DC Bus Voltage Switched Control Method for Three Phase Voltage Source PWM Rectifier Under Rapidly Varying Dynamic Load

IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 07, 2014 | ISSN (online): 2321-0613
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DC Bus Voltage Switched Control Method for Three Phase Voltage
Source PWM Rectifier under Rapidly Varying Dynamic Load
Punya Pratap Singh1
Sarveshkumar2
1
M.Tech Student 2
Assistant Professor
1,2
Department of Electrical Engineering
1,2
M.M.M.U.T. Gorakhpur India
Abstract— More electric aircraft referred to as the general
move in the aerospace industry to increase the amount of
electrically powered equipment on future aircraft. One of the
most important kind of electric loads of the future more
electric aircraft is the aircraft electric actuator but its power
characteristics possesses rapidly varying nature in the wider
range and constant power nature in the small signal sense.
Due to the problem of varying nature of power
characteristics the problem of flexible voltage regulation
under dynamic loads arises. For solving this problem dc-bus
voltage switched control method of three phase voltage
source pwm rectifier is presented in this paper. Several
linear controllers are designed on different operating points
of the voltage source rectifier, and one controller is
implemented according to certain switching law. The
stability is checked by the common lyapunov function
method. Simulation results showed the desired control
performance is obtained. In comparison of classical PI
controller the results of switched controller achieves
considerable reduction in the dip and overshoot of the dc
bus voltage under an aircraft’s electric actuator load.
Key words: aircraft electric actuator, ac-dc power
conversion, power conversion, ac motor drives, power
conversion harmonics.
I. INTRODUCTION
Three- Phase voltage source pulse width modulated
rectifiers possess many attractive features, such as control of
dc-bus voltage over a wide range, power regeneration
capabilities, high power factor operation and low harmonic
distortion of input currents [5], [6].Although voltage source
rectifiers are widely used in many industrial applications but
seldom applications have appeared in the aviation industry.
As more electric aircraft (MEA) becoming the main trend
for future aircrafts, there exists a sharp increase of electric
loads in the aircraft power system [7].The aircraft electric
actuator is one of the most important loads of the future
MEA and all electric aircraft power grid [2]. It is a position-
servo system that shoulders the task of driving the aircraft
control surfaces. Unlike the general electric loads, the
aircraft actuators behave as constant power loads (CPLs). In
addition, during an action process of an aircraft actuator, the
input power would vary rapidly within a wide range. These
load characteristics bring significant challenges to the power
source. The advanced PWM rectifiers play an important role
in these aspects, due to more and more attention paid to the
power quality and energy efficiency of the aircraft power
grid. Therefore, a further investigation on the VSRs is quite
important for the aviation industry [1], especially under an
electric actuator load. Lot of research work has been done
on the control performances of the VSRs in the past few
decades [8]-[24].The results in controller design can be
classified as linear design and nonlinear design. With a
linear controller, both the stability and the performance of a
VSR cannot be guaranteed under a wide range rapidly
varying loads [25]. Nonlinear control strategies have been
extensively studied in the last few years, e.g. Feedback
linearization strategy [21] and passivity based Control
methodology [18]. This proposed nonlinear design
Strategies present large complexity, so it is quite necessary
to develop a control method that achieves system stability,
desired performance, and simultaneously, easy to design.
Analysis and synthesis for switched systems have attracted
increasing attention in the control community. Switched
systems are comprised of a collection of subsystems
together with a switching law that specifies the switching
between the subsystems. Switched systems have a wide
range of applications in the physical and engineering
systems, which are mainly due to numerous practical
systems exhibiting switched nature and the growing use of
computers in the control of physical plants. In the aerospace
field, many design problems can be viewed as the analysis
and synthesis of the switched system, such as aircraft
controller design, fault tolerant controller design, stability
analysis of spacecraft formation, angle of attack and normal
acceleration limiter design, and modeling and control of
flow systems [27]. Focusing on wide-range rapidly varying
characteristic of the Load and the background of industrial
application, this paper proposed a switched control strategy
for the VSR based on the concept of switched system.
Several linear controllers are designed for different
operating points of the VSR, and certain controllers are
selected according to the load resistance value. The
proposed control system is modeled by a sixth-order
switched linear system, and stability of the system is
analyzed by the common lyapunov function method
[28].Compared with existing nonlinear control methods, the
proposed switched control strategy is simpler. Compared
with linear control methods, the proposed control strategy
can guarantee system stability and desired performance
under a wide-range rapidly varying load
II. CHARACTERISTICS OF THE ELECTRIC ACTUATOR LOAD
A. Dynamic Nature of the Electric Actuator Load
Fig. 1: Dynamic load profile.

DC Bus Voltage Switched Control Method for Three Phase Voltage Source PWM Rectifier under Rapidly Varying Dynamic Load
(IJSRD/Vol. 2/Issue 07/2014/075)
The aircraft electric actuators that drive the
movements of Control surfaces of an aircraft are rapid
position control systems. The actuator load demands a short
term, high peak power with a fairly low steady state or
background loading of less than 10% of the peak
requirement. This obviously depends on the particular
application, and it is usually called the dynamic load of the
aircraft power grid. Fig. 1 illustrates the dynamic nature of
an electric actuator load as it moves a surface from rest at
one position to rest at another position. There are three basic
parts to the load cycle [30].
 Input of power to accelerate the motor and inertia
of the Load.
 Surface moving against the load (motor delivering
speed and torque).
 Surface holding the load (motor delivering torque
but no speed).
The peak power of the electric actuator reaches
about 16 kVA, which is more than ten times of the lowest
power.
B. Constant Power Nature of the Electric Actuator Load
Generally speaking, the electric actuator is not a typical CPL
Because of the dynamic nature however, the system has the
feedback control with the actuator position command
supplied from a higher level control system of the aircraft.
The feedback makes the system behave as a typical CPL in
small time scales with small-signal negative resistance. The
value of the constant power drawn from the power source
only depends on the operating point within the operating
cycle. Hence, it can be treated as a special CPL. While an
“ideal” CPL can be modeled as the standard nonlinear
model an electric actuator load can be expressed as =
P(t)/v. It means that would rise correspondingly if the dc-
bus voltage of the source falls with the rise of the output
power, which may be a power circuit
Vicious circle for the power source. In conclusion,
both the dynamic nature and the constant power nature of an
electric actuator make big challenges for the power source.
In the following discussion, a switched controlled three
phase VSR with an “ideal” CPL, of which the dynamic
response is the same as that shown in Fig. 1, is designed and
analyzed.
III. MODELING OF PWM CONVERTERS
Fig. 2: AC/DC Voltage Source PWM Converter.
Of the three-phase VSR is shown in Fig. 2. It is usually
assumed that a resistive load is connected to the output
terminal [24]. An improved linear state-space
modeling of a three-phase voltage source rectifier is [22].
= - - ω + ( ) (1)
= - +ω + ( ) (2)
u*
= - u + 3 + 3 (3)
u= (4)
Where , , and represent the
source voltage, the current, and the rectifier input voltage in
the synchronous d−q reference frame, respectively and L
denote the line resistance and the input inductance,
respectively, ω is the source angular frequency, is the
dc-bus voltage, and is the load resistance. Note that in
this paper, a variable resistor R( , ) is employed in order
to simulate the CPL characteristic of the electric actuator,
and for a CPL we have
    
Where denotes the load power
Let R( , ) replace RL in (3), and we get
u*
= - PL + 3 + 3 (6)
Therefore, in this study, VSR under a CPL is
modeled by (1), (2), (4), and (6). In fact, in dc circuits, we
have
Where denotes the load current. From (5) and (7),
we get
R( , ) = R( )= (8)
Therefore, R ( , ) or R ( ) is the input
resistance (the apparent resistance of the load) that can be
calculated by (8).
IV. SWITCHED CONTROL OF VSRS
In this section, a novel switched control method for three
phase VSRs will be presented. The switched control method
aims at well regulation of the dc-bus voltage of VSRs under
a Wide-range rapidly varying load.
A. Switched Control of the DC-Bus Voltage Regulator
Fig. 3: Classical Linear PI Voltage Controller.
Fig. 4: Proposed Dc-Bus Switched Voltage Regulator.
Fig. 4 shows the structure of the proposed switched
control method. Different from the classical linear PI
voltage control scheme that is depicted in Fig. 3 [14], there
are a set of PI sub controllers in the voltage-switched
control method. The gains of different PI sub controllers

correspond to different loads at the dc link. In this study, the
apparent resistance R( , )or R( ) is selected as the
switching law that provides guidelines to select a proper PI
sub controllers when the load changes. Besides, u is
considered as the state variable instead of the conventional
state variable [19], [20]. The variable x4 denotes the
output of the integrator of the PI sub controller. For a
selected PI sub controller i, the control law of the voltage
controller is
i = ( ) + , 1 2 3………n
= u*
- u (10)
Where n is the number of the sub controllers.
B. Current Controller
Fig. 5: Block Diagram of the Current Controller with
Current Forward Feedback Decoupling Network.
The current controller that consists of two PI controllers
( and ) is depicted in Fig. 5 [22], [25], [26]. In this
control scheme, the cross-coupling terms of ωL and
ωL in (1) and (2) are compensated by feed forward at the
last stage of the controller. In consequence, the q-axis
current of that is the active current can be controlled
independently on and u so can the reactive current .
The variables of and are the reference value
of and . For unit power factor when rectifying, is
zero and is set by the outer voltage controller. Let the
variables and ξ1 denote the output of the integrator of
and the output of , respectively, the control law
of is
= ( ) + (11)
= (12)
Similarly, the control law of is given by
= ( ) + (13)
= (14)
= 0 (15)
The control law of the current controller is
= - + - 𝜔L (16)
= - + +𝜔L (17)
V. SIMULATION RESULTS
This section applies the proposed switched control method
to design a VSR for an aircraft ac–dc converter in
accordance with the requirements of the HVdc system stated
in MIL-STD-704 F. The VSR was employed on an aircraft
electric actuator that is a fast dynamic load. Simulation
results are presented.
A. Requirements of the system
A simulation system model based on Fig. 2 is constructed
with the specifications listed in Table I. According to the
requirement of MIL-STD-704 F, normal steady voltage
transient of the 270 V dc systems shall be within the
envelope of 280 and 250 V, and ripple amplitude of the
steady voltage should be less than 6 V.
B. Design of the Switched Controller
Since and are measured by sensors, the apparent R
( ) [or R ( )] that is the switching law of the
voltage controller, is calculated by (8). In this study, its
variety range is mainly within (4–95 Ω). Then, the range (4–
95 Ω) is divided into three switching sub ranges (hence, we
have n =3). The parameters , , , and are listed
in Table II. Sub controller 1, associated with
R( )=(28Ω, +∞), is selected when a low power load is
connected. Sub controller 2, corresponding to R( )=(5
Ω, 28 Ω),which is chosen when a middling load is
connected, is the main controller, because the load RL varies
mainly in the range of (5–28 Ω). Sub controller 3, associated
with R( )=(0 Ω, 5 Ω], is selected when the peak power
takes place. The proportional coefficient of the sub
controller 3 is chosen large enough to achieve rapid
response.
C. Tables and simulation results
Parameter Setting Value
Source Voltage Em (RMS)
DC-Bus Voltage Vdc
Line Inductor L
Inductor Resistance R
DC –Bus Capacitor C
Line Frequency Ω
PWM Carrier Frequency
115 V
270 V
0.5mh
0.2Ω
2000µf
800π Rad/S
16khz
Table 1: Specifications of Three-Phase Pwm Boost Rectifier
Current
controller
=20 =50
Subcontroller1
Subcontroller2
Subcontroller3
= 0.002
= 0.005
= 0.2
= 0.03
=0.1
=0.1
∈ 28 +∞
∈ 5 28]
∈(0,5]
Table 2: Pi Parameters of the Current Controller And
Switched Voltage Controller
Fig. 6(a): Response of the linear PI controller
Fig.6 (a) shows the response of the linear PI
controller the starting-up response is smooth and fast
with a small overshoot. However, the dc-bus voltage drops

down to zero abruptly as the load current climbs up rapidly,
when the motor and load inertia accelerates.
Fig. 6 (B): Response of the Linear PI Controller
Fig. 6(b) shows the response of the linear PI
controller although the system could maintain stability
during the whole Dynamic process, the dc-bus voltage falls
obviously to about 229V when the peak power occurs and
increases to about 285V when the load power drops.
Therefore, the disturbance rejection ability of this controller
is weak and it cannot meet the normal voltage transient
requirements of MIL-STD-706 F.
Fig. 6(C): Response Of The Linear PI Controller
Fig. 6(c) shows the response of the linear PI
controller . Due to the large proportional gain of the
controller, onlysmall dip and peaking in output voltage are
observed. However, there exist too many undesirable
oscillations from 0.5 to 0.7 s. The maximum ripple voltage
is larger than 6 V. Thus, the response cannot meet the ripple
amplitude requirement of MIL-STD-706 F. Furthermore, a
big overshoot appears in power-up situations.
Fig. 6 (D): Response of the Proposed Switched Controller
Fig. 6(d) shows the response of the proposed
switched controller. It can be seen that a balanced and
optimized dc-bus response, which has an acceptable small
ripple, little oscillations during the dynamic process, and a
neglect able small overshoot in power-up situations, is
achieved. The dc-bus voltage falls to 259 V at the peak load
power and the largest overshoot appears at 0.76 s to about
280 V when the load current drops. Therefore, the system
controlled by the switched control method meets the
requirements of MIL-STD-706 F.
VI. CONCLUSION
In this paper, a new switched control method is introduced
to control the VSR. The proposed switched voltage control
approach could provide a simple, effective way to overcome
the problem of wide-range load regulation. Several linear
controllers are designed according to the derived switched
voltage controller for the VSR at different operating points
and a certain controller is selected by the apparent load
resistance value. To achieve better responses, one can
increase the number of sub controllers of the switched
regulator reasonably. Based on the concept of switched
system, the stability of the proposed control scheme can be
attained. Simulation and experimental results of a switched
controlled VSR with an electric actuator load show that the
presented switched control method has a desirable capacity
of regulating dc-bus voltage with such wide-range rapidly
varying dynamic load.
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DC Bus Voltage Switched Control Method for Three Phase Voltage Source PWM Rectifier Under Rapidly Varying Dynamic Load

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DC Bus Voltage Switched Control Method for Three Phase Voltage Source PWM Rectifier Under Rapidly Varying Dynamic Load