This paper presents a new concept for controlling static VAr compensators (SVC) in power systems. It allows thyristor controlled VAr compensators to effectively damp subsynchronous resonance (SSR) oscillations besides controlling the system voltage. Eigenvalue analysis and digital time simulations for the IEEE SSR benchmark system are utilized to investigate the role of the main voltage regulator of the SVC in stabilizing the system and alleviating the SSR modal interactions that may be introduced by the auxiliary speed signal alone. Stability zones are identified to optimize the compensator parameters for economical application.

Application of a Thyristor Controlled Var Compensator for Damping Subsynchronous Oscillations in Power Systems

The first part of the paper describes the relationship between inverter output voltage and radial magnetic force on the inner surface of the stator, which generates vibrations of the stator and causes the magnetic noise. The theoretical results are verified experimentally. In the second part the authors derive the frequency components of the pulse width modulated (PWM) and pulse frequency modulated (PFM) voltage and of the magnetic noise. This is the basis for a calculable spreading of the spectrum by means of PFM, shown in the third part. The purpose is noise reduction and elimination of selected harmonics to avoid mechanical resonances. >

Spectral analysis of the sinusoidal PWM with variable switching frequency for noise reduction in inverter-fed induction motors

The purpose of this paper is to discuss the developments in control strategies for static compensators using programmable high speed digital controllers. Individual phase control of static compensators has been used in the past for balancing and power factor correction of arc furnace and single phase railway loads. With the advancements in programmable high speed controllers based on microprocessor technology, more complex computations can be accurately performed for the additional purpose of regulating and balancing the voltage feeding such loads. Other developments that will be discussed are the use of symmetrical firing angle control to eliminate the even harmonics in the current spectrum and hence, reduce the cost of filtering, and the synchronization of the controller to the phase-locked-loop firing circuit to compensate for frequency variations. The results of simulator studies will be presented.

Individual Phase Control of a Static Compensator for Load Compensation and Voltage Balancing and Regulation

Conventional interlocking of substations is usually expressed by Boolean expressions and realized by electro-mechanical relays. Since these expressions are generated by applying verbally stated interlocking rules to a specific substation configuration, any change of the substation or of the operational philosophy affects them in such a complex way that the problem has to be tackled again in most cases from the very beginning. The proposed topology-based approach suited for microprocessors decouples knowledge-base and implementation, i.e. interlocking rules, and substation configuration. It results in interlocking rules that are independent of a single line diagram and can be applied to all known substation configurations. The rules are divided into mandatory and dependent on operational philosophy. The modularity allows for applying exactly those rules specified in the special project. Any new substation does not require new programming. The inherently fault-tolerant implementation in a 765 kV GIS is briefly described.

Topology-Based Interlocking of Electrical Substations

This paper presents a new microprocessor-based high-speed controller with a simple program language for the control of various kinds of converter-fed ac-drives. Its applications as a flexible controller of different drives is described. From the example of the current control loop the striking processing speed of the controller is shown.

H. Stemmler

Papers

Programmable Processor for the Control of Power Electronic Systems

Ein- und mehrpulsige unterschwingungswechselrichter, steuerverfahren, strom- und spannungsverhaeltnisse