multilevel inverter based statcom for reactive … · multilevel inverter based statcom for...

MULTILEVEL INVERTER BASED STATCOM FOR REACTIVE

POWER COMPENSATION AND HARMONIC MITIGATION BY

USING SRF/MCPWM IN DISTRIBUTION NETWORK

1S.S. Babu, 2R.Elangovan, 3S.Ezhilarasan3,.

1PG Scholar PRIST, Dept. EEE, Deemed To be University, Thanjavur,

[email protected]

2 Assistant Professor, Dept. EEE, Deemed To be University, Thanjavur,

3Associate Professor, Dept. EEE, Deemed To be University, Thanjavur,

[email protected]

Abstract:

Power quality is a set of electrical boundaries that allows a piece of equipment to

function in its intended manner without significant loss of performance or life

expectancy. All electrical devices are prone to failure when exposed to one or more

power quality problems. It is necessary for engineers, technicians, and system

operators to become familiar with power quality. In this paper the solution is given

by Static Compensator (STATCOM) with the desired reference current for Multilevel

inverter based STATCOM for distribution system is employed. Also the harmonic

mitigation and reactive power compensation by using synchronous reference frame

(SRF) is implemented. Reference Frame Theory. The method relies on the

performance of the Proportional-Integral (PI) controller for obtaining the best control

performance of the SAPF. To improve the performance of the PI controller, the

feedback path to the integral term is introduced. In this paper we implement with

SRF based STATCOM control. SRF theory is implemented for the generation of

controlling reference current signals for controller of STATCOM. The

MATLAB\Simulink based model is developed and simulation results are found. The

hardware is implemented and the results were compared with the simulated outputs.

Keywords: Power quality, Voltage spikes, Frequency variation, Power sag,

Harmonics, STATCOM, SRF.

1.0: INTRODUCTION:

Reliability analysis of power systems has been attracting increasing attention.

Regulatory agencies establish reliability standards that, if infringed, result in costly

fines for the utility suppliers [1] . Power Quality (PQ) related issues are of most

concern now days. The widespread use of electronic equipment, such as information

International Journal of Pure and Applied MathematicsVolume 119 No. 12 2018, 2061-2071ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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technology equipment, power electronics such as adjustable speed drives (ASD),

programmable logic controllers (PLC), energy-efficient lighting etc led to a complete

change of electric loads nature. These loads are simultaneously the major causers and

the major victims of power quality problems [2]. Due to their non-linearity, all these

loads cause disturbances in the voltage waveform. The FACTS devices offer a fast

and reliable control over the transmission parameters, i.e. Voltage, line impedance,

and phase angle between the sending end voltage and receiving end voltage. On the

other hand, the custom power is for low voltage distribution, and improving the poor

quality and reliability of supply affecting sensitive loads. Custom power devices are

very similar to the FACTS. Most widely known custom power devices are

DSTATCOM, UPQC, DVR among them DSTATCOM is very well known and can

provide cost effective solution for the harmonic mitigation, compensation of reactive

power and unbalance loading in distribution system. [3]

2.0: LITERATURE REVIEW:

2.1: DISTRIBUTION NETWORK ISSUES:

With the use of modern high-tech microprocessor based technology in industrial

systems for various applications, electrical distribution and power generation

through renewable energy systems, the power quality is being polluted. To

produce the quality of products, the power supply should be of high quality.

With the use of modern high-tech microprocessor based technology in industrial

systems for various applications, electrical distribution and power generation

through renewable energy systems, the power quality is being polluted. To

produce the quality of products, the power supply should be of high quality.

Quality is a perception [4], and if consumers are happy with the things/service

delivered to them, then one can say that things/service is of good quality. In respect

of electric power, the consumers had less awareness and information 30 years ago.

Now, as more and more people are using electrical gadgets, for various reasons, Power

Quality is a major expectation from all section of people. Most of the consumers are

worried about scheduled/unscheduled load shedding, low voltage, Flickering

(Brownouts), High voltage and Transients. The interest in Power Quality (PQ) is

related to all three parties concerned with the power i.e. utility companies, equipment

manufacturers and electric power consumers, and involves huge loss to the utilities

and consumers [4].

2.2: MULTILEVEL INVERTER WITH MULTIPLE PWM TECHNIQUES:

The multilevel converter has drawn tremendous interest in the power industry. The

general structure of the multilevel converter is to synthesize a sinusoidal voltage from

several levels of voltages, multilevel voltage source converters are emerging as a new

breed of power converter options for high power applications. The cascaded H-bridge

multilevel Inverter uses separate dc sources (SDCSs). The multilevel inverter using

cascaded-inverter with SDCSs synthesizes a desired voltage from several

independent sources of dc voltages, which may be obtained from batteries, fuel cells,

or solar cells [5]. The advent of the transformer less multilevel inverter topology has

brought forth various pulse width modulation (PWM) schemes as a means to control

International Journal of Pure and Applied Mathematics Special Issue

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the switching of the active devices in each of the multiple voltage levels in the inverter

[6].

When utilized at low amplitude modulation indices, existing multilevel carrier-based

PWM strategies have no special provisions for this operating region, and several

levels of the inverter go unused. This paper proposes some novel multilevel PWM

strategies to take advantage of the multiple levels in both a diode-clamped inverter

and a cascaded H-bridges inverter by utilizing all of the levels in the inverter even at

low modulation indices. Simulation results show what effects the different strategies

have on the active device utilization. A prototype 6-level diode-clamped inverter and

an 11-level cascaded H-bridges inverter have been built and controlled with the novel

PWM strategies proposed in this paper [7]

2.3: HARMONIC MITIGATION TECHNIQUES:

Reduces harmonic content in the network which further reduces disturbances in

telecommunication network, misbehavior in control equipments and relay

protections, measuring errors in metering system it Reduces network losses, reduces

equipment overloading & stress on insulation, Reduces cost and generates higher

revenue for the customer, Reduces unplanned outages and increases power

availability.In Modern distribution systems have very complex networks connected

with linear and Nonlinear loads. Nonlinear loads are primary thing for harmonic

distortion in a power system these harmonic distortions will be eliminated by using

MLI and SRF Technology. The internal view of Synchronous Reference Frame Theory

(SRF) control strategy for STATCOM is used In this control strategy the SRF-based

STATCOM control technique is used to generate gate pulses for controlling of

STATCOM. Here from the control strategy is designed with abc frame to d-q frame

conversion block, PLL block, HPF, PI controller, DQ to ABC conversion block and

hysteresis controller [8]-[9].

2.4: REACTIVE POWER COMPENSATION TECHNIQUES:

Shunt compensation of reactive power can be employed either at load level,

substation level or at transmission level. Compensation should be provided as close

as possible to the consumption point to avoid having to distribute this power in the

other part of network. The DSTATCOM is also coming by the STATCOM scheme; it

may operate under the distribution system.Here presents the operating principle of

the intended DSTATCOM which is basically one of the shunt FCATS devices. The

same kind of the STATCOM is the so-called operated in distribution networks is

called as distributed compensator. The key components of the DSTATCOM are a

power VSI module, which is based on the high power semi-conductor device [10].

2.5: SYNCHRONIZATION REFERENCE FRAME:

SRF control is one of the efficient controls to suppress voltage and current harmonics.

It referred d-q technique, in which transformations and its inverse transformations

of a-b-c to d-q-0 are used [11]. The basic SRF Control technique to generate reference

currents from nonlinear balanced /unbalanced load is depicted .These d-q-0


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coordinates comprises of an oscillatory component ( IoSd and IoSq ) and

averaged component ( IASd and IASq ) resulting to oscillatory in nature. In order to

avoid oscillatory response and maintain only averaged components of d-q-0

coordinates, a 2nd ordered Butterworth LPF is used. These averaged components are

stable in nature and are referred to as source current averaged component ( ISdL

).[11]

3.0 CONVENTIONAL METHODS:

3.1: FUZZY LOGIC CONTROLLER:

In FLC, basic control action is determined by a set of linguistic rules. These rules are

determined by the system. Since the numerical variables are converted into linguistic

variables, mathematical modeling of the system is not required in FC.

Fig.1.Fuzzy logic controller

TABLE I: Fuzzy Rules

3.2. PHASE SHIFTER MCPWM TECHNIQUE

Phase shifted multi carrier PWM Phase-shift MCPWM is the most common

strategy for the cascade multilevel inverter, with an improved harmonic performance


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being achieved when each single-phase inverter is controlled using three-level

modulation. To get higher ripple frequency than switching frequency, the phase

shifted PWM can be used for the multilevel inverter. Here each carrier is linked to

an individual cell and by having a suitable phase shift among carriers multilevel

stepped waveform is achieved. As switching device in each cell have same switching

frequency conditions therefore rotation of switching pulses is not required. In this

technique, all the triangular carriers have the same frequency and the same peak-to-

peak amplitude, but the phase shift occurs between any two adjacent carrier waves.

For m Voltage levels (m-1) carrier signals are required and they are phase shifted

with an angle of θ=(360°/m-1). The gate signals are generated with proper comparison

of carrier wave and modulating signal.[12]

Fig. 2. Phase shifted Pulse Width Modulation

Fig. 3. Simplified phase shifted modulation schematic

3.3.LEVEL SHIFTED MCPWM TECHNIQUE

Level shifted multi carrier PWM In this scheme, k-1 carriers (triangular) are

used for k level CMI, each carrier has same amplitude and frequency. which have


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same frequency and amplitude. Here each voltage level is associated with a carrier.

When a particular voltage level is to be generated, reference wave should be higher

than that particular carrier. This scheme will have unequal switching condition for

device in each cell, leads to unequal power distribution among cells hence rotation of

pulses among power cells can not be avoided. It can be further divided into three

types, in phase disposition (IPD), where all the carriers are in phase; [12]alternative

phase opposite disposition (APOD), where all carriers are alternatively in opposite

disposition and phase opposite disposition (POD), where all the carriers above the

zero reference are in phase but in opposition with those below the zero reference.

Fig. 4. Simplified level shifted modulation schematic

Fig. 5. In Phase Disposition Level Shifted Modulation


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Fig. 6 Alternate Phase Opposition Disposition Level Shifted Modulation

4. PROPOSED SYSTEM:

4.0. CONTROL TECHNIQUES.

4.1. SYNCHRONOUS REFERENCE FRAME CONTROL

Synchronous Reference Frame Control is one of the efficient controls to

suppress voltage and current harmonics. It refers d-q technique, in which

transformations and its inverse transformations of a-b-c to d-q-0 are used. The basic

SRF Control technique to generate reference currents from nonlinear

balanced/unbalanced load is depicted in Fig. 5.1. The load currents of abc coordinates

(I Labc ) are transformed into d-q-0 coordinates with the help of modified PLL according

to the equation (1). These d-q-0 coordinates comprises of an oscillatory component

(I~oSd and I~oSq ) and averaged component ( I~ASd and I~ASq ) resulting to oscillatory in

nature. In order to avoid oscillatory response and maintain only averaged components

of d-q-0 coordinates, a 2nd ordered Butterworth LPF is used. These averaged

components are stable in nature and are referred to as source current averaged

component ( I~SdL).[13]

Fig. 8. Shunt Controller using SRF

These reference currents ( IrefSa , IrefSb and IrefSc ) are compared with load currents (

ILa , ILb and ILc ) to generate DSTATCOM reference currents iShabc_ref . The currents of

the DSTATCOM are maintained at reference values using Hysteresis current


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controller. The hysteresis current controller is operated with a lower band 0.25A and

higher band of 0.5A to generate switching pulses to a five level diode clamped MLI-

DSTATCOM

5. RESULTS AND CONCLUSIONS:

System parameters for this study are specified in Table II.

Table II

proposed DSTATCOM System Parameters


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Fig. 9. Output of Multi Level Inverter (Five Level) STATCOM

Fig. 10. THD- 26.37% With non linear load with out DSTATCOM

The design and Analysis of the DSTATCOM has been presented using

MATLAB/SIMULINK software to test its efficacy in mitigating harmonics and

Reactive Compensation. Multi level Inverters have been employed for DSTATCOM

to reduce harmonics. Operating conditions like fault switching are analyzed and

tested. The DSTATCOM presented has shown great performance in alleviating the

harmonics. It can be deduced from the results obtained that MLI DSTATCOM

improves power quality and mitigates harmonics.

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[1] ‘Electrical Power System Quality’ by Yiting Zhao. [2] ‘A Research Review of

Power Quality Problems in Electrical P

[2] L. Tolbert, F.-Z. Peng, T. Habetler, "Multilevel converters for large electric

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[3] V. G. Agelidis, M. Calais, "Application specific harmonic performance evaluation

of multicarrier PWM techniques", Proc. IEEE PESC, pp. 172-178, 1998.

[4] Ghosh A, Ledwich. G., Power Quality Enhancement Using Custom Power

Devices, London, U.K.: Kluwer;2002. Lee Tzung-Lin.

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[7] P. Rao, M.L. Crow, Z. Yang, “STATCOM control for system voltage control

applications,” IEEE Trans. Power Delivery 15 (4) (2000) 1311- 1317.


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[8] P.S. Sensarma, K.R. Padiyar, V. Ramanarayanan, “Analysis and performance

evaluation of distribution STATCOM for compensating voltage fluctuations,” IEEE

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[9] Benysek Grzegorz, Pasko Marian., Power theories for improved power quality,

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[10] Benhabib MC, Saadate S., “New control approach for four-wire active power filter

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[11] Rahmani S, Mendalek N, Al-Haddad K., “Experimental design of a nonlinear

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[12] Kota V.R, Vinnakoti S., “SRF-based control of unified power quality conditioner

for power quality enhancement,” IEEE (EESCO), 2015, Pages: 1-6.

[13] Da Silva CH, Pereira RR, da Silva LEB, Lambert-Torres G, Bose BK, Ahn SU.,

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