Abstract-This paper presents a novel Hybrid Direct Power Converter (HDPC) which overcomes the two main disadvantages of matrix converters, limited voltage transfer ratio and low immunity to grid disturbance. The proposed converter is formed by integrating a reversible auxiliary boost converter in the dc link of the two-stage matrix converter. Therefore the HDPC can provide unity voltage transfer ratio even in the case where the supply voltage is highly unbalanced. The proposed converter also preserves most of the inherent advantages of the conventional matrix converter such as: controllable input power factor, sinusoidal supply currents and bi-directional power flow. A novel predictive current control technique for the HDPC is also proposed for minimum energy storage in the converter. Important aspects of design, control and implementation of the new HDPC are presented including theoretical analysis and simulations. Experimental waveforms at unity voltage transfer using a laboratory prototype are presented to confirm the viability of the proposed idea.
Unbalanced supply voltages can be fully compensated in boost type power converters with active front end if sufficient energy storage is provided by the DC-link capacitor. In converters that have no energy storage, matrix converters for example, the maximum voltage transfer ratio will be reduced if one or more input lines are at a reduced voltage. Traditional control techniques (passive compensation methods) compensate the effect of unbalanced voltage supply for matrix converters but limit the output voltage/powe depending on the unbalance level.This paper proposes two methods to actively (no loss in output voltage capability) compensate the effect of unbalanced voltage supply: the first one shown in Fig. 1(a), utilizes the clamp capacitor, which is normally needed to protect a Direct Power Converter (DPC), to extend the operating range of a Two-Stage DPC during unbalanced supply conditions preserving its theoretic maximum voltage transfer ratio capability; the second one shown in Fig. 1(b) is a new topology based on a hybrid approach, consisting of an H-bridge inverter inserted into the dc-link, which is also able to preserve the output voltage capability under unbalanced supply conditions. Both solutions are validated through simulations.Unbalanced voltage supply cause the input voltage vector locus to become an ellipse, which means that the average over a switching period of the rectified voltage to vary in a much wider range than in the ideal case (sinusoidal and balanced supply voltages). The principle of active compensation is to use energy storage in order to store energy when the rectified voltage is high (positive and negative voltage sequences point in the same direction) which would be used when this is low (the positive and negative sequences point opposite). Fig. 2(a) shows the DC-link voltage seen at the inversion stage terminals when there is no active compensation and the average dc-link voltage reaches a minimum of 440 V, which means that the voltage transfer ratio defined as a ratio between the output voltage divided to the direct sequence of the input voltage is decreased from 0.866 (ideal case) to 0.78. By applying active compensation using the clamp circuit, this is restored back to 0.866 as shown in Fig. 2(b). The price to be paid for improving the converter robustness against grid disturbances is a slightly oversized clamp capacitor, the need to introduce an extra IGBT in the clamp circuit and the degradation of input current quality due to uncontrolled capacitor charging, which is shown in the full paper.Active compensation using an hybrid approach is not only able to restore the voltage transfer ratio, but also stabilizes the average over a switching period and boost its value to a corresponding voltage transfer ratio of 0.909, which means that the voltage delivered to the output side falls within the normal voltage tolerance (±10%) of a motor which will allow this topology to directly compete the well established back-to-back voltage source converters. Non-memberUnbalanced supply volta...
The emphasis on clean and green technologies to curtail greenhouse gas emissions due to fossil fuel-based economies has originated the shift towards electric mobility. As on-road electric vehicles (EVs) have shown exponential growth over the last decade, so have the charging demands. The provision of charging facilities from the low-voltage network will not only increase the distribution system's complexity and dynamics but will also challenge its operational capabilities, and large-scale upgrades will be required to meet the inevitably increasing charging demands. An ultra-fast (UF) charging infrastructure that replicates the gasoline refueling network is urgently needed to facilitate a seamless transition to EVs and ensure smooth operation. This paper presents a review of state-of-the-art DC fast chargers, the charging infrastructure's current status, motivation, and challenges for medium-voltage (MV) UF charging stations (UFCS). Furthermore, we consider the possible UFCS architectures and suitable power electronics topologies for UF charging applications. To address the peak formation issues in the daily load profile and high operational expenses of UFCSs, integration of renewable energy sources and energy storage systems due to their technological and economic benefits is being considered. The benefits of line frequency transformer (LFT) replacement with a solid-state transformer (SST), SST models, SST-based UF chargers, and MV SST-based UFCS architectures, as well as related MV active front-end and back-end power electronics topologies, are presented. Finally, the application of microgrids' hierarchical control architecture is considered for chargers and system-level control and management of UFCSs.INDEX TERMS Electric vehicles (EVs), DC fast chargers, ultra-fast charging stations (UFCS), renewable energy sources (RESs), energy storage systems (ESSs), line frequency transformer (LFT), solid state transformer (SST).
Abstract-Variable voltage and variable frequency conversion of electrical energy from an AC source to an AC load is done in traditional power converters via a DC-link where an energy storage element (electrolytic capacitors) is situated. Despite its well-known benefits, it has the disadvantage of being bulky and to limit the converter lifetime. On the other hand, Direct Power Conversion (DPC) is an attractive concept, which doesn't need an energy storage buffer, but has two main disadvantages: reduced voltage transfer ratio (<0.86) and low immunity to voltage supply disturbances. This paper proposes a new approach to perform the power conversion by mixing various standard topologies of wellknown power converters in order to improve their performance/behavior. Simulation and experimental results prove that the hybrid structures are able to boost the output voltage capability (some above unity) and/or to fully compensate unbalanced voltage supply.
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