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Analysis of Three-Phase Delta-Connected Converter for Compensation of Unsymmetrical Loads
Bejvl, Martin ; Šimek, Petr ; Valouch, Viktor ; Hauptmann, R.
The paper presents possibilities of compensation of general single-phase load connected to the three-phase grid. The compensation is to ensure a symmetrical and pure active load of the three-phase grid. It is documented that after the proposed compensation it is possible to draw symmetrical and pure active current from all phases. A set of multi-level voltage converters is considered as a compensation device. The paper presents a way of determining the reference currents for the converter in its two branches and proposes a method of controlling the converter so that the active power from the grid is equal to the active load of the load. This methodology is documented by the results of a series of simulations for static and dynamic modes of the system.
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Analysis of power conditioning for AC traction feeding
Bejvl, Martin
This report analyses the possibilities of symmetrization and PFC in the 3-phase supply grid if a phase-to-phase RL load is connected between two phases, which is typical for an AC traction load. Two additional converters must be added to the RL load to provide required feature. The converters produce controlled currents and set up the so-called Delta connection with the LR load. The influence of the converter currents on the 3-phase supply currents are analysed. The obtained results are presented both in diagrams and equations.
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Control Strategy of Grid Connected Converter under Unbalanced Conditions
Lettl, J. ; Bejvl, Martin ; Valouch, Viktor
Current-controlled voltage source converters are widely used in grid-connected applications. The negative sequence component of the grid voltage causes pulsating components in powers transmitted through the converterand ripple of the dc voltage in the intermediate circuit. Two strategies of the current reference calculation for a dual current controller were developed and tested in the Matlab/Simulink environment and experimentally verified as well.
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Control Techniques of Grid Connected PWM Rectifiers under Unbalanced Input Voltage Conditions
Bejvl, Martin ; Šimek, Petr ; Škramlík, Jiří ; Valouch, Viktor
Current-controlled voltage source converters are widely used in grid-connected applications,for example at ac drives with indirect frequency converters.The structure and parameters of the PLL are developed and proposed in order to cope with the grid containing both the positive and the negative sequence component, and minimize the wrong frequency transients during phase angle steps and also in the start-up stage. The DSC technique was realised. There is also necessary to compensate the negative sequence component in the grid voltage. The negative sequence component of the grid voltage causes ripple of the dc voltage in the intermediate circuit. Several sophisticated topologies of converter current controller were developed, simulated and tested for this purpose. Results of simulation and experimental tests are provided to evaluate different current control schemes and phase locked loop techniques.
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Multilevel IGBT pulse-controlled rectifier
Bejvl, Martin ; Šimek, Petr ; Škramlík, Jiří ; Valouch, Viktor
A low voltage PWM rectifier 5 kVA based on IGBT multilevel converter has been developed. It is characterized by a low THD value of the grid current and can change the power factor. The modular arrangement of a grid filter makes it possible to test either L or LCL type of grid filters of different parameters. The PWM rectifier is equipped with the vector control of the grid current and superimposed feedback loop of dc voltage.
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