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: 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. · 6.50 Impact Factor
Conference Paper: Analysis of stable area of two-cell cascaded H-Bridge rectifier[Show abstract] [Hide abstract]
ABSTRACT: In this paper, analysis of the stability in two-cell cascaded H-bridge (CHB) rectifier is presented. The stability problem is caused by the couple controllers which are used to balance the DC-link voltages of each cell. The analysis is carried on by phasorial diagram method and general conclusions about the stable area are derived. Based on the conclusions, the stable area is continued to study for a practical control scheme. The index λp is introduced to denote the unbalance degree of the two-cell rectifier. Then the stable area is defined by a group of equations. The stable area expression shows that the grid voltage, DC-link reference voltages and the expected power factor are all contributed to the stable area. Experimental results are given to verify the feasibility and validity of the proposed method.Electrical Machines and Systems (ICEMS), 2011 International Conference on; 01/2011
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ABSTRACT: In this paper, a generalized switching technique for cascaded $H$ -bridge (CHB) converters is proposed. To take advantage of both low- and high-frequency modulation techniques, a hybrid modulation method is utilized. The proposed technique employs the low-frequency switching for voltage balancing of the dc-link capacitors, and the high-frequency sinusoidal pulse-width modulation switching for shaping the input ac current. Using the proposed technique, the stable operating region of CHB converters is extended. The proposed technique is capable of maintaining the dc voltages balanced even under critical operating conditions in which the load of one $H$-bridge cell is removed. The validity and effectiveness of the proposed method is confirmed by several simulation and experimental tests on a seven-level CHB rectifier.IEEE Transactions on Power Electronics 01/2014; 29(9):5044-5053. · 5.73 Impact Factor