series voltage regulation compensator

8/3/2019 Series Voltage Regulation Compensator

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POWER LINE CONDITIONING USING SERIES

VOLTAGE REGULATOR

HARINE RAVICHANDRAN


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Can Multilevel Inverters(MLIs) provide the voltage regulation,which can beconnected to Ac line directly without using transformers, to preventmalfunctioning of sensitive instruments and to improve the voltage reliability ?

The Series voltage regulator(MLIs), regulates the output voltage by injecting voltage in synchronismwith the supply when an upstream sag is detected ,thus protecting the loads from voltage sags.It is acost effective customer based solution to regulate the voltage sag which improves voltage quality atload side and can be directly connected to AC power line. As MLIs synthesize a near sinusoidal voltagefrom several level of DC voltage , can reach high voltages with low harmonics without the use oftransformers.Even though transformers presents advantages in terms of voltage matching, protection

and insulation it increases the cost and reduces the overall efficiency of the compensator.DC voltagesources can be replaced by distributed or renewable energy sources like fuel cells,solar cells etc. TheMLI structure can overcome the shortcomings in solid state switching device ratings, limitations inoperation at high frequency mainly due to switching losses and the problems associated with series-parallel combination of devices that are necessary to obtain capability of handling high voltage andcurrents. I have chosen the cascaded MLI which is having lot of advantages as the power line conditioner.


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The power circuit consists of series of N independent H-bridge (single phasefull bridge ) inverter units, where N depends ono The injected voltage harmonic distortion and current harmonic

distortion requirements.

o The magnitude of the injected voltage requiredo The available power switch voltage ratings

Each H-bridge inverter is fed from separate DC source (SDCS), which may beobtained from batteries ,fuel cells or solar cells.

Each H-bridge inverter can generate three different voltage outputs +Vdc, 0and -Vdc by connecting the DC sources to the AC output by differentcombination of the four switches S1,S2,S3,S4

The AC output of each of the different full bridge are connected in seriessuch that the synthesized output voltage waveform is the sum of theinverter outputs.

The number of output voltage levels m=2N+1 where N is the number ofseparate DC sources.

The advantages of cascaded MLIo Modularised layout and packagingo manufacturing process quick and inexpensiveo better redundancy and high efficiencyo suitable for medium to high power applicationso an ideal interface between a utility and renewable energy sources such

as fuel cell, solar panels etc.

Cascaded MLI


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The Experiment- The working Principle The system configuration of the cascaded multilevel inverter for

series voltage compensation in one phase of a distribution system is

illustrated in figure where ZS and ZL represent the source and loadimpedance's respectively. The back-to-back thyristor bypass in parallel conducts the line

current under normal operating conditions when no sag/swell ispresent and also protects the multilevel inverter from fault current.

Compensation is initiated when a sag or swell is detected (i.e theamplitude of the supply load voltage (VS or VL) deviates from thereference voltage (VRef)).

The back-to-back connected thyristors first have to be forcecommutated before the multilevel inverter starts to inject a voltagein series with the line.


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During sag or swell, all the Full Bridge Inverter units of the multilevelinverter are switched on.

The compensating voltage is injected in synchronism with the supply

voltage under sag conditions and out of synchronism under swellconditions.

At the end of sag/swell or when a load fault current is detected with ananalog circuit, all the FBI units of the MLI are switched into a zero state

before the thyristors are switched on. After a sufficient turn on delay for the thyristors, all FBI units are

switched off. The neuro controller is trained using quasi newton back-propagation

algorithm to synthesize gate pulses. These gate pulses controls the on-time of the devices in FBI depending

upon the output feedback received.

The Experiment- The working Principle


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Pulse Width Modulation(PWM)

Sinusoidal PWM is developed as modulation stratergy. In this method, a number oftriangular carriersare compared with a controlled sinusoidal modulating signal andthe switching rules for the semiconductor devices are decided by the intersection ofthe carrier waves with the modulating signal. For a five-level inverter, a modulatingsignal and four carrier waves are required are shown in Fig. All of the carriers are in

phase and have the same frequency fc and the same peak to peak amplitude Ac.


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The Experiment

The NN is off-line trained using input data (error voltage) and the target(compensating signal) pairs.

The weights obtained after 5000 epochs of the training phase are used

in NN is used to control the inverter on-line.

The error in output voltage is fed as the input to the NN. The

compensating signal instead of the whole modulation signal is collectedas the output of the NN.

Quasi-Newton back-propagation algorithm which has a powerful (fast)

convergence property known as quadratic convergence is employed to

update weights in this work.

This algorithm requires less memory space than other training algorithms.

Training Of Neural Network(NN) controller:


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dSPACE BASED IMPLEMENTATION FOR SEVENLEVEL INVERTER BASED SERIES VOLTAGEREGULATOR


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The specifications of the dSPACE DS1104 system:

Power PC603e running at 250MHz 8 ADC and 8 DAC channels

20 digital input/output lines Incremental encoder interface Serial interface Slave DSP TMS 320F240 for three phase PWM signals 8 MB boot flash RAM, 32 MB SDRAM

The MATLAB and SIMULINK block diagram environments are useful for design andanalysis of control systems. The dSPACE DS1104 controller board provides the means foracquiring data for system identification and implementing discrete time controllers foranalog plants. The dSPACE system consists of three components: the DS1104 controllerboard mounted within a personal computer, a breakout panel for connecting signal linesto the DS1104 controller board and software tools for operating the DS1104 boardthrough the SIMULINK block diagram environment.


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Specifications of chosen arrangemeny(Experiment)


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The Experimental Setup


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Results And Observations

Output voltage of MLI(5 steps, 2 H-bridges connected in series)


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Steady state voltage, current and harmonic spectrum


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The supply voltage sag is generated (measured in volts).And after somecycles load disturbance is also generated.


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When I used the MLI voltage regulator, the output voltage wasmaintained constantly, though there was both load disturbanceand input voltage sag.


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The supply voltage swell is introduced (measured in

volts)and after some cycles load disturbance is alsogenerated.


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When I used the MLI voltage compensation, the outputvoltage was maintained constantly, though there was bothload disturbance and input voltage swell.


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Observations and advantages of my regulator:

The voltage regained its original value within 0.1 Milliseconds

The total harmonic distortion is less in the output even whenboth the disturbances are simulated at the same time as theinjected voltage is from MLI which is approximately asinusoidal voltage .

The voltage redefines within half a cycle, only because of theneural network controller(even though the training of theNN is time-consuming)

The capacity of the compensator system can be increasedjust by adding a full bridge unit in series.

As the devices are operated at 50 Hz, the losses due toswitching is less.


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MY BIGGER AIM!

My compensator can be made more eco-friendly by using

renewable energy sources like solar panels,fuel cells etc. as DCsource to the MLI.

The usage of distributed power resources can be used for highvoltage power system to provide reliable voltage in rural.

The neural network can be trained using yet betteralgorithms.

I have implemented in real time for single phase and lowvoltage due to cost constraints. I will extend to three phasepower voltage so that this inverter can be used to achievereliable voltage for practical use.

series voltage regulation compensator

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