Constantin Vlad Suru

Conservative power theory implementation in shunt active power filtering

This paper analyzes the current decomposition, in three-phase, three-wire systems, based on the Conservative Power Theory (CPT), and the application of these components in the active filtering. The CPT current decomposition gives the active component of the current, the reactive component, which can be compensated or not and the void current. It does not give the asymmetry current component, separately. For this reason, the active shunt compensators based on the CPT have the capability of compensating only parts of the non-active current, as needed. The reactive component can be compensated or not, but the void current, which contains the harmonic content, is normally compensated. A problem of the CPT, latter resolved, is the asymmetry current component which was not included in the first definitions. The aim of this paper is to analyze the performance of an experimental active compensator based on the early CPT definitions and a comparative study with the performances of the same compensator based on the improved CPT definitions.

Configuring and experimental evaluation of a laboratory model for filtering and regeneration in active DC traction substations

The objective of the paper is the presentation of a laboratory model of a system for active filtering and regeneration (SISFREG) developed through an applied research collaborative project in the frame of Partnerships in priority area programme during 2014–2016. The system allows the conversion of the DC traction substations into “active substations”. The main component of the laboratory model is the configurable voltage source inverter (input voltage range 200–560 V DC; output voltage 3×400 V AC; rated power 30 kVA) adequately interfaced with the DC-line and properly controlled in closed loop. The control and monitoring algorithm was implemented on the dSPACE 1103 system. The background of the methodology and the testing structure configuration were made based on the actual conditions prevailing in a substation for DC traction and given the equipment available in the laboratory. The experimental structure contains: the equivalent of the transformer-rectifier traction group; the equivalent of the DC traction motors; the possibility of system to be connected, on the one hand, in the connection point of the traction transformer, and, on the other hand, with the DC line (equivalent catenary). This paper presents several experiments conducted in accordance with the testing protocol, the analysis of the experimental results and the resulted performance of the system, in terms of energy, during both active filtering and regeneration operation modes.

Control algorithm implementation for a filtering and regeneration system used in urban traction DC substations

This paper focuses on the design and implementation of the control algorithm of an active filtering and energy recovery system which transforms the classical DC traction substation into a active substation. For this goal, the active power filter control loops must be tuned not only for the proper operation as an active filter, but also to give the APF the ability to generate back to the power grid the energy intake from the DC line to the compensating capacitor. It will be proved that the transition between filtering operation and energy recovery operation is done automatically, without the intervention of the human operator or of a specially designed system. The correct implementation and tuning of the control algorithm was validated on a complete Simulink model which includes in detail all the sections of the active substation. Moreover, the correct implementation was further experimentally verified on a scale model of the active substation based on a dSpace DS1103 platform. The results obtained both by simulation and on the experimental setup proved the correct answer of the tuned regulators and the overall operation of the active substation. The indirect current control approach was adopted, with the computation of the desired power grid current based on a modified synchronous rotating d-q frame.

The synchronous fundamental dq frame theory implementation and adaptation for the active filtering

The synchronous fundamental dq frame is a time domain method derived from the space vector transformations of three phase systems. While these methods had been extensively used for the analysis of three phase circuits this particular method is suitable for the active filtering. This is because it obtains the non-sinusoidal current fundamental which can be used for the compensating current computation. The compensation result of this method is a sinusoidal grid current, not in phase with the grid voltage, so only the distortion component of the current is compensated, the reactive component has to be compensated by an external circuit, or absorbed from the power grid. In order to compensate the reactive current this method can be adapted to compute not only the load current fundamental, but also the active component of the load current fundamental. Another adaptation of this method is the unity power factor compensation, which implies that the compensated current has the same shape and phase with the grid voltage, so the active power is transported not only on the voltage fundamental, but also on the voltage harmonics. The implementation of this method and its adaptations on an active filtering system are the objectives of this paper.

Study of energetic performances of a power static converter with current-source and parallel resonance inverter for induction heating applications

This paper analyses the energetic performances of an induction heating system for a pipe rolling machine, based on a single-phase current inverter. The study was based both on the real system experimental measurements, as well as on the equivalent Simulink model of the system. The obtained simulation results performed on the measured experimental conditions confirmed the validity of the virtual system. At the same time, the system structure was adopted for a given inductor corresponding to the rolling plant, and for a set of typical pipes. For each pipe, the compensating capacitor value was chosen according to the working frequency corresponding to the thickness of the processed pipe, the resonance frequency of the reactive circuit being equal to the working frequency. The aim of the paper was the performance analysis of the system as well as the power quality analysis at the grid side and at the load side of the system.

Direct current control by constant frequency hysteresis controller in active filtering systems

The aim of this paper is the conversion of the classical hysteresis controller into a constant frequency hysteresis current controller. The classical alternative to the hysteresis controller is the proportional-integrative controller which gives constant switching frequency and overall better performances with a cost of comprehensive parameter tuning and sensitivity at driven system change. The hysteresis controller main advantage is the simplicity and robustness with the cost of variable switching frequency. The compromise between these two solutions is the constant switching frequency hysteresis controller. This goal can be achieved with a combination of the hysteresis comparator and the PWM modulator. The performances are somewhat less good and depend on the compensating capacitor voltage and PI voltage controller parameter adjustment but with the advantage of constant switching frequency. The regulator implementation was validated on a complete active filtering system implemented in Matlab Simulink.

Conservative Power Theory application in shunt active power filtering under asymmetric voltage

This paper analyzes the current decomposition, in three-phase, three-wire systems, based on the Conservative Power Theory (CPT), and its application in the active filtering in non-sinusoidal and unbalanced conditions, by simulation as well as on an experimental workbench. The CPT current decomposition includes, beside the active, reactive and void components, an unbalanced component. This component makes possible for the active filter to compensate also the current unbalance, if desired. This is particularly interesting when the voltage is also unbalanced because of the load unbalance or not. In this case, the compensation will eliminate the voltage asymmetry due to the load current unbalance, but if the grid impedances are not equal on all the three phases, the compensated sinusoidal and balanced current will unavoidably produce asymmetric voltages in the PCC. Moreover, due to the CPT definition of the active current, the grid voltage asymmetry will produce a load current unbalance. The current decomposition based on the Conservative Power Theory was analyzed on various case studies, for a combination of typical nonlinear balanced and unbalanced industrial loads. First, the active filtering system was tested by simulation in the Matlab Simulink environment, and latter the validated system was further tested on an experimental workbench. Because of the Simulink model modular structure, the virtual filtering system was built equivalent to the experimental system.

Bidirectional static system for active D.C. traction substations: Theoretical and experimental evaluation

This paper is focused on the presentation of a active filtering and regeneration system (SISFREG) developed for converting the DC traction substations in active substations. SISFREG will be connected between the catenary-line and the primary of the traction transformer, via a dedicated transformer. The main component of SISFREG is a shunt active power filter based on voltage source inverter structure, whose control guarantees the keeping of the prescribed voltage on the DC-side and the proper current at the inverter output by the indirect control of the supply current. The DC voltage controller is tuned in accordance with the Modulus Optimum criterion and the grid current controller is of hysterezis type. In order to verify the operation of the system and assess its performance, detailed computer simulation studies were conducted using the Matlab/Simulink package. Finally, a laboratory model was designed and build. In order to testing the system and showing its performances, an experimental setup was configured. The experimental results confirmed the good performance of the system during both traction/filtering and regeneration regimes.

DSP control implementation particularities for an active DC traction substation experimental model

The paper focuses on the design and implementation of the control algorithm for the experimental model of an active DC traction substation, paying particular attention to the design flaws and DSP implementation unforeseen problems. The design flaws combined with unforeseen behavior of the DSP control board can lead to system faults like short-circuits or overvoltage and can produce destructive malfunctions to the power equipment. Therefore, the DSP signals which can produce hazards and must be treated with maximum caution are the gating signals for the power IGBTs. These signals are usually generated using hysteresis current regulators and are available at the DSP digital output ports. While generating or inhibiting the gating signals is a matter of control algorithm and is the subject of design flaws (the control algorithm generates a logic “high” signal for the both transistors of an inverter leg, for example) the overlap of the gating signals for one or more inverter legs can appear also because of the initialization steps of the DSP control board. This is a hazardous behavior of the control board and should not normally appear, but caution must be taken especially in the initialization stages (program compiling and loading) when the output ports can change state for short periods of time. To avoid destructive faults, the IGBTs gating signals must be hardware inhibited until the system is fully initialized and ready to run. The behavior of the dSpace DS1103 control board was investigated for both design flaws and hardware unexpected actions. The implemented control algorithm is for a three phase active power filter which also must function as a current output voltage inverter.

Control algorithm design and implementation for a bidirectional PWM boost rectifier

The aim of this paper is the design and implementation of the control algorithm of a PWM boost rectifier capable to handle bidirectional energy flow. For this goal, the boost rectifier control loops must be tuned for the proper operation of absorbing active power from the power grid and transfer it to the dc load at constant output voltage, and also to give the rectifier the ability to generate back to the power grid the energy intake from the dc-link, using the dc-link capacitor as intermediary energy tank. It will be proved that the transition between rectifier operation and inverter operation is done automatically, without the intervention of the human operator or of a specially designed system. The correct implementation and tuning of the control algorithm was validated on a complete Matlab Simulink model which includes in detail all the sections of the rectifier system. The results obtained by simulation proved the correct answer of the tuned dc-link voltage controller and the overall operation of the system for a step changing active load. Because the boost rectifier control algorithm is similar to shunt active filters control algorithm, the indirect current control approach was adopted, which is the most suitable for this purpose.