Series
Content
PEDS2009
A Series-Resonant Single-Phase Step up/down AC Chopper
Chien-Ming Wang*, Maoh-Chin Jiang*, Chang-Hua Lin**, Chia-Hua Liu* and Deng-Jie Yang* * Department of Electrical Engineering, National Ilan University, I-Lan, Tai wan ** Department of Electrical Engineering, Tatung University, Taipei, Taiwan Abstract -- A series-resonant single-phase step up/down ac chopper is presented. The main attribute of the ac chopper topology is the fact that it generates an output ac voltage larger or lower than the input ac one, depending on the instantaneous duty-cycle. This property is not found in the classical ac chopper, which produces an ac output instantaneous voltage always lower than the input ac voltage. The presented single-phase ac chopper is configured by a series-resonant conversion. The presented single-phase ac chopper is a series resonator to configure adaptively the resonant voltage robes. The synthesized sinusoidal waveform (SSW) before output filter is synthesized by a series of sinusoidal amplitude quasi-sinusoidal pulses (QSPs) following the input voltage amplitude. Because the synthesized SSW very closes sinusoidal waveform, the presented single-phase ac chopper can use a simple LC filter to filter the undesired harmonics and get the sinusoidal voltage with low total harmonic distortion (THD). The presented single-phase ac chopper is operated by constant frequency pulse width modulation control technique. Waveform syntheses for the output sinusoidal voltage are clearly analyzed and derived. A typical design example of a 600W series-resonant single-phase ac chopper is examined to assess the system performance. The power efficiency is over 90% when the output power is at maximum output rated power. The total harmonic distortion (THD) when the output power is at maximum output rated power is within 6%.
input voltage amplitude. Because the synthesized SSW very closes sinusoidal waveform, the presented single-phase ac chopper can use a simple LC filter to filter the undesired harmonics and get the sinusoidal voltage with low total harmonic distortion (THD). The constant frequency pulse width modulation (PWM) control strategy is designed to achieve well dynamic regulation characteristic. The properly driving signal of the power switches and the resonant characteristic of LC t ank are also achieved by it. System analysis for predicting and evaluating the proposed ac chopper performance are conducted. A 60Hz 600W ac chopper is designed and realized. The total harmonic distortion (THD) is under 6% before EMI filtering, and the power efficiency is over 90% when the power is maximum rated power. Dm D1
S 2
S 1 L f
Lr
vin
D4
Index Terms – Terms – series resonant, ac chopper
I. I NTRODUCTION The ac voltage regulators have become important equipment for obtain variable ac voltage from a fixed ac source. Because the phase-angle control technique and integral-cycle control technique of thyristors are simplicity, they are traditionally used in the ac voltage regulator. However, the retardation of firing angle causes high low-order harmonic in both output and input sides and a lagging power factor in input side [1]. For improving these problems, the pulse-width modulation control technique is widely used in the ac choppers [2]-[7]. However, there still exit lots of shortcomings including high switching loss, and large EMI. And, one of their characteristics is that the instantaneous average output voltage is always lower than the input ac voltage. It will result in the application range decreases. For overcoming these problems and increasing the power density of the ac chopper, a series-resonant single-phase step up/down ac chopper is presented in this paper with a simple and compact topology. A turn-on zero-current-switching (ZCS) for the power switch is achieved. The synthesized sinusoidal waveform (SSW) before output filter is filter is synthesized by a series of sinusoidal amplitude quasi-sinusoidal pulses (QSPs) following the
D2
D3
C r
C f
S 3
R L
S 4
S m
Fig.1 Circuit topology of the proposed series-resonant single-phase step up/down chopper
II. PRICIPLES OF THE SERIES-R ESONANT ESONANT SINGLE-PHASE STEP UP/DOWN AC CHOPPER The proposed series-resonant single-phase step up/down ac chopper shown in Fig. 1, which primarily comprises a series-resonant power stage and a cycloconverter. The series-resonant power stage composed of a power switch S m, a power diode Dm, a resonant inductance Lr , a resonant capacitance C r r , parallel-loaded with the cycloconverter. The power stage is inherently a parallel-loaded series resonant converter. The cycloconverter composed of power switches S 1-S 4 and an output filter L f and C f . It interlacedly inverts the series of half-period unipolar composite sinusoidal waveform into an alternately bipolar form in a desired period. For ease of analysis, the cycloconverter can be simply thought of a resistive load for the power stage. The equivalent circuit in the positive (negative) half-period of the line input voltage D2 ( D1), D4 ( D3), S m, Dm, S 1 (S 4), S 3 (S 2), vin(t) is composed of D Lr , C r r, L f , and C f // R R L. In the positive (negative) half-period
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of the line input voltage vin(t), the switches S 2 (S 1) and S 4 in discontinuous conduction mode (DCM). For (S 3) are always off, the switch S 1 (S 2) and S 3 (S 4) are always convenience in analysis, it is presumed that all devices are on, and S m performs the conversion function at high ideal and that the losses in Lr , L f , C r, and C f are all frequency switching. The equivalent circuits for describing neglected. They are assumed that the input voltage are their behavior are shown in Fig. 2. The complete approximated a stairway waveform and it is approximate a synthesized resonant output voltage robes and switches constant value in one switching period. Since the circuit drive signal are shown in Fig. 3. It is clearly seen that the operation at positive line input voltage is the same as the output voltage vo(t) is synthesized by resonant voltage circuit operation at negative line input voltage. Only the robes with sinusoidal amplitude and the resonant resonant behaviors in positive line input voltage are synthesized sinusoidal voltage waveform in resonant described in the following. The initial states of the switch capacitor C r very closes sinusoidal waveform. Thus, the S m is off. Before t =t k0, it is assumed that the circuit presented ac chopper can use a simple LC filter to get the operation is in the linearly discharging state . There are sinusoidal output voltage waveform with low THD. The three resonant states in one switching cycle. They are working states include a linear charging and discharging described in the following. state, a resonant state, and a linearly discharging state. Remarkably, the proposed single-phase ac chopper operates Linear charging and discharging state Dm D1
D2
S 2
S 1 L f
Lr vin
i Lr (t)
+ vCr _
i Lf (t) C f
C r
D3
S 3
D4
+ vo _
R L
S 4
S m
Lr V ink
+ vCr _
i Lr (t)
I Lfk
(a) Resonant state
Linear-discharging state
Dm D1
D2
Dm S 2
D1
S 1
D2
S 2
S 1
L f Lr vin
+ vCr _
i Lr (t)
D3
i Lf (t) C f
C r
S 3
D4
L f + vo _
Lr vin
R L
i Lr (t)
+ vCr _
D3
S 4
S 3
D4
S m
i Lf (t) C f
C r
+ vo _
R L
S 4
S m
Lr i Lr (t)
+ vCr _
+ vCr _
I Lfk
(b)
I Lfk (c)
Fig. 2 The equivalent circuits for describing the resonant robes of vCr (t) in the k th switching period
ZCS at t=t k0, the resonant inductor Lr is charged linearly energy by input voltage source and the resonant capacitor C r discharges its energy to the load until t=t k1. Thus, the resonant current i Lr (t) increases and the resonant voltage
Stage I: Linear charging and discharging state, t in [ t k0, t k1]:
This state begins as the power switch S m turns on with
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dynamics. The feedback circuit includes an isolated voltage sensor, a rectifier, a low-pass filter, a voltage error amplifier, a pulse width modulation generator, and a control logic circuit. First, the isolated voltage sensor samples the output voltage signal k ovo. Then, the signal k ovo is rectified and filtered to generate the average dc voltage V a. The voltage error amplifier is necessary to compare the the average dc voltage V a with the reference V ref and generate an error signal vc. The error signal is applied to the pulse width modulation generator. The pulse width modulation generator then generates a square waveform of necessary duty ratio of proposed ac chopper according to the error signal. The square waveform drives then control logic circuit. The gating pulse train for driving the power switches is generated. The gating pulse train is designed to have a fixed period time signal with duty ratio varied.
V ok R L
= I Lfk = D1k I Lrk , avg
(10)
V Crk = V ok
(11)
where D1k R L ⎧ V ink
V D T
2 2 ok 1k s ⎨ D T s + T s ⎩ 2 Lr R L ⎛ DT sV ink V ok ⎞ +⎜ ⎜ Z − R ω ⎟⎟ sin ω r D1k T o L r ⎠ ⎝ V ok ⎞ cosω r D1k T s − 1 ⎡V ok ⎛ V ink ⎟⎟ + +⎜ − DT ⎢ s ⎜ L ω r sin ω r D1k T R R ⎢ s ⎣ L L ⎠ ⎝ r
V ok =
Dm D1
D2
S 2
• cosω r D1k T s
S 1 L f
Lr
vin
C r
D3
S 3
(12)
Thus, the conversion ratio M ( D) can be described as
C f
D4
]}
R L
follow.
S 4
M ( D ) =
V ok
(13)
V ink
S m S m
S 2
S 1
S 3
S 4
Controller
The conversion ratio M ( D) versus the duty ratio D with different loads R L is shown in Fig. 5.
Control Logic and Drive Circuit
Rectifier
R L=60 Ω
Isolated Voltage Sensor
C o n v e r s i o n R a t i o M D
Voltage error amplifier _ PID
PWM
+
Low Pass Filter
V ref
Fig. 4 Control system of the presented single-phase AC chopper.
In proposed ac chopper, i Lr (t ) is in DCM but i Lf (t ) is continuous. Thus, the steady-state description in the k th switching period can then be determined by the average method. The average resonant inductor current can be described as following.
I Lrk , avg =
1 ⎧ V ink 2 2 ⎨ D T s + I Lfk D1′k T s + T s ⎩ 2 Lr
⎛ DT sV ink I Lfk ⎞ ⎜ Z − ω ⎟⎟ sin ω r D1k T s o r ⎠ ⎝ ⎛ V ink ⎞ cos ω r D1k T s − 1 ⎡ + ⎢ I Lfk + ⎜⎜ DT s − I Lfk ⎟⎟ ω r sin ω r D1k T ⎢ s ⎣ ⎝ Lr ⎠
where t − t D = k 1 k 0 T s D1k = and
V ink
D V Crk
]}
R L=30 Ω R L=24Ω R L=20 Ω R L=10 Ω
( )
Duty ratio D
Fig. 5 The conversion ratio M(D) versus duty ratio D with different loads.
Since vin(t)=V m sinωint, the output voltage V ok in the k th switching period can be obtained as V ok = M ( D )V ink = M ( D )V m sin ω in kT s
+⎜
• cos ω r D1k T s
R L=40 Ω
•[ u (t − t k ) − u ( t − t ( k +1) )]
(14)
We assume that there are the number of n discrete V on in one period of the desired vo(t). Thus, the complete output voltage can be expressed as n
(7)
vo =
∑V
ok
=
M ( D )V m sin ω in kT s • [u(t − t k ) − u(t − t ( k +1) ]
k =1
(8) (9)
(15) In reality, if f s>> f in and n is so large, we can approximately obtain (16) vo (t ) ≅ M ( D )V m sin(ω in t ) (16) is truly a sinusoidal waveform of the desired output voltage vo(t).
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IV. DESIGN CONSIDERATIONS AND REALIZATION An example of a single-phase soft-switching ac chopper is designed and realized. The design procedure is described as follows: Step 1 —Input and output data specification. The
input voltage vin(t)=V in,maxsinωint= 155sin(2π×60)t;
The
output voltage vo(t)=V o,maxsinωint=220sin(2π×60)t; The maximum output power P o,max=600W. The switching frequency f s=40kHz The resonant frequency f r=20kHz.
main power switche S m turns on at ZCS and the switch S 1 of cycloconverter turn on and of at ZVS and ZCS. The experimental results shown in Fig. 6, demonstrate that soft-switching function is achieved. The waveforms of resonant voltage vCr (t) and resonant current i Lr (t) are measured and shown in Fig. 7, which exactly meets the simulation result. The waveforms of input voltage and output voltage are simultaneously measured and shown in Fig. 8. The efficiency of the presented single-phase soft-switching ac chopper is also measured, in which the efficiency is over 90% when the output power is at maximum output power 600W. V. CONCLUSION
Step 2 —Decision of the duty cycle D.
A high performance single-phase step up/down ac With the parameters shown in Step 1, the duty cycle D can chopper by a simple and compact characteristic with be obtained from Fig. 5 under the condition of series-resonant conversion is presented. The main attribute P o,max=600W, V o,max=220V, R L = V o2, max / 2 P o , max = 40 , of the ac chopper topology is the fact that it generates an output ac voltage larger or lower than the input ac one, V o,max/V in,max=1.42. Thus, D=0.3. Substituting D=0.3 into depending on the instantaneous duty-cycle. This property (9) yield D1k =0.21. is not found in the classical ac chopper, which produces an Step 3 —Calculation of the resonant parameters. ac output instantaneous voltage always lower than the input ac voltage. The active switches are operated at a The average resonant current I Lrk,avg and the filter current fixed frequency with the pulse width modulation technique. I Lfk can be obtained from (12) as I Lfk,max=5.5A, A resonant cell is built in the power stage to build ZCS for I Lrk,avg,max=26.2A. According to the resonant frequency and turning on the power switches. Thus, lower switching from (7), the characteristic impedance Z o can be obtained losses, lower electromagnetic interference noises, and as in this example. Thus, Z o=1.45Ω higher power efficiency can be achieved. Because the C r = 1 /( Z oω r ) = 5.5μ F and Lr = 1 /(ω r 2C r ) = 11.5μ F . synthesized SSW very closes sinusoidal waveform, the Step 4 —Calculation of the output filter inductor and presented single-phase ac chopper can use a simple LC filter to filter the undesired harmonics and get the capacitor. sinusoidal voltage with low total harmonic distortion For minimizing unnecessary harmonics, the output filter (THD). Total harmonic distortion (THD) at maximum inductor L f =1mH and capacitor C f =4.7μF are selected. output rated power is within 6%. The power efficiency is over 90% when the output power is at maximum output In hardware realization, IGBT’s IRG4PC50UD and rated power can be obtained. The analysis and design of diode’s S30L60 are as power switches and power diodes, circuit has been verified by realization of practical circuit respectively. The commutation phenomenon of power in laboratory. switches are measured and shown in Fig. 6, in which the v DSm i DSm
i DS1
(a)
v DS1
(b) Fig. 6 Commutation waveforms of the main power switch.
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vCr
vCr
i Lr
i Lr
(a)
(b) Fig. 7 The waveforms of resonant voltage vCr (t) and resonant current i Lr (t).
[2] vin
[3]
vo
[4]
[5]
[6]
[7] Fig. 8 Experimental waveforms of vo(t) and vin(t).
REFERENCES [1]
E. El-Bidweihy, K. Al-Badwaihy, M. S. Metwally, and M. El-Eedweihy, ”Power factor of ac controllers for inductive loads” IEEE Trans. Industrial Electron. Contr. Instrumentation, vol. 27, no. 3, pp. 210-212, 1980.
608
B. W. Williams, “Asymmetrically modulated AC choppers,” IEEE Trans. Ind. Electron., vol. IE-29, pp. 181–185, Aug. 1982. S. A. Bhat and J. Vithayathil, “A simple multiple pulse width modulated AC chopper,” IEEE Trans. Ind. Electron., vol. IE-29, pp. 185–189, Aug. 1982. G. Roy, P. Poitevin, and G. Olivier, “A Comparative study of singlephase modulated AC choppers,” IEEE Trans. Ind. Applicat., vol. IA-20, pp. 1498–1506, Nov./Dec. 1984. G. H. Choe, A. K. Wallace, and M. H. Park, “An improved PWM technique for AC choppers,” IEEE Trans. Power Electron., vol. 4, pp. 496–505, Oct. 1989. D. H. Jang and G. H. Choe, “Improvement of Input Power Factor in AC Choppers Using Asymmetrical PWM Technique,” IEEE Trans. Ind. Electron., vol. 42, no. 2, pp. 179–185, April 1995. N. A. Ahmed, K. Amei, and M. Sakui, ,” A New Configuration of Single-Phase Symmetrical PWM AC Chopper Voltage Controller,” IEEE Trans. Ind. Electron., vol. 46, no. 5, pp. 942-951, Oct. 1999.
A Series-Resonant Single-Phase Step up/down AC Chopper
Chien-Ming Wang*, Maoh-Chin Jiang*, Chang-Hua Lin**, Chia-Hua Liu* and Deng-Jie Yang* * Department of Electrical Engineering, National Ilan University, I-Lan, Tai wan ** Department of Electrical Engineering, Tatung University, Taipei, Taiwan Abstract -- A series-resonant single-phase step up/down ac chopper is presented. The main attribute of the ac chopper topology is the fact that it generates an output ac voltage larger or lower than the input ac one, depending on the instantaneous duty-cycle. This property is not found in the classical ac chopper, which produces an ac output instantaneous voltage always lower than the input ac voltage. The presented single-phase ac chopper is configured by a series-resonant conversion. The presented single-phase ac chopper is a series resonator to configure adaptively the resonant voltage robes. The synthesized sinusoidal waveform (SSW) before output filter is synthesized by a series of sinusoidal amplitude quasi-sinusoidal pulses (QSPs) following the input voltage amplitude. Because the synthesized SSW very closes sinusoidal waveform, the presented single-phase ac chopper can use a simple LC filter to filter the undesired harmonics and get the sinusoidal voltage with low total harmonic distortion (THD). The presented single-phase ac chopper is operated by constant frequency pulse width modulation control technique. Waveform syntheses for the output sinusoidal voltage are clearly analyzed and derived. A typical design example of a 600W series-resonant single-phase ac chopper is examined to assess the system performance. The power efficiency is over 90% when the output power is at maximum output rated power. The total harmonic distortion (THD) when the output power is at maximum output rated power is within 6%.
input voltage amplitude. Because the synthesized SSW very closes sinusoidal waveform, the presented single-phase ac chopper can use a simple LC filter to filter the undesired harmonics and get the sinusoidal voltage with low total harmonic distortion (THD). The constant frequency pulse width modulation (PWM) control strategy is designed to achieve well dynamic regulation characteristic. The properly driving signal of the power switches and the resonant characteristic of LC t ank are also achieved by it. System analysis for predicting and evaluating the proposed ac chopper performance are conducted. A 60Hz 600W ac chopper is designed and realized. The total harmonic distortion (THD) is under 6% before EMI filtering, and the power efficiency is over 90% when the power is maximum rated power. Dm D1
S 2
S 1 L f
Lr
vin
D4
Index Terms – Terms – series resonant, ac chopper
I. I NTRODUCTION The ac voltage regulators have become important equipment for obtain variable ac voltage from a fixed ac source. Because the phase-angle control technique and integral-cycle control technique of thyristors are simplicity, they are traditionally used in the ac voltage regulator. However, the retardation of firing angle causes high low-order harmonic in both output and input sides and a lagging power factor in input side [1]. For improving these problems, the pulse-width modulation control technique is widely used in the ac choppers [2]-[7]. However, there still exit lots of shortcomings including high switching loss, and large EMI. And, one of their characteristics is that the instantaneous average output voltage is always lower than the input ac voltage. It will result in the application range decreases. For overcoming these problems and increasing the power density of the ac chopper, a series-resonant single-phase step up/down ac chopper is presented in this paper with a simple and compact topology. A turn-on zero-current-switching (ZCS) for the power switch is achieved. The synthesized sinusoidal waveform (SSW) before output filter is filter is synthesized by a series of sinusoidal amplitude quasi-sinusoidal pulses (QSPs) following the
D2
D3
C r
C f
S 3
R L
S 4
S m
Fig.1 Circuit topology of the proposed series-resonant single-phase step up/down chopper
II. PRICIPLES OF THE SERIES-R ESONANT ESONANT SINGLE-PHASE STEP UP/DOWN AC CHOPPER The proposed series-resonant single-phase step up/down ac chopper shown in Fig. 1, which primarily comprises a series-resonant power stage and a cycloconverter. The series-resonant power stage composed of a power switch S m, a power diode Dm, a resonant inductance Lr , a resonant capacitance C r r , parallel-loaded with the cycloconverter. The power stage is inherently a parallel-loaded series resonant converter. The cycloconverter composed of power switches S 1-S 4 and an output filter L f and C f . It interlacedly inverts the series of half-period unipolar composite sinusoidal waveform into an alternately bipolar form in a desired period. For ease of analysis, the cycloconverter can be simply thought of a resistive load for the power stage. The equivalent circuit in the positive (negative) half-period of the line input voltage D2 ( D1), D4 ( D3), S m, Dm, S 1 (S 4), S 3 (S 2), vin(t) is composed of D Lr , C r r, L f , and C f // R R L. In the positive (negative) half-period
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of the line input voltage vin(t), the switches S 2 (S 1) and S 4 in discontinuous conduction mode (DCM). For (S 3) are always off, the switch S 1 (S 2) and S 3 (S 4) are always convenience in analysis, it is presumed that all devices are on, and S m performs the conversion function at high ideal and that the losses in Lr , L f , C r, and C f are all frequency switching. The equivalent circuits for describing neglected. They are assumed that the input voltage are their behavior are shown in Fig. 2. The complete approximated a stairway waveform and it is approximate a synthesized resonant output voltage robes and switches constant value in one switching period. Since the circuit drive signal are shown in Fig. 3. It is clearly seen that the operation at positive line input voltage is the same as the output voltage vo(t) is synthesized by resonant voltage circuit operation at negative line input voltage. Only the robes with sinusoidal amplitude and the resonant resonant behaviors in positive line input voltage are synthesized sinusoidal voltage waveform in resonant described in the following. The initial states of the switch capacitor C r very closes sinusoidal waveform. Thus, the S m is off. Before t =t k0, it is assumed that the circuit presented ac chopper can use a simple LC filter to get the operation is in the linearly discharging state . There are sinusoidal output voltage waveform with low THD. The three resonant states in one switching cycle. They are working states include a linear charging and discharging described in the following. state, a resonant state, and a linearly discharging state. Remarkably, the proposed single-phase ac chopper operates Linear charging and discharging state Dm D1
D2
S 2
S 1 L f
Lr vin
i Lr (t)
+ vCr _
i Lf (t) C f
C r
D3
S 3
D4
+ vo _
R L
S 4
S m
Lr V ink
+ vCr _
i Lr (t)
I Lfk
(a) Resonant state
Linear-discharging state
Dm D1
D2
Dm S 2
D1
S 1
D2
S 2
S 1
L f Lr vin
+ vCr _
i Lr (t)
D3
i Lf (t) C f
C r
S 3
D4
L f + vo _
Lr vin
R L
i Lr (t)
+ vCr _
D3
S 4
S 3
D4
S m
i Lf (t) C f
C r
+ vo _
R L
S 4
S m
Lr i Lr (t)
+ vCr _
+ vCr _
I Lfk
(b)
I Lfk (c)
Fig. 2 The equivalent circuits for describing the resonant robes of vCr (t) in the k th switching period
ZCS at t=t k0, the resonant inductor Lr is charged linearly energy by input voltage source and the resonant capacitor C r discharges its energy to the load until t=t k1. Thus, the resonant current i Lr (t) increases and the resonant voltage
Stage I: Linear charging and discharging state, t in [ t k0, t k1]:
This state begins as the power switch S m turns on with
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dynamics. The feedback circuit includes an isolated voltage sensor, a rectifier, a low-pass filter, a voltage error amplifier, a pulse width modulation generator, and a control logic circuit. First, the isolated voltage sensor samples the output voltage signal k ovo. Then, the signal k ovo is rectified and filtered to generate the average dc voltage V a. The voltage error amplifier is necessary to compare the the average dc voltage V a with the reference V ref and generate an error signal vc. The error signal is applied to the pulse width modulation generator. The pulse width modulation generator then generates a square waveform of necessary duty ratio of proposed ac chopper according to the error signal. The square waveform drives then control logic circuit. The gating pulse train for driving the power switches is generated. The gating pulse train is designed to have a fixed period time signal with duty ratio varied.
V ok R L
= I Lfk = D1k I Lrk , avg
(10)
V Crk = V ok
(11)
where D1k R L ⎧ V ink
V D T
2 2 ok 1k s ⎨ D T s + T s ⎩ 2 Lr R L ⎛ DT sV ink V ok ⎞ +⎜ ⎜ Z − R ω ⎟⎟ sin ω r D1k T o L r ⎠ ⎝ V ok ⎞ cosω r D1k T s − 1 ⎡V ok ⎛ V ink ⎟⎟ + +⎜ − DT ⎢ s ⎜ L ω r sin ω r D1k T R R ⎢ s ⎣ L L ⎠ ⎝ r
V ok =
Dm D1
D2
S 2
• cosω r D1k T s
S 1 L f
Lr
vin
C r
D3
S 3
(12)
Thus, the conversion ratio M ( D) can be described as
C f
D4
]}
R L
follow.
S 4
M ( D ) =
V ok
(13)
V ink
S m S m
S 2
S 1
S 3
S 4
Controller
The conversion ratio M ( D) versus the duty ratio D with different loads R L is shown in Fig. 5.
Control Logic and Drive Circuit
Rectifier
R L=60 Ω
Isolated Voltage Sensor
C o n v e r s i o n R a t i o M D
Voltage error amplifier _ PID
PWM
+
Low Pass Filter
V ref
Fig. 4 Control system of the presented single-phase AC chopper.
In proposed ac chopper, i Lr (t ) is in DCM but i Lf (t ) is continuous. Thus, the steady-state description in the k th switching period can then be determined by the average method. The average resonant inductor current can be described as following.
I Lrk , avg =
1 ⎧ V ink 2 2 ⎨ D T s + I Lfk D1′k T s + T s ⎩ 2 Lr
⎛ DT sV ink I Lfk ⎞ ⎜ Z − ω ⎟⎟ sin ω r D1k T s o r ⎠ ⎝ ⎛ V ink ⎞ cos ω r D1k T s − 1 ⎡ + ⎢ I Lfk + ⎜⎜ DT s − I Lfk ⎟⎟ ω r sin ω r D1k T ⎢ s ⎣ ⎝ Lr ⎠
where t − t D = k 1 k 0 T s D1k = and
V ink
D V Crk
]}
R L=30 Ω R L=24Ω R L=20 Ω R L=10 Ω
( )
Duty ratio D
Fig. 5 The conversion ratio M(D) versus duty ratio D with different loads.
Since vin(t)=V m sinωint, the output voltage V ok in the k th switching period can be obtained as V ok = M ( D )V ink = M ( D )V m sin ω in kT s
+⎜
• cos ω r D1k T s
R L=40 Ω
•[ u (t − t k ) − u ( t − t ( k +1) )]
(14)
We assume that there are the number of n discrete V on in one period of the desired vo(t). Thus, the complete output voltage can be expressed as n
(7)
vo =
∑V
ok
=
M ( D )V m sin ω in kT s • [u(t − t k ) − u(t − t ( k +1) ]
k =1
(8) (9)
(15) In reality, if f s>> f in and n is so large, we can approximately obtain (16) vo (t ) ≅ M ( D )V m sin(ω in t ) (16) is truly a sinusoidal waveform of the desired output voltage vo(t).
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PEDS2009
IV. DESIGN CONSIDERATIONS AND REALIZATION An example of a single-phase soft-switching ac chopper is designed and realized. The design procedure is described as follows: Step 1 —Input and output data specification. The
input voltage vin(t)=V in,maxsinωint= 155sin(2π×60)t;
The
output voltage vo(t)=V o,maxsinωint=220sin(2π×60)t; The maximum output power P o,max=600W. The switching frequency f s=40kHz The resonant frequency f r=20kHz.
main power switche S m turns on at ZCS and the switch S 1 of cycloconverter turn on and of at ZVS and ZCS. The experimental results shown in Fig. 6, demonstrate that soft-switching function is achieved. The waveforms of resonant voltage vCr (t) and resonant current i Lr (t) are measured and shown in Fig. 7, which exactly meets the simulation result. The waveforms of input voltage and output voltage are simultaneously measured and shown in Fig. 8. The efficiency of the presented single-phase soft-switching ac chopper is also measured, in which the efficiency is over 90% when the output power is at maximum output power 600W. V. CONCLUSION
Step 2 —Decision of the duty cycle D.
A high performance single-phase step up/down ac With the parameters shown in Step 1, the duty cycle D can chopper by a simple and compact characteristic with be obtained from Fig. 5 under the condition of series-resonant conversion is presented. The main attribute P o,max=600W, V o,max=220V, R L = V o2, max / 2 P o , max = 40 , of the ac chopper topology is the fact that it generates an output ac voltage larger or lower than the input ac one, V o,max/V in,max=1.42. Thus, D=0.3. Substituting D=0.3 into depending on the instantaneous duty-cycle. This property (9) yield D1k =0.21. is not found in the classical ac chopper, which produces an Step 3 —Calculation of the resonant parameters. ac output instantaneous voltage always lower than the input ac voltage. The active switches are operated at a The average resonant current I Lrk,avg and the filter current fixed frequency with the pulse width modulation technique. I Lfk can be obtained from (12) as I Lfk,max=5.5A, A resonant cell is built in the power stage to build ZCS for I Lrk,avg,max=26.2A. According to the resonant frequency and turning on the power switches. Thus, lower switching from (7), the characteristic impedance Z o can be obtained losses, lower electromagnetic interference noises, and as in this example. Thus, Z o=1.45Ω higher power efficiency can be achieved. Because the C r = 1 /( Z oω r ) = 5.5μ F and Lr = 1 /(ω r 2C r ) = 11.5μ F . synthesized SSW very closes sinusoidal waveform, the Step 4 —Calculation of the output filter inductor and presented single-phase ac chopper can use a simple LC filter to filter the undesired harmonics and get the capacitor. sinusoidal voltage with low total harmonic distortion For minimizing unnecessary harmonics, the output filter (THD). Total harmonic distortion (THD) at maximum inductor L f =1mH and capacitor C f =4.7μF are selected. output rated power is within 6%. The power efficiency is over 90% when the output power is at maximum output In hardware realization, IGBT’s IRG4PC50UD and rated power can be obtained. The analysis and design of diode’s S30L60 are as power switches and power diodes, circuit has been verified by realization of practical circuit respectively. The commutation phenomenon of power in laboratory. switches are measured and shown in Fig. 6, in which the v DSm i DSm
i DS1
(a)
v DS1
(b) Fig. 6 Commutation waveforms of the main power switch.
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PEDS2009
vCr
vCr
i Lr
i Lr
(a)
(b) Fig. 7 The waveforms of resonant voltage vCr (t) and resonant current i Lr (t).
[2] vin
[3]
vo
[4]
[5]
[6]
[7] Fig. 8 Experimental waveforms of vo(t) and vin(t).
REFERENCES [1]
E. El-Bidweihy, K. Al-Badwaihy, M. S. Metwally, and M. El-Eedweihy, ”Power factor of ac controllers for inductive loads” IEEE Trans. Industrial Electron. Contr. Instrumentation, vol. 27, no. 3, pp. 210-212, 1980.
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B. W. Williams, “Asymmetrically modulated AC choppers,” IEEE Trans. Ind. Electron., vol. IE-29, pp. 181–185, Aug. 1982. S. A. Bhat and J. Vithayathil, “A simple multiple pulse width modulated AC chopper,” IEEE Trans. Ind. Electron., vol. IE-29, pp. 185–189, Aug. 1982. G. Roy, P. Poitevin, and G. Olivier, “A Comparative study of singlephase modulated AC choppers,” IEEE Trans. Ind. Applicat., vol. IA-20, pp. 1498–1506, Nov./Dec. 1984. G. H. Choe, A. K. Wallace, and M. H. Park, “An improved PWM technique for AC choppers,” IEEE Trans. Power Electron., vol. 4, pp. 496–505, Oct. 1989. D. H. Jang and G. H. Choe, “Improvement of Input Power Factor in AC Choppers Using Asymmetrical PWM Technique,” IEEE Trans. Ind. Electron., vol. 42, no. 2, pp. 179–185, April 1995. N. A. Ahmed, K. Amei, and M. Sakui, ,” A New Configuration of Single-Phase Symmetrical PWM AC Chopper Voltage Controller,” IEEE Trans. Ind. Electron., vol. 46, no. 5, pp. 942-951, Oct. 1999.
