| Single-phase full-bridge converter is a classic power electronic converter.Due to its advantages of low cost,small size and high voltage utilization,it is widely used in photovoltaic grid-connected,uninterruptible power supply and other fields,and plays an important role in promoting the strategy of gradually replacing centralized fossil energy with renewable distributed energy.Pulse width modulation(PWM)technology is the key technology for the operation of single-phase full-bridge converters.In the process of approximating the reference waveform,PWM often brings negative effects such as switching loss,current ripple and electromagnetic interference.In order to reduce the side effects of PWM and improve the performance of modulation,this paper takes the single-phase full-bridge topology as the research object,and studies the PWM technology that can be used in the single-phase full-bridge topology.The main contents of the research are as follows:Firstly,the principles of several PWM modulation methods commonly used in single-phase full-bridge inverters are introduced.Combined with the working principle of single-phase full-bridge inverters,a unified PWM modulation method that is convenient for implementation is proposed.In this unified modulation method Next,some PWM modulations that have been proposed can be regarded as special cases of this unified modulation method.Then,the switching loss and the distribution of switching loss caused by several common PWM modulations are compared,and the minimum switching loss condition under constant switching frequency is obtained.The modulation method is equally divided among the four switches.Then,based on the research on modulated waves,a dual-mode modulation is proposed,which enables the single-phase full-bridge topology to output one AC and one DC with different voltages at the same time,or output three DCs with different voltages at the same time,which enriches the single-phase full-bridge topology application scenarios.Secondly,based on the principle that modulation affects the AC side current ripple,the current ripple prediction model,current ripple RMS model and switching loss model of continuous modulation and discontinuous modulation are deduced.Then,based on the current ripple prediction model,using functional analysis,Lagrangian multiplier method and numerical analysis and other mathematical tools,a constant ripple modulation that makes full use of the upper limit of current ripple and a good switching loss performance are deduced.The model predicts variable frequency modulation,and then compares the switching loss performance and EMI performance of traditional constant frequency modulation,constant ripple modulation and model predicted variable frequency modulation under different modulation ratios and different power factor angles.Finally,the component parameters of the main circuit are designed and selected,the LC filter parameters are designed,the selection of DC side capacitors,filter inductors and capacitors,and the selection of the main power module are completed,and a test prototype is built.Through simulation and experiments,the unified modulation method and dual-mode modulation method proposed in this paper are verified,and the theoretical derivation and experimental verification of the current ripple prediction model and the model prediction frequency conversion modulation are carried out.The modulation switching loss performance and harmonic performance are experimentally compared.The results show that the unified modulation method and the dual-mode modulation method have good output waveforms and can operate stably under open-loop conditions.The loss performance and EMI performance of the model-predicted variable-frequency modulation are better than those of the traditional constant-frequency modulation. |
