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附录B 外文原文
Wireless Monitoring of Semiconductor Switches Temperatures in a DC-DC Converter for Power LED Lighting
Wojciech WOJTKOWSKI
Bialystok University of Technology, Electrical Department, Wiejska Street 45D, 15-351 Bialystok, Poland
Keywords: LED lighting, 1-Wire bus, DC/DC converter, IoT, Node-RED, Temperature monitoring system, Wireless measurements.
Abstract. The paper presents a wireless temperature monitoring system of a half bridge resonantDC/DC converter for power LED lighting. The proposed system allows for remote monitoring of fourtemperatures, but the number can be increased if necessary. The temperature monitoring console isavailable on any device connected to the local Wi-Fi network or to the Internet. By implementing thewireless remote monitoring, all important temperatures of the working converter can be monitoredfrom any place with the Internet access. The presented solution is useful in laboratories developingnew topologies of power converters that should be monitored and tested for a long time before anypractical implementation.
Introduction
The semiconductor switches are important in modern power electronic systems. Their condition has huge influence on the overall power system performance and can cause a systemrsquo;s damage in a worst case. One of the most important parameters, which gives information about their condition and which can be relatively easily observed on-line during the system operation, is the temperature of the power semiconductor switches [1]. The power semiconductor devices typically operate in thermally stressful conditions. Temperature is generally considered to be a key parameter in the design of any electronic equipment, and cautions concerning temperature and its relationship to reliability are widely documented [2, 3, 4]. The increasing junction temperature of a power semiconductor device isdirectly related to the increasing power losses and can lead to semiconductor failures [1, 2]. Risingtemperature also decreases the region of the safe operating area of the semiconductor device.Monitoring of the temperature is therefore important for optimal operation and for reliability reasons.If the switch temperature is known during the system operation, the real-time control systems can bedeveloped to improve the reliability.
The most popular methods for estimation of the temperature of the power semiconductor devices ina operating power system using thermo-sensitive electrical parameters are discussed in [3]. The methods are based on measurements of specific parameters like: the transistor threshold voltage, the gate-emitter voltage of IGBT transistors, the collector-emitter voltage under low current levels, the voltage under high current levels, the switching times and the saturation current. Generally all these methods have different characteristics in terms of linearity, sensitivity, calibration needs, accuracy and truly important possibility of calculating the temperature during operation of the power converter. The most suitable method of the semiconductor temperature estimating is measuring of the collector-emitter voltage during conduction of low currents [4]. The impact of temperature on the switching speed indicates that the current switching rate is an effective TSEP (temperature sensitive electrical parameter) for higher current rated devices but there is necessary a sacrifice in the switching speed for enabling the ability of estimating the junction temperature. In particular case it may be a important disadvantage. Authors in [5] propose using of an IR camera for the junction temperature evaluations in a power IGBTs. It seems interesting and can be useful in practice but it is a relatively expensive solution and needs special software to recognize separate temperatures of each monitored switch. Additionally, an automatic control of the power converter may be complicated. There are also
known methods based on the optical fibers [6, 7]. Generally the temperature measurements of power semiconductor devices are important in wide range of applications [8, 9, 10, 11, 12]. The presented solution allows for detection of abnormal states and gives the possibility to test the maximal output power of the monitored system thanks to the temperature monitoring possibility. The system can be extended to monitor temperatures of power LEDs as well. This is crucial in laboratories developing new topologies of power converters for LED lighting that should be monitored and tested for a relatively long time before any practical implementation. The proposed monitoring system is based on digital temperature sensors. The sensors are connected to a single-board microcomputer operating Node-RED based dashboard for the remote control.
The DC-DC Converter Operation Principle
The converter scheme is shown in Figure 1. The main transistors S1 and S2 operate with constantswitching frequency. The Cs1 and Cs2 capacitors improve the turn-off process of the main transistors.The auxiliary So1 and So2 transistors conduction time controls the converter output power. The Ds1and Ds2 diodes should have a possibly short recovery time. The auxiliary So1 and So2 transistorsshould act as unidirectional switches, so the MOSFET transistors are connected in series with theexternal diodes. During conduction states of these transistors, the resonant capacitor Co voltage isequal to zero, and because of that they are switched with zero voltage conditions. Depending onrelation between the equivalent load resistance Ro, resonant circuit parameters and the ratio ofswitching to resonant frequency, the converter may work as a current source which is important forthe power LED lighting [13, 14, 15, 16, 17, 18].
Figure 1. The converter scheme.
When the converter operates as a current source, the capacitance Cf has
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