Power Management of AC Islanded Microgrids using Fuzzy Logic

Abstract

In an islanded AC microgrid consisting of renewable energy sources, battery, and load, the battery balances the difference between power generated by renewable sources and that consumed by the load. However, battery charging capacity is limited and its state of charge needs to be maintained within the safety limits. Furthermore, battery has limited maximum charging and discharging power. This paper proposes a controller based on fuzzy logic to prevent the battery state of charge and charging/discharging power from exceeding their limits regardless of variations in load and intermittent power of renewable sources. The microgrid considered in this paper consists of PV, battery, load and auxiliary supplementary unit. The fuzzy logic controller alters the AC bus frequency which is used by the local controllers of the parallel units to curtail the power generated by PV or to supplement power from the auxiliary unit. The main merits of the proposed controller are simplicity and easiness of implementation without the need for any communication links between the parallel units. Matlab/Simulink results are presented to validate the performance of the proposed controller.

Supervisory Control for Power Management of an Islanded AC Microgrid Using a Frequency Signalling-Based Fuzzy Logic Controller

“…With droop control in AC systems, decentralized control for each converter is achieved with no communication or only low bandwidth communication, such as power line communication [24]. Any DC/AC inverter in a traditional droop control does have an output frequency and a voltage amplitude defined by (1) and (2), respectively [25].…”

“…Maximum Power Point (MPP) Fig. 2 shows the power/frequency droop control for the three units [25] based on (3), (4) and (6). When the bus frequency is shifted up, the PV power is curtailed.…”

“…3. If the bus frequency is shifted down, the DC/AC inverter of the PV unit will deliver power limited by its maximum power determined by the MPPT [25], [26].…”

Hybrid generators‐based AC microgrid performance assessment in island mode

“…Furthermore, the battery system can generate and absorb power to and from the AC bus to balance the power flow by the droop control while the auxiliary supply can only generate power. This might be advantageous when the generation is more than the load which gives the chance inherently to charge the battery if possible [20]. Also, it is worth mentioning that the DC link voltage of the fuel cell‐based unit could be controlled by the inverter side controller or by the DC converter controller [21–23].…”

“…In cascaded control systems, and as a rule of thumb, the inner voltage loop must have a bandwidth that is three to five times higher than that of the outer power loop to preserve the stability and tracking resolution [14]. The modelling of a microgrid adopting the droop controller is well‐established in the literature [7–26]. The inner voltage loop is normally neglected in the modelling because its response time is much faster than the outer droop control loop.…”