Many industrial applications are recently utilizing the advantages of a common dc-bus-based multiple-drive (multidrive) system, such as low installation cost, space savings as well as improved reliability, and flexibility. One of the main drawbacks of such systems is the requirement for a bulky dc capacitor due to the presence of large dc-link current ripples from the harmonic interaction between these multidrive and pulsewidth modulation (PWM) switching. This problem not only increases the cost and volume of the dc-link capacitors but also decreases its lifetime, which must be considered in the design from the industrial aspect. This article proposes a new dc-bus capacitor design method for a multidrive system, focused on the capacitor sizing, cost reduction, and lifetime improvements. First, an analytical model to obtain the dc-link capacitor current in a multidrive system is proposed, which would aid the designers to configure the dc-capacitor current in systems having numerous multiple drives. Next, using the developed analytical model, the dc-link current harmonics are reduced through optimal interleaving of the fundamental output currents in addition to the phase shifting of the carrier waves of the parallel connected inverters. Finally, new capacitor sizing/design is proposed considering the lifetime, power loss, cost, and volume of the dc-link capacitor bank. The proposed approach reduces the volume and cost of dc-cap bank by 50%, and increases the lifetime by four years ($\sim$35 000 h), considering the worst-case scenarios. Experimental and analytical results are given for validation of the proposed method. The results could serve as a guideline for designing the dc-link capacitor in multidrive applications in a low-cost manner.

Temperature sensitive electrical parameters (TSEP) provide an indirect and noninvasive method for on-line junction temperature estimation of power semiconductor devices. It is known that the fundamental of TSEP-based methods is to calibrate the relationship between TSEP and junction temperature in advance. However, the calibration methods in the literature need to open the module, require pretesting, or record the operating data of a converter in the entire power rating range, which are inconvenient in field applications. This article proposes an on-line and noninvasive calibration method by measuring the data at three operating states that are already existed in the regular converter operation. It is achieved by measuring the accessible heatsink/case temperature and TSEP during converter regular operation. The concept, implementation, and error analysis of the proposed method are presented in this article. Experimental verification is given to prove the effectiveness, accuracy, and convenience of the proposed method.

The large amount of harmonic distortion produced by nonlinearity drives may transmit and couple between grid and multiple drives, which changes the stresses of devices as well as the DC-link filters. This paper investigates the lifetime of DC-link capacitors in multiple drives system. Firstly, by decoupling the interactions among grid-connected drives, a simplified equivalent circuit model and its analytical model to obtain the DC-link continuous current in multiple standard and slim drives is proposed, which releases the designers from configuraing the large simulation for multiple drives. Then, applying the lifetime prediction method, the lifetime of DC-link capacitors in multiple drives are investigated, in terms of types of drives, numbers of drives and grid conditions. The results show that the lifetime of the standard drives extend in the multi-drive systems and lifetime of the slim drives decrease in the multi-drive systems, which break the previous mind. Finally, based on the proposed analytical model and lifetime estimation method, the capacitor sizing from reliability aspect for multiple slim drives are given. The outcomes of the lifetime investigation could be a guideline for the design of capacitive DC-link in multi-drive system

This paper deal with the electrical performance of a newly proposed fully composite pylon in Denmark, which has a unibody composite cross-arm at 420 kV highest system voltage level. Electric field consideration along the insulations of the novel unibody cross-arm is one of the most important requirements in the design process of a non-traditional pylon. In this paper, ANSYS finite element software is used to calculate the electric field and potential distribution around and inside the fully composite pylon. Electric field criteria related to the design of composite cross-arms are reviewed and applied for interpreting the electrical performance of the unibody cross-arm at power frequency stresses. Three different designs of non-conductive conductor clamp are assumed for the attachment points between phase conductors and the unibody cross-arm. The side effects of conductor clamp are included in 2D modeling in order to determine the minimum required height for phase conductors at the top of the unibody cross-arm. Considering the side effects of phase conductors at both sides of conductor clamp, the application of steel enclosures with an appropriate diameter is introduced to be used around the phase conductors in order to reduce the electric field magnitudes in the region of the conductor clamp. Finally, the feasibility of utilizing steel enclosures for modifying electric stresses inside the conductor clamp and unibody cross-arm is investigated by a 3D finite element analysis.

In this paper, the lightning shielding performance of a newly designed 400-kV double-circuit composite tower is investigated. Based on a revised electrogeometric model (EGM) method, traditional shielding failure regions located at both sides of a traditional tower are no longer a big issue for the fully composite tower, due to its unusual 'Y' configuration. Instead, a new unprotected region exists in the tower center. The maximum lightning current that can lead to shielding failure and the shielding failure rate of the new tower are calculated. To verify results from the revised EGM method, a scale model test is conducted. Spatial shielding failure probability around the tower is calculated based on the ratio of discharge paths recorded in the test. Moreover, based on test results, the maximum shielding failure lightning currents are obtained. Analysis and results derived from the revised EGM method and scale model test have a small deviation, verifying the feasibility of these two methods in the lightning performance evaluation of the fully composite tower. Both methods confirm that the unusual negative shielding angle of -60° in the newly composite tower provides good lightning shielding performance. The feasibility of the novel composite tower is verified from the lightning protection point of view.