EE-6380

DSTATCOM
Prof. Salman Hameed
Department of Electrical Engineering,
AMU Aligarh
Problems encountered in distribution
• High reactive power burden

• High harmonic currents

• Unbalanced loads

• Excessive neutral currents

• Working principle and Operating modes of DSTATCOM

• Mathematical modelling of a DSTATCOM

• DSTATCOM controller principles

• Application of DSTATCOM

• Advantages of DSTATCOM
Introduction about DSTATCOM
• One way of increasing the power availability is by reducing the high losses in the existing power
transmission and distribution systems.
• In addition, there is a demand for high quality power from customers for custom power devices.
• Compensation for reactive power and unbalance in the power distribution system are key factors
in improving the power quality to the end user.
• Excessive reactive power in the system increases feeder losses and reduces the active power flow
capability of the distribution system whereas unbalance affects the operation of generators and
transformers in the system.
• A Distribution STATic COMpensator (DSTATCOM), a custom power device, connected in shunt with
the load, compensates for the reactive power and unbalance caused by various loads in the
distribution system.
• The performance of the DSTATCOM depends on the control algorithm used for extracting the
reference current components. Here, the working principle of a DSTATCOM is explained and its
mathematical model has been derived.
• The control techniques for voltage regulation, power factor improvement and compensation of
unbalanced systems, for a DSTATCOM, are described here.
 Working Principle of DSTATCOM
• A DSTATCOM is a shunt compensation device that provides an
effective solution for reactive power compensation and voltage
regulation.
• It comprises of a Voltage Source Converter (VSC), a DC capacitor,
a coupling inductor or coupling transformer and a controller.
• The DSTATCOM, connected to the grid through the coupling
inductor at the point of common coupling (PCC), is controlled in
such a way that it exchanges only reactive power with the grid.
• This is achieved by injecting the current in quadrature with the
grid voltage.
Basic structure of a DSTATCOM
DSTATCOM operating modes
• If the magnitude of the DSTATCOM voltage is greater than the grid voltage ( > ), the DSTATCOM
supplies reactive power to the grid, and the DSTATCOM is operating in the capacitive mode.
• If the grid voltage is greater than the DSTATCOM voltage ( > ), the DSTATCOM absorbs reactive
power from the grid, as shown in Figure, and the DSTATCOM is operating in the inductive mode.
• If the grid voltage and the DSTATCOM voltage are of the same magnitude ( = ), there is no
exchange of reactive power between the grid and the DSTATCOM, as shown in Figure, and the
DSTATCOM is operating in the floating state.

Capacitive mode Inductive mode Floating mode

Simplified single-line diagram of the DSTATCOM

• DSTATCOM consists of a DC link capacitor, an IGBT based VSC, a filter and a voltage source to
represent the grid voltage.
• The DSTATCOM is connected through a filter circuit to the grid at the point of common coupling.
Mathematical modelling of a DSTATCOM
The three-phase instantaneous voltages at the PCC are given by

The relationship between the PCC voltages, the inverter output voltages and currents are obtained by writing
the KVL equation for the single line diagram of DSTATCOM.

• Above equations describe the system differential equations in the abc reference frame.
• To control the current injected by the VSC, the transformation of these equations to the
synchronous reference frame is required.
• The Park’s transformation is used for transforming from the abc reference frame to the
synchronous qd0 reference frame.
• As the system is assumed a balanced, only d and q components exist. The transformed results in
the dq frame are given by..

• Neglecting the voltage harmonics produced by the direct and the quadrature axes voltages, we
get..

• According to the power balance theory, the instantaneous power at the AC terminals of the
inverter is equal to the instantaneous power at the DC terminals of the inverter. The power
balance equation is given as
• The current in the DC side of the DSTATCOM

• The DSTATCOM’s state space mathematical model can be written as

• Where, A is
• Since the d and q axes are not stationary, they follow the trajectory of the voltage vector.
• The instantaneous active and reactive powers

• By observing, the performance of the DSTATCOM can be controlled by controlling the active and
reactive components of currents.
• The control algorithm developed in the synchronous reference frame should control the d or the
q component of the current to attain the control objective.
DSTATCOM controller principle
• The DSTATCOM has a voltage source converter (VSC) at its core that can be used for different
application by appropriate control algorithms.
• In the control, a two-level VSC is used to realize the DSTATCOM. The bus voltage is regulated
either by absorbing or by supplying reactive power to the bus.

Schematic of a DSTATCOM
 DSTATCOM controller principle..
• The cascade controller for the voltage
regulation application is shown in Figure.

• For voltage regulation, two voltages are

• One is the AC voltage of the power system

• Both the regulators are of the proportional

• The error is regulated through a PI controller to get ref Id. The ref Iq is obtained by regulating the
ref Vrms and Vrms signals by another PI controller.

• These reference currents are then regulated by comparing the d and q components of currents
with their respective components of reference current in another set of PI regulators, whose
outputs are the d-axis and q-axis control voltages for the DSTATCOM.
DSTATCOM controller principle..
• The voltage magnitude and phase angle are computed from and the computed voltage
magnitude and phase angle are used to generate the three phase sinusoidal reference signals,
without the use of inverse Park’s transformation, to reduce the computation time, as given in
Equations..

• These reference signals are compared with a sawtooth wave to generate the SPWM signals in the
SPWM module.
• With the same reference signal, the switching pulses are generated by the SVPWM algorithm in
the PWM module.
Application of DSTATCOM

Potential applications at the distribution level include

• voltage regulation,

• power factor correction,

• load balancing,

• harmonic filtering.
Advantages
• Power factor to unity
• Harmonic current compensation
• Load balancing
• Distribution line voltage regulation
• Compensation of neutral current
Sources
• https://www.slideshare.net/mangal007/dstatcom
• file:///D:/Power%20System%20Engineering/08_chapter3.pdf
• https://new.abb.com/docs/librariesprovider78/chile-
documentos/jornadas-tecnicas-2013---presentaciones/7-michael-
neutz---power-quality.pdf
• https://www.powershow.com/view0/8e637d-
NTE1Y/STATCOM_UPS_Market_-
_India_Industry_Analysis_Size_Share_Growth_Trends_and_Forecast_
2016_-_2024_powerpoint_ppt_presentation
Thanks