1) Input circuit: Provide the main inverter circuit with DC working voltage to ensure its normal operation.
2) Main inverter circuit: It is the core of the inverter device. This circuit completes the inverter function by turning on and off the power electronic switch. Divided into isolated and non-isolated.
3) Output circuit: Correct, compensate, and adjust the amplitude and phase of the alternating current waveform, frequency, voltage, and current output by the main inverter circuit.
4) Control circuit: Provide a series of control pulses to the main inverter circuit to control the on and off of the inverter switching device, and cooperate with the main inverter circuit to complete the inverter function.
5) Auxiliary circuit: Transform the input voltage into a DC voltage suitable for the control circuit. It contains respective detection circuits.
6) Protection circuit: mainly includes input over-voltage and under-voltage protection, output over-voltage and under-voltage protection, over-current protection, short-circuit protection, island protection, etc.
Schematic diagram of the conversion process of the inverter converting DC to AC: (The semiconductor power switching device switches at a speed of 1/100s under the action of the control circuit to cut off the DC.
The circuit principle of the three-phase grid-connected inverter: (usually a current source inverter)
As shown in the figure above, the circuit is divided into two parts, the main circuit and the microprocessor circuit. The main circuit mainly completes the DC-DC-AC conversion and inverter process, and the microprocessing circuit mainly completes the control process of system grid connection. The purpose of grid-connected control of the system is to maintain the AC voltage value, waveform, and phase output by the inverter within the specified range, so the microprocessor control circuit mainly completes real-time monitoring of voltage and phase, current phase feedback control, and photovoltaic array Maximum power tracking and real-time sine wave pulse width modulation signal generation and so on.
Troubleshooting for Common Faults of Huawei Inverters
1. Low insulation resistance: use the exclusion 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 detect insulation resistance when starting up the inverter to detect problem strings. After finding the problem strings, focus on checking whether the DC connector has a water-immersed short-circuit bracket. Or burn the short-circuit bracket. In addition, you can also check whether there are black spots on the edge of the component itself, which causes the component to leak electricity to the ground grid through the frame.
2. Low bus voltage: If it occurs in the early/late period, it is a normal problem, because the inverter is trying the extreme power generation conditions. If it occurs during normal daytime, the detection method is still the exclusion method, and the detection method is the same as item 1.
3. Leakage current fault: The root cause of this kind of problem is the installation quality problem, which is caused by choosing the wrong installation location and low-quality equipment. There are many fault points: low-quality DC connectors, low-quality components, unqualified installation height of components, low-quality grid-connected equipment or water leakage. Insulation work solves the problem, if it is a material problem, only the material can be replaced
4. DC overvoltage protection: With the pursuit of high-efficiency process improvement of components, the power level is constantly updated and rising, and the open circuit voltage and working voltage of components are also rising. The temperature coefficient must be considered in the design stage to avoid overvoltage in low temperature conditions and cause equipment hard damage.
5. The inverter does not respond when starting up: please ensure that the DC input line is not reversed. Generally, the DC connector has a fool-proof effect, but the crimping terminal has no fool-proof effect. Read the inverter manual carefully to ensure that the positive and negative poles are crimped. very important. The inverter has built-in reverse polarity short-circuit protection, and it will start normally after the normal wiring is restored.
6. Grid failure:
Power grid overvoltage: The preliminary investigation of heavy load (working hours with high power consumption)/light load (rest time with low power consumption) of the power grid is reflected here. Survey the health of the grid-connected point voltage in advance, and communicate with inverter manufacturers Communicating the grid situation and combining technologies can ensure that the project design is within a reasonable range. Don’t take it for granted. Especially in 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 voltage of the original grid exceeding or approaching the safety protection value. If the grid-connected line is too long or the crimping is not good, the line impedance/inductive reactance is too large, and the power station cannot operate normally and stably. The solution is to find the power supply bureau to coordinate the voltage or choose the right grid connection and strictly control the construction quality of the power station.
Grid undervoltage: This problem is the same as the grid overvoltage treatment method, but if an independent phase voltage is too low, in addition to the incomplete load distribution of the original grid, the phase grid power failure or open circuit will also cause this problem. virtual voltage.
Power grid over/under frequency: If such problems occur in the normal power grid, it proves that the health of the power grid is very worrying.
There is no voltage in the power grid: just check the grid-connected line.
Power grid phase loss: Check the phase loss circuit, that is, no voltage line.
Unbalanced three-phase, grid-connected lines plus special equipment lead to abnormal oscillation of grid-connected, ultra-long-distance grid-connected, overvoltage and phase shift of power grid.