In commercial inverters, an LCL filter is considered an integral part to filter out the switching harmonics and generate a sinusoidal output voltage. The existing literature on the averaged virtual oscillator controller (VOC) dynamics is for current feedback before the output LCL filter that contains the switching harmonics or for inductive filters ignoring the effect of filter capacitance. In this work, a new version of averaged VOC dynamics is presented for islanded inverters with current feedback after the LCL filter thus avoiding the switching harmonics going into the VOC. The embedded droop-characteristics within the averaged VOC dynamics are identified and a parameter design procedure is presented to regulate the output voltage magnitude and frequency according to the desired ac-performance specifications. Further, a power dispatch technique based on this newer version of averaged VOC dynamics is presented to simultaneously regulate both the active and reactive output power of two parallel-connected islanded inverters. The control laws are derived and a power security constraint is presented to determine the achievable power set-point. Simulation results for load transients and power dispatch validate the proposed version of averaged VOC dynamics.

Accurate active and reactive power sharing is of utmost importance in an inverter-interfaced AC microgrid. Power droop-control has been proven as a good design tradeoff and communication less technique to achieve load sharing. Implementation of power droop-control requires both the voltage and current tapping at the inverter output to calculate the power and achieve synchronization with rest of the system. On the other hand, recently proposed virtual oscillator controller (VOC) features inherent synchronization using only the current measurement. However, VOC being a non-linear oscillator introduces harmonic distortion in the output. This paper investigates the power sharing capability, dynamic response and harmonics profile for a system consisting of parallel-connected (i) droop-controlled inverter and (ii) virtual oscillator-controlled inverter. It has been demonstrated that power sharing between these two different control techniques can be achieved by properly designing both the droop-controller and VOC-parameters. The harmonic distortion present in the output of VOC results in the harmonic current to flow between the two inverters. The harmonic distortion can be reduced by designing a tightly regulated VOC inverter. However, this results in a slow dynamic response. Several scenarios including the plug-n-play capability, step change in load, and the design trade-off in between dynamic response and harmonic content present in the output is demonstrated through the simulation results.

A control strategy is presented that simultaneously regulates both the active and reactive power of two parallel-connected virtual oscillator controlled inverters. In microgrids with distributed generation sources, it is of vital importance to regulate the output power of each source independently. This facilitates better energy source utilization, reduced losses and stress on the distribution lines. PI controllers are proposed that are used to tune the current and voltage gains of the virtual oscillator controller to regulate the inverter output power. Control laws are presented to determine the values for current and voltage gains to achieve both the active and reactive output power setpoints simultaneously. Further, a security constraint is derived that guarantees the existence of real-valued solutions for current and voltage gains corresponding to the desired output power set-points. The main advantage associated with this security constraint is the confidence that a particular output power setpoint can be achieved. Simulation results show that the VOC inverter with the proposed control strategy follows the desired reference power set-points effectively.

We study the problem of optimal reduced-dimension linear transform coding and reconstruction of a signal based on distributed correlated observations of the signal. In the mean square estimation context this involves finding the optimal signal representation based on multiple incomplete or only partial observations that are correlated. In particular, this leads to the study of finding the optimal Karhunen-Loeve basis based on the censored observations. The problem has been considered previously by Gastpar, Dragotti, and Vetterli in the context of jointly Gaussian random variables based on using conditional covariances. In this paper, we derive the estimation results in the more general setting of second-order random variables with arbitrary distributions, using entirely different techniques based on the idea of innovations. We explicitly solve the single transform coder case, give a characterization of optimality in the multiple distributed transform coders scenario and provide additional insights into the structure of the problem.