Zero-voltage Vectors Research Articles

An improved double‐vector model predictive control strategy for four‐switch three‐phase inverter‐fed permanent magnet synchronous motor based on visualisation analysis considering DC voltage pulsation

AbstractTo address the problem of considerable current distortions in traditional single‐vector model predictive control (MPC) method for four‐switch three‐phase inverter (FSTPI)‐fed permanent magnet synchronous motor, a double‐vector MPC scheme has been studied. However, it still lacks a sufficient theoretical foundation, causing doubts about its effectiveness. To perfect this deficiency, a novel visualisation analysis scheme considering DC voltage pulsation is presented to demonstrate the validity of the traditional double‐vector MPC method for FSTPI. The analysis results reveal for the first time that the traditional double‐vector MPC method is not always superior to the single‐vector method as there is no zero voltage vector for FSTPI. So, a new virtual voltage vector is defined to compensate the deteriorated control performance caused by the absence of zero voltage vectors, based on which an improved double‐vector MPC method is further put forward to reduce the current ripples. Then, the presented visualisation analysis is adopted to demonstrate the validity of the improved MPC strategy under pulsating DC voltage conditions. Finally, a new voltage sector division technology is further put forward to simplify the implementation steps of the presented method. Contrastive experimental studies demonstrate the availability of the improved MPC strategy.

A Model Predictive Control Scheme with Minimum Common-Mode Voltage for PMSM Drive System Fed by VSI

Common-mode voltage (CMV) brings shaft voltage and shaft current, and corrodes the bearings of the permanent-magnet synchronous machine (PMSM), which affects the reliability of the whole PMSM drive system. Since the CMV applied by the zero voltage vectors (ZVVs) is three times that applied by the active voltage vectors (AVVs), a modulation scheme achieving minimum CMV without ZVV is proposed and introduced into the model predictive control structure for the PMSM drive system. Firstly, the whole modulation range is divided into three regions, including the low voltage modulation region (LVMR), high voltage modulation region (HVMR), and over-voltage modulation region (OVMR). Meanwhile, the regional boundary expression is derived. Then, the active zero-state pulse width modulation (AZSPWM) is adopted in LVMR. To improve the steady-state performance, near-state pulse width modulation (NSPWM) without opposite ZVVs is applied to the HVMR. Furthermore, when the reference voltage vector (VV) is located in OVMR, an optimal scheme is proposed to improve the dynamic response. Under the premise of no ZVV existing in the whole modulation region, simulation and experimental results show that the proposed hybrid modulation method can improve the steady-state and dynamic performance of the PMSM drive system.

Common-Mode Voltage Reduction Method Based on Variable Sampling Frequency Finite Control Set-Model Predictive Control for PMSM Drive Systems

In this article, a finite control set-model predictive control (FCS-MPC) with variable sampling time is proposed. A zero-voltage vector appears in the dead time between specific voltage vectors, resulting in an unintentionally large common-mode voltage. Herein, a large common-mode voltage was suppressed, and the load current was controlled using a voltage vector combination that did not cause a zero-voltage vector in dead time. Additionally, to improve the total harmonic distortion (THD) of the load current, the intersection of the predicted current and the command current by all the volage vectors (VVs) in the combination is confirmed. The VV where the intersection occurs is selected as the optimal VV. This optimal VV is applied to the point where the predicted current and the reference current intersect. The applicable range of the sampling time should be selected by considering the calculation time and number of switching. Through the proposed FCS-MPC strategy, not only can the common-mode voltage be limited to within ±Vdc/6, but an improved THD can also be obtained compared to the existing method using fixed sampling. The proposed method was verified through PSIM simulation and experimental results.

A New Four-Step Commutation Method for Indirect Matrix Converter With Active-Voltage Vectors Being Applied

The existing two commutation methods of the rectifier stage for indirect matrix converter (IMC) are zero-current commutation and four-step commutation. The premise of zero-current commutation is that the inverter stage of IMC uses a zero-voltage vector, but when the inverter stage cannot use zero-voltage vectors (such as space overmodulation, common mode suppression modulation, etc.), the four-step commutation is adopted. The conventional four-step commutation method has a complex switching sequence and requires additional sensors. Based on the natural freewheeling characteristic of IMC and the switching sequence of zero-current commutation, a new four-step commutation method is proposed when active-voltage vectors are applied in the inverter stage, first turn off the two switches at 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> and 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> steps, and then turn on the two switches at 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> and 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> steps. The switching sequence of the new four-step commutation is not affected by the polarity of input voltage or output current direction, thus solving the complexity switching sequence problem of the conventional four-step commutation, and does not require additional voltage or current sensors, making the IMC commutation process safer and more reliable. Finally, this paper verifies the effectiveness of the new four-step commutation method of IMC through experiments.

Multi-Adjustment Strategy for Phase Current Reconstruction of Permanent Magnet Synchronous Motors Based on Model Predictive Control

In response to the model predictive control (MPC) driving system, this paper proposes a multi-adjustment strategy for phase current reconstruction based on a coupled current sampling method. The proposed coupled current sampling method eliminates the need to modify the inverter’s internal wiring. The current signals utilized in the proposed method are all external current signals from the inverter and do not involve any current signals from the internal circuitry of the inverter. By analyzing the current sampling mechanism of duty-cycle model predictive control (DC-MPC) as a modulation method, the underlying principles of the non-reconstructible current regions in the coupled current sampling method are revealed. The non-reconstructible regions are accurately delineated into low and high-modulation regions using coupled current sampling. A multi-adjustment strategy for phase current reconstruction is proposed to address the non-reconstructible regions. In the low-modulation regions, phase current reconstruction is achieved through compensated voltage vector pulse injection. In the high-modulation regions, phase current reconstruction is accomplished using the zero-voltage vector insertion approximation method, which maintains the symmetry of the PWM waveform and avoids current distortion. Experimental results on a permanent magnet synchronous motor validate the effectiveness and feasibility of the proposed approach.

Topology and Modulation for a New Indirect Matrix Converter to Reduce the Common-Mode Voltage

In this paper, a new indirect matrix converter (IMC) topology with two insulated gate bipolar transistors (IGBT) set in the upper and lower dc-link is proposed to suppress the common-mode voltage (CMV). Meanwhile, two new space vector modulation (SVM) strategies are redesigned to control this topology. The first strategy utilizes the equivalent zero voltage vectors to replace the zero voltage vectors for reducing the CMV, while the second strategy selects and utilizes specific active voltage vectors and equivalent zero voltage vectors to suppress the CMV based on the input current sector. Comparative simulation and experimental research for the two strategies are carried out for the new IMC topology, which validates that the CMV can be reduced to 57.7% or 37.1% of the one in the conventional IMC system. Besides, the proposed new IMC system is experimentally verified that it can keep a satisfied CMV suppression performance when feeding an induction motor. Moreover, the efficiency analysis also indicates that the new topology will not bring in obvious additional power loss under the proposed SVM strategies even though two IGBTs are added in the dc-link.

Overall Electrical Parameters Identification for IPMSMs Using Current Derivative to Avoid Rank Deficiency

An approach to identify overall electrical parameters for interior permanent magnet synchronous motors (IPMSMs) in steady state is proposed in this paper using current derivative, with which the concerns of rank deficiency can be avoided. It is found that the conventional IPMSM models under d-q frame always neglected the PWM switching effect of inverter and the quantities in these models are always regarded as constant values in steady state, making it untoward to identify all motor parameters simultaneously. Instead, the switching IPMSM model is built to analyze the details of PWM, and full-rank current derivative functions during zero and active voltage vectors are given respectively. Without any injected signals, all electrical parameters including d/q-axis inductance, stator resistance and permanent magnet flux linkage are able to be figured out in steady state by measuring the phase current derivatives. Simulations and experiments are implemented to validate the proposed approach.

An Enhanced Predictive Current Control Scheme for Common Mode Voltage Alleviation and Improvement of Torque Response of PMSM Drive

Predictive current control (PCC) is an effective control scheme with provisions to handle multiple objectives and nonlinear constraints. In the conventional PCC (CPCC) scheme, the application of a zero-voltage vector (ZVV) leads to the generation of large common-mode voltage (CMV), which gradually leads to bearing damage. However, disregarding ZVV can suppress CMV at the expense of large distortions in stator current. To avoid this, the present work deploys synthesized voltage vectors (SVVs) obtained from adjacent active vectors (AAVs) for permanent magnet synchronous motor (PMSM) drive control. In this article, two techniques are proposed for alleviating the CMV. Two AAVs are applied for a fixed duration in the first proposed method. Thus, the effect of neglection of ZVV can be circumvented with the application of two AAVs. In the second method, multivectors are applied to ensure CMV suppression and improvement of the steady-state torque response. Furthermore, an effective voltage vector (VV) preselection scheme using the complex-plane concept is introduced. Unlike the conventional CMV reduction schemes, the proposed VV-preselection evades tangent inverse angle determination and complex transformations. This offers the advantage of reduced computational burden with improved steady-state torque performance. The effectiveness of the proposed schemes is validated by comparing them with CPCC and existing literature.

A Novel SVPWM Fault-Tolerant Strategy for Torque Ripple Reduction of Seven-Phase Induction Machines Under Single-Phase Open-Circuit Fault

The development of multiphase drives has taken on an accelerated pace in the last decades, and fault-tolerance has been the subject of many classic studies. Traditional space vector pulsewidth modulation (SVPWM) would cause significant torque ripple in the case of open-circuit fault, which in turn degrades the fault-tolerant performance of multiphase machines. This work proposes a novel SVPWM fault-tolerant strategy for seven-phase induction machine under a single-phase open-circuit fault. A deeper insight has been provided into the reconstruction of voltage vectors without using reference current, ensuring the generality for various fault-tolerant principles. Subsequently, an eight-sector-based sector division method is proposed, and five specific nonzero voltage vectors and two zero-voltage vectors in each sector are determined to be candidates. Without confliction of switching state, the symmetric modulation module can still be utilized, which will minimize the modifications after fault occurrence. Besides, the close-loop control for harmonic planes can be fulfilled. Finally, experimental results have demonstrated the effectiveness of the proposed SVPWM fault-tolerant approach under both steady and transient states.

A Novel Wider Range Modulation for Indirect Matrix Converter Utilizing Delta-Sigma and Space Vector

The coupling between the rectifier and inverter makes the modulation of the indirect matrix converter (IMC) relatively complicated. A novel modulation method is proposed in this letter, where a space vector modulation without a zero-voltage vector, which is only responsible for adjusting the phase of the output voltage vector, is used for the inverter, and a novel delta-sigma method (ΔΣM) to modulate the input current vector phase and dc-link voltage is adopted by the rectifier. Duty cycles of the inverter are obtained by looking up the table of reference output voltages and updated at a 5-kHz carrier cycle, while switching states of the rectifier change once per cycle at a 40-kHz sampling frequency. By decoupling the rectifier and inverter, modulation of the IMC is greatly simplified. Methods that optimize the selection of rectifier switching states under various output/input voltage transfer ratios are also discussed. Simulations and experimental results are presented to validate the proposed method.

A Novel SVPWM for Open Winding Permanent Magnet Synchronous Machine With Extended Operation Range

In this article, a novel space vector pulsewidth modulation (SVPWM) with the zero sequence current (ZSC) control strategy is proposed to extend the operation range for an open winding (OW) permanent magnet synchronous machine (PMSM). The proposed SVPWM can achieve the ZSC control and extend the operation range by considering voltages in the zero sequence axis and voltage vectors in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha \beta $ </tex-math></inline-formula> -plane, both of which are mapped by switching combinations in an OW drive. The effect of switching combinations with non-null zero sequence voltage (ZSV) on the modulation region of a common-dc bus OW-PMSM is investigated for the first time. The proposed SVPWM has optimal selection of switching combinations on the large hexagon rather than on the small hexagon in the conventional SVPWM for ZSC control and still maintains the controllability of ZSC in the overmodulation region. Compared with the conventional SVPWM strategy, the operation range of OW-PMSM can be extended over 10% with the proposed SVPWM strategy. The performance of both the conventional and proposed SVPWMs is compared experimentally.

Sensorless Control and Inductances Estimation of IPMSMs Using FPGA and High Bandwidth Current Measurement

This paper presents a sensorless control method and a very fast on-line inductances identification of an IPMSM. The current slopes (derivatives) at one active-voltage vector and one zero-voltage vector are measured every PWM cycle to estimate the rotor speed and position with the aim of increasing the estimation accuracy and reducing total harmonic distortion. In addition to these current slopes, the DC bus voltage of the inverter is measured to estimate the machine inductances on-line. The proposed on-line parameter identification method can overcome the drawback of the existing off-line methods, such as: the requirement of a robust mechanical clamping system and test signal generators. The proposed on-line method also addresses the limit of the existing on-line methods, such as slow update and the possibility of incorrect convergence of the estimated parameters. Extensive experimental studies were conducted to verify the effectiveness and robustness of the proposed sensorless control and parameters identification of the IPMSM.

A Novel Representation Method of Space Vector PWM Schemes with Zero Voltage Vector Ratio as a Parameter

Various PWM modulation schemes have been proposed for three-phase voltage source inverters with different representation methods. This paper proposes a novel representation method for various modulation schemes in a unified manner by introducing a variable called the zero-voltage vector ratio. This paper also shows that the proposed method can represent three conventional modulation schemes.

A DPWM Modulation Strategy to Reduce Common-Mode Voltage for Indirect Matrix Converters Based on Active-Current Vector Amplitude Characteristics

Based on the characteristics that the amplitude of active-current vector in the rectifier stage is zero when the zero-voltage vector is used in the inverter stage, and any one from the six active-current vectors can be selected, a novel discontinuous pulsewidth modulation (DPWM) strategy for the indirect matrix converter is proposed in this article to reduce the common-mode voltage (CMV). In this DPWM strategy, the reference current vector in the rectifier stage is synthesized by two adjacent active-current vectors, and the reference voltage vector in the inverter stage is synthesized by two adjacent active-voltage vectors and one zero-voltage vector. When zero-voltage vectors are used in the inverter stage, an appropriate active-current vector with the lowest input phase voltage among the two adjacent active-current vectors is used to produce a lower CMV. Under the same switching loss, the proposed strategy has a better input performance and better output performance in high voltage transfer ratio than conventional SVM. Finally, the effectiveness of the modulation strategy is verified by simulation and experiments.

Analysis of voltage vectors and realization method of torque ripple reduction for BLDCM

BLDCMs are widely used in automotive, industrial and intelligent equipment fields due to their high power density, simple control, and good dynamic performance. However, its non-sinusoidal characteristics have brought problems such as turn-off phase freewheeling to the research and application of BLDCM DTC. This paper proposes the definition, particular characteristic analysis, selection scheme and realization method of the voltage vector, especially the novel zero-voltage vector. Based on the novel zero-voltage and twelve-sector vector selection switch table, an improved PWM modulation strategy in a single cycle is proposed to cooperate with them to achieve the reduction of torque ripple. Finally, the correctness and feasibility of the proposed voltage vector and control strategy theory are verified by a series of experiments.

Optimized Modulation Method for Common-Mode Voltage Reduction in H7 Inverter

The three-phase H7 inverter topology installs an additional power semiconductor switch to the positive or negative node of the DC-link for reducing the common-mode voltage (CMV) by disconnecting the inverter from the DC source during the zero-voltage vectors. The conventional CMV reduction method for the three-phase H7 inverter uses modified discontinuous pulse width modulation (MDPWM) and generates a switching signal for the additional switch using logical operations. However, the conventional method is unable to eliminate the CMV for the entire dwell time of the zero-voltage vectors. It only has the effect of reducing the CMV in a limited area of the space vector where the V7 zero voltage vector is applied. Therefore, this paper proposes an optimized modulation method that can reduce the CMV during the entire dwell time of zero-voltage vectors. The proposed method moves the switching patterns by adding an offset voltage to guarantee that only one kind of zero-voltage vector, V7, is applied in the system. It then turns off the seventh switch only during the zero-voltage vector to disconnect the inverter from the DC source. As a result, the CMV and the leakage current are attenuated for the entire dwell time of the zero-voltage vector. Simulation and experimental results confirm the validity of the proposed method.

Composite Vector Model Predictive Control With Time-Varying Control Period for PMSM Drives

In this article, a composite vector model predictive control (MPC) with a time-varying control period for the permanent magnet synchronous motor (PMSM) drives is proposed. First, the conventional vector selection modes in the MPC method are analyzed. Then, a novel selection mode that selects two nonzero-voltage vectors as optimal voltage vector and has a time-varying control period is developed. Different from the conventional methods, this proposed method can adjust the control period to adapt to the reference voltage vector that is outside the linear modulation range and improve the steady-state control performance. Compared with the conventional three-vector method, this method has the advantages of reducing the switching frequency and suppressing the common-mode voltage due to the reduction use of the zero-voltage vector. Finally, experimental comparison results of different methods validate the effectiveness of the proposed method.

Harmonic Current Suppression of Dual Three-Phase PMSM Based on Model Predictive Direct Torque Control

The traditional direct torque control (DTC) method will produce a larger harmonic current in the x, y subspace when applied to a dual three-phase permanent magnet synchronous machine (DTP-PMSM) because the voltage vector used for DTC is not equal to zero in the x, y harmonic subspace. To mitigate this problem, in this manuscript, a model predictive direct torque control (MPDTC) method is proposed to eliminate the harmonic current in DTP-PMSM. The spatial distribution characteristic DTP-PMSM voltage vector is analyzed; then, the table of vector group can be obtained according to DTC, and each vector group can be combined to obtain the zero-voltage vector in the x, y subspace. According to the cost function, MPDTC selects the vector group and obtains the optimal vector sequence combination to eliminate the harmonic current in the x, y subspace. Furthermore, the MPDTC achieves closed-loop control of harmonic currents in the x, y subspace. The MPDTC can also eliminate harmonic currents caused by other factors. The simulation results show that the method of MPDTC can effectively suppress the harmonic current of DTP-PMSM.

Performance Investigation on SVPWM Sequences Based on Reduced Common-Mode Voltage in Dual Three-Phase Asymmetrical Machine

This paper presents Space Vector Modulation (SVM) sequences that reduce Common Mode Voltage (CMV) in Dual Three-phase Asymmetrical Induction Motor (DTAIM). At first, two existing SVM techniques such as Reference SVM (RSVM) and CMV1 are studied. Additionally, three new switching sequences are developed as CMV2, CMV3 and DCMV3, which reduce peak magnitude of CMV by 66.8% in comparison with RSVM technique. In SVM techniques, to obtain least CMV, zero vectors are usually replaced by two opposite large Active voltage Vectors (AV) with equal time duration. In such topologies like CMV1, total six AVs are utilized to synthesize the reference vector. The proposed SVM technique CMV2 utilizes only five large AVs to synthesize the reference vector and reduces CMV. Selection of five neighbouring AVs is reflected in reduction of harmonic flux trajectories and stator current ripple in proposed techniques. Additionally, two more switching sequences (CMV3 and DCMV3) are developed related to utilization of specific zero voltage vectors in all sectors (7 and 56) that produce zero CMV. These two switching sequences also provide easy implementation feature during the development of c-code program. In this study, CMV and stator current ripple are considered as performance parameters for different SVM techniques. All SVM techniques are analysed by analytical results, computer simulations, and using prototype test setup of DTAIM fed by Dual Three-phase Voltage Source Inverters (DTVSIs).

A Novel Predictive Direct Torque Control Using an Optimized PWM Approach

This article presents a novel predictive direct torque control (DTC) scheme using an optimized pulsewidth modulation (PWM) and a dead-time compensation. In the proposed method, two effective voltage vectors are selected according to the predicted torque and flux errors based on zero-voltage vector. The back electromotive force and flux-torque coupling are also taken into consideration. The torque and flux variations per sampling period are predicted by the zero-voltage vector and the two effective voltage vectors. The switching period of the three voltage vectors (zero, first effective, and second effective) are determined by the torque and flux errors along with the predicted torque and flux variations that have been calculated in the previous step. To improve the prediction result, a dead-time compensation algorithm and a modified PWM switching scheme are adopted to reduce dead-time effect. The detailed implementation of the proposed control scheme is presented. The effectiveness of the proposed predictive DTC-PWM is verified by both simulation and experiments. The results are also compared with the conventional method.