Практика Shadowing: Back to Back HVDC Modular Multilevel Converter for Transient Voltage Part 1 - Изучайте разговорный английский по видео

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This is Jaan Girbadah Sumrur, Assistant Professor at Electrical Engineering Department, Sakhar IBE University.

In our today's video we will discuss one of the research paper which is titled

Back -to -Back HVDC Modular Multi -Level Convertor for Transient Voltage Dib Mitigation in Passive Networks.

In my previous video I explained this research paper, Design and Control of Modular Multi -Level Convertor for Voltage Dib Mitigation.

Now this work is done in 2022 and this work is totally inspired

and this work totally follows basically this work which was done in 2018.

2018. Alright.

This was a thesis performed by a student of Bachelors.

And he worked in CERN, European Organization for Nuclear Research for one year.

Okay.

For nuclear research laboratory like CERN, where the exceptionally high power quality conditioners are required,

So there is a dynamic load, high power quality conditioners are used in CERN.

The immunity against transient voltage dip is a vital importance.

So if there comes the problem of voltage dip on the grid side, this is very important to mitigate that voltage dip.

So the problem statement was to overcome the issue of voltage dip coming on the grid side that was affecting their load.

By using the traditional HVDC MMC back -to -back configuration with properly dimensioned submodule capacitor, voltage diffs can be mitigated instantaneously.

So they performed the steady on MMC back -to -back configuration to mitigate that issue of voltage dip,

improving power quality of the network.

The diminishing of the capacitor is shown as one of the key elements of this paper, yes,

because the fault right through technique applied in this paper is

by using inherent energy storage capacity of the capacitors in the MMV.

That energy in capacitors is basically utilized to compensate for the missing energy of the voltage dip on the grid side.

Firstly, the actual voltage dip statistics recorded at Sun are presented

and described than the traditional capacitor submodule dimension method present compared to proposed energy design rule.

To validate the energy dimension mitigation perform a detailed Simulink model of 220 MVHVDC modulo multilabular consider is described

and the main results are presented.

So here they use MATLAB Simulink.

For this study, the paper concludes with the main conclusion of this study and the future works.

Today's introduction, today several stable solutions.

There are several solutions available for voltage mitigation.

If for smaller load, UPS can be a good solution to get uninterrupted supply.

In case of dip, UPS can work better.

But the limitation here is the size of energy storage, which is preferable for battery storage system, and for small systems this can work.

But for higher rating, the solution of UPS is not interesting, then researchers move towards DVR.

But again, DVR is not the optimum solution.

This paper suggests that the optimum solution is to, if you can afford, then the back -to -back HPDC -MMC can be a good

solution for mitigating voltage -up issues to deliver constant load power supply to dynamic loads.

The idea of using HVDC system completely based on VAC converters to supply a high power demand

with high quality was analyzed in SEVEN where certain operation margin allowed to take over one converter from Nether and Kesa fault.

If no operation margin is kept, all converters are running at one per unit, then another strategy is to implement the mitigate,

has to be implemented to mitigate transient voltage dip.

So if all the converters running at their full capacity one per unit,

then there need to be some fault right through strategy applied to mitigate the voltage dip,

voltage sake issue occurring at the gate side.

One of the solutions used by researchers in previous days was

by allowing higher currents to flow during the time of transient voltage dip.

a compensation effect could be attained.

So if there was a voltage dip, so to compensate that missing energy of the voltage dip or voltage sake,

higher current, probably two times more than normal current, was taken from the grid to mitigate that, to compensate that missing energy.

But this is not a good solution, not recommended.

This solution was investigated in research paper 8, concluding that by allowing two times the nominal current,

the HVDCVAC solution can protect our network from voltage dip.

So they observed that if you, during the voltage dip, if you take two times more current than the normal current,

the voltage dip issue was being solved out.

Regarding the specific voltage dip mitigation for HVDC links, MMC topology results the most interesting.

For these convertors, the electric energy is stored in the capacitor

which they need in any case for the normal operation can be partially used to support the voltage during transient voltage dips.

So as you know that in MMC, in case of half -built cell or full -built cell,

both topologies or every topology has a cell, a capacitor cell.

And one of the key characteristics of MMC is inherent energy storage capability.

So that energy can be utilized to compensate for the missing energy, caused missing energy due to the voltage dip or voltage.

So this capacitor energy can be potentially utilized in this application.

In principle, it could be expected that they provide the fast response thanks to the fast release of energy in the capacitor.

The energy in the capacitor can be released fast.

And fast enough that your DC link does not go to the undervoltage.

And the load should not experience even slight disturbance.

So you should release the capacitor energy very quickly, and this is possible to release it,

so that load may not get disturbance.

This voltage -dependent grid side should not affect the load.

This is the objective.

To explore the potential application of HVDC MMC for voltage -dependent mitigation purpose,

an essential question is how much of capacitor energy is needed for good performance.

This is the question.

So now the question is you need to know how much is missing energy due to the voltage dip

and how much extra energy you need to store in the capacitor to mitigate

that dip issue or to compensate the missing energy.

How much extra energy do you need to store it?

In this sense the first decision to be made is to choice between the transient voltage voltage dip mitigation strategies,

and increasing line current strategy and energy storage based solution.

So there are two approaches.

One approach to mitigate that voltage dip strategy is increasing line current strategy, which is not good, because if you are using increasing line current strategy,

then the higher currents two times more than normal current will flow.

In that case, the converter size will be overrated, converter station will be more costly, more having more footprint weight.

So this is not recommended.

The recommended approach here in this paper, the energy storage -based solution.

But now researchers are working that even the best choices,

the controller design should be such effective that neither we should prefer this line current strategy or energy -based storage system.

But there should be automatic switching.

The controller should be fast enough and robust enough to mitigate this issue.

So researchers are also working in this area.

Anyhow, in this paper the technique suggested is energy storage based solution.

We will discuss energy storage based solution.

The first storage strategy is allowing the rectifier to draw increased current during the voltage dips such

that the DC bus transfers nominal power at all times.

With the inverter synthesizing AC voltage for the load, applying this solution with MMC means

that semi -calorie switching devices in sub -module capacitor must be

highly overrated compared to record rating for normal operating condition in the rectifier, making the solution less elegant and interesting.

Therefore, increasing line current is not good enough because it will increase the overall converter station size cost.

The second study which is one of the one

100

which is the one proposed in this paper is to design the MMC sub -module

101

capacitors according to dedicated energy calculation presented in the energy calculation chapter.

102

The rectifier shall be designed to draw nominal current from the gate during a transient voltage dip,

103

extracting the maximum allowed power to optimize the needed storage for dip mitigation.

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The advantage is that both rectifier inverter will be dimensioned for normal operation condition

105

and by using proposed design method for the overall system design optimum with it.

106

So this is a better approach to use that capacitor energy storage property to mitigate this dip Thank you.

107

In general, the MMC shows very high efficiency and provides several power quality conditioning features to passive networks, such as voltage dip mitigation, reactive power compensation.

108

So reactive power compensation is also possible with MMC -based HVDC system.

109

A passive network in this synopsis in the paper is defined as a network with a short circuit ratio of zero,

110

which means no generation of energy.

111

Okay.

112

Behind acting as a dip mitigation,

113

the inverter can provide reactive power support for the passive load network in two coordinates and even supporting pulsating dynamic loads.

114

So this is an additional advantage

115

that reactive power support of the load is also possible with reactive power controller on the inverter side.

116

In the case of particle excise, this could be a very beneficial feature for it could replace a static VR compensator,

117

so no need of a static VR compensator in this case.

118

If you have back -to -back HVDC MMC system, the rectifier has the ability to support the grid with reactive power injection during phase

119

and can allow power oscillation dipping and grid destabilization.

120

Lastly, the system features steady state control allowing high precision of voltage and frequency regulation for the passive network.

121

So even during this voltage dip, there will be no effect on the load.

122

The load will be getting the constant power supply.

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There will be no disturbance on the load side.

124

This paper is in general analysis of the potential of transient voltage mitigation of an MMC -based HVDs back -to -back link.

125

An important part is the dimensioning of the capacitors.

126

This is very important.

127

Analyze an energy dimensioning chapter, which highlights also the correlation between storage size and dip mitigation performance.

128

So certainly the storage size capacitor dimensioning will depend upon what is the dip severity, how much dip is happening,

129

for how many seconds, how much amplitude of dip is there, depending upon the dip severity, amplitude of the dip, time of the dip,

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capacitor dimensioning will be performed, energy storage size will be performed.

131

And this is performed in detail in the thesis work of this same author.

132

You can also refer to that thesis of this author.

133

After the main simulation model is present, including also the control circuit, the conclusion shows the main result concerning dip mitigation performance.

134

OK, the energy dimensioning, which is very important because it uses capacitor energy storage property.

135

So energy dimensioning of capacitor becomes important.

136

The target of this paper is to show the potential of MMC -based HPD -link system for transient voltage dip mitigation

137

and give insight in energy storage calculation for the modules.

138

This will mean a new proposed design rule for MMC converter when transient voltage dip mitigation is required.

139

The traditional way for storage design in the module

140

which is done in the industry is to design the energy storage of MMC converter around 30 to 40 kilojoule per mva.

141

So converter registration, traditional way of storage design is that range is 30 to 40 kilojoule per mva per converter registration.

142

For a break to break system this results in total system energy because one is a rectifier other is inverter,

143

so total system energy is of 60 to 80 kJ per mVA.

144

But with the object or dip mitigation,

145

a new design for the value of stored energy per mVA has to be derived because this is for the normal case.

146

But if you want to mitigate the voltage dip without taking increased line current strategies then this need to be recalculated.

147

The first step is to analyze the discharge capabilities of submodule capacitors.

148

If the modular multilevel converter is assumed to operate with a DC voltage of 1 per unit,

149

so the requirement is that you need to maintain DC voltage 1 per unit, means whatever the desired reference voltage is, that should be tracked.

150

In per unit it should be 1 per unit.

151

At modulation index of 0 .8 in a steady state.

152

So in a steady state, modulation index value uses, you prefer 0 .8.

153

The inverter is limited to minimum DC voltage input of 0 .8 per unit.

154

That means DC link should not fall below 0 .8 per unit.

155

If it falls below the 0 .8, if it becomes 0 .4, 0 .5 per unit, then the inverter has to operate in our modulation,

156

which is not required, which is a big problem.

157

Our modulation is an issue, and if there comes opposite problem, not the undervoltage, but our voltage in the DC link,

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that is also an issue that will burn the DC cable, our MMC converter station and HVDC can collapse.

159

So both under -voltage and over -voltage in the DC link are not desired.

160

The total energy stored for both inverter and rectifier depends on DC voltage of the bus.

161

The following is the fundamental equation for energy in the capacitor.

162

This is a well -known equation of energy stored in the capacitor 1 over 2 Cv square.

163

With this in mind, the total energy store must be high

164

that after mitigating a dip the DC voltage should not be below 0 .8 per unit based on the previous equation. So, we...

165

We have to make sure that capacitor discharges the energy fast enough so that DC voltage should not fall below 0 .8.

166

This means that capacitor only allowed to discharge up to 36 % of their initial steady -state charge.

167

This result concludes the total energy of the capacitor should be damaged 2 .77 times

168

the missing energy for the inverter operating with modulation index of 0 .8 means if the missing energy,

169

whatever the missing energy is divided by 0 .36

170

this means the missing energy stored in the capacitor should be 2 .77 times more than the missing energy.

171

Calculate the missing energy due to the voltage dip

172

and then you should store 2 .77 times more as compared to E missing, multiplied by E missing.

173

So let's say if E missing is 0 .3 then E stored should be 2 .77 into 0 .3.

174

Second step is to find the missing energy of the system caused by the dip.

175

So a statistical analyzer of all mile voltage dip in a highly sensitive distribution present in figure 1.

176

This shows that this picture shows voltage dip magnitude percentage and for the time,

177

how much time the dip remains.

178

And accordingly, depending upon this curve,

179

we will come to know that how much energy need to be stored in a back -to -back HVDC MMC system.

180

Okay.

181

In a function called dip severity is introduced, dip severity, this function is a dip magnitude multiplied by dip duration.

182

If the dip duration, let us say if it is for 75 millisecond

183

and the dip magnitude is 50 50 % multiplied by 0 .75 ms will be the dip severity. So

184

if you multiply both dip duration with the dip magnitude

185

you will get dip severity where dips are assumed by 3 phase dips.

186

The calculation operates in per unit system with 1 second days per unit in time.

187

This makes power and energy base equal.

188

Figure 2a shows histogram of dip severity for all required dips and log logistic distribution function is fitted to data.

189

As it can be observed the majority of registered voltage dips are included in a window of 50 % at 150 milliseconds.

190

So figure 2a, the data was collected, it was observed

191

that the most repeated pattern of the dip severity was 50 % dip for 150 milliseconds in the CERN network.

192

Figure 2b shows distribution density function rate and the cumulative function

193

essentially shows how to dimension the stored energy of the converter as a function of confidence.

194

With 99 % being the chosen value for the study,

195

more trivially explained that 99 % confidence translates to 99 % of all the voltage diff will be mitigated.

196

So in this research paper,

197

Here the capacitor dimensioning or energy dimensioning is made not 60 to 80 kJ per mEV

198

because this is for the normal case but for voltage dip this needs to be recalculated.

199

So it is designed for such a value so that 99 % of dips are successfully mitigated.

200

The fact that rectifier will always draw a nominal current from the grid means

201

that dip severity in the faked missing energy caused by the dip.

202

So E missing is current dip, change in current dip multiplied by change in V dip multiplied by time in T dip,

203

how much time dip lasts.

204

By graphical solution of our 99 % confidence figure to be the missing energy is seen as 0 .0375 per unit.

205

So if you see here,

206

the missing energy due to the dip in the sun network with

207

that particular load was missing energy in most of the time, 99 % of the time was 0 .0375 per unit.

208

This was the missing energy due to the dip.

209

So if this is a missing energy now, how much energy should be stored in the capacitors?

210

it should be e stored should be 2 .77 times this missing energy

211

so multiply 2 .77 with this value you will get

212

that total stored energy should be 0 .104 per unit of the system for the system

213

Assuming a system of 1 mV rating this means that the reactive inverter together must have an energy of

214

104 .0 .104 means it should have energy of 104 kJ per mVa.

215

Normally it is 60 to 80 kJ per mVa but for the mitigation of voltage dip and for

216

compensating the missing energy

217

and to make sure the 99 percent of the voltage dip

218

severities are successfully mitigated the system should be now having energy storage of 104 kJ per mVA.

219

Now this is the disadvantage

220

that overall energy diminishing is changing overall capacitor sizing will be different

221

so this will make this converter station little bit cost a little bit expensive as compared to normal.

222

So this approach has the disadvantage in terms of cost.

223

Comparing this result with the commonly used 60 to 80 kJ per meter shows by only a slight increase of stored energy.

224

So there is a slight increase, normally it is 80 kJ per mva

225

but to mitigate the voltage it should be the system should be 104 kJ per mva.

226

99 % all volt dips will be mitigated if the system is off, 104 kilojoule per MVA.

227

Energy storage is this one.

228

OK.

229

So in the next part, we will discuss simulation model and the results.

230

Thank you.

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Этот урок разговорной практики построен на видео «Back to Back HVDC Modular Multilevel Converter for Transient Voltage Part 1». Чаще всего повторяются слова: dip, energy, voltage, capacitor, missing. В этом видео 230 предложений и 3097 слов для шедоуинга. Речь длится 21:27. Говорящий держит ровный темп — около 144 слов в минуту, удобный для шедоуинга. Только 77% слов входят в 3000 самых частых слов английского языка, поэтому лексика сложная.

Ключевая лексика этого видео

15 слов из видео, которые стоит выучить, с произношением и значением:

Слово	Произношение	Значение
voltage существительное	/ˈvəʊltɪd͡ʒ/	напряже́ние, вольта́ж
mitigate глагол	/ˈmɪt.ɪ.ɡeɪt/	смягча́ть, уменьша́ть
dimension существительное	/daɪˈmɛn.ʃən/	аспе́кт
severity существительное	/səˈvɛɹ.ə.ti/	стро́гость
dip глагол	/dɪp/	мака́ть, макну́ть
grid существительное	/ɡɹɪd/	се́тка, решётка
reactive прилагательное	/ɹiːˈæktɪv/	реактивный
compensate глагол	/ˈkɑm.pənˌseɪt/	компенси́ровать, возмеща́ть
steady прилагательное	/ˈstɪdi/	усто́йчивый
passive прилагательное	/ˈpæs.ɪv/	пасси́вный, безде́ятельный
magnitude существительное	/ˈmæɡnɪtjuːd/	величина́, разме́р
researcher существительное	/ˈɹiˌsɝ.t͡ʃɚ/	иссле́дователь, иссле́довательница
module существительное	/ˈmɑd͡ʒul/	мо́дуль
calculation существительное	/ˌkælkjuˈleɪʃn̩/	вычисле́ние, исчисле́ние
nominal прилагательное	/ˈnɒm.ɪ.nl̩/	именно́й

Фразовые глаголы, которые вы услышите

Слово	Значение
take over глагол	брать на себя́, взять на себя́

Грамматика в этом видео

Конструкции, которые говорящий использует чаще всего, с точными словами из видео:

Конструкция	В видео
Пассивный залог be + причастие прошедшего времени — важно, что происходит, а не кто это делает	is titled · are required · can be mitigated
Придаточные определительные who / which + предложение — уточнение о человеке или предмете	paper which is · work which was · storage, which is

Произношение, на которое стоит обратить внимание

Звуки «th»: thesis /ˈθisɪs/, synthesize /ˈsɪnθəsaɪz/
Звуки «sh» и «zh»: dimension /daɪˈmɛn.ʃən/, calculation /ˌkælkjuˈleɪʃn̩/, compensation /ˌkɑm.pənˈseɪ.ʃən/, duration /dʒʊˈɹeɪ.ʃən/, equation /ɪˈkweɪ.ʒən/
Длинные слова — следите за ударением: severity /səˈvɛɹ.ə.ti/, compensation /ˌkɑm.pənˈseɪ.ʃən/, successfully /səkˈsɛs.fə.li/, registration /ˌɹɛd͡ʒ.ɪˈstɹeɪ.ʃən/, capability /ˌkeɪ.pəˈbɪl.ɪ.ti/

Звуки, трудные для русскоязычных:

/w/ — губы округлены, это не /v/: equation /ɪˈkweɪ.ʒən/, frequency /ˈfɹiːkwənsi/, requirement /ɹɪˈkwaɪɹmənt/
/h/ — лёгкий выдох, а не русское «х»: inherent /ɪnˈhɪəɹənt/, highlight /ˈhaɪˌlaɪt/, anyhow /ˈɛn.i.haʊ/, histogram /ˈhɪstəˌɡɹæm/
Звонкие согласные в конце слова — не оглушайте их: voltage /ˈvəʊltɪd͡ʒ/, grid /ɡɹɪd/, reactive /ɹiːˈæktɪv/, passive /ˈpæs.ɪv/, magnitude /ˈmæɡnɪtjuːd/

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Что такое техника Shadowing?

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Лексика и советы по произношению к этому уроку

Ключевая лексика этого видео

Фразовые глаголы, которые вы услышите

Грамматика в этом видео

Произношение, на которое стоит обратить внимание

Как заниматься с этим видео

Что такое техника Shadowing?