Summary: Much level is for the voltage type to go against the becoming device to varies technology at present: With the development of technology of superconductive energy storage, the electric current type energy storage efficiency problem of going against the becoming device will be solved, it will be used widely too that electric current type much level goes against the becoming device. It is topological to introduce a new kind of electric current type three-phase direct formula five level in detail, have studied this topological control strategy. Provide emulation and experiment wave form, artificial result and experiment wave form have verified the analysis made in the article.
Keyword: Electric current type much level; Topological; Control strategy

O Foreword
The existing research work about many level current transformers is mainly for the voltage type current transformer Vohage Source Inverter, abbreviated as VSI ,To the electric current type current transformer Current Source Inverter, is abbreviated as CSI It is less to study. This is not merely because of common electric energy such as generator, electric wire netting, battery,etc. belongs to the voltage source, and the energy storage component condenser in VsI compares with energy storage component inductor in CSI, efficiency and volume, price of the energy storage component of energy storage have obvious advantages. However, with the development of superconductive technology, will solve the energy storage efficiency problem of inductance in the electric current type current transformer. Compared with VSI, CSI has one’s own characteristics too, it is easy to realize four quadrants run, and the work is more steady, it is easier to control etc. to export the electric current. So, active to strain the wave APF , without work compensation SVG And in the power system, employ more and more extensive. For going against the becoming device in many level, PWM technology undoubtedly one kind obtains scheme that the ideal outputs. Come generally and say, the control strategy suitable for much level VSI is suitable for much level CSI too, should adopt the control strategy meeting to a different one while being topological. As to sectional much level CSI, each unit CSI is relatively independent in controlling, therefore is easy to adopt PWM technology. As to many level CSI of the direct type, can’t follow the regular modulation method briefly, usually, must consider the following factors while choosing the control strategy in three-phase much level CSI:
1The ones that should maintain electric current of direct-flow side are led continuously openly;
2The electric current guaranteeing to shunt the inductance is balanced;
3Consider the mutual coupling of the three-phase current influence.

Topological analysis of a circuit
Fig. 1 is that five three-phase level CSIs that this text is introduced are topological the following is called direct type five three-phase levels ,Each switch device manage by MOS and one recover the diode connect in series nearly. In the steady state, consider the topological symmetry of the circuit and neglect the line wave of the inductance, inductance flows to can replace each one in the picture through the way that the value is 1/ 2 of the electric current sources while analyzing the circuit. ,Its output level is a I, a I/ 2, 0, 1/ 2. I five level.

CSI in this text, it is two that go against the becoming device ordinarily and connect in parallel at the same electric current both ends of bus bar in view of form, but operation principle its to utilize thought that many level make up, five topological to utilize 4 flow inductance to input electric current to go against the ng device, output the electric current and is divided into two equal divisions level, then carry on the rational distribution, association and receive five necessary level to the three-phase current with the corresponding switch. Take A looks as examples, output level and switch and lead openly and hint that is set out in Table 1.

2 three-phase direct formula five level CSI modulation ways are studied
Much more daily the current transformer PWM control method of level is as follows, much level subdues harmonic PWM SHPWM ,The signal carrier is moved CPS-SPWM ,The switch frequency is optimized SFO-PWM ,The space vector is modulated SVPWM . Five new level CSI modulation ways of three phases shown toward Fig. 1 of this text are the logic PWM technology of a kind of association, use each other bad 120