Controller for a wound rotor slip ring induction machine
AssigneesABB Automation Inc., ABB Industry Oy
InventorsKalyan P. Gokhale, Douglas W. Karraker, Samuli J. Heikkilä
Life of this patent
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Abstract
The direct torque control (DTC) principle is used to control the torque of a wound ring rotor slip induction machine, also known as a doubly fed or cascade machine, by utilizing a solid state inverter on the rotor side. In addition, the DTC principle is used to control the power factor at the stator terminals of the doubly fed machine to a desired level and also to perform the task of synchronization of stator voltage to the grid voltage. An integrated controller is used to implement these three functions.
Claims26
A method for controlling the torque and power factor of a doubly fed machine using direct torque control, comprising the steps of:
- (a) calculating the estimated torque of said machine;
- (b) determining a torque error from said estimated torque and a reference torque;
- (c) calculating the desired rotor flux command Ψr_ref;
- (d) calculating the actual rotor flux Ψr;
- (e) converting said actual rotor flux from the stator reference frame to the rotor reference frame by multiplying Ψr by e−jθm;
- (f) determining a flux error from said desired rotor flux command and said actual rotor flux converted to the rotor reference frame;
- and
- (g) selecting an inverter voltage vector from said torque error and said flux error.
A method for synchronizing a doubly fed machine having an induced stator voltage using direct torque control to an electrical grid having a grid voltage by controlling the tangential motion and radial length of a flux vector for the rotor of said machine, comprising the steps of:
- (a) determining the stator flux vector from said induced stator voltage;
- (b) determining the grid flux vector from said grid voltage;
- (c) calculating the angular error between said stator flux vector and said grid flux vector;
- (d) comparing said angular error to zero to determine an error signal for controlling said rotor flux vector tangential motion;
- (e) calculating the desired rotor flux command Ψr_ref;
- (f) calculating the actual rotor flux Ψr;
- (g) converting said actual rotor flux from the stator reference frame to the rotor reference frame by multiplying Ψr by e−jθm;
- and
- (h) determining a flux error from said desired rotor flux command and said actual rotor flux converted to the rotor reference frame, said flux error for controlling said rotor flux vector radial length;
- and
- (i) selecting an inverter voltage vector from said torque error and said flux error.
A method for synchronizing a doubly fed machine having an induced stator flux vector using direct torque control to an electrical grid having a grid flux vector by controlling the tangential motion and radial length of a rotor flux vector for said machine, comprising the steps of:
- (a) calculating the angular error between said stator flux vector and said grid flux vector;
- (b) comparing said angular error to zero to determine an error signal for controlling said rotor flux vector tangential motion;
- (c) calculating the desired rotor flux command Ψr_ref;
- (d) calculating the actual rotor flux;
- (e) converting said actual rotor flux from the stator reference frame to the rotor reference frame by multiplying Ψr by e−jθm;
- (f) determining a flux error from said desired rotor flux command and said actual rotor flux converted to the rotor reference frame, said flux error for controlling said rotor flux vector radial length;
- and
- (g) selecting an inverter voltage vector from said torque error and said flux error.
In a controller for controlling the torque and power factor of a doubly fed machine using direct torque control, a method comprising the steps of:
- selecting either a first operating mode of said controller for controlling the torque and power factor of said machine or a second operating mode of said controller for synchronizing said machine to an electrical grid;
- said method comprising when said first operating mode is selected the further steps of:
- calculating the estimated torque of said machine;
- determining a torque error from said estimated torque and a reference torque;
- calculating the desired rotor flux command Ψr_ref;
- calculating the actual rotor flux Ψr;
- converting said actual rotor flux from the stator reference frame to the rotor reference frame by multiplying Ψr by e−jθm;
- determining a flux error from said desired rotor flux command and said actual rotor flux converted to the rotor reference frame;
- and
- selecting an inverter voltage vector from said torque error and said flux error.
Dependencies are inferred from the claim text.