1,721,024 research outputs found
Mathematical proof of a harmonic elimination procedure for multilevel inverters
No full textIn this paper, a single phase cascaded H-bridge inverter with s variable dc sources (s≥2), l=2s+1 levels has been considered. A mathematical proof is presented to demonstrate that, under a particular choice of the switching angles, which number corresponds to the number of dc sources i.e. s, and of the dc voltages, all harmonics are eliminated from the output voltage waveform, except those of order n=4p⋅s±1, p=1,2,.... With this method, the dc voltage sources vary linearly according to the modulation index m, while the switching angles do not depend on m. The resulting output voltage has low total harmonic distortion, that remains independent on m. Compared to a conventional selective harmonic elimination procedure and to a pulse amplitude method, the proposed procedure reduces distortion in a wide range of modulation index
DSTATCOM with 5-Level CHB Architecture and Selective Harmonic Mitigation Algorithm, Electric Power System Research
No full textModel Predictive Current Control With Model-Aid Extended State Observer Compensation for PMSM Drive
Full text linkModel predictive current controller is a popular and effective technique to provide fast dynamic response in the field of motor control. However, conventional predictive controllers are susceptible to deteriorating control performance when model mismatch exists, such as changes in motor parameters due to the temperature variations. Therefore, this article proposes a precise model-aid extended state observer (MAESO) compensation-based real-time model predictive current controller with enhanced parameter robustness performance and high bandwidth. The predictive controller is converted into the form of multiparameter quadratic programming for online solution using numerical computational method and the constraints are linearized. In addition, the disturbances estimated by MAESO are fed back to the controller in the form of parameters for cycle-by-cycle compensation without extra controller design. Comparative simulations and experiments under different operating conditions are carried out to verify the effectiveness and superiority of the proposed method.Model predictive current controller is a popular and effective technique to provide fast dynamic response in the field of motor control. However, conventional predictive controllers are susceptible to deteriorating control performance when model mismatch exists, such as changes in motor parameters due to the temperature variations. Therefore, this article proposes a precise model-aid extended state observer (MAESO) compensation-based real-time model predictive current controller with enhanced parameter robustness performance and high bandwidth. The predictive controller is converted into the form of multiparameter quadratic programming for online solution using numerical computational method and the constraints are linearized. In addition, the disturbances estimated by MAESO are fed back to the controller in the form of parameters for cycle-by-cycle compensation without extra controller design. Comparative simulations and experiments under different operating conditions are carried out to verify the effectiveness and superiority of the proposed method
Analysis of Capacitor Current Stress in Five-Level Active Neutral Point Clamped Converter
No full textThis paper derives analytical expression for current stress on capacitors of Five-Level Active Neutral Point clamped Converter (5L-ANPC) connected on load side. In hybrid multilevel structure, semiconductor devices operate at different switching frequencies and may not conduct even when they are gated on. Therefore, the duty ratio expressions used to evaluate current stress in DC-link capacitors may not result a correct expression. Also there is a flying capacitor in the circuit. Expressions are obtained using conduction functions (G). Conduction function is obtained by combination of switching functions (S) of appropriate switches. Results of derived expressions are compared with MATLAB Simulink results to validate the expressions. Difference in current stress on flying capacitor and DC-link capacitor in the same converter leg over sizing, lifetime expectancy and voltage ripple is discussed
Diode Assisted Quasi Z-source Inverter with Discontinuous Current: Analysis and Simulation
No full textIn this paper, the developed topology of the diodes assisted quasi Z-source inverter (DAQZSI) is proposed. This topology is investigated in three states of two-cell DAQZSI, three-cell DAQZSI and n-cell DAQZSI. These topologies are completely analyzed and the boost factor are obtained. High value of boost factor without increasing the number of used active elements is the most important advantage of this inverter in comparison with the conventional Z-source inverter. In addition, the voltage and current equations of used capacitors, diodes and inductors are calculated. Finally, the correctness of the presented analyses is reconfirmed by using the simulation results on the two-cell DAQZSI in EMTDC/PSCAD software
On Flatness-based Controller for Shunt-Connected VSC with LCL-filter for Voltage Dip Mitigation in a Weak Grid
No full textIn this paper, a grid connected shunt converter for mitigation of voltage sags in weak grids is described. The VSC keeps the grid voltage magnitude at the point of connection constant by injecting reactive power to compensate for the voltage dip. A novel flatness-based control (FBC) is proposed for this purpose that gives higher performance and robustness with an inductor/capacitor/inductor (LCL)-filter in between the VSC and the grid. Simulation model includes the practical limitation of voltage source converter output voltage. Then, the simulation results for the FBC under balanced voltage dips are presented and compared with traditional proportional integral controller. Finally, the sensitivity analysis of the FBC for grid impedance and to system parameter variations is presented
Analysis on multilevel inverter powertrains for E-transportation
No full textThe existing electric vehicles uses conventional 2-level inverters with high frequency modulation. But, they manifest some issues like high dv/dt, high torque ripple and high blocking voltage, leading to performance deterioration. Multilevel inverters address these issues and yield quasi sinusoidal output waveform, thus they represent a valuable solution to above issues, but at the cost of increased complexity, cost, and potential failure rate, due to the increased component count. Therefore, while developing multilevel converters for powertrains, the optimal number of levels has to be determined which affects overall performance and cost. Hence, accurate trade-offs among various parameters which are critical for the wide acceptance of the technology are a prerequisite. Therefore, this article is dedicated towards an evaluation of the effects of the number of levels in multilevel converters for e-powertrains and recommends a unique choice to enhance vehicle performance over conventional 2-level inverters. To validate the simulation results, a prototype of powertrain is implemented and the output is fed to a 3-phase permanent magnet synchronous machine. It is also concluded that use of multilevel inverter is worthwhile compared to the conventional 2-level inverter for electrification of the car fleet
Seven-level cascaded inverters for Uninterruptible Power Supply (UPS) applications
No full textThis paper considers single phase seven-level cascaded H-bridge (CHB) inverters for Uninterruptible Power Supplies (UPS) applications and proposes a fundamental switching frequency procedure, based on graphic analysis, to improve the output waveform quality. It fixes the first switching angle and gets the other two by intersection of harmonics functions set to zero. The performances of the proposed procedure, in terms of total harmonic distortion (THD), are compared with those obtained by a procedure that identifies the two remain optimal switching angles through a THD minimization algorithm. Experimental results are obtained by measurements performed on a prototype built at DigiPower laboratory. The agreement between computed and experimental results confirms the accuracy of the presented procedure
Selective Harmonic Elimination Procedure for Uniform Step Asymmetrical 7-Level CHB Inverter
No full textMultilevel converters offer high power capability, low switching losses and low harmonic content in output wave-forms. Their main disadvantage is their complexity requiring a great number of power devices and passive components rather than a complex control circuitry. The use of asymmetrical topologies allows to reduce the number of power devices. This paper proposes a three-phase uniform step asymmetrical seven-level cascaded inverter composed by two II-bridges. A simple selective harmonic elimination graphical procedure is introduced to calculate the value of switching angles capable to eliminate fifth and seventh harmonics. The proposed method is compared to multiple optimization methods in order to assess its performance. Simulation results are validated using a small scale laboratory prototype of a three phase seven-level cascaded H-bridge inverter controlled by STM32F407 microcontroller
DC Current Suppression in CHB-STATCOM With Model Predictive Control Employing Current Transformers
Full text linkDC current injection is a common problem in grid-tied inverters and it is especially emphasized when current transformers are employed to sense the current. Although the dc current elimination is already addressed for linear controllers, it is not faced for model predictive control. This manuscript proposes a dc current elimination strategy for cascaded H-bridge (CHB) static synchronous compensators controlled by finite control set model predictive control (FCS-MPC). In addition to the two optimization layers of typical FCS-MPC, this article proposes using a third optimization layer to balance the voltages of the clusters. This article demonstrates that the dc current is suppressed by minimizing the imbalance among the clusters through the common-mode voltage. The algorithm is simple to implement and the ac output current is not affected. Validation is carried out with a five-level CHB-STATCOM, and a classical approach is compared
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