Performance of PWM Rectifier with Different Types of Load

IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 07, 2014 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 65
Performance of PWM Rectifier with different types of load
Mr. Rajendra Singh1 Mr. Avinash Maurya2
1,2
Department of Electrical Engineering
1,2
Madan Mohan Malaviya University of Technology, Gorakhpur, Uttar Pradesh, India
Abstract— The paper presents the decoupled vector control
of the PWM rectifier with the nonlinear DC-link voltage
regulation and the load compensating feed forward. The
concept of the proposed control system is based on Voltage
Oriented Control with Space-Vector Pulse Width
Modulation (SV-PWM). For the high-performance
operation of the PWM rectifier and the satisfactory current
tracing the decoupled current control has been introduced.
The performance of the linear PI controller of the DC-link
voltage is strictly dependent on its settings and it may
introduce a disadvantageous voltage overshoot under a
heavy load impact. In order to improve the transient
response of the DC-link voltage control loop a load
compensation has been proposed. The different approach to
the control of the DC-link voltage based on the regulation of
the square power of the DC voltage has been introduced.
Key words: Three Phase Controlled Voltage Source, Boost
Inductors, Three lags Bridge, Capacitors, Discrete Space
Vector Pulse Width Modulation Generator, Scaling gain,
NOT gate
I. INTRODUCTION
Nowadays the adjustable speed drives with the squirrel-cage
induction motors are intensively developed. In these drives
the angular velocity and the electromagnetic torque are
precisely controlled using mostly the voltage source
inverters. For years most of the electrical drives with the
voltage inverters have been supplied from the power
distribution line through the thyristor rectifiers. Such
frequency converters were supposed to provide the smooth
control of the amplitude of the basic harmonic of the output
voltage neglecting the influence of the line-side rectifier on
the grid. The frequency converters supplied by the thyristor
and diode rectifiers are characterized by the disadvantageous
properties as the lack of the possibility of the regenerative
braking of the induction motor, the intake of the non-
sinusoidal distorted currents from the grid at the power
factor different from the unity. The flow of the non-
sinusoidal currents in the power distribution line causes the
distorted voltage drops over the other power devices being
supplied from the grid. The distorted voltages are also
inappropriate for the line transformers since more heat is
produced especially in case of the high power ratings.The
control strategies for the AC/DC line-side converters have
been adapted from the methods elaborated for the vector
control of the induction motors. The classical control
techniques require the strict knowledge of the values of the
line and load parameters since the PI control performance is
strictly dependent on the proper identification of the line
chokes inductance and the DC-link capacitance.
Recently more stress has been put on the
elaboration of the nonlinear control algorithms for the PWM
rectifiers in order to eliminate the disadvantageous influence
of the variations of the line and load parameters on the
converter operation [4, 6, 9]. In this paper a method of the
compensation of the load impact and the efficient control of
the DC-link voltage has been proposed. The presented
method has been implemented and verified on the hardware
application of the DSP-based controlled PWM rectifier.
II. MATHEMATICAL MODELS OF PWM RECTIFIERS
The voltage-source PWM rectifier has the topology
presented in Fig.1 [10]. The converter’s bridge consists of
the six fully-controllable power switches (IGBTs,
MOSFETs, GTOs) connected to the three-phase grid
voltages Vas,Vbs,Vcs via the three symmetrical line chokes
of the resistance Ra and the induction La.
During the operation of the AC/DC line-side
converter its transistors are being switched by the rectifier’s
control system producing the pulse-width modulation
scheme based on the principles of a chosen control strategy.
Fig. 1: Three-phase voltage-source PWM rectifier
In order to reach the sufficient quality of the line
currents in case of the voltage-source PWM rectifier the
high switching frequency has to be provided. The switching
signals are denoted as S11, S21 and S31for the particular
phases respectively. The relationship between the converter
input voltages Vconva, Vconvb, Vconvc and the DC-link voltage
Vdc depends on the instantaneous states of the power
switches and can be described in a form of equations (1).
2
,
2
,
2
312111 dc
c
dc
b
dc VS
V
VS
V
VS
Va






A set of diffential equations can describe the
dynamic model of PWM rectifier

(IJSRD/Vol. 2/Issue 07/2014/016)
[
dia
𝑑𝑡
dib
𝑑𝑡
dic
𝑑𝑡]
=
[
−
ra
La
0 0
0 −
ra
La
0
0 0 −
ra
La]
+
1
𝐿
[
Vas − Va
Vbs − Vb
Vcs − Vc
]
According to Park transform,
[
did
𝑑𝑡
diq
𝑑𝑡
] =
1
La
[
−𝑅 −𝜔𝑅
𝜔𝑅 −𝑅
] [
id
iq
] +
1
La
[
Vd
Vq
] −
1
La
[
Vd
Vq
]
The control design of a PWM rectifier is often
performed in a synchronous frame rotating with the angular
velocity corresponding to the grid pulsation . Thus the
mathematical model of the voltage-source PWM rectifier in
the d-q coordinates can be formulated in the set of the
differential equations (2).
dcq
a
adaq
a
a
aq
ad
a
dcd
a
aqad
a
a
ad
add
ddL
dc
dc
VS
L
ii
L
R
i
dt
d
e
L
VS
L
ii
L
R
i
dt
d
iS
CCR
V
V
dt
d
2
1
1
2
1
2
3





Assuming that the power conversion is lossless the
power balance of the PWM rectifier can be described by the
nonlinear differential equation (3).
III. VOLTAGE ORIENTED CONTROL OF PWM RECTIFIERS
The Voltage Oriented Control technique for the AC/DC
line-side converters originates from Field Oriented Control
for the induction motors. It provides the fast dynamic
response since the current control loops are applied. The
properties of the control systems based on the VOC strategy
are different depending on the involved PWM technique.
The hysteresis pulse-width modulation method provides the
on-line current tracking thus the influence of any
disturbances is minimized and the better robustness of the
control system is achieved.
On the other hand the varying switching frequency
introduces an additional stress in the power switches and
requires the higher values of the parameters of the input
filter. The Space-Vector PWM technique reduces the higher
harmonics content in the line currents since the constant
switching frequency of the power transistors is provided [3].
Fig.3 presents Voltage Oriented Control with SV-PWM for
the AC/DC line-side converters.
Due to the vector transformation to the d-q
reference frame the AC-side control variables are hence the
DC signals. Thus the steady-state errors are easily
eliminated via the PI controllers. The reference values of the
converter input voltages are computed in the current
controllers based on the values of the current tracking errors
(7).
   
   dtiikiikV
dtiikiikV
gqgqrefigqgqrefpconvq
gdgdrefigdgdrefpconvd




IV. PWM RECTIFIER CONTROL TECHNIQUE
PRINCIPLE
Let us consider the electrical scheme presented on figure
18a.
It represents a DC motor fed by a six-pulse
rectifier. The electrical equivalent circuit of the DC motor is
described by an inductance La in series with a resistance Ra
in series with an induced voltage Va which characterizes the
electromotive force, as illustrated in figure 18b.
The IGBT are modelled by an ideal model which
traduces the state of the switch:
-VS = 0 when the IGBT is state-on
-IS = 0 when the IGBT is state-off
Similar to the diode rectifier, there are 13 operating
phases to describe:
-1 phase of discontinuous conduction mode (P0)
All the IGBT are state-off
-6 phases of classical conduction P1 to P6 (figure
15c)
P1: S11 and S 31 state-on,P2: S 11 and S22 state-
on
P3: S 32 and S 22 state-on, P4 : S 32 and S 12
state-on
P5: S 21and S 12 state-on, P6 : S 31 and S 21 state-
on
-6 phases of overlap O1 to O6 (figure 15d)
O1: S 11, S 31 and S 22 state-on,
O2: S 11, S 32 and S 22 state-on

The different operating phases are illustrated in
figure 15. The equations that govern an operating phase are
the same whatever we work on a diode rectifier or a
controlled rectifier.
V. EXPERIMENTAL STUDIES OF PROPOSED CONTROL
TECHNIQUE
The experimental verification of the proposed control
method has been carried out on the laboratory prototype
with the power converter and the fixed-point DSP. The
power unit of the proposed prototype of the AC/DC line-
side converter is based on the 3.3 kW IGBT power module
by EUPEC® with the electronic interface EiceDRIVER™
6ED003E06-F [2].
For the reliable confirmation of the excellent
dynamic performance of the proposed nonlinear control
system of the PWM rectifier the comparative analysis has
been carried out. The Voltage Oriented Control of the PWM
rectifier without the load compensation and the current
decoupling system from Fig.3b has been examined. The
experimental results have been obtained at the same grid and
load conditions as well as the computational rates of the
control system. Fig.8 demonstrates the transient of the grid
currents in the d-q coordinates and the response of the DC-
link voltage control loop to the step change of the converter
load.
VI. CONCLUSIONS
The paper presents the real-time application of the
decoupled control system of the PWM rectifier based on the
Voltage Oriented Control technique. The compensation of
the load current has been introduced to provide the high-
performance operation of the AC/DC line-side converter.
The disadvantageous influence of the rapid changes
of the converter load has been minimized by the
introduction of the feed forward of the load current based on
the load current sensor. The feed forward information about
the actual converter load has contributed to the considerable
improvement of the transient response of the DC-link
voltage. The high quality of the grid currents has been
provided by the application of the Space-Vector Pulse
Width Modulation with the switching frequency of 5 kHz.
The operation of the proposed control method has
been successfully examined on the laboratory setup of the
PWM rectifier with the fixed-point digital signal processor.
VII. SIMULINK MODEL
REFERENCES
[1] The Essence of Three-Phase PFC Rectifier Systems,
Thomas Friedli, Member, IEEE, Michael Hartmann,
Member, IEEE, and Johann W. Kolar, Fellow, IEEE
[2] P. Walther, “A new rectifier system high efficient,
high dense, modular, quick to install and superior for
service,” inProc. 15th Int. Telecom. Energy Conf.,
Sep. 27–30, 1993, vol. 2, pp. 247–250.
[3] A. Pietkiewvicz and D. Tollik, “Cost/performance
considerations for 1- phase input current shapers,”
nProc. 16th Int. Telecom. Energy Conf., Apr. 11–15,
1994, pp. 165–170.
[4] A. Kuperman, U. Levy, J. Goren, A. Zafranski, and
A. Savernin, “High power Li-ion battery charger for
electric vehicle,” inProc. 7th Int. Compat. Power

Electron. Conf.-Workshop, Jun. 1–3, 2011, pp. 342–
347.
[5] J. W. Kolar, T. Friedli, and M. Hartmann, “Three-
phase PFC rectifier and ac–ac converter systems—
Part I, Tutorial,” inProc. 26th IEEE Appl. Power
Electron. Conf. Expo., Mar. 6–10, 2011, pp. 1–268.
[6] D. A. Paice, Power Electronics Converter Harmonics:
Multipulse Methods for Clean Power. Hoboken, NJ:
Wiley, 1999. [6] P. Pejovic, Three-Phase Diode
Rectifiers with Low Harmonics.NewYork: Springer,
2007.

Performance of PWM Rectifier with Different Types of Load

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Performance of PWM Rectifier with Different Types of Load