Power converter's optimisation and design. Discrete cost function with genetic based algorithms

Discrete learning-based intelligent methodology for heart disease diagnosis

This note gives a complete characterization of the cost function which is the dual of a homogeneous Cobb-Douglas production function.! The main result is that a continuous cost function has a first-order Taylor series approximation interpretation if and only if it is the dual of a homogeneous Cobb-Douglas production function. In other words, all Taylor series expansions of cost functions, when expanded jointly in prices and output, will collapse to the Cobb-Douglas form when terms of secondand higher-order are dropped. This is surprising, for it means not only that the cost function is homogeneous in prices as dictated by economic theory, but that in order to have a first-order Taylor series approximation interpretation it must be homogeneous in output as well. The analysis was motivated by the work of Barnett and others who have demonstrated that the second-order Taylor series expansions used to estimate cost, indirect utility, and profit functions frequently fail to satisfy certain regularity properties.2 The objective of this paper was to identify the functional forms of all continuous functions which provide a first-order Taylor series approximation to an arbitrary cost function at a point. While one would not expect to find any acceptable first-order approximations for cost functions since they cannot model arbitrary substitution possibilities, that expectation is rigorously confirmed here. The analysis is an extension of Eichhorn (1974, 1978) and Stehling (1975), and is similar to Fare and Sung (1986).

‘Thin’ power electronics concentrates on the design of minimal and cost effective power converters. Part of the research effort targets the direct processing of an AC input to an AC output without the use of an intermediate DC stage. Particular examples include the inverterless active filter and the controllable network transformer, both of which in their simplest form employ a buck switcher as the active element. Existing analysis of these circuits has dealt with a continuous approximation to the modulating function with applications to relatively high switching frequencies. This paper addresses the problem of selecting a low frequency switching pattern that achieves the correct transformation of an AC input composed of a set of arbitrary harmonics into an AC output containing a desired set of harmonics. This is achieved by constructing a model of the converter in the frequency domain so as to allow a systematic description of the interaction between linear filters and the buck converter via a set of non-linear equations that closely approximate the behaviour of the physical circuit. These equations are set in the form of a constrained optimization problem, the solution of which represents an optimal switching pattern that satisfies a set of harmonic constraints. The method is presented in a general way, facilitating direct application to other systems composed of linear filters and a buck converter. The inverterless active filter is considered as an example problem and the method is used to construct optimal switching patterns that provide harmonic correction of the current drawn by a three phase passive rectifier.

This paper discusses concepts of a 20 kVA power converter design and key differences between discrete IGBT and module-based design approaches. Module-based power converters have been typically employed in academic and research institutes for power levels of 10 kVA and more. However, with advancement in IGBT technologies and the growing need to minimize system size and weight, designs based on discrete devices are now an attractive alternative for such power levels. A simple procedure is presented for power converter design that includes power loss evaluation, heat-sink thermal characterization, thermal model of overall system and sizing of DC link capacitor. Using the same, a state-of-the-art discrete device and module-based power converters are designed. A comparison is subsequently made, where it is shown that discrete approach yields a compact and economic design up to a power level of 20 kVA. A key objective of this work is to lay emphasis on laboratory design of power converters. This enables a graduate level student to build a converter from start and in the process gain insights into the underlying engineering design aspects.

As a result of increasing the demand of power converters in electric aircrafts and electric vehicles, the power converter must be designed to deliver better, faster and cheaper performance. Finding the appropriate LC filter is the first step of the power converter design. Considering the desired losses, weight and cost, the optimization method is key in LC filter design. The value of the filter components has been optimized to satisfy the design of specific objective function such as maximizing the quality factor of the filter or minimizing the attenuation of harmonics distortion. Controllers help reduce harmonics distortion in filters. The proportional-integral controller as the first control method, has been used to control the power converters (buck converter, single and three phase inverter). This type of the controller can maintain the bandwidth and the stability margin of the controlled system within desired range. The PI controllers in different systems have been tuned by root locos, bode plot and pole placement methods. Then the sliding mode controller, which does not need the average model of power converter and has a high level of stability in different performance condition (such as load variations), has been applied to the single phase inverter. As the last control step, the three phase inverter with low switching frequency has been controlled in stationary frame with multiloop controller which provides sufficient bandwidth to eliminate low level voltage harmonics even in low switching frequency. This type of the controller doesn’t need park transformation which reduces the calculation time. The optimized value of the controller gains has been investigated by minimizing the integral of time-weighted absolute error or reducing the multiplication of raise time, settling time and the overshoot of the output voltage. The Matlab simulation and optimization toolbox has been used to verify the performance of the proposed controllers and also find the optimized value of filters components and controllers gains.

Power converter design and compensation design using numerical optimization techniques have been presented before in the literature. However, most of the work is limited to a particular topology and ideal component values. Also, prior works only focus on a proof of concept and do not demonstrate a full-fledged design tool aimed at the compensation design across multiple compensation types and converter topologies. This paper presents a web based, easy to use compensation design tool (Re-Comp), integrated into an industry leading online power design tool, WEBENCH Power Designer, used by thousands of power engineers worldwide. Re-Comp allows users to quickly design and optimize compensation networks to meet desired loop specifications. The proposed tool provides a robust design and ensures loop stability over the entire operating range of converter and perturbations in component parameters. Hybrid optimization algorithm used in the backend to design the compensation network combines the benefits of fast convergence of Conjugate Gradient method and robustness of Differential Evolution. Re-Comp also allows users to design with real components from a large database of passive components from all major vendors.

One confusing question over a long period of time is how transfer the discrete function transfers into continuous function. Recently the issue has been resolved but some details of the transformation process will be introduced in the paper. The correlation coefficients of 100,000 values are established from the two groups of data with the range between -1 and 1, creating a histogram from these correlation coefficient values known as “the probability mass function.” The coefficient values are brought into the discrete distribution function, so that transfers into the discrete cumulative function, next converted into a continuous cumulative function, next which is differentiated to get the density function, so that it is easy to being research analysis. A model will be established during the process of the conversion what the medium is “the least squares algorithm.” Finally, when the integral of the area within the range of the density function equals to 1, this implies that the transformation complete succeeds from the discrete function to the continuous function.

The wirewound resistors (WRs) are one of the most popular passive components in modern power converters. They are used for many purposes, including sensing, current limitation, discharging, braking, etc., therefore depending on their main target, they are constructed prioritizing one of its characteristics. At the same time, one of the specifics of WR is significant parasitic reactance, which must be taken into account. This feature significantly impacts the operation of power converters, therefore, all side effects have to be carefully analyzed and countermeasures have to be implemented. In order to eliminate gap in this area, the authors provide a detailed insight into the design of various circuits with WRs in power converters and formalize the design process, highlighting 11 checkpoints. The authors share their 20-years experience in this field and illustrate 5 the most popular mistakes with oscillograms, which simplifies the misstep localization. It saves at least 1 iteration of prototyping and saves significant resources. This paper is mainly addressed to young researchers, however it could also be useful for experienced engineers without solid background in design with WRs.

This paper is concerned with the design and implementation of a power controller for variable-speed permanent-magnet synchronous generators. In this system, ac-to-dc and dc-to-ac power converters are designed to convert single-phase, three-wire, variable-voltage and variable-frequency power generated by synchronous generator to that with constant-voltage and constant-frequency. In ac-to-dc power converter, the half-controlled, three-phase rectifier is built to implement the sequential-switching of switches in power converter; therefore, no rotor-position detector is needed for power converter connected with generators. The dc-to-ac power converter controlled by differential- and common- voltage modes is designed for a single-phase, three-wire inverter to yield balanced output voltage under unbalanced loads. A low-cost, 32-bit digital signal processor (DSP, TMS320F2808) is used to implement the combined drive system of generator with 220W capacity. Experiments are given to justify the analysis.

Power electronics is a branch of electrical and electronic engineering concerned with the analysis, design, manufacture and application of switching power converters. Power converters are devices interposed between sources of electrical energy and loads which usually convert that energy to some other form, where efficiency has always been a cardinal consideration in their design and application. The energy conversion function can be implemented in four basic forms: AC/AC; AC/DC; DC/AC; and DC/DC. The most general case is polyphase AC to polyphase AC. Each conversion function corresponds to the appropriate power converter; one can deduce that if a converter topology is postulated to implement the most general function, a polyphase AC to polyphase AC, then power converter topologies capable of implementing all other functions can be derived therefrom. A topology postulated to fulfill the most general function is called the general switching matrix; all other power converter topologies can be derived from it by applying the appropriate functional restriction leading to topological simplifications.

Early diagnosis of Alzheimer's and epilepsy requires monitoring a subject's development of symptoms through electroencephalography (EEG) signals over long periods. Wearable devices enable convenient monitoring of biosignals, unlike complex and costly hospital equipment. The key to achieving a fit and forgettable wearable device is to increase its operating cycle and decrease its size and weight. Instead of batteries, which limit the life cycle of electronic devices and set their form factor, body heat and environmental light can power wearable devices through energy-scavenging technologies. The harvester transducers should be tailored according to on the application and the sensor placement. This leaves a wide variety of transducers with an extensive range of impedances and voltages. To realize an autonomous wearable device, the power converter energy harvester, has to be very efficient and maintain its efficiency despite potential transducer replacement or variations in environmental conditions. This thesis presents a detailed design of an efficient integrated power converter for use in an autonomous wearable device. The design is based on the examination of both power losses and power transfer in the power converter. The efficiency bound of the converter is derived from the specifications of its transducer. The tuning ranges for the reconfigurable parameters are extracted to keep the converter efficient with variations in the transducer specifications. With the efficient design and the manual tuning of the reconfigurable parameters, the converter can work optimally with different types of transducers, and keeps its efficiency in the conversion of low voltages from the harvesters. Measurements of the designed converter demonstrate an efficiency of higher than 50% and 70% with two different transducers having an open-circuit voltage as low as 20 mV and 100 mV, respectively. The power converter should be able to reconfigure itself without manual tunings to keep its efficiency despite changes in the harvesters' specifications. The second portion of this dissertation addresses this issue with a proposed design methodology to implement a control section. The control section adjusts the converter's reconfigurable parameters by examining the power transfer and loss and through concurrent closed loops. The concurrent loops working together raise a serious concern regarding stability. The system is designed and analyzed in the time domain with the state-space averaging (SSA) model to address the stability issue. The ultra-low-power control section obtained from the SSA model estimates the power and loss with a reasonable accuracy, and adjusts the timings in a stable manner. The entire control section consumes only 30 nW dynamic power at 10 kHz. The control section tunes the converter's speed or its working frequency depending on the available power. The frequency clocks the entire architecture, which is designed asynchronously; therefore, the power consumption of the system depends on the power available from the transducer. The system is implemented using 0.18 µm CMOS technology. For an input as low as 7 mV, the converter is not only functional but also has an efficiency of more than 40%. The efficiency can reach 70% with an input voltage of 50 mV. The system operates in a range of just a few of millivolts to half a volt with ample efficiencies. It can work at an optimal point with different transducers and environmental conditions.

The feasibility of using the piezoelectric material for power transformation has been investigated for low profile DC/DC power converter design. This paper presents a systematic way to design a DC/DC power converter with a piezoelectric transformer (PT). The electrical equivalent circuit for the PT is developed. This model explains why the loss of the PT strongly depends on load and switching frequency. The two-port power flow method is employed to calculate the maximum efficiency of the PT. A complete PT converter, composed of amplifier, the PT and its matching networks, is built. Both experimental and simulated results of PT converter demonstrated that the above study is truly useful for designing the PT converters. >

In the fast-evolving landscape of artificial intelligence (AI) technology, significant strides have been taken to streamline and automate the design of power converters. However, prevalent limitations in existing AI-aided design approaches underscore the need for innovative solutions. Firstly, a lack of robustness to operational diversity hampers adaptability, requiring a complete AI model building from scratch when conditions, modulation strategies, or performance metrics for evaluation change. Secondly, the challenging trade-off between dataset size and design accuracy prolongs data acquisition through hardware experiments. Thirdly, the industry faces reluctance to adopt pure data-driven approaches due to their inherent lack of fundamental and explainable circuit insights. Addressing these challenges, this paper introduces a one-stop optimization methodology, the STAR methodology, tailored for designing modulation parameters for a three-level neutral-point-clamped converter. Leveraging a physics-in-architecture recurrent neural network (PA-RNN), STAR emerges as a robust solution, demonstrating resilience across diverse operating scenarios, accommodating multiple modulation strategies, and evaluating various performance metrics, including current stress, zero voltage switching, zero current switching, and more. The paper provides diverse design cases as user-friendly guidance and validates the methodology’s effectiveness through rigorous hardware experiments. This pioneering approach not only overcomes existing limitations but also paves the way for a more streamlined and adaptable future in power converter design.

Chapter 14 - Power converter solutions and controls for green energy

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