Ziheng Xiao

Nanyang Technological University | ntu · Energy Research Institute

The CLLC resonant converters are preferred for their high-power density and high efficiency. Nevertheless, their dynamic performance deteriorates due to the low impedance characteristic of the resonant tank near resonant frequency. This study proposes optimal switching patterns under specified peak resonant current conditions to enable rapid and...

Generally, the variable switching frequency method is used to operate power converters in triangular current mode (TCM) or near critical conduction mode (CRM) to achieve zero-voltage switching (ZVS). However, this approach faces significant challenges: high peak inductor current, and complex controller design due to varied digital delays in variabl...

The start-up of CLLC resonant converters presents challenges such as high inrush current and voltage surges. Conventional approaches often resort to conservative control parameters, which, albeit effective in mitigating resonant current during start-up, invariably extend the start-up duration. Addressing these challenges, this study investigates th...

With the high penetration of renewable energy sources, the inertia of microgrids has declined. In DC microgrids, the lack of inertia leads to bus voltage fluctuations, which may threaten system stability. To mitigate this issue, virtual inertia can be provided by energy storage units via emulating the inertial properties akin to virtual DC motors....

Owing to the integration and utilization of the parasitic capacitance of the transformer, the LCC resonant converters with a capacitive output filter are widely used in high-voltage power supplies for microwave generation, X-ray, ion implantation, and other fields. However, it is challenging for the LCC to maintain high efficiency in a wide output...

Triangular current mode (TCM) and near critical conduction mode (near-CRM) are popularly used in DC-DC converters to achieve zero-voltage switching (ZVS). However, they encounter a huge peak current problem, more than twice the average current. To solve this problem, this paper proposes a novel trapezoidal current mode (TZCM) for three-level DC-DC...

The multiphase interleaved LLC converter has gained significant popularity in high-power isolation applications. However, due to parameter tolerances, it requires multiple current sensors to balance the currents in parallel channels, thereby increasing sensor cost and hardware complexity. In this paper, a current balancing method with reduced numbe...

In current-fed closed-loop single/three-phase DC-AC converters, precise current sampling is required for better waveform quality and smaller steady-state error. However, interferences caused by switching noise pose challenges to acquiring precise averaging current value. This article presents some considerations regarding precise current sampling f...

The T-type three-level inverter has been widely applied in grid integration system due to its salient features. In this paper, a three-phase four-wire T-type inverter is employed as an active power filter. Due to inconsistencies of capacitances and unbalanced three-phase operation, the capacitor voltages deviate. These unbalanced capacitor voltages...

In this paper, a single-stage isolated three-port AC-DC-DC converter is proposed to function as an interface between two DC ports and one AC port. The introduced asymmetrical modulation scheme facilitates the voltage gain regulation between the two DC ports, enables the bidirectional power transfer among all three ports, and ensures a unity power f...

In this article, NP voltage coordinate control model in two-stage DC-AC converters is originally proposed. In the proposed model, the timely predicted NP current of DC-AC converters is directly used as the power allocation coefficient of DC-DC converters, which helps to compensate NP AC fluctuation. Besides, the decoupled PI control is used to over...

This letter proposes a seamless rotational phase shedding (PS) operating method designed for multiphase DC-DC converters. Utilizing a 15-kW/50 kHz three-phase interleaved synchronous boost converter as an example, the optimal activation of phases is determined by minimizing power losses. Through a comprehensive analysis of total inductor current sa...

Due to the intricate array of control parameters, achieving efficiency optimization for a typical dual active bridge (DAB) prototype becomes a laborious and time-intensive task. Traditional methodologies have revolved around an idealized lossless model of DAB, inevitably leading to a disparity between theoretical ideals and experimental realities....

A precise evaluation of power converter losses is essential for accurately predicting power loss and optimizing control parameters to enhance efficiency across various scenarios and applications. Conventional power loss evaluation methods separate the theoretical analysis and experimental verification stages. Consequently, these methods often suffe...

Conventional optimization approaches for dual active bridge converters (DAB) involve separate analysis and experimental verification stages, which may lead to suboptimal experiment results due to unaccounted parameters. This article presents a data-driven control parameters optimization method for DAB. The theoretical analysis and experimental veri...

DC microgrid clusters are effective solutions for integrating multiple autonomous subgrids at the same and different voltage levels. In such a system, global power management is an essential concern, but it is always degraded by system structures and line impedances of distributed generation units (DGUs). To solve this problem, a decentralized mult...

This paper summarizes the main results and contributions of the MagNet Challenge 2023, an open-source research initiative for data-driven modeling of power magnetic materials. The MagNet Challenge has (1) advanced the stateof-the-art in power magnetics modeling; (2) set up examples for fostering an open-source and transparent research community; (3...

Expanding the voltage gain regulation range while preserving high efficiency of CLLC resonant converters is crucial yet challenging. Previous methods typically expanded the voltage gain range at the expense of a reduced efficiency. This paper aims to unlock the full potential of CLLC resonant converters using full-bridge (FB) and half-bridge (HB) s...

The bulky installation and inevitable flux leakage of magnetic couplers create significant challenges for wireless charging applications in future self-driving vehicles. Ferrite cores and nanocrystalline ribbon cores (NRCs) have superior characteristics in terms of low eddy current loss and high saturation flux density, respectively. This paper pro...

This article presents a swift and seamless start-up method for dual active bridge (DAB) converters, adhering to a predefined current limit. It explores all operation stage trajectories to identify the optimal switching sequence in both constant frequency (CF) and variable frequency (VF) modes. The method seamlessly integrates sophisticated modulati...

This paper introduces a method to enhance the light load efficiency of dual active bridge (DAB) converters through power loss minimization via optimal switching sequences. Peak efficiency points for various operational conditions are identified using a comprehensive power loss calculation approach. Single phase shift (SPS) modulation and trapezoida...

There is a critical need to increase power system inertia during the grid transformation. However, in a low-voltage dc (LVDC) microgrid, many potential inertia contributors, such as energy storage systems, are linked to the local dc bus and managed by their individual distributed controllers. This configuration results in a lack of access to grid f...

Voltage and current balance are essential in an interleaved three-level DC-DC converter. In this paper, a simultaneous voltage and current self-balance mechanism based on near-CRM (critical conduction mode) for an interleaved three-level DC-DC converter is discovered, which can realize current and voltage balancing automatically without sensors. Fi...

This paper presents a method for computer-aided operation and design optimization of resonant converters using time domain analysis. Resonant converters can operate in different operation stage trajectories (OSTs) with the change of two degrees of freedom (2DOFs), namely switching frequency f_s and duty ratio d . The paper calculates...

italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC resonant converters are widely used in high power density and high efficiency applications. Practically, the parasitic capacitors of MOSFETs and diodes, the stray capacitor of the high frequency transformer (HFT), and the deadtime will have a great...

The optimization of dual active bridge converters (DAB) is widely studied and numerous modulation schemes are proposed to enhance the performance of a DAB converter. However, a unified description method both suitable for time and frequency domain analysis still lacks. Besides, the optimization process encounters a difficulty of the potential nonco...

In high voltage (HV) input to low voltage (LV) output dc/dc conversion applications, the input series output parallel (ISOP) structure is widely used and studied. Practically, the ISOP system encounters the below challenges: 1) HV isolated components like the HV isolated and HV input extra auxiliary power supply (APS), the HV isolated high frequenc...

The input series output parallel (ISOP) and input parallel output series (IPOS) system has been extensively researched and applied in academia and industry due to the high DC conversion ratio. Practically, the ISOP and IPOS systems are faced with challenges like relatively immature high voltage (HV) isolated high frequency transformer (HFT), high r...

LLC resonant DC-DC converter has been widely used in high power density and high efficiency applications. Pulse frequency modulation (PFM) is commonly applied due to its wide soft-switching range. In some special cases, phase shift modulation (PSM) is applied to widen voltage regulation range, improve light-load efficiency, or implement a soft star...

High-frequency-link (HFL) electrical quantities, including high-frequency voltages, currents, and instantaneous power, are closely related to the performance of DC-DC converters. However, HFL electrical quantities are usually square, triangular, or trape-zoidal waves and conventional indicators like apparent power or power factor are with vague phy...