Multiphase induction machines (MIMs) are attractive for safety-critical applications, because the... more Multiphase induction machines (MIMs) are attractive for safety-critical applications, because they are able to operate under open-phase fault. On the other hand, algorithms for sensorless speed estimation improve reliability and decrease cost and maintenance. The approach based on rotor slot harmonics (RSHs) is especially popular, due to advantages such as its independence from time-varying parameters. In healthy machines, usually the fundamental or any harmonic component has ideally equal magnitude in all stator phases. The previous RSH-based techniques rely on this characteristic. Conversely, under open-phase fault there is current imbalance, and such imbalance varies with the load. Thus, the existing RSH-based methods are unsuitable for open-phase fault, and alternative ones should be developed. This paper addresses sensorless speed estimation based on RSHs for MIMs under open-phase fault. The main RSHs in faulty situation are studied. Then, accordingly, a speed estimation technique for MIMs under open-phase fault is developed, able to work with good accuracy despite the variable current imbalance. Experimental results are provided.
Dual three-phase machines (D3PMs) are particularly attractive due to their fault-tolerance capabi... more Dual three-phase machines (D3PMs) are particularly attractive due to their fault-tolerance capability. In general, under open-phase (OP) faults, the current references are adapted following a minimum-loss strategy (MLS) or a maximum-torque strategy (MTS). The MLS offers lower copper loss than the MTS for any given torque, but a smaller torque operation range (TOR). The full-range MLS (FRMLS) has recently been proposed, providing minimum copper loss, for each torque value, in the whole TOR (the MTS TOR); however, only one OP was considered. Furthermore, neither the TOR of the MLS nor the copper loss of the MLS or MTS have been assessed with two OPs. Consequently, it is difficult to infer a priori the relevance that the FRLMS may have for two OPs. This paper evaluates the extension of the FRMLS to D3PMs with two OPs. First, the procedure to carry out this extension is described. Then, the convenience of the FRMLS for two OPs is studied for different situations. It is concluded that for two OPs in most cases the FRMLS is substantially better than the MTS and MLS in terms of copper loss and TOR. Experimental results verify the theory.
ABSTRACT Current control performance is key in some ac power conversion applications, such as ren... more ABSTRACT Current control performance is key in some ac power conversion applications, such as renewable energies and motor drives. This paper presents a method for accurate assessment of dq-PI current controllers dynamics. The proposed methodology is based on linear control for multivariable systems. First, the plant and controller matrices are modeled including time-delays and cross-coupling effects. Subsequently, the closed-loop characteristic polynomial is obtained from the sensitivity matrices. Then, a computer-aided process to calculate the system closed-loop poles (eigenvalues of the characteristic polynomial as a function of the control gains) is applied. From some specific constraints (e.g., desired time responses), the optimum tuning is available by inspection of the closed-loop root-loci. Different tests have been performed in a 6 kVA lab-prototype. The experimental results prove the validity and accuracy of the analysis.
Precise knowledge of the plant time constant is essential to perform a thorough analysis of the c... more Precise knowledge of the plant time constant is essential to perform a thorough analysis of the current control loop in voltage source converters (VSCs). As the loop behavior can be significantly influenced by the VSC working conditions, the effects associated to converter losses should be included in the model, through an equivalent series resistance. In a recent work, an algorithm to identify this parameter was developed, considering the inductance value as known and practically constant. Nevertheless, the plant inductance can also present important uncertainties with respect to the inductance of the VSC interface filter measured at rated conditions. This paper extends that method so that both parameters of the plant time constant (resistance and inductance) are estimated. Such enhancement is achieved through the evaluation of the closed-loop transient responses of both axes of the synchronous reference frame when a proportional integral current controller is implemented. Experimental results validate the approach.
Multiphase drives offer enhanced fault-tolerant capabilities compared with conventional three-pha... more Multiphase drives offer enhanced fault-tolerant capabilities compared with conventional three-phase ones. Their phase redundancy makes them able to continue running in the event of faults (e.g., open/short-circuits) in certain phases. Moreover, their greater number of degrees of freedom permits improving diagnosis and performance, not only under faults affecting individual phases, but also under those affecting the machine/drive as a whole. That is the case of failures in the dc link, resolver/encoder, control unit, cooling system, etc. Accordingly, multiphase drives are becoming remarkable contenders for applications where high reliability is required, such as electric vehicles and standalone/off-shore generation. Actually, the literature on the subject has grown exponentially in recent years. Various review papers have been published, but none of them currently cover the state-of-the-art in a comprehensive and up-to-date fashion. This two-part paper presents an overview concerning...
Voltage control of standalone converters with LC filter is usually based on proportional-resonant... more Voltage control of standalone converters with LC filter is usually based on proportional-resonant or proportional-integral controllers, which often require further active damping methods to achieve stability. These solutions place design constraints in the selection of the closed-loop pole locations which limit the achievable bandwidth and increase the design complexity. In contrast, in state-space based controllers, the closed-loop poles can be placed freely through state feedback, which makes them particularly suitable for high order plants and/or low sampling frequencies. Among the modern control methods, direct pole placement is a simple technique that enables the establishment of a straightforward relationship between outcome and design, as opposed to more advanced approaches. This paper presents a discrete state-space voltage controller for standalone converters with LC output filter. The proposed method combines the direct pole placement technique with a virtual disturbance o...
Multiphase machines with symmetrical windings offer various stator winding configurations (SWCs).... more Multiphase machines with symmetrical windings offer various stator winding configurations (SWCs). It is known that, for a given five-phase machine, the pentagon SWC implies, compared with star, smaller voltage rating and greater current rating of the converter. For healthy conditions, the stator copper loss (SCL) and maximum achievable torque (MAT) are almost identical for both SWCs, provided such converter-rating adjustments and negligible circulating currents. Regarding the operation of five-phase machines under open converter leg (especially common fault), the pentagon SWC attains lower SCL (for given torque) and larger MAT than star. However, it is unknown if these characteristics hold (and to which extent) for other phase numbers and SWCs. This study compares for multiple phase numbers the SWCs in terms of converter rating, MAT and SCL, under healthy operation and with an open converter leg. Most importantly, it is shown that, for phase numbers higher than five (the case previously studied), the improvement in performance (especially postfault MAT) by resorting to SWCs other than star can be much larger than for five phases, and it is thus of considerable interest. The most convenient alternatives (often different from the five-phase case) are established. Experimental results with two multiphase drives are included.
Multiphase induction machines (MIMs) are attractive for safety-critical applications, because the... more Multiphase induction machines (MIMs) are attractive for safety-critical applications, because they are able to operate under open-phase fault. On the other hand, algorithms for sensorless speed estimation improve reliability and decrease cost and maintenance. The approach based on rotor slot harmonics (RSHs) is especially popular, due to advantages such as its independence from time-varying parameters. In healthy machines, usually the fundamental or any harmonic component has ideally equal magnitude in all stator phases. The previous RSH-based techniques rely on this characteristic. Conversely, under open-phase fault there is current imbalance, and such imbalance varies with the load. Thus, the existing RSH-based methods are unsuitable for open-phase fault, and alternative ones should be developed. This paper addresses sensorless speed estimation based on RSHs for MIMs under open-phase fault. The main RSHs in faulty situation are studied. Then, accordingly, a speed estimation technique for MIMs under open-phase fault is developed, able to work with good accuracy despite the variable current imbalance. Experimental results are provided.
Dual three-phase machines (D3PMs) are particularly attractive due to their fault-tolerance capabi... more Dual three-phase machines (D3PMs) are particularly attractive due to their fault-tolerance capability. In general, under open-phase (OP) faults, the current references are adapted following a minimum-loss strategy (MLS) or a maximum-torque strategy (MTS). The MLS offers lower copper loss than the MTS for any given torque, but a smaller torque operation range (TOR). The full-range MLS (FRMLS) has recently been proposed, providing minimum copper loss, for each torque value, in the whole TOR (the MTS TOR); however, only one OP was considered. Furthermore, neither the TOR of the MLS nor the copper loss of the MLS or MTS have been assessed with two OPs. Consequently, it is difficult to infer a priori the relevance that the FRLMS may have for two OPs. This paper evaluates the extension of the FRMLS to D3PMs with two OPs. First, the procedure to carry out this extension is described. Then, the convenience of the FRMLS for two OPs is studied for different situations. It is concluded that for two OPs in most cases the FRMLS is substantially better than the MTS and MLS in terms of copper loss and TOR. Experimental results verify the theory.
ABSTRACT Current control performance is key in some ac power conversion applications, such as ren... more ABSTRACT Current control performance is key in some ac power conversion applications, such as renewable energies and motor drives. This paper presents a method for accurate assessment of dq-PI current controllers dynamics. The proposed methodology is based on linear control for multivariable systems. First, the plant and controller matrices are modeled including time-delays and cross-coupling effects. Subsequently, the closed-loop characteristic polynomial is obtained from the sensitivity matrices. Then, a computer-aided process to calculate the system closed-loop poles (eigenvalues of the characteristic polynomial as a function of the control gains) is applied. From some specific constraints (e.g., desired time responses), the optimum tuning is available by inspection of the closed-loop root-loci. Different tests have been performed in a 6 kVA lab-prototype. The experimental results prove the validity and accuracy of the analysis.
Precise knowledge of the plant time constant is essential to perform a thorough analysis of the c... more Precise knowledge of the plant time constant is essential to perform a thorough analysis of the current control loop in voltage source converters (VSCs). As the loop behavior can be significantly influenced by the VSC working conditions, the effects associated to converter losses should be included in the model, through an equivalent series resistance. In a recent work, an algorithm to identify this parameter was developed, considering the inductance value as known and practically constant. Nevertheless, the plant inductance can also present important uncertainties with respect to the inductance of the VSC interface filter measured at rated conditions. This paper extends that method so that both parameters of the plant time constant (resistance and inductance) are estimated. Such enhancement is achieved through the evaluation of the closed-loop transient responses of both axes of the synchronous reference frame when a proportional integral current controller is implemented. Experimental results validate the approach.
Multiphase drives offer enhanced fault-tolerant capabilities compared with conventional three-pha... more Multiphase drives offer enhanced fault-tolerant capabilities compared with conventional three-phase ones. Their phase redundancy makes them able to continue running in the event of faults (e.g., open/short-circuits) in certain phases. Moreover, their greater number of degrees of freedom permits improving diagnosis and performance, not only under faults affecting individual phases, but also under those affecting the machine/drive as a whole. That is the case of failures in the dc link, resolver/encoder, control unit, cooling system, etc. Accordingly, multiphase drives are becoming remarkable contenders for applications where high reliability is required, such as electric vehicles and standalone/off-shore generation. Actually, the literature on the subject has grown exponentially in recent years. Various review papers have been published, but none of them currently cover the state-of-the-art in a comprehensive and up-to-date fashion. This two-part paper presents an overview concerning...
Voltage control of standalone converters with LC filter is usually based on proportional-resonant... more Voltage control of standalone converters with LC filter is usually based on proportional-resonant or proportional-integral controllers, which often require further active damping methods to achieve stability. These solutions place design constraints in the selection of the closed-loop pole locations which limit the achievable bandwidth and increase the design complexity. In contrast, in state-space based controllers, the closed-loop poles can be placed freely through state feedback, which makes them particularly suitable for high order plants and/or low sampling frequencies. Among the modern control methods, direct pole placement is a simple technique that enables the establishment of a straightforward relationship between outcome and design, as opposed to more advanced approaches. This paper presents a discrete state-space voltage controller for standalone converters with LC output filter. The proposed method combines the direct pole placement technique with a virtual disturbance o...
Multiphase machines with symmetrical windings offer various stator winding configurations (SWCs).... more Multiphase machines with symmetrical windings offer various stator winding configurations (SWCs). It is known that, for a given five-phase machine, the pentagon SWC implies, compared with star, smaller voltage rating and greater current rating of the converter. For healthy conditions, the stator copper loss (SCL) and maximum achievable torque (MAT) are almost identical for both SWCs, provided such converter-rating adjustments and negligible circulating currents. Regarding the operation of five-phase machines under open converter leg (especially common fault), the pentagon SWC attains lower SCL (for given torque) and larger MAT than star. However, it is unknown if these characteristics hold (and to which extent) for other phase numbers and SWCs. This study compares for multiple phase numbers the SWCs in terms of converter rating, MAT and SCL, under healthy operation and with an open converter leg. Most importantly, it is shown that, for phase numbers higher than five (the case previously studied), the improvement in performance (especially postfault MAT) by resorting to SWCs other than star can be much larger than for five phases, and it is thus of considerable interest. The most convenient alternatives (often different from the five-phase case) are established. Experimental results with two multiphase drives are included.
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Papers by Jesús Doval-Gandoy