Procedure to match the dynamic response of MPPT and droop-controlled microinverters

Abstract

Due to the absence of communication needs and great reliability, the droop-control technique is a great choice for controlling of inverters that are subjected to load sharing or to work in an islanded mode. On the other hand, current-controlled inverters are often used in grid-connected systems due to their fast response to power the implementation of maximum power point tracking (MPPT) algorithms to maximize the power extracted from these systems. However, the application of such algorithms in gridconnected droop-controlled systems is hampered by differences in the dynamic responses of the respective techniques. In this context, this study presents the development of a strategy that enables a push-pull converter controlled by MPPT and a low-power plug and play grid-connected inverter governed by droop control to operate stably even under variations in solar radiation. The goal is achieved based on the following two approaches: designing the dclink capacitor properly and using a control loop in order to adapt the droop curves in accordance with the available input power. Theoretical analysis and experimental results have proven the viability of the approach.

Procedure to Match the Dynamic Response of MPPT and Droop-Controlled Microinverters

“…As a matter of fact, it can provide acceptable performance in order to operate together with MPPT, as it can be seen in Figs. 7 and 8 and also confirmed by the experimentations in [21]. Still comparing Figs.…”

“…It can be noticed that in all simulations, the final value of the dc-link voltage was 430 V, exactly the same desired value. This shows the effectiveness of (21). It can also be noticed that due to lower capacitance, the 120 Hz oscillations of the dc-link voltage are higher in Simulation (c).…”

“…In practice, it is not simple to implement a derivative compensator. Hence, in order to dispense the implementation of this compensator, the k p constant was tuned in such a way to meet two main requirements: first, setting the droop curve in order to obtain a first-order response with the shortest possible settling time during the power transfer [24] and, second, finding a value for k p that is small enough in order to guarantee that the system cutoff frequency will nullify the second pole effect, presented in (21).…”

“…In this context, in continuity to the work presented in [21], this paper presents the development of a strategy that enables a push-pull converter controlled by MPPT and a low-power plug and play grid-connected inverter governed by droop control to operate stably even under variations in solar radiation. That is, this paper is concerned specifically on matching MPPT and the droop-control technique during the grid-connected operation.…”