CAPACITANCE REDUCTION USING RIPPLE SUPPRESSION CONTROL OF SINGLE PHASE ENERGY STORED QUASI-Z-SOURCE INVERTER

The energy stored Quasi-Z-source Inverter (qZSI) allows integrate energy storage in addition to the other energy source mainly for output power smoothening. Single phase inverter suffers from double-frequency power ripple in the input side and also in the energy storage that is transferred there from the ac-side. In qZSI must be used large electrolytic dc capacitors in the impedance network to suppress this 100 Hz ripple. Also to suppress this ripple can be applied two types of power decoupling: passive power decoupling and active power decoupling. In this paper is analyzed passive power decoupling that is realized by means of the modified control strategy that produces the time-varying shoot-though duty cycle to mitigate power ripple without deteriorating of the output power quality. The validity of proposed control strategy was confirmed by simulation results that were obtained in PSIM software

Impact of Component Losses on the Efficiency of a New Quasi-Z-Source-Based Dual Active Bridge

Part 16: Optimization Techniques in EnergyInternational audienceThe paper analyzes the impact of the component losses on the efficiency of the novel DC/DC converter. The converter is a combination of the quazi-Z-source (qZS) network and dual active bridge (DAB). In the analysis the mathematical loss models of the proposed DC/DC converter are derived and efficiency is estimated. Eventually the efficiency is verified experimentally

Exploring the Limits of Early Predictive Maintenance in Wind Turbines Applying an Anomaly Detection Technique

The aim of the presented investigation is to explore the time gap between an anomaly appearance in continuously measured parameters of the device and a failure, related to the end of the remaining resource of the device-critical component. In this investigation, we propose a recurrent neural network to model the time series of the parameters of the healthy device to detect anomalies by comparing the predicted values with the ones actually measured. An experimental investigation was performed on SCADA estimates received from different wind turbines with failures. A recurrent neural network was used to predict the temperature of the gearbox. The comparison of the predicted temperature values and the actual measured ones showed that anomalies in the gearbox temperature could be detected up to 37 days before the failure of the device-critical component. The performed investigation compared different models that can be used for temperature time-series modeling and the influence of selected input features on the performance of temperature anomaly detection.publishedVersio

Digest of "Implementation Possibilities of SMD Capacitors for High Power Applications"

Focus is on implementation possibilities of surfacemount device (SMD) to be used in high power applications. SMD capacitors reduce the size and dimensions of a power circuit and increase the flexibility of placement of other components. Ceramic and electrolytic capacitors are compared by means of voltage ripple, volume, labour-intensity and impedance. A 1 kW experimental setup of a quasi-Z-Source inverter (qZSI) based converter was built to compare SMD capacitor performance in the quasi-Z-source (qZS) network. Operation waveforms in both input voltage extremes showed that no significant visual differences exist in the performance of the two types of capacitors.  Differences in voltage ripple were found in the electrolytic and ceramic capacitor case. This fact could be caused by high temperature on the electrolytic capacitors when the voltage ripple damping capability decreases. The heat reduction could be achieved by selecting capacitors with smaller impedance and higher permissible ripple current. If labour intensity and price are not essential, then SMD ceramic capacitors can be recommended for high power applications. Electrolytic capacitors could be implemented only in the case of paralleling them in order to reduce total impedance

Operation of Resonant DC/DC Converter in the BUCK Operation Regime

The series resonant DC/DC converter with isolation transformer is investigated. When switching frequency of input inverter bridge is above the resonant one a shortening of the naturally half-waves of current through a L-C resonant circuit takes place resulting in a circulating current through the DC supply source reducing a mean value of supply current and also reducing load voltage in respect to the one at normally resonant case. The main relations for the case with strong voltage supply source are obtained and operation regimes at raised switching frequency investigated using a computer modeling. Some conclusions are made for proper calculation of parameters. It is shown that the shape of the resonant circuit current at raised frequency grows to the triangular one and that asks for proper correction of the expressions obtained for sinusoidal case. Applying qZ input link processes quite differ from observed for the strong supply – arise charging of the capacitors of the link by influence of circulating current and this phenomena impedes to reducing of the load voltage. That qZ link does not allow to create proper regulation of load parameters.

Current Sensorless Control Algorithm for Single-Phase Three-Level NPC Inverter

Current measurement becomes challenging task in power converters operating at high switching frequencies, moreover traditional control system requires two control loops – first (slow) regulates DC-link voltage, second (fast) controls the shape of current, that all together results in complicated transfer function and long transition periods. The current sensorless control allows neglecting mentioned problems. This research delivers solution of CSC implementation in single-phase three-level neutral point clamped inverter for the first time. Mathematical equations were defined for inductor current peaks and transistor conduction time during DCM and CCM, as well as, major problem of current fitting between different voltage levels (consequently with different current peak-to-peak values) was solved, providing two solutions – pre-fitting and post-fitting trajectories. The verification of our theoretical assumptions and analytical equations were confirmed by the simulation analysis. Challenges of real experiments are discussed in the conclusions

Modelling of Bidirectional Three-Phase Four-Wire Three-Level NPC MLC under Single-Loop Current Sensorless Control

Single-loop current sensorless control allows for abolishing of the instantaneous current measurement in the control system using only a single control loop with voltage feedback to stabilise the DC-bus voltage. This approach eliminates current sensors in the control circuit, benefiting from saving space on the printed circuit board and minimising power dissipation in the current measurement circuitry. This paper focuses on the single-loop current sensorless control applied to bidirectional three-phase four-wire three-level NPC MLC by simulation analysis and demonstrates the performance of the proposed current control algorithm in the rectifier and inverter modes and the step response with power direction change and grid-voltage change. In capacitor voltage balancing, an additional controller is applied, which is capable of compensating for the voltage asymmetry caused by adding a 2.5 kOhm resistor in parallel to one of the DC-bus capacitors. Our results demonstrate good performance of the proposed control method both in the inverter and rectifier modes, showing stable current shape in the low power and full power modes with acceptable harmonics content, meeting the requirements of the IEC 61000-3-2 standard for Class A devices. The analysis showed that the proposed control approach is suitable for industrial application

КВАЗИ-ИМПЕДАНСНЫЙ DC/DC ПРЕОБРАЗОВАТЕЛЬ С ПОСЛЕДОВАТЕЛЬНЫМ РЕЗОНАНСНЫМ LC-ЗВЕНОМ И МЯГКОЙ КОММУТАЦИЕЙ

This paper discusses further modifications of the recent popular qZS-based DC/DC converter design by the introduction of the resonant LC circuit in series to the primary winding of the isolation transformer. The primary aim is to achieve the zero voltage and zero current switching of transistors. As an additional benefit of the resonant LC circuit, the converter is able to perform the voltage buck function simply by changing the switching frequency of the transistors. The control principle of the converter and its main operating modes are explained. The theoretical assumptions are experimentally verified by help of the small-scale testbench of the converter.Предложена модификация схемы квази-импедансного DC/DC преобразователя путем последовательного включения резонансного LC-звена и первичной обмотки изолирующего трансформатора. Это позволяет достичь коммутации транзисторов при нулевом токе и нулевом напряжении. К дополнительным преимуществам предложенной схемы DC/DC преобразователя можно отнести способность понижать напряжение путем изменения частоты коммутации транзисторов. Рассмотрен принцип управления преобразователем и его основные режимы работы. Предложенные гипотезы были экспериментально подтверждены с помощью лабораторного макета.Предложена модификация схемы квази-импедансного DC/DC преобразователя путем последовательного включения резонансного LC-звена и первичной обмотки изолирующего трансформатора. Это позволяет достичь коммутации транзисторов при нулевом токе и нулевом напряжении. К дополнительным преимуществам предложенной схемы DC/DC преобразователя можно отнести способность понижать напряжение путем изменения частоты коммутации транзисторов. Рассмотрен принцип управления преобразователем и его основные режимы работы. Предложенные гипотезы были экспериментально подтверждены с помощью лабораторного макета

Wireless Battery Chargers Operating at Multiple Switching Frequencies with Improved Performance

The operation of wireless battery chargers at multiple switching frequencies may lead to a noticeable suppression of conducted and radiated electromagnetic interference (EMI) at the cost of decreased efficiency (mainly at lower load resistances) and increased peak and root mean square values of currents of power components of the wireless battery charger. Moreover, the reduction in conducted EMI is only moderate (<8.3 dB). Therefore, a novel approach based on modified resonant circuits and a modified control technique to obtain better reduction in the conducted and radiated EMI without significantly compromising other performance characteristics of the wireless battery charger is proposed and validated by using simulations and experiments. It is shown in this paper that the wireless charger operating at multiple switching frequencies with the proposed approach for the performance improvement has a more effective implementation of the four-switching frequency spread-spectrum technique with better conducted and radiated EMI reduction at all load resistances, lower values of peak and RMS currents at all load resistances, and higher efficiency in constant current mode and in the beginning of constant voltage mode (at lower values of the load resistances) than that of the conventional wireless charger operating at multiple switching frequencies