High-Gain Single-Stage Boosting Inverter for Photovoltaic Applications

Abstract—

This paper introduces a high-gain single-stage boosting inverter (SSBI) for alternative energy generation. As compared to the traditional two-stage approach, the SSBI has a simpler topology and a lower component count. One cycle control was employed to generate ac voltage output. This paper presents theoretical analysis, simulation and experimental results obtained from a 200 W prototype. The experimental results reveal that the proposed SSBI can achieve high dc input voltage boosting, good dc–ac power decoupling, good quality of ac output waveform, and good conversion efficiency.

A Novel Buck–Boost AC–AC Converter With Both Inverting and Noninverting Operations and Without Commutation Problem

Abstract—

This paper proposes a new type of ac–ac converter which can operate as traditional noninverting buck and boost converters, and inverting buck–boost converter as well. The proposed converter uses six unidirectional current flowing and bidirectional voltage blocking switches, implemented by six reverse blocking insulated-gate bipolar transistors (IGBTs) or series MOSFET–diode pairs, two input and output filter capacitors, and one inductor. It has no shoot-through problem of voltage source (or capacitor) even when all switches are turned-on, and therefore, pulsewidth modulation dead-times are not needed resulting in high-quality waveforms, and solves the commutation problem without using bulky and lossy RC snubbers or dedicated soft-commutation strategies. It has smaller switching losses because only two switches out of six are switched at high frequency during each half-cycle of input voltage, and it can use power MOSFETs as body diode never conducts, making it immune from MOSFET failure risk which otherwise may occur due to poor reverse recovery problem of body diode. The non-inverting buck–boost mode of the proposed converter can be used in applications with both step-up and step-down demand, while the inverting buck–boost mode can also be used in its application as dynamic voltage restorer. Detailed analysis of the proposed converter is given, and experimental results are also provided.

BOOST MODE

 BUCK MODE

An Islanding Detection Algorithm for Inverter-Based Distributed Generation Based on Reactive Power Control

Abstract—
 For the inverter-based distributed generation (DG) under constant power control, this paper analyzes the relationship between the active/reactive power mismatch and frequency deviation, respectively, during islanding and finds that the frequency variation trends caused by active and reactive power mismatches may be opposite. In order to eliminate the nondetection zone (NDZ) and detect islanding rapidly, an innovative islanding detection algorithm is presented based on a reactive power control strategy. The strategy provides the reactive power reference for the DG to guarantee the consistency of the frequency variation trends caused by both active and reactive power mismatches, thus accelerating the islanding detection speed. In addition, the introduction of the voltage variation into the proposed reactive power control strategy can regulate voltage dynamically in grid-connected mode and further shorten the islanding detection time as well. According to the antiislanding test system in the IEEE Std. 929-2000 and IEEE Std. 1547-2003, several case studies are carried out in the power systems computer-aided design/EMTDC environment. The simulation results show that the proposed algorithm has the zero NDZ property and can detect islanding rapidly. Moreover, the algorithm also performs effectively for load imbalance conditions as well as for the system with multiple DGs.

Comparison of SPWM Multilevel Inverter Fed PMSM drive with Two level Inverter Fed Drive

Abstract-
Permanent magnet synchronous motors (PMSM) are becoming popular over Induction machines in the field of modern variable speed AC drives especially in electric vehicle (EV) and hybrid EV. Its advantages include high power density,high torque to current ratio, high efficiency and ease of control.Field Oriented Control of PMSM can be easily implemented usingdynamic model. Torque ripple in permanent­magnet synchronousmotors is generally undesirable. Superior performance of MultiLevel Inverter (MLI) over two-level inverter can be utilizedto improve the performance of the PMSM drive system. Inthis study both SPWM (Sinusoidal Pulse Width Modulation)based 2-level, 3-level and 5-level inverter fed PMSM drive wereconsidered. These techniques are studied through simulation in MATLAB/SIMULINK environment and the performances of both the techniques are compared. The effectiveness of MLI fed driveover 2-level are verified from the sim ulation results.

Elimination of Commutation Failures of LCC HVDC System with Controllable Capacitors

Abstract—

This paper presents a novel hybrid converter configuration for conventional Line-Commutated Converter (LCC) HVDC technology aiming to eliminate commutation failures under serious faults. Dynamic series insertion of capacitors during commutation is utilized to increase the effective commutation voltage. The operating principles are presented followed by detailed mathematical analysis for both zero impedance single-phase and three-phase faults in order to select the required capacitor size and its voltage level. The performance of the proposed method is validated by simulation results in Real Time Digital Simulator (RTDS) and the results show that the proposed converter configuration is able to eliminate commutation failures under both fault cases. Consequently partial power transferring capability during single-phase fault and fast fault recovery from three-phase fault can be achieved. Further simulation results show that the harmonic content of inverter AC voltage and current are not significantly increased and the voltage stress of the thyristor valve is comparable to that of the original benchmark system.

Frequency and Voltage Control Strategy of Standalone Microgrids With High Penetration of Intermittent Renewable Generation Systems

Abstract—

In this paper, we propose a frequency and voltage control strategy for a standalone microgrid with high penetration of intermittent renewable generation systems, which might cause large frequency and voltage deviation in the system due to unpredictable output power fluctuations. To this end, a battery energy storage system (BESS) is suggested for generating the nominal system frequency instead of a synchronous generator, from a frequency control perspective. This makes the system frequency independent of the mechanical inertia of the synchronous generator. However, a BESS has a capacity limitation; a synchronous generator is used to maintain the state of charge (SOC) of the BESS at a certain value. For voltage control, we proposed that a reactive power/active power (Q/P) droop control be added to the conventional reactive power controller. By adding a Q/P droop control, renewable generation acquires a voltage-damping effect, which dramatically alleviates the voltage fluctuation induced by its own output power fluctuation. Simulation results prove the effectiveness of the proposed control strategy from both frequency and voltage control perspectives.

An Improved Control Method for Multiple Bidirectional Power Converters in Hybrid AC/DC Microgrid

Abstract—

In this paper, an improved control method for multiple bidirectional power converters is proposed to reduce the circulating current and power-sharing deviation among converters when the hybrid ac/dc microgrid operated in island mode, which can enhance the security of parallel converters. First, a unified detection method for circulating current and power-sharing deviation is described. Then, the improved control method for bidirectional converters in hybrid microgrid operated in island mode is presented to reduce circulating current and power-sharing deviation, which includes the droop controller used to achieve automatic power sharing and the improved virtual impedance controller used to further reduce circulating current and power-sharing deviation. At last, simulation and experiment results verified that the proposed control method can simultaneously achieve circulating current reduction and automatic power sharing, and does not decrease the output power capability of converter. The proposed control method is suitable for the configuration that has a specific bus between bidirectional power converters, and the ac bus connected to ac loads and the host grid.