Leopold Herman

A Proportional-Resonant Current Controller for Selective Harmonic Compensation in a Hybrid Active Power Filter

This paper deals with reactive power compensation and harmonics elimination in medium-voltage industrial networks using a hybrid active power filter. It proposes a hybrid filter as a combination of a three-phase, two-level, voltage-source converter connected in parallel with the inductor of a shunt, single-tuned, passive filter. This topological structure greatly decreases the voltage and current stress over the elements of the active filter. Since the topology is composed of a single-tuned branch, the control algorithm also has to ensure sufficient filtering at other harmonic frequencies. We propose using a proportional-resonant, multiloop controller. Since the controller is implemented in a synchronous-reference frame, it allows us to use half the number of resonators, compared with the solution using proportional-integral controllers in the harmonic-reference frame. Theoretical analyses and simulation results obtained from an actual industrial network model in PSCAD verify the viability and effectiveness of the proposed hybrid filter. In addition, the simulation results are validated by a comparison with the results obtained from a real-time digital simulator.

Hybrid active filter for power factor correction and harmonics elimination in industrial networks

In modern industrial processes, the number of nonlinear loads - known to be a major source of current harmonics - is constantly growing. At the same time, the number of reactive-power compensators operating in these networks is growing too. Though the compensators are not the source of harmonic distortions, they may cause high amplifications of harmonics by creating resonance conditions. This can cause malfunctions or even loss of equipment. This paper presents a hybrid compensator as a combination of three-phase shunt LC passive compensator connected in series with a small-rating active compensator. The main objective of the presented hybrid capacitor system is to compensate reactive power. The active part of the filter is used to improve the filtering performance of the passive part and prevent the resonance amplifications of current harmonics. As a result, no harmonic resonance occurs under any system condition. The effectiveness of the hybrid compensator is demonstrated on a realistic industrial-network model by means of simulations.

Optimal control of reactive power compensators in industrial networks

Due to the presence of large number of reactive power compensators at different voltage levels in a typical industrial network, many combinations of the settings of compensators are possible, all of which are not appropriate in terms of harmonic conditions in the network. Thus, it is rather hard for an operator to make an optimal decision how to operate and predict all of the potentially dangerous situations. The most dangerous resonance conditions are those which occur in the vicinity of the harmonic components present in the network. For save and reliable operation it is thus necessary to prevent such conditions from happening. In this paper a concept of virtual compensator is proposed, addressing the above issues of reactive power compensation in industrial networks. An algorithm is introduced, which resolves alternatives for each operating point and provides to the operator the optimal combination of setting to be implemented. The effectiveness of the proposed algorithm is demonstrated on the realistic industrial network model by means of simulation.

Performance of a parallel hybrid active filter with selective harmonic control

This paper presents a hybrid power filter as a combination of a three-phase, two-level, voltage-source converter connected in parallel with the inductor of a shunt, single-tuned, passive filter. This topological structure greatly decreases the voltage and current stress over the elements of the active filter. Since the topology is composed of a single-tuned branch, the control algorithm also has to ensure sufficient filtering at other harmonic frequencies. We propose using a proportional-resonant (PR), multi-loop controller. Theoretical analyses along with simulation results obtained from a Real-Time Digital Simulator (RTDS) verify the viability and effectiveness of the proposed hybrid filter.

A parallel hybrid active power filter for resonance damping in industrial networks

This paper presents a hybrid power filter as a combination of small-rating active filter connected in parallel with an inductor of a shunt, passive LC compensator. The main objective of the passive part is to compensate reactive power, while the active part is used to improve filtering performance and damp the resonance amplifications of current harmonics. As a result, no harmonic resonance occurs under any system condition. The effectiveness of the hybrid compensator is demonstrated on a realistic industrial-network model by means of simulations.

Real-time simulations of a parallel hybrid active filter with hardware-in-the-loop

This paper presents hybrid power filter (HPF) performance evaluation procedure by applying special simulation hardware for digital real-time power system simulation (RTDS). RTDS simulator enables real-time calculation of electromagnetic phenomena with calculation time step of even 1-2 μs. Special hardware makes possible of importing and exporting of electrical signals from the simulator to external equipment and therefore so called hardware-in-the-loop (HIL) testing. Such simulations provide an insight in the equipment behaviour and also the influence of this equipment to system operation. In this paper a combination of a three-phase, two-level, voltage-source converter connected in parallel with the inductor of a shunt, single-tuned, passive filter is tested. To control the active part, a proportional-resonant (PR), multi-loop controller is used. The testing has shown a remarkable usefulness of the RTDS simulator for determination of actual electrical system equipment behaviour in various system conditions.

On the use of unbalance definition to control compensators for arc furnaces

The use of the new unbalance definition introduced by some of the authors in a previous paper is considered for the compensation of Light Flicker in networks where there is the presence of large arc furnaces. Some recalls on compensation strategies for arc furnaces are firstly given. Then, the new unbalance definition is briefly recalled in its original formulation in frequency domain and extended the time domain in order to use it in a control system for active compensation of harmonics and interharmonics. A preliminary correlation analysis finalized to find the best quantity to calculate the reference values for the active filter is performed. A numerical case-study and experimental data obtained during a measurement campaign performed by some of the authors are used to show preliminary results of Light Flicker compensation.

A control strategy of a hybrid active filter for operation with harmonically unbalanced voltages and currents

This paper presents a hybrid active filter to suppress harmonic resonances and to reduce harmonic distortion under unbalanced conditions in medium voltage industrial networks. The proposed hybrid filter is a combination of a three-phase, two-level, voltage-source converter connected in parallel with the inductor of a shunt, single-tuned, passive filter. This topological structure greatly decreases the voltage and current stress over the elements of the active filter. Since in the industrial networks the voltages and currents are usually unbalanced, the control algorithm also has to ensure sufficient filtering of unbalanced harmonics. We propose using a proportional-resonant (PR), multi-loop controller, that allows to half the number of resonators, compared with the conventional solution of using proportional-integral (PI) control principle. Theoretical analyses and design considerations are presented, and experimental results obtained with a Real-Time Digital Simulator (RTDS) and DSP coded control algorithm are provided to validate viability and effectiveness of the proposed hybrid filter.

Stochastic modelling of distribution networks operation

For purpose of power network operation analysis deterministic methods for load flow calculation are commonly used, for example Newton-Raphson method in its full or simplified version. Method is known for its robustness and is suitable for analyses of HV and MV networks. On the other hand it is less appropriate to model LV networks using solely deterministic methods, since consumption in LV networks is far from being deterministic. In contrary it is highly stochastic. Therefore modeling of LV distribution network should involve combination of deterministic and stochastic methods. Stochastic part must be supported with databases containing suitable amount of accurate data of interest.

Mathematical Modeling and Control Algorithms of STATCOMs

In this chapter, different STATCOM control algorithms will be introduced. The algorithms are derived on the basis of STATCOM mathematical models in the α-β coordinate system and in the synchronously rotating d-q coordinate system. In the first part of the chapter, both mathematical models are derived from the three-phase STATCOM model, and the mathematical process is described in detail. In the second part, four different control algorithms are described: d-q control algorithm for balanced and unbalanced conditions, time-optimal current-control algorithm and Proportional-Resonant (PR) multi-loop controller.