Voltage Vector Research Articles

The simulation analysis of stator flux droop minimization in direct torque control open-end winding induction machine

<span lang="EN-US">Direct torque control (DTC) using dual-inverter technique is one of the best topologies for electric vehicle (EV) as it offers abundant selection of voltage vectors to drive the induction machine (IM). This dual-inverter technique also more reassuring as the system still workable even any of its voltage supply is disrupted or the power pack is drained. However, during the uneven voltage supply, the movement of voltage vectors is interrupted and will move obliquely especially in medium voltage vectors. This situation will lead to the faulty movement of the voltage vectors in the default sector definitions and lead to huge flux droop, which later could impose to distort phase current. This paper proposes an optimal sector definition based on the preset voltage ratio between the two inverters. The voltage vectors can be mapped tangentially to the flux vector, minimizing the flux droop and improving the phase current waveform when the proposed sector is utilized. The effectiveness of the proposed sector is tested using MATLAB/Simulink software and the exact parameter from the induction machine.</span>

A Novel Double-Voltage-Vector Model-Free Predictive Current Control Method for Two-Level Voltage Source Inverters

An improved model-free predictive current control (MFPCC) scheme based on double-voltage-vector for two-level voltage source inverters (2L-VSIs) is proposed in this paper. First, two basic voltage vectors are chosen in each control period, whose durations are calculated based on the cost function. Then, a novel current gradient updating method is developed by using the applied two voltage vectors to calculate the current gradients of the remaining six voltage vectors. As a result, the stagnation effect can be eliminated and current ripples and total harmonic distortion can be reduced effectively. In addition, due to the nature of vector diagram symmetry, the processing of current gradient updating is simplified and the calculation speed is increased. The effectiveness of the proposed scheme is verified by simulation and experimental results from the 2L-VSI system.

Modulated Model-Free Predictive Current Control for Voltage Source Inverters With Stagnation Elimination and Sampling Disturbance Suppression

Model-free predictive current control (MFPCC) has been widely used in voltage source inverters (VSIs). The output current performance of look-up-table-based MFPCC is affected by the number of the applied voltage vectors (VVs), the current gradient updating and the sampling disturbance. To improve the current performance, a novel modulated MFPCC is proposed for VSI, while real-time current gradient updating and sampling disturbance suppression can be achieved. First, three basic VVs are picked, whose duration time are computed according to the current gradients. Second, an advanced current gradient updating method is presented by establishing the equations of different current gradients under different VVs. Furthermore, the sampling disturbance effect on MFPCC is analyzed and an extended state observer is designed to suppress such effect. Simulation model and experimental platform of the VSI system are structured to verify the preponderance of the proposed MFPCC in reducing the total harmonic distortion of output current.

A simple duty cycle control technique to minimize torque ripple in open-end winding induction motor

Modern electric vehicles (EVs) that drive an induction motor (IM) fed by a traction inverter are fast gaining popularity due to their simple configuration and robustness. The direct torque control (DTC) technique is one of the best control methods to drive the IM, especially in open-end winding configurations, as it offers more voltage vectors. However, the existence of hysteresis controllers and improper switching technique causes larger torque ripples that leads to variable switching frequency. The study will be focused on the open-end winding induction motor where the direct current (DC) power is fed from both sides of the stator windings using the dual inverter configuration. To minimize the torque ripples, a simple switching technique using the duty cycle control method is proposed by injecting a high-frequency square wave into the default inverter switching status to form the new pattern of voltage vectors. The effectiveness of the proposed technique is tested through MATLAB/Simulink software and validated experimentally with a lab-scale setup using a dSPACE controller. The findings show that the proposed method reduces torque ripple by over 50% while keeping the DTC's simple structure.

An Improved High-Frequency Voltage Injection Method for Interturn Short-Circuit Fault Detection in PMSMs

The inter-turn short-circuit fault (ITSCF) is a common incipient fault for the permanent magnet synchronous machine (PMSM) drive system. In recent years, the high-resolution ITSCF detection method that combines the high frequency (HF) signal injection and zero-sequence voltage measurement has been put forward. However, for the traditional HF signal injection technique, nonnegligible voltage distortion may occur when the injection frequency is close to the PWM carrier-frequency. In addition, the injected voltage varies with the operating conditions of the PMSM. These drawbacks of the traditional HF signal injection technique greatly limit the ITSCF detection performance using HF signal injection. To further improve the ITSCF detection performance, an improved HF injection scheme is proposed in this paper. In the proposed method, the six active voltage vectors are injected into the PMSM in certain orders to realize a rotating voltage injection, and the injection frequency is up to five-sixth of the PWM carrier-frequency. By employing the proposed injection method, the ITSCF detection sensitivity can be much improved. And the ITSCF detection performance is not affected by the operation conditions of the PMSMs. Finally, the simulations and experiments are carried out to verify the proposed method.

An Improved Modulation Strategy With Torque Ripple Suppression Method for OEW-PMSM Drives With Common DC Bus

The open-end winding permanent magnet synchronous machine drive with common dc bus has zero sequence loop, which inevitably generates the zero sequence current (ZSC). Due to the existence of the third harmonic flux linkage, ZSC causes the zero sequence torque and augments the torque ripple. In this paper, an improved modulation strategy with torque ripple suppression method is presented. Firstly, to reduce the computation burden, a modified alternate sub-hexagonal center pulsewidth modulation (ASHCPWM) strategy is designed. The switching duration time of two inverters can be obtained by the projection of voltage vector on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc</i> coordinate frame. Secondly, a ZSC suppression method based on the time compensation coefficient is adopted for the modified modulation strategy, which can restrain ZSC and reduce torque ripple. Thirdly, to further reduce torque ripple, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current injection method is employed in the control scheme. Finally, three methods are presented in simulation and experiments for comparison, namely the deadbeat predictive current control (DPCC) method with conventional ASHCPWM, the DPCC method with sample-averaged zero-sequence current elimination PWM, and the proposed DPCC method with modified ASHCPWM and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current injection. The results test the effectiveness of the proposed method.

Zero-Vector-Regulation-Based Closed-Loop Power Distribution Strategy for Dual-DC-Port DC–AC Converter-Connected PV–Battery Hybrid Systems

The dual-dc-port dc-ac converter-connected photovoltaic (PV)-battery hybrid systems present high-efficiency and low-cost features with single-stage power conversion as PV and battery are connected to the grid directly. However, it is challenging to achieve flexible power distribution in this configuration due to its coupled features in grid-side current tracking and power distribution. To deal with this issue, this paper proposes a zero vector regulation-based closed-loop power distribution strategy for the dual-dc-port dc-ac converter-connected PV-battery hybrid systems. By modeling the dual-dc-port dc-ac converter as an equivalent two-level one, an extra control freedom for power regulation is accessible and a closed-loop power control is adopted for flexible power distribution by zero vector regulation. With the proposed power distribution strategy, the desirable quality of the grid-side current is achieved without complicated voltage vector synthesis, along with good adaptivity to different modes/voltages and flexible power control. Besides, detailed power distribution discussion and analysis with different proportions of zero vector are carried out. Finally, the islanded microgrid experimental tests are conducted to verify its effectiveness and feasibility.

Deadbeat Power Distribution Control of Single-Stage Multiport Inverter-Fed PMSM Drive for Hybrid Electric Vehicles

Single-stage multiport inverter (SSMI)-fed motor drives are promising solutions for multisource hybrid electric vehicles (HEVs) since the dc-dc converter is removed and all the active power is delivered within a single power conversion stage. However, this topology presents inherent coupled issues in controller design because power distribution should be achieved simultaneously in addition to stator current control. To address this issue, an equivalent two-level model is proposed to achieve decoupled control of the SSMI, where stator current control is achieved by regulating the active vectors, and power distribution is achieved by regulating the zero vectors. A deadbeat power distribution scheme is developed under the equivalent two-level model. The proposed scheme provides these advantageous features: fewer computational burdens without complicated sector selection and dwell time calculation under the unevenly distributed voltage vector diagram, fewer adjusted parameters, and fast dynamic response. Moreover, the power distribution capability of the SSMI with the proposed scheme is also analytically revealed. A series of experimental results demonstrate the excellent performance of the proposed deadbeat power distribution control scheme.

Virtual Voltage Vector-Based Sequential Model-Free Predictive Control for Multiparalleled NPC Inverters

Parallel inverters are widely used in the micro-grid systems to meet the demand for increased power capacity and enhanced reliability. However, unbalanced connections between the parallel inverters may cause a spike in the zero-sequence circulating current (ZSCC), leading to performance degradation. To address this issue, a virtual voltage vector-based sequential model-free predictive control method is proposed in this paper for parallel converters. Specifically, extended state observer (ESO) and virtual voltage vectors are introduced into the finite control-set model predictive control (FCS-MPC) architecture to cope with the multi-objective including ZSCC inhibition and robustness performance improvement. Next, to prevent the adjusting of weighting factors, a sequential model-free predictive control solution is constructed. The main feature of the proposed control methodology is that the reliability and robustness of the controlled system can be significantly enhanced without knowing the accurate mathematical models and parameters. Finally, the effectiveness of the suggested approach is verified by performance evaluation.

Space Vector Pulsewidth Modulation Strategy for ANPC-5L Inverter Based on Model Predictive Control

SVPWM strategies for active neutral-point-clamped five-level (ANPC-5L) inverters have multiple control degrees of freedom and control objectives. However, traditional SVPWM strategies are hard to realize optimal control of multiple objectives due to the objectives are coupled with each other. To address this problem, an SVPWM strategy based on model predictive control (MPC) is proposed. In the pulse generation process of the proposed SVPWM, all control degrees of freedom are utilized to achieve optimal control of multiple objectives through MPC. Firstly, voltage vector sequences that meet the requirements of CMV are selected. Then, a cost function is constructed to realize optimal control of the neutral point potential (NPP) and three floating capacitors (FCs) voltage. The proposed strategy has advantages such as high control accuracy and producing low CMV. Finally, the effectiveness of the proposed strategy is validated by a 150kW three-phase ANPC-5L inverter prototype.

Duty-Cycle Correction-Based Model Predictive Current Control for PMSM Drives Fed by a Three-Level Inverter With Low Switching Frequency

In this paper, a duty-cycle correction-based model predictive current control (DC-MPCC) is proposed for permanent magnet synchronous motor (PMSM) supplied by a neutral-point clamped three-level voltage source inverter (NPC-3LVSI). Unlike the conventional MPCC, which evaluates the impact of basic voltage vectors on the concerned state variables, the proposed DC-MPCC modifies the output voltage levels with optimized duty-cycle corrections. Firstly, the last three-phase voltage levels are assumed to be kept during the next control period. Then, the current tracking error and neutral-point potential are predicted. After that, the voltage levels are modified with zero, one, or two state changes, which formulate seven candidate solutions. Subsequently, the duty-cycle corrections of the modified voltage levels are computed based on the principle of minimizing current tracking error and neutral-point voltage drift. Finally, the optimal switch sequence is generated by evaluating and sorting a cost function with a penalty on switch actions. The proposed DC-MPCC features variable switching instants, relatively lower sampling frequency, and satisfactory performance under low switching frequency. Experimental tests carried out on a NPC-3LVSI fed PMSM drive, with 100 Hz fundamental frequency and 400 Hz switching frequency, accompanied by a video demonstration, validate the effectiveness of the proposed method.

A nine-switch inverter with reduced leakage current for PV grid-tied systems using model-free predictive current control

To address the leakage current problem of transformerless three-phase inverters for photovoltaic (PV) grid-tied systems, H8 and improved H8 inverters were proposed to alleviate the leakage current of the PV grid-tied systems to a certain extent. However, these inverters cannot avoid the high-frequency switching of the generated common mode voltages (CMVs) among multiple levels, resulting in the unsatisfactory effect of the leakage current suppression of these inverter topologies. In order to solve these problems, an auxiliary power supply based nine-switch (AP-H9) inverter with reduced leakage current is proposed in this paper. A DC auxiliary circuit containing a switch is added to the inverter based on the H8 inverter, and one or more diodes are connected in reverse parallel with other corresponding switches to form the H9 inverter topology. By properly controlling the nine switches and using the reverse diodes to divide the DC voltage , the CMV of the system is limited to 2/3 times of the DC voltage, which can effectively suppress the leakage current of the PV grid-tied system. In addition, a model-free predictive current control (MFPCC) method based on ultra-local model is presented to eliminate the dependence of inverter control performance on system parameters. This method uses the voltage and current information of the previous two moments to realize the online update of the gain and dynamic part of the ultra-local model, and then obtain the predicted voltage vector for the next moment. Moreover, the switching loss optimization constraint is considered in the cost function to further improve the efficiency of the inverter. Finally, an experimental prototype is developed. The simulation and experimental results show that the proposed inverter and its control method can effectively suppress the leakage current of PV grid-tied system, and are insensitive to parameter changes.

Compensation-Voltage-Injection-Based Neutral-Point Voltage Fluctuation Suppression Method for NPC Converters

Three-level neutral-point clamped (NPC) inverters are widely used in the new energy power generation, motor drive, and many other occasions. However, the neutral-point voltage imbalance of an NPC inverter will affect the output of the inverter system, and the control of the neutral point voltage has become a popular research topic. In this paper, a compensation-voltage-injection-based neutral-point voltage balancing method is proposed. During the switching cycle, the average value model of the neutral-point current under different voltage vectors is applied to calculate the value of the compensation voltage that needs to be injected. The self-balance of the neutral-point voltage based on a switching cycle is realized, and the influence of modulation ratio and power factor on equalization ability is discussed. A MATLAB/Simulink simulation model and a small power prototype are established to verify the effectiveness of the method, and the simulation and experimental results show that the proposed method can effectively suppress the neutral-point voltage fluctuation in a wide range of modulation ratios and power factors.

SVPWM control strategy for Novel Interleaved High Gain DC converter fed 3-level NPC Inverter for Renewable Energy Applications

The high-gain DC converter is a crucial step in the conversion process for raising the voltage from PV panels to the desired voltage level in renewable energy applications. This article proposes a three-phase grid connected PV system with a novel interleaved high gain DC converter fed 3-level Neutral-Point-Clamped (NPC) Inverter. The novel high-gain DC converter consists of an interleaved boost converter (IBC) at its input side, a switched capacitor cell, a passive clamp circuit, and a voltage multiplier unit (VMU). The interleaved arrangement eliminates the input current ripple, and the VMU is utilized to improve the overall voltage gain besides the reverse recovery problem of diodes. The proposed converter is operated at a duty cycle D = 0.6 and a high voltage conversion ratio of 17.5 which is ideal for sustainable energy applications. This paper uses the proposed converter for a grid-connected solar PV system with an NPC inverter controlled using Space Vector Pulse Width Modulation (SVPWM) technique. The SVPWM strategic approach is a prevalent modulation technique for NPC inverter due to its extensibility in choosing the ideal voltage vectors. It uses an active filter, which is more dependable, dynamically better behaved, and capable of operating accurately under distorted grid voltages under varying load conditions. The proposed grid-associated PV system with a novel interleaved converter and 3-level NPC inverter is employed in Matlab/SimPower System and experimentally verified. Power loss and efficiency calculations were performed on the DC converter side, and the efficiency was 96.07%. NPC inverters have a THD of 22.2%. Results from simulations and experiments indicate that the suggested topology can efficiently extricate the maximal amount of power from PV modules and inject energy into the grid system with excellent steady-state and dynamic performance.

Flexible Sector Detector-Based Mismatch Supply Voltage in Direct Torque Control Doubly Fed Induction Machine: An Experimental Validation

Direct Torque Control (DTC) of Induction Motors (IMs) is popular in motor drive applications because of its robust and simple control structure. The IM winding can be controlled on both sides using dual inverter technique which more effective for Electric Vehicle (EV) with a greater number of voltage vectors. However, the battery performance of the dual inverter will deteriorate unevenly on both sides, resulting in fluctuating voltages for the EV system. This will lead to the generation of distorted stator currents and a significant droop in the stator flux, which in turn can increase the total harmonic distortion (THD) in the system. Additionally, the performance of torque may not be able to regulate effectively. This paper examines the effect of unstable voltage on voltage vector mapping performance with tilted angles and proposes new sector definitions based on voltage ratio conditions. Moreover, the proposed sector for each predefined voltage ratio is tested under three-speed conditions. The proposed technique effectiveness is validated through hardware experiments using a dSPACE 1104 controller and retuning the stator current for proper waveform. This approach improves the stator current waveform, improves stator flux droop, enhances torque regulation and minimizes the THD in the DTC system.

Low-complexity model predictive control of a four-level active neutral point clamped inverter without weighting factors

Abstract The four-level active neutral point clamped (ANPC) inverter has become increasingly widely used in the renewable energy industry since it offers one more voltage level without increasing the total number of active switches compared to the three-level ANPC inverter. The model predictive current control (MPCC) is a promising control method for multi-level inverters. However, the conventional MPCC suffers from high computational complexity and tedious weighting factor tuning in multi-level inverter applications. A low-complexity MPCC without weighting factors for a four-level ANPC inverter is proposed in this paper. The computational burden and voltage vector candidate set are reduced according to the relationship between voltage vector and neutral point voltage balance. The proposed MPCC shows excellent steady-state and dynamics performances while ensuring the neutral point voltage balancing. The efficacy of the proposed MPCC is verified by simulation and experimental results.

Direct torque control and space vector modulation‐based direct torque control of brushless doubly‐fed reluctance machines

AbstractThis paper establishes the torque equation of brushless doubly‐fed reluctance machines (BDFRMs) expressed by power winding or control winding (CW) flux vectors and the defined flux vectors generated by magnetic field modulation. On this basis, the direct torque control theory of BDFRM is established. The derivative expression of torque and CW flux are derived for accurately analysing the effect of CW voltage vectors and machine operation points on torque and CW flux. In addition, the space vector modulation‐based direct torque control strategy of BDFRM is proposed, which can keep the switching frequency constant. The two methods are compared and analysed through experimental results.

Computationally-Efficient Model Predictive Control of Dual-Output Multilevel Converter in Hybrid Microgrid

This paper presents a hybrid microgrid configuration with a flying capacitor dual-output (FCDO) converter. The output ports of the FCDO converter can directly interface ac sources/loads operating at different amplitudes and frequencies without additional ac/dc/ac converter units. Compared to the conventional configuration, the hybrid microgrid with the FCDO converter operates at multilevel voltages, reduced power conversion stages, less power switch count, and fewer control loops. The paper also presents a cascaded model predictive control (CMPC) algorithm for such configuration to control the variables, namely three-phase dual-output currents, ac/dc bus and FC voltages, and active/reactive power. The proposed CMPC sequentially executes multiple single-objective MPC units with adaptive dynamic reference (ADR) models to control the multivariable. The controller first obtains the optimum voltage vector for each output port by minimizing the output current errors, where the ADR model generates the appropriate references. Finally, the controller identifies the optimum state from the determined voltage vector pair by minimizing the FC voltage errors. Unlike conventional MPC, the CMPC algorithm reduces the computational burden of the controller and attains multivariable control without additional control loops and weighting factors. Furthermore, the converter's performance with CMPC algorithm is validated experimentally on a low-power hybrid microgrid.

An Improved Model Predictive Torque Control for Switched Reluctance Motors With Candidate Voltage Vectors Optimization

This paper proposes an improved model predictive torque control (MPTC) strategy for switched reluctance motor (SRM) drives with candidate voltage vectors (CVVs) optimization, which can suppress the torque ripple effectively and enhance the system efficiency. This MPTC method is improved by three aspects. Firstly, the flux linkage calculation is removed compared to conventional MPTC. Secondly, the electric cycle of SRM is divided into six sectors based on the ideal torque contribution profile and the commutation region of the motor is redefined. Finally, CVVs of each sector are adopted based on phase torque characteristics and the total number of CVVs is reduced to 2 or 3 at each control period. The cost function is designed for the torque ripple suppression and copper loss minimization by selecting the optimal voltage vector from CVVs. This improved MPTC method avoids mass useless computation compared to conventional MPTC and no longer relies on hysteresis control loops compared to DTC method. In the simulation and experimental verification on a three-phase 12&#x002F;8 SRM, the proposed MPTC method effectively reduces the torque ripple, improves the torque&#x2013;ampere ratio and system efficiency, and improves dynamic response compared to DTC method.

Fault-Tolerant Predictive Control for Five-Leg Dual-Mover Permanent-Magnet Motor Drives

In this paper, a fault-tolerant predictive control (FTPC) is proposed for the post-fault operation of five-leg dual-mover primary permanent-magnet linear motor (PPMLM) drives with open circuit fault (OCF). In the post-fault operation, one phase winding and one voltage-source-inverter (VSI) leg are lost. As a result, there are four VSI legs and five healthy phase windings from two movers. Especially, one VSI leg is shared by two movers. The objects of FTPC are to reduce the computation burden and improve the performances. Firstly, A minimum copper loss principle is designed to distribute the reference current for two movers. Secondly, two global optimal mover voltage vectors (MVVs) for two movers are respectively determined by geometrical location. Thirdly, the two global optimal MVVs are respectively modified as two local optimal MVVs, in which the influence of the common leg is considered. Finally, two synthesized voltage vectors are obtained to improve the steady-state performances. Meanwhile, 60% of the computation burden can be reduced by using FTPC. The effectiveness of the proposed FTPC have been verified by experimental results.