Development of 50-Kv 100-Kw Three-Phase Resonant Converter for 95-Ghz Gyrotron Sung-Roc Jang, Jung-Ho Seo, and Hong-Je Ryoo

6674 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 63, NO. 11, NOVEMBER 2016 Development of 50-kV 100-kW Three-Phase Resonant Converter for 95-GHz Gyrotron Sung-Roc Jang, Jung-Ho Seo, and Hong-Je Ryoo Abstract—This paper describes the development of a and high power density, the operation of high-power vacuum 50-kV 100-kW cathode power supply (CPS) for the operation devices requires low output voltage ripple with low arc energy. of a 30-kW 95-GHz gyrotron. For stable operation of the gy- This is because the output voltage ripple and the arc energy rotron, the requirements of CPS include low output voltage ripple and low arc energy less than 1% and 10 J, respec- are closely related to the stability of the output power of the tively. Depending on required specifications, a three-phase electron beam and the safety of the device, respectively. It is series-parallel resonant converter (SPRC) is proposed for clear that a higher value of the output filter capacitor allows designing CPS. In addition to high-efficiency performance a lower value of the output voltage ripple. On the other hand, of SPRC, three-phase operation provides the reduction of the energy stored in the power supply output, which may in- the output voltage ripple through a minimized output filter component that is closely related to the arc energy. For al- stantaneously be discharged to vacuum devices because of the lowing symmetrical resonant current from three-phase res- arc, is proportional to the value of the output filter capacitor. In onant inverter, the high-voltage transformers are configured order to achieve low output voltage ripple with low arc energy, as star connection with floated neutral node. This facilitates a pulse step modulator (PSM) has been proposed to operate a balanced voltage on each secondary winding. In addition, gyrotron [1], [2]. Compared with other proposed designs, based distinctive design of the high-voltage rectifier is introduced, taking into consideration the effective series stacking of largely on alternating current (ac) voltage regulation or a star- diodes by means of the parallel resonant capacitor. In partic- point controller, the PSM-based high-voltage power supply is ular, the implementation of the high-voltage part including expected to be highly reliable owing to low stored energy. Other transformer and rectifier is presented in detail. For provid- approaches that use additional solid-state switches to protect the ing high power density and high reliability, effective meth- load against the arc have been proposed [7]. A crowbar circuit ods for winding the high-voltage transformer and stacking rectifier diodes are discussed. Finally, the developed CPS connected in parallel with the load helps us to limit the energy achieves 95.5% of maximum efficiency, 0.92 of maximum from the power supply to the load, and a crowbar switch using power factor, 500 W/liter of power density, 0.6% of output a solid-state device exhibits short response time such that the voltage ripple, with 8.3-J arc energy. load can be effectively protected. Another method used to limit Index Terms—DC–DC power converters, gyrotrons, the arc energy by means of a solid-state switch is to insert a fast pulsed power supplies. opening switch between the power supply output and the load. Further research on the reduction of the ripple as well as the arc I. INTRODUCTION energy has been presented for electrostatic precipitator appli- ESEARCH on high-power vacuum devices, such as mag- cation [21]. Presented inductive adder topology which consists R netron, klystron, and gyrotron, has grown in recent times of high-voltage converter modules in series, and uses the phase owing to the development of various industrial applications in- shifting control technique between each module shows many cluding medical, military, environmental, and aerospace. The advantages including decrease of the output ripple as well as the recent proliferation of applications requiring high voltage and stored energy. power has led to a greater focus on the development of the high- Based on the basic concept of the inductive adder [21] and voltage power supplies [1]–[22]. In addition to the general re- the operating principle of the series-parallel resonant converter quirements of high-voltage power supplies, efficient operation, (SPRC) [22], the design and the implementation of a 50-kV 100-kW CPS for a 30-kW 95-GHz gyrotron are described in this Manuscript received January 12, 2016; revised March 14, 2016; ac- paper. A three-phase resonant converter based on half-bridge cepted May 23, 2016. Date of publication June 29, 2016; date of SPRC module is proposed for achieving desired specifications. current version October 7, 2016. This work was supported by the Korea Electrotechnology Research Institute Primary Research Program For balanced three-phase operation, the star configuration with of MSIP/NST (16-12-N0101-49). floated neutral node is suggested for three high-voltage trans- S. R. Jang is with the Electric Propulsion Research Center, Korea formers that are connected to each of three half-bridge resonant Electrotechnology Research Institute, Changwon 641-120, South Korea, and also with the University of Science and Technology, Daejeon 13557, inverters. In addition, a distinctive design of a high-voltage South Korea (e-mail: [email protected]). rectifier is introduced for minimizing component count. J.-H. Seo is with the Department of Energy and Power Conversion Generally, the parallel resonant capacitor is connected in Engineering, University of Science and Technology, Daejeon 13557, South Korea (e-mail: [email protected]). parallel with the transformer primary or secondary winding H.-J. Ryoo is with the School of Energy Systems Engineering, Chung- [22]. On the other hand, the proposed rectifier circuit for Ang University, Seoul 06974, South Korea (e-mail: [email protected]). CPS uses the capacitors which are connected in parallel with Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. rectifier diodes for balancing voltage of each diode as well Digital Object Identifier 10.1109/TIE.2016.2586021 as for implementing the parallel resonant capacitor. With 0278-0046 © 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information. JANG et al.: DEVELOPMENT OF 50-KV 100-KW THREE-PHASE RESONANT CONVERTER FOR 95-GHZ GYROTRON 6675 TABLE I SPECIFICATIONS OF CPS FOR A 30-KW95-GHZ GYROTRON Input Voltage 380 Vac ± 10% Maximum output voltage, Vo,max −50 kV Maximum output current, Io,max −2A Maximum output power, Po,max 100 kW Maximum pulse width, PWmax 3s Maximum duty cycle, D max 50% Output voltage ripple at rated voltage 0.6% Arc energy, E Arc 8.3 J Maximum Efficiency, ηmax 95.5% Maximum Power Factor, PFmax 0.92 Protections Arc (overcurrent) Overtemperature Overvoltage Fig. 1. Proposed circuit of SPRC module for CPS. range so that CPS can control the required output voltage from considerations such as high-voltage insulation and cooling −5to−50 kV. of components, the detailed implementation of the proposed The operating principle of SPRC have been already intro- circuit is discussed to improve power density with reliable duced and well known [13], [15], [19], [20], [22]. Therefore, operation. Especially for high-voltage part which is immersed this paper intends to omit the description about the operating in insulation oil, compact design and arrangement are presented principle of SPRC and deal with a detailed design of CPS. including the high-voltage transformer and rectifier. Section II presents the design of CPS based on three-phase SPRC with respect to the required specifications summarized A. Design of SPRC Module for CPS in Table I. Feasibility and performance of the proposed The proposed circuit of SPRC module is shown in Fig. 1. circuit is verified by PSpice simulation. In Section III, the Compared with the conventional circuit of SPRC, it is worth detailed implementation including a special winding method noting that the parallel resonant capacitor (Cp , dashed line) is ac- for high-voltage transformer and a compact design of rectifier tually not connected in parallel with the transformer primary or circuit is described. Finally, the performance of the developed secondary winding. For implementing the parallel resonant ca- CPS is experimentally proven from the point of view of its pacitor, the proposed circuit uses the capacitors (CD1 1 −CD1 N ) efficiency, power factor, output voltage ripple, and arc energy. that are originally installed for balancing the voltage between series stacked diodes. Thus, the capacitors which are connected in parallel with the diodes play the role of the parallel reso- II. DETAILED CIRCUIT DESIGN OF CPS nant capacitor. Because it should be discharged and charged SPRC which operates in continuous-conduction mode and for forward and reverse biasing of diode, respectively. From has above-resonance switching frequency range has the advan- the transformer secondary side, equivalent parallel capacitor tages of zero voltage (ZV) turn-on and relatively low conduction can be regarded as the parallel of two capacitors (CD1, CD2) loss compared with other resonant converter mode of opera- where CD1 is equivalent capacitor for series connection of tions. Moreover, the lossless snubber capacitor which can be CD1 1 −CD1 N (CD1 1 /N). Accordingly, the value of Cp is cal- 2 connected in parallel with the semiconductor switches reduces culated as n ×(CD1 +CD2) where n is the transformer turns turn off switching loss by decreasing the slope of the voltage ratio (n2/n1). By choosing suitable value of CD1 and CD2,ef- rise across the switches. However, it should be noted that there is fective balancing of voltage between the series stacked diodes additional consideration in choosing the value of snubber capac- as well as inserting the parallel resonant capacitor can be simul- itance for achieving ZVS.

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