Luowei Zhou

Unified constant-frequency integration control of active power filters-steady-state and dynamics

An active power filter (APF) is a device that is connected in parallel to and cancels the reactive and harmonic currents from a group of nonlinear loads so that the resulting total current drawn from the AC mains is sinusoidal. This paper presents a unified constant-frequency integration (UCI) APF control method based on one-cycle control. This method employs an integrator with reset as its core component to control the pulse width of an AC-DC converter so that its current draw is precisely opposite to the reactive and harmonic current draw of the nonlinear loads. In contrast to previously proposed methods, there is no need to generate a current reference for the control of the converter current, thus no need for a multiplier and no need to sense the AC line voltage, the APF current, or the nonlinear load current. Only one AC current sensor is used to sense the AC main current and one DC voltage sensor is used to sense the DC capacitor voltage. The control method features constant switching frequency operation, minimum reactive and harmonic current generation, and simple analog circuitry. It provides a low cost and high performance solution for power quality control. Steady-state and dynamic study is presented in this paper. Design example is given using a two-level AC-DC boost topology. A prototype was developed to demonstrate the performance of the proposed APF. This control method is generalized to control a family of converters that are suitable for APF applications. All findings are supported by experiments and simulation.

A novel active power filter based on the least compensation current control method

A new least compensation current technique to detect the harmonic and reactive current for active power filters is presented in this paper. With the technique, a novel active power filter based on the least compensated current control is proposed, in which the measurement of harmonic and reactive current and the generation of compensated current are completed in the same closed-loop. Compared with the existing control methods of active power filter, the proposed method has simpler structure, quicker dynamic, higher reliability and better compensation performance. Simulating and experimental results are provided that verified theoretical predictions and demonstrate the effectiveness of the proposed control method and circuit configuration.

DC Link Active Power Filter for Three-Phase Diode Rectifier

In this paper, a dc link active power filter (APF) for three-phase diode rectifier is proposed. The proposed dc link APF, which is composed of two series-connected bidirectional boost converters, intends to eliminate the input current harmonics. It is paralleled at the dc link of the diode rectifier and is coupled to the ac input with three line-frequency switches. Compared with the full power processed power factor correction (PFC) solution, the dc link APF is partially power processed in that it only compensates for the harmonic current component at the dc link. Thus, it features with lower power processing. Moreover, it exhibits better total harmonic distortion of the ac line current when compared with the traditional ac side shunt APF. Voltage and current loop models are developed for average current control, and the selection of the current loop bandwidth is presented. Switching stresses of the ac APF, the dc link APF, and the six-switch PFC are also calculated and analyzed. Experimental and simulation results demonstrate the effectiveness of this dc link APF.

Double-Frequency Buck Converter

Improving the efficiency and dynamics of power converters is a concerned tradeoff in power electronics. The increase of switching frequency can improve the dynamics of power converters, but the efficiency may be degraded. A double-frequency (DF) buck converter is proposed to address this concern. This converter is comprised of two buck cells: one works at high frequency, and another works at low frequency. It operates in a way that current in the high-frequency switch is diverted through the low-frequency switch. Thus, the converter can operate at very high frequency without adding extra control circuits. Moreover, the switching loss of the converter remains small. The proposed converter exhibits improved steady state and transient responses with low switching loss. An ac small-signal model of the DF buck converter is also given to show that the dynamics of output voltage depends only on the high-frequency buck cell parameters, and is independent of the low-frequency buck cell parameters. Simulation and experimental results demonstrate that the proposed converter greatly improves the efficiency and exhibits nearly the same dynamics as the conventional high-frequency buck converter. Furthermore, the proposed topology can be extended to other dc-dc converters by the DF switch-inductor three-terminal network structure.

Monitoring Potential Defects in an IGBT Module Based on Dynamic Changes of the Gate Current

Potential defects inside an insulated gate bipolar transistor (IGBT) module can be seen as precursors of being about to wear out, and are important for health monitoring of the IGBT module which is used to enhance reliability. A method for detecting defects in the IGBT module by identifying dynamic changes of the gate current is presented in this paper. It is based on the fact that parasitic elements inside the IGBT module are affected by local damage induced by aging over time, and subsequently, these influences are easily distinguished by dynamic changes of the gate current. The proposed prognostic approach is based on relevance vector machine framework, which can give accurate predictions and allow operators to observe unhealthy IGBT modules inside a power converter, and then take appropriate measures timely to avoid breakdown. The parasitic elements involved in the gate circuit are extracted, and their contributions to dynamic changes of the gate current are also discussed. Finally, a confirmatory experiment is carried out, and the correctness of the proposed method is verified.

An LED Driver With Dynamic High-Frequency Sinusoidal Bus Voltage Regulation for Multistring Applications

In order to obtain sufficient luminance and achieve high reliability, light-emitting diodes (LEDs) are usually arranged in parallel strings in many high-power applications. Since current imbalance should be avoided among the parallel LED strings, a multichannel constant current LED driver with dynamic high-frequency sinusoidal voltage regulation is proposed in this paper. The proposed driver is composed of one resonant inverter and several LCL-T resonant rectifiers. The number of the rectifiers equals to that of the LED strings. The rectifier whose output current is sensed and closed-loop controlled is called master rectifier and all the others slave rectifiers. The resonant inverter is used to convert dc voltage into high-frequency sinusoidal bus voltage and the LCL-T resonant rectifiers are included to drive LED strings with constant current. The amplitude of the high-frequency sinusoidal bus voltage is dynamically regulated to ensure the output current of the master resonant rectifier to be constant by a closed-loop controller. Since the output current of the slave rectifier is linear with the amplitude of the bus voltage as the master rectifier, there are not any auxiliary circuits included in the slave rectifier while the output current balancing is achieved. Finally, a 200-W prototype with one master and fifteen slave rectifiers is built to verify the performance of the proposed driver.

An Active Clamp High Step-Up Boost Converter with a Coupled Inductor

An active clamp high step-up boost converter with a coupled inductor is proposed in this paper. In the proposed strategy, a coupled inductor is adopted to achieve a high voltage gain. The clamp circuit is included to achieve the zero-voltage-switching (ZVS) condition for both the main and clamp switches. A rectifier composed of a capacitor and a diode is added to reduce the voltage stress of the output rectifier diode. As a result, diodes with a low reverse-recovery time and forward voltage-drop can be utilized. Since the voltage stresses of the main and clamp switches are far below the output voltage, low-voltage-rated MOSFETs can be adopted to reduce conduction losses. Moreover, the reverse-recovery losses of the diodes are reduced due to the inherent leakage inductance of the coupled inductor. Therefore, high efficiency can be expected. Firstly, the derivation of the proposed converter is given and the operation analysis is described. Then, a steady-state performance analysis of the proposed converter is analyzed in detail. Finally, a 250 W prototype is built to verify the analysis. The measured maximum efficiency of the prototype is 95%.

Junction temperature management of IGBT module in power electronic converters

Abstract IGBT power module is the key component of the power electronic converter, but it has the lowest reliability. The junction temperature is the crucial factor which affects power module’s reliability. To some extent, the power handling capability of the converter depends on the thermal stress of the power module. Thermal management is an effective method to improve the reliability of power device, as well as enhance the power capability. For this purpose, this paper introduces the reliability design to the power converter’s traditional compensation controller design for the first time. A new concept of generalized dual-loop controller, which includes temperature control loop and electric power control loop, is proposed. The reliability and stability of the system are both considered, with the help of the hybrid controller, the power converter can operate steadily with higher reliability. The novelty of this paper is to improve the thermal control method of carrier frequency adjustment through experimental implementation during the full life cycle of the converter. The target is to control the temperature variation to be almost a constant value as well as extend the lifetime of the converter. IR sensor is used to measure the chip temperature of the unpackaged IGBT module. The temperature variation and the average temperature are all considered in thermal management, from the reliability improvement point of view. At last, the idea is digital implemented based on a varying load of power inverter system with real-time measurement of the chip’s surface temperature.

A Reconfigurable Structure DC–DC Converter With Wide Output Range and Constant Peak Power

This paper presents a reconfigurable structure dc-dc converter with wide output range and constant peak power (RS-WOCP). This converter is an extension of the traditional isolated dc-dc converter with two output channels by adding an active switch and two diodes. Theoretical analysis indicates that the proposed RS-WOCP converter is able to smoothly reconfigure the output channels in parallel or series to realize wide output voltage range. With this approach, the output voltage is shared equally in the series operating mode and so is the output current in the parallel operating mode. Therefore, the power rating of devices is significantly reduced and the output rectifiers and filters can distribute power losses and thermal stresses. Operating principle, control strategy, modeling, and stability analysis are illustrated in this paper. An experimental prototype of a 200-W DSP-based RS-WOCP converter was built. The experimental results have verified the steady-state performance and fast dynamic response in the whole output voltage range. Comparisons with two close relatives of wide output converters show that the proposed RS-WOCP converter is advantageous for wide output range constant peak power applications.

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

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.