Search

This article presents a maximum torque per ampere strategy for a five-phase synchronous reluctance drive. The approach is developed considering general machine parameters and is formalized as a constrained optimization problem. The optimal solution is found analytically by using Lagrange’s multipliers method and is based on the computation of the eigenvalues and eigenvectors of the inductance derivatives matrix. The proposed approach is evaluated both numerically and experimentally. It is also compared with other current references control strategies, effectively showing a reduction of the machine rms currents for the same developed torque. The same approach can also be extended to machines with a different number of phases. [ABSTRACT FROM AUTHOR]

Inverter's performance and operating mode may be negatively affected by inverter input (dc‐link) current and voltage ripple. It is a common experience that even theoretically balanced loads with perfectly balanced supply voltages, such as multiphase ac motors supplied by pulse‐width modulation (PWM) inverters, in practice show a certain degree of current unbalance, in the range of a few percent, which introduces a low‐frequency instantaneous power oscillation. This reflects in current and voltage low‐frequency ripple on the dc‐link inverter side (i.e. at the double‐fundamental frequency). A possible method to analyse this matter is through the symmetric sequence components. In particular, based on the first negative current sequence component and by considering the equivalent dc‐link impedance calculated at the dominant double‐fundamental frequency, the amplitude of the corresponding dc‐link voltage ripple component is calculated in this work for a general multiphase load. Finally, the design of the dc‐link capacitor in multiphase inverters is proposed considering requirements referred to the double‐fundamental dc voltage ripple. The feasibility of the proposed developments has been verified for three‐, five‐ and seven‐phase inverters by both numerical simulations and comprehensive experimental tests, always showing a good matching. [ABSTRACT FROM AUTHOR]

Recent developments in power electronics are making the multiphase machines a competitive alternative to the conventional three-phase counterparts. Due to their fault-tolerant features, multiphase drives represent a robust technology in high-power/high-current, safety-critical applications. Besides, their introduction to transportation electrification is gaining importance. Among the multiphase solutions, the multi-three-phase machines are receiving a lot of attention by the industry since they use the well-consolidated three-phase technology, thus reducing the design time and also the cost. Therefore, this article proposes a modular vector control scheme for multi-three-phase permanent magnet synchronous motors. The proposed solution uses a modular modeling approach for the independent and decoupled torque control of each three-phase unit, allowing the implementation of torque-sharing strategies among the three-phase sets of the machine. The developed modular control has been validated on a nine-phase permanent magnet machine. [ABSTRACT FROM AUTHOR]

When multiphase drives are used for specific applications, the modular solutions are preferred as they use consolidated power electronics technologies. The literature reports two modeling approaches for multiphase machines having a modular configuration of the stator winding. The first approach is the vector space decomposition (VSD) that models the energy conversion as for an equivalent three-phase machine. The main alternative to the VSD is the multistator (MS) modeling that emphasizes machine modularity in terms of torque production. Both approaches have advantages and disadvantages for multiphase machines with a modular structure. Therefore, this article aims to combine the VSD and MS approaches, defining a new matrix transformation and, hence, developing a new modeling approach for multiphase machines with a modular structure. The proposed transformation allows a decoupled and independent torque control of the sets composing the machine, preserving the torque regulation's modularity. Together with a new vector control scheme, it has been applied to a modular permanent magnet synchronous machine (PMSM) with a nonstandard spatial shift between windings. Experimental results are presented for a nine-phase PMSM prototype with a triple-three-phase stator winding configuration. [ABSTRACT FROM AUTHOR]

This article presents a generalized approach toward the dc-link voltage switching ripple analysis in the two-level multiphase pulsewidth modulation (PWM) voltage source inverters with a balanced load. Since the voltage ripple is one of the crucial sizing criteria for a dc-link capacitor, a simple and practical equation for designing the dc-link capacitor, based on the maximum (peak-to-peak) value of the dc-link voltage ripple, has been proposed for the multiphase inverters. The amplitude of the dc-link voltage switching ripple is analytically derived as a function of operating conditions. The effect of the number of phases on the dc-link capacitor size is investigated as well. It is found that considering the same total output current, the dc-link capacitor size is reduced by increasing the number of phases up to seven. However, from the point of view of the dc-link capacitor size, there are no benefits of further increasing the number of phases. Reference is made to two commonly used modulation strategies—sinusoidal PWM and continuous symmetric centered PWM (i.e., space vector). The mathematical models are derived with an aim to provide the precise dc-link capacitor sizing and hence improve the power density of the whole system. The comparison of different phase numbers has been made. Proposed theoretical developments are verified by the simulation and experimental tests. [ABSTRACT FROM AUTHOR]

Testing the high-power machines in general is not an easy task. One of the standard tests is the full-load test. This test typically requires another machine, of the same or higher power rating, to be coupled to the tested one. For multiphase machines, which are commonly designed for high-power applications, this test can be conducted in a different way. In order to simplify full-load test, this paper proposes a new method that is applicable for multiple three-phase machines with even number of neutral points. The method is based on indirect rotor-field oriented control. It enables evaluation of the efficiency and the thermal design in the case of synchronous machines and the segregation of the constant and stator variable losses for induction machines, without the need for coupling another machine as a load. In the presented method, the full-load test conditions on the stator are obtained by circulating the rated active power flow in a closed loop from one winding set to another. The only power used during the test is to cover machine and converter losses. The proposed control scheme is unique and is based around y-component from the vector space decomposition subspace. It is validated through the simulation and experimental results. [ABSTRACT FROM AUTHOR]

A space‐vector pulse‐width modulation (SVPWM) algorithm for a three‐level asymmetrical six‐phase drive based on vector‐space decomposition approach is presented in this study. A modification in zero‐plane of the transformation matrix is proposed in order to meet the requirement that the realisation of sinusoidal output phase voltages can be obtained through the chosen output leg voltage space vectors. Furthermore, a method of choosing the switching sequences based on all possible one‐level transitions of the leg voltages, i.e. a permutation method, is introduced. The algorithm is then validated experimentally and obtained results show that the developed method successfully achieves the desired fundamental phase voltage, though low‐order harmonics are present due to uncompensated inverter dead time. Finally, the performance of the proposed SVPWM algorithm is compared with several carrier‐based PWM algorithms including in‐phase disposition with 'double min–max injection'. This is a little‐known type of injection, which is verified to obtain identical performance as the presented multilevel algorithm. [ABSTRACT FROM AUTHOR]

This paper introduces a method which can accurately transfer active and reactive power between sets of three-phase windings of a multiphase induction machine. The machine has to have a multiple of three phases (3, 6, 9, etc.), with each three phases representing one set. The paper demonstrates first that the sets do not share the power in the same way as they share a torque. Therefore, the paper proposes a method that is capable of achieving accurate power sharing. This is ensured by considering the whole power that is transferred through the air-gap to/from a set, instead of considering only a power that is transferred between that set and a rotor shaft. A complete control algorithm of the proposed method is given. Experiments and simulations verify theoretical considerations and the proposed control. [ABSTRACT FROM AUTHOR]

The analysis and assessment of the pulsewidth modulation (PWM) techniques is commonly based on the comparison of the total harmonic distortion (THD) results. THD is usually calculated by application of the Fourier transformation and by taking a limited number of harmonics into the consideration. In this paper, derivation of analytical formulas for the phase voltage THD is presented. The considered system is a symmetrical multiphase star-connected load, supplied from a multilevel pulsewidth-modulated voltage-source inverter (VSI, three-phase case is also covered). The solution is based on the Parseval's theorem, which links frequency spectrum and time domain through the average power (i.e., root-mean-square (rms) squared value) of the signal. The assumption throughout the derivations is that the ratio of the switching to fundamental frequency is high. Derivations are based on the integration of the power of the PWM signal in a single switching period over the fundamental period of the signal. Only ideal sinusoidal reference voltages are analyzed, and no injection of any type is considered. Formulas for phase voltage THD for any number of phases are derived for two- and three-level cases, for the most commonly used carrier-based methods. Comparison of the analytically obtained curves with simulation and experimental results shows a high level of agreement and validates the analysis and derivations. [ABSTRACT FROM AUTHOR]

This paper presents a novel modulation strategy for a seven-phase three-level inverter, aimed at variable-speed drive applications. Developed space vector pulsewidth modulation (SVPWM) strategy is based on vector space decomposition (VSD) approach and an analysis of multidimensional space vector projections in mutually orthogonal planes. The algorithm represents an extension of a recently developed five-phase three-level SVPWM algorithm and is considerably more complex, due to the existence of three mutually orthogonal planes in a seven-phase system. The difficulties of generalization of space vector strategies, which stem from the nature of the multiphase systems, are highlighted. Increasing the number of phases from five to seven increases the number of switching states from 3 ^5 = 243 to 3^7 = 2187 and the number of orthogonal planes from two to three. This considerably affects the complexity of the offline calculations. However, the final implementation of the algorithm is simple. Developed SVPWM algorithm is compared to an equivalent carrier-based strategy and it is shown that they yield identical performance. The complexity of the algorithms for real-time implementation is compared. Simulation and experimental results, obtained using neutral-point clamped inverter, verify the theoretical developments. [ABSTRACT FROM AUTHOR]

The article presents a novel carrier-based pulsewidth modulation technique for multiphase neutral point clamped converters. The technique is aimed to actively control the neutral point (NP) potential while supplying the desired set of line-to-line voltages to the load. Standard techniques are either based on the sole common mode voltage injection or on the sole multistep switching mode; contrarily, the proposed algorithm combines these two approaches to take advantage of their main benefits. The technique performs well for each number of phases, for each modulation index, and for each type of load. It can control in closed-loop the NP voltage to any desirable value with a reduced number of switching transitions. The proposed approach has been experimentally validated and compared with other carrier-based algorithms. [ABSTRACT FROM AUTHOR]

In this article, a new pulsewidth modulation technique is proposed for the output voltage control and the dc-bus capacitors voltage balancing of a multipoint-clamped multilevel converter. The voltage equalization is achieved by allowing each converter's leg voltage to switch through multiple levels in a single modulation period (multistep operation). The approach is generalized with respect to the number of levels and phases and can be applied regardless of the converter operating conditions. Nevertheless, the multistep behavior generally leads to an increase of the average switching transitions rate. In the proposed method, this drawback is mitigated with an online adaptive selection of the number of switching levels. The algorithm is validated through an extensive hardware-in-the-loop testing and compared to other approaches. [ABSTRACT FROM AUTHOR]

In multiphase machine drives, accuracy of the estimated machine parameters is crucial for effective performance prediction and/or control. While a great amount of work has been done on parameter estimation for three-phase machines, corresponding discussions for six-phase machine remain scarce. It has been proven in the literature that the effect of mutual leakage inductance between different winding layers has a significant impact on the equivalent machine reactance, which challenges the standard separation method of stator and rotor leakage inductances from the measured locked-rotor impedance. In this paper, parameter identification of an asymmetrical six-phase induction machine using six-phase no-load and locked-rotor tests is discussed. A zero-sequence test using an improved equivalent circuit is proposed to improve the accuracy of the estimated parameters. The concept is verified using experimental results obtained from a low-power prototype asymmetrical six-phase machine. [ABSTRACT FROM AUTHOR]

This paper studies pulse width modulation (PWM) techniques suitable for a four-level five-phase open-end winding (OeW) drive. The drive comprises a five-phase induction machine, supplied using two two-level voltage source inverters with isolated and unequal dc-link voltages, in the ratio 2:1. A decoupled carrier-based (CB) PWM modulation strategy, based on unequal voltage reference sharing between the two converters, is introduced in this paper. The stability of dc-link voltages in OeW drives is investigated next, using a novel analysis technique. Several modulation methods are analyzed and the results show that application of the coupled PWM technique, with carriers having in-phase disposition, leads to overcharging of the capacitor in the dc-link of the inverter intended to operate with the lower dc-link voltage. On the other hand, the proposed decoupled CB PWM scheme naturally eliminates the dc-link capacitor overcharging problem. These findings are verified experimentally, using open-loop V/f control. Two different decoupled CB modulation methods are compared and the best performing modulation method is selected and incorporated further into an OeW drive with field-oriented control. The presented steady state and transient experimental results demonstrate that the decoupled CB PWM technique is suitable for high-performance variable speed drive applications. [ABSTRACT FROM AUTHOR]

Three-phase multilevel (ML) inverters are used in many medium- and high-power applications such as motor drives and grid-connected systems. Despite the fact that numerous pulsewidth modulation (PWM) techniques for ML inverters have been developed, the impact of these modulation schemes on the peak-to-peak output current ripple amplitude has not been addressed yet. In this paper, analysis and comparison of current ripple for two-level (2L) and three-level (3L) voltage source inverters are given. Reference is made to optimal and popular modulation, so-called centered PWM, easily obtained by both carrier-based modulation (phase disposition, with proper common-mode voltage injection) and space vector modulation (nearest three vectors). It is shown that the peak-to-peak current ripple amplitude in 3L inverters can be determined on the basis of the ripple in 2L inverters, obtaining the same results as by directly analyzing the output voltage waveforms of the 3L inverters. This procedure can be readily extended to higher level numbers. The proposed analytical developments are verified by both numerical simulations and experimental tests. [ABSTRACT FROM PUBLISHER]