C. H. da Silva

A Digital PLL Scheme for Three-Phase System Using Modified Synchronous Reference Frame

This paper proposes a novel phase-locked loop (PLL) control strategy to synthesize unit vector using the modified synchronous reference frame (MSRF) instead of the traditional synchronous reference frame. The unit vector is used for vector rotation or inverse rotation in vector-controlled three-phase grid-connected converting equipment. The developed MSRF-PLL is fast in transient response compared to standard PLL technique. The performance is robust against disturbances on the grid, voltage wave with harmonic distortion, and noise. The proposed algorithm has been analyzed in detail and was fully implemented digitally using digital signal processor TMS320F2812. The experimental evaluation of the MSRF-PLL in a shunt active power filter confirms its fast dynamic response, noise immunity, and applicability.

DSP Implementation of Three-Phase PLL using Modified Synchronous Reference Frame

This paper proposes a new algorithm for three-phase digital PLL based on modified synchronous reference frame (MSRF). This MSRF-PLL is suitable DSP implementation applied to grid connected utility equipments. The algorithm guaranty fast transient response, robust operation under grid disturbance and noise tolerance. The strategy does not use PI controller, what improves the transient response and accuracy of synchronizing output signal. The algorithm is described in details and the practical results, under all types of severe disturbances, are presented and discussed.

Dead-time compensation in Shunt Active Power Filters using fast feedback loop

In PWM inverters, a time delay between consecutive semiconductor switching is introduced to prevent a short circuit in the DC link. This action causes the dead-time effect, which is detrimental to the performance of inverters. This paper deals with a new technique that speedup the feedback loop in Shunt Active Power Filter, in order to compensate the dead-time effect. A simple method based on an average value theory can be used to compensate this effect. For Shunt Active Power Filters (SAPF), the compensation can be done in two different ways, one for the feedforward configuration and the other for the feedback one. This paper presents both techniques and discusses the details, advantage of the feedback implementation with a new fast feedback loop that guaranties the dead-time compensation and the overall stability. Experimental results are presented showing the effectiveness of the proposed technique.

Optimizing the Series Active Filters Under Unbalanced Conditions Acting in the Neutral Current

This paper discusses the limitations of the series active power filter operating in unbalanced three-phase four-wire systems and proposes the insertion of series active impedance to neutral wire. The control of this active impedance uses a modified synchronous reference frame controller (MSRFC) in order to mitigate the flow of zero sequence harmonic components. The performance of the combined system, constituted of two series active filters, is simulated with and without the insertion of a series active filter to the neutral wire and the results arc presented. The simulation confirms the viability of proposition and the discussions show the importance of using this proposed structure when series active filters, based on three-phase synchronous reference frame controller (SRFC), is used as control strategy in unbalanced four-wire systems.

Modified Synchronous Reference Frame strategy for single phase hybrid active power filter

This paper evaluates a hybrid active series power filter (HASPF) based on the Modified Synchronous Reference Frame, when the third harmonic passive filter is the chosen compensator at first. The performance of the system is compared with and without the active compensation. The practical results exhibits as close a passive filter can be tuned to an absolutely compensation. The algorithm of the HASPF is executed by the DSP TMS320F2812, and the inverter switching frequency is 20 kHz.

Improving the dynamic response of shunt active power filter using modified Synchronous Reference Frame PLL

This paper evaluates an algorithm for three-phase active shunt power filter using a digital PLL based on Modified Synchronous Reference Frame (MSRF). The Modified Synchronous Reference Frame PLL (MSRF_PLL) algorithm guaranty fast transient response, robust operation under grid disturbance, noise tolerance and does not use PI controller. Therefore, it improves the transient response and accuracy of compensating harmonic currents. The PLL algorithm is applied to a Three Phase Shunt Active Power Filter and the system behavior is described in details and the practical results, under load variation and steady stated harmonic compensation, are presented and discussed.

Harmonic detection with LMS adaptive notch filter and transient detection

This paper presents the application of the adaptive filters for harmonic detection in shunt active power filters. Improve the transient response time of the adaptive filter is the final objective of the strategy. The Least Mean Square (LMS) algorithm was used to adjust the coefficients of the adaptive notch filter. An algorithm based on the Clarke Transformation was used to detect the load current amplitude transients and then modify the step-size value. Simulations using Matlab/Simulink are presented to clarify the algorithm. Also practical implementation is performed using the DSP Texas Instruments TMS320F2812 and the experimental results depicted.

Improving the convergence time of adaptive notch filters to harmonic detection

This paper presents the application of adaptive notch filters for harmonic detection in shunt active power filters (SAPF). The orthogonal input signals to the adaptive notch filter are generated using the Clarke transformation of the load currents in such way that the Phased Looked Loop (PLL) is not necessary any more. The least mean square (LMS) and recursive least square (RLS) algorithms were used to adjust the coefficients of the adaptive notch filter. The final objective of the described strategy is to improve the speed of convergence of the adaptive notch filter, reducing the steady-state error and the transient response. All these features are very important to real time applications in active power filters. Simulations using Matlab/Simulink are presented to clarify the algorithm. Also, the implementation of the technique in a shunt active power filter is performed using the DSP Texas Instruments TMS320F2812, and the experimental results depicted.

Implementation of a grid-forming converter based on modified synchronous reference frame

Renewable resources power generation systems are mainly constituted by power converters. These converters can be controlled in several ways to execute different functions inside microgrids. Some of the converters cannot operate on isolated grids, that is, without connection to the electrical grid. Therefore, there are converters whose purpose is to provide a voltage reference so that other converters continue to deliver power independent of grid presence. These devices are called grid-forming converters and are usually constituted by a converter associated to an energy storage system. This paper presents the practical implementation of a grid-forming converter using the Modified Synchronous Reference Frame as base structure for the converter control. The developed control strategies are described along with experimental results of a single-phase 5 kVA prototype.

Application of adaptive filters in active power filters

This paper presents a new idea applied to adaptive filters for harmonic detection in shunt active power filters. Improve the speed of convergence of the adaptive filter and reduces the steady-state error are the finals objectives of the strategy. Two cases are presented and discussed, one with a Finite Impulse Response (FIR) adaptive filter with 32 coefficients and another with an adaptive notch filter. The Least Mean Square (LMS) algorithm was used to adjust the coefficients in the both cases. An algorithm based on Coulon oscillator principle was used to determine the load current amplitude and then modify the step-size value. Simulations using Matlab are presented to clarify the algorithm. Also practical implementation is performed using the DSP Texas Instruments TMS320F2812 and the experimental results depicted.