L.E.B. 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.

A stator flux oriented vector-controlled induction motor drive with space vector PWM and flux vector synthesis by neural networks

A stator flux oriented vector-controlled induction motor drive is described where the space vector PWM (SVM) and stator flux vector estimation are implemented by artificial neural networks (ANN). Artificial neural networks, when implemented by dedicated hardware ASIC chips, provide extreme simplification and fast execution for control and feedback signal processing functions in high performance AC drives. In the proposed project, a feedforward ANN-based SVM, operating at 20 kHz sampling frequency, generates symmetrical PWM pulses in both undermodulation and overmodulation regions covering the range from DC (zero frequency) up to square-wave mode at 60 Hz. In addition, a programmable cascaded low-pass filter (PCLPF), that permits de offset-free stator flux vector synthesis at very low frequency using the voltage model, has been implemented by a hybrid neural network which consists of a recurrent neural network (RNN) and a feedforward neural network (FFANN). The RNN-FFANN based flux estimation is simple, permits faster implementation, and gives superior transient performance when compared with a standard DSP-based PCLPF. A 5-hp open loop volts/Hz controlled drive incorporating the proposed ANN-based SVM and RNN-FFANN based flux estimator was initially evaluated in the frequency range of 1.0 Hz to 58 Hz to validate the performances of SVM and flux estimator. Next, the complete 5 hp drive with stator flux oriented vector control was evaluated extensively using the PWM modulator and flux estimator. The drive performances in both volts/Hz control and vector control were found to be excellent.

Improving the dynamic response of active power filters based on the synchronous reference frame method

This paper presents a new strategy for improving the dynamic response of active power filters that use the synchronous reference frame method (i/sub d/-i/sub q/ method). The strategy is based on the substitution of conventional filtering by a efficient, faster and simpler process requesting less computational burden. Such modification produces a faster transient response during compensation process that lasts 1/6 of the fundamental voltage period (or 1/3, if there is even order harmonics in the currents). Due to its fast response, the proposed modification makes it possible the application of the id-iq method to a single phase. With such a feature, this method becomes suitable for the harmonic compensation of unbalanced loads, still keeping a fast dynamic response. The paper describes the strategy and presents the simulations and the experimental results.

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.

Using rough sets techniques as a fault diagnosis classifier for induction motors

This paper describes the ongoing research on rough sets based classifier applied to induction motors fault diagnosis through motor current signature analysis (MCSA). The results of mechanical failures detection and how a rough sets based classifier is used as a monitoring system using current signature analysis in predictive maintenance are described in this paper.

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.

A DSP based torque meter for induction motors

This work describes the steps to implement a torque meter for three phases induction motors, based on stator voltage and machine current measurement. The strategy is based on stator flux synthesis through Programmable Cascaded Low-Pass Filters (PCLPF). The electromagnetic torque estimation is processed by a DSP microprocessor in real time. The PCLPF filter outlines the problem of necessary numeric integration to calculate the stator flux starting from the samples of stator voltage and current. The Programmable Cascaded Low-Pass Filter is implemented using recurrent neural network (RNN-PCLPF) trained by an algorithm based on Kalman filter. The DSP based implementation of a torque meter results in an equipment with the same precision when comparing with torque meters based on torsion of metallic axes, with known elastic constant and strain gauges.

Ultracapacitor-based ride-through system for adjustable speed drives applied to critical process

Many industrial plants rely on adjustable speed drives (ASD) for critical process applications. However, most ASD are susceptible to power disturbances, specially voltage sags and momentary interruptions. ASD tripping in industrial process can be very costly due to defective units produced as well as production down time. This paper presents an ultracapacitor-based ride-through system for adjustable speed drives applied to critical process. The complete system is composed by an unifield power quality conditioner (UPQC) and a two-quadrant chopper.

A Methodology to Extract Rules to Identify Attacks in Power System Critical Infrastructure

This paper presented an alternative technique to improve the security of electric power control systems by using anomaly detection to identify attacks and faults. By using rough sets classification algorithm, a set of rules can be defined. The alternative approach tries to reduce the number of input variables and the number of examples, offering a more compact set of examples in order to fix the rules to the anomaly detection process. An illustrative example is presented.

An Active Resonance Damper for Distribution Systems Using an ARIMAX Parameter Estimator

This work presents a control algorithm for an active resonance damper. This kind of equipment must act as harmonic impedance in order to damp harmonic propagation throughout a distribution feeder. This harmonic resistance must be equal to the characteristic impedance of the distribution feeder in order to achieve optimized compensating currents. As the analytical calculation of this impedance is a non-trivial (and maybe, impossible) task, it is proposed an ARIMAX least-squares based parameters estimator to determine, on line, the optimal value for the harmonic resistance.