Thermal Stress Balance Predictive Control Method and System Applicable to Multilevel Converter

Abstract

The invention discloses a thermal stress balance prediction control method and system suitable for multilevel converters, and relates to the control technology of power electronic converters. The thermal stress balance predictive control method and system first constructs a cost function according to the reference value of the control variable and the output prediction value of the control variable, determines the optimal total output level and level increment, and then determines the ability to act according to the level increment Finally, design the switch distribution function according to the junction temperature value, determine the modules that need to act, and distribute the level increment to the modules that need to act. In this control method, the cost function is designed according to the output prediction value, and there is no correction, which ensures Output accuracy; the switch distribution function is based on the junction temperature value used to reflect the thermal stress of each module, and the switch state of the module is determined through the switch distribution function, achieving the effect of multi-module thermal stress balance.

Description

technical field [0001] The invention belongs to the control technology of power electronic converters, in particular to a thermal stress balance prediction control method and system suitable for multilevel converters. Background technique [0002] With the gradual development of my country's economy, the demand for medium-high voltage and high-power converters has gradually increased, and the demand for its capacity has even reached hundreds of MVA. However, due to the limitations of the withstand voltage level and capacity of power electronic devices, traditional two-level converters cannot meet the existing industrial needs in many cases. In order to improve the ability of power electronic devices to handle relatively high power, multilevel converters have attracted extensive attention from the academic community, and scholars from various countries have carried out a lot of research work. The multi-level converter is a new type of high-voltage and high-power converter st...

AI Technical Summary

Problems solved by technology

At present, it has been applied to reduce the uneven thermal stress of parallel devices and suppress the junction temperature fluctuation of wind power converters. Although it has strong versatility, this method usually requires additional hardware circuits.

The thermal stress control of the modulation layer of the inverter is to change the switching sequence of the power device by changing the modulation method, and then improve the device loss. This method uses the unique redundant switching state of the inverter to achieve thermal optimization without adding additional circuits. , high value in engineering applications, but usually only for specific topologies

The thermal stress control of the converter control layer is to optimize the thermal stress by adjusting the state variables related to the junction temperature, such as switching frequency, output power and DC side voltage, etc., but its thermal control target is difficult to be compatible with other control targets. Stress control usually affects the output effect

The thermal stress control of the system control layer is to use the complementary operating characteristics of different devices in the system to coordinate the control objectives of each device, and to optimize the thermal stress of the devices in the converter under the premise of ensuring that the overall performance of the system remains unchanged. The complementary characteristics of different devices have little impact on the overall cost and output performance of the system. It is an ideal thermal control strategy, but its versatility is poor and it is difficult to apply to converters used alone

[0005] The thermal stress control strategies mentioned above are mostly based on loss optimization or junction temperature smoothing. By reducing the thermal stress of power devices or reducing the thermal swing to improve thermal performance, the problem of thermal stress balance between multilevel converter modules relatively little research

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