This paper discusses the problems and solutions of applying reactive compensation, either static or dynamic, to industrial power systems supplying large blocks of dc power from diode or thyristor converters. The resonance between power capacitors and system reactance can produce high harmonic voltages caused by the harmonic currents generated by converters. The interaction between these harmonic voltages and regulating systems can be minimized by the use of suitable filters. The design of these filters should eliminate the interaction between power system and load and reduce harmonic current flow. Different methods of reactive power control are also discussed.

Reactive Compensation and Harmonic Suppression for Industrial Power Systems Using Thyristor Converters

A general, sampled-data representation of the dynamics of arbitrary power electronic circuits is proposed, to unify existing approaches· It leads, via compact and powerful notation, to disciplined modeling and straightforward derivation of small-signal models for perturbations about a nominal cyclic steady state. Its usefulness is further illustrated by considering the representation and analysis of a class of symmetries in circuit operation. Results of application of this methodology to modeling the small-signal dynamics of a series resonant converter are described. The results correlate well with simulation results obtained on MIT's Parity Simulator. What is of more significance to the theme of this paper is the fact that the small-signal model is obtained in a completely routine way, starting from a general formulation and working down to the actual circuit; this contrasts with the circuit-specific analyses that are more typical of the power electronics literature. The paper also discusses the automatability of the above procedure, pointing out that the key ingredients for automatic generation of dynamic models from a circuit specification are now available.

A general approach to sampled-data modeling for power electronic circuits

A new HVDC-HVAC analytical model is presented in this paper. The model comprises three subsystems: AC system, PLL and DC system. The model is structured in such a manner to enable small signal analysis of HVDC-HVAC interactions and possible problems arising from these interactions, CIGRE HVDC Benchmark model is used as a test system. Model verification, performed using PSCAD/EMTDC simulations, showed good response matching for all DC and AC system variables. As an example of application of this model the influence PLL dynamics on the system stability is studied offering the important rules for tuning of PLL gains.

Analytical modelling of HVDC-HVAC systems

Following a brief review of the use of stated space models for switched power electronic systems, we illustrate the need for care in extending the use of state-space averaging techniques, and point out the possible relevance of averaging methods of classical mathematical physics. The existence of potentially useful control synthesis procedures for periodically-varying state-space systems is finally outlined.

http://ieeexplore.ieee.org/iel7/7083606/7083607/07083657.pdf

Extended averaging and control procedures

An overview is given of the design criteria applicable to a variable-speed dc drive with dual-converter power supply. The control strategy, machine-converter and controller transfer functions, the problems associated with discontinuous conduction, and power flow reversal are considered. A representative bibliography of the voluminous literature on this topic is included.

https://ieeexplore.ieee.org/iel5/5/31199/01451963.pdf

Four-quadrant DC variable-speed drives&#8212;Design considerations

The paper is concerned with the stability of closed-loop control systems incorporating controlled rectifiers. A suitable small-signal model for a convertor is developed which takes into account the discrete behaviour of the controlled rectifier. This model permits the use of standard sampled-data control-system theory in the stability analysis of the system. Contrary to usual practice, the a.c. system reactance is not neglected in the modelling. It is shown that the commutation angle is an important factor in the determination of stability boundaries. Finally, again-correction factor is employed to allow for the effect of the ripple under finite-commutation-angle conditions. Discrete Laplace transformation (z transformation) is used throughout the analysis together with root-locus techniques. Stability boundaries derived from the new model and other existing models are compared, and it is shown that experimental results are in good agreement with the theory developed in this paper.

Stability study of controlled rectifiers using a new discrete model

A previously established model for the small-signal behaviour of thyristor-rectifier control loops is extended to rectifiers involving an asynchronous delay-type firing circuit. It is shown that this type of firing circuit behaves like a positive-feedback loop across the rectifier, and that the order of the system is increased by one unit.

Extension of a small-signal model for thyristor-rectifier control loops when using an asynchronous delay-type firing circuit

A compensation method for thyristor rectifier control-loops

Sampled-data control systems, of which the open-loop transfer function is such that the corresponding impulse response is discontinuous at the origin, cannot be studied with the usual z formula. The z transfer function of such systems is established when it can be assumed that there is no instantaneous transmission, or when the sampler is not a usual Dirac sampler.

R. Prajoux

Papers

Stability study of controlled rectifiers using a new discrete model

Extension of a small-signal model for thyristor-rectifier control loops when using an asynchronous delay-type firing circuit

A compensation method for thyristor rectifier control-loops

z transfer functions of sampled-data control systems with a discontinuous error signal