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Abstract--This paper presents a boost-multilevel inverter design with integrated battery energy storage system for standalone application. The inverter consists of modular switched-battery cells and a full-bridge.It is multifunctional and has two modes of operation: the charging mode which charges the battery bank and the inverter mode which supplies AC power to the load. This inverter topology requires significantly less power switches compared to conventional topology such as cascaded H-bridge multilevel inverter, leading to reduced size/cost and improved reliability. To selectively eliminate low-order harmonics and control the desired fundamental component, nonlinear system equations are represented in fitness function through the manipulation of modulation index and the Genetic Algorithm is employed to find the optimum switching angles. A 7-level inverter prototype is implemented and experimental results are provided to verify the feasibility of the proposed inverter design. In recent years, multilevel inverters have been receiving wide attention and becoming hot topologies for renewable energy applications [5], [6]. Multilevel inverters can be classified into three types that are flying- Index Terms--

This paper presents an improved stator flux estimation technique based on a voltage model with some form of low-pass (LP) filtering. In voltage-model-based stator flux estimation, an LP filter is normally used instead of a pure integrator to avoid integration drift problem due to dc offset, noise, or measurement error present in the back electromotive force. In steady-state condition, the LP filter estimator will degrade the performance and efficiency of the direct torque control (DTC) drive system since it introduced magnitude and phase errors, thus resulting in an incorrect voltage vector selection. The stator flux steady-state error between the LP filter and a pure integrator estimator technique is derived and its effect on the steady-state DTC drive performance is analyzed. A simple method is proposed to compensate for this error which results in a significant improvement in the steady-state drive performance. Simulation based on this technique is given and it is verified by experimental results.

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This paper presents a simple flux regulation for a direct torque control (DTC) of induction motor (IM), to improve speed and torque estimations at low and zero speed regions. To accomplish this, a constant switching frequency controller (CSFC) is used to replace the3-level hysteresis torque comparator of a DTC IM. The DTC of IM utilizing CSFC (DTC-CSFC) retains the simple structure of a look-up table based DTC drive. With DTC-CSFC, constant switching frequency is maintained, and at the same, the flux droop problem that normally occurs in DTC with the hysteresis controller (DTC-HC) at low speed is solved; subsequently, the stator flux and torque estimations at low speed are also improved. In the proposed system, the speed feedback for the closed loop speed control is estimated using an extended Kalman filter (EKF), which requires heavy real-time computation. However, due to the simple structure of DTC-CSFC, small sampling time, hence large control bandwidth is possible. The performance of the speed sensorless DTC-HC and DTC-CSFC are compared experimentally under different operating conditions. With the improved stator flux regulation, experimental results of the DTC-CSFC showed a significant improvement in speed and torque estimations at very low and zero frequency operations. Index Terms-Constant switching frequency controller, direct torque control, extended Kalman filter, flux regulation, induction motor.S 0885-8993 (c)