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- 1. A High-Performance Single-Phase AC-DC Power Factor Corrected Boost Converter for plug in Hybrid Electric Vehicle Battery Chargers 1 Fariborz Musavi Student Member IEEE Wilson Eberle Member IEEE 2 William G. Dunford Senior Member IEEE Delta-Q Technologies Corp. Burnaby, BC, Canada fmusavi@delta-q.com Abstract -- In this paper, several conventional plug in hybrid electric vehicle charger front end AC-DC converter topologies are investigated and a new bridgeless interleaved PFC converter is proposed to improve the efficiency and performance. Experimental and simulation results of a prototype boost converter converting universal AC input voltage to 400 V DC at 3.4 kW are given to verify the proof of concept, and analytical work reported in this paper. Index Terms—Bridgeless PFC, Interleaved PFC, PFC boost converter, PHEV charger. I. INTRODUCTION A plug-in hybrid electric vehicle (PHEV) is a hybrid vehicle with a storage system that can be recharged by connecting the vehicle plug to an external electric power source [1]. The accepted charger power architecture includes an AC-DC converter with power factor correction (PFC) [2] followed by an isolated DC-DC converter with input and output EMI filters [3], as shown in Fig. 1. Selecting the optimal topology and evaluating power loss in the power semiconductors are important steps in the design and development of these battery chargers. The front-end AC-DC converter is a key component of the charger system, and a proper topology selection is essential to meet the regulatory requirements of input current harmonics [4-6], output voltage regulation and implementation of power factor correction [7]. 1 The University of British Columbia Kelowna, BC, Canada | 2 Vancouver, BC, Canada 1 wilson.eberle@ubc.ca, 2 wgd@ece.ubc.ca II. REVIEW OF EXISTING TOPOLOGIES A. Conventional Boost Converter The conventional boost topology is the most popular topology for PFC applications. It uses a dedicated diode bridge to rectify the AC input voltage to DC, which is then followed by the boost section, as shown in Fig. 2. In this topology, the output capacitor ripple current is very high [8] and is the difference between diode current and the dc output current. Furthermore, as the power level increases, the diode bridge losses significantly degrade the efficiency, so dealing with the heat dissipation in a limited area becomes problematic. Due to these constraints, this topology is good for a low to medium power range up to approximately 1kW. For power levels >1kW, typically, designers parallel semiconductors in order to deliver greater output power. The inductor volume also becomes a problematic design issue at high power. LB D1 DB D4 Vin D2 D3 QB Co L O A D Fig. 2. Conventional PFC boost converter Fig. 1. Simplified system block diagram of a universal battery charger In the following sub-sections, three existing continuous conduction mode (CCM) AC-DC PFC boost converters are evaluated, and a solution is proposed for front end AC-DC converter. B. Bridgeless Boost Converter The bridgeless configuration topology avoids the need for the rectifier input bridge yet maintains the classic boost topology [9-16], as shown in Fig. 3. It is an attractive solution for applications >1kW, where power density and efficiency are important. The bridgeless boost converter solves the problem of heat management in the input rectifier diode bridge, but it introduces increased EMI [17, 18]. Another disadvantage of this topology is the floating input
- 2. line with respect to the PFC stage ground, which makes it impossible to sense the input voltage without a low frequency transformer or an optical coupler. Also in order to sense the input current, complex circuitry is needed to sense the current in the MOSFET and diode paths separately, since the current path does not share the same ground during each half-line cycle [11, 19]. Fig. 5. Proposed bridgeless interleaved (BLIL) PFC boost converter TABLE I REVIEW OF EXCISING TOPOLOGIES FOR BOOST CONVERTER ConventioBridgeless Interleaved BLIL Topology nal PFC PFC PFC PFC Power Rating < 1000 W < 2000W < 3000W > 3000W EMI / Noise Fig. 3. Bridgeless PFC boost converter Fair Poor Best Fair Capacitor Ripple High High Low Low High High Low Low Magnetic Size Large Medium Small Small Efficiency Poor Fair Fair Best Input Main C. Interleaved Boost Converter The interleaved boost converter, Fig. 4, is simply two boost converters in parallel operating 180° out of phase [2022]. The input current is the sum of the two inductor currents ILB1 and ILB2. Because the inductors’ ripple currents are out of phase, they tend to cancel each other and reduce the input ripple current caused by the boost switching action. The interleaved boost converter has the advantage of paralleled semiconductors. Furthermore, by switching 180° out of phase, it doubles the effective switching frequency and introduces smaller input current ripples, so the input EMI filters will be smaller [23-25]. It also reduces output capacitor high frequency ripple, but it still has the problem of heat management for the input diode bridge rectifiers. In the following section, a new bridgeless interleaved boost PFC converter is proposed in order to improve overall efficiency of the AC-DC PFC converter, while maintaining all the advantages of the existing solutions. Fig. 4. Interleaved PFC boost converter III. BRIDGELESS INTERLEAVED BOOST TOPOLOGY The bridgeless interleaved (BLIL) PFC converter shown in Fig. 5 is proposed to address the problems discussed in section II. This converter introduces two more MOSFETs and two more fast diodes in place of 4 slow diodes used in the input bridge of the interleaved boost PFC converter. A detailed converter description and steady state operation analysis is given in the following section. Table 1 shows the advantages and disadvantages of each topology. Ripple IV. CIRCUIT OPERATION AND STEADY STATE ANALYSIS To analyze the circuit operation, the input line cycle has been separated into the positive and negative half cycles as explained in sub-sections A and B that follow. In addition, the detailed circuit operation depends on the duty cycle, therefore positive half cycle operation analysis is provided for D > 0.5 in sub-section C and D < 0.5 in sub-section D. A. Positive Half Cycle Operation Referring to Fig. 5, during the positive half cycle, when the AC input voltage is positive, Q1/Q2 turn on and current flows through L1 and Q1 and continues through Q2 and then L2, returning to the line while storing energy in L1 and L2. When Q1/Q2 turn off, energy stored in L1 and L2 is released as current flows through D1, through the load and returns through the body diode of Q2 back to the input mains. With interleaving, the same mode happens for Q3/Q4, but with a 180 degree phase delay. The operation for this mode is Q3/Q4 on storing energy in L3/L4 through the path L3-Q3Q4-L4 back to the input. When Q3/Q4 turn off, energy is released through D3 to the load and returning through the body diode of Q4 back to the input mains. B. Negative Half Cycle Operation Referring to Fig. 5, during the negative half cycle, when the AC input voltage is negative, Q1/Q2 turn on and current flows through L2 and Q2 and continues through Q1 and then L1, returning to the line while storing energy in L2 and L1. When Q1/Q2 turn off, energy stored in L2 and L1 is released as current flows through D2, through the load and returns
- 3. through the body diode of Q1 back to the input mains. With interleaving, the same mode happens for Q3/Q4, but with a 180 degree phase delay. The operation for this mode is Q3/Q4 on storing energy in L3/L4 through the path L4-Q4Q3-L3 back to the input. C. Detailed Positive Half Cycle Operation and Analysis for D > 0.5 The detailed operation of the proposed BLIL PFC converter depends on the duty cycle. During any half cycle, the converter duty cycle is either greater than 0.5 (when the input voltage is smaller than half of output voltage) or smaller than 0.5 (when the input voltage is greater than half of output voltage). Fig. 6 shows the three unique operating interval circuits of the proposed converter for duty cycles greater than 0.5 during positive half cycle operation. Waveforms of the proposed converter during these conditions are shown in Fig. 7. a) Interval 1: Q1 and Q2 are “ON”, and body diode of Q4 conducting Fig. 7. BLIL PFC boost converter steady-state Waveforms at D > 0.5 b) Intervals 2 and 4: Q1, Q2, Q3 and Q4 are “ON” Since the switching frequency of proposed converter is much higher than the frequency of input line voltage, the is considered constant during one switching input voltage period . The input voltage is given by: (1) √2 In a positive half cycle of the input voltage, the duty ratio of the proposed converter determines the following voltage relation: (2) c) Interval 3: Q3 and Q4 are “ON”, and body diode of Q2 conducting Fig. 6. BLIL PFC boost converter operating at D > 0.5 The intervals of operation are explained as follows. In addition, the ripple current components are derived, enabling calculation of the input ripple current, which provides design guidance to meet the required input current ripple standard. Interval 1 [t0-t1]: At t0, Q1/ Q2 are ON, and Q3/Q4 are off, as shown in Fig. 6-a. During this interval, the current in series
- 4. inductances L1 and L2 increases linearly and stores the energy in these inductors. The ripple currents in Q1 and Q2 are the same as the current in series inductances L1 and L2, where the ripple current is given by: ∆ 1 (3) The current in series inductances L3 and L4 decreases linearly and transfers the energy to the load through D3, Co and body diode of Q4. The ripple current in series inductances L3 and L4 is given by: 1 ∆ (4) The input ripple current is the sum of currents in L1/L2 and L3/L4: 1 (5) ∆ Interval 2 [t1-t2]: At t1, Q3/Q4 are turned on, while Q1/Q2 remain on, as shown I Fig. 6-b. During this interval, the current in the four inductors each increase linearly, storing energy in these inductors. The ripple currents in Q1 and Q2 are the same as the ripple current in series inductances L1 and L2 as given by. ∆ ∆ Similarly, the ripple currents Q3 and Q4 are the same as the ripple current in series inductances L3 and L4: ∆ D. Detailed Positive Half Cycle Operation and Analysis for D < 0.5 Fig. 8 shows the operating interval circuits of the proposed converter for duty cycles smaller than 0.5 during the positive half cycle. The waveforms of the proposed converter during these conditions are shown in Fig. 9. The intervals of operation are explained as follows. Similarly, the ripple currents in Q3 and Q4 are the same as the ripple current in series inductances L3 and L4: (7) The input ripple current is the sum of currents in L1/L2 and L3/L4: ∆ (8) a) Intervals 1 and 3: Body diodes of Q2 and Q4 conducting Interval 3 [t2-t3]: At t2, Q1/Q2 are turned off, while Q3/ Q4 remain on, as shown in Fig. 6-c. During this interval, the current in series inductances L3 and L4 increases linearly and stores the energy in these inductors. The ripple currents in Q3 and Q4 are the same as the ripple current in series inductances L3 and L4: ∆ 1 (9) The current in L1 and L2 decreases linearly and transfers the energy to the load through D1, Co and body diode of Q2. The ripple current in series inductances L1 and L2 is given by: ∆ 1 b) Interval 2: Q1 and Q2 are “ON”, and body diode of Q4 conducting (10) The input ripple current is the sum of currents in L1/L2 and L3/L4: ∆ 1 (11) Interval 4 [t3-t4]: At t3, Q3/Q4 remain on, while Q1/Q2 are turned on, as shown I Fig. 6-b. During this interval, the currents in the four inductors each increase linearly, storing energy in these inductors. The ripple currents in Q1 and Q2 are the same as the ripple currents in L1 and L2: (13) The input ripple current is the sum of currents in L1/L2 and L3/L4: ∆ (14) (6) ∆ (12) c) Interval 4: Q3 and Q4 are “ON”, and body diode of Q2 conducting Fig. 8. BLIL PFC boost converter operating at D < 0.5
- 5. Interval 2 [t1-t2]: At t1, Q1/Q2 turn on, while Q3/Q4 remain off, as shown in Fig. 8-b. During this interval, the current in series inductances L1 and L2 increases linearly, storing energy in these inductors. The ripple currents in Q1 and Q2 are the same as the current in series inductances L1 and L2, where the ripple current is given by: ∆ (17) The current in series inductances L3 and L4 decreases linearly and transfers the energy to the load through D3, Co and body diode of Q4. The ripple current in L3 and L4 is: ∆ (18) The input ripple current is the sum of the currents in L1/L2 and L3/L4: (19) ∆ Interval 3 [t2-t3]: At t2, Q1/Q2 are turned off, while Q3/Q4 remain off, as shown in Fig. 8-a. During this interval, the current in series inductances L1 and L2 decreases linearly and transfers the energy to the load through D1, Co and body diode of Q2. The ripple current in series inductances L1 and L2 is given by: ∆ (20) Similarly, the current in the series inductances L3 and L4 also decreases linearly, transferring the energy to the load through D3, Co and body diode of Q4. The ripple current in series inductances L3 and L4 is: ∆ (21) The input current is the sum of currents in L1/L2 and L3/L4: ∆ Fig. 9. BLIL PFC boost converter steady-state waveforms at D < 0.5 Interval 1 [t0-t1]: At t0, Q1 and Q2 turn off, while Q3 and Q4 remain off, as shown in Fig. 8-a. During this interval, the current in series inductances L1 and L2 decreases linearly and transfers the energy to the load through D1, Co and body diode of Q2. The ripple current in series inductances L1 and L2 is: ∆ (15) In addition, the current in the series inductances L3 and L4 also decreases linearly, transferring the energy to the load through D3, Co and body diode of Q4. The ripple currents in series inductances L3 and L4 is: ∆ (15) The input current is the sum of currents in L1/L2 and L3/L4: ∆ (16) (22) Interval 4 [t3-t4]: At t3, Q3/Q4 are turned on, while Q1/Q2 remain off, as shown in Fig. 8-c. During this interval, the current in series inductances L3 and L4 increases linearly and stores the energy in these inductors. The ripple currents in Q3 and Q4 are the same as the current in series inductances L3 and L4, where the ripple current is given by: ∆ (23) The current in series inductances L1 and L2 decreases linearly and transfers the energy to the load through D2, Co and body diode of Q4. The ripple current in L1 and L2 is: ∆ (24) The input ripple current is the sum of currents in L1/L2 and L3/L4: (25) ∆ The operation of converter during the negative input voltage half cycle is similar to the operation of converter during the positive input voltage half cycle.
- 6. V. SIMULATION RESULT TS PSIM simulation software was used to v verify steady state waveforms of each component. Fig. 10 s shows the PSIM simulation circuits of the proposed BLIL PFC converter. As it C can be seen the power stage section of conv verter consists of four boost inductors – Ld1 to Ld4, four fas boost diodes – st Db1 to Db4, four switches – Q1 to Q4 and t their body diodes Dq1 to Dq4. Also it consists of two curren loops and one nt voltage loop. The sensed input voltage is m multiplied by the compensated output voltage, and then generates a control signal to be compared with the switching career waveforms to generate the gating signals for ma FETs. ain Fig. 11 shows the PSIM simulati results of a BLIL PFC ion boost converter. The input current is in phase with input voltage, and it has close to unity power factor. Also the y output voltage is regulated at arou 400V, with a 120 Hz und low frequency ripple. The converte is operating at 70 kHz er switching frequency, 240 V input voltage and 3.4 kW output v power. Fig. 10. PSIM simulation circuit for the proposed BLIL PFC boost converter L Fig. 11. Simulation waveforms for the proposed BLIL PFC boost converter including output voltage, input voltage and in nput current VI. EXPERIMENTA RESULTS TAL An experimental prototype, illust trated in Fig. 12, was built to verify the operation of the proposed converter. Fig. 13 shows the input voltage, input curren and PFC bus voltage of nt the converter under the following test conditions: Vin = 240 t V, Iin = 15 A, Po = 3400 W, fsw = 70 kHz. The input current is 0 in line and phase with the input volt tage, and its shape is close to a sinusoidal waveform. In order to verify the quality of the input current, its
- 7. is available from the mains feed to charge the batteries, reducing charging time and electricity costs. 2.5 Harmonic Current (A) 2 EN 61000-3-2 Class D Limits (A) Amplitude (A) Vin = 120 V 1.5 Amplitude (A) Vin = 240 V 1 0.5 0 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 harmonics up to 39th harmonic order are given and compared with the EN 61000-3-2 standard. Fig. 14 shows the input current harmonics versus harmonic numbers at full load for 120 V and 240 V input voltages. It is clearly shown that the generated harmonics are well below IEC 61000-3-2 standard for the input line harmonics which is required for PHEV chargers. In Fig. 15, the input current total harmonics distortions are given at full load and for 120 V and 240 V input voltages. It can be noted that mains current THD are smaller than 5% from 50% load to full load and it is compliant to IEC 6100-3-2. Another parameter to show the quality of input current is power factor. In Fig. 16, the converter power factor is shown at full load for different input voltages. As it can be seen, power factor is greater than 0.99 from 50% load to full load. Harmonics Order Fig. 14. Input current harmonics at full load for Vin = 120 V and 240 V 45 40 35 30 THD (%) 20 cm 25 Vin=240 20 15 Vin=120 10 5 Fig. 12. Breadboard prototype of BLIL PFC boost converter 3500 3500 2500 2000 1500 1000 3000 Input Voltage 3000 Output Voltage 500 0 0 Output Power (W) Fig. 15. Total harmonics distortion vs. output power at Vin = 120V and Vin = 240V 1.02 1 Vin=240 0.92 0.9 Vin=120 0.88 0.86 2500 2000 1500 0.84 1000 The efficiency of converter versus output power for different input voltages is provided in Fig. 17. High efficiency over entire load range is achieved in this topology, enabling fewer problems with heat dissipation and cooling systems. Furthermore, a higher efficiency means more power 0.94 500 Fig. 13. Proposed BLIL PFC experimental waveforms; Test Condition: Po = 3400W, Vin = 240V, Iin = 15A 0.96 0 Input Current Power factor 0.98 Output Power (W) Fig. 16. Power Factor vs. output power at Vin = 120V and Vin = 240V
- 8. 100 [7] 99 [8] 98 Efficiency (%) 97 [9] 96 95 Vin=240 V 94 Vin=220 V [10] 93 Vin=120 V 92 [11] 91 Vin=90 V [12] 3500 3000 2500 2000 1500 1000 500 0 90 Output Power (W) Fig. 17. Efficiency vs. output power at Vin = 90V, Vin = 120V, Vin = 220V and Vin = 240V VII. CONCLUSION A high performance AC-DC boost converter topology has been presented in this paper for the front-end AC-DC converter in PHEV battery chargers. The proposed converter topology has been analyzed and performance characteristics presented. A prototype converter was built to verify the proof-of-concept. The theoretical waveforms were compared with the simulation results and the results taken from prototype unit. Also some key experimental waveforms are given. Finally input current harmonics at each harmonic order was compared more explicitly with the IEC 6100-3-2 standard limits. The total harmonics distortion and power factor was measured on prototype unit and showed great results. The converter topology shows a high input power factor, high efficiency over entire load range and excellent input current harmonics. It is an excellent option for single phase PFC solution in higher power applications. [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] REFERENCES [1] [2] [3] [4] [5] [6] K. Morrow, D. Karner, and J. Francfort;, "Plug-in Hybrid Electric Vehicle Charging Infrastructure Review," U.S. Departent of Energy Vehicle Technologies Program, 2008. Singh, B.; Singh, B.N.; Chandra, A.; Al-Haddad, K.; Pandey, A.; Kothari, D.P.;, "A review of single-phase improved power quality ACDC converters," Industrial Electronics, IEEE Transactions on vol. 50, pp. 962 - 981 2003 Petersen, L.; Andersen, M.;, "Two-Stage Power Factor Corrected Power Supplies: The Low Component-Stress Approach " in IEEE Applied Power Electronics Conference and Exposition, APEC. vol. 2, 2002, pp. 1195 - 1201. 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