| With the increasingly prominent problems such as energy shortage and environmental pollution With the increasingly prominent problems of energy shortage and environmental pollution,a single centralized power supply method based on fossil energy can no longer meet the demand for larger capacity,cleaner and more power supply forms for the development of the national economy.Energy interconnection,multi-port,multi-form,multi-flow power supply energy routers have become the key core equipment for building the future energy Internet and meeting future power supply needs.It connects different ports to the common DC bus through a large number of AC/DC and DC/DC converters,so as to realize the energy exchange between multiple sources and multiple loads.Therefore,the premise of the safe and reliable operation of the system is to maintain the stability of the DC bus voltage of the energy router.According to the mechanism and frequency characteristics of DC bus voltage fluctuation,the fluctuation can be divided into disturbance type(caused by switching of various power sources or loads,etc.),oscillation type(caused by unbalance of power grid or load,harmonics,etc.)two categories.This paper mainly studies oscillation-type fluctuations(of which the 5th and 7th are the most common),and intends to carry out research on the low-frequency fluctuation mechanism and suppression method of the DC bus voltage of the energy router.The main research contents are as follows:First,an energy router topology based on DC bus is proposed.Compared with energy routers of other structures,there are no problems such as frequency stability,which avoids problems such as phase synchronization caused by the AC bus.The paper analyzes the structural characteristics,functions and working principles of the external ports of the energy router in detail.According to whether the energy router is connected to the grid,its working mode is divided into grid-connected mode and off-grid mode,and the grid-connected mode is subdivided into three modes according to the power flow.Through the mathematical modeling of the AC port and DC port converters of the energy router in different working modes,the low frequency fluctuation mechanism of the DC bus voltage of the energy router is analyzed.Then,based on the low-frequency fluctuation mechanism of the DC bus voltage of the energy router,corresponding suppression methods are proposed: passive decoupling and active decoupling of the energy router.The passive decoupling circuit is given and its working principle is analyzed,and the expression of the low-frequency harmonic voltage of the DC bus is theoretically deduced when the AC port of the energy router contains a series of low-frequency harmonic currents.The relevant simulations and experiments are carried out to verify the correctness of the theoretical analysis on the low-frequency harmonic voltage of the DC bus of the energy router.At the same time,the DC bus capacitance of the energy router is theoretically deduced in the case of passive decoupling.In order to reduce the DC bus capacitance of the energy router and improve the system reliability,this paper proposes a DC bus harmonic based on a bidirectional buck-boost additional circuit.Power active decoupling method to absorb any combination of low frequency harmonics on the DC bus of the energy router.At the same time,this paper proposes a new decoupling control scheme based on low-frequency harmonic current feedforward,which achieves the purpose of stabilizing the DC bus voltage of the energy router with fewer capacitors.Finally,the bidirectional buck-boost active decoupling circuit is applied to the energy router.Through a series of the related comparative experiments,it is verified that the bidirectional buck-boost active decoupling circuit is used to absorb the DC bus of the energy router.The applicability of low-frequency harmonics of any order combination,and the superiority of the active decoupling control strategy proposed in this paper. |
