|Ⅰ Working principle of inverter|
|Ⅱ Classification of inverter|
|Ⅲ Common faults of inverter|
|Ⅳ The difference between an inverter and a transformer|
The inverter is a DC to AC transformer. What happens with the converter is a voltage inversion process. The converter converts the AC voltage of the grid into a stable 12V DC output. The inverter converts the 12V DC voltage output by the adapter into high-frequency and high-voltage AC. The core part of the inverter and the adapter is a PWM integrated controller. The adapter uses UC3842, and the inverter uses TL5001. The operating voltage range of TL5001 is 3.6~40V. TL5001 has 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.
Simple schematic diagram of inverter
Input interface part: The input part has 3 signals including 12V DC input VIN, working enable voltage ENB and Panel current control signal DIM. VIN is provided by the Adapter, and the ENB voltage is provided by the MCU on the motherboard, and its value is 0 or 3V. When ENB=0, the inverter does not work, and when ENB=3V, the inverter is in a normal working state. The DIM voltage is provided by the mainboard, and its variation range is between 0 and 5V, and different DIM values are fed back to the feedback terminal of the PWM controller. The current provided by the inverter to the load will also be different. The smaller the DIM value, the greater the current output by the inverter.
Voltage starts circuit: When ENB is high, it outputs a high voltage to light the panel's backlight tube.
PWM controller: It is composed of the following functions: internal reference voltage, error amplifier, oscillator and PWM, over-voltage protection, under-voltage protection, short-circuit protection, output transistor.
DC conversion: A voltage conversion circuit is composed of MOS switch tubes and energy storage inductors. The input pulse is amplified by the push-pull amplifier to drive the MOS tube to switch so that the DC voltage charges and discharges the inductor. In this way, the other end of the inductor can get AC voltage.
LC oscillation and output circuit: to ensure the 1600V voltage required for the lamp to start, and to reduce the voltage to 800V after the lamp is started.
Output voltage feedback: When the load is working, the sampled voltage is fed back to stabilize the voltage output of the I inverter.
According to the nature of the source
Active inverter: It is an inverter that connects the current in the current circuit to the grid on the AC side without directly connecting to the load.
Passive inverter: An inverter that makes the current in the current circuit directly connected to the load on the AC side without connecting to the grid (that is, inverting the DC power into a frequency or adjustable frequency AC power supply to the load).
According to grid type
It is divided into an off-grid inverter and a grid-connected inverter.
According to topology
It is divided into the two-level inverter, three-level inverter, multi-level inverter.
According to power level
It is divided into high-power inverters, medium-power inverters, and small-power inverters.
1) Small and medium power inverter
Small and medium power inverter power supply is one of the important links in the independent AC photovoltaic system. Its reliability and efficiency are vital to promoting photovoltaic systems, effectively using energy, and reducing system costs. Therefore, photovoltaic experts in various countries have been working hard to develop inverter power supplies suitable for household use.
2) Multiple series inverters
Multiple series inverters have many advantages when applied to electric vehicles. The series structure output voltage vector types are greatly increased, which enhances the flexibility of control and improves the accuracy of control. At the same time, it reduces the fluctuation of the neutral point voltage of the motor. The bypass feature of the inverter can improve the flexibility of charging and regenerative braking control.
As people are increasingly concerned about the environment, the development of electric vehicles has an opportunity. In urban transportation, electric buses have become a priority for development due to their large capacity and high comprehensive benefits. Most electric buses use three-phase AC motors. Due to the large motor power, the components in the three-phase inverter need to withstand high voltage and high current stress. Higher dv/dt makes electromagnetic radiation serious and requires good Heat dissipation.
The high-power inverter with a multiple series structure reduces the voltage stress of a single device and reduces the requirements for the device. The reduced dv/dt value and electromagnetic radiation make the heating of the device greatly reduce. Due to the output, the levels types increase, and the control performance is better.
Multiple series inverters are suitable for high-power electric vehicle drive systems. The use of multiple series-connected structures can reduce the risk of multiple batteries connected in series, reduce the switching stress of the device and reduce electromagnetic radiation. But the number of batteries required has increased by a factor of 2.
The multiple series structure output voltage vector types are greatly increased, thereby enhancing the flexibility of control and improving the accuracy of control. At the same time, it reduces the fluctuation of the neutral point voltage of the motor. In order to maintain the balance of the power of each battery, it is necessary to ensure that the discharge time of the battery is consistent during operation. Through the bypass mode, the battery pack can be charged flexibly and the torque of regenerative braking can also be controlled.
Use the elimination method. Unplug all the strings on the input side of the inverter, and then connect them one by one. Use the function of the inverter to check the insulation resistance to detect the problem string. After finding the problem string, check whether the DC connector has a water-immersed short-circuit bracket or fusing and short-circuiting the bracket. In addition, you can also check whether the component itself has black spots burned at the edge, causing the component to leak electricity to the ground grid through the frame.
If it occurs in the morning/night time period, it is a normal problem, because the inverter is trying to limit power generation conditions. If it occurs in normal daylight, the detection method is still the elimination method, and the detection method is the same as item 1.
If the leakage current is too large, remove the input terminal of the PV array, and then check the external AC grid. The DC and AC terminals are all disconnected, and the inverter will be powered off for 30 minutes. If you can restore it, continue to use it. If you can’t restore it, just contact a professional engineer.
As components pursue high-efficiency process improvements, power levels continue to update and rise, while component open-circuit voltage and operating voltage are also rising, temperature coefficient issues must be considered at the design stage to avoid over-voltage at low temperatures causing.
Please make sure that the DC input line is not reversed. Generally, the DC connector has a fool-proof effect, but the crimping terminal does not have a fool-proof effect. It is important to read the inverter manual carefully to ensure the positive and negative poles before crimping. The inverter has built-in reverse connection short-circuit protection, and it will start normally after normal wiring is restored.
The preliminary survey of the power grid heavy load (large power consumption working hours)/light load (small power consumption rest time) is reflected here, and the health of the grid-connected point voltage is investigated in advance, and the grid situation is communicated with the inverter manufacturer. The combination of technology can ensure that the project design is within a reasonable range, especially for rural power grids. Inverters have strict requirements on grid-connected voltage, grid-connected waveform, and grid-connected distance. Most of the grid overvoltage problems are caused by the light load of the original grid. If the voltage exceeds or approaches the safety protection value or the grid-connected line is too long or the crimping is not good, the power station will not be able to operate normally and stably.
Can a transformer be used as an inverter? The answer is no. An inverter is a device that is essentially different from a transformer. It is input by DC and output AC. The working principle is the same as that of a switching power supply, but the oscillation frequency is within a certain range. For example, if the frequency is 50HZ, the output is AC 50HZ. Therefore, the inverter is a device that can change its output frequency. A transformer generally refers to a device in a specific frequency range, which is input by AC and then output AC, only changing the size of the output voltage. For example, industrial frequency transformers are those transformers commonly seen. The input and output are both alternating currents and can only work in the range of 40-60HZ.
The inverter converts DC power into AC power, while a transformer is an electrical device that uses the principle of electromagnetic induction to convert electrical energy. It can convert a voltage and current of AC electrical energy into another voltage and current alternating current of the same frequency.
Simply put, an inverter is an electronic device that converts low-voltage (12 or 24 volts) direct current into 220 volts alternating current. Because we usually rectify 220 volt AC power into DC power to use, and the inverter has the opposite effect, hence the name. We are in a "mobile" era that is a mobile office, mobile communication, mobile leisure, and entertainment. In the mobile state, people not only need low-voltage DC power supplied by batteries or batteries but also need 220 volt AC power that is indispensable in our daily environment. Inverters can meet our needs.