Multi-dimensional Modulation For Cascaded H-bridge Rectifier Based On Two-dimensional Modulation

In recent years,with the development of renewable energy and active distribution networks,research on emerging power electronic equipment such as medium and high voltage high power electronic transformers and energy storage converters has gradually risen.In order to adapt to the application requirements of medium and high voltage AC grids,a cascaded H bridge rectifier(CHBR)circuit is adopted,and a multi-stage conversion structure composed of high-frequency DC / DC has become the mainstream of this type of power electronic conversion device research.The CHBR structure,as the pre-stage of the converter connected to the AC grid,reduces the voltage stress of the power semiconductor switches and realizes the application of low-withstand voltage IGBTs in medium and high voltage converters.Therefore,this article takes the single-phase CHBR circuit topology as the research object and analyzes the influence of its N-bridge cascade rectifier circuit modulation strategy on the DC-side voltage balance performance.First of all,the research background and significance of CHBR are introduced,and the current research status of CHBR at home and abroad are summarized,including CHBR rectification control,DC-side voltage balance control,modulation and modulation expansion strategies.Based on the summary of the work of domestic and foreign research scholars,follow-up research is carried out with modulation strategy as a breakthrough.The CHBR circuit topology consists of N single-phase H-bridge structures connected in series.Taking a two-bridge cascade rectifier circuit as an example,its working principle,equivalent circuit,and four-quadrant operation characteristics are analyzed in detail.Then the dq coordinate system of the CHBR system is established.Based on the state-space model,the overall control scheme is established according to the mathematical model,and the relevant controller parameters are designed,and the correctness of the control and design is verified by MATLAB simulation.Secondly,the application of a two-dimensional modulation strategy in a two-cascade H-bridge topology is introduced.In order to reflect the advantages of this modulation strategy,the maximum and minimum voltage absorption capacity of the bridge is analyzed from an energy perspective.Based on the two-dimensional modulation trajectory,a multi-dimensional extended modulation strategy is proposed.This strategy extends the multi-N bridge cascade topology while inheriting the advantages of the two-dimensional modulation strategy.More efficient operations have certain practical significance.Then,the advantages of this expansion strategy over traditional multi-dimensional modulation strategies are analyzed theoretically.The difference in balance performance is reflected by the maximum and minimum voltage absorption capacity of the voltage bridge,and a three-dimensional The comparison chart will make the balance performance more intuitive.The MATLAB simulation software validates the theoretical analysis from multiple angles and demonstrates the effectiveness and superiority of the proposed strategy.Considering the dead-band effect when CHBR is working in the field,the impact of dead-band time when multi-bridge expansion strategy is applied is analyzed,and according to the traditional dead-band compensation strategy,the multi-dimensional expansion strategy is converted into the multi-dimensional expansion strategy In this way,the grid-connected current waveform is effectively improved and the current harmonics are reduced.Finally,the effectiveness of the dead-band compensation strategy is verified by simulation.Finally,a single-phase CHBR experimental platform was set up.Introduced the general requirements for the construction of the experimental platform,and analyzed the hardware system design in detail,including main device selection,main power board design,sampling circuit design,drive circuit design,dead-band circuit design,control circuit design,etc.;The main flow chart of software system design is included,including main program design,AD sampling program design,control,and modulation program design,protection program design,etc.Finally,the relevant experimental verification is done based on the theory and simulation analysis of the proposed strategy.Mainly include: waveform display of AC side voltage and current,rectifier stage AC side voltage,DC side voltage,grid-connected current THD,and other waveforms during steady-state operation;DC bridge balance performance of two bridge to four bridge cascade rectification under the same experimental conditions Contrast waveform diagrams;comparison of DC-side voltage balance performance between conventional modulation strategies and proposed modulation strategies when the load is abrupt,comparison diagrams of calculation time before and after the expansion strategy is simplified,etc.,prove the effectiveness of the proposed multi-bridge cascade expansion strategy from an experimental perspective Sex and superiority.