An Integrated Learning Boost Converter Control Strategy For Cascade STATCOM

As an important part of flexible ac transmission system, STATCOM can exchange reactive power with power system by changing the output voltage to improve system voltage, suppress voltage fluctuation and flicker, raise the power factor, and so on. When the cascade H-bridge multilevel topology has applied to STATOM, the AC side can be directly connected to the power system by linked inductance without additional transformer, which reduces the area and cost. For this connection, the DC side is connected by isolated DC capacitors. As a result, the design has two tasks, one is to meet the power system’s reactive power control and the other is to meet the H-bridges’DC voltage control.However, cascade STATOM is constructed by cascade H-bridges, which make it a strong-coupled and multiple variable nonlinear system. It is very difficult to build the model and realize the controller. Meanwhile, existing perturbations give a negative impact to the control, which makes it is difficult to simultaneously realize the reactive power control and the DC voltage control. So it is very necessary to ask the control system have much stronger robustness.This paper first gave the advantages of cascade STATOM, introduced the carrier phase shifted SPWM strategy applied to cascade STATOM, compared the influence of reactive current detection on current’s tracking and DC voltage control, elaborated the basic principle of reactive power compensation and PCC’s voltage compensation.By equivalent circuit conversion, the control of cascade STATOM could be changed into the control of a single H-bridge module. This paper proposed the current control based on passivity or boost converter. Compared this two current control, an integrated learning boost converter control strategy for cascade STATCOM was proposed, which integrated learning control was used to eliminate the steady-state error and improve the system robustness.Through theoretical analysis, the distribution difference of H-bridge modules’DC voltage at steady-state only related to the difference among pulse delay, missed loss and shunt loss. The stable DC voltage control could be auto realized by boost converter power control, and balance control of DC voltage could be realized Based on droop characteristic.At last, based on the above theoreticals, this paper developed a±3Mvar, lOkV STATOM equipment. The design technology, physical images and field operating results were given in detail. Applications showed that the control strategy proposed by this paper could get a satisfied performance.