## 1 Introduction  
Microwave signals are amplified using space traveling wave tube amplifiers [1] (STWTA) as an important component of satellite systems. Typically, a TWTA comprises a traveling wave tube [2] (TWT) and an electronic power conditioner [3] (EPC). An interaction between a beam wave and an electromagnetic wave contributes to the amplification of microwave power when a TWT is utilized. Additionally, the EPC converts the satellite bus voltage [4] (typically ranging from 30 to 100 V DC) to the required electrode voltage (ranging from a few kV to a few hundred kV DC) through high-frequency power converters. Since the primary power conversion is the most significant aspect of the EPC, it must be considered when designing the circuit [5]. Presently, the main power conversion is categorized into two major types: single-stage power conversion and two-stage power conversion. The greatest advantage of single-stage conversion is its simplicity, and it is used in applications such as phase-shifted full-bridges [6, 7, 8], asymmetric half-bridges [9, 10, 11], three-transistor push-pulls [12], and so on. However, all of these single-stage topologies suffer from the same issue: stringent input voltage and load quality requirements. The application of a single-stage power conversion cannot satisfy the requirements of satellites. Consequently, two-stage power converters are increasingly utilized in the EPC. There are two types of topologies that have become dominant applications: boost and full-bridge [13], and buck and phase-shifted full-bridge [14]. In boost and full-bridge topologies, the control loop response time is very slow, and the surge current is high [15]. Furthermore, the complexity of the control systems of buck and phase-shifted full-bridge converters negatively impacts their reliability, and this topology cannot work in ZVS or ZCS when the load is not heavy [16]. Two other two-stage cascade transformations, flyback and asymmetrical half-bridge, and forward and push-pull, are rarely used due to their poor efficiency. In these two-stage topologies, forward and push-pull have the highest efficiency, which is 91.47% [17]. The statistics indicate that STWTAs consume 70% to 90% of DC consumption. Additionally, they contribute to 35% of the total weight in radar systems [18]. Therefore, power conversion topology must be continuously enhanced to meet the requirements of higher efficiency [19] and the miniaturization of on-board equipment. Buck and push-pull, and boost and push-pull are two different topologies, as shown in Figure 1. Based on the system requirement, if EPC has some malfunctions or failures, it cannot affect other modules in the satellite. If in the fault mode, the power switch (the red one) in Figure 1a can be turned off and thus can prevent affecting the bus voltage in the satellite. However, in Figure 1b, the power switch (the red one), when turned off, cannot prevent affecting the bus voltage, and it must include an additional protective circuit. Moreover, if ZVS and ZCS need to be realized in a boost and push-pull topology, extra inductance and capacitance (the blue ones) need to be added to the circuit, which increases the complexity of the circuit. Motivated by the above analysis and practical application, this paper presents a two-stage converter topology with a high efficiency: buck and push-pull, where the push-pull converter is implemented in ZVS and ZCS. The buck regulator is used to pre-regulate the voltage in hard switching. In addition, the high-voltage output is achieved through a soft-switching push-pull converter. The block diagram of this two-stage converter is shown in Figure 2. Closed-loop feedback is applied in the buck regulator to provide stable voltage for the push-pull circuit, and the push-pull circuit works in an open-loop state with a high output voltage after a doubler rectifier circuit.