STATEMENT REGARDING PRIOR DISCLOSURE BY THE INVENTORS

Aspects of this technology are described in an article “Capacitor Balancing and Common-Mode Voltage Reduction of a SiC Based Dual T-Type Drive System Using Model Predictive Control” published in IEEE Transactions on Power Electronics, Vol. 35, Issue 3, 10704-10711, on Jul. 31, 2019, which is incorporated herein by reference in its entirety.

STATEMENT OF ACKNOWLEDGEMENT

The inventors acknowledge the support provided by the Center of Energy and Geo-Processing (CeGP), King Fand University of Petroleum and Minerals, through funded Project No. GTEC1701, and funding support provided by King Abdullah City for Atomic and Renewable Energy (K.A.CARE).

BACKGROUND

Technical Field

The present disclosure is directed to methods and systems for predictive torque control and capacitor balancing of a silicon-carbide (SiC) based dual T-type drive system using a reduced set of switching states for model predictive control.

Description of Related Art

The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.

T-type multilevel converters (MLCs) are conventionally used as reduced switching element topologies for diode clamped converters (DCC). Compared to two-level (2L) voltage source converters (VSCs), the T-type MLC performs with lower harmonic contents, which is essential in any industrial drive application. (See Norambuena, Margarita, Samir Kouro, Sibylle Dieckerhoff, and Jose Rodriguez. “Reduced Multilevel Converter: A Novel Multilevel Converter With a Reduced Number of Active Switches.”IEEE Transactions on Industrial Electronics65, no. 5 (2018): 3636-3645, incorporated herein by reference in its entirety). Furthermore, compared to conventional DCCs, the T-type multilevel converter reduces the converter losses by 30-40% at a certain switching frequency range (up to 12 kHz). (See M. Schweizer; J. W. Kolar, “Design and implementation of a highly efficient three-level T-type converter for low-voltage applications,”IEEE Trans. Power Electron,vol. 28, no. 2, pp. 899-907. 2013; A. Salem, F. De Belie, et. al., Evaluation of a dual-T-type converter supplying an open-end winding induction machine.” InIndustrial Electronics Society, IECON2013-39th Annual Conference of the IEEE,pp. 749-754. IEEE, 2013; Salem, A., M. F. Elsied, Joachim Druant, Frederik De Belie, Amrane Oukaour, Hamied Gualous, and Jan Melkebeek. “An advanced multilevel converter topology with reduced switching elements.” InIndustrial Electronics Society, IECON2014-40th Annual Conference of the IEEE,pp. 1201-1207. IEEE, 2014; and M. Elsied, A. Salem, A. Oukaour, H. Gualous, H. Chaoui, T. Youssef, F. De Belie, J. Melkebeek, and O. Mohammed. “Efficient power-electronic converters for electric vehicle applications.” In 12th IEEE Vehicle Power and Propulsion Conference(VPPC), pp. 978-983. 2015, each incorporated herein by reference in their entirety).

Model predictive control (MPC) is a method of process control that is used while satisfying a set of constraints. MPC is based on iterative, finite-horizon optimization of a plant model, such as power system balancing models. At time t the current plant state is sampled and a cost minimizing control strategy is computed (via a numerical minimization algorithm) for a relatively short time horizon in the future: [t, t+T]. Specifically, an online or on-the-fly calculation is used to explore state trajectories that emanate from the current state and find (via the solution of Euler-Lagrange equations) a cost-minimizing control strategy until time t+T. After the first step of the control strategy is implemented, the plant state is sampled again and the calculations are repeated starting from the new current state, yielding a new control and new predicted state path. The prediction horizon keeps being shifted forward. The advantage of MPC is that it allows a current timeslot to be optimized, while taking into account the future time evolution of the system. This is achieved by optimizing a finite time-horizon, but only implementing the current timeslot and then optimizing again repeatedly. Additionally, MPC can anticipate future events and take control actions accordingly. Proportional integral derivative (PID) controllers do not have this predictive ability.

Model predictive control has been used to drive power converters. (See F. Wang, X. Mei, J. Rodriguez, and R. Kennel, “Model Predictive Control for Electrical Drive Systems—An Overview,”Ces Trans. Electr. Mach. Syst.,vol. 1, no. 3, pp. 219-230, 2017; S. Vazquez, J. Rodriguez, M. Rivera, L. G. Franquelo, and M. Norambuena, “Model Predictive Control for Power Converters and Drives: Advances and Trends,”IEEE Trans. Ind. Electron.,vol. 64, no. 2, pp. 935-947, 2017; and S. Vazquez, J. I. Leon, L. G. Franquelo, J. Rodriguez, H. a. Young, A. Marquez, and P. Zanchetta, “Model predictive control: A review of its applications in power electronics,”IEEE Ind. Electron. Mag.,vol. 8, no. 1, pp. 16-31, 2014; and Salem, A., Mamdouh, M., Abido, M. A., “Predictive Torque Control and Capacitor Balancing of a SiC-Based Dual T-Type Drive System” published in IEEE Transactions on Power Electronics, Vol. 35, Issue 3, 10704-10711, on Jul. 31, 2019 each incorporated herein by reference in their entirety).

In particular, finite control set MPC (FCS-MPC) may be adapted to a power converter and represents a potential alternative to sophisticated pulse width modulation techniques required for complex power converters. In FCS-MPC, the converter voltage vectors (VVs) are tested individually in a predefined cost function. The voltage vector that minimizes the cost function will be selected as the optimal one and applied on the next control sample. The cost function normally consists of summations of predicted deviations of the controlled variables compared with their reference values. Therefore, not only torque and flux can be controlled in electrical motor drives, but also capacitor balancing and common-mode voltage (CMV) mitigation of multilevel converters can be realized in the same cost-function. (See Dzung, Phan Quoc, Nguyen Dinh Tuyen, Nguyen The Tien, and Nguyen Chan Viet. “Model predictive current control for T-type NPC inverter using new on-line inductance estimation method.” InRegion10Conference(TENCON), 2016IEEE,pp. 316-321. IEEE, 2016; and Barros, J. Dionisio, J. Fernando A. Silva, and Élvio G A Jesus. “Fast-predictive optimal control of NPC multilevel converters.”IEEE Transactions on Industrial Electronics60, no. 2 (2013): 619-627, each incorporated herein by reference in their entirety).

Three-level (3L) T-type capacitor voltage balancing has been investigated using pulse-width modulation (PWM) techniques. (See Choi, Ui-Min, June-Seok Lee, and Kyo-Beum Lee. “New modulation strategy to balance the neutral-point voltage for three-level neutral-clamped inverter systems.”IEEE Transactions on Energy Conversion29, no. 1 (2014): 91-100; Choi, Ui-Min, Frede Blaabj erg, and Kyo-Beum Lee. “Method to minimize the low-frequency neutral-point voltage oscillations with time-offset injection for neutral-point-clamped inverters.”IEEE Transactions on Industry Applications51, no. 2 (2015): 1678-1691; Ding, Ran, Jun Mei, Jianfeng Zhao, Zhihong Zhao, and Jie Tian. “A simplified balance factor based midpoint voltage deviation eliminating method for T-type three-level inverter.” InSmart Grid and Clean Energy Technologies(ICSGCE), 2016International Conference on,pp. 328-333. IEEE, 2016; and Choi, Ui-Min, Hyun-Hee Lee, and Kyo-Beum Lee. “Simple neutral-point voltage control for three-level inverters using a discontinuous pulse width modulation.”IEEE Trans. Energy Conyers28, no. 2 (2013): 434-443, each incorporated herein by reference in their entirety). However, the extension of these techniques to five-level (5L) converters (dual three-level) has some technical limitations in terms of computation and execution times.

5L nested DCC capacitor balancing has been studied using MPC. (See Dekka, Appa Rao, and Mehdi Narimani. “Capacitor Voltage Balancing and Current Control of a Five-Level Nested Neutral Point Clamped Converter.”IEEE Transactions on Power Electronics(2018); and Li, Junjie, and Jianguo Jiang. “Active Capacitor Voltage-Balancing Methods Based on the Dynamic Model for a Five-Level Nested Neutral-Point Piloted Converter.”IEEE Transactions on Power Electronics33, no. 8 (2018): 6567-6581, each incorporated herein by reference in their entirety).

Prior work by some of the inventors of the present disclosure investigated capacitor balancing for the dual T-type topology using switching state redundancy based on an off-line study. (See A. Salem, T. Youssef, F. De Belie, J. Melkebeek, O. Mohammed, and M. Abido. “DC link capacitor voltage balancing of a dual three-level T-Type AC drive using switching state redundancy.” In 10th Biennial International Electric Machines and Drives Conference.2017, incorporated herein by reference in its entirety).

Another related important problem in AC drives is the common mode voltage (CMV). The CMV affects the bearings of the induction motor (IM) and may reduce its lifetime. (See Salem et al. (2017); and Julian, Alexander L., Giovanna Oriti, and Thomas A. Lipo. “Elimination of common-mode voltage in three-phase sinusoidal power converters.”IEEE Transactions on Power Electronics14, no. 5 (1999): 982-989, each incorporated herein by reference in their entirety). Two well-known approaches have been used to address this problem, i.e., CMV reduction (CMVR) and CMV elimination (CMVE). The CMVE method was based on selecting the voltage vectors (VVs) that produce zero CMV. This technique reduced the number of possible voltage vectors for the drive system control. On the other hand, the CMVR decreased the CMV value by PWM techniques or by using an MPC technique. (See A. Salem, and M. A. Abido. “T-Type Multilevel Converter Topologies: A Comprehensive Review.”Arabian Journal for Science and Engineering(2018): 1-23, incorporated herein by reference in its entirety).

CMVR using PWM techniques for different types of converters has been a topic of research. A synchronous optimal PWM technique was used to reduce the CMV of a modular multi-level converter (MLC) connected to an open ends induction motor (OEIM). (See E. Amarendra, and A. Rathore. “Optimal pulse width modulation for common-mode voltage elimination scheme of medium-voltage modular multilevel converter-fed open-end stator winding induction motor drives.”IEEE Transactions on Industrial Electronics64, no. 1 (2017): 848-856, incorporated herein by reference in its entirety). However, this MLC topology had the drawback of having separate capacitors for each switching module (half H-bridge topology) which increased the power circuit complexity.

In Zhang et al., a carrier based PWM was used to reduce the CMV of a 2L matrix converter. (See Zhang, Jianxin, Mei Su, Wenjing Xiong, Yao Sun, Xiaochao Hou, and Xing Li. “Carrier-based modulation strategy of indirect matrix converters for common-mode voltage reduction.” InFuture Energy Electronics Conference and ECCE Asia(IFEEC2017-ECCE Asia), 2017IEEE3rd International,pp. 534-538. IEEE, 2017, incorporated herein by reference in its entirety). However, due to protection issues, the matrix converter is not widely used in industrial drive applications.

Another research work introduced the CMVR and capacitor balancing of a single 3L T-type MLC using a finite control set (FCS) MPC, where 19 switching states were used to mitigate the CMV. The MPC code consumed 100 μs, which was too high for 3L converters. (See Xing, Xiangyang, Alian Chen, Zicheng Zhang, Jie Chen, and Chenghui Zhang. “Model predictive control method to reduce common-mode voltage and balance the neutral-point voltage in three-level T-type inverter.” InApplied Power Electronics Conference and Exposition(APEC), 2016IEEE,pp. 3453-3458. IEEE, 2016, incorporated herein by reference in its entirety).

A switching function model is a mathematical representation for the voltage source converters that provides a view of the converter switching states (SS). (See Holmes, D. G., Lipo, T. A., “Pulse Width Modulation for Power Converters: Principles and Practice,” Book, USA:Wiley-IEEE Press, John Willy and Sons,Inc., October 2003, incorporated herein by reference in its entirety).

Silicon Carbide (SiC) MOSFETs have been used in power electronic converters, which lowers energy consumption during turning on/off transitions as well as lowering turn-on resistance as compared to conventional silicon IGBT switches. However, the fast on/off transitions affect the ringing of the converter output voltage if the electromagnetic interference (EMI) is not considered during the converter design. Therefore, the use of the SiC MOSFETs in complicated power circuits, as the case in 5L converters, needs further development.

Although CMVE reduces the eddy currents in bearings, none of the prior research has thoroughly addressed the impact of CMVE on core losses. CMVE has a negative impact on core losses due to the harmonic increase in the absence of some voltage vectors used in the CMVE technique. (See Salem, A., A. Abdallh, Paavo Rasilo, Frederik De Belie, M. N. Ibrahim, Luc Dupre, and Jan Melkebeek. “The effect of common-mode voltage elimination on the iron loss in machine core laminations of multilevel drives.”IEEE Transactions on Magnetics51, no. 11 (2015): 1-4, incorporated herein by reference in its entirety).

Accordingly, it is one object of the present disclosure to provide methods and systems for common mode voltage reduction (CMVR) in an induction motor driven by a 5-level converter in order achieve better drive system performance and lower harmonic content. A reduced switching state MPC incorporates CMVE/CMVR, DC link capacitor balancing and machine torque control. Use of the reduced switching state MPC of the present disclosure significantly reduces the computation time and improves the MPC performance.

SUMMARY

In an exemplary embodiment, a method is described for reducing computation time for model predictive control (MPC) of a 5 level dual T-type multilevel converter connected to a three-phase open ends induction motor (OEIM), each multilevel converter including two capacitors and a plurality of plurality of silicon carbide MOSFET semiconductor switches, comprising determining a set of switching states of the plurality of silicon carbide MOSFET semiconductor switches, identifying a reduced set of switching states from the set of switching states, storing the reduced set, calculating a first set of cost functions which include motor fluxes, motor torques, common mode voltage and capacitor voltages for each switching state of the reduced set of switching states, summing the first set of cost functions to generate a first set of summed cost functions, minimizing the first set of summed cost functions, identifying a voltage vector which minimizes the first set of summed cost functions, generating a plurality of gating signals for the plurality of silicon carbide semiconductor switches using the voltage vector, applying the plurality of gating signals to the plurality of SiC semiconductor switches to operate the OEIM with decreased motor flux ripples, decreased motor torque ripples and balanced capacitor voltages, wherein calculating the first set of cost functions with the reduced set of switching states reduces the computation time for model predictive control of the converter switches.

In another exemplary embodiment, a system for reducing computation time for model predictive control (MPC) of a 5 level dual T-type multilevel converter connected to a three-phase open ends induction motor (OEIM) having first, second and third phase paths connected between a first end and a second end is described, comprising a first three-level T-type converter connected to the first end of the OEIM and a second three-level T-type converter connected to the second end of the OEIM, a first voltage source block connected to the first converter and a second voltage source block connected to the second converter, each voltage source block including 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 each three-level T-type converter includes first, second and third phase legs, 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 terminal of one of the phase paths, a third switch connected between the positive connector and the terminal of the one of the phase paths and a fourth switch connected to the negative connector and the terminal of the one of the phase paths, wherein each switch is a SiC MOSFET semiconductor switch in parallel with a diode, wherein the diodes of the first and second series connected switches are antiparallel to each other, and wherein the diodes of the third and fourth switches are parallel to each other, a plurality of sensors configured for measuring system parameters, and a control system having circuitry connected to the switches of each three-level T-type converter and the plurality of sensors, the control system having circuitry and program instructions stored within that, when executed by one or more processors, cause the one or more processors to determine a reduced set of switching states which lower the computation time for model predictive control of the converter switches.

In another exemplary embodiment, a non-transitory computer readable medium having instructions stored therein that, when executed by one or more processor, cause the one or more processors to perform a method a non-transitory computer readable medium having instructions stored therein that, when executed by one or more processors, cause the one or more processors to perform a method for reducing computation time for model predictive control (MPC) of a 5 level dual T-type multilevel converter connected to a three-phase open ends induction motor (OEIM), each multilevel converter including two capacitors and a plurality of plurality of silicon carbide (SiC) MOSFET semiconductor switches, comprising determining a set of switching states of the plurality of switches, selecting a reduced set of switching states from the set of switching states, calculating a set of cost functions which include motor fluxes, motor torques, common mode voltage and capacitor voltages for each switching state of the reduced set of switching states, summing the set of cost functions to generate a first set of summed cost functions, minimizing the first set of summed cost functions, identifying a voltage vector which minimizes the first set of summed cost functions, generating a plurality of gating signals for the plurality of silicon carbide semiconductor switches using the voltage vector, applying the plurality of gating signals to the plurality of SiC semiconductor switches to operate the OEIM with reduced motor flux ripples, motor torque ripples and balanced capacitor voltages, wherein calculating the set of cost functions with the reduced set of switching states decreases the computation time for model predictive control of the converter switches.

The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure, and are not restrictive.

