Implementation of a New MRAS Speed Sensorless Vector Control of Induction Machin

ABSTRACT:

In this paper, a novel rotor speed estimation method using model reference adaptive system (MRAS) is proposed to improve the performance of a sensorless vector control in the very low and zero speed regions. In the classical MRAS method, the rotor flux of the adaptive model is compared with that of the reference model. The rotor speed is estimated from the fluxes difference of the two models using adequate adaptive mechanism. However, the performance of this technique at low speed remains uncertain and the MRAS loses its efficiency, but in the new MRAS method, two differences are used at the same time. The first is between rotor fluxes and the second between electromagnetic torques. The adaptive mechanism used in this new structure contains two parallel loops having Proportional-integral controller and low-pass filter. The first and the second loops are used to adjust the rotor flux and electromagnetic torque. To ensure good performance, a robust vector control using sliding mode control is proposed. The controllers are designed using the Lyapunov approach. Simulation and experimental results show the effectiveness of the proposed speed estimation method at low and zero speed regions, and good robustness with respect to parameter variations, measurement errors, and noise is obtained.

KEYWORDS:

1.      Induction motor

2.      Lyapunov function

3.      Model reference

4.      Adaptive system (MRAS)

5.      Sensorless control

6.      Speed estimation

7.      Vector control

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of the new MRAS observer.

EXPECTED SIMULATION RESULTS:

Fig. 2. Speed estimation error.

Fig. 3. Speed tracking error.

Fig. 4. Rotor flux.

Fig. 5. Load torque and Rs variations.

Fig. 6. Classical MRAS observer: Reference, actual, and estimated speed

for load torque and Rs variations.

Fig. 7. Classical MRAS observer: Zoom of Reference, actual, and estimated

speed for load torque and Rs variations.

Fig. 8. Speed of induction motor.

Fig. 9. Speed zoom.

Fig. 10. Speed estimation error.

Fig. 11. Speed tracking error.

 CONCLUSION:

In this paper, a new MRAS rotor speed observer was proposed to improve the performance of sensorless vector controller of induction machine. The control robustness is achieved by a sliding-mode controller and its stability is proved using a Lyapunov approach. Simulation and experimental results for different speed profiles had shown, on the one hand, that the proposed new MRAS observer was able to estimate accurately the actual speed at low and zero speed when the conventional MRAS observer is limited. On the other hand, the robustness of the proposed observer regarding load torque and stator resistance variations, especially at low and zero speed, is much better than the classical observer.

REFERENCES:

[1] J. W. Finch and D. Giaouris, “Controlled AC electrical drives,” IEEE Trans. Ind. Electron., vol. 55, no. 2, pp. 481–491, Feb. 2008.

[2] J.-I. Ha and S.-K. Sul, “Sensorless field-orientation control of an induction machine by high-frequency signal injection,” IEEE Trans. Ind. Appl., vol. 35, no. 1, pp. 45–51, Jan./Feb. 1999.

[3] C. Caruana, G.M. Asher, and M. Sumner, “Performance of high frequency signal injection techniques for zero-low-frequency vector control induction machines under sensorless conditions,” IEEE Trans. Ind. Electron., vol. 53, no. 1, pp. 225–238, Feb. 2006.

[4] F. Peng and T. Fukao, “Robust speed identification for speed-sensorless vector control of induction motors,” IEEE Trans. Ind. Appl., vol. 30, no. 5, pp. 1234–1240, Sep./Oct. 1994.

[5] C. Schauder, “Adaptive speed identification for vector control of induction motors without rotational transducers,” IEEE Trans. Ind. Appl., vol. 28, no. 5, pp. 1054–1061, Sep./Oct. 1992.

A Hysteresis Current Controller for Grid-Connected Inverter with Reduced Losses

ABSTRACT:

In this paper, a hysteresis current controller with reduced losses for three-phase grid-connected inverter is proposed. In the proposed hysteresis current controller, one of the inverter phase is clamped to the positive or negative inverter buses depending on the polarity of the phase current. Totally, each inverter phase is clamped for the duration of one third of the fundamental output period. As the inverter phase is inactive when the current is the highest, the switching losses are reduced. Simulation and experimental results are included to show the effectiveness of the proposed controller.

KEYWORDS:

1.      Current controller

2.      Hysteresis

3.      Grid-connected inverter

4.      Losses

5.      Clamped

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig.1. Power controller of grid-connected inverter

 EXPECTED SIMULATION RESULTS:

Fig.2. Output current and switching pattern of: (a) conventional hysteresis

current controller, (b) proposed hysteresis current controller

CONCLUSION:

A simple hysteresis current controller with reduced losses has been proposed in this paper. In the proposed current controller, one of the inverter phase is clamped to the positive or negative DC bus, depending on the polarity, when the magnitude of the current is the greatest. This lead to reduction of the average switching frequency as well as the switching losses. Simulation and experimental results have shown that the proposed hysteresis controller is able to reduce the switching losses without sacrificing the output current waveform.

REFERENCES:

[1] S. Jain and V. Agarwal, “A Single-Stage Grid Connected Inverter Topology for Solar PV Systems With Maximum Power Point Tracking,” IEEE Trans. Power Electron., vol. 22, no. 5, pp. 1928- 1940, 2007.

[2] M. Mohseni and S. M. Islam, “A new vector-based hysteresis current control scheme for three-phase PWM voltage-source inverters,” IEEE Trans. Power Electron., vol. 25, no. 9, pp. 2299– 2309, 2010.

[3] M. P. Kazmierkowski and M. A. Dzieniakowski, “Review of current regulation techniques for three-phase PWM inverters,” Proc. IECON’94 - 20th Annu. Conf. IEEE Ind. Electron., vol. 1, pp. 567– 575, 1994.

[4] Y. Zhang and H. Lin, “Simplified model predictive current control method of voltage-source inverter,” 8th Int. Conf. Power Electron. - ECCE Asia, pp. 1726–1733, 2011.

[5] C. C. Hua, C. W. Wu, and C. W. Chuang, “A digital predictive current control with improved sampled inductor current for cascaded inverters,” IEEE Trans. Ind. Electron., vol. 56, no. 5, pp. 1718–1726, 2009.

A Systematic Method for Designing a PR Controller and Active Damping of the LCL Filter for Single-Phase Grid-Connected PV Inverters

ABSTRACT:

 The Proportional Resonant (PR) current controller provides gains at a certain frequency (resonant frequency) and eliminates steady state errors. Therefore, the PR controller can be successfully applied to single grid-connected PV inverter current control. On the contrary, a PI controller has steady-state errors and limited disturbance rejection capability. Compared with the L- and LC filters, the LCL filter has excellent harmonic suppression capability, but the inherent resonant peak of the LCL filter may introduce instability in the whole system. Therefore, damping must be introduced to improve the control of the system. Considering the controller and the LCL filter active damping as a whole system makes the controller design method more complex. In fact, their frequency responses may affect each other. The traditional trial-and-error procedure is too time-consuming and the design process is inefficient. This paper provides a detailed analysis of the frequency response influence between the PR controller and the LCL filter regarded as a whole system. In addition, the paper presents a systematic method for designing controller parameters and the capacitor current feedback coefficient factor of LCL filter active-damping. The new method relies on meeting the stable margins of the system. Moreover, the paper also clarifies the impact of the grid on the inverter output current. Numerical simulation and a 3 kW laboratory setup assessed the feasibility and effectiveness of the proposed method.

KEYWORDS:

1.      Single phase

2.      Grid-connected

3.      LCL filter

4.      Active damping

5.      Proportional resonant (PR) controller

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. Two-stage single-phase PV system with LCL-filter control scheme.

EXPECTED SIMULATION RESULTS:

 Figure 2. Grid voltage and injected current at full load with nominal parameters: simulation results. (a) Grid voltage sag; (b) grid voltage swell.

Figure 3. Grid voltage and injected current at full load with inductor L1 variation: simulation results. (a) Inductor L1 increased by 20%: grid voltage sag; (b) Inductor L1 increased by 20%: grid voltage swell; (c) Inductor L1 decreased by 20%: grid voltage sag; (b) Inductor L1 decreased by 20%: grid voltage swell.

Figure 4. Grid voltage and injected current at full load with inductor L2 variation: simulation results. (a) Inductor L2 increased by 150%: grid voltage sag; (b) inductor L2 increased by 150%: grid voltage swell; (c) inductor L2 decreased by 20%: grid voltage sag; (b) inductor L2 decreased by 20%: grid voltage swell.

Figure 5. Grid voltage and injected current at full load with capacitor C variation: simulation results. (a) Capacitor C increased by 20%: grid voltage sag; (b) capacitor C increased by 20%: grid voltage swell; (c) capacitor C decreased by 20%: grid voltage sag; (b) capacitor C decreased by 20%: grid voltage swell.

 CONCLUSION:

The stability analysis of the system composed by a PR controller and an LCL filter together is not easy: the frequency responses may affect each other and the PR controller design becomes complex. The traditional method based on trial-and-error procedures, is too time-consuming, and the design process is inefficient. This paper provides a detailed analysis of the frequency response influence between the PR controller and the LCL filter. In addition, the paper presents a systematic design method for the PR controller parameters and the capacitor current feedback coefficient, used in the active damping of the LCL filter. Using the new parameters, a numerical simulation shows that the system meets the requirements of stable margins and current tracking steady-state error. The robustness of the current controller is verified through several experimental tests carried out on a 3 kW platform varying the system parameters. The Bode diagrams of the system varying inductor, capacitor, and grid impedance values confirmed that the controller parameters enhance robustness against the system parameters variation. Moreover, the system remains stable even in case of grid voltage fluctuation. Both the simulation and the experimental results assess the validity of the proposed design method.

REFERENCES:

1. Carrasco, J.M.; Franquelo, L.G.; Bialasiewicz, J.T.; Galvan, E.; Guisado, R.C.P.; Prats, A.M.; Leon, J.I.; Moreno-Alfonso, N. Power-electronic systems for the grid integration of renewable energy sources: A survey. IEEE Trans. Ind. Electron. 2006, 53, 1002–1016.

2. Wessels, C.; Dannehl, J.; Fuchs, F.W. Active Damping of LCL-Filter Resonance based on Virtual Resistor for PWM Rectifiers—Stability Analysis with Different Filter Parameters. In Proceedings of the 2008 IEEE Power Electronics Specialists Conference, Rhodes, Greece, 15–19 June 2008; pp. 3532–3538.

3. Castilla, M.; Miret, J.; Matas, J.; de Vicuna, L.G.; Guerrero, J.M. Control design guidelines for single-phase grid-connected photovoltaic inverters with damped resonant harmonic compensators. IEEE Trans. Ind. Electron. 2009, 56, 4492–4501.

4. Yi, L.; Zhengming, Z.; Fanbo, H.; Sizhao, L.; Lu, Y. An Improved Virtual Resistance Damping Method for Grid-Connected Inverters with LCL Filters. In Proceedings of the 2011 IEEE Energy Conversion Congress and Exposition (ECCE 2011), Phoenix, AZ, USA, 17–22 September 2011; pp. 3816–3822.

5. Parker, S.G.; McGrath, B.P.; Holmes, D.G. Regions of Active Damping Control for LCL Filters. In Proceedings of the Energy Conversion Congress and Exposition (ECCE), Raleigh, NC, USA, 15–20 September 2012; pp. 53–60.

Single-Stage Buck-Derived LED Driver With Improved Efficiency and Power Factor Using Current Path Control Switches

ABSTRACT:

This paper proposes a single-stage light-emitting diode (LED) driver based on an inverted buck topology, using current path control switches. The proposed circuit consists of a control circuit, a bridge diode, and an inverted buck converter with multiple switches connected to the LED segments in parallel. Whereas the typical buck LED driver operates with a fixed LED forward voltage, the proposed driver operates with a variable LED forward voltage, according to the input voltage level. Because of this capability to adjust the LED forward voltage, it can reduce the current ripple and the switching frequency with a small inductance value. In addition, it enables operation with LED lamps of a wide voltage range, while simultaneously achieving small dead-angles. The detailed operation principles are described, and the design considerations for the proposed driver are discussed. The proposed driver circuit and control operation are verified experimentally using a 7 W hardware prototype with four LED segments. The obtained experimental results show that, under a 110 Vrms input voltage, the proposed driver achieves a power factor of 0.94 with a small dead-angle and an efficiency of 94 %.

KEYWORDS:        

                                                                                        

1.      Buck power factor collection (PFC)

2.      Constant off-time control

3.       Light-emitting diode (LED) driver

4.      Scalable LED string

SOFTWARE: MATLAB/SIMULINK

PROPOSED CIRCUIT DIAGRAM:

Fig. 1. Proposed single-stage LED driver..

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results for the proposed LED driver operated at

110Vrms/60 Hz. (a) Overall waveforms. (b) Switching waveforms at input peak

CONCLUSION:

This paper proposes an offline LED driver based on the inverted buck converter. The proposed driver is configured as a hybrid combination of buck topology and multiple switches, which connect to the several LED segments. The proposed driver can reduce both the switching frequency and the LED current ripple using relatively small inductors, because it can adjust the LED forward voltage according to the input voltage level. In addition, it has small dead-angles and achieves high efficiency values when used with high output voltages. The features and operation principles of the proposed LED driver have been described in detail. The overall schematic was presented, and its control method discussed. A 7 W prototype LED driver was implemented and tested. The obtained experimental results verify the operation and performance levels of the proposed driver. At 110 Vrms, it exhibits simultaneously a high efficiency (94 %) and a high PF value (0.94).

REFERENCES:

[1] T. Komine, and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights,” IEEE Trans. Consumer Electron., vol. 50, no.1, pp.100-107, Jan. 2004.

[2] D. A. Steigerwald, J. C. Bhat, D. Collins, et al., “Illumination with solid state lighting technology,” IEEE Journal of Selected Topics in Quantum Electronics, vol. 8, no. 2, pp. 310–320, Mar. 2002.

[3] N. Narendran and Y. Gu, “Life of LED-based white light sources,” IEEE Display Technol., vol. 1, no. 1, pp. 167-151, Aug. 2005.

[4] T. Hao, J. Lam, and P. K. Jain, "A New High Power Factor, Soft-switched LED Driver without Electrolytic capacitors," in Proc. IEEE APEC, 2013, pp.823-828.

[5] Y. Y Hsieh, and Y. Z. Juang, “Analysis and Suppression of Over current in Boost LED Drivers,” IEEE Display Technol., vol. 9, no. 5, pp. 388-395, May 2013.