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Monday, 27 January 2020

Single Phase Bidirectional H6 Rectifier/Inverter

Transformer-less photovoltaic (PV) inverters are more widely adopted due to high efficiency, low cost and light weight, etc. However, H5, HERIC, etc. transformer-less PV inverters do not have the bidirectional capability for solar energy storage system in the future. With topology derivation history reviewed from rectifier to inverter, the essence of bidirectional rectifier/inverter is revealed to find a reverse power flow approach. Therefore, this paper proposes an advanced bidirectional technique for a selected H6 inverter topology with only modulation strategy modified, while the others remain the same. For the H6 circuitry in both rectifier and inverter modes, excellent three level DM voltage feature is achieved, while leakage current issue is eliminated at the same time with improved modulation method. Simulations and experimental results verify the proposed single phase bidirectional H6 rectifier/inverter technique.
1.      H6 inverter
2.      Rectifier
3.      Improved modulation
4.      Bidirectional power flow
5.       Leakage current



Figure 1 Selected H6 inverter


(a)     Ac grid voltage, ac current, DM voltage and CM voltage in rectifier mode

(b) Switching pulses S1&S4, S2&S3, S5, S6 in rectifier mode

(c) Expanded switching pulses S1&S4, S2&S3, S5, S6 in rectifier mode

(d) Ac grid voltage, ac current, DM voltage and CM voltage in inverter mode

(e) Switching pulses S1&S4, S2&S3, S5, S6 in inverter mode

(f) Expanded switching pulses S1&S4, S2&S3, S5, S6 in inverter mode
Figure 2 Bidirectional H6 rectifier/inverter modulation method simulation Results

(a) Current stress

(b) Voltage stress
Figure 3 H6 rectifier device stress

Aiming solar energy storage system, this paper improves a grid-tied single phase H6 PV inverter from unidirectional power flow to bidirectional power flow. A unified hybrid modulation method is proposed for both rectifier and inverter modes. The main advantages of the proposed solution can be summarized as:
1) Compared with the traditional hybrid modulation method for power rejection to grid only, a simple modification in the switching patterns is just needed for solar energy storage system with H6 type topology.
2) Battery storage is adopted for emergency usage in small solar energy storage system. Therefore, a slight cost of efficiency decreases in rectifier mode due to the partly used body diodes is acceptable, and the excellent DM/CM voltage features of the H6 circuitry in both rectifier and inverter modes are totally achieved.
3) The improved hybrid modulation method would be easily modified and applied to other H6 and similar topologies.
[1] R. Teodorescu, M. Liserre, and P. Rodriguez, Grid converters for photovoltaic and wind power systems. Hoboken, NJ, USA: Wiley, 2011.
[2] Rik W. De Doncker. Power Electronics – key enabling technology for a CO2 neutral electrical energy supply. Available:
[3] Generators connected to the low-voltage distribution network. Available: anwendungsregel-2011-08.html.
[4] T. Kerekes, R. Teodorescu, P. Rodriguez, G. Vazquez, and E. Aldabas, "A  new high-efficiency single-phase transformerless PV inverter topology, " IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 184-191, 2011.
[5] R. Bojoi, L. R. Limongi, D. Roiu, and A. Tenconi, "Enhanced power quality control strategy for single-phase inverters in distributed generation systems," IEEE Trans. Power Electron., vol. 26, no. 3, pp. 798–806, 2011.

Friday, 17 January 2020

A Torque Ripple Compensation Technique for a Low Cost Brushless DC Motor Drive

This paper presents a torque ripple compensation technique for a Brushless DC (BLDC) motor drive that is operated without a DC link capacitor. The motor drive, which uses a single switch control strategy, resembles that of a buck converter during operation at any switching state. A simple buck converter based model is therefore proposed to predict the behaviour of the BLDC motor drive at constant speed. Using the model, the impact of operation without the DC link capacitor on the torque produced by the BLDC motor drive is investigated in detail. Theoretical behaviour of the BLDC motor drive is compared with Matlab/Simulink based simulations to demonstrate the validity of the compensation technique and the analysis. Experimental results of a 250 W prototype motor drive are also presented to further validate the theoretical analysis as well as the effectiveness of the proposed technique. Results convincingly indicate that the BLDC motor drive with torque ripple compensation offers comparable performance.

1.      Brushless machines
2.      Torque ripple compensation



Fig. 1. (a) A typical BLDC motor drive; and (b) a BLDC motor drive without
a DC link capacitor.

Fig. 2. Case 1 with M1 for E = 95V: (a) vin(t) and E; (b) im(t) by theoretical
analysis; (c) im(t) by simulation; and (d) im(t) by experiment.

Fig. 3. Case 2 with M2 for E = 80V: (a) vin(t) and E; (b) im(t) by theoretical
analysis; (c) im(t) by simulation; and (d) im(t) by experiment.

Fig. 4. Case 3 with M1 for E = 65 V: (a) vin(t) and E; (b) im(t) by
theoretical analysis; (c) im(t) by simulation; and (d) im(t) by experiment.

Fig. 5. A comparison between the comprehensive model and the simple
model: (a) case 1 with M1; (b) case 2 with M2; and (c) case 3 with

Fig. 6. Proposed compensation for case 1: (a) simulated im(t) without a capacitor and with a 150 μF capacitor; (b) simulated im(t) with proposed compensation; (c) experimental im(t); and (d) DC link voltage with proposed compensation.

Fig. 7. Proposed compensation for case 3: (a) simulated im(t) without a capacitor and with a 150 μF capacitor; (b) simulated im(t) with proposed compensation; (c) experimental im(t); and (d) DC link voltage with proposed compensation.

A simple mathematical model and a compensation technique for inherent torque ripples of a BLDC motor drive, operated without a DC link capacitor, have been proposed. The simplicity of the model permits the controller to be implemented on inexpensive microcontroller platforms with very low resources. With the proposed technique for compensating torque ripples, comparable performance to a conventional BLDC motor drive with a large DC link capacitor can be achieved. However, with the torque ripple compensation technique, the overall complexity of the motor drive has been increased, which is a major disadvantage. Based on the application, major augmentations in both hardware and firmware may be required. The good agreement between the theoretical results, simulated results and experimental results demonstrate the accuracy of the simple buck model and the effectiveness of the proposed compensation technique. The proposed compensation technique is expected to be useful for manufacturing low cost BLDC motor drives with comparable performance.
[1] R. Krishnan, Electric Motor Drives, Modeling, Analysis, and Control. Prentice Hall, 2001.
[2] R. Krishnan, Permanent Magnet Synchronous and Brushless DC Motor Drives. CRC Press, 2010.
[3] J. F. Gieras, Permanent Magnet Motor Technology - Design and Applications: CRC Press, 2010.
[4] V. Sankaran, F. Rees, and C. Avant, “Electrolytic capacitor life testing and prediction,” in Industry Applications Conference, 1997. Thirty- Second IAS Annual Meeting, IAS ’97., Conference Record of the 1997 IEEE, vol. 2, Oct. 1997, pp. 1058–1065.
[5] H. K. Samitha Ransara and U. K. Madawala, "A Low Cost Brushless DC Motor Drive," in 6th IEEE Conference on Industrial Electronics and Applications, (IEEE ICIEA), Jun. 2011, pp. 2723-2728.

Thursday, 16 January 2020

Design of Speed Control and Reduction of Torque Ripple Factor in BLdc Motor Using Spider Based Controller

It is a very difficult process to achieve smooth drivers for the motor operating under variable speed mode. In brushless direct current motor (BLdc) when back electromotive force waveform is of trapezoidal type, the developed torque is constant in ideal conditions. However, practically, torque ripple is present in  the output torque because of the physical design of the motor and its parameters. Also, the produced ripples are associated with the control and driver side of the motor. In the previous literature, the drive without a dc-link capacitor is presented but the torque ripple reduction is not effective. Hence in another work, the usage of the small capacitor is recommended and the results are improved. In this work, the quick stabilization with torque ripple reduction is presented using a bio-inspired algorithm-based technique in a BLdc motor drive. A Spider based controller is built to generate the pulse width modulation signals applied to the inverter and the control signal applied to the capacitor. The effect of utilizing small dc-link capacitor, on the torque ripple reduction and speed control is investigated. The performance is also compared with the case of large capacitor utilization and without a capacitor case. The proposed control strategy is verified experimentally by implementing with dsPIC30F4011 and the hardware circuit.
1.      Brushless direct current (BLdc) motor
2.      Dc-link capacitor
3.      PWM sequence
4.      Spider based controller
5.      Spider web construction

Fig. 1. Proposed technique for torque ripple compensation.


 Fig. 2. im compensation. (a) Im (A) - without capacitor. (b) Im (A) - with
capacitor. (c) Im (A) - with small capacitor. (d) Im (A) - with spider.

Fig. 3. Torque comparison. (a) Torque (Nm) - without capacitor. (b) Torque  (Nm) - with capacitor. (c) Torque (Nm) - with small capacitor. (d) Torque (Nm) - with spider.

 Fig. 4. Speed comparison. (a) RPM (speed) - without capacitor. (b) RPM (speed) - with capacitor. (c) RPM (speed) - with small capacitor. (d) RPM  (speed) - with spider.

The method of designing a three-phase BLdc motor drive by using a single-phase voltage source is presented with the intention of employing small dc-link capacitor. In addition, the strategy for reducing torque ripple concern which is generally presenting in BLdc motor is considered in the work. The mathematical equations are developed to determine the capacitor rating and the parameters are set in the simulation to validate the theoretical results. The utilization of a small dc-link capacitor is evaluated by assessing the torque compensation waveform and current compensation  waveform with the capacitor-less case and large capacitor case. Besides, the application of spider web building algorithm in generating the necessary switching control pulses are observed by comparing waveforms with the utilization of fuzzy based control algorithm also with the capacitor and without capacitor case. The utilization of spider web-based control algorithm to develop the control pulses make the system to  be more stabilized with respect to its speed. Though the scheme has a switch and a small capacitor as additional components, the total price of the drive is reduced. Similarly, the control process used for the switches is simple, extra components are not used.  When the large capacitors are used, the motor reliability is reduced since the large capacitors are rated for the small period only. In addition, the simulation results are validated by designing the corresponding hardware using dsPIC30F4011 and the simulation results are validated.
[1] H. Le-Huy, R. Perret, and R. Feuillet, “Minimization of torque ripple in brushless DC motor drives,” IEEE Trans. Ind. Appl., vol. IA-22, no. 4,  pp. 748–755, Jul. 1986.
[2] J. Y. Hung, and Z. Ding, “Design of currents to reduce torque ripple in brushless permanent magnet motors,” IEE Proc. B (Electric Power Appl.), vol. 140, no. 4, pp. 260–266, 1993.
[3] E. Favre, L. Cardoletti, and M. Jufer, “Permanent-magnet synchronous motors: A comprehensive approach to cogging torque suppression,” IEEE Trans. Ind. Appl., vol. 29, no. 6, pp. 1141–1149, Nov./Dec. 1993.
[4] D. C. Hanselman, “Minimum torque ripple, maximum efficiency excitation of brushless permanent magnet motors,” IEEE Trans. Ind. Electron., vol. 41, no. 3, pp. 292–300, Jun. 1994.
[5] Z. Q. Zhu, L. J.Wu, and M. L. Mohd Jamil, “Distortion of back-EMF and torque of PM brushless machines due to eccentricity,” IEEE Trans. Magn. vol. 49, no. 8, pp. 4927–4936, Aug. 2013.

Sunday, 5 January 2020

Design of a PEV Battery Charger with High Power Factor using Half-bridge LLC-SRC Operating at Resonance Frequen

This paper presents a two stage battery charger for plug-in electric vehicles (PEV) based on half-bridge LLC series resonant converter (SRC) operating at resonance frequency. The first stage is power factor correction (PFC) stage comprising of boost converter topology using hysteresis band control of inductor current. The PFC stage reduces the total harmonic distortion (THD) of the line current for achieving high power factor and regulates the voltage to follow the battery voltage at DC link capacitor. The input of the boost converter is a single phase 50 Hz, 220V AC from grid. At the second stage, a half bridge LLC-SRC is used for constant-current, constant-voltage (CC-CV) based battery charging and for providing galvanic isolation. The resonant converter is designed to operate around resonance frequency to have maximum efficiency and low turnoff current of power switches to reduce switching losses. The circuit is simulated using MATLAB Simulink with 1.5 Kw maximum output power. Simulation results show that the PFC  stage achieves THD less than 0.07% and high power factor value  as 0.9976. The DC/DC stage meets all the CC-CV charging requirements of the battery over wide voltage range 320V—420V for depleted to fully charged battery.
1.      LLC Resonant converter
2.      PEV battery charger
3.      PFC
4.      Hysteresis band control
5.      FHA


Fig.1. Typical power architecture of a battery charger.


Fig. 2. Schematic of the proposed battery charger.

Fig. 3. Boost inductor current for a half cycle of input voltage.

Fig. 4. AC voltage and current after power factor correction.

Fig. 5. LLC-SRC operating at key point A (V0 = 320V, and I0 = 3.57A).

Fig. 6. LLC-SRC operating at key point B (V0 = 360V, and I0 = 3.57A).

Fig. 7. LLC-SRC operating at key point C (V0 = 420V, and I0 = 3.57A).

Fig. 8. LLC-SRC operating at key point D (V0 = 420V, and I0 = 0.25A).

In this paper, a 1.5 kW PEV battery charger with emphasis on the design of LLC-SRC for DC-DC stage of the battery charger is presented. A method for improvement in the power  factor with boost converter is presented using hysteresis current control to keep line input voltage and current in phase using  phase shift in inductor current. Simulation results show that the PFC stage achieves minimum THD as 0.07% and a power factor of 0.9976 having line current and voltage in phase. The LLC-SRC is designed to operate around resonance frequency to achieve maximum benefits of LLC converter,  having minimum circulating energy, avoiding hard  commutation of secondary rectifier diodes. Simulation results for the converter performance are presented which show that the turning off current of power switches have very low value throughout the charging process and is below 2.4A. Hence, the converter have minimum switching and conduction losses.
[1] H. Wang, S. Dusmez, and A. Khaligh, "A novel approach to design EV battery chargers using SEPIC PFC stage and optimal operating point tracking technique for LLC converter," Applied Power Electronics Conference and Exposition (APEC), 2014 Twenty-Ninth Annual IEEE, pp.1683-1689, 16-20 March 2014.
[2] H. Wang, S. Dusmez, and A. Khaligh, "Design and Analysis of a Full-Bridge LLCBased  PEV Charger Optimized for Wide Battery Voltage Range," Vehicular Technology, IEEE Transactions on, Vol. 63, No. 4, pp.1603-1613, May 2014.
[3] J. Deng, S. Li, S. Hu, C.C. Mi, and R. Ma, "Design Methodology of LLC Resonant Converters for Electric Vehicle Battery Chargers," Vehicular Technology, IEEE Transactions on, Vol. 63, No. 4, pp.1581-1592, May 2014.
[4] Marian K. Kazimierczuk, "Pulse-width Modulated DC-DC Power Converters," Ohio, USA: John Wiley & Sons Ltd, pp. 129-134, 2008.
[5] H. Wang, and A. Khaligh, "Comprehensive Topological Analyses of Isolated Resonant Converters in PEV Battery Charging Applications," Transportation Electrification Conference and Expo (ITEC), 2013 IEEE, pp.1-7, 16-19 June 2013.