Novel PLL for power converters under unbalanced and distorted grid conditions

A novel phase-locked loop (PLL) with simple structure is proposed in the present work for three-phase power converters under adverse grid conditions. Based on a synchronous rotating frame PLL (SRF-PLL), multi-resonant harmonic compensators with the ability of accommodating frequency deviations are employed in the feedback path of a pre-filter. As a result, the negative-sequence component and harmonic distortions of grid voltage can be attenuated. Different from existing methods, only classical regulators are used, avoiding complicated networks for the decoupling of unbalance and harmonics and thus greatly simplifying the control algorithm. The proposed method is analysed and designed in both the continuous s-domain and discrete z-domain, whereby stable, fast, accurate, and robust responses are achieved. Simulation results have been obtained to show the improved performance of the proposed PLL compared with two widely used methods

Reduction of current harmonics in grid-connected PV inverters using harmonic compensation - conforming to IEEE and IEC standards

This paper deals with the reduction of harmonics generated by Grid-Connected PV Inverters to conform to the harmonic limits set by the IEEE and IEC standards. An analysis of the current harmonics present in the output current of a grid-connected inverter will be presented. The inverter will be current controlled by a Proportional-Resonant (PR) current controller. The design and testing of the PR current controller will be presented. This paper will also deal with the application of harmonic compensation to make the inverter compliant to the standards, by using selective harmonic compensators in addition to the Proportional-Resonant (PR) controller. Both simulation and experimental results will be presented. Testing was carried out on a Grid-Connected PV Inverter which was designed and constructed for this research.peer-reviewe

Design of PR current control with selective harmonic compensators using Matlab

This paper presents a procedure to design a Proportional Resonant (PR) current controller with additional PR selective harmonic compensators for Grid Connected Photovoltaic (PV) Inverters. The design of the PR current control and the harmonic compensators will be carried out using Matlab. Testing was carried out on a 3kW Grid- Connected PV Inverter which was designed and constructed for this research. Both simulation and experimental results will be presented.peer-reviewe

An Adaptive Digital Control Technique for Improved Performance of Grid Connected Inverters

Grid connected voltage source inverters may be controlled in the stationary reference frame by means of the infinite impulse response (IIR) P+Resonat regulator. This regulator is able to correctly track fixed frequency sinusoidal references, but does not perform well if the frequency of the electric grid voltage is varied. In order to avoid the lack of precision to track variable frequency sinusoidal references, an adaptive IIR filter structure is proposed which offers good tracking properties even if the frequency of the grid voltage varies. This filter adapts its coefficients in real time and is inherently stable no matter the adaptation process, thus overcoming one of the most important drawbacks of the IIR filter structure. Furthermore, this structure is perfectly suited to be programmed in fixed point digital signal processors (DSPs) because of some important numeric properties, i.e., it has a high mapping precision and a low round-off accumulation, and it avoids quantization limit cycle oscillations. The proposed adaptive controller has been tested by means of the TI TMS320F2812 DSP. The obtained experimental results show up that this controller allows the correct tracking of a sinusoidal reference, even if this reference is time variant.This work was supported by the Spanish Ministry of Science and Innovation under Grant ENE2012-37667-C02-01. Paper no. TII-11-622.González Espín, FJ.; Patrao Herrero, I.; Figueres Amorós, E.; Gabriel Garcerá (2013). An Adaptive Digital Control Technique for Improved Performance of Grid Connected Inverters. IEEE Transactions on Industrial Informatics. 9(2):708-718. https://doi.org/10.1109/TII.2012.2225437S7087189

A New Control Method for Single-Phase Grid-Connected Inverter Using Instantaneous Power Theory

Because of installation for local consumers and since it is free of all contaminations, connecting photovoltaic cells to the grid via single-phase inverter is significantly on the rise. In this paper, a new simple current control is proposed for a single-phase grid-connected voltage source inverter. Using the PQ theory and modelling a single-phase system as an unbalanced three-phase system, a method is provided for reference current generation. In the proposed method, it is not necessary to generate a fictitious phase for the current signal. Also, the removal of adjusting filter parameters which were used to generate fictitious current signal increases the simplicity of the control system and reduces computational efforts, especially in the presence of distortion in the current. The simulation results confirm that the proposed method provides a precise and fast current control with minimum harmonic distortions