PERFORMANCE ANALYSIS OF D-STATCOM COMPENSATOR(8)

The supply voltage may be expressed as:

Vs=V1Sinwt

Load current is made up of active current (ip), reactive current (iq) for positive sequence and negative sequence current (i-) can be decomposed in parts as:

The control algorithm is based on the extraction of current component in phase with the unit voltage template. To estimate fundamental frequency positive sequence real component of load current, the unit voltage template should be in phase with the system voltage and should have unit amplitude further it must be undistorted.

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PERFORMANCE ANALYSIS OF D-STATCOM COMPENSATOR(7)

COMPENSATOR(7)

SRF isolator extracts the dc component by low pass filters (LPF) for each id and iq realized by moving averager at 100Hz. The extracted DC components iddc and iqdc are transformed back into a-P frame as shown below:
Performance Analysis-10

From here the transformation can be made to obtain three phase reference currents in a-b-c coordinates using Reverse Park’s transformation and Clark’s transformation. The reactive power compensation can also be provided by keeping iq component zero for calculating reference currents.

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PERFORMANCE ANALYSIS OF D-STATCOM COMPENSATOR(6)

The p-q theory has the following limitations

• The source voltages are unbalanced and non-sinusoidal.
• It needs a large number of transducers of measurements and intensive computation. It tends to make the system operation complex.

Disadvantages of P-Q theory

• Delay in computation due LPF used for filtering power signals
• This theory uses volt signals to compute instantaneous active and reactive powers, if any variations in supply voltage causes inaccurate measurements
• It is not applicable for single phase systems and three phase systems with neutral.
• Complete harmonic suppression is not achieved in case of nonlinear loads.
• A larger filter inductance is required to filter the harmonics

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PERFORMANCE ANALYSIS OF D-STATCOM COMPENSATOR(4)

The p-q theory uses a b 0 transformations and various definitions of active and reactive powers. The transformation of 3-Phase quantities (a-b-c) of stationary reference frame into 2-Phase quantities (a Ь 0) stationary reference frame is achieved by applying Clark’s transformation.

Performance Analysis-2Performance Analysis-3

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PERFORMANCE ANALYSIS OF D-STATCOM COMPENSATOR(3)

COMPENSATOR(3)

The performance of the DSTATCOM depends on the control algorithm i.e. the extraction of the current components. For this purpose there are many control schemes which are reported in the literature and some of these are instantaneous compensation, instantaneous symmetrical components, synchronous reference frame (SRF) theory, computation based on per phase basis, and scheme based on neural network. Among these control schemes instantaneous reactive power theory and synchronous rotating reference frame are most widely used.

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PERFORMANCE ANALYSIS OF D-STATCOM COMPENSATOR(2)

Fig. 1 shows the basic circuit diagram of the DSTATCOM system with lagging power factor loads connected to 3-phase, 3-wire distribution system. The lagging power-factor load is realized by star connected resistive inductive (R-L) load. Unbalanced load is realized by disconnecting load from phase-a using circuit breaker. The three-phase voltage source converter (VSC) working as a DSTATCOM is realized using six IGBT switches with anti-parallel diodes. At ac side the interfacing inductors are used to filter out the high frequency components of the compensating currents.

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PERFORMANCE ANALYSIS OF D-STATCOM COMPENSATOR(1)

COMPENSATOR(1)

A power system is said to be well designed only if it provides good voltage profile. In the early days of power transmission in the late 19th century problems like voltage deviation during load changes and power transfer limitation were observed due to reactive power unbalances. Today these Problems have even higher impact on reliable and secure power supply in the World of Globalization and Privatization of electrical system and energy transfer. The development in fast and reliable semiconductors devices (GTO and IGBT) allowed new power electronic Configurations to be introduced to the tasks of power Transmission and load flow control.

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Representative APR 391%

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