This article presented a new structure for the grid-connected multilevel inverters (MLIs) circuit with the ability of the cascaded connection. The proposed inverter is capable of transformerless connection of distributed generation resources to the network. The control system manages the power injection to the grid by minimizing the output current harmonics as well as exchanging reactive power with the grid. The self-balancing state of the capacitors' voltage is occurred only with the switching technique without any measurement sensors. An enhanced phase-locked loop (EPLL) and a proportional resonant (PR) controller are employed for the proposed asymmetric MLI. An important feature of the proposed inverter is the ability of stable performance and fast dynamics of the control system to the changes of the reference values. Simulation and experimental results are presented in order to validate the performance accuracy of the proposed MLI.

This paper aims to present a novel switched-capacitor multi-level inverter. The presented structure generates a staircase near sinusoidal AC voltage by using a single DC source and a few capacitors to step-up the input voltage. The nearest level control (NLC) strategy is used to control the operation of the converter. These switching states are designed in a way that they always ensure the self-voltage balancing of the capacitors. Low switching frequency, simple control, and inherent bipolar output are some of the advantages of the presented inverter. Compared to other existing topologies, the structure requires fewer circuit elements. Bi-directional power flow ability of the proposed topology, facilitates the operation of the circuit under wide range of load behaviors which makes it applicable in most industries. Besides, a 13-level laboratory prototype is implemented to realize and affirm the efficacy of the MATLAB Simulink model under different load conditions. The simulation and experimental results accredit the appropriate performance of the converter. Finally, a theoretical efficiency of 92.73% is reached.

Dielectric barrier discharge plasma actuators have attracted a lot of attention to use as new technologies for active flow control. In this paper, an experimental investigation of a single unsteady plasma actuator driven by two simultaneous sinusoidal high voltages is carried out. The aerodynamic performance of this plasma actuator is investigated for flow control of a wind turbine blade. Leading edge separation control at Reynolds number of 0.26 × 10 6 and in a wide range of angles of attack including linear, stall, and post-stall regions is considered as the test case. The momentum imparted by the plasma actuator to flow is investigated via measuring induced electric wind velocity, which represents that the induced velocities in the steady mode, with v max ≅ 5 m / s, are higher than that of the unsteady mode. The important aspect of exciting the unsteady dielectric barrier discharge plasma actuator in this new approach is improving its efficiency through increasing the authority of momentum addition to flow and reducing the minimum input power for discharge ignition relative to its typical grounded structure. This can be very important practically in flow control applications where the amount of consumed energy is a substantial factor in determining the actuator's efficiency. The obtained aerodynamic results reveal that the unsteady plasma actuator has the best operation in post-stall angles of attack, which is of great importance for operation characteristics of wind turbine blades. The power spectral density of pressure time series illustrates that the unsteady plasma actuator affects the flow through instabilities of the separation layer and vortex shedding structure.

This paper presents a transformerless step-upmultilevel inverter based on a switched-capacitor structure. One of the main contributions of the proposed topology is replacing the separated DC voltage sourcewith capacitorswhich are charged at predetermined time intervals. Therefore, a high-level staircase voltage waveform can be achieved by discharging some of these capacitors on the load. The other contribution of the proposed structure is to eliminate themagnetic elements which traditionally boost the input DC voltage. In addition, asymmetrical or unequal amounts of capacitor voltages create more voltage levels, which enable voltage level increments without increasing the number of semiconductor devices. This paper introduces a self-balanced boost Switched-CapacitorsMultilevel Inverter (SCMLI) which is able to create a nearly sinusoidal voltage waveform with a maximum voltage of up to 45 times that of the input voltage DC source. Higher level output voltage levels are also achievable by extending the circuit topology. After determination of the switching angles and selecting the proper switching states for each level, an offline NLC method is used for modulation, which eases the control implementation. Analysis, simulation and experiments are carried out for a 91-level inverter (45 levels for positive and negative voltages and one for zero voltage) are presented.