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This paper presents a modification of the Vienna rectifier (VR) to obtain more than three voltage levels at the DC line connection, while preserving the unity power factor at the AC grid side. The proposed unidirectional multilevel there-phase rectifier, called the “Negev rectifier”, has a reduced device count and utilizes a unique novel Time Division Multiplexed based control scheme, which makes the challenging N-level VR expansion possible. The Negev rectifier can serve as a grid interface for supplying dc voltage to multilevel inverters with 4 up to 7 voltage levels, eliminating the burden of inverter-side voltage balancing control. The Negev hardware can be constructed by two complementary topologies, making it suitable for either high current or high voltage applications. [ABSTRACT FROM AUTHOR]

As penetration of distributed generation increases, the electrical distribution networks may encounter several challenges mainly related to voltage control. The situation may deteriorate in case of a weak grid connected to an intermittent source such as photovoltaic (PV) generation. Fast varying solar irradiance can cause unacceptable voltage variations that may not be easily compensated by slow-responding utility equipment. The PV inverter can be used to control the grid voltage by injecting/absorbing reactive power. A small-signal model is derived in order to study the stability of a PV inverter exchanging reactive power with the grid. This paper also proposes a method that utilizes the available capacity of the PV inverter to support the grid voltage without violating the rating of the inverter and the maximum voltage that the inverter's switching device can withstand. The method proposed in this paper is validated using PSCAD/EMTDC simulations. [ABSTRACT FROM PUBLISHER]

The flying-capacitor-based multilevel converter is one of the well-known breeds of the multilevel power converters. This paper proposes a new flying-capacitor-based multilevel converter to minimize the number of flying capacitors (FCs) and power switches. The advantage of the proposed FC-based multilevel converter in comparison with the conventional flying-capacitor multicell converter is that it needs fewer FCs. Also, in comparison with the stacked multicell converter, the proposed multilevel converter requires fewer semiconductor switches. In order to balance the voltage of the FCs in proposed multilevel converter, a new active voltage balancing method which is fully implemented using logic-form equations is presented. The proposed voltage balancing method measures output current and FC voltages to generate switching states to produce the required output voltage level, as well as balance the FCs voltages at their reference values. The output voltage of the proposed multilevel converter controlled with suggested active voltage balancing method can be modulated with any pulse-width-modulation (PWM) method, such as phase-shifted-carrier PWM or level-shifted-carrier PWM. Simulation results and experimental measurements of proposed FC-based multilevel converter are presented to verify the performance of the proposed converter, and its novel switching and modulation strategy, which is based on the active voltage balancing method. [ABSTRACT FROM PUBLISHER]