A test rig for thermal analysis of heat sinks for power electronic applications

This paper discusses the design and manufacture of a test rig for practical thermal analysis of the temperature distribution across forced air-cooled heat sinks. High-temperature gradients across power electronic modules that have a large area of semiconductor structure can result in premature failure of the components due to mechanical stress-related fatigue. Computer modelling and simulations predict the temperature distribution across the heat sink, but physical temperature measurements are required to validate these results. In order to acquire these temperature readings, a bespoke test rig is designed and manufactured. Temperature readings obtained using this test rig are applied for comparison to those obtained by computer simulation and, hence provide validation of the computer simulation results

TFIIH is an elongation factor of RNA polymerase I

TFIIH is a multisubunit factor essential for transcription initiation and promoter escape of RNA polymerase II and for the opening of damaged DNA double strands in nucleotide excision repair (NER). In this study, we have analyzed at which step of the transcription cycle TFIIH is essential for transcription by RNA polymerase I. We demonstrate that TFIIH associates with the rDNA promoter and gene-internal sequences and leaves the rDNA promoter in a complex with RNA polymerase I after start of transcription. Moreover, mutations in the TFIIH subunits XPB and XPD found in Cockayne syndrome impair the interaction of TFIIH with the rDNA, but do not influence initiation complex formation or promoter escape of RNA polymerase I, but preclude the productivity of the enzyme by reducing transcription elongation in vivo and in vitro. Our results implicate that reduced RNA polymerase I transcription elongation and ribosomal stress could be one factor contributing to the Cockayne syndrome phenotype

Inverter Temperature Monitoring of Cordless Tool Motor Drives

Nowadays, with the recent advances in battery technologies, cordless tools are gaining more popularity and many manufacturers have enhanced their series of autonomous devices with powerful instruments like circular saws and punches. However, the development of battery-operated tools is not an easy task and many challenging problems must be solved. The most significant of these are limited working time without recharging and controllability of the motor drives. As a result, tool manufacturers are substituting conventional universal motor drives with permanent magnet synchronous motor drives, which require more complicated electronics, but can provide the desired characteristics. In order to guarantee normal operation and satisfy safety standards, devices have to properly handle any possible hazardous situations. One of these situations is overheating of inverter switches, thus, the temperature of each transistor has to be monitored. This task is typically implemented using negative temperature coefficient (NTC) resistors, whereby voltage is sensed by analog to digital converter of microcontroller. This article proposes a software algorithm for temperature estimation and monitoring of each inverter switch, which allows excludes NTCs, decreasing overall costs and saving space on the printed circuit board. Proper operation of the developed technology is proven by the experimental results and safety certification according to UL60730

Instant Closing of Permanent Magnet Synchronous Motor Control Systems at Open-Loop Start

Nowadays, position sensorless permanent magnet synchronous motor drives are gaining popularity quite rapidly, and have become almost standard in many applications such as compressors, high speed pumps, etc. All of these drives involve estimators to calculate the speed and the position of the rotor, which are necessary for proper operation of vector control. While these estimators, with the exception of injection-based ones, work well in the middle and high-speed ranges, they cannot operate at low speeds. In order to overcome this problem, sensorless control systems include different starting techniques, with the most popular being open-loop starting. In this approach, the motor is accelerated in open-loop mode until it reaches the speed where estimator operates stably, then the control system is closed. However, the weakest point of this method is the technology of closing the system, which typically creates transients and can even be the cause of loss of stability. This paper proposes a method for instant and seamless transition from open-loop to closed loop which works perfectly under different load conditions. Other starting techniques are considered and compared with the proposed method

Design of Constraints for Seeking Maximum Torque per Ampere Techniques in an Interior Permanent Magnet Synchronous Motor Control

The efficient control of permanent magnet synchronous motors (PMSM) requires the development of a technique for loss optimization. The best approach is the implementation of power loss minimization algorithms, which are hard to model and design. Therefore, the developers typically involve maximum torque per ampere (MTPA) control, which optimizes Joule loss only. The conventional MTPA control requires knowledge of motor parameters and can only properly operate when these parameters are constant. However, motor parameters vary depending on operating conditions; thus, conventional techniques cannot be used. Furthermore, many industrial drives are designed for self-commissioning, and they do not have prior information on motor parameters. In order to solve this problem, various MTPA-seeking techniques, which track the minimum of motor current, have been developed. The dynamic performance between these seeking algorithms and maximum deviation from the true MTPA trajectory are defined by the constraints in most cases, in which proper design improves the dynamic behavior of MTPA-seeking algorithms. This paper considers a PMSM, which was designed to operate in the saturation area and whose MTPA trajectory significantly deviates from the same curve constructed for the initial unsaturated parameters. This paper considers existing approaches, explains their pros and cons, and demonstrates that these methods do not utilize full potential of the motor. A new constraint design was proposed and explained step by step. The experiment verifies the proposed technique and demonstrates improvements in efficiency and dynamic behavior of the seeking algorithm

Offline Measurement of Stator Resistance and Inverter Voltage Drop Using Least Squares

Modern industrial and commercial electrical drives are typically designed to control motors of different types, operating under scalar, field-oriented or direct torque control. These drives execute various algorithm such as sensorless control, temperature monitoring, etc., which require the knowledge of motor drive parameters. In order to do this, the inverters allow data to be input manually or execute self-commissioning routines before running the motor. The parameters necessary for proper operation include motor phase resistance and inverter voltage drop, which are especially important in low-speed range. This paper presents an offline technique for estimation of mentioned parameters, which can be obtained with enough precision for the overwhelming majority of applications. The proposed algorithm consequently injects DC-current of several levels into the stator of a motor, measuring the corresponding voltages. Each pair of current and voltage is a point in the voltage current characteristic of motor drive, thus set of these points maybe approximated with a first order polynomial using least squares method. The parameters of polynomial are desired inverter voltage drop and phase resistance. The experimental Section analyzes estimation errors and their dependence on the number of injected levels, their values and filtering capability of measuring algorithm. After that, the authors give suggestions on algorithm parameters selection, depending on the demanded precision. Finally, the authors demonstrate a mass-producing dishwasher motor drive, which adopted this technique

Oforty

17 p. 36 cm

Pʹesy, piano, op. 13

13 p. 36 cm. 1. Legenda.--2. Ofort.--3. Valʹs

Fast Square Root Calculation without Division for High Performance Control Systems of Power Electronics

The calculation of square roots is a frequently used operation in control systems of power electronics for different applications: motor drives, power converters, etc. At the same time, the execution of this procedure significantly loads microcontrollers and uses its power, which can be utilized for performing other important tasks. Therefore, it restricts the size of code, which can be processed by the microcontroller and compels developers to limit the number of functions, or to decrease execution frequency of a program. Thus, the calculation of square roots is a bottle-neck in implementation of high-performance control systems, thus effective optimization of this task is extremely important in modern and efficient devices. In respect that many applications do not need precise calculation of square roots, the optimization of execution time can be achieved by decreasing of precision of the result. The proposed technique is based on the approximation of parabola with hyperbola, which allows you to rapidly find the approximate value of a square root. Taking into account that many digital signal processors (DSP) are not equipped with an effective divider, the developed algorithm does not use divisions, so it can be executed faster. The payback for this optimization is approximation error with a maximum of 0.5%, however, it is acceptable for the overwhelming majority of control systems