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This paper proposes a robust current controller (CC) and dc-link voltage controller based on $\mu $ -synthesis and $H_{\infty }$ method, respectively, for a single-phase photovoltaic (PV) converter with an LCL-filter under weak grid operation. The $\mu $ -synthesis CC guarantees system robustness against weak grid uncertainties such as grid impedance variations and voltage harmonics. Moreover, the controller compensates the system delays arising from the calculation, pulsewidth modulation, and zero order hold, as well as delay uncertainties. The CC only uses the grid current feedback which eliminates the requirement for additional loops or state measurements utilized in partial or full state-feedback systems. In addition, the $H_{\infty }$ dc-link voltage controller minimizes the bus voltage fluctuations caused by variations of PV system power generation. Also, the controller ensures system robustness against such power variations, which conventional controllers fail to perform. Moreover, power decoupling is achieved by the control system without any auxiliary circuit. In addition, the stability and robust performance of the phase-locked loop in a weak grid with major impedance changes is verified. Simulation and experimental results prove the superior performance of the proposed controllers in both cases of a nominal system and a system with deviated parameters. [ABSTRACT FROM AUTHOR]

A new distributed control scheme and charge flow analysis is presented for voltage balancing of series connected battery cells using nondissipative modular power electronics. Each modular bridge is connected across two battery cells using a high frequency transformer and an asymmetrical half-bridge. This results in using one switch and one diode per battery cell. Intrabridge charge transfer equalizes the voltage of two battery cells within a module using coupled transformer windings. Each modular bridge is connected to adjacent bridges by connecting transformer windings within each module. This allows interbridge charge transfer and the balancing of pairs of battery cells, both within adjacent bridge modules and modules more removed. The proposed controller uses a distributed control strategy whereby the control of each modular bridge monitors its own battery cell voltages and also those of adjacent bridges, thus reducing the number of feedback sensors. Detailed analysis is presented that quantifies the flow of charge between a number of series connected battery cells ($ N$ battery cells). A per-unit design methodology is used to illustrate the system charge flow characteristics. Simulations, design guidelines and experimental results are presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

An alternative transmission line design method is proposed that reduces the required conductor-to-ground clearance by injecting third harmonic voltage. In this method, third harmonic voltage is injected to the line, such that the peak amplitude of phase voltages is reduced by 13.4% while the fundamental component remains intact. The injected third harmonic voltage does not influence the load or generation sides. The objective is to utilize the insulating strength of the conductor-to-ground clearance almost continuously rather than only during the crest voltage, as opposed to conventional ac lines. With this approach, for the same fundamental voltage level, the proposed line requires lower conductor-to-ground clearance. This could considerably reduce the line construction capital investment by using shorter transmission towers. Furthermore, the existing ac lines could be upgraded with this method to increase their ground clearance, if desired. Injection of third harmonic voltage can also increase the loadability of existing ac lines, if the new phase-to-phase clearance is met. In this paper, the operation of a power transmission line with injected third harmonic voltage and practical consideration for its implementation are studied. [ABSTRACT FROM AUTHOR]

The first part of this article reviews the concepts of apparent power and power factor in single-phase circuits with non-negligible line impedances. The study is based on the well-known definition that the apparent power is the maximum load power subject to constant line losses and constant load voltage. In reality, however, all transmission/distribution lines have some finite impedance, and thus, the constant voltage condition cannot be maintained at the load terminals. In this article, the constant load voltage condition is relaxed and allowed to change, as long as it remains within acceptable range of application. This is a scenario that better reflects the realistic situations. Modified expressions for the apparent power and power factor are derived and discussed. The second part of the article presents a new concept called the current factor as the ratio of the minimal current to the actual current while keeping the load power constant. The current factor coincides with the power factor when the line impedances are neglected. The article explains how the current factor can be superior to the power factor when the line impedances are not negligible. The current factor is then extended to non-sinusoidal current factor for a non-linear load and is examined. [ABSTRACT FROM AUTHOR]

A simple and effective space vector pulse width- modulation technique for six-phase voltage-source-inverter-fed split-phase induction motors is presented in this paper. The approach employs dual three-phase space vector modulators equipped with overmodulation schemes that compensate for the voltage gain reduction due to the use of two independently controlled three-phase inverters. It secures full control of the voltage gain up to the maximum achievable gain with negligible low-order harmonics and utilizes a simple classification algorithm for the implementation of the space vector modulation (SVM) in both linear and overmodulation modes. Experimental results are provided to verify the validity of the proposed SVM split-phase approach. [ABSTRACT FROM AUTHOR]