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In this paper, a phase-locked-loop (PLL)-assisted internal model (IM) adjustable-speed controller for brushless dc (BLDC) motors is proposed. Major contributions include proposing a new adjustable-speed module structure of PLL controllers for BLDC motor drives and integrating an IM control strategy and a novel complete motor current sensing scheme. By employing the proposed PLL-assisted IM control method, the controller can be made more robust and accurate. In addition, due to properly integrating the motor current sensing scheme with the pulsewidth modulation control, the hardware implementation of the BLDC motor drive can be made rather compact and enable further integration into chips to reduce the cost and enhance the current regulation performance. Finally, a prototype of the proposed controller is also constructed and applied to an industrial blower to verify the feasibility of the proposed control. Experimental results show that both accurate steady state and fast transient speed responses can be achieved. Moreover, compared with the conventional induction motor drives for industrial blowers, the proposed PMBLDC drives can achieve much higher efficiency with less volume and weight. Index Terms--Brushless machines, current control, motor drives, phase-locked loops (PLLs).

In this paper, a general definition of circulating currents for each phase of each paralleled converter with different load sharing is first proposed. Then, based on this definition, the corresponding circulating current index [[gamma].sub.kj] and unbalance rate [[beta].sub.j] for paralleled converter j are proposed to provide one with a quantitative measure about the serious status of power quality. Third, the corresponding general model of circulating currents is also derived for understanding the governing dynamic behavior of circulating currents. Fourth, based on the derived model, the proposed coordinate control strategy is then proposed for different load sharing controls, as well as elimination of circulating currents. Furthermore, a prototype system is also constructed, and the proposed coordinate control is implemented using TMS320F2812 digital signal processor. Both simulation and experimental results indeed show the effectiveness of the proposed coordinate control. Index Terms--Circulating currents, parallel system, three-phase boost rectifiers.

In this paper, first, the effect of the interior permanent-magnet synchronous-motor (IPMSM) stator resistance to the maximum available motoring or regenerative braking torque is clarified. Then, a drive operating point is interpreted geometrically as the intersecting point of the torque-demand curve with either the maximum torque per ampere (MTPA) trajectory or the voltage-constraint curve inherently imposed by the motor and inverter under different control modes. Based on this principle, a novel voltage-constraint-tracking (VCT) field-weakening control scheme for IPMSM drives is proposed. The proposed method can automatically determine the desired MTPA or field-weakening control modes and provide a smooth transition between these two modes. No machine parameters are required in the field-weakening control mode, and no dc-link voltage sensor is used, rendering the proposed scheme rather robust. In addition, the minimum copper-loss operation can be preserved in the VCT-based control to achieve high efficiency. The proposed control method has a simple structure so that it can easily be implemented by modifying a conventional vector-controlled drive system for practical applications. Finally, a DSP-based prototype drive is constructed to verify the feasibility of the proposed scheme, and some experimental results are provided to demonstrate the satisfactory features. Index Terms--Field-weakening control, interior permanent-magnet synchronous motor (IPMSM), maximum torque per ampere (MTPA) control, minimum copper-loss operation.

In this paper, definition of the circulating currents of multiphase paralleled converters is first presented, and the circulating-current-generating mechanism is clearly explained. Thus, based on this definition, an averaged model of the circulating current is proposed. It is seen from this model that the circulating current consists of not only the zero-sequence but also the nonzerosequence components. The governing differential equation also shows explicitly the relation between the circulating currents and the affecting factors such as different pulse width-modulation strategies. With this understanding, a simple coordinate control is then presented to reduce the circulating current. The phenomenon of the intrinsic circulating current is also explained. Furthermore, a prototype system is constructed, and the proposed control is implemented using TMS320F2812 DSP. Both simulation and experimental results verify the validity of the proposed theory and control. Index Terms--Circulating current, parallel system, three-phase boost rectifiers.

In this paper, a novel robust field-weakening control strategy is proposed for surface-mounted permanent-magnet motor drives to achieve fast dynamic response and minimum copper loss over four-quadrant operation regions. First, a closed-form solution of the maximum available torque-producing current is proposed for calculating the corresponding bounds in real time to achieve both fast response and automatic field-weakening control. Second, the partial field-weakening concept and the classification of ten operation regions for four-quadrant operations are proposed. It is seen that consideration of the stator resistance is crucial to achieve the fastest response. Third, a robust tuner based on the proposed virtual maximum phase voltage amplitude together with a minimum copper-loss controller based on the partial field-weakening concept is proposed to achieve minimum copper loss over the entire operating range. Fourth, a dc-link voltage sensorless control version is also proposed which is very useful in electrical vehicle applications. Finally, a digital-signal-processor-based prototype driver is also constructed to verify the validity of the proposed control strategy. Index Terms--Field-weakening control, minimum copper loss, surface-mounted permanent-magnet (PM) synchronous motor.

In this paper, a linear torque control strategy is first proposed for interior permanent magnet synchronous motor drives to fully utilize the reluctance torque and simplify the controller design. The proposed linear torque control strategy also extends the existing maximum torque per ampere control in the constant torque limit region up to the entire field-weakening region. It is found that in an intermediate speed region, called partial field-weakening region, the existing maximum torque per ampere control can still be applied under lighter load condition. In addition, the proposed control can also achieve the objective of minimum copper loss (i.e., maximum torque per ampere) for the entire speed range. Sound theoretical basis is given in the context. Moreover, an adaptive limiter is proposed for efficiently implementing the proposed control strategy over the entire speed range. Finally, a prototype is also constructed by using a fixed-point DSP TMS320F240 and some experimental results are given to verify the validity of the proposed control strategy. Index Terms--Constant torque limit control, field-weakening control, interior permanent magnet synchronous motor (IPMSM), linear torque control.

In this paper, a constantly sampled current controller is proposed such that the controlled current can track the command within a specified error bound to guarantee the desired power quality. The authors further propose a simple two-value inner bound for current error comparison to determine the right time to add the zero-mode control to reduce both the switching frequency and the resulting current error. Moreover, an upper bound of the constant sampling period for the controller to guarantee the desired performance is derived and some design criteria are given for proper coordination among the design parameters. Finally, some simulation and experimental results are given to demonstrate the feasibility of the proposed current controller. Index Terms--Constant sampling, current controller, two-value inner bound.

In this paper, a constantly sampled current-controlled pulsewidth-modulation (PWM) strategy is proposed such that the controlled current can follow the command within a specified error bound to guarantee the desired good power quality. According to different previous switch statuses, a different inner bound is proposed for current error comparison to add the zero-mode control at the proper time to further reduce the switching frequency. Moreover, an analytic expression of the upper bound of the constant sampling period for the current controller to guarantee the desired performance is derived and some design criteria are given for proper coordination among the circuit parameters. Finally, some simulation and experimental results are given to demonstrate the validity of the proposed current-controlled PWM scheme. Index Terms--Constant sampling, current-controlled pulsewidth-modulation (PWM) strategy, inner bound.

In this paper, a single-layer piezoelectric-transformer (SLPT)-based driver is realized for driving a cold-cathode fluorescent lamp (CCFL). First, a half-bridge resonant inverter is adopted for driving the SLPT and the CCFL to achieve zero-voltage-switching (ZVS) effect. In addition, a PQ-plane-design-oriented approach is presented for determining the power circuit parameters. Second, a feedback controller is proposed to match the power circuit control requirement. The feedback controller provides the proper switching frequency for the drive to be operated at the most efficient frequency. In addition, functions of dimming control and no-load protection are also available from the controller. Third, a small-signal model is derived and the closed-loop stability analysis is made to guarantee the stable tracking of the command signal of the controller. Finally, a hardware prototype is also constructed to verify the effectiveness of the proposed driver. Index Terms--Cold-cathode fluorescent lamp, piezoelectric transformer, resonant inverter, zero-voltage switching.

In this paper, first a set of generalized zero-space vectors is proposed. Based on this concept, a novel single-stage three-phase pulsewidth modulation (PWM) boost-buck ac-dc converter is then proposed to achieve clean sinusoidal input current, unity power factor, adjustable dc voltage, and fixed switching frequency and to be insensitive to input voltage distortion as well as simplify the control of all switches. By choosing proper switching sequences such that the largest magnitude line current is conducted through the antiparallel diodes without switching action, the switching loss and thermal stress can be reduced greatly. Finally, a prototype is constructed, and experimental results are given to validate the proposed converter. Index Terms- Boost-buck ac/dc converter, generalized zero-space vector, space vector, three-phase

In this paper, a basic closed-form duty cycle control law is first derived for the proposed ac/dc converter to achieve clean sinusoidal input current, adjustable dc voltage, controllable power factor and bidirectional power flow capability, and fixed switching frequency, without using any current sensor. Then, a second dead-band scheme is derived from the previous basic form to achieve the same function and to reduce switching loss and thermal stress. Similarly, a four-switch scheme is also derived to provide a new operation mode to enhance the reliability of the converter. Modified control laws of the above family are also considered to handle the effect of unbalanced input voltage. It is very interesting to see that a unified theory can be used to give the above family of duty cycle control laws under both balanced and unbalanced input voltage. Some simulation and experimental results are presented for verification. Index Terms - AC/DC converter, closed form, duty cycle control.

The minimum singular value of the Jacobian matrix of the load flow equation may have been preferred as an indicator of voltage collapse when the static voltage stability of power systems is studied. In this paper we propose a highly efficient algorithm to calculate the smallest singular value of a Jacobian matrix of the load flow equation by employing the non-iterative characteristic of an Incremental Condition Estimation (ICE) method and the sparsity characteristic of large scale power networks. Both theoretical basis and computation cost of the algorithm are also detailed in the context. Finally, a practical application example is also given for demonstration. Keyword - Voltage stability, Stability index, Minimum singular value.

An instantaneous peak detector for three-phase variable frequency sinusoidal signals is proposed. The three-phase characteristic is fully used in the proposed detector to achieve instantaneous response and frequency independence characteristics. A very simple hardware implementation circuit is also presented for minimizing the number of analog computational components. Moreover, the proposed detector possesses excellent linearity and low sensitivity to small voltage unbalance and harmonic distortion. Because of its promising accuracy and transient response, it can be used in many systems such as the voltage regulator of an uninterruptible power supply (UPS), an automatic line voltage regulator, or electric generators, etc., to improve the system transient performance. Theoretical analysis, hardware implementation, and some experimental results are also detailed in this paper.

In this paper, a novel vector control hysteresis current controller for induction motor drives is proposed. Coordination of three phase switches is made in the d-q phase plane. In addition to the current error, information of the current error derivative is further employed so that one can take full advantages of adding the zero voltage vector for reducing the switching frequency. A simple hardware implementation is also proposed such that merits of the conventional hysteresis current controller can still be kept. Theoretical basis and some simulation and experimental results are also covered in this context.

In this paper, a very simple vector control algorithm is proposed for micro-based induction motor drives. The proposed method controls the motor torque directly and linearly to achieve instantaneous torque response without oscillation. The merits of this control method include its simple architecture and obviating the coordinate transformation. At the same time, a new space vector-based current controller is proposed to serve as a quick response torque controller of the proposed drive system. In addition to the current error, information on the current error derivative is further employed so that one can take more advantages of adding the zero voltage vector for reducing the switching frequency. As a result, the efficiency can be greatly increased. It is seen that through integration of the above two parts, the proposed drive system is very simple to implement and has very nice performance.

In this paper, an improved hysteresis current controller is proposed. It coordinates the switching of the three-phase switches in the d-q phase plane. In addition to the current error, information of the current error derivative is further employed so that one can take more advantage of adding the zero voltage vector for reducing the switching frequency. A simple hardware implementation of the improved hysteresis current controller is also proposed such that merits of the conventional hysteresis current controller can still be kept. Theoretical basis and some simulation and experimental results are presented to demonstrate the validity of the improved hysteresis current controller.

In this paper, first, the conventional rotor field orientation vector control method is modified to achieve a simple architecture which obviates the generation of the unit vector and the time varying coordinate transformation such that even a low cost 8 bit microcomputer can be used for implementation. Second, a new current inverter is proposed to effectively coordinate with the proposed vector control algorithm. It has very nice tracking performance and lower switching frequency. As a result of this integration, the involved computation is much reduced and the efficiency can be greatly increased. Finally, a prototype system is implemented using a low cost signal chip microcomputer. Some simulation and experimental results are also given in the context.

In this paper, a step-up/down single-phase ac-to-dc converter without current sensor is proposed to achieve high performance and simple control logic. The converter adopts a front-end diode rectifier so that only one active switch is required. The familiar state-space averaging technique for discontinuous mode dc to dc converters is extended to model the proposed ac to dc converter. Unlike the existing model, which is valid only for very low frequency range, namely below line frequency, the proposed model is applicable up to half switching frequency. Design of the controller is detailed for reference. Finally, some selected experimental results are presented to verify the proposed theory.

In this paper, an equivalent dc duty cycle for the generalized zero-voltage space vectors is proposed such that control of the three-phase ac part and the dc part of the converter circuit can be integrated to achieve the ideal characteristic of single-stage step-up/down ac/dc converter. Depending upon how many modes are chosen and which class of generalized zero-voltage space vectors is selected to increase the equivalent dc duty cycle, different control strategies can be obtained. It is seen that not only the control of the six switches is simplified but also the deadtime circuit for avoiding short circuit of the same arm can be eliminated for the proposed converter. In addition, some guidelines for selecting the LC parameters are described briefly and experimental results given for verifying the validity of the proposed converter. Index Terms--AC/DC converter, duty cycle, space vector, three phase.

Derives a closed-form duty cycle control law based on the linear combination of two sets of continuous duty cycle control laws. Description of the circuit of the three-phase boost rectifier; Output voltage bounds for different control laws.