Why is the three-phase inverter power supply unbalanced:
(1) On the distribution network side, there are a large number of unbalanced single-phase loads, resulting in the area of the distribution station. In most areas, the degree of three-phase unbalance varies.
(2) Randomness and uncertainty in the process of electricity consumption by consumers and the increasing use of high-power loads increase the load on the single-phase grid and lead to three-phase unbalance. The imbalance of the three-phase variable frequency power supply can seriously affect the distribution network and the customer side. This is mainly reflected in the following aspects:
(1) increase the power loss of the line, in the four-wire distribution network side of the three-phase inverter power supply, the current flows through the neutral line, not only in the phase line, but also in the three-phase load imbalance when the neutral line, power loss, which increases the grid. Performance losses.
(2) Increase the power loss of the distribution transformer. As an important configuration of the low-voltage distribution network side, distribution transformers can lead to an increase in distribution losses when using single-ended, three-phase, and inverter power supplies.
(3) Zero sequence currents generated by distribution transformers increase as the three-phase unbalance increases. The local temperature of the distribution transformer increases due to eddy current losses and this leads to a reduction in the service life of the equipment.
(4) It affects the normal operation of electrical appliances and the three-phase imbalance leads to a decrease in the quality of the power supply, which in turn affects the operation of electrical appliances. Reducing the three-phase imbalance not only stabilizes the power quality of the grid, but also reduces the power loss of the grid and saves energy.
How to carry out the unbalance treatment of three-phase inverter power supply?
In order to fundamentally solve the three-phase imbalance problem from the idea of load balancing, a control method centered on variable frequency power supply is being developed. This method can not only adjust the load to the maximum balance within a certain range, but also ensure the stability of the network power quality during the adjustment process, and realize the phase change in the case of continuous power supply to the load to achieve the overall balance.
Since the three-phase imbalance is a real-time dynamic variable, the linearity requirement must also be satisfied. In view of the above requirements, the general idea of studying the three-phase imbalance management based on variable frequency power supply is to establish an intelligent management terminal in the distribution station area, on the low-voltage user side, for sensing and real-time analysis of the degree of three-phase imbalance in the area, and obtaining the load balance by analyzing the commutation instruction in the distribution process;.
As the core component of the phase change device, the inverter power supply is installed between the three-phase grid side and the load side, and plays an important role in the whole changeover by receiving the commands issued by the intelligent management terminal to carry out the changeover. In addition, the network control center corresponds more closely to the information flow of the ubiquitous Internet of Things and plays an important role in constructing smart networks.
The three-phase imbalance problem in power grids becomes more and more serious as the economy grows and the power load on the grid increases rapidly.
Currently, there exist three main solutions for three-phase unbalance.
1.This method must use manual phase changing to record the three-phase imbalance in the area for a long period of time and analyze it to balance the load and connect it to each phase. However, the safety requirements cannot be met because the power supply is disconnected during the phase change process.
2. Connect reactive power compensation device at the distribution side to control the three-phase imbalance in the grid. The reactive power compensation device regulates the current of the lower phase by absorbing the current of the higher of the three phases. However, this device has a limited effect on the overall regulation of the production line and does not ensure the overall balance of the production line.
3. The unbalanced grid of the three-phase inverter power supply is controlled by the commutation technology of the intelligent mechanical switch. This technology can maintain the overall balance by real-time detection and control of the intelligent mechanical switch, but it will have an impact on the grid and load during the commutation process.
