Mains Period Research Articles

СРАВНИТЕЛЬНАЯ ОЦЕНКА МЕТОДОВ УСРЕДНЕНИЙ ДЛЯ ФИЛЬТРАЦИИ ИЗМЕРИТЕЛЬНЫХ СИГНАЛОВ

To improve the quality of manufactured products, it is necessary to improve all technologicalprocesses, which requires increasing the accuracy of the entire measuring path as a whole.For this it is necessary to carefully analyze systematic, random and fluctuating errors in the measurementchannel and take all measures to reduce them. Digital filtering or averaging of intermediatemeasurements (observations) according to certain rules is a radical means of improving theaccuracy of measurements performed. The aim of this work is to compare the quality of suppressionof near-real noise interference using the eight most well-known averaging methods. A model of the measurement path and a general block diagram for modeling the measurement process on acomputer under the influence of random interference are proposed for eight averaging algorithms.As a criterion for evaluating the quality of averaging methods, the ratios of absolute error variancesand mean square deviations before the computing device and after applying the specified averagingalgorithm are taken. Based on the simulation results, the following conclusions are made. 1. All averagingalgorithms provide suppression of random error components of complex interference to thelevel of 40–60 dB. Three algorithms are the best: arithmetic mean AR, a-truncated mean AU5 and atenderizedmean AB5, which provide for the suppression of 5 % of anomalous results. With an increasein the number of observations, the suppression coefficients increase proportionally. 2. Thesampling time must be a multiple of the duration of the 50 Hz AC mains period (20 ms). The optimalnumber of observations (measurements) is 100–128; with 128 measurements, the division operationis reduced to a simple shift, and the averaging result can be obtained in 1–2 μs. 3. When experimentallyapplying the AR averaging method for filtering a highly noisy measurement signal in a communicationline with a length of 800 m, a decrease in the spread of ADC output codes was observedfrom ± 3.5 % to ± 0.1 % after filtering (AR, 64 measurements in 40 ms).

Cyclic Signals and Systems in Power Line Communications

This paper provides a comprehensive discussion about the characteristics of power line communication (PLC) channels related to its synchronization with the mains period. This fact constitutes an interesting and distinguishing feature of these kind of channels. Under the mains voltage presence, the behavior of some loads connected to the power network allows representing the transmission medium as a linear periodically time varying (LPTV) system. Some components in the received noise exhibit periodicity as well, in terms of impulsive waveforms synchronized with the mains period and other cyclostationary (CS) signals. This fact has been taken into account in the design of PLC systems, for instance by defining medium access control (MAC) frames synchronized with the mains period and by adapting the modulation to the cyclic signal-to-noise ratio (SNR) to improve the system performance. Hence, in PLC, it is of particular interest to describe the general relations of LPTV systems and CS signals when both have a common period, which is the purpose of this work. It is not aimed at providing new mathematical tools for the analysis of these cyclic signals and systems, which have been extensively developed over the last five decades, but to serve the readers of the PLC community more accessible mathematical relations that can be applied to the practical problems they have to face. A review of recent works dealing with the cyclic properties of PLC channels and transmission techniques aware of these strategies is included as well.

99.1% Efficient 10 kV SiC-Based Medium-Voltage ZVS Bidirectional Single-Phase PFC AC/DC Stage

Due to their extremely high energy demand, data centers are directly supplied from a medium-voltage (MV) grid. However, a significant part of this energy is dissipated in the power supply chain since the MV is reduced step-by-step through multiple power conversion stages down to the chip-voltage level. In order to increase the efficiency of the power supply chain, the number of conversion stages must be substantially reduced. In this context, solid-state transformers (SSTs) are considered as a possible solution, as they could directly interface the MV AC grid to a 400 V DC bus, whereby server racks with a power consumption of several tens of kilowatts could be directly supplied from an individual SST. With a focus on the lowest system complexity, the SST, ideally, should be built as simple two-stage system consisting of an MV AC/DC power factor correction (PFC) rectifier stage followed by an isolated DC/DC converter. Accordingly, this paper focuses on the design and realization of a 25 kW, 3.8 kV single-phase AC to 7 kV DC PFC rectifier unit based on the 10 kV SiC MOSFETs. By simply adding an $LC$ circuit between the switch nodes of the well-known full-bridge-based pulse width modulated AC/DC rectifier, the integrated triangular current-mode concept is implemented, which only internally superimposes a large triangular current ripple on the AC mains current and, therefore, enables zero-voltage switching over the entire AC mains period. Special attention is paid to the realization of the MV inductors and their electrical insulation, the AC-input $LCL$ filter to limit electromagnetic interference emissions, and the challenges arising due to cable resonances when connecting the SST to the MV grid via an MV cable. Despite the large insulation distances required for MV, the realized 25 kW MV PFC rectifier achieves an unprecedented power density of 3.28 kW/L (54 W/ $\mathrm {in}^{3}$ ) and a full-load efficiency of 99.1%, determined using a calorimetric measurement setup, which is discussed in detail in the Appendix.

Sine Inverter Controller with 8 Bit Microcontroller

This article describes the design of a sine wave inverter control unit. We will define the basic principles and requirements to control and maintain a good quality of inverter's output. The solution that can achieve full 8 bit output resolution with 10 bit measurement and regulation time shorter than mains period is proposed. Furthermore, the possibilities and ways of implementing the control unit using the 8 bit microcontrollers are described, so it is possible to gain a complete understanding of this issue.

Measurement and Characterization of Load Impedances in Home Power Line Grids

The measurement and characterization of the load impedances in the home/office power grid is the topic of this paper. This is motivated by the interest of exploiting the home power line grid for data communications. The power line communication (PLC) medium is strongly affected by the presence of unmatched and time-variant loads, so we have carried out a measurement campaign on a representative set of devices that can be found in a house or office. The measurement procedure has allowed the investigation of their behavior both in the time and in the frequency domain, over a time span equal to the mains period and within the frequency range 2-30 MHz that is used by broad band PLC systems. We have found a very limited number of devices with an impedance noticeably time-variant. This is because they include, in the power supply unit, an electromagnetic interference filter that significantly reduces the time-variant behavior of the device impedance in the 2-30 MHz band. Furthermore, the impedance of any device is also affected by the presence of a power cord. Finally, from the experimental results, we propose a behavioral classification of the devices based on certain typical time/frequency characteristics of their impedance.

Ultraflat Interleaved Triangular Current Mode (TCM) Single-Phase PFC Rectifier

This paper presents the analysis and realization of a topology suitable to realize a power factor correction (PFC) rectifier with a thickness of only a few millimeters. The low height of the converter requires all components to be integrated into the printed circuit board (PCB). Still reasonable dimensions of the converter PCB are feasible (221 mm × 157 mm for a 200 W PFC rectifier), since PCB-integrated inductors and capacitors allow for high energy densities due to their large surface area which facilitates a low thermal resistance to ambient. A multicell totem-pole PFC rectifier employing a soft-switching modulation scheme over the complete mains period is identified as an adequate topology. The mode of operation is entitled triangular current mode (TCM) due to the triangular-shaped inductor currents. The modulation technique requires a reliable description of the switching transition of a half-bridge in order to provide accurate timing parameters. For this purpose, a simplified model of the nonlinear MOSFETs' output capacitances facilitates closed-form analytical expressions for duty cycle and switching frequency. Furthermore, this paper details the control of three interleaved converter cells which yields a reduction of the input current ripple. A 200 W TCM PFC rectifier with a low height of 5 mm has been realized and measurement results are provided in order to validate the theoretical considerations. The presented TCM PFC rectifier achieves an efficiency of 94.6% and a power factor of 99.3% at nominal power.

Improving mains current quality for three-phase three-switch buck-type PWM rectifiers

Modulation schemes for three-phase three-switch buck-type pulsewidth modulation rectifiers where the switching state of one bridge leg is clamped within a π 3-wide interval of the mains period guarantee minimum switching losses as well as minimum input filter capacitor voltage ripple and minimum dc current ripple. However, as shown in this paper by a detailed analysis of the time behavior of the input filter capacitor voltages within a pulse period such modulation schemes are characterized by the occurrence of sliding intersections of the filter capacitor voltages which causes input current distortion. An advanced modulation scheme is proposed which prevents the input current distortion and allows it to maintain the optimum performance of conventional modulation schemes. The theoretical considerations are finally verified by measurements on a 5-kW hardware prototype.

The method of double averaging: an approach for modeling power-factor-correction switching converters

This paper describes the modeling of power-factor-correction converters under average-current-mode control, which are widely used in switch-mode power supply applications. The objective is to identify stability boundaries in terms of major circuit parameters for facilitating design of such converters. The approach employs a double averaging procedure, which first applies the usual averaging over the switching period and subsequently applies generalized averaging over the mains period. The resulting model, after two averaging steps and application of a harmonic balance procedure, is nonlinear and capable of describing the low-frequency nonlinear dynamics of the system. The parameter ranges within which stable operation is guaranteed can be accurately and easily found using this model. Experimental measurements are provided for verification of the analytical results.

Modelling and control of three-phase∕switch∕level fixed-frequency PWM rectifier: state-space averaged model

A new and simple state model of a three-phase, three-switch, three-level, fixed-frequency pulse-width-modulated rectifier is presented. The modelling approach uses the state-space averaging technique in continuous current mode. The averaging process is applied on two time intervals: the switching period for average current evaluation, and the mains period for average voltage computation. A basic mathematical model of the converter is first established. A simplified time-invariant model is then deduced using the rotating Park transformation. The steady-state regime is analysed on the basis of the model obtained, and converter design criteria consequently discussed. The proposed modelling approach is then verified numerically through a digital implementation of the converter in the Matlab/Simulink framework, using the switching function approach. The numerical results show the reliability of the proposed model that would be then easily applied to the design of suitable duty-cycle-based control schemes.

Resonant solar converter for direct mains connection realized with a ZC-switching SEPIC variant structure

This paper presents a new converter structure that can be defined as a wide output range step down SEPIC type converter (Barbi and Martins 1991, Liu and Lee 1986) in conjunction with a simple DC to AC switch. For this project a SEPIC variant structure was chosen because of the fact that an output voltage close to zero can be achieved by a switching frequency and duty cycle greater than zero. This results in less output current ripple and reduces harmonic distortion. With the resonant switching in the SEPIC part it was possible to improve the efficiency calculated for one mains period in relationship to standard converter types. As a result, the thermal problems could be minimized and the mechanical dimensions optimized. Due to this converter structure and the switching technology, and despite the very high switching frequency, this converter is the ideal application area for IGBT. The structure has been developed especially for a wide output range of DC to DC conversions.

Microwave heating power supply operating in a high power-factor mode

The performance of a switched-mode magnetron power supply is considered in which a rectified, non-filtered mains voltage is applied to the converter input. The system features output voltage boosting at the input voltage zero crossings, and provides high power-factor operation. A closed-form expression for the system gain is obtained with and without active input current shaping. The analytical results show that the system tends to linearize the inherently nonlinear magnetron characteristic, and that a complete linearization could be achieved by frequency modulation within the mains period. The optimum converter component values are identified and the results are verified experimentally.