There are two types of existing direct current (DC) electric spring (DCES), of which the one realised by alternative current electric spring has low power density because of the low‐pass filter with big volume, another one is realised by DC/DC converters but too complicated. In this study, aiming at households' applications, a novel topology is proposed for DCES, using a three‐port DC/DC converter with a bi‐directional boost‐buck converter (BBC) paralleled at one port. Critical load (CL), noncritical load (NCL) and power source are located at separate port. Besides the isolation electrically, the most important advantage is that the NCL is no longer in series with DCES, which is possibly the first attempt to change the connection type of a visual NCL with an electric spring (ES) from series to normal parallel way. With the proposed DCES, CL power is regulated stable while the fluctuations are transferred to the NCL. Meanwhile, the DCES does not provide nor absorb active power at steady‐state. When the battery voltage reaches its lower or upper limits, the protection mechanism will start to ensure safe operations. The effectiveness of the proposed DCES topology and its control has been validated by simulation and experiment results.

DC electric spring (DCES) maintains the voltage stability and improves the power quality in dc microgrid with the inclusion of renewable energy sources. A parallel DCES topology has been recently proposed; it consists of a dc-dc three-port converter and an energy storage system made up of a battery paralleled with the critical load (CL) through a bidirectional buck-boost converter. In this article, an effective energy management system (EMS) is proposed for the parallel DCES topology. After illustrating the DCES operating modes, three functional states are introduced, namely normal, specific time, and emergency, where the normal state refers to the DCES operation under dc microgrid power fluctuations, whereas the specific time and emergency states refer, respectively, to the environment conditions and battery contingent situations. The EMS decides the transitions between the DCES operating modes, changes the operating status of the battery, and realizes multiple charging and discharging mechanism. This gives DCES the capabilities of guaranteeing the voltage stability of CL while keeping the state of charge of the battery within a reasonable range, which extends the lifetime of battery and ensures safe and reliable operation of the whole system. The proposed EMS has been validated by simulation and experimental results.

DC electric springs (DCESs) have been recently developed to improve the voltage stability of a DC microgrid. A lately proposed DCES topology is comprised of a DC/DC three port converter (TPC), a bi-directional buck-boost converter (BBC) and a battery, and is arranged as follows: The TPC input port is fed by a renewable energy source (RES) whilst the two TPC output ports supply a non-critical load (NCL) and a critical load (CL) separately; in turn, BBC together with the battery constitutes the DCES energy storage unit (ESU) and is connected in parallel to CL. In this paper, a set of DCESs with such a topology and with their CLs connected to a common DC bus is considered. The control of the DCESs is built up around a distributed cooperative system having two control levels, namely primary and secondary, each of them endowed with algorithms committed to specific tasks. The structure of the control levels is explicated and their parameters are designed. The control system is applied to a DCES set taken as a study-case and tested by simulation. The results of the tests show the excellent performance of the control system in both regulating the CL DC bus voltage and keeping the state-of-charge of the battery within predefined limits.

The concept of DC electric spring (DCES) has been introduced some years ago to solve the voltage stabilisation issue caused by the high penetration of intermittent renewable energy sources (RESs) into DC power systems. Recently, a featured DCES topology has been proposed, comprising an isolated three‐port DC/DC converter and an embedded energy storage system. The three ports are connected to a DC power system at the supply side, the critical load (CL) and the non‐critical load (NCL) at the user side, whilst the energy storage system is paralleled at the CL port. To improve the performance of the topology, this paper investigates the chance of making soft the switching of the DCES converters. After the DCES operation is analysed, equations describing the currents transients during switching have been worked out, from which the boundary conditions for zero‐voltage switching (ZVS) to occur are formulated and the resultant ZVS zone is illustrated with the help of visual graphs. The boundary conditions are examined to evaluate how the circuit parameters influence the extension of the ZVS zone. The examination shows that a suitable selection of the parameters widens the ZVS zone notably; its optimal extension is then found for a case study. The effectiveness of the ZVS findings for the featured DCES topology is validated by both simulation and experiment results.

The conventional synchronous generator (SG) can regulate the active and reactive power for frequency and voltage stability, when the system fluctuates. In renewable energy generation system (RES), the stability problem of RES can be solved by adding virtual inertia and damping in the control strategy of the grid-connected inverter. The grid-connected inverter and renewable energy system with this kind of control strategy, called as virtual synchronous generator (VSG), acts as a synchronous generator. In this paper, the topology of grid-connected PV array and energy storage system is proposed. The VSG used in grid-connected inverter, is modelled as stator and rotor model by stator voltage equation and rotor motion equation, respectively. Meanwhile, the VSG control mechanism, based on droop control and model of VSG, can be divided as active power-frequency and reactive power-voltage control. Besides, the system stability is analyzed based on small signal model, for the design of inertia and damping. The simulation model is designed by MATLAB/Simulink for the implementation of VSG. In simulation, it is compared that the dynamic regulation performance of VSG with different control coefficient, such as virtual inertia, virtual damping, droop coefficient and integral coefficient. The optimization for regulation performance in simulation provides an appropriate selection method of the control coefficient for VSG.