Air abrasion has a greater effect than CO₂and Er,Cr:YSGG lasers in the treatment of zirconia ceramic surfaces to enhance the bonding strength of resin cement to zirconia. CO₂laser at 4W and Er,Cr:YSGG laser at only 3-W output power can be regarded as surface treatment options for roughening the zirconia surface to establish better bond strength with resin cements.

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The major drawback of most control methods for uninterruptible power supply (UPS) inverters is complexity. In this study, a simple voltage sensorless multi-loop control method is proposed for the single-phase UPS inverter and the parameters are designed systematically based on a frequency domain method. The suggested control scheme uses two nested simple proportional controllers instead of proportional-integral/resonant controllers to regulate the output voltage and produce active resonance damping. In addition, a feedforward compensation of the reference voltage is used to enhance the performance of the control system. The proposed controller does not need any reference frame transformation or integration/derivation of measured quantities in its structure. To reduce the cost and at the same time to improve the reliability of the converter system, the output voltage sensor is replaced by a simple estimation algorithm based on the digital Kalman filter. Experimental results with a 500 VA prototype, as well as simulation results validate the excellent performance of the suggested estimation and control scheme.

This paper addresses a novel and flexible control algorithm based on complex virtual impedance for improvement of power sharing in a multi-bus microgrid with complex impedance of lines. In the proposed method, first, the Extended Impedance-Power droop equations are derived. Using nonlinear droop equations, equivalent resistance and inductance of each DG unit are obtained by active and reactive power, separately. Then, an appropriate algorithm is employed to implement Impedance-Power droop to manage the virtual impedances adaptively. The proposed algorithm can optimally share both active and reactive power, even when the structure is changed without any knowledge of microgrid parameters and high-bandwidth communication links. The parameters of the proposed controller are designed based on the nominal power of inverters. Moreover, the stability margin of the system is analyzed. Finally, the feasibility of the proposed control scheme is confirmed via simulations and experiments.