196 Series MCU in the use of air conditioner inverter （part 2）

196 Series MCU in the use of air conditioner inverter （part 2）




2 air-conditioning inverter main circuit



Air conditioner inverter mainly consists of the following components:



2.1 Main circuit



It is in the form of DC / AC power inverter circuit. Input voltage DC600V, through the input contactor, pre-charging circuit, supporting the supply capacitor inverter. SIEMENS of Germany the main switching devices use the company's two units IGBT modules, together with the output filter circuits inverter air conditioning. Output isolation transformer used to be three-phase four-wire power.



2.2 Control Circuit



N87C196MC microprocessor and peripheral chips constitute a small amount of power control circuit is very simple. SCM produces three-phase 6-channel SPWM signal, while completing the input voltage, output voltage, input current and other sampling, detection protection, blocking SPWM pulse signal, protecting IGBT functions.



2.3 Drive Circuit



Inverter drive circuit to drive adoption of Japanese Mitsubishi IGBT designed for application specific integrated circuit M5 7962L, plus a small amount of external components constitute. SPWM signal output N87C196MC amplified through the external circuit directly to the drive module, driver module to directly drive IGBT tube, maximum driving 400AIGBT. When M57962L detected IGBT tube C, E voltage is high and 8V, and the IGBT tube opened at this time when the duration is greater than 2.5 μ s, then the issue of fault signals, while the blockade drive waveform, and the issue of fault signal to the N87C196MC , microcontroller interrupt generated EXTINT blockade separate ways SPWM signals, high-speed turn-off IGBT.



3 Software Design



Software is the core of the whole control system, all the circuits are software services, which determines the performance of inverters, such as the output voltage stability, the output harmonic content.



The output voltage value, current limit values by the Swiss company LEM Hall sensors to detect, after compilation to protect the circuit and N87C196MC, by N87C196MC on-chip A / D converted into digital channels. The output voltage for a given value as a basis for computing as a regulator.



4 Experimental results and conclusions



In accordance with the above circuit has produced a three-phase 35kVA air-conditioning power supply. The main parameters are input DC600V, three-phase output 380V/50HZ. Take carrier frequency 6kHz, no signal time of 2.5 μ s. With output filter (filter capacitor 50 μ F, inductance O.6mH) after the output voltage, using the power analyzer FLUKE test, total harmonic content of 3%, efficiency 97%.



Experiments show that the inverter air-conditioning in the development process, using INTEL's MCS N87C196MC, the entire control circuit only add a small amount of peripheral devices, compact structure, reduce costs and improve reliability. The test to obtain a relatively good result. At the same time, simply by changing the software, the system can be used for single-phase inverter power source, the application is very flexible, so authors believe that N87C196MC MCU in the motor control field dragging a good practical value.



To learn more about power inverter, please visite http://www.szpowerinverter.com/ and http://www.bestekltd.com/, or mail to sale38@0102.cn.