CHAPTER 2. A SURVEY of PREVIOUS SINGLE-STAGE PFC CIRCUITS
2.1 The Familiar Single-Stage Single-Switch PFC Rectifiers
Many papers have been presented about single-stage PFC rectifiers with boost-type ICS in the past ten years. The survey will focus on the topologies of the single-stage PFC rectifiers.
Each of them contains a boost ICS and a dc-dc converter in a cascade type. Through the inspection of the locations of the storage capacitors along the energy flow paths in these topologies, two categories were identified [28]. In the first category, the capacitor is in series with transformer. In the other one, the capacitor is in parallel with transformer.
In the topology type of series connection, the bulk capacitor stores and transports energy in series between boost ICS and dc-dc converter. Fig. 2.2 shows the common structure. In this type, [28] proposes BIFRED (Boost Integrated with Flyback Rectifier /Energy Storage/Dc-dc converter) and BIBRED (Boost Integrated with Buck Rectifier /Energy Storage/Dc-dc converter)designs. Both the BIFRED and BIBRED consist of a boost-type ICS cascaded by a flyback converter or a buck converter correspondingly, the two circuits are shown in Fig. 2.3.
The ICS in such a circuit is simply implemented by a boost inductor, a diode and switch. The boost cell operates in discontinuous conduction mode (DCM) and the dc/dc cell operates in either DCM or continuous conduction mode (CCM). If the dc/dc converter operates in CCM,
Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
series path
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
Capacitor in BIFRED,
BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS
Capacitor in parallel path Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single - stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
series path
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
Capacitor in BIFRED,
BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS
Capacitor in parallel path Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single - stage PFC with
boost - type ICS.
Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
series path
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
Capacitor in BIFRED,
BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS
Capacitor in parallel path Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single - stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
series path
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
Capacitor in BIFRED,
BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS
Capacitor in parallel path Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single - stage PFC with
boost - type ICS.
Fig. 2.1 Tree of single -stage PFC with boost - type ICS
Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
Capacitor in BIFRED,
BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS
Capacitor in parallel path Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single -stage PFC with
boost - type ICS Single -stage PFC with boost -type ICS
BIFRED, BIBRED
A new family
Magnetic feedback
Magnetic switch Single -stage PFC
with boost -type ICS
BIFRED, BIBRED
The proposed family
Magnetic feedback
Magnetic switch Fig. 2.1 Tree of single - stage PFC with
boost - type ICS.
the converter suffers from high voltage stress in the bulk capacitor. Besides, the circuit has a bulk inductor in the boost cell circuit.
Filters
Stage LOAD
Vo
Stage LOAD
Vo
Power Stage Cb
Power
Stage LOAD
Vo
Power Stage Power
Stage LOAD
Vo
Power Stage Cb
ICS dc/dc converter
Filters
Stage LOAD
Vo
Stage LOAD
Vo
Power Stage Cb
Power
Stage LOAD
Vo
Power Stage Power
Stage LOAD
Vo
Power Stage Cb
ICS dc/dc converter
Fig. 2.2 Structure for capacitor in series path.
Vac
ICS dc/dc converter
Vac
ICS dc/dc converter
(a) dc/dc converter ICS dc/dc converter ICS
(b)
Fig. 2.3 Single-stage PFC characterized by an energy storage capacitor in the series path of the energy flow, (a) BIBRED (b) BIFRED presented in [3].
For the other type, using parallel connection, the bulk capacitance is not in the series path with respect to the transformer in dc-dc converter but in a parallel fashion instead. The corresponding circuit topology has three-terminal structure as shown in Fig. 2.4. The practical circuit shown in Fig. 2.5 (a) is presented by [7]. The boost cell operates in DCM and naturally forms input current shaper and the power factor can achieve 98% when a suitable ratio for Lin/LN1 is selected. Besides, the dc/dc converter can operate in either DCM or CCM. However, if the dc/dc converter operates in CCM, the voltage across bulk capacitor will vary with the load current. Furthermore, it suffers from high voltage stress under high-line and light-load condition.
Filters and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
Power
Stage LOAD
Vo
Power Stage Cb
ICS dc/dc converter
Filters and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
Power
Stage LOAD
Vo
Power Stage Power
Stage LOAD
Vo
Power Stage Cb
ICS dc/dc converter
Fig. 2.4 The three-terminal structure for arranging the capacitor in parallel path.
For the circuit shown in Fig. 2.5(a), Fig. 2.5(b) shows that the voltage across bulk capacitor, VCB, will be over 450V/dc when the input voltage approaches 220V/ac and the ratio of Lin/LN1 is lower than 0.6.
Vac Vac
Lin D1
CB
NP NS D3
S1 D2
Lf
Cf
VO
RL ICS
dc/dc converter
LN1
Vac Vac Vac Vac
Lin D1
CB
NP NS D3
S1 D2
Lf
Cf
VO
RL ICS
dc/dc converter
LN1
(a)
600
500
400
300 180 190 200 210 220 230 240 250 260
Vac(rms) [V]
VCB[V]
Lin/LN1=0.45
0.550.65
0.75 600
500
400
300 180 190 200 210 220 230 240 250 260
Vac(rms) [V]
VCB[V]
Lin/LN1=0.45
0.550.65
0.75
(b)
Fig. 2.5 The ICS implemented by three-terminal structure [7], (a) circuit, (b) VCB and Vac.
2.2 Circuit Technologies for Reducing the Voltage Stress of Bulk Capacitor Although the above topologies [7] can achieve high power factor up to 98%, it needs to face the problem of high voltage across bulk capacitor. The high dc-bus voltage presents high stress in bulk capacitor and switching components. A compromising solution was presented in [8], [9], and [29]. A topology using a fashion of negative magnetic feedback is implemented by adding an extra-winding in power transformer, as shown in Figs. 2.6 and 2.7. The winding connecting as a negative magnetic feedback fashion provides another energy flow path. While the bulk capacitance charging the transformer, the ICS also charges the transformer too.
Consequently, the voltage of bulk capacitance required to provide the constant output voltage can be reduced. The small trade off is that this solution has smaller power factor. However, it can conform to standard IEC61000-3-2 class D, and the solution can keep the dc bus voltage below 450V.
In [30]-[32], two extra windings in power transformer are added to form magnetic feedback loops and each design consists of a boost cell and a dc-dc converter to operate in CCM as shown in Fig. 2.8. In [33]-[37], a magnetic switch concept is introduced by adding another extra winding in power transformer to further drive boost cell in CCM. The operation in CCM is good for the dc-bus voltage being less affected by the load current The circuits are shown in Figs. 2.9 and 2.10. While the boost cell and dc/dc converter operate in CCM, two gain benefits are presented: lower conduction power loss in switching components and lower switching ripple in input and output sides.
Filters and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
LOAD
Vo Cb
Power Stage Power Stage Filters
and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
LOAD
Vo Cb
Power Stage Power Stage Filters
and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
LOAD
Vo Cb
Power Stage Power Stage Power Stage Power Stage Filters
and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
LOAD
Vo Cb
Power Stage Power Stage Filters
and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
LOAD
Vo Cb
Power Stage Power Stage Power Stage Power Stage Filters
and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
LOAD
Vo Cb
Power Stage Power Stage Power Stage Power Stage Filters
and Rectifier
Lb
Vac
Filters and Rectifier
Lb
Vac
LOAD
Vo Cb
Power Stage Power Stage Power Stage Power Stage
Fig. 2.6 The three-terminal structure for adding an extra winding in power transformer.
Vac Vac
Lin D1
CB
NP NS D3
S1 N1
D2
Vac Vac Vac Vac
Lin D1
CB
NP NS D3
S1 N1
D2
Fig. 2.7 Circuit with an extra winding in transformer [3,10,11].
Vac Vac
Lin D1
CB
NP NS D3
S1 N1
D2 N2
Vac Vac Vac Vac
Lin D1
CB
NP NS D3
S1 N1
D2 N2
Fig. 2.8 Circuit with two extra windings in transformer [3].
Vac Vac
Lin
CB
NP NS D3
S1 N1
Vac Vac Vac Vac
Lin
CB
NP NS D3
S1 N1
Fig. 2.9 Circuit with magnetic switch winding in transformer [3].
Vac
Vac
Lin
CB
NP NS D3
S1 N1
D2 D1
Vac
Vac
Vac
Vac
Lin
CB
NP NS D3
S1 N1
D2 D1
Fig. 2.10 Circuit with magnetic switch winding in transformer [3].
2.3 The Proposed New Design for Reducing the Voltage Stress of Bulk Capacitor
The converters mentioned in last section are related single stage PFC rectifiers with ICS function. They successfully reduce the voltage stress of bulk capacitor by employing one or more windings connected in a fashion of negative magnetic feedback or magnetic switch.
Although the negative feedback magnetic winding is added to power transformer, they still need to use bulk inductors Lb (or Lin) in boost cell to achieve the ICS function.
The single-stage converter designed with three-terminal parallel structure as shown in Fig. 2.5(a) is a pretty flexible design. Many improved ICS designs are based on this structure.
In this structure, two current flow paths are implemented through diodes D1 and D2
respectively. The new design proposed in this dissertation is also based on the circuit of Fig.
2.5(a) with a negative magnetic feedback design. The design concept is shown in Fig. 2.11. In the proposed topology, the bulk inductor of boost cell, Lin shown in Fig. 2.11, is replaced by adding an extra winding N1. The extra winding is implemented in the power transformer and connected in a negative magnetic feedback structure so that the goal for reducing the dc bus voltage can be reached. To complete the ICS function a small inductor L1 sketched by a dotted line in Fig. 2.11 is added. Since the inductance of L1 is smaller than one-tenths of LN1 in the proposed design, it can be implemented by the leakage inductance of the winding N1 in low power application. Therefore, the total volume of magnetic material can be reduced via the new design.
Vac Vac
Lin
D1
CB
NP NS D3
S1 D2
Lf Cf
VO RL LNp
L1 N1
Vac Vac Vac Vac
Lin
D1
CB
NP NS D3
S1 D2
Lf Cf
VO RL LNp
L1 N1
Fig. 2.11 The schematic to obtain the proposed design.
In the new design, the winding number N1 is greater than that in the circuit like Fig. 2.7 so that the power input loop is in reverse bias within the switch on duration instead of using the switch on operation in the those converters mentioned above. By this design Lin can be removed. Winding N1 operates as a magnetic switch in the switch off duration and provides a power-in loop. However, a small L1 is needed to obtain controllable and satisfying ICS function and also guarantee the reduction of the voltage of the bulk capacitance. Another function of inductor L1 is that L1 can provide soft-switching-on for diode D1 and soft-switching-off for diode D2.
The alternative sketch of the proposed circuit is shown in Fig. 2.12. Although it looks like the ICS shown in Fig. 2.7, the location of winding N1 and the operation theorem are different. In Fig. 2.7 the bulk inductance Lin is magnetized in the switch on duration and demagnetized in the switched off duration. In the proposed design, the timing is converse. In Fig. 2.7 the ratio N1/NP has to be smaller than that in the proposed one in order to achieve a better power factor. In the proposed design, a larger ratio N1/NP is used to achieve higher power factor. Therefore, a better voltage reduction of VCB can be achieved in the proposed circuit. Furthermore, the inductor Lin of Fig. 2.7 can not be substituted by leakage inductor of winding N1 in low power application because the inductor Lin and winding N1 are not in series.
The design considerations of the proposed circuit are trying to conform to the four main demands indicated in page 1 of chapter 1. The additional winding N1,which can functionally
RL N1 N2N3
Vac
C1
C3
C2
L1 Dr
D2 D1
S1
D3
+ VC1
-+ VC2
-+ VN1
-iN1
iN3 iN2
iS1 iD1
iC2
VS1 -+
Tr
Vo +
-Lf
Cf
n1: n2: n3
RL N1 N2N3
Vac
C1
C3
C2
L1 Dr
D2 D1
S1
D3
+ VC1
-+ VC2
-+ VN1
-iN1
iN3 iN2
iS1 iD1
iC2
VS1 -+
Tr
Vo +
-Lf
Cf
n1: n2: n3
Fig. 2.12 Proposed simple flyback AC/DC converter
replace the bulk inductor, has successfully simplified the circuit of Fig. 2.5 into Fig. 2.12.
The input current shaper consists of winding N1, inductor L1, diodes D1, D2 and switch S1
in Fig. 2.12. The average current of iN1 will automatically track the rectified input voltage VC1
at the time period when the voltage, VC1+Vo(n1/n3), is greater than VC2. The automatically shaping feature of the line current can save a current shaping controller. In the proposed circuit needs only one controller to regulate the output voltage of dc/dc cell as that in the conventional dc/dc converter. Therefore, the feedback control bandwidth is designed to cover two times of the line frequency to minimize the line frequency output ripple and simultaneously enhance the output dynamic response.
Through the charging operation for capacitance C2, the voltage of VC2 will be smaller than the voltage, Vm+Vo(n1/n3), when dc/dc cell operates in CCM. Actually while the line
Through the charging operation for capacitance C2, the voltage of VC2 will be smaller than the voltage, Vm+Vo(n1/n3), when dc/dc cell operates in CCM. Actually while the line