**1. Introduction**

Modern society needs much more electric power than in the past [1]. Therefore, the power generation sector is focused on power generation and transmission [2]. As a result, the instability of high-power direct current (DC) transmission technology was emphasized [3].

High voltage direct current (HVDC) transmission systems can be divided into voltage source converter (VSC) and current source converter (CSC) HVDC systems according to the switching element of the converter [4]. VSC HVDCs using insulated gate bipolar transistor (IGBT) have a small installation area and does not require reactive power compensation facilities [5]. It can also be used in a variety of ways because it has free bidirectional transmission and does not require an alternating current (AC) voltage source [6].

If a problem occurs in the transmission line of the VSC HVDC, a fault current is generated by the fast waveform [7]. This can cause the entire grid of multi-terminal HVDC to be blocked or severely adversely affect the power elements connected to the transmission line [8,9]. Therefore, DC circuit breaker technology that can safely manage fault current has been proposed [10].

DC circuit breaker technology can be divided several ways, of which the zero-crossing breaking method safely manages fault current by generating zero current in the main transmission line and turning off the switch [11,12]. The performance of a DC circuit breaker is an indicator of the breaking time of the main transmission line and the amount of leakage current to the outside [13–15]. Therefore, it is very important to manage electric current on the transmission line elements during high-power transmission [16].

DC circuit breakers (DCCBs) are generally classified by switch type into mechanical DCCB, semiconductor DCCB, and hybrid DCCB [17]. Hybrid DCCB is considered the most suitable type of DC circuit breakers for HVDC because it solves the problem of slow operation speed, the disadvantage of mechanical DCCB, and power loss, the disadvantage of semiconductor DCCB [18]. In general, hybrid DCCB places a mechanical switch on the main transmission line through steady-state current, so the current does not pass through the semiconductor switch in the on-state [19].

The breaking direction of the DC circuit breaker can be either unidirectional or bidirectional [20]. In a bidirectional DCCB, the breaker can operate normally regardless of the location of the main transmission line, which facilitates mass production and reduces manufacturing costs [10]. In this paper, we simulated a hybrid bidirectional HVDC DCCB using a zero-crossing method assuming VSC-based HVDC transmission.

Section 2 describes the mechanism of current flow through the circuit operation process and how it is used as a bidirectional DCCB. Section 3 describes the simulation results and analysis. Initially, detailed simulation conditions are specified, and the reverse charging process, blocking inductor and ground inductor are analyzed in order from Sections 3.1–3.3. In Section 3.4 we will analyze the use of switching elements and energy dissipation to increase the reliability of the DCCB and conclude in Section 4.
