Multi‐functional distributed generation control scheme for improving the grid power quality

Abstract

The large-scale integration of renewable energy sources require routine planning. Renewable sources are expected to be a key element of future power systems. With many challenges ahead, thinking out of the box is necessary in order to equip the power system with additional advanced functionalities and capabilities to combat the anticipated challenges. The associated equipment of distributed generation can be seen as a grid asset upgrade because of the increased number of elements connected to the grid, such as grid side converters (GSC) of photovoltaics and battery storage systems. It therefore makes sense to think of ways to diversify the role of distributed renewables in a way that benefits the grid, consumers, and prosumers in terms of power quality. In parallel with the diversified role of distributed renewables, this approach can be also thought of as a systematic process of developing, operating, maintaining and upgrading the grid. The work proposes an advanced, multi-function GSC control technique for improving the distribution grid power quality by enabling the injection of asymmetric, DC and harmonic currents in case it is needed. Injecting for example such currents locally through the GSC of a residential photovoltaic system can compensate undesired characteristics of the prosumer loads in order to allow the flow of symmetric and high quality currents between the prosumer and the distribution grid (irrespective of the load conditions). The proposed control technique consists of a Phase-Locked Loop (PLL) necessary for synchronization purposes and advanced PQ and current controllers necessary for injecting the reference currents. Experiments and simulation results are presented to validate the performance of proposed control technique.

Phase Balancing and Reactive Power Support Services for Microgrids

“…In case an existing solution (as the one used in Reference [25]) for the inverter controller is used to provide the Q-PB service, priority will always be given to reactive power support while unbalance As can be seen in Figure 10 the positive sequence reactive power reference of the PV inverters (Q +1 * PV ) was decreased during the noon due to the reduction of the weights (w n ) associated with the PV systems caused by the increase of their energy production (reduction of the available capacity for ancillary services (Î as )). This change on the adaptive weights is also reflected on the ESS in which its reference positive sequence reactive power (Q +1 * ESS ) was increased during that time to compensate the availability reduction of the PV systems.…”

“…From the distribution system operator point of view, these remarkable improvements can have a great impact on the power quality, the energy losses and the effective utilization of the grid. In case an existing solution (as the one used in Reference [25]) for the inverter controller is used to provide the Q-PB service, priority will always be given to reactive power support while unbalance compensation would be provided only in case there would be enough available inverter capacity. On the other hand, the proposed solution enables the fair compensation of Q-PB service due to the new developed inverter controller while the priority is set according to the loading conditions at the MG's PCC.…”

“…However, the development of these solutions come with a significant capital cost for the system operator or for the consumer. Another solution to compensate loading asymmetries and harmonic distortions at the building level is proposed in References [24][25][26]. The grid tied inverter of a PV or ESS is enhanced with advanced capabilities to compensate prosumer asymmetries.…”

Control Scheme for Phase Balancing of Low-Voltage Distribution Grids

“…This solution imposes a high cost capital investment by the DSO or the grid owner. Another approach to achieve phase balancing and harmonic compensation is proposed in [14]- [16], where the grid tied inverter of a PV system is enhanced with advanced functionalities in order to compensate the prosumer asymmetric loading conditions at the building level. The deployment of these solutions requires additional current sensors to locally measure the building loading conditions and it is only effective for buildings that are equipped with PVs or a BSS.…”

A Sensor-less Control Scheme for Grid Tied Inverters to Provide Phase Balancing Services to the Distribution Grid

“…This solution requires a high capital investment for batteries and the converter, while space restrictions should also be considered within the substation. Alternative solutions have been proposed in [6]- [11], where grid tied inverters of PV systems are utilized not only for injecting properly the produced power into the grid, but also for providing ancillary services to benefit the grid operation. In [6] and [7], the inverters are also used to compensate the harmonic distortion imposed by the prosumer's non-linear loads.…”