loop. Reference torque from 2 to −2 N • m. (a) Conventional DTC method. (b) M1. (c) M2. (d) Proposed DTC method.

image004Fig. 4. Dynamic and steady-state performances when reference speed changes from 200 to −200 r/min. (a) Conventional DTC. (b) Proposed DTC.

image005Fig. 5. Steady-state performance of the proposed DTC method with different control parameters: Ka = 0.7, Kb = 0.0005 (rated condition: 400 r/min,5 N • m).

CONCLUSION:
This paper has proposed, analyzed, and experimentally verified a simple and effective method for determining the appropriate duty ratio in DTC three-phase PMSM drives to reduce the torque ripple and the steady-state error of torque, accounting for the influence of machine angular velocity. A simple estimated method is proposed to obtain the range of the key control parameters. Compared to the existing duty-based DTC methods, the proposed method can achieve the decent performance of torque and flux at the lower price of increased average communication frequency.
The proposed duty ratio determination has the following features.
1) Simple structure: Compared to conventional DTC, just a very simple duty ratio regulator is added.
2) Parameter independent: Unlike the previous duty-based methods, where many parameters such as stator inductance and PM flux are required, in the proposed DTC method, only the torque error and speed are needed to compute the duty ratio, which makes it robust to parameter variation.
3) Outstanding steady-state performance over a wide range of operating regions, even when speed is reversed.
4) Similar excellent transient response to the conventional DTC.
Although the analysis and experiments in this paper are based on the DTC of three-phase PMSM drives, the proposed duty ratio determination can be also extended for general use and applied to the other machines of switching-table-based direct torque and power control methods, which may exhibit the same problem of ripple and/or steady-state error.

REFERENCES:
[1] I. Takahashi and T. Noguchi, “A new quick-response and high-efficiency control method of an induction-motor,” IEEE Trans. Ind. Appl., vol. IA-22, no. 5, pp. 820–827, Sep. 1986.
[2] M. Depenbrock, “Direct self-control (DSC) of inverter-fed induction machine,” IEEE Trans. Power Electron., vol. 3, no. 4, pp. 420–429, Oct. 1988.
[3] G.W. Chang, G. Espinosa-Perez, E. Mendes, and R. Ortega, “Tuning rules for the PI gains of field-oriented controllers of induction motors,” IEEE Trans. Ind. Electron., vol. 47, no. 3, pp. 592–602, Jun. 2000.
[4] A. K. Jain and V. T. Ranganathan, “Modeling and field oriented control of salient pole wound field synchronous machine in stator flux coordinates,” IEEE Trans. Ind. Electron., vol. 58, no. 3, pp. 960–970, Mar. 2011.
[5] S. Mathapati and J. Boecker, “Analytical and offline approach to select optimal hysteresis bands of DTC for PMSM,” IEEE Trans. Ind. Electron., vol. 60, no. 3, pp. 885–895, Mar. 2013.