Current Sensorless Control for DualActiveBridge DC-DC Converter with EstimatedLoadCurrent Feedforwar

Abstract

This paper proposes a current sensorless control strategy for the dual active bridge (DAB) converter with nonlinear disturbance observer (NDO) based load current feedforward. The proposed method can regulate both the dc-bus voltage and the current of the DAB converter without current sensors. Several performance indexes are established for the parameter design and a detailed design method is presented in this paper. When a single-phase H-bridge inverter is connected, the double-frequency oscillation from the feedback path is suppressed by proper parameter design, while the transient response of dc-bus voltage can be further improved by the NDO-based load current feedforward with a notch filter in the feedforward path.

Existing System

AC–AC Dual-Active-Bridge Converter.

Proposed System

This paper proposes a current sensorless control strategy based on the transient dc bias characterization of the transformer current. Then, the NDO-based load current feedforward is designed for the DAB converter to improve the dynamic performance of the system. Comparing with the traditional dual-loop control strategy and the load current feedforward strategy, the proposed control strategy can regulate the dc-bus voltage, the output current of the DAB converter, and introduces the feedforward of load current without current sensors. Only measurement of input and output voltage is needed and it does not increase the communication burden of the system. The small signal model with parameter deviation coefficient of the converter is constructed, which is independent of the steady-state operating point. Consequently, it is accurate enough to describe the dynamic performance of the system in the whole power range. Moreover, the disturbance brought about by the input voltage can be eliminated inherently by the proposed control strategy. The steady-state performance and the dynamic performance are derived to establish several performance indexes for parameter design. A parameter design method is proposed for the closed-loop system and the NDO with dc load or single-phase H-bridge inverter connected to DAB. The design method can design the parameters of the system based on different design targets. When single-phase H-bridge inverter is connected, the double-frequency oscillation in the feedback path is suppressed by proper parameters, while the transient response of dc-bus voltage can be improved further by NDO-based load current feedforward with a notch filter in the feedforward path. As a result, the negative phase introduced by the notch filter can be avoided. The dead-time effect on the current estimation error and the dynamic performance is also analyzed. The robustness analysis is carried out to show good ability against the parameter variation.

Architecture

The topology of DAB converter