A simplified control system for series connected, AC-DC PWM converters, for back-to-back multiterminal systems

Voltage source PWM rectifiers are able to work with near sinusoidal current waveforms and unity or even leading power factor. From the point of view of the DC link, these rectifiers reverse power through current instead of voltage reversal, allowing back-to-back multiterminal converter topologies. However, some problems related with this system are the complexity of the control circuit, the stability of the system and the DC voltage-sharing between converters. This paper analyzes these problems and proposes a simple solution. Based on the detection of the DC current instead of the DC voltage, using a unique and predefined PWM pattern, stored in an EPROM, for each converter. The patterns are phase shifted following the load current variations, allowing control of the voltage of the DC link. The main characteristics of this solution are: (a) there is no master rectifier (all are hierarchically identical); (b) the stability does not depends on the size of the DC capacitors; (c) it can work at leading power factor for all load conditions; and (d) it can be adjusted to work at zero regulation. Computer simulations, mathematical analyses and some experimental results with a 2 kW voltage regulated PWM prototype are included in the paper.<>