introduction
With the continuous development of power electronics technology, the application of frequency conversion speed regulation technology in the field of industrial transmission is more and more extensive, especially the application of AC-DC-AC frequency conversion speed regulation.
The AC-DC-AC variable frequency speed control circuit includes a rectification and inverter part, wherein the inverter part is typically 6 switching units (IGBT or MOS tube), 3 upper and lower arms, and some with a braking unit of 7 Switch unit. Since the reference ground of the control trigger pulse signals of the three units of the upper arm is suspended, the trigger pulses generally need to be separated from each other by four sets of power sources (the upper arm 3 units are respectively powered, and the lower arm shares a set of power sources). Of course, if the software cooperates with the control and gives a charging pulse, the power supply of the three units of the upper arm uses a bootstrap circuit, and only one set of power sources can be used.
Only the case of using four sets of power supplies will be discussed here. The control auxiliary power supply of the inverter has three characteristics:
1) has multiple output voltages. The power supply described in this article has 5V, ±15V, four 16V trigger pulse power supplies, 12V bias power supply, and 24V total 9 output voltages. Among them, the 5V, ±15V output voltage is common, and the remaining output voltages are independent output voltages;
2) Four sets of pulse power supplies require better output voltage consistency and higher voltage regulation accuracy;
3) Four sets of pulsed power supplies are required to provide large instantaneous power, but the average power is small.
To meet the above requirements, it is simple and low-cost. It is a good choice to use the TOPSwitch series of American PI companies. TOPSwitch series products integrate MOS tube and PWM controller in one chip. The peripheral circuit is very simple. The power range covers several watts to hundreds of watts. The chip package is available in various forms. Some chips also have over-temperature and over-current. And input voltage overvoltage, undervoltage and other protection functions, can flexibly adapt to the design of many power supplies. PI also introduced auxiliary design software for the TOPSwitch family of products to allow users to quickly and accurately design the required power supply. When I was working on a servo controller project, the auxiliary power supply was designed with TOPSwitch products. As a typical example, the design method and key points are briefly introduced below.
Circuit not counted
Power supply design requirements
Input voltage VIN range: 180VAc ~ 240VAc. The output voltage amplitude and rated load are: Vo1: 5.8V, 1A; Vo2: 15V, 0.2A; Vo3: -15V, 0.2A; Vo4: 24V, 0.1A; Vo5 : 16V, 0.2A; Vo6: 16V, 0.1A; Vo7: 16V, 0.1A; Vo8: 16V, 0.1A; VBIA: 12V, 0.02A. Reliable operation, small space and low cost.
TOPSwitch device selection
In this power supply, Po=22.44w, the power supply works in the closed control cabinet. In order to work reliably, it should have protection measures such as over temperature, over current and input over and under voltage. After comprehensive consideration, we chose TOPSwitch-GX series. TOP243R device. When the input voltage is 230VAC±15%, the maximum output power of the device is 29W under the working environment of the adapter (corresponding to the closed environment), and there are protection functions such as over temperature, over current and input over and under voltage, “R†type. The package facilitates the use of the PCB copper layer to dissipate heat, eliminating the need for a heat sink.
High frequency transformer design
For the power supply design using the TOPSwitch series, PI has introduced PI Expert's auxiliary design software. As long as the input power supply design requirements, the software will quickly and accurately give the design results, including the recommended TOPSwitch series products, transformer cores and transformer primary and secondary winding parameters. However, the current version only supports up to 5 sets of secondary output windings. If the output windings are larger than 5 sets, the transformer winding parameters can be manually calculated as follows:
Where VACMIN is the minimum input AC voltage, Po is the output power, fL is the input line voltage frequency, tC is the bridge rectified conduction time, typically 3ms, η is the efficiency (generally 0.8), CIN is the input filter capacitor (general Take 2 to 3 times (μF) of the output power (w).
Where VOR is the reflected voltage. For the TOP2XX series devices, VOR ≤ 135V, here take 135V. When the VDS is the main switch, the voltage drop between the D and S terminals is 10V.
In the formula, KRP is the ratio of ripple current to peak current. In continuous operation mode, for 230VAC input, KRP ≥ 0.6, where KRP is 0.6.
Then fs is the working switching frequency, where fs=132KHz, then
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