Patent ID: 11870373
Assignee: KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H | IPC H

Claim 4:
5. A system for torque control and capacitor voltage balancing of a dual three-level (3L) T-type multilevel converter, comprising:
an open ends three-phase induction motor (OEIM) having a stator, a rotor, and first, second and third parallel phase paths having first ends and second ends;
a first 3L T-type converter connected to the first ends of the first, second and third parallel phase paths and a second T-type converter connected to the second
ends of the first, second and third parallel phase paths;
a first voltage source block connected to the first T-type converter and a second voltage source block connected to the second T-type converter, wherein each voltage source block includes a voltage source and a first capacitor in series with a second capacitor, wherein each voltage source block has a positive connector, a negative connector and a common connector, wherein the common connector is located at a midpoint of the series connection of the first capacitor and the second capacitor;
wherein the first T-type converter includes:
first, second and third phase legs, each phase leg including:
first and second series connected switches, wherein the first switch is connected to the common connector and the second switch is connected to the first end of one of the parallel phase paths;
a set of third switches, each third switch connected between the positive connector and the first end of the one of the parallel phase paths and a set of fourth switches, each fourth switch connected to the negative connector and the first end of the one of the phase paths;

wherein the second T-type converter includes:
first, second and third phase legs, each phase leg including:
first and second series connected switches, wherein the first switch is connected to the common connector and the second switch is connected to a second end of one of the parallel phase paths;
a set of third switches, each third switch connected between the positive connector and the second end of the one of the phase paths and a set of fourth switches, each fourth switch connected to the negative connector and the second end of the one of the phase paths;

a plurality of sensors configured to measure torque deviations in the rotor, flux deviations in the stator, and the voltages of the first and second capacitors of each voltage source block;
a control system having circuitry connected to the switches of each T-type converter and the plurality of sensors, the control system including a central processing unit (CPU) having program instructions stored within that, when executed by one or more processors of the CPU, cause the one or more processors to receive the measured torque deviations and flux deviations and generate gating signals to the first switch, the second switch and the set of third switches of each T-type converter, wherein the gating signals are configured to reduce the torque deviations in the rotor and the flux deviations in the stator of the OEIM and balance the voltages of the capacitors;
wherein the plurality of sensors include:
a plurality of voltage transducers configured to measure the voltages Vc1 and Vc2 of the first capacitors of the first voltage source block and the voltages Vc3 and Vc4of the second capacitors of the second voltage source block and to measure a voltage V3 across the stator;
an encoder configured to measure an angular speed wr, of the rotor of the OEIM;
a plurality of current transducers configured to measure current in each of the phase paths;

wherein the circuitry of the control system includes:
an input/output port configured for receiving a rotor angular speed reference value ωref, a flux weighting factor (KΨ), a rated torque value Trated, a rated stator flux value ∥ψs_rated∥, and a reference stator value ψsref ;

an adder operatively connected to the input/output port and the encoder, the adder configured to subtract the angular speed ωr of the rotor from the rotor angular speed reference value ωref and generate a difference rotor flux value;
a proportional integral derivative (PID) controller connected to the adder and configured to receive the difference rotor flux value and generate a reference torque value Tref, 
wherein the one or more processors of the CPU are configured to receive the reference torque value Tref, the reference stator flux value ωsref, and the voltages of the capacitors and execute the program instructions to generate the gating signals;

wherein the program instructions are configured to:
select a first set of voltage vectors from the voltages of the capacitors;
evaluate a first cost function J1 for each voltage vector of the first set of voltage vectors to generate a set of first cost functions;
minimize the set of first cost functions;
identify a first optimum voltage vector from the first set of voltage vectors which minimizes the set of first cost functions;
identify four redundant switching states of the first optimum voltage vector which minimizes the set of first cost functions;
evaluate a second cost function J2 using the four redundant switching states of the first optimum voltage vector which minimizes the first cost function J1 to generate a set of second cost functions;
minimize the set of second cost functions;
identify a second optimum voltage vector which minimizes the second cost function J2, wherein the second optimum voltage vector includes optimum switching states of the first and second series connected switches, the set of third switches and the set of fourth switches of the first T-type converter and the first and second series connected switches, the set of third switches and the set of fourth switches of the second T-type converter;
update the set of four possible switching states with the optimum switching states of the second optimum voltage vector which minimizes the second cost function J2,

wherein the control system is configured to generate the gating signals for the SiC semiconductor switches using the updated set of four possible switching states; and
apply the gating signals to the switches to actuate the OEIM and balance the voltages of the capacitors.