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This paper proposes a multi-loop voltage balancing strategy for half-bridge voltage balancers. The proposed multi-loop scheme consists of a voltage controller and a current variation controller without current sensors. The proposed current variation controller (CVC) aims to regulate the derivative of the average inductor current to be zero at the steady-states as well as to increase the damping of the entire control loop. Furthermore, the CVC is implemented based on a current sensorless scheme. For this purpose, a simple method for detecting current variation by using dc-link voltages and a control model is also proposed. To secure the stability of the proposed CVC with the current sensorless method, a well-known type II regulator is adopted, and its design procedure is detailed. The proposed multi-loop strategy is applied to a 2.4-kW half-bridge voltage balancer. Both simulation and experimental results show good agreements with the theoretical analyses. [ABSTRACT FROM AUTHOR]

A bipolar low-voltage DC (LVDC) distribution system used in residential and building applications requires AC–DC converters and voltage balancers that balance the two DC bus polarities. The bipolar DC bus voltage level only relies on the voltage balancer tied with the AC grid. An isolated DC–DC converter for an energy storage system (ESS) with the voltage balancing capability is proposed to prevent the bipolar voltage level collapse caused by the failure of the grid-tied voltage balancer. The proposed converter topology is an enhanced three-port dual-active-bridge (DAB) converter which can balance the bipolar DC voltage level without complex control. Furthermore, it has less current stress in power switches than that of the conventional three-port DAB converter. The effectiveness of the proposed converter is verified with a 3-kW prototype converter. [ABSTRACT FROM AUTHOR]

In this paper, a hierarchical control strategy is introduced to control a new three-port multidirectional DC-DC converter for integrating an energy storage system (ESS) to a bipolar DC microgrid (BPDCMG). The proposed converter provides a voltage-balancing function for the BPDCMG and adjusts the states of charge (SoC) of the ESS. Previous studies tend to balance the voltage of the BPDCMG buses with active sources or by transferring power from one bus to another. Furthermore, the batteries available in BPDCMGs were charged equally by both buses. However, this power sharing method does not guarantee efficient operation of the whole system. In order to achieve a higher efficiency and lower energy losses, a triple-layer hierarchical control strategy, including a primary droop controller, a secondary voltage restoration controller and a tertiary optimization controller are proposed. Thanks to the multi-functional operation of the proposed converter, its conversion stages are reduced. Furthermore, the efficiency and weight of the system are both improved. Therefore, this converter has a significant capability to be used in portable BPDCMGs such as electric DC ships. The converter modes are analyzed and small-signal models of the converter are extracted. Comprehensive simulation studies are carried out and a BPDCMG laboratory setup is implemented in order to validate the effectiveness of the proposed converter and its hierarchical control strategy. Simulation and experimental results show that using the proposed converter mitigates voltage imbalances. As a result, the system efficiency is improved by using the hierarchical optimal power flow control. [ABSTRACT FROM AUTHOR]

In this paper, a new three-port multidirectional DC-DC converter is proposed for integrating an energy storage system (ESS) to a bipolar DC microgrid (BPDCMG). The proposed converter provides a voltage-balancing function for the BPDCMG and adjusts the charge of the ESS. Thanks to the multi-functional operation of the proposed converter, the conversion stages of the system are reduced. In addition, the efficiency and weight of the system are improved. Therefore, this converter has a significant capability when it comes to use in portable BPDCMGs such as electric DC ships. The converter modes are analyzed and small-signal models of the converter in each of the independent modes are extracted. Finally, comprehensive simulation studies are carried out and a BPDCMG laboratory prototype is implemented in order to verify the performance of the proposed voltage balancer using the burst mode control scheme. [ABSTRACT FROM AUTHOR]

This paper analyzes the load unbalance problem and voltage fluctuation problem in a 3-wire DC distribution system. It also analyzes a solution to these problems; a positive Buck-Boost voltage balancer is proposed and explored in order to fulfill the requirements of high quality power supply for the loads on its load side. Compared with the conventional balancer, a positive Buck-Boost converter is added to solve the voltage fluctuation problem, and the theories and methods of the voltage balancer are extended to analyze the working principle, derive the design equations, explore the stability, and calculate the efficiency. Both simulations and small power experiments are carried out to verify the validity of the working principle, the topology, and the control strategy. [ABSTRACT FROM AUTHOR]