high fq link of asymetry inverter model.ppt

8/10/2019 high fq link of asymetry inverter model.ppt

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Non-Isolated High-Frequency-Link to Feed Auxiliary

Bridges of AsymmetricalCascaded Multilevel

Inverter


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Presentation layoutIntroduction Advantage of Multilevel inverterLiterature survey on operation of different multileveltopologyNon isolated high frequency link of asymmetriccascaded multilevel inverter Basic operation of bidirectional buck-boostconverter proposed topology

operation of proposed topology control scheme of proposed topology simulation result conclusion


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IntroductionNumerous industrialapplications require higherpower apparatus in recentyears. Multilevel inverter isintroduced for the abovecause.

Multilevel inverters arecurrently consider as one ofthe industrial solution for highdynamic performance andpower-quality demandingapplication

It can cover a power rangefrom 1 to 30 MWIt can be easily interfaced tothe renewable energysources.


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Advantage of Multilevel inverter

Multilevel inverters have a higher voltage operating capabilityThey are able to generate output voltages with very low distortionand reduced voltage derivatives dv/dt. They are able to bring in input current with very low inputdistortion.

They are able to produce smaller common mode (CM) voltage.In addition, using complicated modulation methods, CM voltagescan be eliminated.They can be functioned with a much lower switching frequency.

The disadvantage of the multilevel converter is that it required a hugeamount of semiconductors switches.

Another disadvantage which is to be mention is that the small voltagesteps are typically formed by isolated voltage sources which may notalways be readily available and series capacitors require voltage

balance.


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Diode Clamped multilevel inverter

Component number

Levels m

Switchesand paralleldiodes

2(m-1)

Capacitors m-1

ClampDiode

(m-2)(m-1)


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Advantages

When the number of levels is high enough, harmonic contentwill be low enough to avoid the need for filters.Efficiency is high due to all devices which are being switchedat the fundamental frequency.We are able to control the reactive power flow.The control method is easy for a back to back intertiesystem.

Disadvantages

Excessive clamping diodes are being required when thenumbers of levels get high.It is hard to do a real power flow control for individualconverter.


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Flying Capacitor multilevel inverter

Component number

Levels m

Switchesand paralleldiodes

2(m-1)

DC LinkCapacitors

m-1

Clamp

capacitors (m-2)

(m-1)/2


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Advantages

Huge amount of storage capacitors will provide additional ridethrough capabilities during power rage.

Switch combination redundancy are provided for balancing differentvoltage levels.

When the number of levels is high enough, the harmonic contentwill be low enough not to use the the filter.

We are able to control both the real and reactive power flow, andmaking a possible voltage source converter candidate for high voltagedc transmission.

Disadvantages

When the number of converter levels get high, a huge amount ofstorage capacitors is required. Those high level systems are moredifficult to package and those bulky capacitors are expensive.

The switching frequency and switching losses will sore high for realpower transmission and the converter control will get very complicated.


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Cascaded H-Bridge multilevel inverter


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Component Number Levels m Switches and paralleldiodes

2(m-1)

DC Link Capacitors m-1/2


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Advantages

The least number of components are required comparingamong all multilevel converters in order to obtained thesame number of voltage levels.

Modularized circuit layout and packaging is possible as

each level has the same structure, and there are no extraclamping diodes or voltage balancing capacitors.Soft switching can be used.

Disadvantages

It required separate dc sources for real power conversions,and therefore its application is limited.


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PWM for multilevel inverters

Multilevel PWM methods uses high switchingfrequency carrier waves in comparison to the referencewaves to generate a sinusoidal output wave.

To reduce harmonic distortions in the output signalphase-shifting techniques are used .

There are several methods that change disposition ofor shift multiple triangular carrier waves. The number

of carrier waves used is dependent to the number ofswitches to be controlled in the inverter.


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Asymmetrical multilevel inverters can generate very highnumber of levels in output voltage. power shared by lower voltage bridges is very small compare to the

bridges with highest voltage. Application of asymmetric topology is having the advantage of high

number of levels, but the power handled by different bridges of aphase is quite different. Most of the power is handled by the highestvoltage bridge.

The auxiliary bridges are fed by high frequency link isolatedconverters. But, this high frequency link requires too many powerelectronic devices that reducing efficiency.

Here proposes a novel technique to integrate bi-directional nonisolated buck-boost converter with the conventional asymmetric CHBinverter. This will feed the auxiliary source with the help of twoswitches.

Non isolated high frequency link of asymmetric cascadedmultilevel inverter


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Bi-directional Buck-Boost Converter

In buck boost converter use two IGBT with reversediode to make it bi-directionalWhen DC source transfer power to capacitor,S1 IGBT

and S2 Diode workingwhen R L is negative, DC source fed by capacitorvoltage.S2 IGBT and S1 Diode operating in regeneratingmode.


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(a)Source is building current in the inductor,(b) Inductor current is pumped in to the capacitor.


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(a) Capacitor is releasing its charge by buildingcurrent in the inductor.

(b) Inductor is returning its energy to the source.


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Conventional asymmetric nine level H-bridge inverter


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Circuit diagram of the bi-directional converter integratedasymmetric CHB inverter with two H-bridges.


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(a) Main source is building current in the inductor,(b) Inductor current is pumping energy to the dc bus capacitor

of the auxiliary source


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(a) DC-bus capacitor of the auxiliary bridge is releasing charge bybuilding current in the inductor

(b) Inductor current is pumping its energy back to the source.


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Current loop control strategy for converter


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Gate pulse across switch Q12 and gate pulse across switch Q21


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DC-bus voltage of the auxiliary bridge, output current and line

voltage


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Inverter switchesoperating atfundamental

frequency of 50Hz .The total harmonic

distortion (THD) ofload current is

1.99% and that ofline to line voltage

is 6.03% .


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when inverterswitches

operating athigher switching

frequency of

10KHz.The totalharmonic

distortion (THD)of load current is2.19% and that of

line to linevoltage is 9.41% .


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Conclusion


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Thanking You

high fq link of asymetry inverter model.ppt

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