J. Ignacio Candela

Grid Voltage Synchronization for Distributed Generation Systems Under Grid Fault Conditions

The actual grid code requirements for the grid connection of distributed generation systems, mainly wind and photovoltaic (PV) systems, are becoming very demanding. The transmission system operators (TSOs) are especially concerned about the low-voltage-ride-through requirements. Solutions based on the installation of STATCOMs and dynamic voltage regulators (DVRs), as well as on advanced control functionalities for the existing power converters of distributed generation plants, have contributed to enhance their response under faulty and distorted scenarios and, hence, to fulfill these requirements. In order to achieve satisfactory results with such systems, it is necessary to count on accurate and fast grid voltage synchronization algorithms, which are able to work under unbalanced and distorted conditions. This paper analyzes the synchronization capability of three advanced synchronization systems: the decoupled double synchronous reference frame phase-locked loop (PLL), the dual second order generalized integrator PLL, and the three-phase enhanced PLL, designed to work under such conditions. Although other systems based on frequency-locked loops have also been developed, PLLs have been chosen due to their link with dq0 controllers. In the following, the different algorithms will be presented and discretized, and their performance will be tested in an experimental setup controlled in order to evaluate their accuracy and implementation features.

Harmonic Compensation Analysis in Offshore Wind Power Plants Using Hybrid Filters

The harmful effects of harmonics are an important issue in wind power plants (WPPs), especially in offshore applications. In offshore WPPs, the wind turbines are linked to the network through high-power converters that produce harmonics at relative low frequencies. Moreover, in the network of a WPP, the propagation of noncharacteristic harmonics and the effect of resonance contribute as well in boosting the harmonic distortion. In this paper, a solution for compensating the harmonics in a WPP by means of using hybrid filters is proposed. In this paper, not only the filtering solution is tested, but also a method for finding the best place where to connect the filter, based on a modal analysis or a harmonic modal resonance analysis, is implemented. The proposed solution has been tested by considering the model of a real 400-MW offshore WPP as the study case. As it will be shown, the hybrid filter is capable of damping the resonances in the plant, while the analysis conducted permits us to optimize its location in the plant.

Decentralized Primary Control of MTDC Networks With Energy Storage and Distributed Generation

Multiterminal dc networks are drawing a lot of interest lately in applications related to distributed generation, particularly in those that also integrate energy storage (ES). A few approaches for controlling the operation of such systems have been proposed in the literature; however, the existing structures can be significantly enhanced. This paper proposes an improved primary control layer, based on custom droop characteristics obtained by combining concepts of droop and dc-bus signaling control. This approach is designed to be generic and takes into account the various operating states of the network. Five operating bands, similar to the operating states of the ac grids, as well as various droop characteristics for different elements connected to the dc network, are defined. For the ES, the state of charge is taken into account at the primary control level and included in the droop characteristic, creating a two-variable droop surface. The proposed control strategy is validated through simulation and experimental results obtained from a case study that involves a micro dc network composed of a photovoltaic generator, a lead-acid battery, and a connection point to the ac grid.

Adaptive Droop for Control of Multiterminal DC Bus Integrating Energy Storage

Multiterminal dc (MTDC) systems are drawing a lot of interest lately in applications related to distributed generation, especially in those that integrate wind or photovoltaic (PV) generation with energy storage (ES). Several approaches for controlling the operation of such systems have been proposed in the literature; however, the existing structures are mainly application specific and, thus, can be still improved in order to provide a more generic approach. This paper proposes an improved primary control layer for an MTDC system. The concept is based on the combination of a droop control method and dc bus signaling in order to provide a more generic and flexible solution. In this paper, different droop characteristics are proposed for the various elements connected to the dc bus. All of them are specifically tailored around five operation bands, which depend on the dc bus voltage level. Special attention is paid to the integration of ES: the state of charge (SoC) is considered at the primary control level, yielding a surface characteristic that depends on the SoC and the dc bus voltage. The scaling of the system has been analyzed together with the proposed control strategy and the overall operation has been validated through simulations by considering a 100 kW PV system with energy storage. Experimental results were obtained on a scaled laboratory prototype rated at 10 kW.

An overview of harmonic analysis and resonances of large wind power plant

This paper presented an overview of harmonic analysis and resonance in large wind power plant. The harmonic related problem becomes a concern as the growing numbers of nonlinear load and the increased possibility of harmonic resonances occurrence. In WPP, several conditions may contribute to the resonance phenomenon that will amplify the effect of the harmonic frequency. General overview of international standards and grid codes and basic modeling of WPP for harmonic analysis is also presented. Furthermore, an overview of the harmonic analysis methods are reviewed with emphasize given on the harmonic resonance analysis. A simple three-bus system example is evaluated applying three resonance analysis methods.

Study on harmonic resonances and damping in wind power plant

Harmonic resonance is among imperative aspect need to be analyzed in a wind power plant (WPP). It becomes complex since it involves a large network with high operating power. This paper presents a study on harmonic resonances in a WPP, particularly on parallel resonance. Important factors including length of cable, number of operating wind turbine and usage of output grid-side filter are analyzed. The damping of resonance by using common passive filter and an alternative hybrid filter is also explored. An aggregated WPP model of 400 MW with 40 wind turbines of 10 MW each are used as a study case.

Harmonic resonance damping in Wind Power Plant

Harmonic is one of main concern in Wind Power Plant (WPP) as growing usage of power electronic converter is observed. Besides the injection of harmonic by individual wind turbine (WT) as source of harmonic, its propagation in network and problem of resonance is also an issue. By implementing passive filter for harmonic mitigation, additional resonance peak is observed due to its interaction with system side impedance. This paper explores the solution for harmonic mitigation with capability of damping resonance in WPP. An aggregated model of 400-MW WPP network is analyzed in correlating resonance and amplification. A passive filter and hybrid filter is designed to mitigate harmonic accordingly. It is shown that hybrid filter able to provide damping capability and improve the performance.

Posicast control — A novel approach to mitigate multi-machine power system oscillations in presence of wind farm

In this paper, application of Posicast control method to generator excitation system is presented. The method is one of the simplest possible control design methods that can be applied to damp the oscillations caused by changing the excitation reference signal. Stability and robustness of the designed controller are shown using extensive time domain simulations. All the detailed simulations are carried out in MATLAB/Simulink environment.

Application of Posicast control method to generator excitation system

Application of Posicast control method to generator excitation system is presented in this paper. Presented control method is one of the simplest control design methods which can be installed in generators excitation to damp the oscillations caused by changing the excitation reference signal. Stability of the designed controller is shown using extensive time domain simulations. Performance of Posicast controller in IEEE power system standard models with presence of PV power plant is evaluated in MATLAB/Simulink environment.

Correction to "Decoupled Double Synchronous Reference Frame PLL for Power Converters Control" [Mar 07 584-592]

In the above titled paper (ibid., vol. 22, no. 2, pp. 584-592, Mar 07), the full version of Fig. 8 was not displayed. The correct version is presented here.