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

Full Soft-Switching High Step-Up Current-Fed DC-DC Converters with Reduced Conduction Losses

 ABSTRACT:

Two variants of the full soft-switching high step-up DC-DC converter are proposed. The main advantage of the converters is the minimized conduction losses by the use of the four-quadrant switches and a specific control algorithm. Simulation was performed to verify the principle of operation and to estimate the losses.

KEYWORDS:

1.      DC-DC power converters

2.       Photovoltaic systems

3.      Soft switching

4.       Step-up

5.       Isolated

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1. Full soft-switching high step-up DC-DC converter

Fig. 2. Proposed converter topology with four four-quadrant switches.

EXPECTED SIMULATION RESULTS:

Fig. 3. Simulated voltage and current waveforms of S1 (a), S2 (b), S7.1 (c), S5 (d) for the proposed converter topology with a single four-quadrant switch

CONCLUSION:

The proposed converters allow soft-switching of the both inverter and rectifier switches without any auxiliary passive elements and clamping circuits.

As seen from simulation results, the topology with a single four-quadrant switch has higher efficiency than the topology with four four-quadrant switches, but at the same time, it has few disadvantages that could affect the final choice of topology:

- Step-up factor is slightly lower than in the topology with four four-quadrant switches;

- The switching interval e (and the symmetrical interval in another half-period) must be of strictly right duration, which is equal to the time of current redistribution between switches S4 and S2. The shorter duration of this interval will result in high switching losses and, in extreme cases, can lead to damage of the switch S4. The significantly longer duration will result in current increase through the switch S2 and eventually may result in the boost inductor saturation.

- The original topology and the topology with four four quadrant switches does not have the problem with the longer duration of this switching interval and so they have lower requirements to the control system in dynamic mode. This means that proposed converter with four four-quadrant switches allows robust soft-switching commutation, which is hard to achieve in galvanically isolated current-fed DCDC converters.

The main disadvantage of the topologies is the presence of four switches in series in the inverter stage on the path of the current flow during the energy transfer interval. This leads to the conduction losses higher than in the conventional phase shifted full-bridge topology. Nevertheless the switching losses are lower due to the introduced soft-switching. It means that switching frequency could be increased while maintaining the efficiency at acceptable level.

Future work will be devoted to the experimental verification of the proposed converters and further control algorithm optimization.

REFERENCES:

[1] A. Blinov, D. Vinnikov, and V. Ivakhno, “Full soft-switching high stepup dc-dc converter for photovoltaic applications,” 2014 16th European Conference on Power Electronics and Applications (EPE’14-ECCE Europe), pp. 1–7, Aug 2014.

[2] Y. Sokol, Y. Goncharov, V. Ivakhno, V. Zamaruiev, B. Styslo, M. Mezheritskij, A. Blinov, and D. Vinnikov, “Using the separated commutation in two-stage dc/dc converter in order to reduce of the power semiconductor switches’ dynamic losses,” Energy Saving. Power Engineering. Energy Audit, 2014.

[3] A. Blinov, V. Ivakhno, V. Zamaruev, D. Vinnikov, and O. Husev, “Experimental verification of dc/dc converter with full-bridge active rectifier,” 38th Annual Conference on IEEE Industrial Electronics Society (IECON 2012), pp. 5179–5184 , Oct 2012.

[4] R.-Y. Chen, T.-J. Liang, J.-F. Chen, R.-L. Lin, and K.-C. Tseng, “Study and implementation of a current-fed full-bridge boost dc-dc converter with zero-current switching for high-voltage applications,” IEEE Transactions on Industry Applications, vol. 44, no. 4, pp. 1218–1226, July 2008.

[5] J.-F. Chen, R.-Y. Chen, and T.-J. Liang, “Study and implementation of a single-stage current-fed boost pfc converter with zcs for high voltage applications,” IEEE Transactions on Power Electronics, vol. 23, no. 1, pp. 379–386, Jan 2008.

Full Soft-Switching High Step-Up Dc-Dc Converter For Photovoltaic Applications

 ABSTRACT:

In this paper a full soft-switching high step-up DC-DC converter is introduced as an alternative approach to module integrated converters for photovoltaic applications. The presented operation principle and key equations can be used as design guidelines for component and parameter estimation in practical applications. The proposed DC-DC converter was verified by help of simulations and experiments. Power loss analysis based on the semiconductor datasheet values showed that the converter tends to achieve an efficiency of 92. 8% at the maximum power point.

KEYWORDS:

1.      DC-DC power conversion

2.       Photovoltaic power systems

3.       MOSFET switches

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1: Generalised topology of the proposed DC-DC converter.

EXPECTED SIMULATION RESULTS:

Fig. 2: Simulated voltage and current waveforms of MOSFET SI (a), MOSFET Tl (b), transformer

primary (c) as well as the input and output voltage and current waveforms (d).

Fig. 3: Converter regulation characteristics at different irradiation levels (a) and cell temperatures (b).

Fig. 4: Experimental voltage and current waveforms of Tl MOSFET (a), SI MOSFET (b) and S2

MOSFET (c).

Fig. 5: Experimental waveforms of the input (a) and output (b) voltage and current.

CONCLUSION:

The proposed high step-up DC-DC converter allows ZVS of the inverter switches and ZCS of the rectifier switches. The operation principle presented and the mathematical analysis of the converter can be used as design guidelines for component and parameter estimation in practical applications. The operation of the converter was verified with the 300 W experimental prototype and the experimental waveforms were found to correspond to the estimated ones. The major limitation of the converter lies in the diodes connected in series to the inverter transistors. The static losses in these diodes will contribute a major portion of the total converter losses. In the future these diodes will be replaced by MOSFETs, external snubber capacitors for rectifier switches will be introduced and the implementation possibilities of wide-bandgap semiconductors will be also addressed.

REFERENCES:

[1] Walker, G.R.; Sernia, P.C., "Cascaded DC-DC converter connection of photo voltaic modules", 33rd Annual Power Electronics Specialists Conference PESC'2002, vol. I, pp.24-29, 2002.

[2] Forcan, M.; Tusevljak, J.; Lubura, S.; Soja, M., "Analyzing and Modeling the Power Optimizer forBoosting Efficiency of PV Panel", IX Symposium Industrial Electronics INDEL'2012, pp. 198-193, Banja Luka, November 01-03,2012.

[3] Kasper, M.; Bortis, D.; Friedli, T.; Kolar, J.W., "Classification and comparative evaluation of PV panel integrated DC-DC converter concepts," Power Electronics and Motion Control Conference (EPEIPEMC), 2012 15th International, pp.LSle.4-1,LSle.4-8, 4-6 Sept. 2012.

[4] Christian Peter Dick "Multi-Resonant Converters as Photovoltaic Module-Integrated Maximum Power Point Tracker", PhD Thesis 2010, available: http://darwin.bth.rwth-aachen.de/opus3/volltexte/20 1 0/3267 /pdf/3267 .pdf

[5] Kasper, Matthias; Ritz, Magdalena; Bortis, Dominik; Kolar, Johann W., "PV Panel-Integrated High Step-up High Efficiency Isolated GaN DC-DC Boost Converter," Proceedings of 2013 35th International Telecommunications Energy Conference 'Smart Power and Efficiency' (INTELEC), pp.I-7, 13 17 Oct. 2013.