R. R. Pereira

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.

Smart Impedance: A New Way to Look at Hybrid Filters

Smart impedance is a new way to look at hybrid active power filters. As originally proposed in the literature, hybrid active filters were presented to improve the physical limitation of tuned passive filters. A new conditioner named smart impedance is proposed to eliminate the need of passive filter tuning procedure, the whole tuning process is performed electronically. The proposed topology is able to manipulate the displacement power factor and perform multiple frequency harmonic current mitigation at the same time. In weak systems, where the source impedance is not negligible, like in smart grids, smart impedance guaranties the voltage regulation and stability. The smart impedance control strategy uses proportional resonant controller, which allows phase-locked loop-less power system synchronization. Smart impedance system is composed of an active converter, a coupling transformer, and a capacitive unit, arranged as three phase or single phase equipment.

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.

Modified Synchronous Reference Frame Strategy for Selective-Tuned Single Phase Hybrid Active Power Filter

This paper shows the behavior of same structure of an hybrid active series power filter (HASPF) tuned in three different frequencies. The developed strategy is based on the Modified Synchronous Reference Frame Controller. The initial structure of the passive filter was chosen to be tuned for the fifth harmonic. The performance of the system is compared with and without the active compensation. The ability of the hybrid topology in changing the resonant frequency is shown. The active hybrid structure is first tuned for the fifth harmonic, further it is electronically re-tuned to the third and finally to the seventh harmonic. Practical results exhibits these tuning changes showing as close as the passive filter can approach the absolutely compensation for a chosen frequency. The algorithm of the HASPF is executed in the DSP TMS320F2812 and the inverter switching frequency is 20 kHz.

A New Strategy to Step-Size Control of Adaptive Filters in the Harmonic Detection for Shunt Active Power Filter

This paper presents a new strategy to improve the applicability of adaptive filters for harmonic detection in shunt active power filters (SAPF). The final objective of the strategy is improving the speed of convergence of the adaptive filter and reduces the steady- state error. 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. Simulations using Matlab are presented to clarify the algorithm. Also practical implementation is performed using the DSP Texas Instruments TMS320F2812 and the results depicted. Important aspects concerning the calculation time of the adaptive filter, convergence speed during changes in the load and the steady-state error, are presented.

Smart impedance: Expanding the hybrid active series power filter concept

Hybrid active series power filters, as originally proposed in the literature, presents a way to improve the physical limitation of tuned passive filters. However, these improvements are restricted to a single filter parameter, i.e., quality factor or tuned factor. To overcome these limitations, a hybrid system composed by active impedance, capacitor bank and appropriated control strategy, called smart impedance, is proposed. The system completely eliminates the necessity of the classical passive filter tuning procedure, which requires capacitor/inductor association for each frequency. All tuning issues are performed electronically. The proposed topology is able to manipulate, at the same time, the displacement power factor, harmonic current frequency compensation (single or multiple), quality factor and tuned factor. Practical results demonstrate the smart impedance performance and its interaction with the power system under multiples harmonics frequencies along with the displacement power factor compensation. The proposed system is simpler and more efficient than those reported in the literature. The control algorithm is executed using the DSP TMS320F2812 and the inverter switching frequency is 20 kHz.

A Hybrid Active Var Compensator (HAVarC)

This paper proposes a modification on the Hybrid Active Series Filter (HASF) creating a topology named Hybrid Active Var Compensator (HAVarC) suitable to manipulate, in continuous way, the displacement power factor or voltage regulation. The HAVarC is composed by a small rating Active Power Filter (APF) in series with a capacitor bank. The main objective of this topology is to control the reactive power injected by the capacitor into the system by controlling the voltage applied on its terminals. The system automatically compensates the reactive power flow in order to guarantee the desired displacement power factor (DPF) or rated voltage and no power system parameters knowledge are necessary to the correct operation of the topology. Also the system guaranties the absence of inrush current or voltage surge in the power system at all operation modes.

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.