## 1 Introduction
In the literature there are three main techniques of AC/DC conversion [25]: direct rectification of AC signals into DC, AC rectification plus the DC/DC conversion and direct AC-DC conversion. The first alternative only rectifies the input signal, thus providing a low signal level due to losses in the rectifier. In the second one, the signal is rectified into DC first and it is transformed later into the desired DC level with a DC/DC converter, usually a boost converter that steps up the voltage: if compared with other alternatives, the number of steps required reduces its efficiency. For example, [26] proposes a full-bridge AC/DC rectifier with a DC/DC buck-boost converter. In the first stage, the rectifier has 34% efficiency. The buck-boost converter efficiency of the second stage has power losses between 18% and 46%. Thus, the two-stage system efficiency is reduced to a 54.12% in the best case, basically due to the rectifier losses. Another example of two stage power conversion is shown in [27]. This research uses a full-bridge rectifier and a Synchronous Electrical Charge Extraction (SECE) topology with shared inductor. In this case, three piezoelectric harvesters generate the AC input signal, where a full bridge rectifier is included per each harvester, and the three inputs in a single SECE converter for the DC/DC operation are combined. This solution improves the efficiency of the system; however, a multisource system is needed. Ref. [28] develops an AC/DC direct converter, but the efficiency achieved is only 45%. Their solution consists of a direct AC/DC bridgeless boost converter and a diode voltage multiplier. The voltage multiplier could be an alternative to avoid the bridge rectifier, however, the efficiency of this type of architecture is not the best due to the input voltage levels and the use of diodes in the first stage of the architecture. One of the challenges of small wind harvesters is the low power that they deliver to the load. Therefore, the aim of this research is to improve the small wind harvester design, achievinghigher power output. Thus, in the first stage of this work, the mini-wind harvester is defined as a three-phase equivalent model, and later, the system is developed, tested and verified with experimental measurements to demonstrate the improvement of the efficiency and power output and show the improvement in the state of the art of current wind harvesters. The other issue analyzed regarding the current progress of the technology is the power management architectures for the AC generators, specifically to those that generate microvolts, such as the electromagnetics. As has been remarked, the two-stage power manager introduces high losses to the system, basically, due to the diodes' losses at the rectifier stage. The objective of the present work is to develop an efficient three-phase converter translating the efficient converters from power electronics concepts to low power electronics. Thus, eliminating the rectifier stage and the two stage converters. So, this paper analyzes different architectures, suggests devices and evaluates the parameters that characterize the performance of AC/DC converter, aiming for voltage, power, efficiency, and current waveforms. The results obtained are used to identify the most suitable architecture, devices, and parameters in order to obtain the best performance and maximum efficiency of the harvester for the proposed AC/DC converter architecture.