Suppression Of DC Bus Voltage Fluctuation Of Ultra-low Frequency Inverter Power Supply

Alternating current is widely used in industrial production and scientific research,but on many occasions,the power frequency alternating current output by the power grid cannot be directly used,and a power source is needed to control and transform the electrical energy.Variable frequency power supply has important applications in aerospace,metallurgy,geological exploration and other fields.AC-DC-AC variable frequency power supply is widely used because of its flexible voltage and frequency regulation and high output power quality.When the output frequency of the AC-DC-AC variable frequency power supply is very low,the DC bus voltage may have a large fluctuation,affecting the normal operation of the power supply,and even causing damage to the power supply.In this thesis,the causes and suppression methods of the DC bus voltage fluctuation of the variable frequency power supply formed by the cascade of PFC circuit and full-bridge inverter circuit are studied in depth.Firstly,introduce the working principle of variable frequency power supply,and design the parameters of the power supply.Analyze the causes and influencing factors of various ripples in the DC bus voltage.Then,the voltage loop and current loop of the PFC circuit are corrected.By deducing the transfer function from the inverter input power to the DC bus voltage,it analyzes the influence of the ac component in inverter input power,the capacitance of the DC bus and the bandwidth of the voltage loop on the ripple of the frequency of 2f_o in the DC bus voltage.In order to suppress the voltage ripple with a frequency of 2f_o,according to its relationship with the bandwidth of the voltage loop,a method of adding a band stop filter to the voltage loop and increasing the bandwidth of the voltage loop is designed;from the perspective of increasing the response speed to the AC component of the inverter input power,the load current feedforward method is designed.The simulation results show that when the output frequency of the inverter is very low,these two methods can effectively suppress the voltage ripple of 2f_o in the DC bus.And then,in order to suppress the voltage ripple of 100 Hz and 100Hz±2f_o in the DC bus,a bidirectional Buck/Boost circuit is connected in parallel on the DC bus.From the perspective of reducing the volume of the energy storage element in the decoupling circuit and ensuring the power factor of the power supply,determine the suppression scheme adopted at different power supply output frequencies,and design the circuit parameters.From the perspective of controlling the input power of the decoupling circuit,the input current control method of the bidirectional Buck/Boost circuit is designed;from the perspective of suppressing the DC bus voltage fluctuation,the DC bus voltage control method of the bidirectional Buck/Boost circuit is designed.The simulation results show that both methods can effectively suppress the DC bus voltage fluctuations.Finally,build a digital simulation platform for variable frequency power supplies.The sampling of the circuit is realized by an analog circuit,and the digital controller and the PWM signal generation module are realized by a C language program to simulate a hardware platform controlled by DSP.The simulation results show that the designed digital controller can make the power supply work normally,and the DC bus voltage fluctuation can be effectively suppressed.