Abstract
This paper explores the application of multifunctional inverters connected to the electrical network, to propose an adaptable system to individually control reactive power, load imbalance, and harmonic currents. Based on Conservative Power Theory (CPT), the dynamic compensation of Power Quality (PQ) indices is carried out under different conditions of demand and energy generation. First, a set of global factors for reactive power, imbalances, and current harmonics is introduced, which are effective even for bidirectional power flows in systems with harmonic voltage distortion and/or voltage unbalance. This set of factors gives rise to a multiobjective decision-making algorithm to estimate coefficients of proportionality, which instantly considers the reference signals linked to the disturbances, enabling to individually keep track of the target values of each of the PQ indices, as customarily established through standards or electricity utility criteria. As a result, this proposed approach allows a multiobjective operation of the inverter connected to the network, thereby allowing maximum use of energy generated, as well as limiting energy losses of distribution networks, and enhancement of the PQ of a prosumer. Finally, to illustrate the effectiveness of the proposed approach, different case studies were simulated with this set of case studies, including one representative real case containing a PV system connected to the network and a non-linear unbalanced load with variable demand.
Highlights
Low power quality (PQ), and other elements such as low power factor, significant harmonic distortions, and high levels of current imbalance due to the inductive loads, nonlinear loads and unbalanced loads, create a series of problems for the electricity utilities, and for small, medium and large industrial users
The need to enhance the PQ is estimated by using the information provided by the PQ indices as measured at the point of common coupling (PCC) and those enforced by standards
The conformity factors in (19) can be calculated based on the currents in the load and in the inverter (Kirchhoff’s Currents Laws), waiving the need for direct sensory examination of the grid current. This means that using (19) and the pre-set values, for the factors, through (18) and (13), it is very easy to get the reference signs for compensation as shown in (20). This strategy corresponds to multiobjective compensation, in which it is possible to ensure that all the PQ indices, such as power factor, harmonic distortion, and imbalance, remain within the ranges established by normative regulations or by the utilities, even under conditions where there is variable demand and energy generation
Summary
Low power quality (PQ), and other elements such as low power factor, significant harmonic distortions, and high levels of current imbalance due to the inductive loads (motors), nonlinear loads (electronic power devices) and unbalanced loads (both single-phase and two-phase), create a series of problems for the electricity utilities, and for small, medium and large industrial users. The work here proposed is different from others, as it allows selectivity and flexibility as necessary to fully comply with the restrictions regarding PQ and power factor, directly on the grid side, even under conditions where there is bidirectional energy flow This means that a multiobjective compensation system is developed to regulate the exchange of energy at the point of common coupling (PCC) of a prosumer. The need to enhance the PQ is estimated by using the information provided by the PQ indices as measured at the PCC and those enforced by standards Based on this principle, the proposed control system allows the exploitation of the inverter in a multiobjective manner, both regarding energy injection (bidirectional flow, considering variable generation and demand) as well as minimizing each PQ index individually.
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