A brief introduction to the working principle of the inverter

An inverter is a type of power electronics whose primary function is to convert direct current (DC) into alternating current (AC). This conversion process is an integral part of modern electronic devices, especially when it is necessary to switch from battery power to alternating current.

The working principle of the inverter is based on pulse-width modulation (PWM) technology. PWM technology is an effective modulation method that controls the transmission of energy by changing the width of the pulse, so as to achieve the purpose of adjusting the voltage. The PWM integrated controller is one of the core components of the inverter, which controls the entire inverter process. PWM controller chips commonly used in inverters include UC3842 and TL5001.

An inverter typically consists of an inverter bridge, control logic, and filtering circuitry. The inverter bridge is a key part of the voltage conversion, and it consists of four power switches, usually using IGBTs or MOSFETs as power switches. The control logic part includes oscillator, PWM, over-voltage protection, under-voltage protection, short-circuit protection, etc., which ensure the stability and safety of the inverter under various working conditions. The filter circuit is responsible for removing the high-frequency noise generated by the inverter process and outputting a smoother sine wave or square wave alternating current.

The input part of the inverter contains a voltage start-up loop, which usually contains three signals: 12V DC input VIN, operating enable voltage ENB, and panel current control signal DIM. The VIN is provided by the adapter, and the ENB is usually provided by the microcontroller (MCU) on the motherboard, which has a value of 0 or 3V to control whether the inverter is working. The DIM voltage is provided by the motherboard and ranges from 0~5V, which determines the amount of current provided by the inverter to the load. When ENB is high, the inverter outputs a high voltage to light up the backlight tube of the display.

The output voltage feedback part of the inverter is responsible for monitoring and adjusting the output voltage to keep the voltage stable at the load end. The PWM controller compares the received feedback voltage with the internal reference voltage, adjusts the PWM signal through the error amplifier and oscillator, drives the power switch tube, and controls the voltage and current output of the inverter.

In the circuit of an inverter, many electronic components need to be considered for positive and negative polarity according to their working principle. For example, diodes and regulators have a clear positive and negative polarity, which can cause damage if reversed. Inductance and resistance do not need to consider polarity. The main power components of an inverter include field effect transistors (MOSFETs), IGBTs, transformers, capacitors, diodes, comparators, etc. In small-volume, low-voltage systems, MOSFETs are more common because they have a lower on-state voltage drop and a higher switching frequency; In high-capacity systems, IGBT modules are widely used due to their high voltage resistance and high current acceptance capacity.

The working principle of the fully controlled inverter is mainly realized by the full-bridge inverter main circuit with single-phase output. The AC element adopts an IGBT tube, and the PWM pulse width modulation is used to control the conduction or cut-off of the IGBT tube. With such control, an AC voltage can be generated on the transformer. After being processed by the LC AC filter, the output of the inverter can form a relatively pure sine wave AC current.

Inverters are widely used in various electrical equipment, such as air conditioners, home theaters, power tools, computers, TVs, etc. They are capable of converting direct current energy into alternating current that is suitable for the use of these devices. The output frequency and voltage of the inverter are generally 220V and 50HZ, which meet the standard power supply requirements of household appliances.

IGBT is an important component in modern inverter technology. It is an insulated-gate bipolar transistor that combines the high-speed performance of a power MOSFET with the low resistance characteristics of a bipolar device, making it suitable for a wide range of power conversion applications. IGBTs have obvious advantages in medium and high-capacity systems due to their high input impedance, low voltage control power consumption, simple control circuits, and high withstand voltage. With the development of semiconductor technology, the manufacturing process of IGBT continues to advance, which promotes the improvement of its performance and the expansion of application fields.

In summary, the inverter realizes the conversion of DC power to AC power through PWM technology, core controller, power switch tube, control logic and filter circuit. Knowledge of its operating principles and components is essential to understanding the design and application of inverters. With the development of technology, inverters have made progress in improving efficiency, reducing costs, and enhancing reliability, providing more stable and efficient power support for the use of various electronic devices.

The principle and application of inverter in photovoltaic power generation system

At present, China's photovoltaic power generation system is mainly a DC system, that is, the electric energy emitted by the solar cell is charged to the battery, and the battery directly supplies power to the load, such as the solar household lighting system used more in northwest China and the microwave station power supply system away from the grid are DC systems. This kind of system has a simple structure and low cost, but due to the different DC voltages of the load (such as 12V, 24V, 48V, etc.), it is difficult to achieve the standardization and compatibility of the system, especially for civil power, because most of them are AC loads, it is difficult for photovoltaic power supply powered by DC power to enter the market as a commodity. In addition, photovoltaic power generation will eventually achieve grid-connected operation, which must adopt a mature market model, and the AC photovoltaic power generation system will become the mainstream of photovoltaic power generation in the future.

The role of inverters in photovoltaic power generation systems is crucial, converting the direct current generated by solar cells into alternating current to meet the needs of various types of AC loads. In the current photovoltaic power generation system, the DC system is widely used because of its simplicity and low cost, especially in the northwest region and remote areas without power grids. However, due to the difference in DC voltage, it is difficult to standardize and compatible the system, especially for civil power that mainly uses AC loads. With the advancement of photovoltaic power generation technology, AC photovoltaic power generation system will gradually become mainstream, because it can better integrate into the existing grid structure and follow a mature market model.

As a key component of the photovoltaic power generation system, the inverter has the following requirements:

1. High efficiency: In order to maximize the use of solar cells and improve the efficiency of the entire system, the inverter needs to have a high conversion efficiency.

2. High reliability: In unattended photovoltaic power stations, the inverter needs to have reliable circuit design and component selection, and at the same time have various protection functions, such as preventing DC polarity reversal, AC output short circuit, overheating and overload, etc.

3. Wide range of DC input voltage: Considering the change of solar cell and battery voltage, the inverter needs to be able to work normally under a wide range of DC voltage, while maintaining the stability of the AC output voltage.

4. Output waveform quality: In medium and large capacity systems, the inverter should output alternating current close to the sine wave to reduce harmonic loss, ensure the normal operation of the load equipment, and meet the grid quality requirements during grid-connected operation.

The main types of inverters are push-pull inverter circuits, full-bridge inverter circuits and high-frequency step-up inverter circuits. The push-pull circuit has a simple structure, but the transformer utilization rate is low and not suitable for inductive loads. The full-bridge inverter circuit overcomes the shortcomings of the push-pull circuit, but the circuit structure is complex and requires a special drive circuit and dead time control. High-frequency step-up inverter circuits combine high-frequency conversion technology to achieve high power density and higher efficiency, but the circuit complexity increases.

The control circuit is an important part of the inverter, which can realize square wave output or sine wave output. Square-wave output inverters often use pulse-width modulation integrated circuits, such as SG3525 or TL494, while sine wave output inverters are microprocessor-controlled, such as Intel's 80C196MC, which can provide higher quality AC output.

With the continuous development of power electronics and microelectronics, the design and performance of inverters will continue to be optimized, which will promote greater progress in grid connection, efficiency and reliability of photovoltaic power generation systems, and provide more efficient and flexible solutions for renewable energy applications.