1. System function description
The wind power solar power plant inverter power system developed by LPCS2000B has the main function of inverting the direct current from the solar cells into three-phase alternating current and feeding it into the power grid. And solve the problems of maximum conversion efficiency, harmonic interference and protection in grid-connected inverters.
2. System functional block diagram
3. System control part description
The function completed by the control part is to control the power part to generate a voltage in the same phase as the power grid, and to track the actual output power, so that the output power of the power supply is equal to the maximum output power of the solar cell.
The control part is the LPCS2000B power control board. The core device of the control board is the industrial DSPTMS320F2801 produced by TI. The DSP multi-channel high-speed ADC sampling is used to monitor the grid voltage, solar cell terminal voltage, solar cell output current, and DC regulated output voltage. At the same time, the DSP generates switch operations for voltage regulation and commutation, producing a sine wave output.
The system can be controlled by a local control panel, while providing remote control based on the RS232 interface.
4. Description of system power
a) Solar cell square array
It is composed of 50Wp polycrystalline silicon solar cell modules, with 24 modules connected in series and 9 sub-square arrays connected in parallel. Open circuit voltage DC510V, short circuit current DC27A, best working voltage DC408V, best working current DC25A.
b) DC voltage regulating circuit
Modulate the DC voltage generated by the solar cell into a 100Hz, 220V (RMS) bun waveform.
c) Full bridge commutation circuit
Reversing the 100Hz unipolar bun waveform to a 50Hz bipolar AC waveform.
d) Three-phase transformer
Through the three-phase transformer, it is coupled with the transmission network.
5. MPPT to improve solar energy efficiency
The maximum power point tracking control (MPPT) strategy monitors the output power of the photovoltaic array in real time, uses interference observation control algorithms to predict the maximum power output of the array under current operating conditions, and meets the requirements of maximum power output by changing the current impedance. When the temperature and light intensity are constant, the relationship between the solar cell terminal voltage and the output power.
6. System protection description
a) On-grid protection
As part of the power system, the photovoltaic grid-connected system needs to be connected with protection devices. On the one hand, it protects the photovoltaic power generation system to prevent the island effect; on the other hand, it needs to install relay protection devices to prevent line accidents or power instability.
These protection functions include low-voltage protection, over-voltage protection, low-frequency protection, over-frequency protection, over-current protection and island protection.
b) The island problem
The inverter loses the voltage of the grid system on which the grid connection is based. This situation is called the island effect. The islanding effect may complicate the reconnection of the power grid and cause harm to the components in the power grid.
This system uses two island detection technologies, passive and active, to ensure that islands are reliably detected and to ensure equipment safety.
7. System electromagnetic compatibility interference treatment
a) Filter
By installing a differential mode filter at the output wires of the controller and the photovoltaic array, the influence of electromagnetic interference caused by the wires between the photovoltaic array and the photovoltaic array and the controller is eliminated.
By connecting capacitors of suitable capacitance in parallel with the positive and negative poles of the output of the photovoltaic array, the interference caused by the fluctuation of the output voltage of the photovoltaic array is eliminated.
In the photovoltaic power generation system operated by buttons or relays, a filter capacitor is added to the control circuit.
b) Lightning protection
On the one hand, a lightning rod is installed; on the other hand, a lightning arrester is installed at the output lead connection of the photovoltaic array.
c) Ground
Connect the shell of the system and the grounding terminal of the lightning arrester to the ground to ensure the safety of the system and the person.
Single-point grounding is used for signal grounding to prevent conducted interference between circuits and common ground conducted interference.
d) Electromagnetic shielding
Install conductive gasket in the shell, apply conductive material to the joints, adjust the spacing of the fastening nails, install a metal mesh at the large opening, turn the large hole into multiple small holes, and use a single-point grounding for the entire shielding layer.
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