In this paper, a phase shifted control scheme is compared with conventional control scheme applied to an isolated dc-dc converter configuration with full-bridge ...
2008 IEEE Region 10 Colloquium and the Third International Conference on Industrial and Information Systems, Kharagpur, INDIA December 8 -10, 2008. Paper ID: 219
Design and Implementation of Isolated High Power DC/DC Boost Converter Using DSP Pravin D. Patel
Miteshkumar N.Priyadrshi
Vinod P. Patel
Electrical Engineering Department B.S.Patel Polytechnic Mehsana, India Pravin.patel@ganpatuniversity.com
R & D Department Veeral Control Pvt. Ltd. Gandhinagar, India mitesh343@yahoo.com
R & D Department Amtech Electronics (I) Ltd. Gandhinagar, India Vinodp@amtechelectronics.com
Abstract— A DC-DC converter of 10 KW capacity for converting 144 V DC voltage available as a battery supply to 600 V DC for battery backup drive is presented in this paper. The converter uses full bridge inverter - transformer -rectifier scheme to provide galvanic isolation between input and output and uses IGBTs to switch at 6 KHZ. The simulation results are shown and discussed. In this paper, a phase shifted control scheme is compared with conventional control scheme applied to an isolated dc-dc converter configuration with full-bridge inverter at the primary side and a fast recovery rectification method at the secondary side of the transformers. The proposed scheme is illustrated and experimentally verified by a 600V, 10kW prototype.
II.
3 PHASE SUPPLY
SYSTEM LEVEL DESIGN
RECTIFIER
THREE PHASE INVERTER
C
3 PHASE INDUCTION MOTOR
T BATTERY SUPPLY
ISOLATED BOOST DC-DC CONVERTER
Fig.1 Application of Isolated boost converter in ac drive
Keywords- Full bridge Converter, Isolated converter, Battery back up drive
I.
INTRODUCTION
The utilization of dc-dc switching converters have been extensively increased in many different applications in recent years due to their compactness, low weight, high efficiency and other advantages. The High power DC converter has a wide spectrum of the applications in the medical, industrial and military areas.[1] The DC-DC converter provides galvanic isolation through a high-frequency transformer and provides a suitably varying DC voltage to the battery depending on its state of charge. Since two stages of power conversion are involved, it is essential that each stage operate at very high efficiency so that the overall efficiency is reasonably high.[2]The simple example would be an X-ray generator [3], DC link for AC/DC Drive. However, in large power systems wherever the input line voltage and output current may have fast and large variations, the role of control strategy selection on dynamic response becomes more essential.[4] This converter has been shown to perform quite well for power application ranging from 2-10Kw.This paper presents an converter design approach that takes into consideration of various converter components, source and load studied. The simulation studies are carried out and results of the system is demonstrated for steady state conditions. The experimental studies are carried out on a 10-kW prototype and the experimental results are also presented and discussed.
A. Power Topology Selections Selection of a topology of dc-dc converters is determined not only by input-output voltages, which can be additionally adjusted with the turns ratio in isolated converters, but also by power levels, voltage and current stresses of semiconductor switches, and utilization of magnetic components. For the high power full bridge converter is the best choice.[5] The full-bridge converter is used at high (several kilowatts) power and voltage levels.[6] The advantage of this system is voltage stress on power switches is limited to the input voltage source value. In the resonance converter high accuracy is needed for the design of the inductor and the capacitor.. In the hard switching schemes the switching loss is the main considerable factor for higher efficiency. So to reduce the switching losses the switching frequency chooses between 5 kHz to 10 kHz. A disadvantage of the full-bridge converter is a high number of semiconductor devices.[7] The basic block diagram of full bridge converter is shown in Fig.2. DC SUPPLY
FULL BRIDGE INVERTER
DSP CONTROL CARD
HIGH FREQUENCY STEP UP TRANSFORMER
DIODE BRIDGE RECTIFIER
OUT PUT FITER
LOAD
FEED BACK SIGNAL(V &I)
Fig.2 Block Diagram of Full Bridge DC-DC converter
978-1-4244-2806-9/08/$25.00© 2008 IEEE
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2008 IEEE Region 10 Colloquium and the Third International Conference on Industrial and Information Systems, Kharagpur, INDIA December 8 -10, 2008. Paper ID: 219 B. Full Bridge Converter Design In this section design of the DC-DC Converter is detailed. Peak current of IGBT Switch of inverter(IQpeak) is calculated by following equation. Where IDavg is average current pass through diode .Dr is maximum duty ratio for full cycle. Po + (4 × I Davg × Dr ) I Q peak = (Vdc − 2) × Dr (1) Transformer Design is complex other than any component in this topology. The area product (Ap) of transformer gives size of core and window as shown in using (2). Using (2) one has to choose the core size available in market. Here Kf is windows fill factor and J is current density.
Ap =
8 VAsec × 10 1 (1 + ) 4 × K f × Bmax × J η
Dr 2
Using (2) one can find the core area product and using (3) one can approach towards how many turns required for primary and secondary of transformer.
(2)
The no. of primary turns(Np) is given by (3) and hence as per turns ratio no. of secondary turns calculated. 8 V primax × 10 Np = (3) 4 × Ac × f × Bmax Diode should have less reverse recovery time as much as possible. The current through diode (Id (rms)) is given by
I d(rms) =
Where typical ferrite cores can only operate up to a flux saturation level (Bsat) of 0.49 Tesla, an amorphous metal core can operate at 1.56 Tesla. The C-core also allows for single phase and three phase transformer designs. Amorphous magnetic cores have superior magnetic characteristics, such as lower core loss, when compared with conventional crystalline magnetic materials. Combined with operating at permeability similar to high-end ferrites and the flexibility of manufacturing large cores sizes these cores can be an ideal solution. When comparing Iron Powder to Amorphous core, the amorphous core will tend to be less expensive, and have lower losses, smaller physical size, better heat dissipation, and are mechanically rugged. [6]
D. Control Loop Design Control system should be able to adjust duty cycle in order to regulate the output voltage with input voltage and load variation. The power topology is shown in Fig.3 The conventional conrol scheme[10] is shown in Fig.4.When switches SW1,SW4 are turn on simulataneously,at the same time SW2,SW3 will be off.On the next half cycigle SW2,SW3 are on,simulataneously SW1,SW4 are off. The dead band is required to avoid short circuit the supply link.The gate pulses
× I out
(4) LC filter inductor and capacitor designed using (5) below. Ripple factor(r) is given by Vr, p − p 2 1 r= × 100% = × (5) 3 wc • wL 2 2Vdc C. Transformer Design Transformer is a major contributor to the weight and volume of a power supply. Major area of transformer design considerations of high power and high frequency dc-dc converter are core material selection, copper loss minimization, skin effect, leakage inductance, temperature. The Characteristics of a good core material include low specific core losses (losses per unit volume) at high frequency, high saturation flux density, high power/weight ratio and good thermal and mechanical properties. Transformer determines about 25% of the overall volume and more than 30% of the overall weight of power supply. For the most favorable combination of low cost, high Q, high stability, and lowest volume, ferrites are the best core material choice for frequencies from 10 KHz to 50 MHz.
Fig.3. Simulation of dc-dc full bridge converter
SW 1 SW 4
Ton T off
DT
SW 2 SW 3
Ton T off
Fig.4 Conventional Control of Full Bridge DC-DC converter
978-1-4244-2806-9/08/$25.00© 2008 IEEE
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2008 IEEE Region 10 Colloquium and the Third International Conference on Industrial and Information Systems, Kharagpur, INDIA December 8 -10, 2008. Paper ID: 219 toolbar. Fig.7 shows transformer primary voltage wave for conventional control scheme with Dr=0.5,the dark line shows the wave forms it should be and the actual simulation wave is shown with light line. Here the energy stored in half cycle will be back when all switches are off. In the FB-PWM converter, when all four switches are turned off, the load current freewheels through the rectifier diodes [8]. In this case the energy stored in the leakage inductance of the power transformer causes severe ringing with switch junction capacitances. This creates the need for using snubbers that
Ton T off
SW 1 DT
SW 2
SW 3 DT
z
SW 4 Vprimary
Fig.5 phase shift control scheme
are generated according to conventional method in simulation and get studied as shown in Fig 6. The phase shifted conrol scheme is shown in Fig.5.The simulation of full bridge dc-dc converter using both the control scheme was implemented on PSIM5.0 simulation tool and found that the phase shifted control scheme is better when variable dutycycle required.[8][9] The gate pulses of IGBTs are generated using phase shift control scheme using DSP is shown in experimental results. III.
Fig.7 Results of transformer primary voltage according to gate pulses of IGBTs for conventional control scheme with Dr=0.5. [X axis:1cm=0.10mS. Trace-1 Y axis:1div=50V, Trace-2. Yaxis:1div=0.2V]
SIMULATION RESULTS
Here, conventional control scheme and phase shift control scheme simulated as shown in Fig.3 with DLL block. Fig.8 and Fig.9 shows Voltage-mode control technique adopted to control output dc voltage and its results. Transformer rating taken in simulation as follows: Transformer turns ratio=1: 5.3 Magnetizing inductance=5 mH Primary Leakage inductance = 2.5µH Secondary leakage inductance=21µH The results are shown for different reference voltage set.
Fig.6 Results of transformer primary voltage according to gate pulses of IGBTs for conventional control scheme with Dr=0.8 [X axis:1div=0.8mS. Trace-1 Y axis:1div=0.2V, Trace-2. Yaxis:1div=50V]
Fig.8. Simulation Results at 600V reference voltage (a) output Dc voltage (b) Transformer primary voltage wave forms primary peak=142V
increase the overall losses bringing down the efficiency. If snubbers are not used, the selection of the devices becomes more difficult as the voltage rating for these switches has to be much higher. As the voltage rating goes up, the conduction losses and as a result the overall losses increase. At the same
Fig.9. Simulation Results at 165V reference voltage (a) output Dc voltage (b) Transformer primary voltage wave forms primary peak=142V
978-1-4244-2806-9/08/$25.00© 2008 IEEE
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2008 IEEE Region 10 Colloquium and the Third International Conference on Industrial and Information Systems, Kharagpur, INDIA December 8 -10, 2008. Paper ID: 219 time the cost increases as well.[8]In order to minimize the parasitic ringing, the phase shifted control is choose. IV.
CONTROL ALGORITHM
Fig.3 shows implemented core algorithm for the converter using the DLL (Dynamic Link Library) in PSIM software. The same algorithm is implemented in DSP TMS320F2811 for generating the gate pulses for the IGBTs as shown in Fig.10. Texas Instruments TMS320F2811 DSP is used to implemented phase shift control for Full bridge inverter and voltage mode control that maximizes the overall performance of the proposed converter, while allowing the low cost objective to be achieved. The DSP system has a high-speed A/D converter, 16 PWM output channels and serial communication capabilities. In addition, the TMS 320F2811 contains a 12-bit analog-to-digital converter (ADC) having a maximum conversion time of 40 ns that offers up to 16 channels of analog input. The auto sequencing capability of the ADC allows a maximum of 16 conversions to take place in a single conversion session without any CPU overhead. Further, the processor has two modules, which can each accomplish a task such as centered and or edge-aligned PWM generation, programmable dead band to prevent shoot-through faults, and synchronized analog-to-digital conversion.[10] By implementing the control via DSP, the proposed approach offers increased flexibility[11], insensitivity to temperature
V.
EXPERIMENTAL RESULTS
A prototype converter was designed and fabricated for a power transfer of 10 kW, switching at 6 kHz, for an input voltage of 144 V dc and a nominal output voltage of 600 V dc. Here due to battery supply is not available, rectified dc power supply is used as input power supply of 144V dc.For input rectified filter L=0.5mH, 20A and C=2mF, 500V is taken in prototype.
Start
initialization of interrupt vector,register/ variables,defined subroutins
ADC Scaning
Is Start bit = 1 & Fault bit = 0
Fig.11 Experimental Set up
drifts and minimizes component cost. The proposed DC-DC converter design includes the capability to detect any overcurrents, over-temperatures, over voltages or other shut down conditions to prevent damage to the inverter system.
HF transformer: Core: AMCC125 (C- core),
No
Transformation ratio: 1:5.3,
Yes Set the reference voltage
Raise Vref from 0 to Vset
Verr =Vset
- Vactul
A
PI controller
limiter
V=Vcarrier - Vpi out Gate pulse generation for full bridge inverter
Check for the Fault
if fault bit=0
No
stop all gate pulse generation
Yes A
Fig.10. Control algorithm for generating gate pulses of full bridge inverter
Fig.12. Gate pulses of complementary switches X axis:20µS/div, Y axis:5V/div
978-1-4244-2806-9/08/$25.00© 2008 IEEE
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2008 IEEE Region 10 Colloquium and the Third International Conference on Industrial and Information Systems, Kharagpur, INDIA December 8 -10, 2008. Paper ID: 219 Output L-C filter: L=1mH,20A, C=4 mF, 2000V. Fig.11 shows the experimental set up diagram with DSP control card. Figs.12-15 shows the experimental waveforms of configurations of the proposed prototype at 3.6kW load.
Fig.13. Phase shifted gate pulses X axis:50µS/div, Y axis:5V/div
The gate pulse of 6 kHz is generated for h- bridge inverter and tested on the converter module using both the methods like conventional control scheme and phase shift control scheme. Fig.12 shows gate pulses of complementary switches of one leg of H-bridge inverter. The dead band is taken care between two switches about 3.3µS.Fig. 13 show phaseshifted gate pulses for 6 kHz. The transformer primary voltage wave is shown in Fig.14. The transformer leakage inductance does the severe ringing with the parasitic capacitance of switches. This ringing associated with the conventional full-bridge DC converter solved using phase shift control scheme. The Output voltage regulated with varying duty cycle of full bridge inverter using phase shift control scheme. Overall, the experimental results are satisfactory and matched the prediction from design and simulations. Fig.15 shows the output voltage 600V achieved. Fig.16 shows the hardware setup for prototype module.
V.
Fig.14. Transformer primary voltage changes Y-axis (50 V/div) X-axis (33uSec/div)
CONCLUSION
Isolated DC-DC converter topologies are compared and full bridge converter topology is selected due to more advantages than other topology on high Power application. The power topology component rating is decided and the full bridge DC converter topology simulated using PSIM6.0 software tool. The phase shift control scheme is simulated and checked for varying duty cycle and hence varying output voltage using DSP TMS320F2811.The experimental results get matched with simulation results. A laboratory prototype of the converter is being constructed and related issues are being studied. REFERENCES [1]
[2] Fig.15. Output voltage 600V, Y axis:200V/div, X axis:10mS/div [3] [4] [5] [6] [7] [8] [9]
J.S.M.Nakaoka, H.Takano,“High-Voltage transformer parasitic resonant PWM DC-DC high-power converters and their performance evaluations” IEEE trans. on Industrial Electronics, Vol-2, pp.572-577, July1997. Rajapandian Ayyanar and Ned Mohan “Full-Load-Range-ZVS Hybrid DC-DC Converter with Two Full-Bridges for High-Power Battery Charging”, IEEE conf. on telecommunications energy ,pp. 8. June 1999. J.Takahashi, H.Takano “A state-of-the-art 50kw-10khz soft-switching assisted PWM dc-dc converter for x-ray power generator”, IEEE Power Convergence Conference vol. 3, pp. 165–170. April 1993. W. Lu, X.Wu, L. Zhengyu, Z. Qian, “Wide input voltage isolated dc-dc converter with interleaving control”, power electronics motion control conference, pp.94-99, Aug.2006. M .H. Rashid, “Power electronics handbook”, Academic press, USA, pp. 223–224,2001. A .I. Pressman, “Switching power supply design.” The McGraw-Hill Companies, 2nd Edison, India, pp. 37–104,1999 P.C.Sen, “ Modern Power electronics”, Wheeler publishing, India,1st Edison, pp.501-512, 1998. M. Zimmermann., G.D.Silva, A.Peres, E. Deschamps , “PWM strategies for high-voltage isolated DC-to-DC converter for rectifier systems”, IEEE Telecommunication conference,pp.415-420.,Sept-2005. Elton Pepa, “Adaptive control of a step-up full-Bridge DC-DC converter for variable low input voltage applications,” M.S. thesis, Dept. of
Fig.16. Hardware set up for isolated high power converter module
978-1-4244-2806-9/08/$25.00© 2008 IEEE
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2008 IEEE Region 10 Colloquium and the Third International Conference on Industrial and Information Systems, Kharagpur, INDIA December 8 -10, 2008. Paper ID: 219 Electrical Eng., Virginia Polytechnic Institute and State Univ., Virginia, USA, 2004. [10] S.P.Pitchai, B.Umamaheswari, “A low cost design solution-DSP based active power factor corrector for SMPS / UPS (single phase)”, American Journal of Applied Sciences, vol.3, no.1, pp.1675-1681, 2006 [11] Rajesh Gopinath, Sangsun Kim, Jae-Hong Hahn, Matthew Webster, Jon Burghardt, Steven Campbell, Douglas Becker, Prasad Enjeti, Mark Yeary, Jo Howze,“ Development of a low cost fuel cell inverter system with DSP control,” IEEE Transaction on power electronics, Vol. 19, No. 5, pp. 302-305, September 2004. [12] Pravin D. Patel, Mitesh N. Priyadarshi, Vinod P. Patel, Prof.D.B.Dave, “Implementation of High Power Isolated DC/DC Boost Converter Using DSP”, 2nd National conference on computational Intelligence in power apparatus and systems,CIPS-2008,SRM University, Chennai, April 18-19,2008,pp.595-598.
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