Cascaded Multi-phase Electric Drive
Publication Date: 2014-Apr-30
The IP.com Prior Art Database
This paper proposes a cascaded multi-phase electric drive, including: a multi-phase power transformer, including at least one primary winding and a first number of secondary windings, said primary winding being electrically connectable to a source of multi-phase AC power; a first number of power units, each of said first number of power units having input connected with a corresponding one of said first number of secondary windings, and a multiple of said first number of power units being serially connected with respective others of said power units in each phase output line connectable to a multi-phase AC load; a main controller; and a first number of power unit controllers, each of which being adapted for controlling corresponding one of said first number of power units; wherein: said main controller is adapted for transmitting output voltage reference to each of said power unit controllers controlling the power units in the same phase output line; and said power unit controller is adapted for controlling switching of the corresponding power unit according to PWM pattern in consideration of said output voltage reference received from said main controller. Therefore, the amount of calculation load for the main controller can be reduced.
Cascaded Multi-phase Electric Drive
This paper relates to the field of a cascaded multi-phase electric drive, and more particularly to control system for cascaded multi-phase electric drive.
Cascaded multi-phase electric drives are used in industry to provide variable electric power to AC motors. These same drives can be used in other applications not related to specifically to motors but where a variable-output voltage or frequency is desired. Typical drives have an AC input power source and some type of conversion apparatus, usually using solid-state devices, for converting the fixed AC input voltage into a variable-voltage and/or variable-frequency output. One such type of drive is described in U.S. Pat. No. 5,625,545, which is incorporated herein by reference. That patent describes a power supply used as a drive which utilizes a number of power cells (power units) arranged to produce a three-phase AC output. Such multiple power units in series can be utilized to provide higher voltage outputs than would be available with only a single power unit.
The switches in each of the power units of the cascaded multi-phase electric drive are switched in pairs during normal operation. The switching has a fixed period and amplitude but variable duty cycle, it is thus called pulse-width modulation (PWM). Switching commands for PWM are generated by comparing the output voltage reference to a set of triangular or saw-tooth waveforms called carriers. In a conventional cascaded multi-phase drive, it is the main controller which, for the respective one of the power unit, generates the carrier, makes the comparison between the carrier and the output voltage reference, and upon the comparison result transmits on-off command to the corresponding power unit controller such that the power unit controller can control the switching of the power switches of the power unit. Since the cascaded multi-phase electric drive has a multiple of power units for the same phase output line and their carries are phase shifted with respect to each other, on-off commands from the main controller to the different power units are not in phase but have a time shift with respect to each other; namely different sequence of on-off command signal is sent to respective one of the power units in the same phase output line. The more of the power unit to be controlled by the main controller, the more workload the main controller needs to handle.
It is therefore an objective to reduce the workload of the main controller of a cascaded multi-phase electric drive.
According to one aspect, it proposes a cascaded multi-phase electric drive, including: a multi-phase power transformer, including at least one primary winding and a first number of secondary windings, said primary winding being electrically connectable to a source of multi-phase AC power; a first number of power units, each of said first number of power units having input connected with...