资料来源: Bazzi, 康涅狄格州大学电气工程系, 斯托斯, CT。
dc/dc 转换器是将直流电压和电流从一定的电平转换到另一个电平的电力电子转换器。通常情况下, 电压转换是 dc/dc 转换器的主要用途, 在单个转换器中存在三种主要转换类型: 向上、向下、向上或向下。其中最常见的步进转换器是升压转换器 (参考此集合视频: dc/dc 升压转换器), 而最常见的步进转换器是降压转换器。(请参阅此收藏视频: dc/dc 降压转换器。降压升压转换器也经常执行步进和步下功能, 和反激转换器可以被认为是特殊类型降压升压转换器, 在电气隔离是实现之间的输入和输出端口。(请参阅此集合视频: 反激转换器。
dc/dc 转换器拓扑众多, 它们的控制、建模和操作改进 (如效率、可靠性、性能等) 都是持续关注的领域。该实验提供了一个非常灵活的工具, 研究和分析的性能的升压, 降压, 和反激式转换器, 所有在一个单一的板 HiRel 电源杆板。
本实验的目的是介绍 HiRel 系统中的功率极板的主要部件和性能, 这是在三的 dc/dc 变换器实验中使用的电路板。
A PWM pulse is expected to be seen on the oscilloscope screen. The duty cycle is a major control variable for DC/DC converter as it adjusts the period during which a MOSFET or any other semiconductor actively-controlled switch is on. All input-output voltage relationships of DC/DC converters rely on the value of this duty ratio, along with some other variable in some converter topologies.
The switching frequency is critical in component selection as the maximum operating frequency of components varies by component type and design. Higher switching frequencies typically yield smaller voltage and current ripples but require larger capacitors and inductors.
DC/DC converters are very common in DC power supplies used to charge electronics, and to supply power to many other electronic circuits. For example, any motor drive will require some smaller DC power supplies to power its low-power electronics, protection circuits, and high-power gate drives. Computer processors and other peripherals and accessories require very well-regulated DC voltages that are provided by DC power supplies. Renewable energy systems, e.g. solar photovoltaic panels, require DC/DC converters to regulate the DC output voltage of the panels, since solar irradiance and ambient temperature vary causing variation in the solar panel's voltage and current outputs. Many more industrial, transportation, military, and other applications use DC/DC converters instead of linear regulators due to their high efficiency, high performance, and excellent regulation.
The HiRel Power Pole Board is a tool for studying and analyzing the performance of simple DC-DC converter circuits. DC-DC converters take DC voltage inputs and produce DC voltage outputs with a different value. For example, boost converters step up voltage, while buck converters step down voltage. These converters can be assembled and tested on a bread board, but can be evaluated more simply using a pre-made demonstration board, such as the HiRel Systems Power Pole Board. This video will introduce the major components and capabilities of the Power Pole Board, which is used in experiments with boost, buck, and flyback converters in this collection.
The HiRel Power Pole Board has five major sections. The first is the primary side, which has filter capacitors that are used in the converter circuits, a sensor for measuring current through the circuit, and connectors V1 and COM that connect to a DC voltage source or a load. The second section is the secondary side, which also has filter capacitors and a current sensor. This section has connectors labeled V2 and COM that connect to a DC voltage source or a load. Here the load is shown as a planar power resistor. For the DC-DC converter experiments in this collection, the load is a power potentiometer, which can be adjusted based on the requirements of the circuit and test. Depending on the converter typology, one of these two sections acts as the input side, connected to a DC voltage source, while the other is the output side that is connected to a load. The third section is the power pole, which contains the components at the core of the DC-DC conversion process. The power pole has two metal oxide semiconductor field effect transistors, or MOSFETs, and two diodes. The upper MOSFET and upper diode are mounted back to back on a single heat sink. Similarly, the lower MOSFET and lower diode are mounted on one heat sink. Also included in this section are gate drivers that convert a switching signal to the voltage levels that turn the MOSFETs on and off. The fourth section has connections for a daughter board, which carries a magnetic component, such as an inductor or transformer. Two daughter boards are used for the DC-DC converter experiments: the BB board and the flyback board. The fifth section contains electronics that generate switching pulses for the MOSFETs and provide over-current and over-voltage protection for the circuit. An external DC power supply can be connected to the HiRel Power Pole Board through a DIN connector. Main Switch S90, which is next to the DIN connector, turns on power to all of the low power circuits on the board. Now that we’ve seen the main sections of the HiRel Power Pole Board, let’s set up the board and show how it will be used in DC-DC converter circuits.
Before using the Power Pole Board, it must be configured to generate switching pulses for the MOSFETs. First, plug the external DC power supply into the DIN connector. Then, turn on Main Switch S90. The green LED by Switch S90 illuminates to indicate that power is applied to the board. Locate selector switch bank S30 and set the first switch to TOP FET. With this setting, the pulses that turn the MOSFETS on and off control the upper MOSFET. If this switch is set to BOTTOM FET, the pulses control the lower MOSFET. Now, set the second switch to PWM Internal. In this position, pulse with modulated signals generated on the board turn the selected MOSFET on and off. If this switch is set to PWM External, then an external source, like a function generator or microcontroller controls the MOSFET.
Connect a 10X probe to Channel 1 of an oscilloscope. Clip the probe’s ground lead to the ground terminal of the board and the probe tip to the PWM terminal. To see the offset of the pulse with modulated signal, set Scope Channel 1 for DC coupling. The oscilloscope screen should show a train of pulses to the driver for the upper MOSFET. Check the control signal directly by removing the probe tip from the PWN terminal and clipping it to the gate terminal by the upper MOSFET. A pulse train should be visible on the scope. Clip the probe tip to the PWM terminal again. The duty ratio of this pulse train determines the on time of the MOSFET as a percentage of the period. This duty ratio is a major control variable because it affects the relationship between a DC-DC converter’s input and output voltages. To change the duty ratio of the pulse with modulated signal, adjust potentiometer RV64. The duty ratio may be varied from zero to one. Because a component’s maximum operating frequency by type and design, the switching frequency is a critical parameter in the performance of DC-DC converters. In addition, higher switching frequencies typically yield smaller output voltage and current ripples for a given combination of capacitor and inductor. Change the frequency of the pulse with modulated signal by adjusting potentiometer RV60. Observe how the number of pulses on the oscilloscope screen increases or decreases as the potentiometer is adjusted. Next, set the first switch of selector switch bank S30 to BOTTOM FET. Remove the probe tip from the PWM terminal and clip it to the gate terminal by the lower MOSFET. Finally, confirm that the gate of the lower MOSFET receives the switching pulse.
Because of their high efficiency and excellent regulation, DC-DC converters are used in many commercial applications. Three common converters are introduced here and covered in subsequent videos in this collection. Boost converters generate a DC output voltage that is greater than the DC input, therefore boosting up the supply voltage. The video “DC/DC Boost Converter” explains the operation of boost converters, accompanied by experiments using the HiRel Power Pole Board. Buck converters generate a DC output voltage that is less than the input. In other words, buckling down or decreasing the supply voltage. The video “DC/DC Buck Converter” discusses how buck converters work and demonstrates their use with experiments on the HiRel Power Pole Board. Flyback converters generate a DC output voltage that can be either greater than or less than the DC input. Please watch the video “Flyback Converter” to see how they are derived from the joining of a buck converter with a boost converter to obtain the behavior of both.
You’ve just watched Jove’s introduction to the HiRel Power Pole Board. You should now understand the design of the board, how to set it up, and how to use it for experiments with DC-DC converter circuits. Thanks for watching!
