Selection-based capacitor voltage balancing control for modular multilevel converters

Luo, Wei,Ma, Yifan,Zheng, Changbao The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.10

The modular multilevel converter (MMC) is a promising topology for high-power converters. The capacitor voltage balancing method for the submodules (SMs) is one of the key technologies in terms of modular multilevel converters. Aiming at the problems of the large calculation burden and the high switching frequency in the traditional capacitor voltage balancing method, an improved balancing method based on a novel selection algorithm for MMCs is proposed in this paper. The proposed method can avoid the sorting operation of the arm SM voltages in each control cycle without reducing the control precision of the capacitor voltages. In addition, it greatly improves the sorting efficiency. Thus, a criterion for algorithm rerun is introduced, which makes the MMC controller avoid reordering the capacitor voltages and leave the control signals unchanged when the capacitor voltages experience small changes. Finally, simulation and experimental results confirm the feasibility and effectiveness of the proposed method.

Improvement of One-Cycle Controller Response with a Current Mode Controller

Mohsen Ruzbehani,Luowei Zhou,Nasser Mirzaei 전력전자학회 2010 JOURNAL OF POWER ELECTRONICS Vol.10 No.1

The most important feature of the one-cycle control method is its excellent ability in line disturbance rejection. However, when it is used as a controller in dc-dc converters, it has an undesirable transient response. The voltage overshoot at the transient time, which usually exists in one-cycle controlled converters, is unwanted in many applications and it is sometimes hazardous. In this paper, it is shown that the combination of a one-cycle controller with a current mode controller, can improve the transient response and consequently the overshoot can be controlled. Therefore, the combined controller has the excellent line disturbance rejection of a one-cycle controller and the output current limiting capability of current mode controllers. Because in this scheme a one-cycle controller is the master controller, the problem of instability of current mode control, will not happen. By simulation and a practical prototype, the capability of the method is shown.

Junction Temperature Prediction of IGBT Power Module Based on BP Neural Network

Junke Wu,Luowei Zhou,Xiong Du,Pengju Sun 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.3

In this paper, the artificial neural network is used to predict the junction temperature of the IGBT power module, by measuring the temperature sensitive electrical parameters (TSEP) of the module. An experiment circuit is built to measure saturation voltage drop and collector current under different temperature. In order to solve the nonlinear problem of TSEP approach as a junction temperature evaluation method, a Back Propagation (BP) neural network prediction model is established by using the Matlab. With the advantages of non-contact, high sensitivity, and without package open, the proposed method is also potentially promising for on-line junction temperature measurement. The Matlab simulation results show that BP neural network gives a more accuracy results, compared with the method of polynomial fitting.

Duty Ratio Predictive Control Scheme for Digital Control of DC-DC Switching Converters

Pengju Sun,Luowei Zhou 전력전자학회 2011 JOURNAL OF POWER ELECTRONICS Vol.11 No.2

The control loop time delay caused by sampling, the zero-order-holder effect and calculations is inevitable in the digital control of dc-dc switching converters. The time delay will limit the bandwidth of the control loop and therefore degrade the transient performance of digital systems. In this paper, the quantization time delay effects with different time delay values based on a generic second-order system are analyzed. The conclusion that the bandwidth of digital control is reduced by about 20% with a one cycle delay and by 50% with two cycles of delay in comparison with no time delay is obtained. To compensate the time delay and to increase the control loop bandwidth, a duty ratio predictive control scheme based on linear extrapolation is proposed. The compensation effect and a comparison of the load variation transient response characteristics with analogy control, conventional digital control and duty ratio predictive control with different time delay values are performed on a point-of-load Buck converter by simulations and experiments. It is shown that, using the proposed technique, the control loop bandwidth can be increased by 50% for a one cycle delay and 48.2% for two cycles of delay when compared to conventional digital control. Simulations and experimental results prove the validity of the conclusion of the quantization effects of the time delay and the proposed control scheme.

Duty Ratio Predictive Control Scheme for Digital Control of DC-DC Switching Converters

Sun, Pengju,Zhou, Luowei The Korean Institute of Power Electronics 2011 JOURNAL OF POWER ELECTRONICS Vol.11 No.2

The control loop time delay caused by sampling, the zero-order-holder effect and calculations is inevitable in the digital control of dc-dc switching converters. The time delay will limit the bandwidth of the control loop and therefore degrade the transient performance of digital systems. In this paper, the quantization time delay effects with different time delay values based on a generic second-order system are analyzed. The conclusion that the bandwidth of digital control is reduced by about 20% with a one cycle delay and by 50% with two cycles of delay in comparison with no time delay is obtained. To compensate the time delay and to increase the control loop bandwidth, a duty ratio predictive control scheme based on linear extrapolation is proposed. The compensation effect and a comparison of the load variation transient response characteristics with analogy control, conventional digital control and duty ratio predictive control with different time delay values are performed on a point-of-load Buck converter by simulations and experiments. It is shown that, using the proposed technique, the control loop bandwidth can be increased by 50% for a one cycle delay and 48.2% for two cycles of delay when compared to conventional digital control. Simulations and experimental results prove the validity of the conclusion of the quantization effects of the time delay and the proposed control scheme.

Improvement of One-Cycle Controller Response with a Current Mode Controller

Ruzbehani, Mohsen,Zhou, Luowei,Mirzaei, Nasser The Korean Institute of Power Electronics 2010 JOURNAL OF POWER ELECTRONICS Vol.10 No.1

The most important feature of the one-cycle control method is its excellent ability in line disturbance rejection. However, when it is used as a controller in dc-dc converters, it has an undesirable transient response. The voltage overshoot at the transient time, which usually exists in one-cycle controlled converters, is unwanted in many applications and it is sometimes hazardous. In this paper, it is shown that the combination of a one-cycle controller with a current mode controller, can improve the transient response and consequently the overshoot can be controlled. Therefore, the combined controller has the excellent line disturbance rejection of a one-cycle controller and the output current limiting capability of current mode controllers. Because in this scheme a one-cycle controller is the master controller, the problem of instability of current mode control, will not happen. By simulation and a practical prototype, the capability of the method is shown.

Junction Temperature Prediction of IGBT Power Module Based on BP Neural Network

Wu, Junke,Zhou, Luowei,Du, Xiong,Sun, Pengju The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.3

In this paper, the artificial neural network is used to predict the junction temperature of the IGBT power module, by measuring the temperature sensitive electrical parameters (TSEP) of the module. An experiment circuit is built to measure saturation voltage drop and collector current under different temperature. In order to solve the nonlinear problem of TSEP approach as a junction temperature evaluation method, a Back Propagation (BP) neural network prediction model is established by using the Matlab. With the advantages of non-contact, high sensitivity, and without package open, the proposed method is also potentially promising for on-line junction temperature measurement. The Matlab simulation results show that BP neural network gives a more accuracy results, compared with the method of polynomial fitting.

High Step-Down Multiple-Output LED Driver with the Current Auto-Balance Characteristic

Luo, Quanming,Zhu, Binxin,Lu, Weiguo,Zhou, Luowei The Korean Institute of Power Electronics 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.4

A high step-down multiple-output LED driver is proposed in this paper. Firstly, the derivation of the driver with dual-output is presented and its operation principle and steady state performance are analyzed in detail. Secondly, a high step-down N-channel LED driver is proposed and its current auto-balance characteristic and step-down ratio are analyzed. Finally, an experimental prototype is built and the experimental results are given. The theoretical analysis and experimental results show that the proposed driver has the following virtues: First, if load balancing is achieved, the voltage gain is 1/N that of a Buck driver, where N is the number of channels. Second, each output automatically has an equal output current, without requiring more current close-loop control circuits than a Buck driver. Last, the voltage stresses of the switches and diodes are lower than those of a Buck driver, meaning that lower voltage switches and diodes can be used, and a higher efficiency can be expected.

Bandgap Engineering of Monolayer MoS2 under Strain: A DFT Study

Can Li,Bowen Fan,Weiyi Li,Luowei Wen,Yan Liu,Tao Wang,Kuang Sheng,You Yin 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.11

In this paper, density functional theory calculations are used to investigate the monolayer MoS2 in terms of the strain by analyzing the structure parameters: the bandgap, the density of states (DOS) and the Milliken charges. The calculations indicate that an increasing external stain tends to depress the ripple structure with a shorter S-S interlayer spacing and to enlarge the length of the Mo-S bond. Tensile strain dramatically alteres the bandgap; however, compressive strain almost does not. The change in the bandgap is explained by an analysis of the DOS, the partial density of states (PDOS), the structure parameters and the Mulliken charge distribution. The effects of strain on the Mulliken charge and the length of the Mo-S band cause bandgap differences under tensile and compressive strain.

Direct Current Control Method Based On One Cycle Controller for Double-Frequency Buck Converters

Quanming Luo,Shubo Zhi,Weiguo Lu,Luowei Zhou 전력전자학회 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.3

In this paper, a direct current control method based on a one-cycle controller (DCOCC) for double frequency buck converters (DF buck) is proposed. This control method can make the average current through the high frequency and low frequency inductors of a DF buck converter equal. This is similar to the average current control method. However, the design of the loop compensator is much easier when compared with the average current control. Since the average current though the high frequency and low frequency inductors is equivalent, the current stress of the high frequency switches and the switch losses are minimized. Therefore, the efficiency of the DF buck converter is improved. Firstly, the operation principle of DCOCC is described, then the small signal models of a one cycle controller and a DF buck converter are presented based on the state space average method. Eventually, a system block diagram of the DCOCC controlled DF buck is established and the compensator is designed. Finally, simulation and experiment results are given to verify the correction of the theory analysis.