A Novel Topology and PWM
Single-Phase Three-Level Rectifier
Krismadinata C. Student Member, J. Selvaraj Student Member and N.A. Rahim Senior Member
Centre of Power Electronics, Drives and Automation Control
University of Malaya Kuala Lumpur, Malaysia
krismadinata@um.edu.my
Abstract— This paper describes a novel topology and pulse width
modulation (PWM) multilevel single-phase rectifier. A singlephase rectifier based on the conventional two-level full-bridge
rectifier and one bidirectional switch is proposed. The novel
rectifier gives three levels voltage to the input rectifier. A novel
PWM switching algorithm with two references waveforms of the
same phase and amplitude but difference offset and a carrier
triangular waveform is simulated in PSIM and laboratory
prototype is designed to demonstrate the rectifier. The switching
algorithm is implemented in Digital Signal Processor (DSP)
TMS320F2812. Simulation and experimental results show that
both are in close agreement.
loss, lower electromagnetic interference and lower acoustic
noise. However, this scheme can easily be applied to medium
and low power applications.
Keywords: Pulse width modulation, Single-Phase three-level
rectifier, TMS320F2812
I.
INTRODUCTION
The AC-DC conversion is used increasingly in a wide
diversity of applications: power supply for microelectronics,
household-electric appliances, electronic ballast, battery
charging, DC-motor drives, power conversion, etc... [1].
Some of the most well known problems in AC/DC
converters are reducing the line harmonic currents designing
the effective filter system and fast transient response. In time
AC/DC converters have been dominated by uncontrolled
rectifiers or line-commutated phase-controlled rectifiers. Such
converters have the inherent drawback that their power factor
decreases when the firing angle increases, and the lower order
harmonics of line current are quite high [2],[3].
The single phase voltage sourced two-level PWM
rectifier system shown in Fig. 1 with four switches is becoming
a popular choice as a front end for high power railway traction
drives. A unipolar or bipolar PWM voltage waveform can be
generated on AC terminal of the rectifier. It can provide a
regulated output voltage with the potential of drawing unity
power factor low distortion current from the ac supply. Low
distortion and high power factor are important attributes to a
power supply system that is becoming increasingly polluted
with harmonics.
In recent years, research and development of multilevel
converters for high power applications have attracted more
attention due to the increased energy awareness in the global.
A multilevel scheme provides a number of advantages over the
conventional technology, especially for high power or medium
voltage applications [4–7]. The advantages of multilevel
converters over the two-level converters are improved voltage
waveform on the AC side, smaller filter size, lower switching
Fig. 1 The single phase two-level PWM rectifier
II. REVIEW TOPOLOGY THREE LEVEL
SINGLE-PHASE RECTIFIER
According to previous literatures [2]-[18], there are ten
topologies three-level single-phase rectifier.
Fig. 2 Two bidirectional switch mid point rectifier
A single-phase multilevel rectifier depicted in Fig.2 consists
of a single-phase diode bridge circuit as a main power circuit,
and two bi-directional switches (Sa; Sb) connected between the
each input terminal (A, B) and the neutral point (N) of the dcside capacitors (C1;C2). A filter inductor (Ls) is connected in
series with an ac voltage-source (vs) and the rectifier [8][9].
directional switches with the diode embedded unidirectional
switch namely four diodes and one switch [13]
Fig. 7 shows neutral point diode clamped rectifier
[14]. The circuit configuration consists of one boost inductor,
two dc-bus capacitor, two power diodes, two neutral-point
clamped diodes and power switches with antiparallel diodes.
Fig. 3 The single-phase three-level Boost type rectifier
Fig. 3 shows the configuration of single-phase threelevel boost type rectifier. The system is composed of a boost
inductor Ls, two capacitor Cd1 and Cd2, eight diodes and three
power switches. This configuration is controlled to achieve
high power factor, regulate dc link voltage and keep balanced
neutral point voltage.[10]
Fig. 6 The single-phase three-level rectifier with the diode embedded switches
Fig. 4 Single-phase three-level rectifier with a bidirectional switch
In Fig. 4 shows the configuration of single-phase
three-level rectifier with function of power factor corrector and
active filter [11]. This configuration consists of full-bridge
conventional rectifier and a bidirectional switch with the two
common-emitter (CE) unidirectional switches. For the singlephase three-level rectifier that composed of full-bridge
conventional rectifier and two directional switches can be
shown in Fig. 5 [12].
Fig. 7 The three-level neutral point diode clamped rectifier
Fig. 8 There-level diode-clamped rectifier
Fig. 5 The single-phase three-level rectifier with two bidirectional switches
While in Fig. 6 shows the single-phase three-level rectifier that
composed of full-bridge conventional rectifier and two
Figure 8 shows a single-phase three-level PWM
rectifier, with a neutral-point diode-clamped topology [15],
used to achieve power-factor correction and DC bus voltage
regulation. Eight switches and four clamped diodes with a
voltage stress of half the DC-link voltage are used to generate
five voltage levels on the AC terminal of the rectifier. Fig. 9
gives a single-phase rectifier, with a capacitor-clamped
topology [16], used to achieve three-level PWM operation.
Eight switches with a voltage stress of half the DC-link voltage
and two flying capacitors are adopted in this circuit topology.
The voltage across the flying capacitors is equal to half the
DC-bus voltage.
An asymmetrical single-phase rectifier can be shown
in Fig. 10 to achieve power factor corrector an ac side and to
obtain a constant dc-link voltage on dc side. Six active
switches are used in the adopted rectifier to generate threelevel voltage [13].
Fig. 12 illustrates single-phase multilevel rectifier is
based on series connection of two full-bridge cell. Two dc bus
voltages are provided in this rectifier. The stress of each power
switch is equal to dc bus voltage. Increasing the connection
number of full-bridge cell, the more voltage levels are obtained
[17].
III. PRINCIPLE OF PROPOSED TOPOLOGY
Fig. 9 There-level capacitor-clamped rectifier
The proposed single-phase three-level rectifier
topology is shown in Fig. 12. It consists of inductor boost, the
conventional two-level full-bridge rectifier, one bidirectional
switch and two capacitors. There are three ways to obtain a
bidirectional switch: the diode embedded unidirectional switch
(namely, four diodes and one switch), the two common-emitter
(CE) unidirectional switch, or the two common-collector
unidirectional switch (CC). The diode-embedded switch
requires only one gate driver and one active switch, which is
more convenient for implementation than the other two
configurations are [19].
Fig. 10 The single-phase asymmetric three-level PWM rectifier
Fig. 12 The proposed three-level PWM rectifier
Two reference signals Vref1 and Vref2 will take turns to
be compared with the carrier signal at a time. If Vref1 exceeds
the peak amplitude of the carrier signal Vcarrier, Vref2 will be
compared with the carrier signal until it reaches 0. At this point
onwards, Vref1 takes over the comparison process until it
exceeds Vcarrier. This will lead to a switching pattern as shown
in Fig. 13. Switches S1, S3 and , S5 will be switching at the rate
of the carrier signal frequency while S2 and S4 will operate at a
frequency equivalent to the fundamental frequency. Table 1
illustrates the level of Vinv during S1-S5 switch on and off.
Modulation index Ma for five-level PWM inverter is
given as [18]
A
(3)
Ma = m
2Ac
Fig. 11 Three-level rectifier with series connection of two full-bridge cells
where Ac is the peak-to-peak value of carrier and Am is the peak
value of voltage reference Vref. Since in this work two
reference signals identical to each other are used, equation (3)
can be expressed in terms of amplitude of carrier signal Vc by
replacing Ac with Vc. and Am = V ref1 = V ref2 = V ref .
M =
V ref
Vref1
Vcarrier
Vref2
−Vcarrier
(4)
2V c
(b)
Vref1
Vref1
Vcarrier
Vref2
Vref2
−Vcarrier
S5
S1
(c)
S3
Vref1
S2
Vcarrier
S4
Fig. 13. Switching pattern for single-phase five-level inverter
TABLE 1
INVERTER OUTPUT VOLTAGE DURING S1-S5 SWITCH ON AND OFF
S1
OFF
ON
OFF or
(ON)
OFF
OFF
S2
OFF
OFF
ON
or
(OFF)
ON
ON
S3
OFF
OFF
OFF or
(ON)
S4
ON
ON
ON
or
(OFF)
OFF
OFF
OFF
ON
S5
ON
OFF
Vinv
+Vpv/2
+Vpv
OFF
0
ON
OFF
-Vpv/2
-Vpv
If M>1, higher harmonics in the phase waveform is
obtained. Therefore, M is maintained between 0 and 1. If the
amplitude of the reference signal is increased higher than the
amplitude of the carrier signal, i.e. M>1, this will lead to over
modulation. Large values of M in sinusoidal PWM techniques
lead to full over modulation [15]. Fig. 14 shows the carrier and
reference signals for different values of M.
Vcarrier
Vref1
Vref2
−Vcarrier
(d)
Fig. 14. Carrier and reference signals for different values of modulation index,
M (a) M=0.3. (b) M=0.5. (c) M=0.7. (d) M=1.2.
From the PWM modulation, the analysis of harmonic
components in the proposed inverter can be preformed. The
output voltage produced by comparison of the two reference
signals and the carrier signal can be expressed as [21]
Vo (θ ) = A0 +
∞
∑ (A
n
cos nθ + B n sin nθ )
(5)
n =1
If there are P pulses per quarter period, and it is an
odd number, the coefficients Bn and Ao would be a zero where
n is an even number. Therefore, the equation (5) can be
rewritten as
Vo (θ ) =
∞
∑ A cos nθ
(6)
n
n =1,3....
−Vcarrier
An = −
Vref2
(a)
2V dc
nπ
∑∑ [(− 1)
P
4
int (i/2 )
]
sin(nα m +i )
m =0 i =1
(7)
where m is a pulse number. The Fourier series coefficients of
the conventional single-phase full-bridge rectifier by sinusoidal
PWM is given as
An =
4V dc
nπ
∑ [(− 1)
P
m =1
m
]
sin(nα m )
(8)
IV. SIMULATION & EXPERIMENT RESULT
In order to demonstrate the feasibility of the proposed
scheme, a prototype rectifier was implemented in the
laboratory. The mains voltage is 240 V with 50 Hz. The input
inductance is about 3.15mH. The power switches were
implemented by IGBT IRG4PH50UD. The capacitance of two
capacitors is 2200 μF. The output rated power is 1000 W in the
laboratory prototype. The dc-link voltage is equal to 450 V in
the adopted rectifier. PSIM software is used to simulate the
design prototype. The switching algorithm of this rectifier is
implemented in fix-point 32-bit eZdsp board TMS320F2812.
Its peripheral units allow a straightforward implementation of
the algorithm strategy.
2 >
Fig. 18. Measured waveform of line current 5A/div, 5ms/div
Fig. 15 Simulation of ac side voltage Vab of the adopted rectifier
Fig. 19 Simulation waveform of dc side output voltage of the adopted rectifier
1 >
1>
Fig. 16. Measured waveform of ac side voltage Vab of the adopted rectifier
250V/div, 5ms/div
Fig. 20. Measured waveform of dc side output voltage 250V/div, 5ms/div
Fig. 17 Simulation waveform of line current of the adopted rectifier
In Fig. 15 can be shown five-level voltage generated in ac
side rectifier. This result is similar with experiment result in
Fig. 16. Line current that flowed in inductor can be shown in
Fig.17. This current near sinusoidal although this rectifier still
open loop condition and this is verified in experiment result as
shown in Fig. 18. Output voltage of rectifier can be shown as
in Fig. 19 and 20. This output still have ripple because of open
loop condition.
V. CONCLUSION
This paper presents a novel topology and PWM for
single-phase three-level rectifier. Five voltage levels are
generated based on three-level PWM scheme. The operation of
the PWM switching algorithm scheme has been verified both
by simulation and experimentally. Simulation and
experimental results show that both are in close agreement.
This topology still operate in open loop condition therefore can
be developed to close loop condition. This rectifier has
possibility to implement in active power filter.
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