R&D On Variable Velocity Variable Frequency Technology Of Mid-high Voltage Three-level

Medium-high voltage motors play an important role in industrial applications. We need to adopt variable velocity variable frequency technology in order to improve the production process , to reduce energy consumption and increase boon & rationality. However, variable velocity variable frequency technology of medium-high voltage are not mature , having not been promoted and applied in large-scale, because the limit of device manufacturing process, control methods and the production cost. In this issue, a device of variable velocity variable frequency on medium-high voltage three-level is developed to reduce energy consumption and improve the cost-effective for the previous problems.After analysis and comparison, the topology of uncontrollable rectifier, diode clamped three-level inverter is chosen in main circuit. We adopt vvvf control and SPWM modulation waveform . The system consists of the main circuit, the control section, optical transmission unit, drive circuit, detection and protection unit, the neutral point voltage balancing control unit, keyboard and display unit, parameter storage circuit, relay access control and power components.87C196MH SCM is used as control center. After full analysis of the main circuit works, the 6-channel SPWM wave from SCM waveform generator is transformed through the programmable logic device and we get control signal of 12 switch for three-phase . With the fiber optic and driver circuit, it brings about the precision of signal transmission and decrease of electromagnetic interference.Dynamic parameter adjustment function is included in the program , so the system can quickly respond to user commands and adjust the frequency device output when running.This paper carries out a theoretical analysis and program design for neutral point potential imbalance. The hardware circuit constantly tests DC bus voltage difference, which is proportionally converted to frequency signal. The cycle of frequency signal is measured by SCM capture unit and the duty cycle of the upper and lower leg switch is calculated changed. After experiments with a load, neutral point potential is always maintained within the allowable range, to achieve a dynamic balance.This study develops a prototype of three-level frequency control and carries out a large number of experiments. Experimental results show that the prototype is running stable & reliable and the test targets meet the requirements to prove the correctness and feasibility of the formula.