Single DC-link Current Sensor Research Articles

Saliency-Based Sensorless Control Using Current Derivative in IPMSM Drives With Single DC-Link Current Sensor

In vector-controlled drive systems, a position sensorless drive with a single current sensor (SD-SCS) is an attractive system due to the minimum number of sen- sors. However, when the saliency-based SD-SCS is applied, the position estimation accuracy is deteriorated due to the errors in the injected pulse width modulated voltage and the reconstructed current. This paper proposes a current derivative-based sensorless control using a tri-active vector pulse width modulation (TAVPWM) to enhance the saliency-based SD-SCS. First, the TAVPWM scheme, which eliminates the current reconstruction dead zone in the low-modulation region, is adopted to improve the low- speed drive. Next, the derivatives of the phase currents are utilized and analyzed to minimize the position estimation error in the overall operating regions. Lastly, the transition strategy with respect to the speed is proposed for the full-speed sensorless drive. Owing to the proposed method, the switching frequency increases up to 16 kHz and the audible noise is virtually eliminated in the saliency-based SD-SCS. Furthermore, the enhanced dynamic performance is verified by various experimental results.

Low-Cost Direct Torque Control for Induction Motor Using Single DC-Link Current Sensor

Low-Cost Direct Torque Control for Induction Motor Using Single DC-Link Current Sensor

Expanding Limit of Minimum Sampling Time Using Auxiliary Vectors for PMSM Drives With Single DC-Link Current Sensor

Phase current reconstruction (PCR) strategy can improve the fault tolerance of permanent magnet synchronous motor (PMSM) drives. The PCR precision is largely affected by the unmeasurable zones and time-sharing sampling errors. The upper limit (Tlimit) of PCR allowable range can reflect the requirement of different PCR methods for the minimum sampling time (Tmin). With a longer Tlimit, there is sufficient time for sampling, even if Tlimit is halved due to the symmetrical waveform. Therefore, the extension of Tlimit is the key to eliminate the unmeasurable zones and time-sharing sampling errors. In this paper, a method to increase Tlimit is proposed, which introduces the suitable auxiliary vectors (AVs) in different regions to extend the duration time of the sampling vectors. With the help of a longer Tlimit (12.5%Ts), its possible to eliminate all the unmeasurable zones and time-sharing sampling errors, relieve the pressure on the hardware of current loop, improve the sampling accuracy, and facilitate the reliable operation of the drive. Besides, the switching action times of IGBTs can be reduced by about one-third in the high modulation area. The proposed method is finally proved to accurately reconstruct the phase currents by the experimental results on the PMSM prototype.

Direct Thrust Force Fault-Tolerant Control of Primary Permanent Magnet Linear Motor With Single DC-Link Current Sensor for Metro Application

In order to improve the fault-tolerant control (FTC) ability of the current sensor of the primary permanent magnet linear motor (PPMLM) drive system, the direct thrust force control (DTFC) strategy with single DC-link current sensor is proposed. According to the principle of voltage vector equivalence, the present basic voltage vector is equivalent to two adjacent sub-basic voltage vectors to achieve the equivalence of the present candidate voltage vector. The principle of different phases based on the fact that the DC-link current is equal to or opposite to one of the phase currents is introduced. The output sequence of the two sub-basic voltage vectors is determined by the principle of different phase mode to ensure that the measured currents in the two adjacent periods are any two-phase currents in the three phases, and then the third-phase current is calculated. Finally, the effectiveness and correctness of the proposed DTFC (P-DTFC) is verified by simulation and experiment.

Low-Cost Multistep FCS-MPCC for PMSM Drives Using a DC Link Single Current Sensor

In this article, a low-cost multistep finite control set model predictive current control (FCS-MPCC) using a dc link single current sensor is proposed for permanent magnet synchronous motor (PMSM). In order to reduce the system cost, the single dc link current sensor is used to reconstruct the three-phase current. Different from the current reconstruction technology of field-orientated control strategy, there are some problems of the existed current reconstruction technology applied for finite control set model predictive control (FCS-MPC). First, the optimal switching state of FCS-MPC in each cycle is not fixed, and only contains at most one phase current information for reconstruction, which will cause the reconstruction failure. Therefore, a multiperiod sampling method is proposed to obtain the different two-phase current information to reconstruction. Second, the uncertainty of the two-phase reconstruction current interval will lead to current error, so this article proposes a variable period compensation method to solve this problem. Moreover, in order to improve the system closed-loop performance without significantly increasing the computational cost and enhance the system reliability, a low-cost multistep FCS-MPCC strategy based on the reconstructed three-phase current is proposed for PMSM. Finally, simulation and experimental results validate the effectiveness of the low-cost multistep FCS-MPCC method using a dc link single current sensor reconstruction for PMSM.

Phase Current Reconstruction Error Suppression Method for Single DC-Link Shunt PMSM Drives at Low-Speed Region

The extensive application of vector phase shift modulation method in permanent magnet synchronous motor drive systems with single dc-link current sensor results in obvious current ripple in the low-speed region. The patterns of these ripples vary greatly in different sectors, leading to nonnegligible phase current reconstruction errors. In this article, an estimation of the local average current change rate (ELAC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> R) based reconstruction error suppression method within the switching cycle is proposed to resolve this problem. By comparing the actual and the ideal sampling points, the increase of current ripple and the reconstruction error caused by the combination of the vector phase shift and the single current sensor sampling in the low-speed region are modelled and analyzed. Then according to equivalent modelling of the current ripple between the ideal and the actual sampling points, the more accurate phase current information can be quickly obtained based on the sampling value. The compensation process is significantly simplified and the computation burden of the processor is reduced. Experimental results show that the performance of current reconstruction can be improved effectively with less harmonic content with the proposed method.

Simplified Current Control Strategy for Permanent-Magnet Synchronous Motors With Rotor Flux Distortion

In permanent-magnet synchronous motor (PMSM) drives, many current control strategies are presented to compensate the effects of rotor flux distortion on torque performance. These strategies are usually realized in the synchronously rotating reference frame and at least two-phase current sensors are used. Although the technique of phase current reconstruction enables three-phase currents to be obtained with a single dc-link current sensor, two-phase current controllers and complex coordinate transformations are still necessary. In this article, a simplified current control strategy for low-power PMSM drives is proposed. First, a torque allocation law is designed to resolve the reference electromagnetic torque into the reference three-phase currents with compensation for rotor flux distortion. Second, the reference three-phase currents are further converted into the reference dc-link current according to the averaging theory. Third, the amplitude and waveform control of three-phase currents are fulfilled by using dc-link current controller and ac-side pulsewidth modulation, respectively. This strategy can compensate the effects of rotor flux distortion on torque performance and is easy to implement with only one current sensor and one controller. Simulation and experimental results demonstrate the effectiveness of the proposed strategy.

Dual-Vector Located Model Predictive Control With Single DC-Link Current Sensor for Permanent-Magnet Linear Motor Drives

In this article, a dual-vector located model predictive control (DL-MPC) method based on a single dc-link current sensor is proposed for the permanent-magnet linear motor drive system. In DL-MPC, the phase currents are reconstructed by sampled dc-link current and selected active voltage vector (VV). Meanwhile, the sunk number of phase current is defined to evaluate the accuracy of current reconstruction. The first-optimal and second-optimal VVs are determined by dual-vector location. The second-optimal VV is selected for the voltage source inverter when the sunk number exceeds the threshold. Compared with traditional MPC schemes, DL-MPC has smaller current tracking error and better dynamic performance. Meanwhile, DL-MPC has more accurate current reconstruction and lower computation burden than that of the traditional MPC. The effectiveness of DL-MPC is verified by both theoretical analysis and experimental results.

DC-Link Current Control with Inverter Nonlinearity Compensation for Permanent Magnet Synchronous Motor Drives

For permanent magnet synchronous motors (PMSMs) supplied with a voltage source inverter, current control strategies are commonly implemented under the synchronously rotating reference frame. In order to simplify the system structure, three-phase currents can be measured with a single DC-link current sensor using the phase current reconstruction technique. However, it still needs to follow the conventional AC current control approach. In this paper, a DC-link current control method for PMSMs is proposed to further simplify the control system. The problem of phase current control was separated into the problems of amplitude control and phase control. Then, amplitude control was achieved using a closed-loop controller directly tracking the DC-link current; while phase control was achieved by AC-side pulse width modulation (PWM) following the phase angle of back electromotive force. The compensation for nonlinear distortion of the inverter was taken into account during the control process. Finally, the proposed method realized three-phase current control with a single current sensor and controller, and achieved the purpose of electromagnetic torque control. Experimental results demonstrate the effectiveness of the proposed method.

Direct Thrust Force Control of Primary Permanent-Magnet Linear Motors With Single DC-Link Current Sensor for Subway Applications

Because both magnets and windings can be mounted in the mover, the primary permanent-magnet linear motor (PPMLM) has a low-cost advantage for subway applications. In this paper, a novel direct thrust force control (DTFC) with single dc-link current sensor is proposed for PPMLM traction system in subway applications. The first phase current is directly measured by the dc-link current sensor. The second phase current is sensed with a limited delay, which is strictly limited by the limited measurement delay principle. The third phase current is calculated based on the condition that the summation of the three phase currents is zero. During the current reconstruction, no motor parameters are required. Because PPMLM may sink in the same phase for a long time and affect the current reconstruction accuracy, the single optimal target is proposed to re-select the original voltage vector. Compared with the conventional DTFC scheme, the proposed one has nearly the same performances; especially, the maximum speed and response time remain nearly unchanged. The effectiveness of the proposed DTFC scheme is verified by experimental results.

Multiple-Positions-Coupled Sampling Method for PMSM Three-Phase Current Reconstruction With a Single Current Sensor

Three-phase current reconstruction techniques with a single current sensor have been studied for permanent magnet synchronous machines (PMSMs) drive system due to its reducing cost and volume. In order to minimize the current reconstruction dead zone in the conventional method with a single dc-link current sensor, a strategy to couple multiple available positions through the single current sensor is proposed in this paper. With the proposed method, two independent equations of the stator currents can be obtained by sampling the single current sensor twice in both zero voltage vectors and active voltage vectors. By solving these two equations, the phase current reconstruction can be achieved accurately, which moves the current reconstruction dead zone toward six corner area of the space vector hexagon. Meanwhile, in order to guarantee the proposed method suitable in the whole linear modulation region, the suitable selection of the pulsewidth modulation switching period is analyzed in detail. Furthermore, the optimal selections of multiple sampling positions are discussed to lower the actual implementation difficulty of the proposed method. Finally, the experimental results on the PMSM demonstrate that the reconstructed phase currents with the proposed method can be always in consistent with the actual measured currents under different working conditions.

A High Frequency Injection Technique With Modified Current Reconstruction for Low-Speed Sensorless Control of IPMSMs With a Single DC-Link Current Sensor

This paper proposes a high frequency injection technique applied for low-speed sensorless control of interior permanent magnet synchronous machines (IPMSM) with a single dc-link current sensor. The three-phase currents, which can be reconstructed by the measurement of a dc-link current sensor, always suffer from the immeasurable regions. The most challenging problem exists in the low modulation region, where no phase current can be measured by the dc-link current sensor, and it is rarely solved without PWM modifications. This paper proposes a six-direction square wave high frequency injection method to extend the voltage vector to the measurable region to achieve the three-phase current reconstruction and saliency-based sensorless control without modifying the space vectors of the pulse width modulation (PWM). In addition, the paper comes up with a modified reconstruction scheme to reduce the reconstruction error and improve the accuracy of the position estimation. This low-speed sensorless strategy using a single dc-link current sensor is implemented in dSpace platform and the performance is evaluated by experiments.

Phase Current Reconstruction and Control of Three-Phase Switched Reluctance Machine With Modular Power Converter Using Single DC-Link Current Sensor

According to the modular power converter, a novel phase current reconstruction method using single dc-link current sensor is proposed for three-phase switched reluctance machine (SRM), and the control method is implemented with the reconstructed phase current as well. A highly integrated modular power converter is constructed by a three-phase full bridge and a dual switch module. The phase windings are in star-connection, and the bipolar phase currents are applied. Based on the special operating modes and single pulse width modulation signal injection, the dc-link current is decoupled and the phase current in both magnetization and demagnetization regions is reconstructed, which is very critical for the implementation of some advanced methods that require complete period phase current. The conventional control methods of the SRM, such as single-pulse voltage and hysteresis current control methods, are carried out under different operating conditions with both simulation and experiment to verify the effectiveness of the proposed method, and the reconstruction errors and performance influences are detailed analyzed as well.

A Novel Open-Circuit Fault Diagnosis Method for Voltage Source Inverters With a Single Current Sensor

For the purpose of reducing cost and volume, as well as to increase reliability in hostile environments, techniques of reconstructing three-phase current through a single current sensor have been reported for a three-phase alternating current motor vector control system. Based on the phase current reconstruction method, this paper proposes a novel open-circuit fault diagnosis method for the low-power voltage source inverter in the three-phase permanent-magnet synchronous motor drive. Other than sampling the single dc-link current sensor, the zero voltage vector sampling method (ZVVSM) is adopted to implement the fault diagnosis. By placing the single current sensor at a special position, ZVVSM is able to sample current during the two zero voltage vectors and reconstruct the three-phase currents. The reconstructed three-phase currents are used to generate the diagnostic variables that can detect and locate the faulty power switches. The PWM modulation strategy remains unchanged in this method and the reconstructed phase currents are with less waveform distortion and less harmonic contents, which are suitable for the fault diagnosis. The effectiveness of the proposed method is verified by experiments.

A three-phase current reconstruction technique using a single current sensor based on active vector pulse insertion

A single dc-link current sensor to reconstruct all three inverter phase currents has been proposed for the purpose of cost reduction and sensor fault tolerance in the motor drive. A novel phase current reconstruction scheme, with the immeasurable areas reduced, has been reported in the paper to tackle the problems caused by the presence of regions in the voltage vector plane where the phase currents are not directly measured. An active vector pulse insertion method achieves this objective by applying additional active voltage vectors in the brief intervals, and guaranteeing the invariant duty cycle in three-phase leg configuration during each fundamental frequency cycle. The effectiveness of the proposed reconstruction algorithm has been verified via a permanent magnet synchronous motor drive with 500 W rated power. Simulation and experimental results are provided to confirm the attractive performance characteristics of the resulting current reconstruction and regulation using the active vector pulse insertion method.

A Hybrid Fault-Tolerant Strategy for Severe Sensor Failure Scenarios in Late-Stage Offshore DFIG-WT

As the phase current sensors and rotor speed/position sensor are prone to fail in the late stage of an offshore doubly-fed induction generator based wind turbine (DFIG-WT), this paper investigates a hybrid fault-tolerant strategy for a severe sensor failure scenario. The phase current sensors in the back-to-back (BTB) converter and the speed/position sensor are in the faulty states simultaneously. Based on the 7th-order doubly-fed induction generator (DFIG) dynamic state space model, the extended Kalman filter (EKF) algorithm is applied for rotor speed and position estimation. In addition, good robustness of this sensorless control algorithm to system uncertainties and measurement disturbances is presented. Besides, a single DC-link current sensor based phase current reconstruction scheme is utilized for deriving the phase current information according to the switching states. A duty ratio adjustment strategy is proposed to avoid missing the sampling points in a switching period, which is simple to implement. Furthermore, the additional active time of the targeted nonzero switching states is complemented so that the reference voltage vector remains in the same position as that before duty ratio adjustment. The validity of the proposed hybrid fault-tolerant sensorless control strategy is demonstrated by simulation results in Matlab/Simulink2017a by considering harsh operating environments.

A Six-Phase Current Reconstruction Scheme for Dual Traction Inverters in Hybrid Electric Vehicles With a Single DC-Link Current Sensor

This paper presents a six-phase current reconstruction scheme for dual traction inverters in hybrid electric vehicles (HEVs) with a single dc-link current sensor. During the phase current reconstruction, one of the inverters is proposed to operate using active vectors, whereas the other inverter operates using nonactive vectors. An advanced phase-shift scheme for all pulsewidth-modulated (PWM) signals based on the sequence of duty cycles is implemented. PWM signals are considered in three types: large, medium, and small duty cycles. Then, the minimum phase-shift scheme is applied to each type of PWM signal to ensure the minimum duration of the active vector for stable current reconstruction. With this proposed phase-shift scheme, the maximum allowable modulation index and dc-link voltage utilization are improved. In addition, the relationship between the minimum required time for stable phase current reconstruction and the maximum allowable modulation index is derived theoretically. The effectiveness of the proposed method is verified by both simulation and experimental results. With this scheme, cost and volume of dual inverters in HEVs are reduced, considering the lower number of current sensors.

Fast Switching Direct Torque Control Using a Single DC-link Current Sensor

This paper presents a fast switching direct torque control (FS-DTC) using only a single DC-link current sensor. In FS-DTC, six new active voltage complex space vectors (CSVs) are synthesized by the conventional active voltage space vectors (SVs). The corresponding sectors are rotated in the anticlockwise direction by 30 degrees. A selection table is defined to select the CSVs. Based on the "Different Phase Mode", the output sequence of the selected CSV is optimized. Accordingly, a reconstruction method is proposed to acquire the phase currents. The core of the FS-DTC is that all of the three phase currents can be reliably reconstructed during every two sampling periods, which is the result of the fast switching between different phases. The errors between the reconstructed and actual currents are strictly limited in one sampling period. The FS-DTC has the advantages of the standard DTC scheme such as simple structure, quick torque response and robustness. As can be seen in the analysis, the FS-DTC can be thought of as an equivalent standard DTC scheme with 86.6% of the maximum speed, 173.2% of the torque ripple, and 115% of the response time of the torque. Based on a dSPACE DS1103 controller, the FS-DTC is implemented in an induction machine drive system. The results verify the effectiveness of the FS-DTC.

Low-Cost SVM-DTC Strategy of Induction Machine Drives Using Single DC-link Current Sensor

In conventional direct torque control (DTC) using space-vector modulation (SVM) of induction machine (IM) drives, at least three current sensors are needed. In this paper, a low-cost SVM-DTC strategy is proposed, in which only a single current sensor is used. The position of the voltage space vector is divided into two areas: effective and non-effective area. If it is located in the non-effective area, the voltage space vector will be shifted into the effective area with minimum distortion. Further, the switching frequency remains constant. The simulation is carried out on a MATLAB/Simulink platform and the simulated results verify the effectiveness of the proposed strategy.

Inductor Current Measurement and Regulation Using a Single DC Link Current Sensor for Interleaved DC–DC Converters

Inductor current measurements using only a single dc link current sensor in an interleaved dc-dc converter is introduced in this paper. This technique is appealing for the interleaved dc-dc converter because it minimizes the number of current sensors, thereby reducing sensor cost, weight, and volume. A combination of analytical and experimental results is provided to confirm that the single dc link current sensor technique is capable of achieving attractive performance characteristics in the areas of inductor current reconstruction, inductor current regulation, and output voltage regulation for the interleaved dc-dc converter.