An energy-based control for an n-H-bridges multilevel active rectifier
ABSTRACT This paper deals with the control of a multilevel n-H-bridges front-end rectifier. This topology allows n distinct dc buses to be fed by the same ac source offering a high loading flexibility suitable for traction applications as well as for industrial automation plants. However, this flexibility can lead the system to instability if the dc buses operate at different voltage levels and with unbalanced loads. Thus, linear controllers, designed on the basis of the small-signal linearization, are not effective any longer and stability can not be ensured as large-signal disturbances occur. The use of a passivity-based control (PBC) designed via energy considerations and without small-signal linearization properly fits stability problems related to this type of converter. The system has been split into n subsystems via energy considerations in order to achieve the separate control of each dc bus and its stability in case of load changes or disturbances generated by other buses. Then, a set of n passivity-based controllers (one for each subsystem) is adopted: the controllers are linked using dynamical parameters computed through energy balance equations. Hence, the system dc buses are independent and stable as experimental results demonstrate.
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ABSTRACT: The cascaded H-Bridge multilevel active rectifier is an emerging converter topology, which offers significant advantages, such as modularity and high flexibility for a wide range of applications, including traction systems, industrial automation plants, uninterruptable power supplies, and battery chargers. However, the need for stable operation of the H-Bridge cells at asymmetrical voltage potentials and unbalanced loads imposes demanding requirements, in terms of an advanced and accurate control strategy. This paper introduces a simple and powerful solution to the mentioned problems, based on constrained Model Predictive Control (MPC). The proposed nonlinear controller achieves low input current harmonic distortion with almost unity power factor, as well as independent regulation of the H-Bridge cells, both under steady state and transient conditions. The effectiveness of the novel control algorithm is demonstrated by means of simulations as well as preliminary experimentation on a single-phase laboratory setup.Energy Conversion Congress and Exposition (ECCE), 2011 IEEE; 10/2011
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ABSTRACT: In this paper, a new cascade active-front-end converter based on dual-boost/buck converters is proposed for an intelligent universal transformer (IUT), which allows adjusting the power factor to control both the active and reactive powers between medium and low voltage levels. Compared to the traditional cascade H-bridge converter, it has much enhanced system reliability owing to no shoot-through problems and lower switching loss with the help of using power MOSFETs. In addition, a unified control scheme is proposed for active-reactive power control and individual voltage balancing control, which is modular and easy to implement. In the end, a laboratory three-unit cascade active-front-end converter based on the half-bridge dual-boost/buck converter is constructed and tested. The experimental results verified the feasibility and effectiveness of the proposed active-front-end converter and the unified control scheme for IUT.IEEE Transactions on Industrial Electronics 01/2012; 59(12):4671-4680. · 5.17 Impact Factor
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ABSTRACT: In this paper, an indirect control strategy for multilevel cascaded H-bridge rectifiers is introduced. The indirect control does not need any current sensors, hence the system reliability increases. Using this method, controllable power factor with nearly sinusoidal ac current could be achieved. All dc link voltages are regulated to a constant reference voltage, even if they consume various amounts of power. In the proposed strategy, the multicarrier phase-shifted sinusoidal pulsewidth modulation (MPS-SPWM) technique is used in order to eliminate low order harmonics, while the maximum switching frequency is limited to 500Hz. Additionally, no extra ac filters are needed at the ac side since the total harmonic distortion is below 5%. To verify the validity and effectiveness of the proposed control strategy, several simulations are carried out on a 7-level cascaded H-bridge rectifier in PSCAD/EMTDC environment.01/2012;