“This design uses ARM as the control core, combined with push-pull boost circuit and SPWM inverter circuit, to realize the conversion of 12VDC input voltage into 110VAC AC sinusoidal voltage output. Experiments show that the inverter has the characteristics of small voltage ripple, high dynamic response and full digital, which can meet the actual needs.
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This design uses ARM as the control core, combined with push-pull boost circuit and SPWM inverter circuit, to realize the conversion of 12VDC input voltage into 110VAC AC sinusoidal voltage output. Experiments show that the inverter has the characteristics of small voltage ripple, high dynamic response and full digital, which can meet the actual needs.
1. Overall system plan
1.1 Overall Design Block Diagram
As shown in Figure 1, the inverter system consists of a boost circuit, an inverter circuit, a control circuit and a feedback circuit. The low-voltage DC power supply DC12V is boosted, rectified and filtered by the booster circuit to obtain about DC170V high-voltage direct current, and then the full-bridge inverter circuit DC/AC conversion and LC filter filter to obtain AC110V sinusoidal alternating current.
The inverter takes the ARM controller as the control core. The feedback signals of the output voltage and current are processed by the feedback circuit and then enter the on-chip AD of the ARM processor. After AD conversion and digital PI operation, the corresponding SPWM pulse signal is generated to change the SPWM signal. The modulation ratio can change the size of the output voltage, so as to complete the closed-loop control of the entire inverter.
1.2 SPWM scheme selection
1.2.1 PWM power chip solution
Using ordinary PWM power control chips, such as SG3525, TL494, KA7500, etc., the advantage of this type of chip is that it can directly generate PWM signals, but its disadvantage is that the waveform linearity is not good, and the oscillator is dependent on the charging and discharging circuit. To generate waveforms, many additional circuits are required when the PWM chip is to generate the SPWM signal.
The inverter is a device that converts DC power (battery, storage battery) into AC power (usually 220V 50HZ sine wave or square wave). Our common emergency power supply generally inverts the DC battery to 220V AC. In simple terms, an inverter is a device that converts direct current to alternating current.
Whether it is in a remote village, or in the field or in an emergency of power failure, the inverter is a very good choice. The most common is the UPS power supply used in the computer room. In the event of a sudden power failure, the UPS can invert the DC power in the battery to AC for the computer to use, thereby preventing data loss caused by sudden power failure.
This article will introduce two relatively simple inverter circuit diagrams. A simple inverter circuit diagram is attached. Interested friends can study it. It is indeed a very fulfilling thing to make an inverter by yourself. The following is a more common inverter circuit diagram.
The above is an inverter circuit diagram that is relatively easy to make. It can invert the 12V DC power supply voltage to 220V mains voltage. The circuit is driven by a multivibrator composed of BG2 and BG3, and then driven by BG1 and BG4 to control BG6 and BG7 work. Among them, the oscillation circuit is powered by the regulated power supply of BG5 and DW group, which can make the output frequency relatively stable. During production, the transformer can be selected with a common dual 12V output mains transformer. You can choose the appropriate 12V battery capacity according to your needs.
Below is an electrical diagram of a high efficiency sine wave inverter powered by a 12V battery. First use a voltage doubling module to double the voltage to supply power to the op amp. Can choose ICL7660 or MAX1044. Op amp 1 generates a 50Hz sine wave as a reference signal. Op amp 2 acts as an inverter. Op amp 3 and op amp 4 act as hysteretic comparators. In fact, the operational amplifier 3 and the switch tube 1 constitute a proportional switching power supply. Op amp 4 and switch tube 2 are the same. Its switching frequency is not stable. When the output signal of operational amplifier 1 is in positive phase, operational amplifier 3 and the switch tube work. At this time, the output of op amp 2 is negative phase. At this time, the potential of the positive input terminal of the operational amplifier 4 (constantly 0) is always higher than the potential of the negative input terminal, so the output of the operational amplifier 4 is always 1, and the switch is turned off. When the output of op amp 1 is in negative phase, the opposite is true. This realizes that the two switches work alternately.
When the reference signal is higher than the detection signal, that is, the signal at the negative input terminal of op amp 3 or 4 is higher than the signal at the positive input terminal by a small value, the comparator outputs 0, the switch is turned on, and the detection signal increases rapidly. When a small value is higher than the reference signal, the comparator outputs 1, and the switch is turned off. It should be noted here that the comparator has a positive feedback process when the circuit is flipped, which is the characteristic of the hysteresis comparator. For example, on the premise that the reference signal is lower than the detection signal, as the difference between them keeps getting closer, at the moment when they are equal, the reference signal is immediately higher than the detection signal by a certain value. This “certain value” affects the switching frequency. The larger it is, the lower the frequency. Here it is selected as 0.1~0.2V.
Editor’s comment: The inverter with square wave output has high efficiency. For electrical appliances designed with sine wave power supply, most electrical appliances are applicable except a few electrical appliances that are not applicable. The inverter with sine wave output does not have this disadvantage. , but there is a disadvantage of low efficiency, how to choose this needs to be based on your own needs.
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