Digital control of a modular multilevel voltage source

In the proposed paper, we are giving a deeper insight into a control technique of a modular multilevel voltage source. Since the voltage source is used in the research of an increased permeability of a cell membrane, stringent demands regarding magnitude (over 1 kV), output current (more than 10 A) and voltage shape (rectangular pulses with high du/dt slope) should be fulfilled. The presented topology consists of eight individually controlled DC voltage sources - modules - that can be arbitrarily connected in series to obtain the desired output voltage. Operation of the modular multilevel voltage source is based on a principle of a digital-to-analog converter, thus magnitude of a particular module u_n is twice as high as the magnitude of the predecessor (u_n = 2u_n-1). With an appropriate control of output transistors, which connect individual modules in series to form a common output pulse, a total of 2ⁿ different output voltage levels with the resolution of u₁ can be obtained.