Implementation of a Half-Bridge Single-Stage Converter Control Using ...
PEDS2009
Implementation of a Half-Bridge Single-Stage Converter Control Using DSP Sheng-Yuan Ou, Member, IEEE, Chen-Hung Tien and Cheng-Wei Tsai Department of Electrical Engineering National Taipei University of Technology Taipei, Taiwan [email protected] Abstract—A novel control method used in the half-bridge single-state power converter is presented in this paper. This proposed control scheme is to enlarge load regulation range in discontinuous conduction mode (DCM), while the new duty pattern will be derived to perform the variable-frequency control. Compared to the conventional control methods, the proposed duty cycle pattern within a switching period is directly proportional to the absolute value of instantaneous source voltage and the output can be regulated by varying the switching frequency using digital signal processor (DSP) control wherein TMS320F2812 manufactured by TI is utilized. Compared to conventional control methods, the proposed is simpler to upgrade the power factor and efficiency. Experimental results show good conformation with the theoretical analysis. Keywords-DSP control; half-bridge converter; single-stage; DCM; variable-frequency control
I.
INTRODUCTION
Generally, the DC output can be obtained from two-stage converters [1], recently a family of single-stage power converters is provided [2-6]. There is only one power conversion stage to function power factor correction and DC output regulation, with the component count reducing thereby the cost and the volume down, and with the efficiency increasing because of single-stage architecture. In addition, a DCM variable-frequency control method is presented in [7], wherein the switching frequency is inversely proportional to load current and the duty pattern is defined to one minus the proportion of the absolute instantaneous source voltage to the output voltage, that is, v ⎞ 1⎛ d1 = ⎜⎜1 − S ⎟⎟ 2 ⎝ VCB ⎠
easily and successfully to acquire benefits comprising control simplification and flexibility. The operation principles and the experimental results are shown in the following sections. II.
VARYING DUTY PATTERN AND VARIABLE-FREQUENCY CONTROL
The proposed duty cycle pattern and the variable-frequency control strategy used in the half-bridge single-stage power converter shown in Fig. 1 are illustrated in this section. The conventional variable-frequency control method can be seen in [7], wherein the duty pattern is depicted in Fig. 2. While using the conventional control method in half-bridge topology, the actually measured source voltage and current waveforms are shown in Fig. 3, in which the larger the source voltage and the smaller the duty and the duty is smallest about θ=90o obviously. There are some drawbacks resulted from that, including the larger harmonic amount, lower power factor and more current stress on power devices, especially around zero crossings because the source current profile can not follow the voltage waveform profile. Now the power factor is below 0.9. The proposed duty pattern differs from the traditional one in that the proposed duty pattern is directly proportional to the instantaneous source voltage over the voltage on bulk capacitor as below vs (2) VCB where constant Ka is designed to keep the converter operating in DCM. d1 = Ka
(1)
where vs is the instantaneous source voltage and VCB is mean voltage on bulk capacitor. There are some advantages in this scheme, including higher voltage output and less lowfrequency components in source input. But when applied to the half-bridge topology, one obvious drawback is exhibited that the source profile can not follow the sinusoidal source voltage, resulting in lower power factor and higher distortion. Therefore the duty pattern must be modified under this variablefrequency control method used in half-bridge topology. To this end, the duty pattern is redefined as a proportion to the absolute value of source voltage in this paper. DSP-TMS320F2812 is used to implement the variable-frequency control strategy
S1 D1 L iL
D5
iC1 C1
D3
1:n ＋ vCB －
D7
iLo
iCo CO
+ vL vs
+ vLo LO
D4 D2 S2
D6
iC2 C2
＋ vCB －
D8
Figure 1. Proposed half-bridge single-stage power converter.
280
＋ R VO －
PEDS2009 cycle and the high-side power switch S1 and the free-wheeling diode D2 are switching responsible for negative-half-cycle in the proposed control strategy to obtain the higher PF generally.
vS
III.
t
EXPERIMENTAL RESULTS
A prototype converter was built to verify the validity of the proposed control scheme. Experiments are conducted on an exemplary system with the following parameters : VO=200V, PO=50~100W, L=490μH, LO=168μH, and fs=36~66kHz. Figs. 7(a), (b) and (c) illustrate the waveforms of the source current and voltage in detail with PO=50W, 70W and 100W, the power factors are 0.951, 0.985 and 0.988 respectively. Corresponding switching frequencies are 66 kHz for PO=50W, 47kHz for PO=70W and 36kHz for PO=100W. In general, an AC capacitor is used to shunt with the utility source to filter the harmonics in the shown source current so that the filtered source current approximates the sinusoidal wave. From Fig. 6, it is clear that the input source current can follow the source voltage exactly, so the PF is up to 0.95. The relationship between switching frequency and various output power is shown in Fig. 8 and PF curve is depicted in Fig. 9. It can be clearly seen that the regulation of the output voltage is fulfilled through tuning the switching frequency.
iL t
VGS
t
Figure 2. Duty pattern and related waveforms using conventional control method.
H.B Single-Stage Converter Figure 3. Actually measured waveforms of source current and voltage using conventional control method.
Vout
vs Gate driver
Through some derivation processes, Ka can be found as 1 VCB (3) Ka = 2 Vm where Vm represents the amplitude of source voltage. From the output voltage characteristic, we can conclude that a higher switching frequency should be adopted with a lighter load, and vice versa. Fig. 4 illustrates the entire system block diagram and Fig. 5 depicts the schematic diagram of the proposed control strategy implemented within DSP, in which ADC and VFC perform analog-to-digital-conversion and voltagefrequency-conversion. The control signal Ka|vs|/VCB which is the above-mentioned duty cycle pattern is formed in the DSP and will be compared to a triangular carrier that has a tunable frequency fs. The switching frequency is determined from the difference between the output voltage and the reference voltage. An extra merit of the presented control method is that the inverse proportionality of the switching frequency to the load level means a self-adaptive mechanism. Furthermore, the duty pattern with proposed control scheme and related waveforms are depicted in Fig. 6. Furthermore, the P/N cycle diagnose circuit is used to distinguish the positive-half-cycle and negative-half-cycle of the source voltage. It is noted that in addition to varying duty pattern and switching frequency modulation, the low-side power switch S2 and the freewheeling diode D1 are switching responsible for positive-half-
PWM_1,2
positve/ negative
Feedback circuitry
DSP
0V
Figure 4. Proposed system block diagram.
Gate Driver
VO V_err
PWM1 and 2
PWM
Vb
VFC
F
V_ref d1
Va
P/N CycleDiagnose
d1 = Ka
vS VCB
sinθ
Sin Table
DSP
Figure 5. Proposed control scheme.
281
ADC
PEDS2009 vS
t
iL t
VGS
t
Figure 8. Relationship between switching frequency and output power.
Figure 6. Duty pattern and related waveforms using proposed control method.
輸輸功功 (PF)
1 0.98 0.96
PF 0.94 0.92 0.9 40
50
60
70
80
90
100
110
output power(W) (W) 輸輸輸輸 Figure 9. Relationship between switching frequency and output power.
IV.
CONCLUSIONS
(a)
A novel half-bridge power converter and its duty pattern under switching frequency modulation are presented in this paper. The varying duty cycle can improve the input power factor and the regulation of the output voltage is fulfilled through tuning the switching frequency. In a reasonable range of switching frequency from 36kHz to 66kHz, experiments with the prototype converter show that under a regulated Vo of 200V, the adjustable output power range is from 50W up to 100W. The proposed duty pattern and the switching frequency modulation control is especially suitable for the proposed power converter.
(b)
[1]
REFERENCES
[2] [3]
[4] [5] [6]
(c) Figure 7. Source voltage (Ch3 : 100V/div with 2ms/div) and source current (Ch4 : 5A/div with 2ms/div) waveforms for (a) Po=50 W with fs=66 kHz (b) Po=70 W with fs=47 kHz and (c) Po=100 W with fs=36 kHz.
[7]
282
Y. Jiang, F. C. Lee, G. Hua, and W. Tang, “A novel single phase power factor correction scheme,” in Applied Power Electronics Conference and Exposition, 1993, pp. 287–292. T. F. Wu, and T. H. Yu, ” Unified Approach to Developing Single-Stage Power Converter,” Aerospace and Electronic Systems, IEEE Trans, vol. 34, Jan. 1998, pp. 211–223. J. Qian, Q. Zhao, and F.C. Lee, “Single-Stage Single-Switch Power Factor Correction AC/DC Converters with DC Bus Voltage Feedback for Universal Line Applications”, Power Electronics, IEEE Trans, vol. 13, Nov. 1998, pp.1079 – 1088. M. Qiu, G. Moschopoulos, H. Pinheiro, and P. Jain, “Analysis and Design of a Single Stage Power Factor Corrected Full-Bridge Converter”, APEC '99, vol. 1, March 1999, pp.119–125. R. Redl, and L. Balogh, “Design Considerations for Single-Stage Isolated Power-Factor-Corrected Power Supplies with Fast Regulation of the Output Voltage”, APEC '95, vol. 1, March 1995, pp.454–458. M. H. L. Chow, K. W. Siu, C. K. Tse, and Y. S. Lee, ”A novel method for elimination of line-current harmonics in single-stage PFC switching regulators”, IEEE Trans, vol. 13, Jan. 1998, pp.75–83. Yu-Kang Lo, Jing-Yuan Lin and Sheng-Yuan Ou, "SwitchingFrequency Control for Regulated Discontinuous-Conduction-Mode Boost Rectifiers", IEEE Trans. on Industrial Electronics, vol. 54, no. 2, pp. 760–768, Appril 2007.
PEDS2009
283
Implementation of a Half-Bridge Single-Stage Converter Control Using DSP Sheng-Yuan Ou, Member, IEEE, Chen-Hung Tien and Cheng-Wei Tsai Department of Electrical Engineering National Taipei University of Technology Taipei, Taiwan [email protected] Abstract—A novel control method used in the half-bridge single-state power converter is presented in this paper. This proposed control scheme is to enlarge load regulation range in discontinuous conduction mode (DCM), while the new duty pattern will be derived to perform the variable-frequency control. Compared to the conventional control methods, the proposed duty cycle pattern within a switching period is directly proportional to the absolute value of instantaneous source voltage and the output can be regulated by varying the switching frequency using digital signal processor (DSP) control wherein TMS320F2812 manufactured by TI is utilized. Compared to conventional control methods, the proposed is simpler to upgrade the power factor and efficiency. Experimental results show good conformation with the theoretical analysis. Keywords-DSP control; half-bridge converter; single-stage; DCM; variable-frequency control
I.
INTRODUCTION
Generally, the DC output can be obtained from two-stage converters [1], recently a family of single-stage power converters is provided [2-6]. There is only one power conversion stage to function power factor correction and DC output regulation, with the component count reducing thereby the cost and the volume down, and with the efficiency increasing because of single-stage architecture. In addition, a DCM variable-frequency control method is presented in [7], wherein the switching frequency is inversely proportional to load current and the duty pattern is defined to one minus the proportion of the absolute instantaneous source voltage to the output voltage, that is, v ⎞ 1⎛ d1 = ⎜⎜1 − S ⎟⎟ 2 ⎝ VCB ⎠
easily and successfully to acquire benefits comprising control simplification and flexibility. The operation principles and the experimental results are shown in the following sections. II.
VARYING DUTY PATTERN AND VARIABLE-FREQUENCY CONTROL
The proposed duty cycle pattern and the variable-frequency control strategy used in the half-bridge single-stage power converter shown in Fig. 1 are illustrated in this section. The conventional variable-frequency control method can be seen in [7], wherein the duty pattern is depicted in Fig. 2. While using the conventional control method in half-bridge topology, the actually measured source voltage and current waveforms are shown in Fig. 3, in which the larger the source voltage and the smaller the duty and the duty is smallest about θ=90o obviously. There are some drawbacks resulted from that, including the larger harmonic amount, lower power factor and more current stress on power devices, especially around zero crossings because the source current profile can not follow the voltage waveform profile. Now the power factor is below 0.9. The proposed duty pattern differs from the traditional one in that the proposed duty pattern is directly proportional to the instantaneous source voltage over the voltage on bulk capacitor as below vs (2) VCB where constant Ka is designed to keep the converter operating in DCM. d1 = Ka
(1)
where vs is the instantaneous source voltage and VCB is mean voltage on bulk capacitor. There are some advantages in this scheme, including higher voltage output and less lowfrequency components in source input. But when applied to the half-bridge topology, one obvious drawback is exhibited that the source profile can not follow the sinusoidal source voltage, resulting in lower power factor and higher distortion. Therefore the duty pattern must be modified under this variablefrequency control method used in half-bridge topology. To this end, the duty pattern is redefined as a proportion to the absolute value of source voltage in this paper. DSP-TMS320F2812 is used to implement the variable-frequency control strategy
S1 D1 L iL
D5
iC1 C1
D3
1:n ＋ vCB －
D7
iLo
iCo CO
+ vL vs
+ vLo LO
D4 D2 S2
D6
iC2 C2
＋ vCB －
D8
Figure 1. Proposed half-bridge single-stage power converter.
280
＋ R VO －
PEDS2009 cycle and the high-side power switch S1 and the free-wheeling diode D2 are switching responsible for negative-half-cycle in the proposed control strategy to obtain the higher PF generally.
vS
III.
t
EXPERIMENTAL RESULTS
A prototype converter was built to verify the validity of the proposed control scheme. Experiments are conducted on an exemplary system with the following parameters : VO=200V, PO=50~100W, L=490μH, LO=168μH, and fs=36~66kHz. Figs. 7(a), (b) and (c) illustrate the waveforms of the source current and voltage in detail with PO=50W, 70W and 100W, the power factors are 0.951, 0.985 and 0.988 respectively. Corresponding switching frequencies are 66 kHz for PO=50W, 47kHz for PO=70W and 36kHz for PO=100W. In general, an AC capacitor is used to shunt with the utility source to filter the harmonics in the shown source current so that the filtered source current approximates the sinusoidal wave. From Fig. 6, it is clear that the input source current can follow the source voltage exactly, so the PF is up to 0.95. The relationship between switching frequency and various output power is shown in Fig. 8 and PF curve is depicted in Fig. 9. It can be clearly seen that the regulation of the output voltage is fulfilled through tuning the switching frequency.
iL t
VGS
t
Figure 2. Duty pattern and related waveforms using conventional control method.
H.B Single-Stage Converter Figure 3. Actually measured waveforms of source current and voltage using conventional control method.
Vout
vs Gate driver
Through some derivation processes, Ka can be found as 1 VCB (3) Ka = 2 Vm where Vm represents the amplitude of source voltage. From the output voltage characteristic, we can conclude that a higher switching frequency should be adopted with a lighter load, and vice versa. Fig. 4 illustrates the entire system block diagram and Fig. 5 depicts the schematic diagram of the proposed control strategy implemented within DSP, in which ADC and VFC perform analog-to-digital-conversion and voltagefrequency-conversion. The control signal Ka|vs|/VCB which is the above-mentioned duty cycle pattern is formed in the DSP and will be compared to a triangular carrier that has a tunable frequency fs. The switching frequency is determined from the difference between the output voltage and the reference voltage. An extra merit of the presented control method is that the inverse proportionality of the switching frequency to the load level means a self-adaptive mechanism. Furthermore, the duty pattern with proposed control scheme and related waveforms are depicted in Fig. 6. Furthermore, the P/N cycle diagnose circuit is used to distinguish the positive-half-cycle and negative-half-cycle of the source voltage. It is noted that in addition to varying duty pattern and switching frequency modulation, the low-side power switch S2 and the freewheeling diode D1 are switching responsible for positive-half-
PWM_1,2
positve/ negative
Feedback circuitry
DSP
0V
Figure 4. Proposed system block diagram.
Gate Driver
VO V_err
PWM1 and 2
PWM
Vb
VFC
F
V_ref d1
Va
P/N CycleDiagnose
d1 = Ka
vS VCB
sinθ
Sin Table
DSP
Figure 5. Proposed control scheme.
281
ADC
PEDS2009 vS
t
iL t
VGS
t
Figure 8. Relationship between switching frequency and output power.
Figure 6. Duty pattern and related waveforms using proposed control method.
輸輸功功 (PF)
1 0.98 0.96
PF 0.94 0.92 0.9 40
50
60
70
80
90
100
110
output power(W) (W) 輸輸輸輸 Figure 9. Relationship between switching frequency and output power.
IV.
CONCLUSIONS
(a)
A novel half-bridge power converter and its duty pattern under switching frequency modulation are presented in this paper. The varying duty cycle can improve the input power factor and the regulation of the output voltage is fulfilled through tuning the switching frequency. In a reasonable range of switching frequency from 36kHz to 66kHz, experiments with the prototype converter show that under a regulated Vo of 200V, the adjustable output power range is from 50W up to 100W. The proposed duty pattern and the switching frequency modulation control is especially suitable for the proposed power converter.
(b)
[1]
REFERENCES
[2] [3]
[4] [5] [6]
(c) Figure 7. Source voltage (Ch3 : 100V/div with 2ms/div) and source current (Ch4 : 5A/div with 2ms/div) waveforms for (a) Po=50 W with fs=66 kHz (b) Po=70 W with fs=47 kHz and (c) Po=100 W with fs=36 kHz.
[7]
282
Y. Jiang, F. C. Lee, G. Hua, and W. Tang, “A novel single phase power factor correction scheme,” in Applied Power Electronics Conference and Exposition, 1993, pp. 287–292. T. F. Wu, and T. H. Yu, ” Unified Approach to Developing Single-Stage Power Converter,” Aerospace and Electronic Systems, IEEE Trans, vol. 34, Jan. 1998, pp. 211–223. J. Qian, Q. Zhao, and F.C. Lee, “Single-Stage Single-Switch Power Factor Correction AC/DC Converters with DC Bus Voltage Feedback for Universal Line Applications”, Power Electronics, IEEE Trans, vol. 13, Nov. 1998, pp.1079 – 1088. M. Qiu, G. Moschopoulos, H. Pinheiro, and P. Jain, “Analysis and Design of a Single Stage Power Factor Corrected Full-Bridge Converter”, APEC '99, vol. 1, March 1999, pp.119–125. R. Redl, and L. Balogh, “Design Considerations for Single-Stage Isolated Power-Factor-Corrected Power Supplies with Fast Regulation of the Output Voltage”, APEC '95, vol. 1, March 1995, pp.454–458. M. H. L. Chow, K. W. Siu, C. K. Tse, and Y. S. Lee, ”A novel method for elimination of line-current harmonics in single-stage PFC switching regulators”, IEEE Trans, vol. 13, Jan. 1998, pp.75–83. Yu-Kang Lo, Jing-Yuan Lin and Sheng-Yuan Ou, "SwitchingFrequency Control for Regulated Discontinuous-Conduction-Mode Boost Rectifiers", IEEE Trans. on Industrial Electronics, vol. 54, no. 2, pp. 760–768, Appril 2007.
PEDS2009
283
