In the PV inverter application scenario, if the load demand for power is relatively high, a single inverter may not be able to meet the user's needs, and multiple inverters need to be connected in parallel to provide energy for the load together. However, due to the inverter common start will cause a relatively large inrush current, in the project will generally asynchronous start two inverters, first by an inverter for the load to provide energy, and then the other in parallel, to deliver energy.
Inverter Topology
Realization Methods
The two basic conditions for grid paralleling are equal phase and equal amplitude of output voltage. When two inverters are started asynchronously, their respective output voltage magnitude and phase may be different, and forcing them to be connected to the grid will cause more damage to both devices. Therefore, it is necessary to achieve equal amplitude and phase of the inverter output voltage in the synchronization link.
Phase Adjustment
To achieve phase synchronization, the basis is to be able to obtain the phase of the main network or the main inverter, so as to be able to adjust the phase of the other device, and then meet the conditions of grid connection.
Phase locking is carried out by means of a single synchronized coordinate system, obtaining the angular frequency of the first-start inverter and integrating to obtain the angle.
The main process is described as follows according to the principle of single synchronous coordinate system phase locking, through the coordinate transformation to get the dq-axis component of the inverter output voltage, if the phase is consistent, the d-axis and the reference vector of the output voltage is in the same direction, and the q-axis component is zero. The q-axis component is zero. After the difference between the q-axis component and zero, PI operation is carried out to get the angular frequency and the target angular frequency, and then the angle can be obtained by integrating.
Output Voltage Amplitude Adjustment
When there is voltage at the output of the first inverter, it means that the first one has begun to work, at this time, the output voltage of the first inverter is collected, the amplitude is obtained, and after dq transformation, it is used as the target value of the latter inverter, and then the power regulation is carried out after the system is stabilized.
