D
Journal of Energy and Power Engineering 6 (2012) 283-286
DAVID
PUBLISHING
Single-Phase Full Bridge PWM Rectifier with Load
Current Feedforward
Kazutaka Itako1 and Takeaki Mori2
1. Department of Electronic and Electrical Engineering, Kanagawa Institute of Technology, Kanagawa 243-0292, Japan
2. Department of Home Electronics, Kanagawa Institute of Technology, Kanagawa 243-0292, Japan
Received: January 06, 2011 / Accepted: May 31, 2011 / Published: February 29, 2012.
Abstract: Many conventional switching power supplies in computers and low power motor drive systems operate by rectifying the
input AC line voltage and filtering it with large electrolytic capacitors. This results in undesirable side effects such as the generation
of distorted input current waveform. The input power factor is also poor. Further, the input current has the shape of narrow pulses,
which in turn increases its value. The reduction in input current harmonics and improved power factor operation of motor drive
systems and switching power supplies are important from the energy saving point of view and also to satisfy the harmonic standards.
This paper proposes a full bridge PWM rectifier with load current feedforward. The proposed approach has some advantages,
including a quick response for the load fluctuation, the reduction of the number of sensors and simplified control, as compared with
the conventional methods. From simulated results, it is clarified that the proposed control method is effective and useful.
Key words: Power factor correction, power quality, converter control, DC power supplies, grid-connecting inverter.
1. Introduction
PWM (pulse width modulation) techniques are
widely used on switching power converters to
improve the input current waveform and the input
power factor. And, new main circuit configurations
and new control methods have been investigated [1-6]
to obtain the high performance. These methods are
suitable for power factor improvement and harmonic
currents reduction. Despite the good adaptiveness of
the most popular control method for power factor
correction and harmonic currents reduction, there are
following problems associated with this approach:
(1) The response for the load power fluctuation is
marginally slow due to detecting the load power
fluctuation from the deviation of the capacitor voltage,

even if the PI regulators are optimized;
(2) By using a load current feedforward, a rapid
response for the load power fluctuation may be
Corresponding author: Kazutaka Itako, associate professor,
research fields: power factor correction, PV generation system
and fuel cell system. E-mail: itako@ele.kanagawa-it.ac.jp.
obtained. However, it requires at least four sensors for
sensing the input voltage, input current, DC output
voltage and load current.
In response to these concerns, this paper proposes
an alternative power factor correction and harmonic
currents reduction control system for a full bridge
PWM rectifier [7]. The characteristics of the proposed
approach are clarified by the simulations. This control
system has the feature as shown in the following:
(1) The response for the load power fluctuation is
quick due to detecting directly the load power
fluctuation from the load current;
(2) This control system will bring more simplified
system configuration due to using only two sensors
for sensing the input voltage and load current,
decreasing the cost.
2. Proposed Control System
2.1 Operating Principle
Fig. 1 shows the circuit configuration of a PWM
rectifier with bidirectional power-flow capability. This
284
Single-Phase Full Bridge PWM Rectifier with Load Current Feedforward
converter is identical to the four-quadrant inverter [8].
In this figure, e (f = 50 Hz) is the instantaneous value
of line voltage, ip is the instantaneous value of input
current and, v is the input voltage of the rectifier. The
vD which is smoothed with the large capacitance C is
the DC voltage including a permitted ripple. The L is
an additional inductance to reduce the ripple in input
current ip at the finite switching frequency fC.
In Fig. 1, when indicating the switching state of
each leg by a binary variable 1 or -1, depending on the
upper or lower transistor being conductive, the
switching states of rectifier can be described as (1, 1),
(1, -1), (-1, 1) and (-1, -1).
The pulse generation process of the switching
methods is concretely illustrated in Fig. 2. The
transistors are controlled based on the comparison of
the carrier wave and the modulating wave. This is the
method which can reduce the switching frequency fC
of the transistors. That is, although the transistors are
switched at fC, v is switched twice as much (2fC).
In Fig. 1, one out of these two sensors is a DC
current sensor, another one is an AC voltage sensor.
Slight change in the line frequency and amplitude
must be accounted for by sensing the input voltage.
The accurate values of the line frequency and
amplitude are used in order to obtain the suitable
control angle
 and the modulation index MI of the
modulating wave vref is shown in Fig. 2. Assuming e
to be sinusoidal, the fundamental frequency
components of v and ip in Fig. 1 can be expressed as
phasors V and Ip, respectively. Because of a fairly
large capacitance C, the voltage vD can be assumed to
be DC, that is, vD = VD. The vD chopped by the PWM
pattern as shown in Fig. 2 shapes the voltage v.
In Fig. 2, the modulating wave vref normalized with
the maximum value of carrier wave is
vref  MI sin(t   )
(1)
with MI being the modulation index (0  MI 
1.0). Therefore, instantaneous value v1 of V is
proportional to vref and can be expressed in the
following equation.
Fig. 1
Main control diagram of proposed system.
Fig. 2
Pulse generation process.
v1  VD MI sin(t   )
V MI
V  D
2
(2)
(3)
In Fig. 2, a phasor diagram for the unity power
factor is shown in Fig. 3. In this phasor diagram,
E
cos
LI P
  tan 1
E
V
(4)
(5)
Therefore, from Eqs. (3) and (4),
MI 
2E
VD cos
(6)
When the VD is controlled to arbitrary value VDref,
required MI can be obtained from following equation.
MI 
2E
VDref cos 
(7)
Assuming that the energy efficiency and input
power factor are 100%, Ip can be expressed in
following equation,
Single-Phase Full Bridge PWM Rectifier with Load Current Feedforward
285
Fig. 3 Phasor diagram.
IP 
VDref I L
(8)
E
Fig. 4
Lower limit of 1/K2 vs.
Substituting for Ip from Eq. (8) into Eqs. (5) and (7),
 and MI for iL can be expressed in the following
equations.
L
diP
 ev
dt
(13)
C
dv D
 i DN  i L
dt
(14)
and
 LVDref 
iL   tan 1 ( K1iL )[rad ] (9)
2
E


  f  (iL )  tan 1 
K2
MI  f MI (i L ) 
cos 
(10)
where, iL is the load current which is assumed to be an
ideal DC current source. v in Eq. (13) and iDN in Eq.
(14) can be expressed as the following equations.
where,
K1 
 L/Rin.
LVDref
E2
1
v  ( S1  S 2 )vD
2
2E
and K 2  V
Dref
(11)
Even if the E and  change, by renewing the values
of K1 and K2 in Eq. (11), unity power factor and
harmonic currents reduction will be realized. Because
MI must be less than or equal to 1.0 in order to realize
the unity power factor for the load variation, the
following condition derived from Eq. (10) must be
satisfied.
2
 L 
1
 
1  
K2
 Rin 
(12)
where, Rin = Ｅ/Ip. Fig. 4 shows the plot of the lower
limit of 1/K2 as a function of  L/Rin. By applying the
Rin in the maximum power to Eq. (12) and satisfying
the condition of this equation, unity power factor can
be realized in the required power range.
2.2 Circuit Equations
In Fig. 1, the circuit equations are expressed in the
following.
(15)
and
iDN 
1
( S1  S 2 )iP
2
(16)
3. Simulation Results
The circuit conditions: the effective value of the
line voltage = 100 V, VDref = 150 V, L = 10 mH, C =
500 F and fC = 10 kHz, where because an internal
impedance of the utility source is normally much
smaller than an additional reactance, only the
additional inductance is considered.
Figs. 5a and 5b show the simulated transient
characteristics of this control system when the load
power is changed from 75 W to 150 W and then from
150 W to 75 W, and the load power is changed from
75 W to -75 W and from -75 W to 75 W for step
formed, respectively. From these figures, it is clarified
that there is not the oscillatory behavior on vD
accompanied by the load change and the response of
the input current is very quick.
Single-Phase Full Bridge PWM Rectifier with Load Current Feedforward
286
(a) Generative mode
Fig. 5
(b) Generative mode and regenerative mode
Transient characteristics of this system on the step load change.
4. Conclusions
In this paper, the new control method of a full bridge
PWM rectifier for the harmonic currents reduction and
power factor correction is discussed. By using this
method, a quick response for the load fluctuation can
be obtained and the simplified circuit configuration
with half number of required sensors and reduction of
the cost may be realized.
From these results, it is clarified that proposed
control method is effective and useful.
[2]
[3]
[4]
[5]
Acknowledgments
This work was supported by “High-Tech Research
Center” Project for Private Universities: matching
fund subsidy from MEXT (Ministry of Education,
Culture, Sports, Science and Technology), 2007-2011.
[6]
[7]
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