Busbar Technology Research Articles

Busbar technology development for the HL-LHC inner triplet magnets

The busbars for the HL-LHC magnets are made of Nb-Ti/Cu conductor, the insulation system, and the auxiliary equipment to align the busbars with respect to the magnet coldmasses. This paper presents design options concerning the integration of the busbars inside the coldmass with a fixed point, and a reinforced insulation system for the flexible busbar part using thin PEEK tubes. Prototype splices for interconnecting Nb3Sn and Nb-Ti Rutherford cables, and round and flat 18 kA Nb-Ti cable have been produced and first test results are presented.

Thermal Analysis of Busbars from a High Current Power Supply System

Copper busbar technology is widely used with the aim to achieve electrical connections with power distribution systems because of their flexibility and compactness. The thermal analysis takes into account the heat conduction and convection of a copper busbar system used to supply a test bench with high currents in order to check the electro-thermal behaviour of power circuit breakers during overload and short circuit conditions. This paper proposes a mathematical model for busbars used within a high current power supply. The obtained thermal model can be used to analyse the thermal behaviour of busbars in steady-state conditions at different values of the electric current, cross-section and length of the busbar. Also, the mathematical model allows to calculate the temperature distribution along the busbar at different values of the contact resistances at junction points with other conductors. There is a good correlation between calculated, simulated and experimental results.

Qualification of conductive adhesives for photovoltaic application - accelerated ageing tests

In order to achieve a fast and reliable qualification of promising conductive adhesives for solar cells, different accelerated ageing test sequences, accompanied with analyses on material level are conducted. Damp-heat followed by damp heat at a current range of 8 A; humidity freeze and thermal cycling. The testing procedure in the herein presented work is adapted to identify advantages and also weaknesses of the materials in combination with the entire design. The conductive adhesives replace the lead-based soldering thereby allowing a lower processing temperature. Another potential reduction of material costs is the use of double redundant fingers instead of busbars. In this way, a considerably smaller amount of silver is needed. The interconnectors are glued between theses double redundant fingers with the conductive adhesive. Another advantage of the gluing is the possibility of using groove structured interconnectors that allow an increase in power of the solar module by reflecting light back to the solar cell.As major degradation indicator the performance of the modules containing conductive adhesives, redundant fingers and groove structured interconnectors is measured before and after the exposition of the solar module to different accelerated ageing tests and compared to the reference solar module with flat interconnectors soldered on busbars. After the accelerating ageing test damp heat (DH), there was already a clear difference in viability of the conductive adhesives. For two conductive adhesives, module power losses were comparable to the reference, for a third one power losses amounted to 14 %. The loss in power is caused by an increase in serial resistance. Analyses of the adhesives indicate a relation between the degradation in damp-heat and the adsorption of humidity of the material. Different subsequent aging tests (after DH) showed the feasibility of this innovative technology, but also unveiled weaknesses compared to a traditional soldered busbar technology. Two of the three conductive adhesives have fulfilled the IEC 61215 criteria in terms of power loss after damp heat, humidity freeze and thermal cycling.

Solder joint stability study of wire-based interconnection compared to ribbon interconnection

For the comparative study with focus on mechanical long-term stability, we perform a temperature cycle (TC) test-to-failure for 1250 cycles according to IEC 61215 with laminated solar cell strings. The strings were produced with Multi Busbar (MBB) solar cells interconnected by wires and with solar cells with 3 busbars (3BB) interconnected by ribbons. One module sample comprises two electrically isolated 3-cell strings, one for each technology. The 3BB string displays a power loss of more than 5 % after 850 cycles, while the MBB string only exceeds 5% loss after 1250 cycles. After TC 1250 the 3BB string shows a degradation of -8.2 % in FF and -8.0 % in power, while the MBB string shows a degradation of -6.2 % in FF and of -5.3 % in power.In the second comprehensive comparative study we use for each interconnection technology 15 cells for isothermal storage (up to 130 °C, 42.8h) and 10 modules for TC (up to 400 cycles). Each reliability analysis includes IV and EL characterization as well as adhesion force measurements and microsection analysis. After TC 400 the MBB interconnection shows less than 1 % degradation in efficiency compared to 4-5 % degradation for 3BB ribbon interconnection in a common module setup. The cells and modules show that most of the electrical contacts are still intact with respect to the EL image after 42.8 h isothermal storage and TC 400, although the average peel forces degraded from about 2 N/mm to less than 0.5 N/mm.Both studies indicate a superior mechanical long-term stability for Multi Busbar technology compared to ribbon interconnection.

Multi-busbar Solar Cells and Modules: High Efficiencies and Low Silver Consumption

Ideally, future photovoltaic modules show higher power output without increasing costs during cell production or module interconnection. Today significant losses occur during stringing the cells in a module by using standard 3- busbar technology. In this paper an elegant approach for a front side design is discussed by using more busbars than the widely used 3-busbar design for the solar cell front electrode. Simulations demonstrated that the multi-busbar design allows higher cell and module efficiencies compared to a state of the art 3-busbar cell design, and in the same time reduces the amount of silver needed for the front electrode. “A conventional full area Al BSF and standard screen printing for the front contact was used for the 6” Cz-Si multi-busbar solar cells and efficiencies of up to 19.5% have been reached. The solar cells were analyzed on cell and module level and a reduction in Ag consumption for the front electrode of >50%abs could be achieved using the multi-busbar cell design. An additional silver reduction was achieved by replacing the rear side Ag/Al pads with tin pads for the soldering process. These changes in solar cell design reduce significantly the metallization costs and in the same time increase the efficiency.

Busbar heating during transient conditions

Busbar technology is more and more used to realize connections within power supply systems as an answer to the problem of compactness. The integrated problem on heat conduction and radiation-convective heat exchange describes the temperature regime in current conductors and busbars of power electrical equipments such as circuit breakers or high breaking capacity fuses. Beside steady-state conditions, the transient thermal regime of busbar has an important influence upon whole power supply system from the thermal behaviour point of view. Hence, in this paper, a mathematical model is proposed for the transient conditions of the busbar heating. The busbar lengthwise heating with two different electrical contacts at its end terminals has been obtained. The influence of current on the heating distribution has been investigated. To validate the thermal model some experimental tests have been done. It observes a good correlation with the calculations.

Minimization of wiring inductance in high power IGBT inverter

The wiring inductance is one of main causes limiting the use of the inverter in hard commutation mode, particularly when voltage, current and switching frequency are increased. The busbar technology is the means that allows one to reach low wiring inductance between DC source and power switches in spite of relatively long connections. This paper deals with studies of busbar structure applied to the high power inverters in order to improve their performances. Two structures of wiring are tested; the traditional one and busbar technology. Experimental and simulation results show that this last technique permits to obtain very low wiring inductance so that no snubber circuits are needed.

Modeling of low inductive busbar connections

The high power levels required by many power electronic applications well as the very low switching times encountered in new semiconductor devices have created a need for low wiring inductances. The busbar technology is an effective industrial way to reduce the interconnection inductance between (for instance) the feeding source and the converter. It consists of a stacking of several copper sheets, each separated from the other by a dielectric. The connections between these sheets and the different devices are made with screws. The authors present a way of modeling a busbar. Using a simulation tool, InCa, dedicated to inductance and resistance calculations, it is possible to obtain the L, R equivalent circuit of a busbar. Moreover, it allows the determination of the current density in any cross section of any busbar sheet. In order to validate the modeling, a chopper structure using this kind of connection has been realized and measurements have been made.