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Wind generators within a wind power plant (WPP) will produce different amounts of active power because of the wake effect, and therefore, they have different reactive power capabilities. This paper proposes an adaptive reactive power to the voltage (Q–V) scheme for the voltage control of a doubly fed induction generator (DFIG)-based WPP. In the proposed scheme, the WPP controller uses a voltage control mode and sends a voltage error signal to each DFIG. The DFIG controller also employs a voltage control mode utilizing the adaptive Q–V characteristics depending on the reactive power capability such that a DFIG with a larger reactive power capability will inject more reactive power to ensure fast voltage recovery. Test results indicate that the proposed scheme can recover the voltage within a short time, even for a grid fault with a small short-circuit ratio, by making use of the available reactive power of a WPP and differentiating the reactive power injection in proportion to the reactive power capability. This will, therefore, help to reduce the additional reactive power and ensure fast voltage recovery. [ABSTRACT FROM AUTHOR]

This paper proposes a hexagon voltage manipulating control (HVMC) method for ac motor drives operating at voltage limit. The command output voltage can be determined simply by the torque command and the hexagon voltage boundary in the absence of motor current-regulating proportional-integral (PI) control gains, additional flux weakening (FW) controllers, and observers for closed-loop control. These attributes reduce the time and effort needed for calibration of the controller in the nonlinear voltage-limited region. The proposed HVMC accomplishes the “true” maximum available voltage utilization, allowing for higher efficiency than that of the current vector controller (CVC) alone in the FW domain. In addition, a voltage selection rule was proposed to determine the unique HVMC solution between two possible voltage vectors. The successful application of the control approach was corroborated by a graphical and analytical analysis. The proposed control approach is potentially applicable to a wide range of control designs for ac drives. [ABSTRACT FROM PUBLISHER]

This paper reports a comprehensive optimization process of the associated passive components of three-phase front-end interleaved boost converters to enhance the power density. The effects of the circulating zero-sequence current between the rectifiers were analyzed in detail, and the mean input current model was developed in the presence of a circulating current. The model was then incorporated into the development of a physics-based average current controller to compensate for the input current low-order harmonic distortions without sacrificing the system power density. The proposed method is expected to be an attractive solution for enhancing the power density of consumer electronic applications needed to meet the harmonic regulations. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage-limited finite-settling-step direct torque and flux control (FSS-DTFC) method with a constant switching frequency for torque-controlled interior permanent-magnet synchronous motors (IPMSMs). The proposed control law dynamically scales the voltage vectors on the hexagonal voltage boundary to ensure the maximum torque capabilities under the given operating conditions while simultaneously regulating the stator flux linkage magnitude under flux-weakening operation. Instead of relying on classical overmodulation methods at voltage limits, this paper developed two independent voltage truncation rules to facilitate the possible voltage vector choices. The analytical solution led to the dynamic voltage modification at each time step with respect to the available inverter voltage. The voltage-limited FSS-DTFC approach has potential advantages in achieving a fast transient torque trajectory and direct manipulation of the stator flux linkage while exploiting the maximum voltage excitation. [ABSTRACT FROM AUTHOR]

A hybrid maximum voltage utilization controller is developed for interior permanent-magnet synchronous motors over a wide operating range. The structure of the controller combines the current vector control (CVC)-type maximum torque per ampere controller and the modulating voltage-scaled controller (MVSC). The hybrid structure provides a smooth transition from the CVC to the proposed MVSC mode by deactivating the current regulator in the flux weakening region. A seamless transition to a full six-step modulation can be realized by adjusting the scaling gain, which is a significant merit in terms of power utilization for wide flux weakening applications. This paper also examines the torque control accuracy under motor parameter drifts to determine how to decouple its effect using a voltage disturbance state-filter design. [ABSTRACT FROM AUTHOR]

This paper proposes a wide-speed direct torque and flux control method associated with the inverter voltage and current constraints of interior permanent-magnet synchronous motors. The proposed approach has potential advantages controlling torque and flux linkage at the voltage and current limits, since no integrators are employed for torque control or flux weakening. The transition between the non-limited operation and maximum voltage modulation can be achieved automatically without modifying the control law. To confirm this, we provide a graphical and analytical analysis that naturally leads to a unique stator voltage vector selection on the hexagon. The proposed controller can maximize the available inverter voltage and generate a higher output torque than conventional current vector controllers at high speeds. The method developed in this paper also retains the beneficial features of classical direct torque control, such as its fast dynamics and direct manipulation of the stator flux linkage for flux weakening. [ABSTRACT FROM AUTHOR]

This paper presents a nonparametric approach to failure detection of broken rotor bars in inverter-fed induction motors (IMs). We lay the mathematical foundation for a diagnostic model of a rotor bar fault that captures the rotor bar high-frequency (HF) characteristics. The model shows that the HF equivalent motor resistance can be used as a direct indicator of broken rotor bars. It should be emphasized that the proposed detection methodology is applicable to any shape of rotor slot design by incorporating the idea of synchronous reference frame based injection and by taking the HF resistance as the fault detector. The proposed detection technique is also insensitive to other motor parameters and is effective under arbitrary load conditions. The full time-domain-based signature process provides efficient detection and enhances fault isolation. The identification scheme was implemented and tested on an inverter-fed 1.5-kW IM. [ABSTRACT FROM AUTHOR]

In this paper, we propose an injection-based axis switching (lAS) sensorless control scheme using a pulsating high-frequency (HF) signal to minimize position detection error and velocity estimation ripple resulting from the zero-current-clamping (ZCC) effect for surface-mounted permanent-magnet motors. When a pulsating carrier-signal voltage is injected in an estimated synchronous frame, the envelope of the resulting HF current measured in the stationary reference frame follows an amplitude-modulated pattern. Using this information, the lAS technique allows one to avoid multiple zero crossings of HF currents by adjusting the current phase angle according to the load condition. At no-load condition, the pulsating voltage is injected only on the d-axis, while the d-axis current is controlled to a certain nonzero value. Under a load condition, the injection voltage is switched to the q-axis, while the d-axis current drops back to zero. Thus, the proposed sensorless control enforces a much better estimation performance in a region of ZCC without a predefined offline commissioning test than the standard pulsating injection scheme. Experiments illustrate the effectiveness of the proposed method in suppressing the estimation error caused by the ZCC disturbance and in extending the system bandwidth. [ABSTRACT FROM AUTHOR]

Presents information on a study which focused on a stator transient inductance estimation scheme used to guarantee the performance of high-speed operation of an induction machine. Voltage and current constraints; Machine inductance detuned effect in flux-weakening region; Simulation results; Conclusions.

Presents information on a study describing how a deep-bar effect of an induction machine can be negligible by performing the proper field-oriented control. Methodology of the study; Simulation results; Experimental results; Conclusions.

Looks at an approach which uses the PWM inverter to identify the induction machine parameters. Importance of accurate induction machine parameters; Problem usually encountered with the inverter; Reference to the implementation of the proposed method.

Presents information on an overmodualation technique for interior permanent magnet synchronous machine (IPMSM), with focus on the concept of torque control. Implementation of the technique to a inverter system; Characterization of the operation of the electrical drive system with a current controller; Difference between the machine terminal voltage and the machine-back electromotive force (EMF); Effects of current regulation performance on torque production.

This paper presents a π/4-multiple-coupled two-phase linear hybrid stepping motor (LHSM) that has two windings per phase, one of which shares the other phase winding. The proposed motor shows a unique ability to deliver low cogging force without any complex control scheme or additional power electronics hardware in microstepping control. An analytical and experimental comparison between conventional π/2- and π/4 multiple-coupled LHSM confirms the effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

This paper proposes a power controller used for three-phase inverters with small dc-link capacitors fed by a single-phase diode rectifier. The effect of the reactive power was investigated based on a power flow analysis between a dc-link and three-phase inverter. These results enable the development of a direct active/reactive power controller in discrete time instead of adopting a classical proportional-integral (PI)-type current regulator, which directly leverages the total power flow of the system. A suitable reactive power selection method was presented to improve the overall system efficiency. The command voltage vector at each discrete time step can be simply and intuitively determined by an inverter power without requiring motor current-regulating PI gains and additional control functions. The proposed controller regulates an average motor velocity/airgap torque while simultaneously shaping a grid-side current with a high power factor and low harmonics to meet IEC61000-3-2 requirements. The proposed structure can be applied to three-phase inverters for a broad family of ac motors, such as induction and permanent magnet synchronous motors. [ABSTRACT FROM AUTHOR]

This paper presents a multilevel step-up dc/dc converter for dc-grid-based offshore wind energy conversion applications. The main features of the proposed multilevel converter are as follows: 1) the voltage stress of the power devices can be reduced, making it suitable for high-voltage applications; 2) the boost inductor can be reduced significantly, leading to the outstanding dynamic performance; and 3) high-voltage gain can be obtained and thus is well-suited for high-gain applications. Theoretical analysis was carried out for a four-level step-up converter, based on which, the converter can be extended to any arbitrary number of levels. The proposed four-level converter was verified by a simulation and evaluated by comparing with a conventional multilevel dc/dc converter in terms of the component stress and power device count. The developed topology was implemented on a 2-kW prototype converter to evaluate its feasibility. [ABSTRACT FROM AUTHOR]

This paper presents a high-efficiency multilevel flying-capacitor (FC) dc/dc power conversion with a lower passive component rating and power device count for distributed renewable energy systems. A resonant technique is adopted for the proposed dc/dc converter to achieve zero-current switching (ZCS) for all switches. Theoretical analysis is carried out for the proposed quintuple topology with three active switches. The proposed converter is evaluated to the conventional FC converter, in terms of the component rating and count, to highlight its advantages with respect to the power density and cost. The experimental results of a 1-kW prototype FC converter are presented to validate the theoretical analysis and principles, as well as attest the feasibility of the proposed topologies. [ABSTRACT FROM PUBLISHER]

Recently, the interest in offshore wind farms has been significantly increased because of the stronger and more stable winds at sea, which will lead to a higher power production. DC/DC power conversion solutions are becoming more popular for fulfilling the growing challenges in the high-voltage (HV) dc-connected offshore wind power industry. This paper presents several multilevel modular dc/dc conversion systems based on the capacitor-clamped (CC) module concept for high-power offshore wind energy applications. Two types of the CC modules, namely, the double-switch (DS) module and the switchless (SL) module, are discussed. A soft-switching technique is adopted to achieve minimal switching losses and the maximum system efficiency. Theoretical analysis is carried out for the $2n+1$-level cascaded configurations based on the CC modules. The inherent interleaving property of the proposed configurations effectively reduces the output voltage ripple without adding extra components. A cascaded hybrid topology is developed by the combination of DS and SL modules. The proposed hybrid topology achieves higher efficiency and lower component count. The cascaded hybrid approach is evaluated in terms of the power device count, reliability, and efficiency against other HV dc/dc topologies to demonstrate its advantage for HVDC-connected offshore wind farms. The experimental results of two 5-kW prototype CC converters are presented to validate the theoretical analysis and principles as well as attest the feasibility of the proposed topologies. [ABSTRACT FROM PUBLISHER]

This paper presents a discrete time deadbeat-direct torque and flux controller (DB-DTFC) for interior permanent magnet synchronous machines (IPMSMs). A Gopinath-style discrete time flux linkage observer is developed which contains two different flux estimation methods based on current and voltage models for flux linkage. This observer produces correctly estimated flux linkages needed for accurate DB-DTFC implementation. In order to eliminate the sampling delay due to a characteristic of digital control computation, a complex vector model-based rotor reference frame current observer is also developed. Combining the discrete time current and flux linkage observers, the correct single time step (deadbeat) air-gap torque and stator flux linkage control at the (constant) switching frequency is achieved and experimentally evaluated. [ABSTRACT FROM AUTHOR]

In this paper, a novel control scheme compensating for source voltage unbalance and current harmonics in series-type active power filter systems combined with shunt passive filters is proposed, which focuses on reducing the delay time effect required to generate the reference voltage. Using digital all-pass filters, the positive voltage sequence component out of the unbalanced source voltage is derived. The all-pass filter can give a desired phase shift and no magnitude reduction, unlike conventional low or high-pass filters. Based on this positive-sequence component, the source phase angle and the reference voltage for compensation are derived. This method is easier to implement and to tune controller gains. In order to reduce, the delay time effect in the voltage control loop, the reference voltage is predicted a sampling period ahead. The validity of the proposed control scheme has been verified by experimental results. [ABSTRACT FROM AUTHOR]