“In the previous article, Xiaobian introduced the single-phase Inverter. In order to improve everyone’s understanding of inverters, this article will introduce high-frequency inverters. In this article, you will learn the working principle, classification, characteristics of high-frequency inverters, and know the difference between high-frequency inverters and low-frequency inverters.
In the previous article, Xiaobian introduced the single-phase inverter. In order to improve everyone’s understanding of inverters, this article will introduce high-frequency inverters. In this article, you will learn the working principle, classification, characteristics of high-frequency inverters, and know the difference between high-frequency inverters and low-frequency inverters.
1. Working principle of high frequency inverter
A high-frequency inverter is a DC to AC transformer, which is actually a voltage inversion process with the converter. The working principle of the high-frequency inverter is that the converter converts the AC voltage of the grid into a stable 12V DC output, and the inverter converts the 12V DC voltage output by the Adapter into high-frequency high-voltage AC; both parts are also The commonly used pulse width modulation (PWM) technique is used. The core part is a PWM integrated controller, the Adapter uses the UC3842, and the inverter uses the TL5001 chip. The working voltage range of TL5001 is 3.6~40V, and it is equipped with an error amplifier, a regulator, an oscillator, a PWM generator with dead zone control, a low-voltage protection circuit and a short-circuit protection circuit.
1. Input connection[Part:Theinputparthas3signals12VDCinputVINworkenablevoltageENBandPanelcurrentcontrolsignalDIMVINisprovidedbyAdapterENBvoltageisprovidedbyMCUonthemainboarditsvalueis0or3VwhenENB=0theinverterdoesnotworkandwhenENB=3VtheinverterisinnormalworkingstateandtheDIMvoltageisdeterminedbyProvidedbythemainboardthevariationrangeisbetween0~5VanddifferentDIMvaluesarefedbacktothefeedbackterminalofthePWMcontrollerandthecurrentprovidedbytheinvertertotheloadwillalsobedifferentbigger[部分：输入部分有3个信号，12V直流输入VIN、工作使能电压ENB及Panel电流控制信号DIM。VIN由Adapter提供，ENB电压由主板上的MCU提供，其值为0或3V，当ENB=0时，逆变器不工作，而ENB=3V时，逆变器处于正常工作状态而DIM电压由主板提供，其变化范围在0~5V之间，将不同的DIM值反馈给PWM控制器反馈端，逆变器向负载提供的电流也将不同，DIM值越小，逆变器输出的电流就越大。
2. Voltage startup circuit: When ENB is at high level, it outputs high voltage to light up the backlight lamp of Panel.
3. PWM controller: It consists of the following functions: internal reference voltage, error amplifier, oscillator and PWM, overvoltage protection, undervoltage protection, short circuit protection, and output transistor.
4. DC conversion: A voltage conversion circuit is composed of a MOS switch tube and an energy storage Inductor. The input pulse is amplified by a push-pull amplifier and then drives the MOS tube to perform switching action, so that the DC voltage charges and discharges the inductor, so that the other end of the inductor can Get AC voltage.
5. LC oscillation and output circuit: ensure the 1600V voltage required for starting the lamp, and reduce the voltage to 800V after the lamp is started.
6. Output voltage feedback: When the load is working, the sampling voltage is fed back to stabilize the inverter voltage output.
2. Classification of high frequency inverters
1. Square wave inverter
The AC voltage waveform output by the square wave inverter is a square wave. The inverter circuits used by such inverters are not exactly the same, but the common feature is that the circuits are relatively simple and the number of power switch tubes used is small. The design power is generally between one hundred watts to kilowatts. The advantages of square wave inverter are: simple circuit, cheap price and easy maintenance. The disadvantage is that because the square wave voltage contains a large number of high-order harmonics, additional losses will be generated in the load electrical appliances with iron core inductance or transformer, which will interfere with the radio and some communication equipment. In addition, this type of inverter also has shortcomings such as insufficient voltage regulation range, insufficient protection function, and relatively large noise.
2. Step wave inverter
The AC voltage waveform output by this type of inverter is a staircase wave, and there are many different circuits for the inverter to realize the staircase wave output, and the number of steps of the output waveform varies greatly. The advantage of the ladder wave inverter is that the output waveform is significantly improved compared with the square wave, and the high-order harmonic content is reduced. When the ladder reaches more than 17, the output waveform can achieve a quasi-sine wave. When the transformerless output is used, the overall efficiency is very high. The disadvantage is that there are many power switch tubes used in the ladder wave superposition circuit, and some circuit forms also require multiple sets of DC power input. This brings trouble to the grouping and wiring of the solar cell array and the balanced charging of the battery. In addition, the step wave voltage still has some high frequency interference to radios and some communication equipment.
3. Features of high frequency inverter
1. Wide input voltage range, high voltage regulation accuracy and strong environmental adaptability;
2. Adopt special microprocessor control, digital technology, international leading;
3. Pure sine wave output, excellent electrical performance indicators;
5. Optionally choose bypass priority or inverter priority;
6. Input and output electrical isolation, can withstand the impact of computer load power-on surge;
7. High-efficiency inverter, low no-load loss;
8. Advanced manufacturing technology, generous and beautiful products;
9. With input over-voltage, under-voltage and reverse connection protection; output overload and short-circuit protection; mains bypass high and low voltage protection;
10. In the case of no DC, it can be started with AC power on;
11. Fully automatic maintenance, suitable for unattended station.
Fourth, the difference between high frequency inverter and low frequency inverter
1. According to the frequency spectrum division table formulated by the Institute of Electrical and Electronics Engineers (IEEE), the low frequency frequency is 30~300kHz, the intermediate frequency frequency is 300~3000kHz, the high frequency frequency is 3~30MHz, and the frequency range of 30~300MHz is very high frequency , at 300~1000MHz is UHF. Compared with the low-frequency signal, the high-frequency signal changes very quickly and has sudden changes; the low-frequency signal changes slowly and the waveform is smooth.
2. The power supply and the signal are different. The voltage provided by the power board is generally 0 (DC power) or 50Hz (AC power). The signal can be said to be high frequency or low frequency (or other frequencies), but the power board is not easy to say, because it is only used for power supply, the frequency is very low, and what must be said is only low frequency.
3. The advantages of high-frequency inverters are mainly light weight, small size, low standby power, and high efficiency (relatively save electricity). The disadvantage is that the impact resistance is not as good as the power frequency inverter (that is, the low frequency you said), and it may not be able to carry electrical appliances such as food mixers and hand drills. The disadvantage of low frequency is that it is heavier and larger, the price may be slightly higher, and its own loss will be slightly larger (a bit of electricity). The advantage is that it is relatively solid, and the ability to take impact electrical appliances will be better.