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In this paper, a variable dc bus control strategy is evaluated for a bidirectional grid connected electric vehicle (EV) charger topology. The EV charger under consideration comprises of an ac-dc 3-φ active rectifier stage followed by a dc-dc dual active bridge (DAB) converter. The voltage of the common dc-link between the ac-dc stage and the dc-dc stage is regulated such that it follows the voltage...
A full bridge modular multilevel converter (FBMMC) can work in buck and boost modes. It is thus suitable for grid-connected applications in which the dc link voltage varies over a wide range. In this work the emphasis is set on the steady-state analysis of the grid-connected FBMMC under different levels of the dc link voltage. Two control strategies for the dc capacitor voltage are considered and...
A novel topology is proposed that interfaces between one or multiple DC sources and a three-phase machine. The DC-side converter consists of two half-bridges that form a specialized converter. The half-bridges operate at a reduced voltage which reduces inductor effort and switching losses. The resulting four DC-link levels power two three-phase bridges that can drive open-winding machines. The circuit...
This paper presents a case study of different control approaches for a single phase Dual Active Bridge (DAB) based MVDC Shipboard power system (SPS). The Line Regulating Converters (LRCs) are based on DAB topology and the load side converters or Point of Load Converters (POLs) are based on buck topology. The tightly controlled POLs exhibit a constant power load (CPL) behaviour, which has a destabilising...
A dual active bridge (DAB) converter is a widely used structure in the low voltage direct current (LVDC) distribution system. In the case of the conventional single-level DAB, the higher the input and output voltage, the higher the voltage stress that the power switch must withstand. To solve this problem, a multi-level structure can be applied to the DAB converter to have low voltage stress of the...
This paper discloses the development of modular front-end medium-voltage solid-state transformer (SST) to show system level design, circuit topology, and prototype test results. Each multilevel front-end module consists of two stages: (1) ac to dc boost converter with power factor correction dc and (2) isolated dc-dc LLC converter. The proposed system has been designed, simulated, and fabricated with...
A novel virtual voltage control strategy is proposed for modular multilevel converter in order to reduce the quantity of voltage sensors at the terminal. The output voltage of the inverter is obtained through the upper and lower arm currents of the converter and used to trace the reference active and reactive power, respectively. According to the Routh-Hurwitz criterion, the root trajectory of the...
This paper gives a detailed analysis about the causes of the voltage distortion caused by dead time in dual active bridge (DAB) DC-DC converter. The zero-crossing point of the equivalent leakage inductor's current is the definitive factor for various voltage distortion phenomena, which is determined by dead time and phase-shift ratios. Based on the switching characterization of DAB in dual-phase-shift...
For Dual Active Bridge (DAB) converters a large number of modulation schemes exist, which allow to operate the converter in a wide voltage/power range at a very high efficiency. However, the implementation of these modulation schemes and the transition between the schemes during transient conditions is relatively complicated. Therefore, a simple and flexible concept for generating the PWM signals...
The challenge of integration and control of electric energy posed by microgrid can be addressed by introducing the solid state transformer proposed by the FREEDM center. This research focuses on the voltage regulation issue of SST by adopting dynamic phasor-based modeling and internal model control based nested loop PI control. The main contribution of the paper is use of internal model control design...
This paper discusses the dead-time effect of dual bridge series resonant DC/DC converter (DBSRC). The phase-shift modulation is usually adopted in DBSRC. However, the phase-shift angle is usually small, and voltage polarity reversal (VPR) may occur in dead-time, which may deteriorate EMI/EMC and increase loss. This paper analyzes the commutation of DBSRC when VPR occurs and proposes a method to eliminate...
In this paper, a new DC ice-melting scheme based on hybrid modular multilevel converter (MMC) is proposed considering the problems of existing DC ice-melting device, such as high harmonic content, complicated mode switching operation, large size and so on. In the scheme, a novel structure of MMC is composed of the upper bridge arm all using full bridge sub-module (FBSM) and the lower bridge arm all...
In this paper, a Boost type control strategy is proposed to solve the problems of large power backflow and low conversion efficiency in dual active bridge bidirectional DC-DC converter which occur in the traditional phase-shifted control strategies. In the condition that the main topology circuit is not changed, the control strategy proposed in this paper can make the circuit work in Boost state every...
Aiming at solving the problem of low efficiency of energy transmission in bidirectional energy storage system under the condition of large voltage difference between DC bus and battery, a novel phase angle modulation control strategy based on dual active bridge DC-DC converter is proposed in this paper. Under the control strategy, the energy stored in the inductor reaches the maximum during each switching...
Solar electrical energy generation and its conversion techniques gain more attention because Photo Voltaic (PV) power generation system is more attractive due to its advantages among all the RESs (Renewable Energy Sources). In this paper, Isolated SEPIC(Single-Ended Primary-Inductance Converter)converter fed grid connected Multilevel Inverter is proposed. SEPIC converter is a buck-boost derived topology...
Nearest level modulation is one of the main modulation strategies in the modular multilevel converter (MMC), which has obvious advantage in the converter with a large number of voltage levels. To ensure the effect of voltage balancing, the capacitor voltages of submodules are usually required to be collected and sorted all the time, and a great deal of voltage acquisition modules are needed to achieve...
This paper presents the design and implementation of zero-voltage-zero-current switching (ZVZCS) technology in a full bridge DC/DC converter with digital control in a 20 kW multi-functional arc welding machine application. A comprehensive analysis is undertaken including power stage topology design, output voltage digital control design and power loss comparison between hard switching and ZVZCS. Experimental...
Inside the meshed LVDC distribution grids the power flow is predominantly limited by the line impedances. In order to achieve economical and flexible operation of the meshed LVDC distribution grids, it is required to control the power flow. For that end, the line impedances need to be adjustable. The line impedance can be controlled by a DC-DC transformer, however, it needs to be rated for the full...
This paper proposed a hybrid power system with combined advantageous features of switching power supply and linear power amplifier. The switching power supply would provide the primary output voltage and power to the load, while the linear power amplifier would act as a correcting amplifying device to compensate for power ripple as a way to stabilize voltage output. Combination of these two components...
In this paper, the essential reason of causing the dual-side reactive currents in the isolated dual active bridge (DAB) DC-DC converter is revealed. It is because that the output voltages of the two H-bridge converters of the DAB converter can not keep their polarities the same as the inductor current all the time. The constraint between the two inner phase shifts and the outer phase shift is determined...
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