Primary Side Constant Power Control Scheme for LED Drivers Compatible with TRIAC Dimmers

Zhang, Junming,Jiang, Ting,Xu, Lianghui,Wu, Xinke The Korean Institute of Power Electronics 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.4

This paper proposes a primary side constant power control scheme for TRIAC dimmer compatible LED drivers. The LED driver is a Flyback converter operated in boundary conduction mode (BCM) to minimize the switching loss. With the proposed control scheme, the input power of the Flyback converter can be controlled by the TRIAC dimming angle, which is not affected by AC input voltage variations. Since the output voltage is almost constant for LED loads, the output current can be changed by controlling the input power with a given conversion efficiency. The isolated feedback circuit is eliminated with the proposed primary side control scheme, which dramatically simplifies the whole circuit. In addition, the input current automatically follows the input voltage due to the BCM operation, and the resistive input characteristic can be achieved which is attractive for TRIAC dimming applications. Experimental results from a 15W prototype verify the theoretical analysis.

Simplified 2-D Analytical Model for Winding Loss Analysis of Flyback Transformers

Junming Zhang,Wei Yuan,Hulong Zeng,Zhaoming Qian 전력전자학회 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.6

The winding loss analysis of a flyback transformer is difficult and ambiguous because the primary side current and the secondary side current differs both in shape and phase, especially for DCM (Discontinuous Conduction Mode) operation. Meanwhile, the fringing field caused by the air gaps further makes the traditional 1-D loss analysis model not directly applicable. The paper gives a thorough investigation into the phase shift of winding currents, which indicates that the phase shift of the high order harmonics is still close to 180º out-of-phase. Based on the analysis, a simplified 2-D winding loss analytical model for flyback transformers considering the effects of low order harmonics is proposed. By neglecting the y components of the fringing field, the proposed model has an acceptable accuracy and a simple form that is similar to the conventional 1-D model. The power loss calculated with the proposed analysis model is verified by FEA (Finite Element Analysis) simulations and experimental results.

Primary Side Constant Power Control Scheme for LED Drivers Compatible with TRIAC Dimmers

Junming Zhang,Ting Jiang,Lianghui Xu,Xinke Wu 전력전자학회 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.4

This paper proposes a primary side constant power control scheme for TRIAC dimmer compatible LED drivers. The LED driver is a Flyback converter operated in boundary conduction mode (BCM) to minimize the switching loss. With the proposed control scheme, the input power of the Flyback converter can be controlled by the TRIAC dimming angle, which is not affected by AC input voltage variations. Since the output voltage is almost constant for LED loads, the output current can be changed by controlling the input power with a given conversion efficiency. The isolated feedback circuit is eliminated with the proposed primary side control scheme, which dramatically simplifies the whole circuit. In addition, the input current automatically follows the input voltage due to the BCM operation, and the resistive input characteristic can be achieved which is attractive for TRIAC dimming applications. Experimental results from a 15W prototype verify the theoretical analysis.

Simplified 2-D Analytical Model for Winding Loss Analysis of Flyback Transformers

Zhang, Junming,Yuan, Wei,Zeng, Hulong,Qian, Zhaoming The Korean Institute of Power Electronics 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.6

The winding loss analysis of a flyback transformer is difficult and ambiguous because the primary side current and the secondary side current differs both in shape and phase, especially for DCM (Discontinuous Conduction Mode) operation. Meanwhile, the fringing field caused by the air gaps further makes the traditional 1-D loss analysis model not directly applicable. The paper gives a thorough investigation into the phase shift of winding currents, which indicates that the phase shift of the high order harmonics is still close to $180^{\circ}$ out-of-phase. Based on the analysis, a simplified 2-D winding loss analytical model for flyback transformers considering the effects of low order harmonics is proposed. By neglecting the y components of the fringing field, the proposed model has an acceptable accuracy and a simple form that is similar to the conventional 1-D model. The power loss calculated with the proposed analysis model is verified by FEA (Finite Element Analysis) simulations and experimental results.

Mesenchymal Stem Cells Modified with Stromal Cell-Derived Factor 1б Improve Cardiac Remodeling via Paracrine Activation of Hepatocyte Growth Factor in a Rat Model of Myocardial Infarction

Junming Tang,Jianing Wang,Linyun Guo,Xia Kong,Jianye Yang,Fei Zheng,Lei Zhang,Yongzhang Huang 한국분자세포생물학회 2010 Molecules and cells Vol.29 No.1

Mesenchymal stem cells (MSCs) are a promising source for cell-based treatment of myocardial infarction (MI), but existing strategies are restricted by low cell survival and engraftment. We examined whether SDF-1 transfection improve MSC viability and paracrine action in infarcted hearts. We found SDF-1-modified MSCs effectively ex-pressed SDF-1 for at least 21days after exposure to hy-poxia. The apoptosis of Ad-SDF-1-MSCs was 42% of that seen in Ad-EGFP-MSCs and 53% of untreated MSCs. In the infarcted hearts, the number of DAPI-labeling cells in the Ad-SDF-1-MSC group was 5-fold that in the Ad-EGFP-MSC group. Importantly, expression of antifibrotic factor, HGF, was detected in cultured MSCs, and HGF expression lev-els were higher in Ad-SDF-MSC-treated hearts, compared with Ad-EGFP-MSC or control hearts. Compared with the control group, Ad-SDF-MSC transplantation significantly decreased the expression of collagens I and III and matrix metalloproteinase 2 and 9, but heart function was im-proved in d-SDF-MSC-treated animals. In conclusion, SDF-1–modified MSCs enhanced the tolerance of engrafted MSCs to hypoxic injury in vitro and improved their viability in infarcted hearts, thus helping preserve the contractile function and attenuate left ventricle (LV) remodeling, and this may be at least partly mediated by enhanced paracrine signaling from MSCs via antifibrotic factors such as HGF.

A Novel Control Strategy for Improving the Performance of Hybrid Active Power Filters

Wen Junming,Zhang Miao,Lu Jianhang,Guan YiChuan,Wu Shiyu,Feng Chunshou 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.6

Hybrid active power filters (HAPF) are effective harmonic compensation devices. However, the inductor voltage is too low, so the DC-bus voltage can not get enough power flow. Thus, the compensation performance and stability of HAPF can be reduced. Theoretically, increasing the inductor voltage can improve the DC side control performance. Therefore, the relevant mathematical model is established, and systematic analysis is carried out. To improve the performance of HAPF, a new double closed-loop control strategy is proposed. To sum up, the main variable of the outer loop control is the inductor voltage. The current flow direction can be changed by changing the value of the inductance voltage to improve the inductance voltage and realize the stability of the DC-side voltage. Secondly, from the transfer function and the Bode Plots, the introduction of the inverter output current inner loop results in significant resonant spike suppression of the system. Compared with the self-excitation control method with voltage feedforward, this new control method is easy to implement and very effective in DC-bus control. Simulation and experimental results show that the compensation effect of HAPF is improved, the DC-side voltage is stable, and the system can operate safely and reliably.

Mesenchymal Stem Cells Modified with Stromal Cell-Derived Factor 1${\alpha}$ Improve Cardiac Remodeling via Paracrine Activation of Hepatocyte Growth Factor in a Rat Model of Myocardial Infarction

Tang, Junming,Wang, Jianing,Guo, Linyun,Kong, Xia,Yang, Jianye,Zheng, Fei,Zhang, Lei,Huang, Yongzhang Korean Society for Molecular and Cellular Biology 2010 Molecules and cells Vol.29 No.1

Mesenchymal stem cells (MSCs) are a promising source for cell-based treatment of myocardial infarction (MI), but existing strategies are restricted by low cell survival and engraftment. We examined whether SDF-1 transfection improve MSC viability and paracrine action in infarcted hearts. We found SDF-1-modified MSCs effectively expressed SDF-1 for at least 21days after exposure to hypoxia. The apoptosis of Ad-SDF-1-MSCs was 42% of that seen in Ad-EGFP-MSCs and 53% of untreated MSCs. In the infarcted hearts, the number of DAPI-labeling cells in the Ad-SDF-1-MSC group was 5-fold that in the Ad-EGFP-MSC group. Importantly, expression of antifibrotic factor, HGF, was detected in cultured MSCs, and HGF expression levels were higher in Ad-SDF-MSC-treated hearts, compared with Ad-EGFP-MSC or control hearts. Compared with the control group, Ad-SDF-MSC transplantation significantly decreased the expression of collagens I and III and matrix metalloproteinase 2 and 9, but heart function was improved in d-SDF-MSC-treated animals. In conclusion, SDF-1-modified MSCs enhanced the tolerance of engrafted MSCs to hypoxic injury in vitro and improved their viability in infarcted hearts, thus helping preserve the contractile function and attenuate left ventricle (LV) remodeling, and this may be at least partly mediated by enhanced paracrine signaling from MSCs via antifibrotic factors such as HGF.

An Isolated Bidirectional Modular Multilevel DC/DC Converter for Power Electronic Transformer Applications

Wang, Zhaohui,Zhang, Junming,Sheng, Kuang The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.3

With high penetration of renewable energies, power electronic transformers (PETs) will be one of the most important infrastructures in the future power delivery and management system. In this study, an isolated bidirectional modular multilevel DC/DC converter is proposed for PET applications. A modular multilevel structure is adopted as switching valves to sustain medium voltages to achieve modular design and high reliability. Only one high-frequency transformer is used in the proposed converter, which significantly simplifies the circuit and galvanic insulation design. A dual-phase-shift modulation strategy is proposed to regulate the output power and achieve a simple voltage balancing control. A down-scaled (2 kW/20 kHz) prototype is constructed to demonstrate the proposed converter and verify the control strategy. The experimental results comply with the theoretical analysis well, with the highest power efficiency reaching 97.6%.

An Isolated Bidirectional Modular Multilevel DC/DC Converter for Power Electronic Transformer Applications

Zhaohui Wang,Junming Zhang,Kuang Sheng 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.3

With high penetration of renewable energies, power electronic transformers (PETs) will be one of the most important infrastructures in the future power delivery and management system. In this study, an isolated bidirectional modular multilevel DC/DC converter is proposed for PET applications. A modular multilevel structure is adopted as switching valves to sustain medium voltages to achieve modular design and high reliability. Only one high-frequency transformer is used in the proposed converter, which significantly simplifies the circuit and galvanic insulation design. A dual-phase-shift modulation strategy is proposed to regulate the output power and achieve a simple voltage balancing control. A down-scaled (2 kW/20 kHz) prototype is constructed to demonstrate the proposed converter and verify the control strategy. The experimental results comply with the theoretical analysis well, with the highest power efficiency reaching 97.6%.

Modular Multilevel Power Electronic Transformer

Zhaohui Wang,Junming Zhang,Kuang Sheng 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

In this paper, a modular multilevel power electronic transformer structure for power distribution system is discussed. The proposed structure consists of two completely decoupled power stages. Modular multilevel converter is adopted as the front-end ac-dc stage to convert the medium ac voltage to medium dc voltage, or vice versa. Galvanic isolation and voltage conversion are realized by the cascaded dc-dc stage. Only one high frequency transformer is used in the dc-dc converter, which dramatically simplifies the circuit and galvanic isolation design. A dual phase shift control method is proposed to regulate the output and balance the submodule voltage in the dc-dc stage. To verify the effectiveness of the proposed converter and control method, a down-scaled prototype is constructed. The experimental results comply with the theoretical analysis very well.