## 1 Introduction  
Single-phase AC-DC-AC converters with the same input/output frequencies can be found in multi-electric aircraft [1], such as power interface units, standby power supplies, uninterruptible power supplier, etc. Large DC-link energy storage capacitors are usually used to adsorb pulsating power, which is harmful to the system, but the presence of the large electrolytic capacitor will lead to larger volume, heavier weight, and higher price [2]. So, a great deal of research is devoted to reducing DC-link capacitor size and mitigating second-order power in the single-phase converter. At present, non-electrolytic capacitive methods can be divided into two categories: active methods and passive methods [3]. The main idea of the passive methods is to use passive components or passive networks instead of large electrolytic capacitors for energy storage. The simplest passive method is to replace the large electrolytic capacitor with multiple small-capacity non-electrolytic capacitors (such as film capacitors) in parallel, but its obvious disadvantages such as low withstand voltage, large volume, and high price limit its practical applications. In [4; 5; 6; 7; 8], a resonance unit is used to replace the traditional DC energy storage unit, eliminating large-capacity energy storage components, while also realizing soft-switching, and the dynamic performance of the system is also improved. However, due to the shortcomings of the resonant unit itself, the circuit will generate higher voltage and current stress, and the conduction loss will also increase. In addition, this passive method also has the disadvantages of large volume and heavy weight. The active methods mainly can be grouped into reducing or transferring the instantaneous power difference. Some control strategies are proposed in [9; 10]. The instantaneous power difference between AC and DC sides is narrowed by injecting third and fifth harmonics actively into the AC side. However, this kind of method is at the cost of reducing the power factor of the power converter, so it is only suitable for occasions where the power factor requirement is not high. Another way to directly reduce the instantaneous power difference is to allow greater pulsation of the output current, which has been studied a lot in [11; 12]. The pulsation of the output power also increases and when the instantaneous input and output power are similar, a smaller non-electrolytic capacitor can be used to balance the energy difference. This kind of method is mostly used for light-emitting diode (LED) driving, which may cause flicker, and the system efficiency is low. It is only suitable for occasions where the DC side load is not sensitive to pulsating current. The second active method that achieves the transfer of pulsating power through additional circuits is described in [13; 14; 15]. The basic idea is to transfer the instantaneous power difference to an additional non-DC-link energy storage capacitor through an external circuit to achieve DC bus power decoupling, but it adds additional hardware cost and control cost, and it also increases the system loss. A method that only changed the control algorithm without adding auxiliary circuits is proposed in [16; 17; 18]. However, this method is only designed for specific circuit, and huge calculation workload is needed to obtain its control algorithm by analyzing the switching states of each circuit. The six-switch converter adopting the idea of components multiplexing instead of the traditional single-phase back-to-back converter is used to solve the above issues in this paper. On this basis, a non-electrolytic capacitance method without changing the circuit structure or adding auxiliary circuits is proposed. This method improves the traditional modulation strategy based on the principle of minimum energy storage. While ensuring the stable operation of the converter, it not only reduces the fluctuation of the DC bus capacitor voltage in the line frequency cycle, but also improves the quality of the output waveform.