
发表于 2007124 00:04:59

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Response from Dr. Sood
Thanks the time of Dr. Sood and Mr. John Cheng took. I am very excited to hear about the opinion of Dr. Sood.
Thanks Dr. Sood to explain the reason why he wrote in the book of "Applications Of Static Converters In Power Systems" as follows:"
"The first 25 years of HVDC transmission were sustained by converters having mercury arc valves till the mid1970s. The next 25 years till the year 2000 were sustained by linecommutated converters using thyristor valves. It is predicted that the next 25 years will be dominated by forcecommutated converters [4]. Initially, this new forcecommutated era has commenced with Capacitor Commutated Converters (CCC) eventually to be replaced by selfcommutated converters due to the economic availability of high power switching devices with their superior characteristics." in my opinion, I think the LCC, CCC(CSCC) and VSCHVDC is not the relationship of replacement each other. they are the relationship of complement each other. VSCHVDC can't instead of LCCHVDC. I think that's the reason why China now builds so many EHVDC and UHVDC, although we are doing some research of VSCHVDC..
I also have some questions about the comments of Dr. Sood as follows:
1, Dr Sood wrote that "each link has its own particularities, and there can be some new aspects to learn", Can Dr. Sood give some examples about the new aspects?
Each new link has its own special problems. Some may be related to resonances, others to operational characteristics depending on the AC network they are feeding into. Specially, China with its many links will be facing problems due to interactions between different ties which are in close proximity to each other. The cheapest version is LCC. If there are commuation problems due to weak AC system, then CCC can be used. If the power capability is low (less than 300 MW) then light HVDC can be used for high quality power. Again, it all depends on the attached AC system.
China is going for EHVDC because of bulk power (6000MW), pointtopoint transmission only. Economics is a big reason for this.
2, "Suitable simulation and other studies can help tremendously in doing a good planning"I agree with Dr. Sood very much. I want to know why Dr. Sood does not use the electromagnetic transient software fo pscad/EMTDC. Also how to define the "Suitalbe simulation", and how to verify the validity and adaptive of HVDC models which you represented. Dr. Sood give some examples about the dynamic analysis of HVDC in the chapter of 10, "TYPICAL DISTURBANCES IN HVDC SYSTEMS", I do not konw how to determine the parameters of KP, KI and some measurement time constant like UD, ID. The step response is just to verify whether they can meet the requirements of system design. Does Dr. Sood have some other solution to determine the parameters? like frequency domain analysis or root locus analysis? And how to use the small signal analysis determining the parameters independently and collectively?
I use the EMTP RV program which is similar to EMTDC, or I should state that EMTDC is similar to EMTP. The new version of EMTP RV is vastly enhanced (graphical user interface, machine models, VSC Converter models etc). The tools are all based on the Dommel algorithm. I encourage the reader to visit the website of www.emtp.com <http://www.emtp.com>
The determination of gain parameters is complicated. The theoretical calculations are only approximations based on the data available of the system. The calculations have to be supplemented with simulation studies, and then by actual measurement. There are solutions available to calculate these parameters based on root locus analysis. And I do use them. I supplement these claculations with simulation studies for faster results.
3, I don't think that the multiterminal HVDC is a promising technique in China because of the distance of resource and load center. Also the technique is not flexible in system operation and too complicated in system control. What's the opinion of Dr. Sood?
Three terminal operation is feasible, and we have shown that in Quebec (1600 kms, 2000MW). However, it is more complicated control than two terminal transmission. More than 3 terminals is very risky, and not recomended. Again, HVDC is useful and used only in particular circumstances, not in ALL circumstances. HVDC will complement AC transmission, not supplant it.
I will read the Dr. Sood's book again, I think it is beneficial for me to learn more from that book and this discussion. Thanks Dr. Sood again.
Now I am focusing on modeling HVDC syetem detaildly just for ABB tech and SIENMENSE tech. Could Dr. Sood give me some suggestions?!
This is very essential; we have been doing this all our life, and still not fully trained. I am learning even now.
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Also I want to know the opinion of Dr. Sood about the tool of simulation. Now China focuses on modeling the detailed model in electromagnetic transient software PSCAD/EMTDC, and modeling the model on the RTDS. Could Dr. Sood give some suggestions about this?
Both EMTP and EMTDC are suitable tools. RTDS is good for testing actual (hardware) controllers. I use EMTP RV.
Also I focus on modeling these for BTBHVDC, EHVDC, UHVDC and EHVAC and analyzing the interaction of AC/DC."
I do the same. The models are getting better all the time. 
