Technical Documents

This paper shows one possible approach of AC-AC power transformation using pure solid-state switches and passive components without an intermediate magnetically-based transformer. It is based on the concept of capacitor-based transformation of power from one voltage level to another. It offers some useful features: (1) internal redundancy sufficient to obviate the need for the spare transformer normally supplied with magnetic transformation, (2) absence of toxic insulating oil, (3) ease of manufacture, being modular in construction, (4) inherent phase-shifting capability, and (5) the ability to convert between primary and secondary nodes differing in frequency and/or wave-shape. The new architecture enriches the existing SST family and introduces a configuration that requires fewer converter stages. The simulation results will show that the proposed SST can transform one AC voltage to another AC voltage using pure solid-state devices and be bi-directional, exactly as a magnetically-based conventional transformer, but with even more functions, such as fast and dynamic control over the output voltage, and fully controllable output power by shifting the phase angle of the transformer output voltage. In addition, the grid side reactive power can be controlled. Another unique feature is to use the resonant circuits for soft switching (zero-current switching) while charge exchanging between the first node and the transformer, and between the second node and the transformer. The total DC voltage of the submodule (SM) column is stable, and the individual SM capacitor voltage is sorted and balanced. The over-current protection mechanism detects faults and isolates the transformer. The results will successfully demonstrate that the proposed distribution SST is a pure solid-state transformer that only uses a single converter stage and no magnetically-based transformer but still has the function of the conventional transformer, as well as it provides additional features that can contribute to the future smart distribution grid.

The key concept of this new metric, termed Inverter Penetration Short Circuit Ratio, or IPSCR, is that the short circuit strength which is available within a certain region may come from a combination of conventional sources and IBRs. As the proportion of the generation mix moves towards IBRs, the IPSCR calculated will fall, indicating an overall weakened system. This metric has been tested in the ATC system with some success.

Their news release following the meeting stated: “On electricity and strategic infrastructure, ministers agreed to explore collaboration on new and enhanced inter-jurisdictional electricity transmission interties….&… , increased cross-border transmission of clean energy and enhanced resiliency of the North American electricity grid.”

Their news release following the meeting stated: “On electricity and strategic infrastructure, ministers agreed to explore collaboration on new and enhanced inter-jurisdictional electricity transmission interties….&… , increased cross-border transmission of clean energy and enhanced resiliency of the North American electricity grid.”

That’s changed with the prospect of major DC Grids overlaying systems in Europe and North America. Apart from the anticipation of DC Grids, a more efficient DC-to-DC power transformer could serve a host of other purposes in the rapid growth of dc as a form of energy delivery, utilization, and even generation.

The objective was to see if any DC configuration and DC voltage could, using existing tower geometry and conductor current capability, achieve a target loading of 2,300 MW.

It considers the advantages and limitations of capacitive circuits widely used for that purpose at the electronics level, but also seeks to take advantage of the capabilities inherent in power-level thyrsitors and IGBT’s within the bridge architecture of commonly used MMCs. The paper cites the criteria by which various capacitor-based schemes can be judged as well as means by which relatively smooth dc output and input wave-forms can be achieved within the limitations of what is basically a pulse-based energy transfer mechanism.

Reference: Kent Søbrink (Eltra), Peter Løvstrøm Sørensen (Eltra), Eric Joncquel (EDF R&D) and Dennis Woodford (Electranix Corporation), “Feasibility Study Regarding Integration of the LÆSØ SYD 160 MW Wind Farm Using VSC Transmission”, CIGRE SC14 Colloquium, Three Gorges Dam Site, Friday August 31, 2001.

This paper introduces the latest simulation algorithm used in the EMTDC program (called the Instantaneous Solution) and makes comparisons against small time step solutions (to show the effectiveness of Interpolation).

Reference: Garth Irwin and Dennis Woodford, Ani Gole (University of Manitoba), “Precision Simulation of PWM Controllers”, IPST 2001, p. 161, Rio de Janeiro, June, 2001.

Reference: A. Gole, P. Demchenko, D. Kell, Garth Irwin, “Integrating Electromagnetic Transient Simulation with Other Design Tools”, IPST 2001, p. 681, Rio de Janeiro, June, 2001.

This paper introduces modifications to the standard control system library components in PSCAD to make them compatible with interpolated signal information:

A.M. Gole, S.A. Woodford, J.E. Nordstrom, G.D. Irwin, “A Fully Interpolated Controls Library for Electromagnetic Transients Simulation of Power Electronic Systems”, IPST 2001, p. 681, Rio de Janeiro, June, 2001.

D.A. Woodford and M.Z. Tarnawecky, “Compensation of Long Distance AC Transmission Lines by Shunt Connected Reactance Controllers”. IEEE Transactions on Power Apparatus and Systems, Vol. PAS-94, March/April, 1975.

aSome Hydro Quebec and Manitoba Hydro engineers said it was not possible. One engineer said he would only believe a digital simulation of a dc link if core saturation instability was demonstrated. Well we did it and this paper was the evidence that indeed dc transmission could be accurately simulated:

D.A. Woodford, A.M. Gole, R.W. Menzies, “Digital Simulation of DC Links and AC Machines,” IEEE Transactions on Power Apparatus and Systems, Vol. PAS-102, No. 6, June 1983, pp1616.aSome Hydro Quebec and Manitoba Hydro engineers said it was not possible. One engineer said he would only believe a digital simulation of a dc link if core saturation instability was demonstrated. Well we did it and this paper was the evidence that indeed dc transmission could be accurately simulated:

D.A. Woodford, A.M. Gole, R.W. Menzies, “Digital Simulation of DC Links and AC Machines,” IEEE Transactions on Power Apparatus and Systems, Vol. PAS-102, No. 6, June 1983, pp1616.

Garth participated in an extensive study to see if indeed the guidelines CIGRE had published on insulation coordination of dc substations could hold up when accurate simulation was applied. The results were presented in a report sponsored by the Canadian Electricity Association. A summary of this report was published as:

N.L. Diseko, G.D. Irwin, D.A. Woodford, R.L. Vaughan, “Performance of Metal Oxide Arresters in HVDC Stations,” Paper 33-208, CIGRE 1990 Session, Paris, August 1990.

In the middle of this study, a severe geomagnetic storm took out an SVC on the Hydro Quebec system which led to a system wide blackout. The report is:

T. Maguire, D. Woodford, “Geomagnetic Induced Current Effect on SVC Operation,” CEA Report 316 T 745, March 1990.

There is a good chance that a transmission circuit converted to dc will be coupled to a parallel ac circuit on the same tower or right-of-way. Electromagnetic coupling from the ac circuit to the dc circuit may effect the performance of the dc transmission line unless specific design considerations are instigated. Of concern is extinction of the secondary arc when a dc pole conductor is faulted. Will the coupling from an ac circuit maintain the arc?

D. Woodford, “Secondary Arc Effects in AC/DC Hybrid Transmission”, IEEE Transactions on Power Delivery, April 1993, Vol. 8, No. 2, pp 704- 711.

Building on Hermann Dommel’s network solution method, some ideas from the Netomac digital simulation program and from the University of Manitoba, extensive development on the EMTDC program was undertaken. To balance solution speed and precision in switching, “interpolation” was applied to the EMTDC solution method. The value of this work is now evident when we use PSCAD/EMTDC to investigate Voltage Sourced Converter applications and where switching precision to within a tenth of a microsecond is essential:

P. Kuffel, K. Kent, G. Irwin, “The Implementation and Effectiveness of Linear Interpolation Within Digital Simulation” Proceedings of IPST’95, International Conference on Power System Transients, Lisbon, September 3-7, 1995, pp 494-504.

A.M.Gole, I.T.Fernando, G.D.Irwin, O.B.Nayak, “Modeling of Power Electronic Apparatus: Additional Interpolation Issues”, International Conference on Power Systems Transients (IPST97), Seattle, June 22-26, 1997, pp. 23-28.

A simple method for testing the sensitivity for controllers to interact was developed through the concept of “Global Gain Margin” analysis:

D.A. Woodford, “Electromagnetic Design Considerations for Fast Acting Controllers,” IEEE Transactions on Power Delivery, Vol. II, No. 3, July 23-27, 1995, pp 1515-1521.

Overhead transmission lines have been the normal located on designated rights-of-way. Acquiring new right-of way for overhead ac transmission lines is usually challenging to permit and in some jurisdiction impossible to obtain.

To minimize the adverse effects of high voltage electric power transmission lines, new technologies are forthcoming that when applied may be more acceptable. By judicious compacting of high voltage direct current (HVDC) and high voltage alternating current (HVAC) transmission systems, existing rights-of-way can be utilized, such as along roads or rail lines. A concept for compacting transmission lines for this purpose is presented.

D.A. Woodford, “Compact High Voltage Electric Power Transmission”