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Vehicle High and Low Voltage Power Converter (DC/DC converter)


Pure Electric Vehicles’ power batteries could only provide relatively stable high-voltage DC power. It cannot meet different requirements of power supply of different in-car electric equipment. Thus an in-car power frequency converter patch is needed, such as a DC/DC frequency converter.

The key technology of DC / DC converter

The core function of the DC/DC converter is mainly realized by various related power topology circuits. There are many types of power topology circuits, mainly composed of several basic topologies and related derivative topologies. There are three basic power topologies: BUCK (buck type), BOOST (boost type) and BUCK-BOOST (inverting buck-boost). The circuit structure of the three basic topologies, the relationship between the input and output voltage and the duty cycle (Duty Cycle) and the main operating waveforms.

The above three basic topologies are all non-isolated topologies. After introducing a high-frequency transformer in the basic topological circuit, various corresponding isolated topologies are formed. Since the basic function of the on-board DC/DC converter is to convert the high voltage of the high-voltage power battery into the low voltage required by the low-voltage system (12V, 24V, 48V, etc.), the high and low voltage needs to be electrically isolated due to safety regulations. The DC/DC converter power system needs to adopt an isolated topology to achieve the electrical isolation required by the system.

Typical case of DC/DC converter

The main power circuit adopts a phase-shifted full-bridge topology to meet a wide input voltage range. The typical input range is 200-250V and 400-750V. At the same time, the output stage adopts a synchronous rectifier circuit to meet high-current and high-power applications, improve efficiency and improve thermal design.

The developing trends of DC/DC Frequency Converters

The developing trends of main technologies of in-car DC/DC converters focus on high-responsibility, wide temperature working range, waterproof and shake proof classes, radiation technologies, high transformation efficiency, high power density, smaller size and intelligent checking and so on. These could be described in detail from some aspects.

a) Integrated Design

In-car DC/DC converters will not be an independent unit in the future, it will be integrated with drive, PDU and OBC, the needs of 2-in-1, 3-in-1 and N-in-1 will be requested more and more. Therefore, the integration and modularization design of DC/DC converters will be the main developing direction in the future.

b) Improvement of Electrical Performance

The whole car’s requirement on in-car DC/DC converters’ power density grows rapidly, more power smaller size are the main goals.

c) Improvement of Electromagnetic Compatibility

In-car DC/DC converters’ main power open tube work in high-frequency open status during high-pressure environment which will becomes the source of electromagnetic interference. It is due to this, the EMC capacity must be improved instantly by soft open technology & filter design.

d) Needs of Telecommunications

In-car DC/DC converters’ signal telecommunications are turned from early analog control to today’s CAN telecommunications, online upgrade support, UDS and specific frame CAN recalling. They are more and more closer to the integration with VCU.

e) Optimization of Structure

The whole car’s requirements on in-car DC/DC converters’ shaking & protection level increases instantly, especially for N-in-1’s full sealing ability. At the same time, the inner radiation project also needs to be optimized from full glue filling to non-gluing processing to achieve the goal of lightweight design.

This is all of the week’s DC/DC frequency converter intro, in next few weeks, we will continue provide detailed intros on electric vehicles’ patches.

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