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Car Novel Single-phase sinusoidal power supply

Print View , by: iSee ,Total views: 34 ,Word Count: 1429 ,Date: Wed, 26 Aug 2009 Time: 10:02 PM


With the development of society, more and more cars with people's daily lives, while the vehicle is generally used for DC voltage 12V, can not be used directly for portable electronic devices. To this end, vehicle power supply (DC 12 V voltage is to convert the AC 220 V/50 Hz power supply) in the development of growing attention.

Traditional power commonly used vehicle inverter frequency transformer processing program, which there is bulky, efficiency and low defects. With the new power electronic devices and power electronics technology, using high-frequency chain programs to achieve the non-frequency transformer inverter circuit, can solve the problems of traditional automotive power supply, while still enabling the power supply board the output voltage more stable and smooth.

A vehicle power supply circuit structure and functional analysis of

Vehicle power supply system as shown in Figure l. 12V DC voltage high frequency inverters and high frequency rectification, to get a meet the requirements: 350V DC voltage, that part of the control signal generated by the TL494 chip. After another full-bridge DC / AC inverter circuit, to be 220V/50Hz AC voltage output. In order to ensure reliable operation of the system to prevent the main circuit of the control circuit interference, using the main, control circuit fully isolated approach, that is driving the signal with the optical isolators, the feedback signal isolation transformers, auxiliary power transformer isolation.

For the entire system, the inverter circuit can work properly determine whether the whole system running. Therefore, the focus of juice-based inverter control and inspection on.

Car Novel Single-phase sinusoidal power supply

1.1 SG3525 Block diagram and pin functions

SG3525 system uses to achieve the output SPWM control signals, the chip block diagram of the pin and the internal network 2 as shown.

Car Novel Single-phase sinusoidal power supply

DC Vs access to 15 after the two routes from the feet all the way added to or non-doors; the other way sent to the reference voltage regulator input, resulting in a stable +5 V reference voltage. +5 V and then sent to the internal (or external) circuit as the power of other components.

Oscillator to an external capacitor GT feet 5 feet 6 to an external resistor RTo oscillator frequency f by an external resistor RT and capacitor CT decision, f = 1.1 8/RCTo inverter bridge switching frequency is set at lOkHz, taking GT = O. 22μF, RT = 5 kΩ. The oscillator output is divided into two-way, all the way to the clock pulses sent to the bistable flip-flop and two non-gate; another way to saw-tooth form sent to the comparator noninverting input comparator inverting input Then the error amplifier output. The error amplifier output and the sawtooth voltage comparator compares the output with an error amplifier output voltage level to change the width of the square wave pulse, and then this square wave pulse delivered to the door or an input. The other two non-gate inputs, respectively, and the oscillator sawtooth bistable flip-flop. Bistable flip-flop 2 output complementary, alternating high-low output, the PWM pulse sent to the transistor V1 and V2 of the base, the role of sawtooth wave is to add dead-time to ensure the V1 and V2 not accompanied by conduction. Finally, V1 and V2 respectively, a difference of 180 ° output phase of the PWM wave.

1.2 SPWM modulation signal generation

To get the output sinusoidal voltage, it is necessary to make the inverter circuit SPWM control signals to control the power tube switch, the received pulse square-wave output can be re-filtered sinusoidal output voltage. To achieve through the SG3525 output sinusoidal voltage, first of all to get SPWM modulated signals, but to get SPWM modulated signals, you must have to have an amplitude in the l ~ 3 5V, according to the law of change, bread sine wave, it would be added to the SG3525 feet 2 , and compared with the sawtooth, pulse-width modulated sine wave can be obtained to achieve SPWM control circuit diagram in Figure 3 (a) shows, the actual circuit waveforms of various points shown in Figure 3 (b) below.

Car Novel Single-phase sinusoidal power supply

We can see from Figure 3, the benchmark 50Hz square wave generated by the 555 chip, is used to control the output voltage and the reference values of RMS error signal generated by comparison to convert the 50Hz square wave, after low-frequency filtering, get control of sinusoidal signal. When the power supply output voltage changes, will change the amplitude of sinusoidal signal, so that the output pulse width SG3525 corresponding changes have taken place, which constitutes a closed feedback loop, a stabilizing effect on the output waveform.

1.3 Over Current Protection

Over-current protection with current transformer as a current detection element, which has a fast enough response time can be allowed in the IGBT over-current time of its shutdown, has protective effects.

As shown in Figure 1, over-current protection signal from the CT2, by the partial pressure, filtering added to the voltage comparator input of the same phase, as shown in Figure 4. When the in-phase input over-current detection signal than the inverting input reference level is high, the comparator output high, so that D2 from the original reverse-bias state transition is positive guide pass, and to end with the potential to upgrade phase high, so that a stable output voltage comparator has been high. Meanwhile, the over-current signal is also sent to the 10 feet of SG3525. When the SG3525 is 10 feet high, its feet 11 and legs 14 on the output pulse-width modulated pulse will immediately disappear made zero.

Car Novel Single-phase sinusoidal power supply

l.4-driven circuit design

Driving circuit design of both the need to consider the power transistor turn-on, they can quickly establish a drive voltage, but also to consider the need turn-off, they can quickly discharge capacitors on the power transistor gate charge, pull down drive voltage . Specific drive circuit in Figure 5.

Car Novel Single-phase sinusoidal power supply

The working principle is:

1) When the primary side of a control circuit optocoupler drive pulse current flows out of date, optocoupler conduction, so that the base potential of Q1 rapid rise, leading to D2 conduction, the power control gate voltage increase, so that power tube conduction ;

2) When the non-primary side control circuit optocoupler drive pulse current flows out of date, optocoupler does not turn, so that the base potential of Q1 down, while the power transistor gate voltage is also on a high, thus resulting in a Q1 turn-on , gate charge through the power transistor Q1 and the resistors R3-speed discharge, so that rapid and reliable power tube off.

Of course, for the protection of power tube is equally important, so in power between the source and drain pipes to add a snubber circuit to prevent high-power tube positive, reverse voltage of the damage.

2 Experimental results

Based on the above analysis, the experimental prototype experiments, their rated output power of 500 W, filter parameters to take L = 3 mH, c = 2.2μF, prototype running with a load, the measured obtaining the output voltage waveform shown in Figure 6 show.

Car Novel Single-phase sinusoidal power supply

3 Conclusion

Prototype of good quality output voltage waveform, the output voltage stability, strong, and the amplitude largely unaffected by the load change, effect is good. Experiments show that the system proposed in this paper the program is feasible.

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