Nandor Bodo

A Space-Vector Modulation Scheme for Multilevel Open-End Winding Five-Phase Drives

Open-end winding three-phase variable speed drives with dual-inverter supply have been extensively investigated for various applications, including series hybrid powertrains and propulsion motors. The topology is simple to realize while offering a higher number of switching states without the need for capacitor voltage balancing algorithms, when compared to the standard multilevel converters. This paper extends the open-end winding concept to a five-phase drive. A relatively simple space-vector modulation (SVM) algorithm, based on the already well-understood five-phase two-level drive SVM method, is developed. The proposed modulation technique has the advantage of being straightforward to implement and, like its two-level counterpart, is able to generate output voltages with minimum low-order harmonic content. The method generates up to 17-level output phase voltage and, therefore, offers superior harmonic performance when compared to the two-level five-phase modulation. The developed scheme is verified via detailed simulations and experiments, using a five-phase induction machine operating under open-loop V/f control.

A Space Vector PWM With Common-Mode Voltage Elimination for Open-End Winding Five-Phase Drives With a Single DC Supply

Open-end winding three-phase drive topologies have been extensively investigated in the last two decades. In the majority of cases supply of the inverters at the two sides of the winding is provided from isolated dc sources. Recently, studies related to multiphase open-end winding drives have also been conducted, using isolated dc sources at the two winding sides. This paper investigates for the first time a five-phase open-end winding configuration, which is obtained by connecting a two-level five-phase inverter at each side of the stator winding, with both inverters supplied from a common dc source. In such a configuration it is essential to eliminate the common-mode voltage (CMV) that is inevitably created by usual PWM techniques. Based on the vector space decomposition (VSD), the switching states that create zero CMV are identified and plotted. A space vector pattern with large redundancy of switching states is obtained. Suitable space vectors are then selected to realize the required voltage reference at the machine terminals with zero CMV. The large number of redundant states enables some freedom in the choice of switching states to impress these space vectors. Out of numerous possibilities, two particular switching sequences are chosen for further investigation. Both are implemented in an experimental setup, and the results are presented and discussed.

Investigation of Carrier-Based PWM Techniques for a Five-Phase Open-End Winding Drive Topology

This paper discusses the implementation of level-shifted and phase-shifted carrier-based modulation methods, in conjunction with a multiphase open-end winding drive topology. The considered drive is supplied using two five-phase two-level voltage source inverters (VSIs), with input provided from two isolated supplies of equal dc voltages. The topology is known to yield the same space-vector pattern as a corresponding three-level inverter in single-sided supply mode. It is shown in this paper that, with the application of a simple logic, the same phase voltage waveforms result as those obtainable with the appropriate carrier-based modulation scheme applied to the three-level VSI in single-sided supply mode. While the outcomes of the modulation techniques are the same, the open-end winding topology offers certain advantages, such as modularity and absence of capacitor voltage balancing requirements. The analysis is conducted for selected modulation methods using voltage and current waveforms, spectra Fast Fourier Transform (FFT), and total harmonic distortion as figures of merit. Theoretical considerations are verified by means of simulation and experimental results.

Onboard Integrated Battery Charger for EVs Using an Asymmetrical Nine-Phase Machine

This paper considers an integrated onboard charger for electric vehicles that incorporates an asymmetrical nine-phase machine and an inverter into the charging process. The charging is from three-phase mains, and it employs exclusively the power electronic components that already exist on board the vehicle and that are mandatory for the propulsion. No new elements are introduced. Moreover, the charging is achieved without any hardware reconfiguration since the existing elements and their connections are not altered during the transfer from propulsion to the charging mode. Instead, the operating principle is based on additional degrees of freedom that exist in nine-phase machines. These degrees of freedom are employed to avoid electromagnetic torque production in the machine during the charging process, although currents flow through its stator windings. The configuration operates with a unity power factor and is capable of vehicle to grid (V2G) operation as well. A detailed theoretical analysis is given, and the control for the charging/V2G and propulsion modes is discussed. Theoretical analysis is validated by experiments for charging, V2G, and propulsion operating regimes.

Isolated Chargers for EVs Incorporating Six-Phase Machines

This paper considers two isolated solutions for fast charging of electric vehicles (EVs). The isolation is located on the grid side (off board), whereas the rest of the charging apparatus is placed on board the EV, and it entirely consists of the existing power electronics components that would be otherwise used only for propulsion. Thus, substantial savings on space, weight, and cost are achieved. The considered configurations fully incorporate either a symmetrical or an asymmetrical six-phase machine, as well as a six-phase inverter, into the charging process. Due to the nature of the connections, torque production is avoided during the charging/vehicle-to-grid (V2G) modes of operation. Thus, the machines do not have to be mechanically locked, and their rotors naturally stay at standstill. Control schemes for both configurations are elaborated, and theoretical results are validated by experiments for the two configurations in both charging and V2G modes.

A Dual Five-Phase Space-Vector Modulation Algorithm Based on the Decomposition Method

Open-end winding variable speed drives with dual-inverter supply have been extensively investigated for various applications, including series hybrid power-trains and propulsion motors. The topology is simple to realize while offering a higher number of switching states without the need for capacitor voltage balancing algorithms, when compared to standard multilevel converters. The overwhelming majority of work is, however, restricted to the three-phase electric machinery. One of the reasons for this is that inclusion of a multiphase machine leads to exponential increase in the number of possible switching states, and so the design of a suitable space vector modulator (SVM) represents a considerable challenge. This paper considers a relatively simple SVM algorithm based on the decomposition of the three-level space vector decagon into a number of two-level decagons. The proposed modulation technique has the advantage of being relatively simple to implement. The drive produces multilevel load phase voltages with negligible low-order harmonic content. Despite the simplicity of the method, the quality of the output voltages is improved, compared to the previously proposed methods. The developed scheme is verified via detailed simulations and experiments using a five-phase induction machine under open-loop V/f control.

Recent advances in power electronic converter control for multiphase drive systems

Multiphase variable speed drives are nowadays serious contenders for various applications. On the other hand, the multilevel (predominantly three-level) voltage source inverters (VSIs) and matrix ac-ac converters have become industrially accepted technologies in three-phase systems. In recent times, attempts have commenced to integrate multilevel VSIs and matrix converters with the multiphase drive technology. This paper provides a review of recent advances in this area. A general configuration of an n-phase to m-phase matrix converter is considered and the differences with regard to the control of standard three-phase to three-phase matrix converters are underlined. Next, two different topologies of the multiphase multilevel supply are discussed and the emphasis is placed on appropriate pulse width modulation (PWM) techniques that can be used in conjunction with the given converter structure. The first topology utilises multilevel (three-level) VSI and the machines stator multiphase winding is star-connected. In the second topology the winding is open-ended and each side of the winding is connected to a two-level VSI. Carrier-based and space vector based PWM strategies are considered and the performance is illustrated using experimental results.

Multi-level space-vector PWM algorithm for seven-phase open-end winding drives

Open-end winding variable speed drives with dual-inverter supply have been extensively investigated for various applications in the past, based on a three-phase machine configuration. This topology is relatively simple for practical realisation. It offers a higher number of switching states without the need for capacitor voltage balancing algorithms, when compared to the equivalent standard multi-level converter in single-sided supply mode. The extension of the idea to multi-phase machines is however not straightforward. The main reason is that inclusion of a multi-phase machine leads to exponential increase in the number of possible switching states, so that the design of a suitable space vector modulator (SVM) represents a considerable challenge. This paper considers for the first time a seven-phase open-end winding topology. A relatively simple SVM algorithm, based on already developed seven-phase two-level drive SVM method, is used for operation of both inverters. The proposed modulation technique is straightforward to implement and is capable of generating pure sinusoidal output voltages, without any low-order harmonic components. The method generates up to 25-level load phase voltage and therefore offers superior harmonic performance when compared to the two-level seven-phase topology in single-sided supply mode. The developed scheme is verified by simulation, using a seven-phase induction machine operated under V/f control.

An EV Drive-Train With Integrated Fast Charging Capability

This paper proposes a new class of on-board chargers for electric vehicles (EVs). Instead of being placed on-board as a separate unit, the three-phase (fast) chargers reutilize the existing components in EVs, which are already used for the propulsion. These are primarily the inverter and the machine, which however have to be multiphase (with more than three phases). The concept is valid for all multiphase propulsion drives with a prime number of phases higher than three and a single neutral point in motoring and is illustrated in detail for the five-phase inverter/five-phase machine configuration. During the charging mode, electromagnetic torque is not produced in the machine so that the rotor does not require mechanical locking. Hardware reconfiguration between propulsion and fast charging is required, but it is achieved with only two switches, which are the only two nonintegrated elements. The integrated topology is explained in this paper, together with the control scheme, and extension from five phases to higher phase numbers is illustrated using the seven-phase system as an example. Finally, the propulsion-mode operation with complete suppression of low-order harmonics, which map into the second plane, is achieved for the five-phase machine. Experimental verification of theoretical results and proposed control is provided for both charging and vehicle-to-grid mode of operation, as well as for propulsion.

Carrier-based modulation techniques for five-phase open-end winding drive topology

The paper discusses implementation of level-shifted and phase-shifted carrier-based modulation methods, in conjunction with a multiphase open-end winding drive topology. The considered drive is supplied using two five-phase two-level voltage source inverters (VSIs), with input provided from two isolated dc sources of equal dc voltages. The topology is known to yield the same space vector pattern as a corresponding three-level inverter in single-sided supply mode. It is shown in the paper that, with the application of a simple logic, the same phase voltage waveforms result as those obtainable with the appropriate carrier-based modulation scheme applied to the three-level VSI in single-sided supply mode. While the outcomes of the modulation techniques are the same, the open-end winding topology offers certain advantages, such as modularity and absence of capacitor voltage balancing requirements. The analysis is conducted for selected modulation methods using voltage and current waveforms, spectra and total harmonic distortion (THD) as figures of merit. Theoretical considerations are verified by means of simulation and experimental results.