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

Decoupled Double Synchronous Reference Frame PLL for Power Converters Control

Phase, amplitude and frequency of the utility voltage are critical information for the operation of the grid-connected inverter systems. In such applications, an accurate and fast detection of the phase angle, amplotude and frequency of the utility voltage is essential to assure the correct generation of the reference signals and to cope with the new upcoming standards. This paper presents a new phase-locked-loop (PLL) method for single-phase systems. The novelty consists in generating the orthogonal voltage system using a structure based on second order generalized integrator (SOGI). The proposed structure has the following advantages: — it has a simple implementation; — the generated orthogonal system is filtered without delay by the same structure due to its resonance at the fundamental frequency, — the proposed structure is not affected by the frequency changes. The solutions for the discrete implementation of the new proposed structure are also presented. Experimental results validate the effectiveness of the proposed method.

A New Single-Phase PLL Structure Based on Second Order Generalized Integrator

This paper deals with a fundamental aspect in the control of grid-connected power converters, i.e., the detection of the positive-sequence component at fundamental frequency of the utility voltage under unbalanced and distorted conditions. Accurate and fast detection of this voltage component under grid faults is essential to keep the control over the power exchange with the grid avoiding to trip the converter protections and allowing the ride-through of the transient fault. In this paper, the systematic use of well known techniques conducts to a new positive-sequence voltage detection system which exhibits a fast, precise, and frequency-adaptive response under faulty grid conditions. Three fundamental functional blocks make up the proposed detector, these are: i) the quadrature-signals generator (QSG), ii) the positive-sequence calculator (PSC), and iii) the phase-locked loop (PLL). A key innovation of the proposed system is the use of a dual second order generalized integrator (DSOGI) to implement the QSG. For this reason, the proposed positive-sequence detector is called DSOGI-PLL. A detailed study of the DSOGI-PLL and verification by simulation are performed in this paper. From the obtained results, it can be concluded that the DSOGI-PLL is a very suitable technique for characterizing the positive-sequence voltage under grid faults.

New positive-sequence voltage detector for grid synchronization of power converters under faulty grid conditions

In this paper, the performance assessment of three software single-phase phase-locked loop (PLL) algorithms is carried out by means of dynamic analysis and experimental results. Several line disturbances such as phase-angle jump, voltage sag, frequency step, and harmonics are generated by a DSP together with a D/A converter and applied to each PLL. The actual minus the estimated phase-angle values are displayed, providing a refined method for performance evaluation and comparison. Guidelines for parameters adjustments are also presented. In addition, practical implementation issues such as computational delay effects, ride-through, and computational load are addressed. The developed models proved to accurately represent the PLLs under real test conditions.

/pdf/comparison-of-three-single-phase-pll-algorithms-for-ups-4jmd2ukbi7.pdf

Comparison of Three Single-Phase PLL Algorithms for UPS Applications

Recently, several advanced phase-locked loop (PLL) techniques have been proposed for single-phase applications Among these, the Park-PLL and the second-order-generalized-integrator-based PLL are very attractive, owing to their simple digital implementation, low computational burden, and desired performance under frequency-varying and harmonically distorted grid conditions Despite the wide acceptance and use of these two advanced PLLs, no comprehensive design guidelines to fine-tune their parameters have been reported yet Through a detailed mathematical analysis, it is shown that these two PLL structures are equivalent to each other, from the control point of view Then, a linearized model is developed which is valid for both PLLs The derived model significantly simplifies the stability analysis and the parameter design To fine-tune the PLL parameters, a systematic design approach is suggested afterward, which guarantees a fast dynamic response, a high disturbance rejection ability, and a robust performance Finally, the simulation and experimental results are presented to support the theoretical analysis

/pdf/dynamics-assessment-of-advanced-single-phase-pll-structures-3so6k0xa88.pdf

Dynamics Assessment of Advanced Single-Phase PLL Structures

Phase angle, frequency and amplitude of the utility voltage vector are basic information for an increasing number of grid-connected power conditioning equipments, such as PWM rectifiers, uninterruptible power systems (UPS), voltage sag compensators and the emerging distributed generation systems. For these applications, accurate tracking of the utility voltage vector is essential to ensure correct operation of the control system. This paper presents a comparative study of synchronous reference frame PLL algorithms for single-phase systems. Simulation and experimental results, including operation of the PLL structures under distorted utility conditions are presented, to allow a performance evaluation of the PLL algorithms.

Rodrigo P. Campana

Papers

Performance evaluation of PLL algorithms for single-phase grid-connected systems