J. Bergas

Bio: J. Bergas is an academic researcher from Polytechnic University of Catalonia. The author has contributed to research in topics: Reference frame & Test light. The author has an hindex of 6, co-authored 8 publications receiving 1251 citations.

Decoupled Double Synchronous Reference Frame PLL for Power Converters Control

Abstract: This paper deals with a crucial aspect in the control of grid-connected power converters, i.e., the detection of the fundamental-frequency positive-sequence component of the utility voltage under unbalanced and distorted conditions. Specifically, it proposes a positive-sequence detector based on a new decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL), which completely eliminates the detection errors of conventional synchronous reference frame PLL's (SRF-PLL). This is achieved by transforming both positive- and negative-sequence components of the utility voltage into the double SRF, from which a decoupling network is developed in order to cleanly extract and separate the positive- and negative-sequence components. The resultant DDSRF-PLL conducts then to a fast, precise, and robust positive-sequence voltage detection even under unbalanced and distorted grid conditions. The paper presents a detailed description and derivation of the proposed detection method, together with an extensive evaluation using simulation and experimental results from a digital signal processor-based laboratory prototype in order to verify and validate the excellent performance achieved by the DDSRF-PLL

Double Synchronous Reference Frame PLL for Power Converters Control

Abstract: This paper deals with one of the most important issues in the control of grid-connected converters, which is the detection of the positive sequence fundamental component of the utility voltage. The study carried out in this paper conducts to a fast, precise, and robust positive sequence voltage detector offering a good behavior, even if unbalanced and distorted conditions are present in the grid. The proposed detector utilizes a new "double synchronous reference frame PLL" (DSRF-PLL), which completely eliminates the existing errors in conventional synchronous reference frame PLL systems (SRF-PLL) when operating under unbalanced utility voltages. In the study performed in this paper, the positive and negative sequence components of the unbalanced voltage vector are properly characterized. When this unbalanced vector is expressed on the DSRF, the analysis of the signals on the DSRF axes permits to design a decoupling network which isolates the positive and negative sequence components. This decoupling network gives rise to a new PLL structure which detects the positive sequence voltage component quickly and accurately. In this paper, conclusions of the analytical study are verified by simulation and experiment

Synchronous double reference frame PLL applied to a unified power quality conditioner

Abstract: This paper presents a positive sequence voltage detector based on a new "synchronous double reference frame PLL" (SDRF-PLL). This PLL exhibits a fast, precise and robust behavior under unbalanced utility conditions. When amplitude and phase of the positive sequence source voltage are known, various compensation strategies are feasible for the control of the unified power quality conditioner. Four suitable control strategies are shown. The performance of the proposed SDRF-PLL is verified by means of its application in the control of a unified power quality conditioner. In this paper, an analytical study and a verification by simulation are conducted.

Alternative topology for three-phase four-wire PWM converters applied to a shunt active power filter

Abstract: This paper presents an alternative three-phase four-wire converter for active power filter applications. The topology of this converter consists of four switch-legs, and it uses a "split-capacitor" in the DC-bus. In this converter, three legs are destined to control the injected currents in utility lines, while the fourth leg assures a balanced voltage sharing in the DC-bus capacitors. This converter solves the problem of DC-bus voltage imbalance in the three-leg split-capacitor converter. Moreover, this topology allows each leg to be controlled independently, so injected current control is simpler than in the four-leg full-bridge conventional converter, which utilizes a single capacitor on the DC-bus side. In this sense, a simple constant-frequency current control technique is proposed. In this paper, an analytical study and a verification by simulation are conducted.

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

Abstract: 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.

Overview of Control and Grid Synchronization for Distributed Power Generation Systems

Abstract: Renewable energy sources like wind, sun, and hydro are seen as a reliable alternative to the traditional energy sources such as oil, natural gas, or coal. Distributed power generation systems (DPGSs) based on renewable energy sources experience a large development worldwide, with Germany, Denmark, Japan, and USA as leaders in the development in this field. Due to the increasing number of DPGSs connected to the utility network, new and stricter standards in respect to power quality, safe running, and islanding protection are issued. As a consequence, the control of distributed generation systems should be improved to meet the requirements for grid interconnection. This paper gives an overview of the structures for the DPGS based on fuel cell, photovoltaic, and wind turbines. In addition, control structures of the grid-side converter are presented, and the possibility of compensation for low-order harmonics is also discussed. Moreover, control strategies when running on grid faults are treated. This paper ends up with an overview of synchronization methods and a discussion about their importance in the control

Control of Power Converters in AC Microgrids

Abstract: The enabling of ac microgrids in distribution networks allows delivering distributed power and providing grid support services during regular operation of the grid, as well as powering isolated islands in case of faults and contingencies, thus increasing the performance and reliability of the electrical system. The high penetration of distributed generators, linked to the grid through highly controllable power processors based on power electronics, together with the incorporation of electrical energy storage systems, communication technologies, and controllable loads, opens new horizons to the effective expansion of microgrid applications integrated into electrical power systems. This paper carries out an overview about microgrid structures and control techniques at different hierarchical levels. At the power converter level, a detailed analysis of the main operation modes and control structures for power converters belonging to microgrids is carried out, focusing mainly on grid-forming, grid-feeding, and grid-supporting configurations. This analysis is extended as well toward the hierarchical control scheme of microgrids, which, based on the primary, secondary, and tertiary control layer division, is devoted to minimize the operation cost, coordinating support services, meanwhile maximizing the reliability and the controllability of microgrids. Finally, the main grid services that microgrids can offer to the main network, as well as the future trends in the development of their operation and control for the next future, are presented and discussed.

Decoupled Double Synchronous Reference Frame PLL for Power Converters Control

Abstract: This paper deals with a crucial aspect in the control of grid-connected power converters, i.e., the detection of the fundamental-frequency positive-sequence component of the utility voltage under unbalanced and distorted conditions. Specifically, it proposes a positive-sequence detector based on a new decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL), which completely eliminates the detection errors of conventional synchronous reference frame PLL's (SRF-PLL). This is achieved by transforming both positive- and negative-sequence components of the utility voltage into the double SRF, from which a decoupling network is developed in order to cleanly extract and separate the positive- and negative-sequence components. The resultant DDSRF-PLL conducts then to a fast, precise, and robust positive-sequence voltage detection even under unbalanced and distorted grid conditions. The paper presents a detailed description and derivation of the proposed detection method, together with an extensive evaluation using simulation and experimental results from a digital signal processor-based laboratory prototype in order to verify and validate the excellent performance achieved by the DDSRF-PLL

Multiresonant Frequency-Locked Loop for Grid Synchronization of Power Converters Under Distorted Grid Conditions

Abstract: This paper presents a new multiresonant frequency-adaptive synchronization method for grid-connected power converters that allows estimating not only the positive- and negative-sequence components of the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies. The proposed system is called MSOGI-FLL since it is based on both a harmonic decoupling network consisting of multiple second-order generalized integrators (MSOGIs) and a frequency-locked loop (FLL), which makes the system frequency adaptive. In this paper, the MSOGI-FLL is analyzed for single- and three-phase applications, deducing some key expressions regarding its stability and tuning. Moreover, the performance of the MSOGI-FLL is evaluated by both simulations and experiments to show its capability for detecting different harmonic components in a highly polluted grid scenario.

Analysis of D-Q Small-Signal Impedance of Grid-Tied Inverters

Abstract: This paper analyzes the small-signal impedance of three-phase grid-tied inverters with feedback control and phase-locked loop (PLL) in the synchronous reference ( d-q ) frame. The result unveils an interesting and important feature of three-phase grid-tied inverters – namely, that its q–q channel impedance behaves as a negative incremental resistor. Moreover, this paper shows that this behavior is a consequence of grid synchronization, where the bandwidth of the PLL determines the frequency range of the resistor behavior, and the power rating of the inverter determines the magnitude of the resistor. Advanced PLL, current, and power control strategies do not change this feature. An example shows that under weak grid conditions, a change of the PLL bandwidth could lead the inverter system to unstable conditions as a result of this behavior. Harmonic resonance and instability issues can be analyzed using the proposed impedance model. Simulation and experimental measurements verify the analysis.