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In renewable energy-based generation sources a phase locked loop is one of the most popular synchronization techniques. A rapid and precise grid voltage phase and frequency estimation under a wide spectrum of possible grid disturbances is its main objective. This paper compares popular grid synchronization algorithms on grid voltage anomalies. The compared algorithms are divided in three groups: without filtering, with filtering in synchronous reference frame and with filtering in stationary reference frame. The behaviour of the algorithms is tested in a laboratory, using dSpace 1103 as a platform on which the algorithms are compiled and OMICRON CMC 356 as a programmable grid voltage generator. The benchmarks conducted in this paper include voltage sags, grid voltages harmonics, DC offset and frequency step change. The obtained results show that there are significant differences in tested PLL responses for some networks disturbances. [Projects of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 44004 and Grant no. III 44006]

The task of the whole microgrid state-space matrix creation is usually done in a preferred textual programming language, and it presents a complicated, time-consuming, and error-prone job for a researcher without good coding practices. To ease the modeling task, contribute to the adaptation of new microgrid structures, control algorithms, and devices, and to improve the flexibility of the model, a graphical element building block method is proposed in this paper. With the proposed approach model creation of the whole microgrid is reduced to the creation of the individual element state-space model that is linked with other elements in a logical way with a graphical connection. Elements are then grouped into meaningful wholes and encapsulated with the appropriate graphical user interface that enables easy parameter modification and model complexity change. More detailed DC/DC and DC/AC models of converters than those in the literature concerning microgrid stability are presented in this paper. Those converters are incorporated in a microgrid, whose model is created using the proposed approach in MATLAB/Simulink. The dynamic response examination of the model remains easy, just as with all Simulink models, while for the linear system analysis, a specialized toolbox is used.

This paper proposes the enhancement of a synchronous reference frame phase-locked loop in terms of its dynamic response and disturbance rejection capability. The improvements were undertaken in order to upgrade the converter grid support capability required by modern grid codes during grid faults. The proposed repetitive control-based filter is inserted in the loop filter structure of the phase-locked loop. For the initially proposed structure, the necessity of the phase angle error correction term was derived and added at the output of the loop filter. On a set of tests that included (i) phase jump; (ii) voltage sag; (iii) voltage harmonics; (iv) DC offset; (v) random noise and; (vi) frequency change, the synchronization algorithm with the proposed modification showed two desirable characteristics: (i) a high attenuation of oscillations on specific frequencies; and (ii) the instant compensation of the portion of the phase angle jump. Along with the benefits, drawbacks of the proposed synchronization method were noted, the most important being the high dependency of the oscillation attenuation capability on the fundamental frequency drift and susceptibility to high-frequency noise. With the proposed modification, the synchronization algorithm manages to achieve a phase angle settling time not longer than one fundamental frequency period in all of the conducted tests.

This paper analyses symmetrical and unsymmetrical voltage sag effects on the torque and speed deviation in direct torque controlled (DTC) induction motors (IMs) for adjustable speed drives (ASDs). The capability of an ASD for continuous normal operation in case of short supply disturbances is essential for high performance drives. In this paper, an updated scheme is proposed for boosting ASD performances during supply disturbances with voltage reduction. Flux weakening is an effective method to overcome the torque-decreasing problem in case of DC-link voltage diminishing. It is also shown that speed reduction is an efficient procedure to obtain the voltage sag insensitivity of an ASD, which is appropriate for the existing industrial applications. Extensive laboratory testing has been conducted to verify the performances and effectiveness of the proposed control algorithm. The suggested method requires only a modification of converter control software or operating speed change without any additional hardware components. Extended tests under various voltage sags events were carried out on a 1.5 kW laboratory drive, and the obtained results have been compared with an industrial DTC drive.