The document proposes a new control algorithm and topology for a distribution static compensator (DSTATCOM) that allows it to operate in voltage control mode even under a stiff source. A stiff source has negligible feeder impedance, making it difficult for a DSTATCOM to regulate voltage using conventional control schemes. The proposed solution connects an external inductor between the load and source, creating a point of common coupling. A DSTATCOM at the load can then indirectly regulate voltage by controlling the voltage across the inductor. The control algorithm generates reference voltages that also control source currents to be balanced, sinusoidal and in phase during normal operation. This provides fast voltage regulation during disturbances while maintaining the benefits of current control mode during normal operation,

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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 61, NO. 7, JULY 2014 3131
A Multifunctional DSTATCOM Operating
Under Stiff Source
Chandan Kumar, Student Member, IEEE, and Mahesh K. Mishra, Senior Member, IEEE
Abstract—Loads connected to a stiff source cannot be protected
from voltage disturbances using a distribution static compen-
sator (DSTATCOM). In this paper, a new control-algorithm-based
multifunctional DSTATCOM is proposed to operate in voltage
control mode under stiff source. This scheme provides fast voltage
regulation at the load terminal during voltage disturbances and
protects critical loads. In addition, during normal operation, the
generated reference load voltages allow control of the source cur-
rents. Consequently, DSTATCOM injects reactive and harmonic
components of load currents to make source power factor unity.
Simulation and experimental results are presented to verify the
efficacy of the proposed control algorithm and multifunctional
DSTATCOM.
Index Terms—Distribution static compensator (DSTATCOM),
multifunctional, power factor, stiff source, voltage regulation.
I. INTRODUCTION
A distribution static compensator (DSTATCOM) can mit-
igate several power quality (PQ) problems, depending
upon the mode of operation. In current control mode (CCM)
[1]–[6], it injects harmonic and reactive components of load
currents to make source currents balanced, sinusoidal, and in
phase with load voltages. In voltage control mode (VCM)
[7]–[13], it regulates load voltage at a constant value to pro-
tect sensitive loads from voltage disturbances such as sags,
swells, transients, and/or fluctuations. However, the objectives
of these two modes are different and cannot be achieved
simultaneously.
Based on the distance between source and load, a source is
termed as stiff or nonstiff. If the distance is long, then source
is termed as nonstiff and has high feeder impedance, whereas
if the distance is very small, then source is termed as stiff and
has negligible feeder impedance. Generally, a source (stiff or
nonstiff) supplies a permissible range of voltage, which is suffi-
cient for satisfactory performance of load [14]. In this situation,
DSTATCOM should operate in CCM. However, due to grid
faults, the source voltage (stiff or nonstiff) can change at any
time, and then, the VCM operation is required. DSTATCOM
regulates the load voltage by indirectly regulating the voltage
Manuscript received November 28, 2012; revised March 4, 2013 and June 7,
2013; accepted July 19, 2013. Date of publication August 6, 2013; date of
current version January 31, 2014. This work was supported by the Department
of Science and Technology, India, under the project grant DST/TM/SERI/
2k10/47(G).
The authors are with the Department of Electrical Engineering, Indian In-
stitute of Technology Madras, Chennai 600 036, India (e-mail: chandan3107@
gmail.com; mahesh@ee.iitm.ac.in).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TIE.2013.2276778
Fig. 1. Single-phase equivalent circuit of DSTATCOM in a distribution
network.
across the feeder impedance. When a load is connected to
nearly a stiff source, feeder impedance will be negligible [1]–
[4], [15], [16]. Under these circumstances, DSTATCOM cannot
provide sufficient voltage regulation at the load terminal [9].
There is lack of literature addressing the feasibility of the VCM
operation of DSTATCOM under stiff source. In present work,
this problem is addressed while ensuring that, during normal
operation, the advantages of CCM are retained.
This paper proposes a new control-algorithm-based
DSTATCOM topology for voltage regulation even under stiff
source. It is achieved by connecting a suitable external inductor
in series between the load and the source point. The point of
common coupling (PCC) will be the point where external in-
ductor and source are connected. A DSTATCOM connected at
the load terminal provides voltage regulation by indirectly reg-
ulating the voltage across the external inductor. The proposed
control algorithm to obtain variable reference load voltages is
formulated as a function of the desired source current. This
voltage indirectly controls the current drawn from the source
for a permissible range of source voltage. Therefore, the control
algorithm makes source currents balanced, sinusoidal, and in
phase with respective source voltages during normal operation.
During voltage disturbances, a constant voltage is maintained
at the load terminal. Hence, the proposed topology and the
control algorithm make the compensator multifunctional, so
that it provides fast voltage regulation at the load terminal
and additionally provides advantages of CCM while operating
in VCM. Simulation and experimental results are presented
to verify the efficacy of the proposed control algorithm and
multifunctional DSTATCOM.
II. DSTATCOM CONFIGURATION
A neutral-point-clamped voltage source inverter (VSI) topol-
ogy is chosen as it provides independent control of each
leg of the VSI [7]. A single-phase equivalent circuit of
DSTATCOM in a distribution network is shown in Fig. 1. The
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