10 points of attention in the development of switching power supply technology

In the 1960s S, the advent of the switching power supply gradually replaced the linear regulated power supply and SCR phase-controlled power supply. Over the past 40 years, the switch power supply technology has developed and changed rapidly, and has gone through three stages of development: power semiconductor devices, high frequency and soft switch technology, and Integration Technology of switching power supply systems.

Power semiconductors have evolved from bipolar devices (BPT, Scr, and GTO) to MOS devices (such as power MOSFET, IGBT, and IGCT), making the power electronic system possible to achieve high frequency, and greatly reduce the conduction loss, the circuit is also simpler.

Since the 1980s s, the development and research of high-frequency and soft-switch technologies have improved the performance, lighter weight, and smaller size of the power converter. High frequency and soft switch technology have been one of the hot topics in international power electronics research over the past 20 years.
In the middle of the 1990s S, the integrated power electronic system and integrated power electronic module (ipem) technology began to develop. It is one of the new problems that need to be solved urgently in the international power electronics industry.

Focus 1: Performance of Power Semiconductor Devices

In 1998, infineon launched a cold MOS tube, which adopts a "super-junction" structure and is also called an ultra-junction power transistor. Working voltage: 600v ~ 800 V, the on-state resistance is almost reduced by an order of magnitude, and the switching speed is still fast. It is a promising high-frequency power semiconductor device.

When the IGBT appears, the voltage and current values are only 600 V and 25a. For a long period of time, the pressure level is limited to limit V ~ After a long period of research and improvement, the voltage and current ratings of IGBT have reached 1700 V/1200a and 3300 V/1800a, respectively, the single-chip voltage of high-voltage IGBT has reached 6500 v. Generally, the maximum operating frequency of IGBT is 20 kHz ~ A 40 kHz IGBT manufactured based on a new technology in the passthrough (PT) structure. It can work at 150 kHz (hard switch) and 300 kHz (soft switch ).

The Technical Progress of IGBT is actually a compromise between the on-demand voltage drop, fast switch and high voltage capacity. Along with the technological and structural forms, IGBT has been developing in the history of 20 years. It has the following types: pass-through (PT) type, non-pass-through (treaty) type, and SPT type) type, groove type, and electric field cutoff (FS) type.

Silicon carbide SiC is an ideal material for power semiconductor devices. It has the following advantages: high bandwidth and operating temperature (up to 600 ℃) good thermal stability, low on-going resistance, good thermal conductivity, extremely small leakage current, and High PN junction pressure resistance are conducive to the manufacture of high-frequency high-power semiconductor devices with high temperature resistance.

It is foreseeable that silicon carbide will be the most likely new power semiconductor device material to be successfully applied in the 21st century.

Focus 2: Switch Power Density

Increasing the power density of the switch power supply to make it small and lightweight is the goal of people's constant efforts. The high frequency of power supply is one of the hot topics in the international power electronics industry. Power miniaturization and weighting are especially important for portable electronic devices (such as mobile phones and digital cameras. The specific methods to make the switching power supply miniaturized are as follows:

First, high frequency. To achieve high power density of the power supply, the working frequency of the PWM converter must be increased to reduce the volume and weight of energy storage components in the circuit.

Second, piezoelectric transformers are used. The Application of piezoelectric transformer can enable high-frequency power converter to achieve light, small, thin and high power density. The piezoelectric transformer transmits energy by using the special "Voltage-vibration" transform and "vibration-voltage" transform of piezoelectric ceramic material. Its Equivalent Circuit is like a series-parallel resonance circuit, it is one of the hot topics in power transformation.

The third is the use of new capacitors. In order to reduce the volume and weight of power electronic devices, efforts must be made to improve the performance and energy density of capacitors, and to develop new capacitors suitable for Power Electronics and power supply systems, large capacitance, small equivalent series resistance, and small size are required.

Focus 3: High-Frequency Magnetic and Synchronous rectification technology

A large number of magnetic components are used in power supply systems. The material, Structure and Performance of High-frequency magnetic components are different from those of power frequency magnetic components, and many problems need to be studied. The magnetic materials used for high-frequency magnetic components have the following requirements: Low Loss, good heat dissipation, and superior magnetic properties. Magnetic materials suitable for megahertz frequencies are widely used, and nano-crystalline soft magnetic materials have also been developed and applied.

After high frequency conversion, soft switch technology must be developed and applied to improve the efficiency of the switching power supply. It is a hot topic in the international power supply field in the past few decades.

For low-voltage and high-current output soft-switch converters, the way to further improve their efficiency is to reduce the switching mode loss. For example, the Synchronous rectification Sr technology, that is, the switching diode with the power MOS tube as the rectification, can replace the Xiao Yi diode (SBD), can reduce the tube pressure drop, thus improving the circuit efficiency.

Focus 4: distributed power supply structure

The distributed power supply system is suitable for the power supply of large workstations (such as processing stations) and large digital electronic exchange systems composed of ultra-high-speed integrated circuits. Its advantages are that it can implement modular DC/DC converter components; it is easy to achieve n + 1 Power redundancy, improve the system availability, expand the load capacity, reduce the current and voltage drop on the 48 V bus, and achieve even heat distribution and facilitate the design of heat dissipation; transient Response is good; Failure modules can be replaced online.

The distributed power system has two types of structures: one is two-level structure and the other is a three-level structure.

Focus 5: PFC Converter

Because the input end of the AC/DC Conversion Circuit has a rectifying element and a filtering capacitor, when the sine voltage is input, the power factor of the single-phase rectifying power supply is only 0.6 ~ 0.65. With the PFC (Power Factor Correction) converter, the network-side power factor can be increased to 0.95 ~ 0.99, the input current thd is less than 10%. It not only controls harmonic pollution of the power grid, but also improves the overall efficiency of the power supply. This technology is called Active Power Factor Correction. APFC single-phase APFC was developed earlier at home and abroad, and the technology is mature. Although there are many topology types and control strategies of Three-phase APFC, however, further research and development are still pending.

Generally, the High Power Factor AC/DC switching power supply is composed of two-level topology. For low-power AC/DC switching power supply, the two-level topology is used with low overall efficiency and high costs.

If the input power factor is not particularly high, the PFC converter and the subsequent DC/DC converter are combined into a topology to form a single-stage High Power Factor AC/DC Switching Power Supply. Only one main switch is used, this topology enables correction of the power factor to more than 0.8 and adjustable the output DC voltage. It is called a single-tube single-stage s4pfc converter. Focus 6: VRM of Voltage Regulator Module
Voltage Regulator Module is a low voltage, high current output DC-DC converter module, to provide power to the microprocessor.

The speed and efficiency of data processing systems are increasing. To reduce the electric field strength and power consumption of microprocessor IC, the logic voltage of the new generation microprocessor must be reduced to 1 v, the current is as high as 50a ~ 100a, so VRM requirements are: low output voltage, large output current, high current change rate, fast response, etc.

Focus 7: Full Digital Control

The control of the power supply has been completed by analog control and mixed control of modules. Full Digital Control is a new trend and has been applied in many power conversion devices.

However, in the past, digital control was rarely used in DC/DC converters. Over the past two years, high-performance, all-digital control chips for power supply have been developed and the cost has been reduced to a reasonable level. Many companies in Europe and the United States have developed and manufactured digital control chips and software for switching/switching converters.

The advantage of full digital control is that digital signals can be calibrated to a smaller volume than mixed modulus signals, and the chip price is lower. accurate digital correction can be performed on current detection errors, voltage Detection is also more accurate; it can achieve fast and flexible control design.
Focus 8: Electromagnetic Compatibility

The electromagnetic compatibility of high-frequency switching power supply has its own special characteristics. The DI/dt and dv/dt produced by the power semiconductor switch during the switching process lead to powerful electromagnetic interference and harmonic interference. In some cases, strong electromagnetic field (usually near-field) radiation may occur. It not only seriously polluted the surrounding electromagnetic environment, but also caused electromagnetic interference to nearby electrical equipment, and may also endanger the safety of nearby operators. At the same time, the Internal Control Circuit of the Power Electronic Circuit (such as the switch/switch converter) must be able to withstand the EMI produced by the switch action and the interference of the field electromagnetic noise. The above particularity, coupled with the specific EMI measurement difficulties, has many cutting-edge topics in the field of Electromagnetic Compatibility of power electronics. Many universities at home and abroad have carried out research on electromagnetic interference and electromagnetic compatibility of power electronic circuits, and have made many gratifying achievements. The research results in recent years show that the electromagnetic noise source in the switch/switch converter mainly comes from the voltage and current changes caused by the switch function of the main switch device. The faster the change speed, the greater the electromagnetic noise.

Focus 9: Design and Testing Technologies

Modeling, simulation, and CAD are new design tools. To simulate a power supply system, we must first establish a simulation model, including power electronics, converter circuits, digital and analog control circuits, as well as magnetic components and magnetic field distribution models, the thermal model, feasibility model, and EMC model of the switch are also considered. Various models vary greatly. The development direction of modeling is: digital-analog hybrid modeling, Hybrid Hierarchical modeling, and the formation of various models into a unified multi-level model.

Power System CAD, including main circuit and control circuit design, device selection, parameter optimization, magnetic design, thermal design, EMI design and printed circuit board design, availability estimation, computer-aided synthesis and optimization design. Using a simulation-based Expert System for Power Supply System CAD can optimize the designed system performance, reduce design and manufacturing costs, and perform manufacturing analysis, it is one of the development directions of simulation and CAD technology in the 21st century. In addition, the development, research and application of technologies such as thermal testing, EMI testing, and availability testing of power supply systems should also be vigorously developed.

Focus 10: System Integration Technology

The manufacturing features of power supply equipment are: many non-standard parts, high labor intensity, long design cycle, high cost, low availability, etc, the user requires that the power products produced by the manufacturing plant be more practical, more practical, more flexible, less costly. These situations make power supply manufacturers under great pressure and urgently need to carry out research and development of integrated power supply modules, the goal is to standardize, modularize, manufacture, produce in scale, and reduce costs of power supply products.

In fact, the development of power supply integration technology has already gone through the development stages of power semiconductor device modularization, power and control circuit integration, and integration of passive components (including magnetic Integration Technology. In recent years, the development direction is to integrate a small power supply system into a single chip, which can make the power supply products more compact, smaller in size, and reduce the lead length, thus reducing the parasitic parameters. On this basis, integration can be realized, and all components, together with control protection, can be integrated into one module.

In the 1990s s, with the development of large-scale distributed power supply systems, the concept of integrated design was promoted to the integration of power supply systems with larger capacity and higher voltage, improving the integration level, an integrated power electronics module (ipem) emerged ). Ipem integrates Power Devices with circuit, control, detection, and execution components to obtain standard and manufacturing modules. It can be used for both standard design and special design. The advantage is that it can quickly and efficiently provide products to users, significantly reducing costs and improving availability.
In short, power system integration is one of the new problems that need to be solved in the international power electronics industry.

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10 points of attention in the development of switching power supply technology