Research on AC Chopper Power Module with Module ... - IEEE Xplore
Research on AC Chopper Power Module with Module Parallel Control Zhang Jie, Zou Yunping, Yu Weifu, Lin Lei, Li fen Huazhong University of Science and Technology, Wuhan 430074, Hubei Province, China Abstract-Based on the single-phase AC chopper circuit, a novel AC chopper topology with the corresponding PWM method is proposed. To improve high voltage performance, dualloop control including both mean voltage and instantaneous voltage is used in this paper, with duty-cycle feed-forward. At last, parallel operation control method is used to realize the current sharing. The experimental results verify the correctness and feasibility of the proposed topology and control scheme.
I.
components switching on for short circuit and also switching off for open circuit.
INTRODUCTION
Recently, phase-controlled ac voltage regulation circuit has been replaced by ac chopper circuit, because of high THD of output voltage and input-side current. Now, modern sine dimmer must have many advanced features as below: 1) Low cost and simple topology, such as AC/AC chopper circuit; 2) Common zero-line design; 3) Good load adaptability and perfect waveform and performance; 4) High power factor and low current THD at input side; 5) Parallel module design to realize expandable capacity. Based on the traditional ac-ac converter, this paper proposes a novel ac-ac chopper topology and independent PWM method without current detection, which reduces the control difficulty and system cost and overcome the out-of-control problem without current detection. This paper also uses the interleaving and parallel techniques to realize the currentsharing of ac-ac chopper dimmer modules. A brief review of ac-ac chopper techniques is presented in Section II. The operation of the novel ac-ac converter is analyzed theoretically in Section III. Section IV presents the characteristics and design of ac-ac converter module, the PWM realization and control method. Experimental results obtained from 2kW ac-ac converter. The last Section summarizes the conclusions. II. SYSTEM DESCRIPTION A. Figures and Tables The topology of this converter is illustrated in Fig.1: S1 is the main switch and the S2 is the fly-wheeling switch, both of which are the bidirectional components, as shown desperately in Fig 2. The operation of ac-ac chopper forbids both
978-1-4244-1874-9/08/$25.00 ©2008 IEEE
Fig.1 Basic single-phase ac chopping circuit
（a） (b) Fig.2 Bidirectional switching component
Rcs
C2
Fig.3 Single-phase ac chopping basic circuit
The operation principle is illustrated as below: the main switch modulates only according to the ratio of input and output voltage, and the fly-wheeling switches choose to operate in the complementary or independent PWM, which is shown in Fig.4. The operating stages are described as follows: Stage a: when the main switching component VT1 switches on, output voltage uA is equal to input voltage and input chopper current iN is equal to the output inductor current. Stage b: When the main switching component switches off, input chopper current iN is equal to zero. As shown in Fig.4, if input voltage is on positive half of sine wave, T2A operates in the complementary PWM mode and T2B continues on-conduction. At this time, because of the continuality of inductor current, the fly-wheeling switching component T2B realize zero-voltage-switching (ZVS) on and output voltage VAO is equal to zero. Stage c: When the main switching component switches off, the input voltage and output conductor current is
1324
in the relationship of inverse direction, because T2A work in the complementary PWM mode with T1 and T2B always conducts on, fly-wheeling switching component really works on the complementary PWM mode of the main switch. When T2A and T1 both switch off, because of the continuality of the zero-cross inductor current, the deadband time would result in high voltage spike.
Fig.4 Principles and operating waveform
Δu = R2
D2 D1
uN
iL Δt C AO
(1)
G(S ) =
C2
Lk Dk T1A
Rk
⎛L ⎞ R s 2 ⋅ L f ⋅ C f + s ⋅ ⎜ f + Rs ⋅ C f ⎟ + 1 + s R RL ⎝ L ⎠
, and the resonant frequency is
D4
L1
r
Ck ug1A
However, during turn on, the discharging current of parallel capacitor may be very big to damage the main switch. The resonant buffering inductor is used to limit the current, as shown in Fig.5. This section propose a simple PWM synthesizing method that only needs detecting the direction of input voltage, without inductor current detections. Because that the frequency and phase of input voltage are as same as those of output voltage, it is available that we can predicts the frequency and phase of input voltage through only detecting output voltage, in the case that the voltage drop and phase shift on the output inductor is very little and can neglect. When the system starts up, the output voltage is so small that can’t predict the phase of output voltage accurately. Base this reason, we startup the system using complementary PWM control when the output voltage is very little. This paper proposes the synthesis method without detecting input voltage, which inserts a MOD signal to change the system working status, as shown in Fig. 6. Because of the little current for starting up, the according voltage spike is very little, on the condition of little zero-cross voltage, then the voltage stresses of the switching components are limited, that wouldn’t damage the safety of the system. With the increase of output voltage, the system can predict the phase of output voltage so accurately that the control system can compose the independent PWM to chop the ac-ac converter. On the condition of low load or zero load, the undamped or underdamped system can easily oscillate under external perturbs. The transfer function of LC filter system, shown as Fig.6, Gvd is (2) 1
fr =
D3 T2A
D2B
C3 C1
ug2 A
R3 D2 A T2B
R4
Z0
1
(3)
2π L f C f
u0
C4
ug2B
Fig.5 Single-phase AC chopping revised circuit
III. MODULE DESIGN & CONTROL Fig.5 shows the real topology of main circuit. A flywheeling capacitor C3 paralleling fly-wheeling switching component can reduce the voltage spike during the deadband time. During main switching component turns on or off, there is the voltage spike due to the diode reverse recovery current. The high-frequency capacitor is added to parallel two ports of bidirectional switch as so to be charged or discharged by the diode reverse recovery current. Otherwise, the voltage spike by fly-wheeling effect commonly appears at zero-cross, and then the damage to system is limited.
From Fig.7, RLÆ∞,G(fr)Æ∞. In order to improve the stability of the system under zero-load or low-load conditions, adjustable damped filter is used to change the resonant frequency and reduce the resonant peak value.After improving, the transfer function is shown as below: (4) 1 (s +
G(S ) =
RpC p
)
⎡ ⎛ 1 ⎞ R ⎞ ⎛ 1 1 1 1 ⎤ L f C f ⎢s3 + s2 ⎜ + + + s + s 1+ + ⎜ RL C f Rp C p Rp C f L f ⎟⎟ ⎜⎜ RL Rp C f C p ⎟⎟ Rp C p ⎥⎥ ⎝ ⎠ ⎝ ⎠ ⎣⎢ ⎦
We can judge from Routh theorem, that because Rp≠0, the stable conditions can be satisfied. Both bode diagrams can illustrate that the method can effectively reduce the resonant peak value, and then increases the stability of system on the low load condition. The whole dual-loop control system in Fig.8 includes meanvalue and instantaneous-value voltage loops that ensure the appropriate voltage stability, waveform quality, which also
1325
uses the duty-cycle feed-forward to improve the dynamics of the whole system. The mean-value voltage loop can achieve low bandwidth and high low-frequency gain, which guarantees the high steady accuracy. And the instantaneousvalue voltage loop has the high bandwidth, which can get high dynamics to improve the waveform quality of output voltage.
between the modules, and regulate the voltage references basing droop method.
MOD
Fig.8 Current sharing system diagram PWM
PWM
V. EXPERIMENTAL RESULTS
Fig.6 PWM synthesized circuit
IV. PARALLEL ANALYSIS The power modules can be parallel connected to increase the output power level. The diagram of AC/AC module paralleling is shown in Fig.7, which are current sharing inside and controlled by one digital single controller (DSP) with a common input EMI filter. L1
S1
L2
TABLE I
Experiment parameters
L3
C2
S2
In order to demonstrate the theoretical assumptions above, experimental tests were performed as the parameters in Table I are employed. The switches used for main switching are IGBTs IXYS IXDN 75N120 and the diodes used are DIODEs DSEI60-12A. The control system has been implemented using DSP TMS320LF2407A.
RL
L5
L4
S4
2kW
Output voltage
C1
S3
220V
Input voltage
C3
Damped resistor Damped filter capacitor
10Ω 10uF
Output voltage
220V
Parallel inducror
200uH
Filter inductor
270uH
Surge protect capacitor
10nF
Filter capacitor
20uF
Surge protect resistor
10Ω
Fig. 7 Parallel system diagram
To simplify, we analyze the paralleling theorem, as shown in Fig.8, and get that,
U 1 (cos ϕ1 + j sin ϕ1 ) − U 0 Zs U (cos ϕ1 + j sin ϕ1 ) − U 0 ] S1 = U 0 [ 1 Zs I 1* =
（5） （6） (a)
Thinking about that ac-ac chopper can change hardly little frequency and phase, we suppose: ϕ1 = ϕ 2 = ϕ , then
(b) Fig.9 Experiment results
ΔI = ( I 1 − I 2 ) =
(U 1 − U 2 ) ⋅ (cos ϕ + j sin ϕ ) Zs
（7）
ΔU ⋅ (cos ϕ + j sin ϕ ) Zs Because that ωLs
I.
components switching on for short circuit and also switching off for open circuit.
INTRODUCTION
Recently, phase-controlled ac voltage regulation circuit has been replaced by ac chopper circuit, because of high THD of output voltage and input-side current. Now, modern sine dimmer must have many advanced features as below: 1) Low cost and simple topology, such as AC/AC chopper circuit; 2) Common zero-line design; 3) Good load adaptability and perfect waveform and performance; 4) High power factor and low current THD at input side; 5) Parallel module design to realize expandable capacity. Based on the traditional ac-ac converter, this paper proposes a novel ac-ac chopper topology and independent PWM method without current detection, which reduces the control difficulty and system cost and overcome the out-of-control problem without current detection. This paper also uses the interleaving and parallel techniques to realize the currentsharing of ac-ac chopper dimmer modules. A brief review of ac-ac chopper techniques is presented in Section II. The operation of the novel ac-ac converter is analyzed theoretically in Section III. Section IV presents the characteristics and design of ac-ac converter module, the PWM realization and control method. Experimental results obtained from 2kW ac-ac converter. The last Section summarizes the conclusions. II. SYSTEM DESCRIPTION A. Figures and Tables The topology of this converter is illustrated in Fig.1: S1 is the main switch and the S2 is the fly-wheeling switch, both of which are the bidirectional components, as shown desperately in Fig 2. The operation of ac-ac chopper forbids both
978-1-4244-1874-9/08/$25.00 ©2008 IEEE
Fig.1 Basic single-phase ac chopping circuit
（a） (b) Fig.2 Bidirectional switching component
Rcs
C2
Fig.3 Single-phase ac chopping basic circuit
The operation principle is illustrated as below: the main switch modulates only according to the ratio of input and output voltage, and the fly-wheeling switches choose to operate in the complementary or independent PWM, which is shown in Fig.4. The operating stages are described as follows: Stage a: when the main switching component VT1 switches on, output voltage uA is equal to input voltage and input chopper current iN is equal to the output inductor current. Stage b: When the main switching component switches off, input chopper current iN is equal to zero. As shown in Fig.4, if input voltage is on positive half of sine wave, T2A operates in the complementary PWM mode and T2B continues on-conduction. At this time, because of the continuality of inductor current, the fly-wheeling switching component T2B realize zero-voltage-switching (ZVS) on and output voltage VAO is equal to zero. Stage c: When the main switching component switches off, the input voltage and output conductor current is
1324
in the relationship of inverse direction, because T2A work in the complementary PWM mode with T1 and T2B always conducts on, fly-wheeling switching component really works on the complementary PWM mode of the main switch. When T2A and T1 both switch off, because of the continuality of the zero-cross inductor current, the deadband time would result in high voltage spike.
Fig.4 Principles and operating waveform
Δu = R2
D2 D1
uN
iL Δt C AO
(1)
G(S ) =
C2
Lk Dk T1A
Rk
⎛L ⎞ R s 2 ⋅ L f ⋅ C f + s ⋅ ⎜ f + Rs ⋅ C f ⎟ + 1 + s R RL ⎝ L ⎠
, and the resonant frequency is
D4
L1
r
Ck ug1A
However, during turn on, the discharging current of parallel capacitor may be very big to damage the main switch. The resonant buffering inductor is used to limit the current, as shown in Fig.5. This section propose a simple PWM synthesizing method that only needs detecting the direction of input voltage, without inductor current detections. Because that the frequency and phase of input voltage are as same as those of output voltage, it is available that we can predicts the frequency and phase of input voltage through only detecting output voltage, in the case that the voltage drop and phase shift on the output inductor is very little and can neglect. When the system starts up, the output voltage is so small that can’t predict the phase of output voltage accurately. Base this reason, we startup the system using complementary PWM control when the output voltage is very little. This paper proposes the synthesis method without detecting input voltage, which inserts a MOD signal to change the system working status, as shown in Fig. 6. Because of the little current for starting up, the according voltage spike is very little, on the condition of little zero-cross voltage, then the voltage stresses of the switching components are limited, that wouldn’t damage the safety of the system. With the increase of output voltage, the system can predict the phase of output voltage so accurately that the control system can compose the independent PWM to chop the ac-ac converter. On the condition of low load or zero load, the undamped or underdamped system can easily oscillate under external perturbs. The transfer function of LC filter system, shown as Fig.6, Gvd is (2) 1
fr =
D3 T2A
D2B
C3 C1
ug2 A
R3 D2 A T2B
R4
Z0
1
(3)
2π L f C f
u0
C4
ug2B
Fig.5 Single-phase AC chopping revised circuit
III. MODULE DESIGN & CONTROL Fig.5 shows the real topology of main circuit. A flywheeling capacitor C3 paralleling fly-wheeling switching component can reduce the voltage spike during the deadband time. During main switching component turns on or off, there is the voltage spike due to the diode reverse recovery current. The high-frequency capacitor is added to parallel two ports of bidirectional switch as so to be charged or discharged by the diode reverse recovery current. Otherwise, the voltage spike by fly-wheeling effect commonly appears at zero-cross, and then the damage to system is limited.
From Fig.7, RLÆ∞,G(fr)Æ∞. In order to improve the stability of the system under zero-load or low-load conditions, adjustable damped filter is used to change the resonant frequency and reduce the resonant peak value.After improving, the transfer function is shown as below: (4) 1 (s +
G(S ) =
RpC p
)
⎡ ⎛ 1 ⎞ R ⎞ ⎛ 1 1 1 1 ⎤ L f C f ⎢s3 + s2 ⎜ + + + s + s 1+ + ⎜ RL C f Rp C p Rp C f L f ⎟⎟ ⎜⎜ RL Rp C f C p ⎟⎟ Rp C p ⎥⎥ ⎝ ⎠ ⎝ ⎠ ⎣⎢ ⎦
We can judge from Routh theorem, that because Rp≠0, the stable conditions can be satisfied. Both bode diagrams can illustrate that the method can effectively reduce the resonant peak value, and then increases the stability of system on the low load condition. The whole dual-loop control system in Fig.8 includes meanvalue and instantaneous-value voltage loops that ensure the appropriate voltage stability, waveform quality, which also
1325
uses the duty-cycle feed-forward to improve the dynamics of the whole system. The mean-value voltage loop can achieve low bandwidth and high low-frequency gain, which guarantees the high steady accuracy. And the instantaneousvalue voltage loop has the high bandwidth, which can get high dynamics to improve the waveform quality of output voltage.
between the modules, and regulate the voltage references basing droop method.
MOD
Fig.8 Current sharing system diagram PWM
PWM
V. EXPERIMENTAL RESULTS
Fig.6 PWM synthesized circuit
IV. PARALLEL ANALYSIS The power modules can be parallel connected to increase the output power level. The diagram of AC/AC module paralleling is shown in Fig.7, which are current sharing inside and controlled by one digital single controller (DSP) with a common input EMI filter. L1
S1
L2
TABLE I
Experiment parameters
L3
C2
S2
In order to demonstrate the theoretical assumptions above, experimental tests were performed as the parameters in Table I are employed. The switches used for main switching are IGBTs IXYS IXDN 75N120 and the diodes used are DIODEs DSEI60-12A. The control system has been implemented using DSP TMS320LF2407A.
RL
L5
L4
S4
2kW
Output voltage
C1
S3
220V
Input voltage
C3
Damped resistor Damped filter capacitor
10Ω 10uF
Output voltage
220V
Parallel inducror
200uH
Filter inductor
270uH
Surge protect capacitor
10nF
Filter capacitor
20uF
Surge protect resistor
10Ω
Fig. 7 Parallel system diagram
To simplify, we analyze the paralleling theorem, as shown in Fig.8, and get that,
U 1 (cos ϕ1 + j sin ϕ1 ) − U 0 Zs U (cos ϕ1 + j sin ϕ1 ) − U 0 ] S1 = U 0 [ 1 Zs I 1* =
（5） （6） (a)
Thinking about that ac-ac chopper can change hardly little frequency and phase, we suppose: ϕ1 = ϕ 2 = ϕ , then
(b) Fig.9 Experiment results
ΔI = ( I 1 − I 2 ) =
(U 1 − U 2 ) ⋅ (cos ϕ + j sin ϕ ) Zs
（7）
ΔU ⋅ (cos ϕ + j sin ϕ ) Zs Because that ωLs
