John L. Hay

Dynamic Simulation of HVDC Power Transmission Systems on Digital Computers - Generalized Mesh Analysis Approach

This paper introduces and develops a new generalized approach to the dynamic simulation of an HVDC power transmission system. The approach involved is a generalized method of mesh analysis applied to the HVDC network. The simulation of HVDC convertors is characterized by the fact that the network to be solved changes with each discontinuity, such as valve firing and end of commutation. To facilitate such an analysis, topology is used and a technique is developed for the automatic selection of the appropriate network by recognizing the state of conducting and nonconducting valves. The method is inherently suitable for following the natural process of convertor operation which may culminate in various faults. To illustrate this method a simple HVDC system consisting of one convertor at each end is considered. Essential features of the program are shown by deriving waveforms of normal operation, commutation failure, four-valve conduction, bypass valve operation, and backfire.

Dynamic Simulation of Multiconverter HVDC Systems by Digital Computer Part I: Mathematical Model

This paper and a companion paper [7] develop the digital-computer techniques for the dynamic representation of HVDC power links. A digital-computer program is developed which may represent many circuit configurations, different modes of control, and protective devices, and provides a model which offers both accuracy and flexibility. The formation of a mathematical model which represents the converters and their associated ac systems by differential, algebraic, and Boolean equations is described. The requirements of a computer calculation have been born in mind during the construction of this mathematical model. A new topological technique for the representation of converters is introduced. This technique overcomes the problems of representing the discrete switching processes which occur in converter operation. The utilization of tensor analysis and diakoptics facilitates the construction of a flexible mathematical model of the complete systems of multiconverter stations and associated ac circuitry. The techniques presented are specifically designed for the dynamic simulation of HVDC systems; however the theory may be applied to other circuit prolems where switching processes occur.

ESL - A new Continuous System Simulation Language

ESL is a new Continuous System Simulation Language (CSSL) which is being developed under contract from the European Space Agency. It is based on the concepts outlined in Refer ence 6. The main features of the new language are: (1) Models can be built from submodels (2) Separation of model and experiment (3) Advanced discontinuity-handling (4) A parallel segment feature. The implementation of ESL requires both an interpreter and a translator version of the language. The interpreter translates the users program into an intermediate code (H-code) which is then interpreted at run-time. The translator may be used to convert the H-code to FORTRAN-77 to produce a more efficient ex ecutable program of production runs. The entire system (with the exception of a few low-level routines) is being written in FORTRAN-77. A prototype version of the language was installed in August 1983 and is currently undergoing evaluations. Details of this version are given with examples of its use.

Dynamic simulation of ferromagnetic hysteretic behaviour by digital computer

A model is presented which produces the locus on the B-H plane of a ferromagnetic specimen subject to dynamic operating conditions. The model accurately represents the magnetisation curve and the saturation Zoop as well as exhibiting the correct inner loop behaviour. The concept of a primitive magnetic eZe ment is introduced, and the paper illustrates how a finite number of these elements may be combined and their characteristics chosen so as to represent the hysteretic behaviour of a ferromagnetic device. Validation is achieved by comparing experimental and computed results for both symmetrical and asymmetri caZ inner Zoop behaviour. The incremental inductance of an electro-magnetic device may be readily calculat ed from the proposed model which is presented in a form suitable for either digital or analog computer simulation.

Simplified Dynamic Simulation of HVDC System by Digital Computer Part II-Design of Controller and Test Results

The paper introduces and develops a new technique for the design of HVDC control system, by representing the overall HV dc system by an approximate linear control system. From the frequency response of the uncompensated system the time constant of the controller is selected, and then based on the physical limitations the overall gain of the system is adjusted. The paper outlines the step-by-step method for the design of controller (inverse cosine method) by means of a digital computer. The selected control components are tested with the simplified digital models developed in a companion paper,8 and also with a more sophisticated program.1 The test results of the simple and detail program justify the development of the simple- program, and also the method of design for the control components.

Simplified Dynamic Simulation of HVDC System by Digital Computer Part I - Computer Program

The paper presents a dynamic simulation of an HVDC system by digital computer employing converter equations based on averaged values. The converters are represented by perfect dc generators and motors, their outputs are equal to those from real converters with the sixth and higher harmonics being neglected. The converter control circuit of the system is represented by actual hardware. Due to the simplified representation the program enables a considerable saving of computation time with minimal loss of accuracy.

Variable step-length integration routines

an approximate solution which is equivalent to a certain number of terms in a Taylor series, and an approximate evaluation of the error in this solution. In some cases this error estimation is equivalent to evaluating the next term in the Taylor series, and is therefore fairly accurate and can be combined with the original solution, thus increasing its order of accuracy. It would be untrue to say that in such a case the error was known accurately as the magnitude of the last term included will normally be considerably greater than the error. This is not to say that such techniques do not have their uses. It is not uncommon for a series to be evaluated until the last term included falls below a specified magnitude. What must be remembered is that this magnitude gives

Dynamic Simulation of Multiconverter HVDC Systems by Digital Computer Part II: Computer Program

The digital-computer techniques for the dynamic representation of HVDC power links are discussed. A digital-computer program is developed which may represent many circuit configurations, different modes of control, and protective devices. It also provides a model which offers both accuracy and flexibility. The way the mathematical model of a complex electric system which includes numerous switching processes and discontinuities may be programmed for a digital computer is discussed. In addition, methods for optimizing program storage and computer time are described. Selected test studies are also presented. The program developed enables a flexible and accurate simulation of HVDC systems operating normally or under fault conditions. The resulting program will be a highly efficient analytical tool for the system design engineer.