Axis Current Component Research Articles

Three-Level Inverter-PMSM Model Predictive Current Control Based on the Extended Control Set

In the neutral point clamped (NPC) three-level inverter-permanent magnet synchronous motor system, traditional model predictive current control (MPCC) uses the system predictive model to traverse the 27 basic voltage vectors, to achieve the d-q axis current component and neutral point voltage of the multi-objective optimal control. Finite control set model predictive control predicts the state change of the control target at future moments based on a finite number of switching states of the inverter. The control principle of this method is simple and easy to implement, but the control effectiveness of this control strategy is limited because only one basic vector can be selected as the optimum output per control period. In this paper, a model predictive current control strategy based on an extended control set (ECS-MPCC) is proposed, which can improve the control performance of the system by extending the control set to select multiple vectors in a single control period compared to the traditional strategy. In addition, to address the disadvantage of extending virtual space vectors leading to an increase in computation, this paper proposes a fast search method for optimal vector based on region reduction. The proposed method avoids the optimization process traversing all virtual space vectors, thus enabling a fast search for the optimal vector. The experimental results show that the proposed control strategy has good steady-state and dynamic performance.

Digital Current Controller With a Novel Active Damping Design for IPMSM

Internal model control gets wide attentions in electric drives for its outstanding robustness. Underdamped oscillations however, always can be seen in the synchronous <i>d</i>- and <i>q</i>- axis components of the stator currents if without proper extra damping elements included, especially under the low sampling to fundamental frequency ratios. The reasons for these oscillations are analyzed in the discrete-time domain other than as usually done in the continuous-time domain. Following that, a distinctive active damping matrix is proposed for the current closed-loop control of interior permanent magnet synchronous motors (IPMSMs). As a result, the anti-disturbance capability is enhanced, allowing the oscillations, often seen in the <i>d</i>- and <i>q</i>-axis current components, suppressed very well. Compared with other damping methods, the typical PI structure is still retained, which is desired on the point of engineering view. At last, the analysis as well as the damping effectiveness is validated through experiments.

Research on Control Strategy of STATCOM for Suppressing Subsynchronous Oscillation Based on Nonlinear Method

The dq-axis’ current is flowing into the static synchronous compensator (STATCOM) from the power system and the dq-axis’ current reference value form an error signal. After processing the error signal, a trigger pulse is formed to control the turn-on and turn-off of thyristors in STATCOM. At present, various documents generally adopt PI control to process the error signal. But the coefficient of PI control is difficult to set and the response speed of STATCOM under this control is not very satisfactory. In the paper, a STATCOM control strategy based on nonlinear method is proposed. By introducing feedback controlled quantities u 1(t) and u 2(t) into item piq and pid of the STATCOM mathematical model after dq transformation, the aim is to actively control the AC and DC axis current components of STATCOM input system. Based on the principle of nonlinearity, a set of multi-input and multi-output objective functions y 1 and y 2 are found. The dynamic and static performance of the control target is dynamically tracked and constrained by the secondary performance index, thus a closed-loop control system is formed which can quickly reflect the varying reactive power of the system. Finally, PSCAD/EMTDC electromagnetic transient simulation software is used to verify the effectiveness of the STATCOM nonlinear control method of Suppressing sub-synchronous oscillation in power system.

An Improved Torque and Current Pulsation Suppression Method for Railway Traction Drives Under Fluctuating DC-Link Voltage

For railway traction drives, the active front end usually adopts a single-phase rectifier. However, the dc-link voltage of this single-phase rectifier contains a second-order fluctuating component due to the fluctuation of the instantaneous power at both the ac and dc sides. Fed by the fluctuating dc-link voltage, the traction motor suffers from severe torque and current pulsation. The hardware solution with an additional LC resonant filter is simple, but it will reduce the power density of the system. An alternative solution is to eliminate the beat component in the stator voltage/current through modulation ratio or frequency compensation. However, it is difficult to achieve high performance for the conventional feedforward method. In this paper, an improved closed-loop torque and current pulsation suppression method is proposed, which can eliminate the q -axis current pulsation component in the field-oriented control system through frequency compensation. The torque pulsation suppression is also achieved automatically. Simulation and experimental results show that the proposed scheme can effectively reduce the torque and current pulsation in various operation modes compared with the conventional feedforward method.

Realization of Maximum Torque per Ampere Control for IPMSM Based on Inductance Segmentation

In order to solve problems associated with inductance parameter changes on traditional maximum torque per ampere (MTPA) control method for interior permanent magnet synchronous motor, such as large amount of computation, complicated control system, and low control precision, an MTPA control method based on inductance segmentation is proposed. Considering the effects of magnetic saturation, the inductance parameters are processed by segmentation analysis. The Newton iteration method is used to solve the correspondence between the electromagnetic torque and the optimum ${d}$ – ${q}$ axis current components, and the subsection curve is fitted to achieve MTPA control. By analyzing and processing inductance parameters, this control method improves the accuracy of control system. The ${d}$ – ${q}$ axis current reference is realized by piecewise curve fitting to improve the dynamic performance of the system. Finally, the dynamic performance of this method is compared with that of the traditional method through simulation and experiment. The simulations and experiments results show that this method has the advantages of fast dynamic response, high control accuracy, and simple implementation.

Non – Regenerative IPMSM Drive Braking Scheme Based on q – Axis Current Component Limiting

In the paper a non-regenerative braking scheme for high speed Interior Permanent Magnet Synchronous Motor (IPMSM)drive is presented. Due to price constraints, general purpose electric drives with IPMSMs are not equipped with a drive converterwhich allows energy recovery to the primary source. These drives are usually used for driving strictly reactive loads, in which brakingmode is used only during deceleration. Therefore, in these drives it is necessary to use methods for dissipating braking energy in themotor itself and in the inverter. The paper provides theoretical analysis of various methods for non-regenerative IPMSM brakingschemes, mathematical models, and the proposal of one solution suitable for use in high-speed applications based on limiting q – axiscurrent component. Proposed solution controls recovery energy by keeping DC link voltage within given voltage margin, thuspreventing unacceptable voltage rise during braking. Braking strategy is added into common IPMSM Field Oriented Control (FOC)control structure with Maximum Torque Per Ampere (MTPA) and Field Weakening (FW) algorithms. During the braking, MTPAstrategy is suspended and non – regenerative braking is performed instead. In the proposed braking scheme voltage margin is alsotaken into account, by selecting proper d-axis reference current adjusted to the available voltage, so the scheme is also applicable in FWmode.

Characterization of the parameters of interior permanent magnet synchronous motors for a loss model algorithm

The paper provides the results of a detailed experimental study on the variations of the characteristics of an interior permanent magnet synchronous motor, when load, speed and/or magnetization conditions vary. In particular, the characterization is carried out by assessing, for several working conditions, the motor parameters that influence its efficiency. From the knowledge of the variability of these parameters, it is possible to develop a dynamic model of the motor, which accurately describes its behaviour and allows estimating the power losses for whatever speed and load. In order to validate the model, the values of the power losses obtained by using the model are compared with the values measured with experimental tests.The study shows that it is possible to maximize the motor efficiency just acting on the direct axis current component and, therefore, it can be considered a first step towards the definition of a loss model algorithm for a control drive system able to minimize in real-time the power losses of the motor.

Performance of the Phaselet Frames-Based Digital Protection for Distributed Generation Units

This paper presents the development and performance evaluation of a digital protection for interconnected distributed generation units (DGUs). The developed protection detects and responds to transient disturbances (fault and nonfault conditions) based on the magnitudes and phases of the high-frequency sub-band contents, which are extracted from the $d$ – $q$ -axis components of the currents flowing through the point-of-common-coupling (PCC). These magnitudes and phases are extracted by six phaselet frames that are realized by a modulated filter bank that is composed of six digital high-pass filters (HPFs). The coefficients of HPFs are determined by biorthogonal phaselet basis functions. Extracted magnitudes and phases of the high-frequency sub-band contents of PCC $d$ – $q$ -axis current components provide signature information for accurate detection and identification of faults. The performance of phaselet frames-based digital protection is experimentally tested for two wind energy conversion systems (WECSs) and a photovoltaic (PV) system under different fault and nonfault conditions. Test results demonstrate reliable and timely responses, along with negligible sensitivity to the type and control of DGUs, type and location of faults, and loading levels.

Even-phase multi-motor vector controlled drive with single inverter supply and series connection of stator windings

Vector control principles enable independent flux and torque control of an AC machine by means of only two stator d-q axis current components. This means that in AC machines with a phase number greater than three there exist additional degrees of freedom, which are nowadays used to enhance the overall torque production of a multi-phase machine through injection of higher stator current harmonics. However, these additional degrees of freedom can be used to control other machines independently within a multi-motor drive system. To do so, it is necessary to connect in series stator windings of all the multi-phase machines, with an appropriate phase transposition. A vector control algorithm is then applied to each machine separately, total inverter phase current references are created by summation of individual machine phase current references, and supply to the stator windings of the multi-machine set is provided from a single current controlled voltage source inverter (VSI). The concept is introduced in the paper using the general theory of electrical machines, and all the possible situations that may arise for an even number of phases are examined. Although an induction motor drive is considered throughout, the concept is equally applicable to all AC machines with sinusoidal stator and rotor flux distribution. Its main advantage is the potential for saving in the number of inverter legs, compared to an equivalent 3-phase motor drive system. The saving depends on the number of phases and, for an even phase number, comes into existence when the number of phases is 8. Various even phase numbers are considered in detail and appropriate connection diagrams are given. Verification of the proposed multi-phase multi-motor drive is provided by simulation of a 10-phase 4-motor system.