## 1 Introduction
For example, the battery pack is regularly connected to the DC bus, while a DC/DC converter manages the supercapacitor [24; 25]. Finally, in a fully active HESS, each source is managed by a dedicated converter. Some reviews on topologies for HESS have been published in the last few years. According to the analysis reported in [26], multi-input, multi-port, coupled-inductor, switched-capacitor, and z-source/quasi-z-source converter are suitable for a HESS formed by a battery and a supercapacitor. Those topologies provide bidirectional power flow in EVs, DC MGs, and renewable energy applications. Ref. [16] reports a broad analysis of passive, semi-active, and fully active topologies for HESSs formed by a battery and a supercapacitor. That article highlights the strengths, weaknesses, and opportunities associated with each HESS setup. Ref. [27] also reviews the state of the art on HESS topologies, including reconfigurable topologies at the cell and module levels. Similarly, four semi-active HESSs are discussed in Ref. [15], which are based on supercapacitors and batteries. Many works on HESSs with semi-active and fully active configurations have been recently published. In Refs. [28; 29], a PV system with a fully active HESS, formed by a battery, a supercapacitor (SC), and a bidirectional buck-boost converter, is tested with several algorithms, namely classical PI, an ANN, and Model Predictive Control (MPC). In that work, the mathematical model of the controllers is presented, but the implementation of the algorithms is not discussed. In Ref. [30], the combined control between an optimization algorithm and a neural network is applied to a bidirectional DC-DC converter of an EV; the authors state that algorithms enhanced performance and reduced computation time compared with other methods; however, the implementation is not discussed. In Ref. [31], a fully active HESS formed by a PV array, a battery, and a supercapacitor is presented. The control algorithms for each converter are classical PI structures, and the references for the controllers of both the battery and the supercapacitor converters are based on a power management strategy, in which the missing power on the load is first compensated with the battery and later with the supercapacitor. A structure similar to that reported in [31] is proposed in [25], but there is a fuel cell instead of a PV array. In that work, a fuzzy logic algorithm of 36 rules controls an energy management unit (EMU), which distributes the power among sources and sets the references for the centralized algorithm that controls all HESS converters. Table 1 summarizes the characteristics of some works published in recent years with HESSs similar to the solution proposed in this manuscript. The review shows that HESSs are based on SCs and batteries, fully active topologies, and buck-boost converters. Control algorithms are diverse, but the classical PI structure is the most common solution. However, some works adopt control schemes based on intelligent algorithms (ANN, Recalling-Enhanced Recurrent Neural Network--RERNN), optimization algorithms (Sand Cat Swarm Optimization--SCSO, MPC), and non-linear algorithms (Supertwisting Sliding Mode Controller--SSMC). Nevertheless, none of the analyzed references implement the HESS with a Zeta converter managing the storage devices; only one reference controls the system with sliding-mode control, but it does not protect the battery from fast current transients. This manuscript introduces a unique HESS system with a semi-active topology. In this system, the SC is managed by a bidirectional converter, and the battery is directly connected to the DC bus (see Figure 1). The main feature of this setup is the use of a bidirectional Zeta converter and a sliding-mode controller (SMC). The Zeta converter has two key features; it works with any conversion relations and it has a continuous output current. In this way, the Zeta converter can connect any SC with any battery, and it prevents currents with high derivatives in the battery, decreasing its degradation.