In recent years, with the economic development and the improvement of people's living standards, the central air-conditioning system has developed very rapidly in China, and the variable air volume (VariableAirVolume) air-conditioning system has gradually become the development direction of central air-conditioning due to its own advantages. The variable air volume air conditioner realizes indoor temperature control by adjusting the air supply volume of the fan. In order to meet the requirements of intelligent control of buildings and improve comfort and energy saving, the frequency conversion speed regulation technology is replacing the traditional methods such as windshield and multi-speed motor. .
However, the function setting and operation method of the general-purpose inverter are not completely suitable for the requirements of the air-conditioning system, so that many functions are not fully utilized, and in the use, secondary development is often required, and in view of this, we have developed Air-conditioning system fan-specific inverter with temperature controller.
This paper introduces the software and hardware design of the temperature-controlled special frequency converter of air-conditioning fan based on 80C196KC single-chip microcomputer. The implementation method of voltage space vector PWM when using 80C196KC single-chip microcomputer is discussed. The software design method to ensure the accuracy of PWM waveform is discussed.
1The hardware structure and function of the temperature-controlled inverter The inverter adopts the AC-over-voltage structure. The main circuit consists of a diode rectifier, a filter and an inverter circuit. The inverter circuit uses IPM intelligence with built-in drive and protection circuit. Power module. The control circuit is based on the 80C196KC single-chip microcomputer. The peripheral circuits mainly include keyboard display circuit, dead time formation and pulse output circuit, temperature detection circuit, fault detection and protection circuit. In addition, in order to realize communication with the host computer, the RS-485 interface core inverter is also extended with voltage space vector modulation. The three-phase PWM signal is directly generated by the high-speed output port of the 80C196KC, and the six-way circuit is formed by the inverter and the dead time forming circuit. The PWM drive signal is then passed through the opto-isolated circuit to the drive input of each IGBT of the IPM module.
Display circuit meter uses Motorola's serial interface display driver MC14489, which can directly drive 5-digit LED digital tube. In this design, 4-digit LED digital tube is used as the display of working frequency, temperature, etc., and 6 LEDs are indicated. The lamp acts as a segment of the fifth digit tube and is used as a status indication.
The frequency converter is equipped with two working modes of frequency conversion and temperature control. In the frequency conversion operation mode, its working condition is the same as that of the general frequency converter. In the temperature control mode, the LED display and the keypad can be used to complete the temperature display and setting, and the single chip samples the actual temperature from the temperature sensor, and performs closed-loop control on the room temperature according to the set temperature. The temperature control adopts the hybrid type fuzzy. -PI controller, the hybrid Fuzzy-PI controller and its design are specifically discussed in the text, and will not be described here.
Considering the central air conditioning system, the temperature detection point is usually far from the fan, and the temperature detection uses the current type integrated temperature sensor LM334 temperature detection circuit as shown. The setting resistor Rset changes the output current by 1A for every 1IK change of temperature. The absolute temperature to Celsius temperature is converted by the op amp OP-07 and the corresponding resistor, and the current signal from the LM334 is converted into a voltage signal of 0~5V.
The three-phase voltage instantaneous values ​​are Ma, Mb, and Mc, and the voltage space vector is eight switching states corresponding to the three-phase bridge arm. There are eight voltage space vectors, as shown in a), where Mo and M7 are zero vectors. The mountain is 6 non-zero vectors with a length of Udc and a phase difference of 60. They divide the entire space into 6 sectors.
The basic principle of voltage space vector PWM modulation is to approximate a given voltage vector with several switching voltage vectors. As shown in h), if it is located in the I region between Mi and M2, and the angle with the mountain is Y The action times Ti, T2, and To of the mountain, M2, and zero vector can be calculated as follows, and the three-phase PWM waveform is as shown.
When implemented with 80C196KC, three high-speed signals are usually used to generate A, B, and C three-phase PWM signals. When setting HSO, it is necessary to set the command word according to the pin, 00H, 01H, 02H as their corresponding pins. Cleared command word. In the implementation, according to the sector number and the pulse edge, the command word is obtained by looking up the table, and then the corresponding pulse edge is set (ie, the corresponding HSO is loaded). In a PWM inverter, the accuracy of the PWM waveform directly affects the harmonic content of the output voltage. For the single-CPU control system, in addition to generating the PWM signal, the MCU also needs to handle the keyboard display, frequency rise and fall, and temperature control calculation. Therefore, the accuracy of the PWM waveform must be carefully arranged.
122H life is not å˜O"d touch 0 0. In 1 oil should be g according to the total interruption of the f-order design.å²£ Usually, the HSO setting of the PWM waveform can be generated by Tsw interrupt or Tz interrupt, but in this system, other processing requires at least two software timers, and the high-speed output CAM array can only be simultaneously Containing 8 events, pressing Tsw may cause the event to be unable to be set or lost due to CAM full, so ~(5) knows that when the amplitude modulation ratio m is close to 1, / near 30, T = T70, considering the power device Switching time, the low level of the widest phase of the pulse and the high level of the narrowest phase of the pulse should be canceled, that is, the corresponding pulse disappears. In order to facilitate the processing of such pulse disappearance, the first pulse edge (TN1Tff3) of each Tz period is set in the previous Tz interrupt in the program, and the current Tz interrupt is from the second pulse edge of the Tz period (Ton2). Or TOFF2), until the first edge of the next TZ cycle, Toni).
~(5) It can be seen that if segmented synchronous modulation is used, the carrier ratio N=84 amplitude modulation ratio m =1 at 50 Hz, then when Ym£K=57.9, TN2 has the minimum value Ton2=11.3. For the 80C196 series MCU, if in the program Avoid using NORML and some DIVs of some addressing modes, such as long execution instructions. When the clock frequency is 16MHz, the interrupt response time is up to 5.5, so the pulse edge can be fully executed in the Tz interrupt service routine. Set to ensure the accuracy of the pulse time. It is not difficult to understand that in view of the symmetry of the PWM waveform, the same conclusion is reached for TOFF2.
In addition, in order to ensure that the Tz interrupt service routine can be executed in time in the program design, the Tz interrupt utilizes the idle high-speed output pin HS0.3, adopts the HSO interrupt, and has the highest priority. In order to avoid unnecessary judgment when loading HSO in the interrupt service program, the pulse disappearance phenomenon is not distinguished when loading, but the HSO pin of the 80C196 single-chip microcomputer is used to cancel the two opposite events at the same time. The Tz interrupt service routine flow chart is shown. In the figure, the calculation of Ton 1~Tom is performed in two Tz periods before and after a switching cycle, so that in the 16 MHz crystal oscillator, the execution time of the interrupt service routine is up to about 60, and when the switching frequency is not higher than 5 kHz, It is completely feasible for the frequency converter of the air conditioning temperature control system.
3 The inverter developed by the experiment has been tested repeatedly, the work is stable and reliable, and the voltage and current waveforms are better. The measured current waveform with 1.1kW fan load and output frequency 40Hz is given under the variable frequency working mode.
4 Conclusion The temperature-controlled special frequency converter of central air-conditioning fan based on 80C196KC single-chip microcomputer is developed. The hardware circuit is simple, practical, reliable, functional setting, operation and use method, etc. Specialized design for the actual working condition of air-conditioning fan, temperature control adopts Hybrid Fuzzy-pi control with high cost performance.
The paper focuses on the 80C196KC implementation method of voltage space vector PWM. For the temperature-controlled inverter of air-conditioning fan, it has been carefully designed to ensure the accuracy of PWM waveform at higher switching frequency (up to 4~5kHz). The good performance of the frequency converter has been experimentally verified.
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