This paper analyzes the effects of unbalanced voltage on doubly fed induction generators. It also presents a novel control strategy based on direct power control (DPC+) applied to this type of generators, predominant in wind energy applications, that enables them to work under perturbed conditions and achieve optimum results. Although the technique can be implemented to control both rotor converters and grid converters, we will hereby exemplify the former which regulates stator active and reactive power. The results obtained with DPC+ are then compared through experimental tests to indicate that the technique is suitable and achieves good dynamic responses while controlling current distortion, power or torque oscillations. The validation of results has been performed through experimental tests on a 20-kW generator.

Improving the fault ride-through (FRT) capability of doubly fed induction generators (DFIGs) in wind power applications is a very important challenge for the wind power industry. The mathematical models of such generators enable us to analyze their response under generic conditions. However, their mathematical complexity does not contribute to simplifying the analysis of the system under transient conditions and hence does not help in finding straightforward solutions for enhancing their FRT. This paper presents a simplified model of the DFIG, which has been extracted from the classical fifth-order model, which can accurately estimate the behavior of the system while significantly reducing its complexity. In this paper, the mathematical deduction of this model will be presented, and simulations and experimental results will be shown to demonstrate the accuracy and reliability of the proposed algorithm.

Residential rooftop‐mounted solar photovoltaic (PV) panels are being installed at an increasing rate, both in New Zealand and globally. There have been concerns over possible issues such as overvoltage and overcurrent. These PV systems are mostly connected at low voltage (LV). This study presents a case study of simulating the entire LV network from a single utility, comprising 10,558 11 kV–415 V transformers and their associated distribution feeders. These results are also presented by network type. Various solar PV penetration levels are added to the model and the power‐flow results are presented. From these results, possible maximum limits of solar PV penetration are investigated and measures to alleviate overvoltage problems are simulated. The effect of using PV inverters with voltage regulation is simulated. Results show that some minor overvoltage problems can be expected in the future, particularly in urban areas. However, in most cases the overvoltage would not be much higher than the statutory limit of 1.06 p.u.

This paper analyzes the effect of unbalanced voltage over doubly fed induction generators (DFIGs) and presents a novel control strategy, named dynamic programming power control plus (DPPC+), based on dynamic programming control. The high penetration of wind energy in the electrical grids demands for new requirements for the operation of wind energy conversion systems (WECSs). DFIG is the most employed WECS, and the DPPC+ guarantees their operation under unbalance conditions achieving the required objectives. Although the technique can be implemented to control both rotor and grid converters, we hereby expound the former, which regulates stator active and reactive power. The validation of the results obtained with DPPC+ has been performed through the use of experimental tests on a 20-kW test bench, consisting of a DFIG and induction motor drive. The obtained results show that the DPPC+ is suitable for achieving a good dynamic response while controlling current distortion and power and/or torque oscillations for both steady-state conditions and unbalanced voltage dips, showing the low-voltage ride-through capability.

In this review, the state of the art of 23 distributed generation and microgrids standards has been analyzed. Among these standards, 18 correspond mainly to distributed generation while five of them introduce the concept of microgrid. The following topics have been considered: interconnection criteria, operating conditions, control capabilities, power quality, protection functions and reference variables. The revised national standards cover ten countries on four continents, which represents 80% of the countries with the largest installed renewable capacities. In addition, eight other relevant international standards have been analyzed, finding IEEE 1547 as the most comprehensive standard. It is identified a clear need to define a common framework for distributed energy resources (DERs) and microgrid standards in the future, wherein topics, terminology, and values are expressed in a manner that may widely cover the entire diversity in a way similar to how it has already been expressed at the network transport level by the ENTSO-E codes.