Prática de Shadowing: Back to Back HVDC Modular Multilevel Converter for Transient Voltage Part 1 - Aprenda a falar inglês com vídeo
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This is Jaan Girbadah Sumrur, Assistant Professor at Electrical Engineering Department, Sakhar IBE University.
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In our today's video we will discuss one of the research paper which is titled
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Back -to -Back HVDC Modular Multi -Level Convertor for Transient Voltage Dib Mitigation in Passive Networks.
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In my previous video I explained this research paper, Design and Control of Modular Multi -Level Convertor for Voltage Dib Mitigation.
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Now this work is done in 2022 and this work is totally inspired
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and this work totally follows basically this work which was done in 2018.
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2018. Alright.
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This was a thesis performed by a student of Bachelors.
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And he worked in CERN, European Organization for Nuclear Research for one year.
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Okay.
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For nuclear research laboratory like CERN, where the exceptionally high power quality conditioners are required,
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So there is a dynamic load, high power quality conditioners are used in CERN.
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The immunity against transient voltage dip is a vital importance.
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So if there comes the problem of voltage dip on the grid side, this is very important to mitigate that voltage dip.
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So the problem statement was to overcome the issue of voltage dip coming on the grid side that was affecting their load.
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By using the traditional HVDC MMC back -to -back configuration with properly dimensioned submodule capacitor, voltage diffs can be mitigated instantaneously.
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So they performed the steady on MMC back -to -back configuration to mitigate that issue of voltage dip,
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improving power quality of the network.
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The diminishing of the capacitor is shown as one of the key elements of this paper, yes,
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because the fault right through technique applied in this paper is
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by using inherent energy storage capacity of the capacitors in the MMV.
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That energy in capacitors is basically utilized to compensate for the missing energy of the voltage dip on the grid side.
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Firstly, the actual voltage dip statistics recorded at Sun are presented
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and described than the traditional capacitor submodule dimension method present compared to proposed energy design rule.
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To validate the energy dimension mitigation perform a detailed Simulink model of 220 MVHVDC modulo multilabular consider is described
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and the main results are presented.
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So here they use MATLAB Simulink.
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For this study, the paper concludes with the main conclusion of this study and the future works.
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Today's introduction, today several stable solutions.
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There are several solutions available for voltage mitigation.
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If for smaller load, UPS can be a good solution to get uninterrupted supply.
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In case of dip, UPS can work better.
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But the limitation here is the size of energy storage, which is preferable for battery storage system, and for small systems this can work.
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But for higher rating, the solution of UPS is not interesting, then researchers move towards DVR.
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But again, DVR is not the optimum solution.
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This paper suggests that the optimum solution is to, if you can afford, then the back -to -back HPDC -MMC can be a good
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solution for mitigating voltage -up issues to deliver constant load power supply to dynamic loads.
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The idea of using HVDC system completely based on VAC converters to supply a high power demand
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with high quality was analyzed in SEVEN where certain operation margin allowed to take over one converter from Nether and Kesa fault.
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If no operation margin is kept, all converters are running at one per unit, then another strategy is to implement the mitigate,
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has to be implemented to mitigate transient voltage dip.
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So if all the converters running at their full capacity one per unit,
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then there need to be some fault right through strategy applied to mitigate the voltage dip,
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voltage sake issue occurring at the gate side.
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One of the solutions used by researchers in previous days was
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by allowing higher currents to flow during the time of transient voltage dip.
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a compensation effect could be attained.
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So if there was a voltage dip, so to compensate that missing energy of the voltage dip or voltage sake,
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higher current, probably two times more than normal current, was taken from the grid to mitigate that, to compensate that missing energy.
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But this is not a good solution, not recommended.
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This solution was investigated in research paper 8, concluding that by allowing two times the nominal current,
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the HVDCVAC solution can protect our network from voltage dip.
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So they observed that if you, during the voltage dip, if you take two times more current than the normal current,
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the voltage dip issue was being solved out.
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Regarding the specific voltage dip mitigation for HVDC links, MMC topology results the most interesting.
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For these convertors, the electric energy is stored in the capacitor
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which they need in any case for the normal operation can be partially used to support the voltage during transient voltage dips.
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So as you know that in MMC, in case of half -built cell or full -built cell,
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both topologies or every topology has a cell, a capacitor cell.
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And one of the key characteristics of MMC is inherent energy storage capability.
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So that energy can be utilized to compensate for the missing energy, caused missing energy due to the voltage dip or voltage.
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So this capacitor energy can be potentially utilized in this application.
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In principle, it could be expected that they provide the fast response thanks to the fast release of energy in the capacitor.
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The energy in the capacitor can be released fast.
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And fast enough that your DC link does not go to the undervoltage.
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And the load should not experience even slight disturbance.
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So you should release the capacitor energy very quickly, and this is possible to release it,
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so that load may not get disturbance.
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This voltage -dependent grid side should not affect the load.
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This is the objective.
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To explore the potential application of HVDC MMC for voltage -dependent mitigation purpose,
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an essential question is how much of capacitor energy is needed for good performance.
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This is the question.
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So now the question is you need to know how much is missing energy due to the voltage dip
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and how much extra energy you need to store in the capacitor to mitigate
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that dip issue or to compensate the missing energy.
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How much extra energy do you need to store it?
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In this sense the first decision to be made is to choice between the transient voltage voltage dip mitigation strategies,
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and increasing line current strategy and energy storage based solution.
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So there are two approaches.
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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,
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then the higher currents two times more than normal current will flow.
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In that case, the converter size will be overrated, converter station will be more costly, more having more footprint weight.
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So this is not recommended.
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The recommended approach here in this paper, the energy storage -based solution.
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But now researchers are working that even the best choices,
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the controller design should be such effective that neither we should prefer this line current strategy or energy -based storage system.
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But there should be automatic switching.
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The controller should be fast enough and robust enough to mitigate this issue.
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So researchers are also working in this area.
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Anyhow, in this paper the technique suggested is energy storage based solution.
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We will discuss energy storage based solution.
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The first storage strategy is allowing the rectifier to draw increased current during the voltage dips such
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that the DC bus transfers nominal power at all times.
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With the inverter synthesizing AC voltage for the load, applying this solution with MMC means
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that semi -calorie switching devices in sub -module capacitor must be
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highly overrated compared to record rating for normal operating condition in the rectifier, making the solution less elegant and interesting.
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Therefore, increasing line current is not good enough because it will increase the overall converter station size cost.
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The second study which is one of the one
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which is the one proposed in this paper is to design the MMC sub -module
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capacitors according to dedicated energy calculation presented in the energy calculation chapter.
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The rectifier shall be designed to draw nominal current from the gate during a transient voltage dip,
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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
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and by using proposed design method for the overall system design optimum with it.
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So this is a better approach to use that capacitor energy storage property to mitigate this dip Thank you.
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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.
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So reactive power compensation is also possible with MMC -based HVDC system.
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A passive network in this synopsis in the paper is defined as a network with a short circuit ratio of zero,
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which means no generation of energy.
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Okay.
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Behind acting as a dip mitigation,
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the inverter can provide reactive power support for the passive load network in two coordinates and even supporting pulsating dynamic loads.
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So this is an additional advantage
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that reactive power support of the load is also possible with reactive power controller on the inverter side.
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In the case of particle excise, this could be a very beneficial feature for it could replace a static VR compensator,
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so no need of a static VR compensator in this case.
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If you have back -to -back HVDC MMC system, the rectifier has the ability to support the grid with reactive power injection during phase
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and can allow power oscillation dipping and grid destabilization.
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Lastly, the system features steady state control allowing high precision of voltage and frequency regulation for the passive network.
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So even during this voltage dip, there will be no effect on the load.
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The load will be getting the constant power supply.
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There will be no disturbance on the load side.
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This paper is in general analysis of the potential of transient voltage mitigation of an MMC -based HVDs back -to -back link.
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An important part is the dimensioning of the capacitors.
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This is very important.
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Analyze an energy dimensioning chapter, which highlights also the correlation between storage size and dip mitigation performance.
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So certainly the storage size capacitor dimensioning will depend upon what is the dip severity, how much dip is happening,
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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.
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And this is performed in detail in the thesis work of this same author.
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You can also refer to that thesis of this author.
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After the main simulation model is present, including also the control circuit, the conclusion shows the main result concerning dip mitigation performance.
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OK, the energy dimensioning, which is very important because it uses capacitor energy storage property.
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So energy dimensioning of capacitor becomes important.
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The target of this paper is to show the potential of MMC -based HPD -link system for transient voltage dip mitigation
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and give insight in energy storage calculation for the modules.
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This will mean a new proposed design rule for MMC converter when transient voltage dip mitigation is required.
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The traditional way for storage design in the module
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which is done in the industry is to design the energy storage of MMC converter around 30 to 40 kilojoule per mva.
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So converter registration, traditional way of storage design is that range is 30 to 40 kilojoule per mva per converter registration.
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For a break to break system this results in total system energy because one is a rectifier other is inverter,
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so total system energy is of 60 to 80 kJ per mVA.
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But with the object or dip mitigation,
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a new design for the value of stored energy per mVA has to be derived because this is for the normal case.
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But if you want to mitigate the voltage dip without taking increased line current strategies then this need to be recalculated.
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The first step is to analyze the discharge capabilities of submodule capacitors.
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If the modular multilevel converter is assumed to operate with a DC voltage of 1 per unit,
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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.
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In per unit it should be 1 per unit.
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At modulation index of 0 .8 in a steady state.
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So in a steady state, modulation index value uses, you prefer 0 .8.
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The inverter is limited to minimum DC voltage input of 0 .8 per unit.
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That means DC link should not fall below 0 .8 per unit.
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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,
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which is not required, which is a big problem.
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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.
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So both under -voltage and over -voltage in the DC link are not desired.
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The total energy stored for both inverter and rectifier depends on DC voltage of the bus.
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The following is the fundamental equation for energy in the capacitor.
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This is a well -known equation of energy stored in the capacitor 1 over 2 Cv square.
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With this in mind, the total energy store must be high
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that after mitigating a dip the DC voltage should not be below 0 .8 per unit based on the previous equation. So, we...
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We have to make sure that capacitor discharges the energy fast enough so that DC voltage should not fall below 0 .8.
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This means that capacitor only allowed to discharge up to 36 % of their initial steady -state charge.
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This result concludes the total energy of the capacitor should be damaged 2 .77 times
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the missing energy for the inverter operating with modulation index of 0 .8 means if the missing energy,
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whatever the missing energy is divided by 0 .36
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this means the missing energy stored in the capacitor should be 2 .77 times more than the missing energy.
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Calculate the missing energy due to the voltage dip
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and then you should store 2 .77 times more as compared to E missing, multiplied by E missing.
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So let's say if E missing is 0 .3 then E stored should be 2 .77 into 0 .3.
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Second step is to find the missing energy of the system caused by the dip.
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So a statistical analyzer of all mile voltage dip in a highly sensitive distribution present in figure 1.
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This shows that this picture shows voltage dip magnitude percentage and for the time,
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how much time the dip remains.
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And accordingly, depending upon this curve,
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we will come to know that how much energy need to be stored in a back -to -back HVDC MMC system.
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Okay.
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In a function called dip severity is introduced, dip severity, this function is a dip magnitude multiplied by dip duration.
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If the dip duration, let us say if it is for 75 millisecond
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and the dip magnitude is 50 50 % multiplied by 0 .75 ms will be the dip severity. So
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if you multiply both dip duration with the dip magnitude
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you will get dip severity where dips are assumed by 3 phase dips.
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The calculation operates in per unit system with 1 second days per unit in time.
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This makes power and energy base equal.
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Figure 2a shows histogram of dip severity for all required dips and log logistic distribution function is fitted to data.
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As it can be observed the majority of registered voltage dips are included in a window of 50 % at 150 milliseconds.
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So figure 2a, the data was collected, it was observed
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that the most repeated pattern of the dip severity was 50 % dip for 150 milliseconds in the CERN network.
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Figure 2b shows distribution density function rate and the cumulative function
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essentially shows how to dimension the stored energy of the converter as a function of confidence.
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With 99 % being the chosen value for the study,
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more trivially explained that 99 % confidence translates to 99 % of all the voltage diff will be mitigated.
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So in this research paper,
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Here the capacitor dimensioning or energy dimensioning is made not 60 to 80 kJ per mEV
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because this is for the normal case but for voltage dip this needs to be recalculated.
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So it is designed for such a value so that 99 % of dips are successfully mitigated.
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The fact that rectifier will always draw a nominal current from the grid means
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that dip severity in the faked missing energy caused by the dip.
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So E missing is current dip, change in current dip multiplied by change in V dip multiplied by time in T dip,
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how much time dip lasts.
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By graphical solution of our 99 % confidence figure to be the missing energy is seen as 0 .0375 per unit.
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So if you see here,
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the missing energy due to the dip in the sun network with
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that particular load was missing energy in most of the time, 99 % of the time was 0 .0375 per unit.
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This was the missing energy due to the dip.
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So if this is a missing energy now, how much energy should be stored in the capacitors?
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it should be e stored should be 2 .77 times this missing energy
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so multiply 2 .77 with this value you will get
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that total stored energy should be 0 .104 per unit of the system for the system
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Assuming a system of 1 mV rating this means that the reactive inverter together must have an energy of
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104 .0 .104 means it should have energy of 104 kJ per mVa.
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Normally it is 60 to 80 kJ per mVa but for the mitigation of voltage dip and for
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compensating the missing energy
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and to make sure the 99 percent of the voltage dip
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severities are successfully mitigated the system should be now having energy storage of 104 kJ per mVA.
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Now this is the disadvantage
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that overall energy diminishing is changing overall capacitor sizing will be different
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so this will make this converter station little bit cost a little bit expensive as compared to normal.
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So this approach has the disadvantage in terms of cost.
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Comparing this result with the commonly used 60 to 80 kJ per meter shows by only a slight increase of stored energy.
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So there is a slight increase, normally it is 80 kJ per mva
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but to mitigate the voltage it should be the system should be 104 kJ per mva.
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99 % all volt dips will be mitigated if the system is off, 104 kilojoule per MVA.
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Energy storage is this one.
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OK.
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So in the next part, we will discuss simulation model and the results.
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Thank you.
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Vocabulário e dicas de fala para esta lição
Esta aula de conversação usa o vídeo “Back to Back HVDC Modular Multilevel Converter for Transient Voltage Part 1”. As palavras que mais se repetem: dip, energy, voltage, capacitor, missing. Este vídeo tem 230 frases e 3097 palavras para praticar shadowing. A fala dura 21:27. O falante mantém um ritmo estável de cerca de 144 palavras por minuto, confortável para o shadowing. Apenas 77% das palavras estão entre as 3.000 mais comuns do inglês, por isso o vocabulário é exigente.
Vocabulário principal deste vídeo
15 palavras do vídeo que vale a pena aprender, com pronúncia e significado:
| Palavra | Pronúncia | Significado |
|---|---|---|
| voltage substantivo | /ˈvəʊltɪd͡ʒ/ | tensão, voltagem |
| mitigate verbo | /ˈmɪt.ɪ.ɡeɪt/ | mitigar, atenuar |
| dimension substantivo | /daɪˈmɛn.ʃən/ | dimensão |
| severity substantivo | /səˈvɛɹ.ə.ti/ | gravidade, severidade |
| dip verbo | /dɪp/ | mergulhar, imergir |
| grid substantivo | /ɡɹɪd/ | matriz, quadriculado |
| compensate verbo | /ˈkɑm.pənˌseɪt/ | compensar, recompensar |
| steady adjetivo | /ˈstɪdi/ | estável |
| passive adjetivo | /ˈpæs.ɪv/ | passivo |
| magnitude substantivo | /ˈmæɡnɪtjuːd/ | grandeza, magnitude |
| researcher substantivo | /ˈɹiˌsɝ.t͡ʃɚ/ | pesquisador, pesquisadora |
| module substantivo | /ˈmɑd͡ʒul/ | módulo |
| calculation substantivo | /ˌkælkjuˈleɪʃn̩/ | cálculo |
| nominal adjetivo | /ˈnɒm.ɪ.nl̩/ | nominal |
| compensation substantivo | /ˌkɑm.pənˈseɪ.ʃən/ | compensação |
Phrasal verbs que você vai ouvir
| Palavra | Significado |
|---|---|
| take over verbo | tomar posse de, apoderar-se de |
Gramática neste vídeo
As estruturas que o falante mais usa, com as palavras exatas do vídeo:
| Estrutura | No vídeo |
|---|---|
| Voz passiva be + particípio passado — o foco está no que acontece, não em quem faz | is titled · are required · can be mitigated |
| Orações relativas who / which + oração — informação extra sobre uma pessoa ou coisa | paper which is · work which was · storage, which is |
Pronúncia para ficar de olho
- Os sons de “th”: thesis /ˈθisɪs/, synthesize /ˈsɪnθəsaɪz/
- Os sons de “sh” e “zh”: dimension /daɪˈmɛn.ʃən/, calculation /ˌkælkjuˈleɪʃn̩/, compensation /ˌkɑm.pənˈseɪ.ʃən/, duration /dʒʊˈɹeɪ.ʃən/, equation /ɪˈkweɪ.ʒən/
- Palavras longas — acerte a sílaba tônica: severity /səˈvɛɹ.ə.ti/, compensation /ˌkɑm.pənˈseɪ.ʃən/, successfully /səkˈsɛs.fə.li/, registration /ˌɹɛd͡ʒ.ɪˈstɹeɪ.ʃən/, capability /ˌkeɪ.pəˈbɪl.ɪ.ti/
Sons difíceis para falantes de português:
- Consoante final — sem acrescentar um “i” depois: mitigate /ˈmɪt.ɪ.ɡeɪt/, dip /dɪp/, grid /ɡɹɪd/, compensate /ˈkɑm.pənˌseɪt/, magnitude /ˈmæɡnɪtjuːd/
- /l/ final — a língua toca o céu da boca, não vira “u”: module /ˈmɑd͡ʒul/, stable /ˈsteɪ.bəl/, vital /ˈvaɪtəl/, principle /ˈpɹɪn.sɪ.pəl/, fundamental /ˌfʌn.dəˈmɛn.təl/
- /h/ — um sopro suave, diferente do “r”: inherent /ɪnˈhɪəɹənt/, highlight /ˈhaɪˌlaɪt/, anyhow /ˈɛn.i.haʊ/, histogram /ˈhɪstəˌɡɹæm/
Como praticar com este vídeo
- Ouça o vídeo inteiro uma vez sem falar e anote as palavras que você não conhece.
- Faça shadowing frase por frase na velocidade normal, repetindo cada uma até o seu ritmo ficar igual ao do falante.
- Grave a sua voz e compare com o original, prestando atenção a palavras como voltage, mitigate, dimension.
O que é a Técnica de Shadowing?
Shadowing é uma técnica de aprendizado de idiomas com base científica, originalmente desenvolvida para o treinamento de intérpretes profissionais. O método é simples, mas poderoso: você ouve áudio em inglês nativo e repete imediatamente em voz alta — como uma sombra seguindo o falante com 1-2 segundos de atraso. Pesquisas mostram melhora significativa na precisão da pronúncia, entonação, ritmo, sons conectados, compreensão auditiva e fluência na fala.