О "критической" частоте преобразования двухзвенных преобразователей постоянного напряжения со звеном на основе инвертора тока

Abstract

Для двухзвенных преобразователей постоянного напряжения с первичным звеном на основе инвертора напряжения (ИН) на IGBT либо инвертора тока (ИТ) на IGBT с последовательным диодом, причем в ИН используется режим включения ключей в нулях напряжения и снабберного конденсаторного выключения, а в ИТ – выключения в нулях тока и снабберного дроссельного включения, введено понятие «критической» частоты. При частоте преобразования выше «критической», для ключей ИН, из за эффекта «хвоста» тока, статические потери и вместе с потерями выключения превышают статические потери ключей ИТ. Для преобразователей с IGBT различных производителей и предельных напряжений дана оценка величин «критических» частот.Purpose. For two-stage DC/DC converters with stage based on voltage source inverter (VSI) and two-stage DC/DC converters with stage based on current source inverter (CSI) the concept of the «critical» frequency was introduced. As VSI’s power switches the Insulated Gate Bipolar Transistors (IGBT) is used, its turn-on switching occur under Zero Voltage Switching (ZVS) and its turnoff switching occur by using the snubber capacitors. As CSI’s power switches the IGBT with series diode is used, its turn-off switching occur under Zero Current Switching (ZCS) and its turn-on switching occur by using the snubber reactor. For VSI’s power switches, the power loss in IGBT is determined by the IGBT conduction losses and turn-off losses. Due to the effect of the tail current the IGBT turn-off losses under capacitance snubber switching can be reduced by about half compared to the turn-off losses under hard switching, therefore losses will increase with increasing frequency. For CSI’s power switches, the power loss in IGBT and series diode is determined by only the IGBT and series diode conduction losses. To conversion frequencies above the «critical» the total conduction and turn-off losses under capacitance snubber switching in VSI switches exceed the total conduction losses in CSI switches (IGBT and series diode) (switching losses in CSI switches is negligible). The purpose of article is to evaluate values of «critical» frequency for DC/DC converters with IGBT of different vendors and different collector-emitter stress voltage. Methodology. When evaluating loss the data sheets for 180 IGBT modules Semikron, ABB, Westcode, Infineon, Mitsubishi were used. It was assumed that the nominal currents are switched, switched voltage equal to half of the collector-emitter stress voltage, the voltage across the CSI’s series diode is at operating temperature, the VSI switch turn-off energy is equal to half of the energy under hard switching and under operating temperature. Results. For devices with stress voltage 600 V a «critical» frequency have the range 30 - 80 kHz, with 1200 V - 10 - 20 kHz, with 1700 V - 4 - 5 kHz, with 2500 V – 1,3 – 2,5 kHz, with 3300 V – 1,3 – 2,2 kHz, with 4500 – 0,7 – 1,2 kHz and with 6500 V - 560 Hz. Originality. For two stage DC/DC converters with stage based on current source inverter with IGBT based power switches the approach to determining the appropriate frequency is offered. Practical value. It is proved that for two-stage DC / DC converters with the primary stage power switches based on IGBT, for values of power switches stress voltage more than 1700 - 2500 V, the use of CSI as the primary stage becomes attractive, because it allows to provide high enough value of conversion frequency - units of kilohertz.