How can I eliminate initial transient for a 640 kV two terminal VSC based HVDC system?

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merajalam

How can I eliminate initial transient for a 640 kV two terminal VSC based HVDC system?

I have modeled two terminal VSC-HVDC system with a DC voltage +/- 320 kV and 1000 MVA rating. During the start of simulation a huge amount of reactive power is flowing through the network and converter goes in saturated mode. After 400 ms the system comes back to normal and controllers track the reference. why does this happen? Is it because of inrush currents?

Status: Open Feb 21, 2015 - 03:05 PM

HVDC, VSC

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Hasan Alrajhi

Feb 21, 2015 - 05:12 PM

Hi merajalam;

The problem that you mentioned can be solved by two different ways
1- you can build a start up control in your control loop as you can see in this paper."A New Technology for HVDC Start-up and Operation Using VSC-HVDC System"
http://ieeexplore.ieee.org/stamp/stam...

2- You can re-tune the controllers again

Regards
Hasan

Source: http://ieeexplore.ieee.org/stamp/stam...

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merajalam

Feb 24, 2015 - 10:15 AM

Hello Hasan

Below is reactive power and DC voltage output for a symmetric monopole VSC-HVDC. At 0.8 sec there is a full load step change from 0 MW to 800 MW. During the intial duration for about 200 ms the dc voltage is zero and converter demands a reactive current of about 1.25 pu. I am unable to conclude the reasons and its mitigation. Why is it so?
what should be done to avoid converter saturation?

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Hasan Alrajhi

on 2/24/2015 10:31:35 AM | Like (0) | Report

First of all, did you built the converter from scratch? Or you just modified the model that was published by PSCAD support?

By

merajalam

on 2/24/2015 10:37:05 AM | Like (1) | Report

I built this model from scratch. The entire components in this point to point VSC-HVDC model is based on calculation and set by myself. The controllers are also tuned for each of the specific control actions.taking into account the response time of converter and within all the limits.

By

Hasan Alrajhi

on 2/24/2015 10:57:43 AM | Like (0) | Report

O.K. When you designed the DC capacitor, did you consider a time constant?

By

Hasan Alrajhi

on 2/24/2015 11:00:59 AM | Like (0) | Report

Could you please tell me that:
The rated power of the converter
The DC voltage
The value of C that you are using right now

By

Hasan Alrajhi

on 2/24/2015 9:05:49 PM | Like (1) | Report

The DC side capacitor should be around 3uF in case of getting proper response

By

merajalam

on 2/25/2015 3:39:15 AM | Like (0) | Report

converter type = 3 level NPC
rated power of converter = 1000 MVA
DC voltage = +/- 320 kV
Cdc = 70 uF (each connected to ground and +/- pole)
time constant is calculated using 0.5*C*Vdc*Vdc/S comes out to 4.48 ms

Am i right in selecting a good value of capacitor? The capacitance selection is always a confusing one. There are papers where authors chose a high value like in mF. what is the proper way to choose dc capacitor?

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First of all, did you built the converter from scratch? Or you just modified the model that was published by PSCAD support?
I built this model from scratch. The entire components in this point to point VSC-HVDC model is based on calculation and set by myself. The controllers are also tuned for each of the specific control actions.taking into account the response time of converter and within all the limits.
O.K. When you designed the DC capacitor, did you consider a time constant?
Could you please tell me that:
The rated power of the converter
The DC voltage
The value of C that you are using right now
The DC side capacitor should be around 3uF in case of getting proper response
converter type = 3 level NPC
rated power of converter = 1000 MVA
DC voltage = +/- 320 kV
Cdc = 70 uF (each connected to ground and +/- pole)
time constant is calculated using 0.5*C*Vdc*Vdc/S comes out to 4.48 ms

Am i right in selecting a good value of capacitor? The capacitance selection is always a confusing one. There are papers where authors chose a high value like in mF. what is the proper way to choose dc capacitor?

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How can I eliminate initial transient for a 640 kV two terminal VSC based HVDC system?

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