A Comparison of Soft-Switched DC-to-DC Converters for Electrolyzer Application

ABSTRACT:

An electrolyzer is part of a renewable energy system and generates hydrogen from water electrolysis that is used in fuel cells. A dc-to-dc converter is required to couple the electrolyzer to the system dc bus. This paper presents the design of three soft-switched high-frequency transformer isolated dc-to-dc converters for this application based on the given specifications. It is shown that LCL-type series resonant converter (SRC) with capacitive output filter is suitable for this application. Detailed theoretical and simulation results are presented. Due to the wide variation in input voltage and load current, no converter can maintain zero-voltage switching (ZVS) for the complete operating range. Therefore, a two-stage converter (ZVT boost converter followed by LCL SRC with capacitive output filter) is found suitable for this application. Experimental results are presented for the two-stage approach which shows ZVS for the entire line and load range.

KEYWORDS:

1.      DC-to-DC converters

2.      Electrolyzer

3.      Renewable energy system (RES)

4.      Resonant converters.

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 Fig. 1. Block diagram of a typical RES.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation waveforms for LCL SRC with capacitive output filter at full-load (2.4 kW) with V_in = 40V and V_o = 60V: inverter output voltage v_ab ; current through resonant tank inductor i_Lr ; switch currents (i_{S 1} –i_{S 4} ); rectifier input voltage (v_rectin ); voltage across and current through output rectifier diode DR1 .

Fig. 3. Simulation waveforms of Fig. 13 repeated for LCL SRC with capacitive

output filter at 10% load with V_in = 40V and V_o = 60V.

Fig. 4. Experimental waveforms obtained for two stage converter cell (see Fig. 15) at full-load (2.4 kW) with V_in = 40V and V_o = 60V. (a) Voltage v_SW across drain-to-source of boost switch (SW) and gating signal v_g to the boost switch. (b) Inverter output voltage v_ab and current through resonant tank inductor i_Lr . (c) Rectifier input voltage v_rectin and current through parallel inductor L_t , i_Lt . (d) Rectifier input voltage v_rectin and secondary current i_sec . Scales: (a) v_SW (40V/div) and v_g (10V/div). (b) v_ab (100 V/div) and i_Lr (20A/div) (c) v_rectin (100 V/div) and i_Lt (20A/div). (d) v_rectin (100 V/div) and i_sec (20A/div).

.

Fig. 5. Experimental waveforms of Fig. 17 repeated for V_in = 40V and V_o = 40V at I_d = 10 A. Scales: (a) v_SW (40V/div) and v_g (10V/div). (b) v_ab (40V/div) and i_Lr (20A/div). (c) v_rectin (100 V/div) and i_Lt (20A/div). (d) v_rectin (100 V/div) and i_sec (20A/div).

Fig. 6. Experimental waveforms of Fig. 17 repeated for V_in = 60V and V_o = 40V at I_d = 10 A. Scales: (a) v_SW (40V/div) and v_g (10V/div). (b) v_ab (40V/div) and i_Lr (20A/div). (c) v_rectin (100 V/div) and i_Lt (20A/div). (d) v_rectin (100 V/div) and i_sec (20A/div).

CONCLUSION:

A comparison of HF transformer isolated, soft-switched, dc to- dc converters for electrolyzer application was presented. An interleaved approach with three cells (of 2.4kWeach) is suitable for the implementation of a 7.2-kW converter. Three major configurations designed and compared are as follows: 1) LCL SRC with capacitive output filter; 2) LCL SRC with inductive output filter; and 3) phase-shifted ZVS PWM full-bridge converter. It has been shown that LCL SRC with capacitive output filter has the desirable features for the present application. Theoretical predictions of the selected configuration have been compared with the SPICE simulation results for the given specifications. It has been shown that none of the converters maintain ZVS for maximum input voltage. However, it is shown that LCL-type SRC with capacitive output filter is the only converter that maintains soft-switching for complete load range at the minimum input voltage while overcoming the drawbacks of inductive output filter. But the converter requires low value of resonant inductor Lr for low input voltage design. Therefore, it is better to boost the input voltage and then use the LCL SRC with capacitive output filter as a second stage. When this converter is operated with almost fixed input voltage, duty cycle variation required is the least among all the three converters while operating with ZVS for the complete variations in input voltage and load. A ZVT boost converter with the specified input voltage (40–60 V) will generate approximately 100V as the input to the resonant converter for Vo = 60V. Therefore, we have investigated the performance of a ZVT boost converter followed by the LCL SRC with capacitive output filter. It was shown experimentally that the two-stage approach obtained ZVS for all the switches over the complete operating range and also simplified the design of resonant converter.

REFERENCES:

[1] A. P. Bergen, “Integration and dynamics of a renewable regenerative hydrogen fuel cell system,” Ph.D. dissertation, Dept. Mechanical Eng., Univ. Victoria, Victoria, BC, Canada, 2008.

[2] D. Shapiro, J. Duffy, M. Kimble, and M. Pien, “Solar-powered regenerative PEM electrolyzer/fuel cell system,” J. Solar Energy, vol. 79, pp. 544–550, 2005.

[3] F. Barbir, “PEM electrolysis for production of hydrogen from renewable energy sources,” J. Solar Energy, vol. 78, pp. 661–669, 2005.

[4] R. L. Steigerwald, “High-frequency resonant transistor DC-DC converters,”IEEE Trans. Ind. Electron., vol. 31, no. 2, pp. 181–191, May 1984.

[5] R. L. Steigerwald, “A Comparison of half-bridge resonant converter topologies,” IEEE Trans. Power Electron., vol. 3, no. 2, pp. 174–182, Apr. 1988.

A Comparison of Half Bridge & Full Bridge Isolated DC-DC Converters for Electrolysis Application

ABSTRACT:

This paper presents a comparison of half bridge and full bridge isolated, soft-switched, DC-DC converters for Electrolysis application. An electrolyser is a part of renewable energy system which generates hydrogen from water electrolysis that used in fuel cells. A DC-DC converter is required to couple electrolyser to system DC bus. The proposed DC-DC converter is realized in both full-bridge and half-bridge topology in order to achieve zero voltage switching for the power switches and to regulate the output voltage. Switching losses are reduced by zero voltage switching. Switching stresses are reduced by using resonant inductor and capacitor. The proposed DC-DC converter has advantages like high power density, low EMI, reduced switching stresses, high circuit efficiency and stable output voltage. The MATLAB simulation results show that the output of converter is free from the ripples and regulated output voltage and this type of converter can be used for electrolyser application. Experimental results are obtained from a MOSFET based DC-DC Converter with LC filter. The simulation results are verified with the experimental results.

KEYWORDS:

1.      DC-DC converter

2.      Electrolyser

3.      Renewable energy sources

4.      Resonant converter

5.      TDR

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig 1. Half Bridge DC-DC Converter.

Fig 2. Full Bridge DC-DC Converter.

 EXPECTED SIMULATION RESULTS:

Fig 3 (b) Driving Pulses

Fig 4 (c) Inverter output voltage with LC filter

Fig 5 (d) Transformer secondary voltages

Fig 6 (e) Output voltage and current

Fig 7 (b) Driving Pulses

Fig 8 (c) Inverter output voltage with LC filter

Fig 9 (d) Transformer secondary voltage

Fig 10 (e) Output voltage and current

 CONCLUSION:

A comparison of half bridge and full bridge isolated DC-DC converters for Electrolysis application are presented. DC-DC converters for electrolyser system is simulated and tested with LC filter at the output. The electrical performances of the converter have been analyzed. The simulation and experimental results indicate that the output of the inverter is nearly sinusoidal. The output of rectifier is pure DC due to the presence of LC filter at the output. Switching losses are reduced by zero voltage switching. Switching stresses are reduced by using resonant inductor and capacitor The advantages of resonant converter are reduced (di/dt), low switching losses and high efficiency. Switching losses are reduced by zero voltage switching. Switching stresses are reduced by using resonant inductor and capacitor The converter maximizes the efficiency through the zero voltage switching and the use of super-junction MOSFET as switching devices with high dynamic characteristics and low direct voltage drop. Half bridge converter is found to be better than that of full bridge converter.

REFERENCES:

[1] E.J.Miller, “Resonant switching power conversion,”in Power Electronics Specialists Conf.Rec., 1976, pp. 206-211.

[2] V. Volperian and S. Cuk , “A complete DC analysis of the series resonant converter”, in IEEE power electronics specialists conf. Rec. 1982, pp. 85-100.

[3] R.L. Steigerwald, “High-Frequency Resonant Transistor DC-DC Converters”, IEEE Trans. On Industrial Electronics, vol.31, no.2, May1984, pp. 181-191.

[4] D.J. Shortt, W.T. Michael, R.L. Avert, and R.E. Palma, “A 600 W four stage phase-shifted parallel DC-DC converter,”, IEEE Power Electronics Specialists Conf., 1985, pp. 136-143.

[5] V. Nguyen, J. Dhayanchand, and P. Thollot, “A multiphase topology series-resonant DC-DC converter,” in Proceedings of Power Conversion International, 1985, pp. 45-53.

PFC Cuk Converter Fed BLDC Motor Drive

ABSTRACT:

This paper deals with a power factor correction (PFC) based Cuk converter fed brushless DC motor (BLDC) drive as a cost effective solution for low power applications. The speed of the BLDC motor is controlled by varying the DC bus voltage of voltage source inverter (VSI) which uses a low frequency switching of VSI (electronic commutation of BLDC motor) for low switching losses. A diode bridge rectifier (DBR) followed by a Cuk converter working in discontinuous conduction mode (DCM) is used for control of DC link voltage with unity power factor at AC mains. Performance of the PFC Cuk converter is evaluated in four different operating conditions of discontinuous and continuous conduction mode (CCM) and a comparison is made to select a best suited mode of operation. The performance of the proposed system is simulated in MATLAB/Simulink environment and a hardware prototype of proposed drive is developed to validate its performance over a wide range of speed with unity power factor at AC mains.

KEYWORDS:

1.      CCM

2.      Cuk converter

3.       DCM

4.       PFC

5.       BLDC Motor

6.       Power Quality

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. A BLDC motor drive fed by a PFC Cuk converter using a current multiplier approach.

Fig. 2. A BLDC motor drive fed by a PFC Cuk converter using a voltage follower approach.

EXPECTED SIMULATION RESULTS:

             

Fig.3. Simulated performance of BLDC motor drive with Cuk converter

operating in CCM

Fig. 4. Simulated performance of BLDC motor drive with Cuk converter

operating in DICM (L_i).

Fig. 5. Simulated performance of BLDC motor drive with Cuk

converter operating in DICM (L_o).

Fig. 6. Simulated performance of BLDC motor drive with Cuk

converter operating in DCVM.

Fig. 7. Steady state performance of Cuk converter fed BLDC motor drive

at rated condition with DC link voltage as (a) 200V and (b) 50V.

Fig. 8. Test results of proposed BLDC Motor drive showing (a) Supply voltage with inductors currents and intermediate capacitor’s voltage and (b) its enlarged waveforms. (c) Waveform of voltage and current stress on PFC converter switch.

Fig. 9. Test results of proposed BLDC motor drive at rated load on BLDC motor during (a) Starting at DC link voltage of 50V (b) Step change in DC link voltage from 100V to 150V and (c) Change in supply voltage from 250V to 170V.

Fig. 10. Power quality indices of proposed BLDC motor drive at rated load on BLDC motor with (a-c) DC link voltage as 200V at rated conditions (d-f) DC link voltage as 50V at rated conditions (g-i) DC link voltage as 200V and supply voltage as 90V at rated load (j-l) DC link voltage as 200V and supply voltage as 270V at rated load.

CONCLUSION:

A Cuk converter for VSI fed BLDC motor drive has been designed for achieving a unity power factor at AC mains for the development of low cost PFC motor for numerous low power equipments such fans, blowers, water pumps etc. The speed of the BLDC motor drive has been controlled by varying the DC link voltage of VSI; which allows the VSI to operate in fundamental frequency switching mode for reduced switching losses. Four different modes of Cuk converter operating in CCM and DCM have been explored for the development of BLDC motor drive with unity power factor at AC mains. A detailed comparison of all modes of operation has been presented on the basis of feasibility in design and the cost constraint in the development of such drive for low power applications. Finally, a best suited mode of Cuk converter with output inductor current operating in DICM has been selected for experimental verifications. The proposed drive system has shown satisfactory results in all aspects and is a recommended solution for low power BLDC motor drives.

REFERENCES:

[1] J. F. Gieras and M. Wing, Permanent Magnet Motor Technology- Design and Application, Marcel Dekker Inc., New York, 2002.

[2] C. L. Xia, Permanent Magnet Brushless DC Motor Drives and Controls, Wiley Press, Beijing, 2012.

[3] Y. Chen, Y, C. Chiu, C, Y. Jhang, Z. Tang and R. Liang, “A Driver for the Single-Phase Brushless DC Fan Motor with Hybrid Winding Structure,” IEEE Trans. Ind. Electron., Early Access, 2012.

[4] S. Nikam, V. Rallabandi and B. Fernandes, “A high torque density permanent magnet free motor for in-wheel electric vehicle application,” IEEE Trans. Ind. Appl., Early Access, 2012.

[5] X. Huang, A. Goodman, C. Gerada, Y. Fang and Q. Lu, “A Single Sided Matrix Converter Drive for a Brushless DC Motor in Aerospace Applications,” IEEE Trans. Ind. Electron., vol.59, no.9, pp.3542-3552, Sept. 2012.

An Ultracapacitor Integrated Power Conditioner for Intermittency Smoothing and Improving Power Quality of Distribution Grid

 ABSTRACT:

Penetration of various types of distributed energy resources (DERs) like solar, wind, and plug-in hybrid electric vehicles (PHEVs) onto the distribution grid is on the rise. There is a corresponding increase in power quality problems and intermittencies on the distribution grid. In order to reduce the intermittencies and improve the power quality of the distribution grid, an ultracapacitor (UCAP) integrated power conditioner is proposed in this paper. UCAP integration gives the power conditioner active power capability, which is useful in tackling the grid intermittencies and in improving the voltage sag and swell compensation. UCAPs have low energy density, high-power density, and fast charge/discharge rates, which are all ideal characteristics for meeting high-power low-energy events like grid intermittencies, sags/swells. In this paper, UCAP is integrated into dc-link of the power conditioner through a bidirectional dc–dc converter that helps in providing a stiff dc-link voltage. The integration helps in providing active/reactive power support, intermittency smoothing, and sag/swell compensation. Design and control of both the dc–ac inverters and the dc–dc converter are discussed. The simulation model of the overall system is developed and compared with the experimental hardware setup.

KEYWORDS:

1.      Active power filter (APF)

2.      Dc–dc converter

3.      D–q control

4.      Digital signal processor (DSP)

5.      Dynamic voltage restorer (DVR)

6.      Energy storage integration

7.       Sag/swell

8.       Ultracapacitors (UCAP)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. One-line diagram of power conditioner with UCAP energy storage.

EXPECTED SIMULATION RESULTS:

Fig. 2. (a) Source and load rms voltages V_srms and V_Lrms during sag. (b) Source voltages V_sab (blue), V_sbc (red), and V_sca (green) during sag. (c) Injected voltages V_inj2a (blue), V_inj2b (red), and V_inj2c (green) during sag. (d) Load voltages V_Lab (blue), V_Lbc (red), and V_Lca (green) during sag.

Fig. 3. (a) Currents and voltages of dc–dc converter. (b) Active and reactive

power of grid, load, and inverter during voltage sag.

CONCLUSION:

In this paper, the concept of integrating UCAP-based rechargeable energy storage to a power conditioner system to improve the power quality of the distribution grid is presented. With this integration, the DVR portion of the power conditioner will be able to independently compensate voltage sags and swells and the APF portion of the power conditioner will be able to provide active/reactive power support and renewable intermittency smoothing to the distribution grid. UCAP integration through a bidirectional dc–dc converter at the dc-link of the power conditioner is proposed. The control strategy of the series inverter (DVR) is based on inphase compensation and the control strategy of the shunt inverter (APF) is based on id − iq method. Designs of major components in the power stage of the bidirectional dc–dc converter are discussed. Average current mode control is used to regulate the output voltage of the dc–dc converter due to its inherently stable characteristic. A higher level integrated controller that takes decisions based on the system parameters provides inputs to the inverters and dc–dc converter controllers to carry out their control actions. The simulation of the integrated UCAP-PC system which consists of the UCAP, bidirectional dc–dc converter, and the series and shunt inverters is carried out using PSCAD. The simulation of the UCAP-PC system is carried out using PSCAD. Hardware experimental setup of the integrated system is presented and the ability to provide temporary voltage sag compensation and active/reactive power support and renewable intermittency smoothing to the distribution grid is tested. Results from simulation and experiment agree well with each other thereby verifying the concepts introduced in this paper. Similar UCAP based energy storages can be deployed in the future in a microgrid or a low-voltage distribution grid to respond to dynamic changes in the voltage profiles and power profiles on the distribution grid.

REFERENCES:

[1] N. H. Woodley, L. Morgan, and A. Sundaram, “Experience with an inverter-based dynamic voltage restorer,” IEEE Trans. Power Del., vol. 14, no. 3, pp. 1181–1186, Jul. 1999.

[2] J. G. Nielsen, M. Newman, H. Nielsen, and F. Blaabjerg, “Control and testing of a dynamic voltage restorer (DVR) at medium voltage level,” IEEE Trans. Power Electron., vol. 19, no. 3, pp. 806–813, May 2004.

[3] V. Soares, P. Verdelho, and G. D. Marques, “An instantaneous active and reactive current component method for active filters,” IEEE Trans. Power Electron., vol. 15, no. 4, pp. 660–669, Jul. 2000.

[4] H. Akagi, E. H. Watanabe, and M. Aredes, Instantaneous Reactive Power Theory and Applications to Power Conditioning, 1st ed. Hoboken, NJ, USA: Wiley/IEEE Press, 2007.

[5] K. Sahay and B. Dwivedi, “Supercapacitors energy storage system for power quality improvement: An overview,” J. Energy Sources, vol. 10, no. 10, pp. 1–8, 2009.