A Constant Switching Frequency based Direct Torque Control Method for Interior Permanent Magnet Synchronous Motor Drives

 ABSTRACT

Direct torque control (DTC) is known to be a promising candidate for interior permanent magnet synchronous motor (IPMSM) drives. It provides fast dynamic response and good immunity to parameter variations. However, except for its merits, DTC also suffers from two major problems of variable switching frequency and large torque ripples. Research proposals have been published to solve these problems. Nonetheless, most of the proposals present very complex control algorithms. This paper proposes a constant switching frequency based DTC algorithm for IPMSM drives. It is consisted of only one PI regulator and one triangular-wave carrier. The proposed algorithm reduces the torque ripples to a noticeable extent. In-depth analysis and design guidelines of the proposed controller are given. Simulation and experiment results are provided to verify the effectiveness of the proposed method.

KEYWORDS

1.      Interior permanent magnet synchronous motor

2.      Direct torque control

3.      Constant switching frequency

4.      Torques ripple

5.      Carrier Controller stability.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1 Block diagram of the proposed constant switching frequency control algorithm.

EXPECTED SIMULATION RESULTS

Fig. 2 Response of torque reversal from -4Nm to 4Nm. (a) Classical DTC : reference torque (red), real torque (blue); (b) Proposed constant switching frequency DTC : reference torque (red), real torque (blue).

Fig. 3 Response of speed reversal from -375r/min to 375r/min. (a) Classical DTC : subplot 1: rotor electrical speed, subplot 2: reference torque (red), real torque (blue); (b) Proposed constant switching frequency DTC : subplot 1: rotor electrical speed, subplot 2: reference torque (red), real torque (blue).

Fig. 4 FFT analysis of line current at 375 r/min (a) Classical DTC : subplot 1: line current, subplot 2: Frequency Spectrum of line current; (b) Proposed constant switching frequency DTC : subplot 1 : line current, subplot 2: Frequency Spectrum of line current.

CONCLUSION

This paper presents a simple but effective constant switching frequency based direct torque control method. It significantly reduces the torque ripples and maintains nearly all the merits of the classical DTC. The proposed torque regulator is consisted of one PI controller and one fixed frequency triangular-wave carrier. This benefits the real-time implementation by reducing the computational burden. In-depth modeling and small-signal analysis of the proposed regulator are provided. The design of stable torque regulator by using conventional bode plots is discussed. Both simulation and experimental results are given to verify the performance of the proposed control method.

REFERENCES

[1]   Takahashi and T. Noguchi, “A new quick response and high efficiency control strategy of an induction motor,” IEEE Trans. Ind. Applicat., vol. IA-22, no. 5, pp. 820 - 827, 1986.

[2]   L. Zhong and M.F. Rahman, W.Y. Hu, K.W. Lim, M.A. Rahman, “A direct torque controller for permanent magnet synchronous motor drives,” IEEE Transactions on Energy Conversion, vol. 14, no. 3, pp. 637 - 642, 1999.

[3]   L. Zhong and M.F. Rahman, W. Y. Hu and K.W. Lim, “Analysis of Direct Torque Control in Permanent Magnet Synchronous Motor Drives,” IEEE Trans. Power Electron., vol. 12, no. 3, pp. 528-536, May 1997.

[4]   J.-K. Kang and S.-K. Sul, “Analysis of inverter switching frequency in DTC of induction machine based on hysteresis bands,” IEEE Trans. Ind. Electron., vol. 48, no. 3, pp. 545 - 553, Oct. 2001.

[5]   K. Gulez, A.A. Adam and H. Pastaci, “A Novel Direct Torque Control Algorithm for IPMSM With Minimum Harmonics and Torque Ripples,” IEEE Trans. Mechatron., vol. 12, no. 2, pp. 223 - 227, 2007. 

Direct Torque Control of Induction Motor Drive with Flux Optimization

ABSTRACT

MATLAB / SIMULINK implementation of the Direct Torque Control Scheme for induction motors is presented in this paper. Direct Torque Control (DTC) is an advanced control technique with fast and dynamic torque response. The scheme is intuitive and easy to understand as a modular approach is followed. A comparison between the computed and the reference values of the stator flux and electromagnetic torque is performed. The digital outputs of the comparators are fed to hysteresis type controllers. To limit the flux and torque within a predefined band, the hysteresis controllers generate the necessary control signals. The knowledge about the two hysteresis controller outputs along with the location of the stator flux space vector in a two dimensional complex plane determines the state of the Voltage Source Inverter (VSI). The output of the VSI is fed to the induction motor model. A flux optimization algorithm is added to the scheme to achieve maximum efficiency. The output torque and flux of the machine in the two schemes are presented and compared.

KEYWORDS

1.      Direct Torque Control

2.      Induction Motor

3.      Flux Optimzation

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1: Block Diagram of Conventional DTC Scheme

Figure 2: Block Diagram of the Flux Optimized DTC Scheme

EXPECTED SIMULATION RESULTS

Figure 3: Stator d-q flux space vector without flux optimization

Figure 4: Stator d-q flux space vector with flux optimization

Figure 5: Variation of Stator Flux - Conventional DTC Scheme

Figure 6: Variation of Stator Flux - Optimized DTC Scheme

Figure 7: Variation of Mechanical Speed - Conventional DTC

Scheme

Figure 8: Variation of Mechanical Speed - Optimized DTC

Scheme

Figure 9: Electromagnetic Torque - Conventional DTC

Figure 10: Electromagnetic Torque - Optimized DTC

Figure 11: Percentage Efficiency of Flux Optimized DTC

CONCLUSION

In this paper, DTC for an induction motor drive has been shown along with flux optimization algorithm. DTC is a high performance, robust control structure. A comparative analysis of the two DTC schemes, with and without flux optimization algorithm has been presented. With flux optimization implementation, it is observed that the efficiency of the about 87% has been obtained. MATLAB simulation of a 15 Hp IM drive has been presented to confirm the results.

REFERENCES

[1]   Werner Leonhard. Control of Electric Drives. Springer-Verlag Berlin Heidelberg, 1996.

[2]   F. Blaschke. “The Principle of Field Orientation as Applied to The New Transvector Closed Loop Control System for Rotating Field Machines”. Siemens Review, pages 217–220, 1972.

[3]   K. Hasse. “On The Dynamic Behavior of Induction Machines Driven by Variable Frequency and Voltage Sources”. ETZ Archive, pages 77–81.,1968.

[4]   I. Takahashi and T Nogushi. “A New Quick Reponse and High Efficiency Control Strategy of an Induction Motor”. IEEE Trans. Industry Applications, IA -22:820–827, 1986.

[5]   M. Depenbrock. “Direct Self Control (DSC) of inverter-fed induction machines”. IEEE Trans. Power Electronics, 3(4):420–429, 1988.

Direct Torque Control of Induction Motor With Constant Switching Frequency

ABSTRACT

Direct Torque Control (DTC) has become a popular technique for the control of induction motor drives as it provides a fast dynamic torque response and robustness to machine parameter variations. Hysteresis band control is the one of the simplest and most popular technique used in DTC of induction motor drives. However the conventional direct torque control has a variable switching frequency which causes serious problems in DTC. This paper presents the DTC of induction motor with a constant switching frequency torque controller. By this method constant switching frequency operation can be achieved for the inverter. Also the torque and flux ripple will get reduced by this technique. The feasibility of this method in minimizing the torque ripple is verified through some simulation results.

KEYWORDS

1.      Direct torque control(DTC)

2.      Constant switching frequency

3.      Induction motor

4.      Three phase inverter.

SOFTWARE: MATLAB/SIMULINK

  

BLOCK DIAGRAM:

Fig. 1. Block diagram of conventional DTC

EXPECTED SIMULATION RESULTS

Fig. 2. Step response of torque (a) hysteresis based (b) modified torque controller

Fig. 3. Response of torque and speed for squre wave torque reference in

(a) hysteresis based (b)modified torque controller

Fig. 4.(a) Hysteresis based controller (b) modified torque controller

Fig. 5. flux waveform for (a) hysteresis based (b)modified torque controller

Fig. 6. flux locus for (a) hysteresis based (b)modified torque controller

Fig. 7. Frequency spectrum of the switching pattern Sb for (a) hysteresis based (b) modified torque controller

CONCLUSION

This paper presents a constant switching frequency torque controller based DTC of induction motor drive. By using the modified torque controller the switching frequency of the inverter also becomes constant at 10 kHz. As a result, the harmonic contents in the phase currents are very much reduced. So the phase current distortion is reduced. The torque ripple is also reduced by replacing the torque hysteresis controller with the modified torque controller. Moreover, with the modified torque controller, an almost circular stator flux locus is obtained. Without sacrificing the dynamic performance of the hysteresis controller, the modified scheme gives constant switching frequency. This work can be implemented using DSP. The work can be extended by increasing the switching frequency above audible range, i.e. more or equal to 20 kHz. This is an effective way to shift the PWM harmonics out of human audible frequency range. With high switching frequency the harmonic content of stator current will be reduced significantly.

REFERENCES

[1]   John R G Schofield, (1995) “Direct Torque Control – DTC”, IEE, Savoy Place, London WC2R 0BL, UK.

[2]   L.Tang, L.Zhong, M.F.Rahman, Y.Hu,(2002)“An Investigation of a modified Direct Torque Control Strategy for flux and torque ripple reduction for Induction Machine drive system with fixed switching frequency”, 37th IAS Annual Meeting Ind. Appl. Conf. Rec., Vol. 1, pp. 104-111.

[3]   J-K. Kang, D-W Chung, S. K. Sul, (2001) “Analysis and prediction of inverter switching frequency in direct torque control of induction machine based on hysteresis bands and machine parameters”, IEEE Transactions on Industrial Electronics, Vol. 48, No. 3, pp. 545-553.

[4]   D.Casadei, G.Gandi,G.Serra,A.Tani,(1994)“Switching strategies in direct torque control of induction machines,” in Proc. Of ICEM’94, Paris (F), pp. 204-209.

[5]   J-K. Kang, D-W Chung and S.K. Sul, (1999) “Direct torque control of induction machine with variable amplitude control of flux and torque hysteresis bands”, International Conference on Electric Machines and Drives IEMD’99, pp. 640-642

Soft-Switching Current-Fed Push–Pull Converter for 250-W AC Module Applications

ABSTRACT:

In this paper, a soft-switching single-inductor push– pull converter is proposed. A push–pull converter is suitable for low-voltage photovoltaic ac module systems, because the step-up ratio of the high-frequency transformer is high, and the number of primary-side switches is relatively small. However, the conventional push–pull converter does not have high efficiency because of high-switching losses due to hard switching and transformer losses (copper and iron losses) as a result of the high turn ratio of the transformer. In the proposed converter, primary-side switches are turned ON at the zero-voltage switching condition and turned OFF at the zero-current switching condition through parallel resonance between the secondary leakage inductance of the transformer and a resonant capacitor. The proposed push–pull converter decreases the switching loss using soft switching of the primary switches. In addition, the turn ratio of the transformer can be reduced by half using a voltage-doubler of secondary side. The theoretical analysis of the proposed converter is verified by simulation and experimental results.

KEYWORDS:

1.      Current-fed push–pull converter

2.      Photovoltaic (PV) ac module

3.      Soft-switching

SOFTWARE: MATLAB/SIMULINK

 CONTROL BLOCK DIAGRAM:

Fig. 1. Control block diagram of the dc–dc converter and dc–ac inverter using a microcontroller.

EXPECTED SIMULATION RESULTS:

Fig. 2. (a) Carriers and a reference for PWM. (b) Waveforms of primary

switch S1 . (c) Waveforms of primary switch S2 .

Fig. 3. (a) Boost inductor current iLbst . (b) Resonant capacitor voltage vC r .

Fig. 4. (a) Waveforms of tracking the MPP. (b) PWM according to MPPT. (c) Start flag of MPPT.

Fig. 5. Current and voltage waveforms of switch S1 according to ZVS and ZCS.

Fig. 6. Waveforms of resonant capacitor voltage and boost inductor current.

CONCLUSION:

In this paper, the soft-switching single-inductor push–pull converter for PV ac module applications is proposed. Soft switching was confirmed at each part, and MPPT is performed for extracting the maximum power from the PV module. Switches of the primary side operate in the ZVS condition at turn-off and in the ZCS condition at turn-on. The proposed converter maintains a Vo of 400 V to provide ac 220 Vrms for dc–ac inverters. The maximum efficiency is 96.6%. These results were confirmed by simulation and verified by a 250-W experimental setup.

REFERENCES:

[1] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, “A review of single-phase grid-connected inverters for photovoltaic modules,” IEEE Trans. Ind. Appl., vol. 41, no. 5, pp. 1292–1306, Sep. 2005.

[2] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, “Power inverter topologies for photovoltaic modules: A review,” in Proc. IEEE. Ind. Appl. Conf., vol. 2, Oct. 2002, pp. 782–788.

[3] Y. Xue, L. Chang, S. B. Kjaer, J. Bordonau, and T. Shimizu, “Topologies of single-phase inverters for small distributed power generators: An overview,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1305–1314, Sep. 2004.

[4] R. Gonzalez, J. Lopez, P. Sanchis, and L. Marroyo, “Transformerless inverter for single-phase photovoltaic systems,” IEEE. Trans. Power Electron., vol. 22, no. 2, pp. 693–697, Mar. 2007.

[5] T. Shimizu,K.Wada, andN.Nakamura, “Flyback-type single-phase utility interactive inverter with power pulsation decoupling on the DC input for an AC photovoltaic module system,” IEEE Trans. Power Electron.,, vol. 21, no. 5, pp. 1264–1272, Sep. 2006.

Analysis and design of a current-fed zero-voltage-switching and zero-current-switching CL-resonant push–pull dc–dc converter

 ABSTRACT:

A current-fed zero-voltage-switching (ZVS) and zero-current-switching (ZCS) CL-resonant push–pull dc – dc converter is presented in this paper. The proposed push–pull converter topology is suitable for unregulated low-voltage to high-voltage power conversion with low ripple input current. The resonant frequency of both capacitor and inductor is operated at approximately twice the main switching frequency. In this topology, the main switch is operated under ZVS because of the commutation of the transformer magnetising current and the parasitic drain–source capacitance. Because of the leakage inductance of the transformer and the resonant capacitance from the resonant circuit, both the main switch and output rectifier are operated by implementing ZCS. The operation and performance of the proposed converter has been verified on a 400-W prototype.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1 Schematic diagram of the proposed current-fed ZVS–ZCS CL-resonant push–pull dc–dc converter

 EXPECTED SIMULATION RESULTS:

Figure 2 Measured waveforms of gate to source voltage and drain to source voltage a ZVS operations for Q1 and Q2 at the full load b Expanded scale of Fig. 7a in point A

Figure 3 ZCS operations for Q1 and Q2 at the full load

Figure 4 ZCS operations for rectifier diode at the full load

Figure 5 Waveforms of vin, iin, ip and icr at the full load

Figure 6 Waveforms with excessive dead time

 Figure 7 Step change with resistance load

a Load connection

b Load disconnection

 CONCLUSION:

This study proposed, analysed, and quantified a current-fed ZVS–ZCS CL-resonant push–pull dc–dc converter that utilises the commutation of the transformer magnetizing current and the parasitic drain–source capacitance to obtain the main switch to be operated under ZVS. By using the leakage inductance of a transformer and resonant capacitor, a sinusoidal current is formed in this resonant circuit by turning on and off the switch. Thus, both the main switch and the output rectifier can be operated under ZCS. Because this proposed converter includes an input inductance, the input terminal of the converter cannot be added with a filter. This converter can reach a steady state with a small ripple input current, which is especially suitable for unregulated dc–dc conversion from a low-voltage high-current source. From the experimental results, the main switch can be operated using both ZVS and ZCS and the output rectifier can be operated using ZCS. The operating principles and theoretical analysis of this proposed converter were verified by using a 400-W and 65-kHz prototype. The overall efficiency of the converter nearly reached 93% at full output power.

REFERENCES:

[1] SHOYAMA M., HARADA K.: ‘Steady-state characteristics of the push-pull dc-to-dc converter’, IEEE Trans. Aerosp. Electron. Syst., 1984, 20, (1), pp. 50–56

[2] THOTTUVELIL V.J., WILSON T.G., QWEN H.A.: ‘Analysis and design of a push-pull current-fed converter’. Proc. IEEE PESC, 1981, vol. 5, pp. 192–203

[3] REDL R., SOKAL N.: ‘Push –pull current-fed, multiple output regulated wide input range dc/dc power converter with only one inductor and with 0 to 100% switch duty ratio: operation at duty ratio below 50%’. Proc. IEEE PESC, 1981, pp. 204–212

[4] WILDON C.P., DE ARAGAO F., BARBI I.: ‘A comparison between two current-fed push-pull dc-dc converters – analysis, design and experimentation’. Proc. IEEE INTELEC, 1996, pp. 313–320

[5] YING J., ZHU Q., LIN H., WU Z.: ‘A zero-voltage-switching (ZVS) push-pull dc/dc converter for UPS’. Proc. IEEE PEDS, 2003, pp. 1495–1499