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Power Electronics Converters Applications And Design

Three-phase voltage source converters (VSCs) are commonly used as power flow interface in ac/dc hybrid power systems. The ac power grid suffers from unpredictable short-circuit faults and power flow fluctuations, causing undesirable grid voltage dips. The voltage dips may last for a short time or a long duration, and vary the working conditions of VSCs. Due to their nonlinear characteristics, VSCs may enter abnormal operating mode in response to voltage dips. In this paper, the transient response of three-phase VSCs under practical grid voltage dips is studied and a catastrophic bifurcation phenomenon is identified in the system. The converter will exhibit an irreversible instability after the dips. The expanded magnitude of ac reactive current may cause catastrophic consequence for the system. A full-order eigenvalue analysis and a reduced-order mixed-potential-theory-based analysis are adopted to reveal the physical origin of the large-signal instability phenomenon. The key parameters of the system are identified and the boundaries of instability are located. The bifurcation phenomenon and a set of design-oriented stability boundaries in some chosen parameter space are verified by cycle-by-cycle simulations and experimental measurement on a practical grid-connected VSC prototype.

Bifurcation and Large-Signal Stability Analysis of Three-Phase Voltage Source Converter Under Grid Voltage Dips

This paper proposes bidirectional power flow control of a grid interactive solar photovoltaic (PV)-fed water pumping system. A brushless DC (BLDC) motor drive without phase current sensors is used to run a water pump. This system enables a consumer to operate the water pump at its full capacity for 24 hours regardless of the climatic condition and to feed a single-phase utility grid when water pumping is not required. The full utilization of a PV array and motor pump is made possible in addition to an enhanced reliability of the pumping system. A single-phase voltage source converter with a unit vector template generation technique accomplishes a bidirectional power flow control between the grid and the dc bus of the voltage source inverter (VSI), which feeds a BLDC motor. The VSI is operated at fundamental frequency, which minimizes the switching loss. The maximum power point operation of a PV array, and power quality improvements, such as power factor correction and reduction of total harmonic distortion of grid, are achieved in this system. Its applicability and reliability are demonstrated by various simulated results using MATLAB/Simulink platform and hardware implementation.

Grid Interactive Solar PV-Based Water Pumping Using BLDC Motor Drive

Equivalent series resistance (ESR) of output capacitor has a significant effect on the control performance of constant on-time (COT) controlled switching dc-dc converters. In this paper, a discrete-time model of COT-controlled buck converter, with variable sampling frequency, is established. Based upon which, the dynamical effects of the ESR of output capacitor on COT-controlled buck converter are revealed and analyzed. The time-domain numerical simulations of the exact switched state equations, the bifurcation diagrams, and maximal Lyapunov exponents of the discrete-time model are obtained. These results verified by experimental circuit indicate that the ESR of output capacitor is a critical factor for COT-controlled buck converter, which can eliminate the unique pulse bursting phenomenon and shift operation mode from discontinuous conduction mode to continuous conduction mode, as well as control stability.

Dynamical Effects of Equivalent Series Resistance of Output Capacitor in Constant On-Time Controlled Buck Converter

The Electric double-layer capacitor (EDLC) or super-capacitors are becoming increasingly popular for their high specific power and for integrating that feature with batteries, which have a high specific energy. Due to the above reason, we have attempted to understand how to use super-capacitors and characterized them, so that both battery and super-capacitors can be used together, or for low power green energy applications, like various electronics gadgets, how to use only super-capacitors. In this paper, we described the known properties of a super-capacitor relative to a conventional lithium-ion battery. The structural design of the Super-capacitors and also various engineering-based applications, related to consumer electronics, transportation etc. are also described, as a review, in this paper. As we all know, that Super-capacitor's voltage would decay over time as we draw power from it, therefore maintaining the output voltage constant for any DC-DC converter without any battery is difficult. Thus, in this paper we have shown, how we have developed a DC-DC converter circuit, without any battery, which has both feed-back and feed forward control loop, in order to maintain constant output voltage. We also have developed a mathematical equation related to super-capacitor to show the requirement for having a feed-back loop can be eliminated while using super-capacitors which have very low Equivalent Series Resistance (ESR). We have also found that for some super-capacitors one cannot pump infinite current to charge a super-capacitor because the effective parallel resistance reduces as one try to pump large current and therefore charging these capacitors to a given desire voltage may not be possible. Therefore, in order to enhance the efficiency and to reduce the charging time of super-capacitor, we proposed and developed an algorithm having gamma function-based charging methodology for super-capacitor.

How and where to use super-capacitors effectively, an integration of review of past and new characterization works on super-capacitors

A high step-up DC–DC converter with active switched LC -network is proposed in this paper, which can be used in the photovoltaic system as the front-end stage to generate the required DC bus voltage. Based on the transformerless DC–DC converter with an active switched inductor (ASL) network, this proposed converter introduces an active switched capacitor (ASC) network, where only one capacitor and one diode are added, while the voltage gain is efficiently increased by a compound of ASL and ASC networks. The structure of the proposed converter is simple and voltage stresses on the additional diode and capacitor are low. In addition, unlike other voltage-boosting structures that utilized switched capacitor, the proposed converter avoids the extreme instantaneous currents of capacitor. The detailed analysis of the proposed converter and performance comparison with recently published ASL network-based converters are presented. Finally, a 100 W, 20/200 V prototype circuit is operated to verify its performance.

High Step-Up DC–DC Converter With Active Switched LC -Network for Photovoltaic Systems

Total ampere-turns of the primary and secondary windings of a transformer are taken as one of variables to analyze the bifurcation behaviors and the border collision phenomenon on voltage-mode-controlled flyback converter. Six operation modes which are separated by the two borderlines of capacitor voltage and the three borderlines of total ampere-turns are obtained. A class of explicit piecewise smooth discrete-time maps with six operation modes is derived to describe the dynamics of the system. The numerical calculations are carried out, the bifurcation diagrams and the maximal Lyapunov exponent spectrums with the control period as a parameter are obtained. Then, the paper particularly analyzes the stability and existence conditions of main periodic orbits. The structure of bifurcation diagrams and the characteristics of operation modes at the border collision points are studied too. Finally, PSIM simulation and experimental results testify the validity of theoretical analysis.

Bifurcation and Border Collision Analysis of Voltage-Mode-Controlled Flyback Converter Based on Total Ampere-Turns

Non-linear dynamic behaviours in a single DC-DC converter system have been widely investigated in the past three decades. However, with the increasing popularity of microgrids, renewable energy systems and DC distribution power systems, non-linear phenomena analysis of DC cascaded converters system with multi-load converters, which is the most dominant connection among them, is necessitated. Thus, in this study, the complex bifurcation phenomena of one source boost converter (SBC) paralleled with one boost converter and two buck converters are analysed. To stabilise the output voltage in a determinate region, both inner current loop and outer voltage loop controls are used in all sub-converters. Using simulation and experiment analysis, the SBC has coexisting attractors and enters the coexistence of fast-scale and slow-scale instabilities or multi-period orbits in some parameters condition, but all the load converters work in stable state. To explain these phenomena, the discrete mapping of this DC cascaded converters system is established and the derivation of its eigenvalue is conducted. For simplicity, all of the load converters are considered as constant power loads. By analysing the eigenvalues of period-1 and period-2 orbits, the coexisting attractors and the coexisting fast-scale and slow-scale instabilities are explained.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2015.0193

Non-linear dynamic behaviours of DC cascaded converters system with multi-load converters

A novel space vector pulse width modulation (SVPWM) strategy for three-phase four-wire neutral-point-clamped (NPC) inverter is proposed in this paper. The m -mode controllability of a three-phase four-wire NPC inverter, which is modeled as a switched linear system, is investigated. Then, on the basis of analysis of the m -mode controllability, taking the three-level property and the continuity of switching sequence into account, the controllable sets with the three-level property can be a new solution for the NPC inverter. With the sets of less operating modes, new modulation strategies named 18-mode SVPWM strategy, including 18-mode SVPWM(I), 18-mode SVPWM(II), and 18-mode SVPWM(III), are put forward. Compared with the conventional SVPWM strategy, the switching frequencies of the proposed 18-mode SVPWMs modulation strategy are significantly reduced by one-third. Therefore, the overall losses of the system can be reduced and the performance of the inverter can be improved. Finally, the simulation and the experiment results verify the correctness of the proposed approach.

A Novel SVPWM for Three-Level NPC Inverter Based on m-Mode Controllability

Based on the characteristics of dc-dc switching converters and the logical arithmetic method of computer that changes to decimal system from binary system, the main switching block is presented to distinguish the switching behaviors and the degree of the converter's complexity during one switching period. The main symbolic sequence is established to clearly show how the switching modes change in one switching period. Adopting the coarse-grained symbolic sequence method, the secondary switching block and secondary symbolic sequence are established in terms of main switching block too. Hence, the duplicate symbolic sequence is put forward to detect bifurcation types in dc-dc switching converters. Based on the duplicate symbolic sequence, the concept of weight complexity is first defined and utilized to analyze border collision and bifurcation phenomena qualitatively along with Lempel-Ziv (L-Z) complexity. The presented weight complexity and the L-Z complexity are combined to introduce the stability index for guiding circuit design of power electronics. Finally, voltage-mode-controlled flyback converter is used as an example to illustrate the applications of the proposed duplicate symbolic sequence and complexity to detect bifurcation behaviors of the switching system.

Fan Xie

Papers

High Step-Up DC–DC Converter With Active Switched LC -Network for Photovoltaic Systems

Bifurcation and Border Collision Analysis of Voltage-Mode-Controlled Flyback Converter Based on Total Ampere-Turns

Non-linear dynamic behaviours of DC cascaded converters system with multi-load converters

A Novel SVPWM for Three-Level NPC Inverter Based on m-Mode Controllability

Detecting Bifurcation Types and Characterizing Stability in DC–DC Switching Converters by Duplicate Symbolic Sequence and Weight Complexity