Xiaoyong Ren

Three-Mode Dual-Frequency Two-Edge Modulation Scheme for Four-Switch Buck–Boost Converter

Four-switch buck-boost (FSBB) converter features low-voltage stress across the power switches and positive output voltage. They have two active power switches and two synchronous rectifiers, so two freedoms, i.e., the duty cycles of the two active switches, are available to regulate the output voltage. This paper proposes a two-edge modulation (TEM), in which the two active switches are trailing-edge and leading-edge modulated, respectively. Thus, the inductor current ripple can be reduced. Furthermore, a 3-mode TEM is derived to reduce the root-mean-square value of the inductor current to reduce the conduction loss. The line range is divided into three regions, and FSBB operates at boost, buck-boost, and buck modes in the lower, medium, and higher input voltage regions, respectively. At buck and boost modes, only two switches are high-frequency switched, so that the total switching loss is reduced. In the buck-boost mode, the inductor current ripple is very low compared with other two modes. Hence, the switching frequency is lowered to reduce the switching loss. The 3-mode TEM can achieve high efficiency over the line range, which is verified by a 48-V (36-75 V) input, 48-V @ 6.25-A output prototype. The measured efficiency is higher than 96.5% over the line range and the efficiency at the nominal input voltage is 97.8%.

A Bandpass Filter Incorporated Into the Inductor Current Feedback Path for Improving Dynamic Performance of the Front-End DC–DC Converter in Two-Stage Inverter

The instantaneous output power of a two-stage single-phase inverter pulsates at twice the output voltage frequency, generating second harmonic current (SHC) in the front-end dc-dc converter. To reduce the SHC, this paper proposes a virtual impedance based control strategy. For the case of adopting a resistor as the virtual impedance, a closed-loop parameter design method is presented, revealing that the voltage loop crossover frequency is relatively low under such circumstance. To overcome this problem, a control strategy incorporating a bandpass filter (BPF) into the inductor current feedback path is put forward and a damping resistor is further added into the BPF for the purpose of improving the system stability margin. Hence, the proposed control scheme can not only reduce the SHC significantly, but also improve the dynamic performance of the front-end dc-dc converter effectively while guaranteeing the stability of the converter. Finally, a 1-kVA prototype is built and tested in the laboratory, and the experimental results are presented to verify the effectiveness of the proposed control strategy.

Four Switch Buck-Boost Converter for Telecom DC-DC power supply applications

Converters for telecom DC/DC power supply applications often require an output voltage somewhere within a wide range of input voltages. While the design of traditional converters will come with a heavy penalty in terms of component stresses and losses, and with the restrictions on the output voltage. Besides that, the high efficiency around the nominal input is another restriction for traditional converters. A controlling scheme for the four switch buck-boost converter is proposed to achieve high efficiency within the line range and the highest efficiency around the nominal input. A 48 V(36-75 V) input 12 V@25 A output two-stage prototype composed of the proposed converter and a full bridge converter is built in the lab. The experimental results verified the analysis.

Three-level driving method for GaN power transistor in synchronous buck converter

The emerging Gallium-Nitride (GaN) based power transistors offers the potential to achieve higher efficiency and higher switching frequencies than possible with Silicon MOSFETs. This paper will discuss the GaN device characteristics, and based on this, the driving method will be discussed. Then a three-level driving method is proposed to overcome the high reverse conduction loss issue of the GaN power transistor. Finally, a 12V to 1.2V Synchronous Buck converter with a full load current of 20A is built to verify the proposed method. The experimental results show that the proposed method is necessary and effective for efficiency improvement in high switching applications of GaN power transistor.

Second-Harmonic Current Reduction and Dynamic Performance Improvement in the Two-Stage Inverters: An Output Impedance Perspective

The instantaneous output power of the two-stage single-phase inverter pulsates at twice the output voltage frequency, resulting in the second harmonic current (SHC) in the front-end dc-dc converter. Although various control schemes can effectively reduce the SHC, they might make the front-end dc-dc converter suffer from poor dynamic performance. In this paper, a basic approach is proposed from the perspective of the output impedance to give considerations to both the SHC reduction and dynamic performance improvement, indicating that the output impedance of the front-end dc-dc converter should be designed relatively high at twice the output voltage frequency while relatively low at other frequencies. According to the proposed approach, one virtual impedance is introduced to be in series with the original output impedance while the other one is in parallel with the intermediate dc bus capacitor. Taking the buck-derived front-end dc-dc converter as an example, the implementation of the virtual impedance are presented, based on which, different control schemes in the previous publications can be synthesized. Finally, a 1-kVA prototype is fabricated in the lab and a comparative study is conducted on four different control schemes by both the theoretical analysis and experimental verification.

A Hierarchical Active Balancing Architecture for Lithium-Ion Batteries

This paper proposes a hierarchical active balancing architecture for the series-connected lithium-ion batteries. The key point of the architecture is that by grouping the battery string into different packs and introducing the top layer, the coupled influence among the cells in different packs is eliminated, which reduces the required balancing time and the energy loss. The repeated charging and discharging problem is avoided, which is beneficial for increasing the state-of-health. Moreover, the proposed architecture can lower the current rating of the balancing circuits, which helps decrease the required cost and improve the system efficiency. On the basis of the architecture, a balancing control using the state-of-charge of each cell is proposed to achieve the balance for all the cells. Furthermore, to deliver the energy from one pack to any other pack bidirectionally, a multidirectional multiport converter along with the current control method is proposed to serve as the top layer. This converter is different from the conventional three-port converter as it can achieve the arbitrary current flow direction control for any number of ports. The experimental results based on 24 series-connected 200-Ah lithium-ion batteries verified the benefits of the proposed architecture and the balancing circuits. After balancing, 4.1% of the total energy of the battery string is saved. Compared to the conventional adjacent cell-to-cell architecture, the proposed architecture can decrease the balancing time and the energy loss during the balancing process by 27.6% and 44.0%, respectively. In addition, the current rating and the cost of the balancing circuits in the proposed architecture is only 37.5% and 11.5% of that in other references.

Analysis and control of S/SP compensation contactless resonant converter with constant voltage gain

A novel S/SP type compensation contactless resonant converter is proposed in this paper, which features the advantage of constant gain intersection point with zero phase angle of input impedance. Different from S/P compensation, the constant gain value is not only independent of load change but also independent of transformers coupling coefficient change causing by the change of gap or misalignment. The characteristic analysis of the proposed resonant converter is performed in this paper. It is also found that with the proposed S/SP compensation the output voltage gain is not sensitive to the parameter change around the gain intersection point. Therefore, both phase locking control and fixed-frequency control can be employed for the proposed converter. A 60W prototype with PLL control and a 1.5kW prototype with constant frequency control are built to verify the analysis. Experimental results testify the theoretical analysis very well. The efficiency of the fabricated prototype reaches 95.2% with 1.5kW output at 10 cm gap.

Self-Oscillating Contactless Resonant Converter With Phase Detection Contactless Current Transformer

A secondary winding shorted current transformer (CT), called phase detection contactless current transformer (PDCCT) is proposed to provide passive current phase detection solution for self-oscillating contactless resonant converter (SOCRC). The proposed PDCCT can detect the current phase from the secondary side of a contactless resonant converter (CRC) and feedback to the primary side rapidly and accurately regardless of the variable air gap. To guarantee the operation of SOCRC, the time delay in control circuitry are studied and compensated. Steady state and dynamic state experimental results on a 60W SOCRC with PDCCT show the validity of both the accurate detection of PDCCT and the rapidly response of SOCRC.

Characterization and control of self-oscillating contactless resonant converter with fixed voltage gain

To ensure reliable control under variable-load and variable-coupling-coefficient condition, a self-oscillating control method for contactless resonant converters is proposed and discussed. Base on the characterization of four basic compensation topologies, such as the voltage gain, transfer impedance, a simple and general self-oscillating control method for S/S, S/P and P/S topology is proposed. Theoretical and experimental results had shown that the proposed control strategy is capable to lock the switching frequency at load independent frequency. Besides the good regulation, the proposed control method can also realize high efficiency for minimal extra component introduced.

High-Efficiency Switch-Linear-Hybrid Envelope-Tracking Power Supply With Step-Wave Approach

Featuring high bandwidth and high efficiency, the switch-linear hybrid envelope tracking (SLH-ET) power supply has been gaining considerable attentions. This paper proposes a new configuration for SLH-ET power supply, which consists of a switching-mode converter with a step-wave approach and a linear amplifier connected in parallel. The switches in the switching-mode converter are operated only one time in every tracking period, leading to reduced switching loss and, thus, a higher efficiency. The number of the voltage levels and the voltage difference between the adjacent steps are analyzed in terms of the voltage synthesis accuracy and voltage total harmonic distortion. A full feedforward of the output voltage scheme is adopted to make the switching-mode converter provide the most load power and the linear amplifier only provide the ripple current that resulted by the switching-mode converter. Thus, the overall efficiency is improved. A prototype is built aiming for 300-kHz sine-wave tracking, with a 10-26-V output voltage and a 50-W peak output power. The experimental results show that the proposed configuration can obtain higher efficiency as well as high tracking bandwidth.