Dynamic Voltage-Balancing Method of Series Diode Rectifier in Inverter-Type AGPS

Abstract

In negative ion-based neutral beam injector (N-NBI) system, acceleration grid power supply (AGPS) provides ultrahigh dc voltage for accelerator. Because the power supply often occurs in the ignition fault similar to the load short circuit, it will produce complex and violent electromagnetic transient process. The diode rectifier is the last stage of it and the diode rectifier is directly connected to the load of the AGPS. The working voltage of the rectifier reaches hundreds of kV, and a large number of diodes are used in the device in series. Therefore, it is necessary to fully consider the influence of distributed capacitance on voltage balancing and improve the static and dynamic voltage-balancing reliability of diodes. However, discussions about solutions for the dynamic voltage imbalance in the reverse recovery process caused by parasitic capacitance are not sufficient. This article presents a voltage-balancing method in the form of parameter relationships between non-isoparametric resistance-capacitance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> ) snubber circuits. Under the assumption of uniform voltage-sharing, the equivalent parallel circuit of each diode is obtained through constructing isoelectric points, accordingly, the parameter relationships are deduced. In this article, both the distributed capacitance to ground and the distributed capacitance to high voltage are considered in the derivation process; the derived non-equal parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> voltage-balancing method includes not only the buffer capacitance parameter relationship, but also the damping resistance parameter relationship and upper limit, which innovatively explores the important influence of damping resistance on the voltage-balancing effect. Dual-pulse tests on series-connected diodes prototype are carried out; experimental results show that voltage balance ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> of the prototype is only 0.80 with the traditional isoparametric <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> circuit in parallel, while <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> is up to 0.99 with the non-isoparametric <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> circuit designed through the proposed method. The results will be valuable for improving the reliability and device utilization rate of series-connected diodes rectifiers in inverter-type AGPS.