Zhenyu Shan

Transient Mitigation of DC–DC Converters for High Output Current Slew Rate Applications

This paper presents a method of mitigating the transient overshoots of dc-dc converters undergoing large load disturbances. The method involves a small power auxiliary circuit which exists as an energy buffer to provide a smooth absorption and release of excess energy from and to the main dc-dc converter during transients. In the method, the regulation of the current magnitude of the converter and energy storage of the auxiliary circuit are guaranteed by the relevant control schemes. The cost and size of the auxiliary circuit will be relatively small as it only operates intermittently. In this paper, the voltage deviation analysis and the auxiliary circuit design guideline are provided. Experimental results validating the approach are presented.

Large- and Small-Signal Average-Value Modeling of Dual-Active-Bridge DC–DC Converter Considering Power Losses

Average-value modeling (AVM) provides an efficient way to study power electronic systems in large- and small-signal senses. This paper presents a new reduced-order AVM for dual-active-bridge dc-dc converters. The proposed model considers the conduction and transformer power losses as well as the input/output filters, which may be very useful for system-level studies. Based on the large-signal AVM, the small-signal model and the control-to-output transfer function are also derived. The proposed AVM is compared with the full-order generalized average model and the detailed model in predicting large-signal transients and small-signal analysis in the frequency domain. The experimental results confirm that the proposed model yields a high accuracy, which represents an improvement over other existing models.

Pre-Energized Auxiliary Circuits for Very Fast Transient Loads: Coping With Load-Informed Power Management for Computer Loads

The recent development in computer science that the power demand and required time of code execution can be accurately predicted is paving a path that may lead to a new paradigm shift in power supply design. Specifically, while the design of power supplies now normally assumes that load current changes at random times and with unknown magnitudes (within a range), future computer loads may communicate with power supplies to provide information that facilitates power management. Such information would include the exact times of occurrence of load transients and their magnitudes. Following this trend of development where the power supply is “informed” by the load, we propose to use an auxiliary circuit that generates a slowly rising current prior to the occurrence of the actual transient. The slowly rising current can cause the power supply to shift its operation point to a new level slowly without exhibiting output voltage fluctuation. The actual load exhibits very fast current transient, but the combination of actual load and auxiliary circuit behaves as a slowly changing load which can be dealt with by an ordinary power supply capable of handling slowly changing load current. Thus, this method essentially buffers the power supply from large and fast transients. Our proposed approach involves the necessary algorithm for controlling the auxiliary circuit in accordance with the information provided by the microprocessor. The design of the auxiliary circuit is explained and experimental results for a 1.5 V load with 15 A step current are provided for verification.

Classification of Auxiliary Circuit Schemes for Feeding Fast Load Transients in Switching Power Supplies

This paper presents a systematic classification of auxiliary circuit schemes for feeding fast load transients in switching power converters. The classification is based on the types of the implementation methods, practical constraints and performance. In particular, auxiliary circuits are classified according to the ways in which they are connected with the power supplies and loads, as well as the choice of control methods. Designed as a shunt output, the “intruding” type of auxiliary circuits is effective and less dissipative. Moreover, to reduce complexity, auxiliary circuits may be designed in the form of a bridge output, and employs a “non-intruding” type of control scheme. Furthermore, provision of pre-informed loading condition leads to further simplification of auxiliary circuitry and improvement of efficiency. Experimental measurements are provided to support the analysis of the properties of various types of circuits.

Transient mitigation of DC-DC converters using an auxiliary switching circuit

This paper presents a method of mitigating the transient overshoots of DC-DC converters operating with large load disturbances. The method involves a small auxiliary power circuit with a complementary control scheme that provides a smooth absorption and release of excess energy from and to the main DC-DC converter in the events of large load changes. This control mechanism interactively mitigates the large transient overshoots which would otherwise appear at the converter output. Since the control scheme involves an adjustable-energy-storage feature, the proposed solution is effective for any level of step-load change within a pre-specified range.

Augmented Buck Converter Design using Resonant Circuits for Fast Transient Recovery

High-performance buck converters are often required in modern power electronic applications. An augmented buck converter (a main buck converter with augmentation circuits) can achieve fast transient recovery and small output voltage deviation. Compared with other augmentation circuits, a resonant augmentation circuit offers potential electromagnetic interference reduction due to the relatively low di/dt value and compacts the circuit through a reduced inductance for resonance. In this paper, the performance analysis of an augmented buck converter constructed with the resonant circuit are described in detail in terms of voltage-deviation band and power loss. A circuit design and control principle is also proposed for achieving the required voltage deviation for a given transient-detection delay. A 12-to-5-V converter prototype is built to verify the analysis and effectiveness of the proposed methodology. It is demonstrated that the voltage deviation is reduced from 360 to 200 mV using the proposed resonant augmentation circuits and control scheme. The efficiency study shows that the power loss varies from 0.02 to 0.72 W, when the repetition frequency of 5-to-10-A transients changes from 100 to 5 kHz.

A feedforward control method of dual-active-bridge dc/dc converter to achieve fast dynamic response

A dual-active-bridge (DAB) dc/dc converter may interconnect a battery and a dc grid to achieve UPS or peak shaving functions which bring potential benefits to the power distribution for telecom equipment. Such application requires the DAB converter having fast dynamic response. In this work, a feedforward algorithm is proposed to achieve peak-current-control strategy. The proposed approach can facilitate the converter to generate fast response to reference steps comparing with a traditional PI control method, and does not need the leakage inductance information of transformer comparing with other advanced methods. The simulation result is given to verify the effectiveness and feasibility.

Using LED lighting drivers for harmonic current cancellation in intelligent distribution power systems

Harmonic currents injected from low-cost rectifier loads can cause adverse impacts in electrical distribution systems. This paper presents a harmonic cancellation approach using the light-emitting-diode (LED) lighting systems, which are becoming widely considered in commercial, office, and residential buildings and homes. The proposed approach is based on redesigning the existing LED converter controller to absorb/cancel a specific harmonic current injected by other devices. This can be further exploited in conjunction with the energy management system (EMS) and advanced control network, where a smart meter can inform the LED converters of the harmonic currents to be canceled. A maximum capability of injecting individual harmonics by the LED converter is estimated for the 3rd, 5th, and 7th significant harmonics currents. Simulation results are demonstrated to verify the effectiveness of the proposed approach.

Pre-energized compact auxiliary circuit to buffer loads from fast transients with the goal of managing load-informed power

A pre-energized auxiliary circuit can be constructed to buffer fast load transients using advance information from an intelligent load. Such information should include the exact times of load transients and their magnitudes. This paper proposes a compact auxiliary circuit that generates a current half the magnitude of the transient. The proposed circuit builds on earlier work addressing load-informed power and operates to pre-energize the power supply. The goal is to integrate it with an intelligent load.

Digital and analog implementations of nonlinear-feedforward controller for a dual-active-bridge converter

Dual-active-bridge (DAB) topology requires a powerful controller to realize voltage conversion and address fast load transients. A controller with nonlinear feedforward and linear feedback loops is able to facilitate a DAB converter to fulfill this requirement. The nonlinear feedforward loop is designed based on the nonlinear model of the DAB converter. The linear feedback loop is realized as a traditional proportional-integral (PI) control. This paper presents two (digital and analog) implementations of the fast dynamic controller with the proposed nonlinear feedforward and linear feedback loops for the DAB converter. The digital implementation is realized using a digital signal processor (DSP), while the analog implementation is built using analog-operational amplifiers and other conventional elements. The experimental results are shown to verify the effectiveness of the proposed implementations.