C.M. Penalver

Comparison of the FPGA Implementation of Two Multilevel Space Vector PWM Algorithms

Multilevel converters can meet the increasing demand of power ratings and power quality associated with reduced harmonic distortion and lower electromagnetic interference. When the number of levels increases, it is necessary to control more and more switches in parallel. Field programmable gate arrays (FPGAs), with their concurrent processing capability, are suitable for the implementation of multilevel modulation algorithms. Among them, space vector pulsewidth modulation algorithms offer great flexibility to optimize switching waveforms and are well suited for digital implementation. In this paper, two algorithms, 2-D and 3-D, are analyzed and implemented in an FPGA. In order to carry out the implementation, both algorithms have been described in very high speed integrated circuit hardware description language, partly hand coded, and partly automatically generated using the system generator tool. Both implementations are compared in terms of implementation complexity and logic resources required. Finally, test results with a neutral-point-clamped inverter are presented.

Dynamic and steady state analysis of a three phase buck rectifier

Current source rectifiers among other alternatives, offer several advantages over line commutated rectifiers. Advantages include displacement power factor control and reduced line current harmonic distortion. This paper analyzes the current source rectifier (CSR) in transient and steady state, the models are developed in a synchronous reference frame. The load behavior is characterized for two load conditions, resistive load or, in general, increasing current for increasing voltage, and constant output power, decreasing output current for increasing voltage. Constant power operation can occur for a converter system supplying a pulse width modulation (PWM) inverter with high dynamics. Several static converter characteristics such as power factor, real and reactive power are analyzed for both types of load. Transient characteristics are analyzed for both types of load by exact small-signal model with full set of equations.

Real-Time implementation of a SPLL for FACTS

This paper presents a real-time implementation of a software phase-locked loop (SPLL) for use within FACTS systems. The FACTS phase locked loops (PLLs) main characteristics and the disturbances impact over their performance are reviewed making special emphasis on the weak points of the usual three-phase trans-vector-type PLLs. These weak points are mainly slow response under low amplitude AC inputs and three-phase unbalances. Recently some alternatives, specially the adaptive SPLL, solved these typical trans-vector issues. However, the discrete implementation of adaptive SPLL in a programmable device like a microcontroller, a DSP or a FPGA seems very complex. In this work a double-loop SPLL has been developed with the aim of reducting the complexity of a discrete implementation and without losing performance with respect to the adaptive SPLL. The proposed double-loop SPLL has been implemented in real-time using Matlab/Simulink and the fast prototyping platform dSpace DS1103; its high performance and feasibility are shown in the simulation and real-time implementation sections

Shunt active power filter with harmonic current control strategy

This paper presents a single phase shunt active power filter for compensating the power factor and harmonics currents generated by two nonlinear loads, an AC controller with resistive load, and a rectifier with an inductive load. The topology of the filter is based on a single phase inverter with four IGBTs. The filter current is forced to follow a reference; this reference current must be the difference between the sinusoidal input current in phase with the sinusoidal voltage supplying the load and the load current; for calculating the reference current a frequency-independent method has been used. The calculus of the reference current and results of simulation are presented; finally experimental results obtained from a prototype confirm the feasibility of the proposed system.

Three alternatives for implementing space vector modulation with the DSP TMS320F240

Voltage source converters (VSC) and current source converters (CSC) transfer energy from a source to a load in a quantized fashion using semiconductor switches which are turned on and off at fast repetition rates. Space vector modulation (SVM) among other pulsewidth modulation techniques, offer several advantages such as minimizing the number of switchings or improving the utilization of the source voltage. This paper presents three alternatives for implementing SVM in a DSP-controller. The study is performed for a voltage source rectifier (VSR), but as well, it is adequate for a voltage source inverter (VSI). The three alternatives are compared from a theoretical and experimental point of view. The algorithms proposed provide a simple and effective solution for high-performance (VSR). Experimental results are given to verify the implemented algorithms.

Geometric Analysis and Manufacturing Considerations for Optimizing the Characteristics of a Twisted Pair

The geometry of a twisted pair largely determines its electrical characteristics. To improve and refine the value of these characteristics according to preset values, the optimization of the manufacturing processes requires comprehensive knowledge of twisted pair geometry and of how electrical magnitudes are affected by the construction features of the twisted pair. This paper studies the relation between the length of a twisted pair cable and the length of each of the wires that compose the cable, by analyzing concepts such as pitch angle and radius of the helix. In addition, it examines the deformations and irregularities that can occur in the twisted pair during the manufacturing process and their effects on the geometry of the twisted pair. Results showed in this paper are a part of a larger research project carried out in association with the R&D department of a cable manufacturing company, and these results are being applied into the design department of this company.

Multilevel multiphase space vector PWM algorithm applied to three-phase converters

Multilevel technology achieves high power ratings with voltage limited devices. Recently a new space vector pulse-width modulation algorithm for multilevel multiphase voltage source converters with low computational cost has been presented. This algorithm can be used with any number of phases; therefore, it can be also used with classical three-phase topologies. In this paper, the multiphase algorithm is particularized for three-phase converters and compared with an existing multilevel space vector modulation technique. Finally, the algorithm is implemented in a low cost FPGA and it is tested in laboratory with a real prototype by using a neutral point clamped inverter.

Four-dimensional space vector PWM algorithm for multilevel four-leg converters

Four-leg voltage-source converters provide an effective neutral connection in three-phase systems with neutral wire. They can be applied to inverters, rectifiers or active filters to control the neutral current caused by unbalanced or nonlinear loads as well as unbalanced sources. From the modulation point of view, the four-leg converters can be considered as four-phase systems. Hence, the modulation task can be carried out with a generic multiphase modulation algorithm. Recently, a novel space vector PWM technique for multilevel multiphase voltage-source converters has been presented. The four-dimensional space vector PWM algorithm for multilevel four-leg converters presented in this paper is the result of applying such technique to a four-phase converter. Finally, the algorithm is implemented in a low-cost FPGA and it is tested with a prototype by using a five-level cascaded full-bridge inverter.

An approach to real behaviour modeling for traction lead-acid batteries

At the present time, the batteries are the main obstacle in the race toward the total development of the electric vehicles. In this article we present a PSPICE model for lead-acid batteries of traction that represents an approach of the real behavior of these so that it can be analyzed directly from the PSPICE environment. This model is flexible and can be adjusted in function of the type of electrochemical battery.

Novel Harmonic Identification Algorithm based on Fourier Correlation and Moving Average Filtering

With the aim to minimize the harmonic disturbances created by non linear loads, the active power filters have an important role in the improvement of power quality. Active filters need to identify the harmonic components of some specific system currents/voltages to calculate the filter current/voltage references and thus set the power devices switching to compensate for the harmonics. Therefore, the accuracy and quickness in the harmonic identification of the input signals have a very important role in the active filters control performance. This work presents a novel digital algorithm for harmonic identification based on Fourier correlation in quadrature and moving average filtering (MVA). The input signal has harmonic component at well known odd frequencies, and it can be expressed as a Fourier series. Therefore, by multiplying independently two orthogonal unitary signals rotating at a known frequency by the input signal, the output signals have the Fourier coefficients of this frequency shifted to dc and the other coefficients shifted to even harmonics. Then by placing a low pass filter after each multiplier, the dc coefficients are obtained. This correlation method has the problem of a relatively high gain of the employed low pass filters for the lowest order even harmonics. However, by replacing the low pass filter by a MVA comb filter with no dc delay and even harmonics cancellation, the searched coefficient can be obtained accurately and with only the computation and A/D converter delay, which can be neglected for low frequencies applications (50 Hz or 60 Hz the fundamental frequency). It is important to note that the outputs of the multipliers have only even harmonics, so the window width of the MVA can be reduced to half a cycle of the input fundamental signal, reducing the needed resources with respect to Fourier Transform based algorithms, which need an entire cycle window. The performance of the proposed identification method for harmonic identification and for active filtering is demonstrated with experimental results.