Showing papers on "Voltage regulation published in 1999"

Analysis and design of electronic transformers for electric power distribution system

Abstract: A transformer performs many functions such as voltage transformation, isolation and noise decoupling, and it is an indispensable component in electric power distribution systems. However, at low frequencies (60/50 Hz), it is a bulky and expensive component. In this paper, the concept of electronic transformers is further extended and explored for its suitability in power distribution systems. It should be noted that from the input/output behavior, the electronic transformer and the conventional transformer are identical. Possible topologies employing static converters connected on the primary and secondary sides are explored to realize high-frequency operation of the magnetic core. To assist the commutation process, a four-step switching has been developed which does not require the use of snubbers. Reduced size, losses, higher efficiency, and better voltage regulation are some of the advantages of this approach. A 10 kVA design example along with experiment results are discussed. It is shown that a transformer designed with a conventional grain-oriented silicon-steel core can process three times the power at 1 kHz operating frequency as compared to 60 Hz. The proposed method is scalable in voltage/current with the currently available insulated gate bipolar transistor (IGBT) devices connected in series without special snubbers.

Effects of unbalanced voltage on the operation performance of a three-phase induction motor

Abstract: This paper uses a real load test to investigate the effects of an unbalanced voltage supply on an induction motor's performance. Based upon various experiments, including: (1) cases with the same unbalance voltage factor but different unbalanced voltages; (2) cases with only one unbalanced voltage but different degrees of unbalance; and (3) cases with the same positive-sequence voltage but different negative-sequence voltages, the importance of the positive-sequence voltage in the motor's apparent performance and of the negative-sequence voltage in the hidden damage are pointed out. Finally, it is strongly suggested that the related regulations, and a motor's derating factor and temperature rise curves should be based on not only a voltage unbalance factor, but also the magnitude of the positive-sequence voltage.

The theory of instantaneous power in three-phase four-wire systems: a comprehensive approach

Abstract: This paper describes a holistic approach to the theory of instantaneous power in three-phase four-wire systems, focusing on the original theory created in 1983 and a modified theory presented in 1994. The two theories are perfectly identical if no zero-sequence voltage is included in a three-phase three-wire system. However, they are different in the instantaneous active and reactive power in each phase if a zero-sequence voltage and current are included in a three-phase four-wire system. Theory and computer simulations in this paper lead to the following conclusions: an active filter without energy storage components can fully compensate for the neutral current even in a three-phase four-wire system including a zero-sequence voltage and current, when a proposed control strategy based on the original theory is applied. However, the active filter cannot compensate for the neutral current fully, when an already-proposed control strategy based on the modified theory is applied.

Integrated high-quality rectifier-regulators

Abstract: A new family of AC-DC converters is derived which integrate the functions of low-harmonic rectification, low-frequency energy storage, and wide-bandwidth output voltage control into a single converter containing one, two, or four active switches. These converters utilize a discontinuous conduction mode input inductor, an internal energy storage capacitor, and transformer secondary circuits which resemble the bridge, forward, flyback, or Cuk DC-DC converters. A large-signal equivalent circuit model for this family is presented, which uses the "loss-free resistor" concept. Design strategies and experimental results are given. High-performance regulation with satisfactory line-current harmonics is demonstrated with conventional duty-ratio control. Further improvements in line current are possible by simultaneous duty-ratio and switching-frequency control.

A control system for HVDC transmission by voltage sourced converters

Abstract: A national technical project is under way in Japan to develop a high-power voltage sourced converter and its control system for the future DC interconnection between AC systems. Three developed prototype 53 MVA GTO-based converters were manufactured and went into operation. As for the control system, the voltage margin method for two terminal, and the 2-stage DC voltage control method for multi-terminal DC link were developed. Field testing is being carried out at Shin-Shinano Substation of Tokyo Electric Power Company. Satisfactory results verify the superiority of the DC link with voltage sourced converters.

Hybrid topology for multilevel power conversion

Abstract: The present invention provides a multilevel electric power converter including a plurality of DC voltage sources providing different DC source voltage levels. The DC source voltage levels are preferably multiples of each other and may vary in a binary fashion or in a geometric progression with a factor of three to provide a large number of output voltage levels for a given number of inverter levels. The multilevel inverter is preferably implemented as a series connected set of H-bridge inverters, with each H-bridge inverter having an independent DC voltage source providing the desired DC source voltage level. A hybrid modulation strategy may be employed whereby the lowest voltage level inverter is modulated at a high frequency, e.g., by pulse width modulation, and higher voltage level inverters in the multilevel inverter are modulated to provide a low frequency stepped waveform. The combined high frequency pulse width modulated and low frequency stepped waveform has good spectral quality. A high voltage high quality waveform may be generated in this manner by taking advantage of the high voltage blocking capability of switching devices, such as GTO thyristors, in the high voltage inverters in the multilevel inverter, and the high frequency switching characteristics of switching devices, such as IGBTs, in the lowest voltage level inverter in the multilevel inverter. A multilevel inverter in accordance with the present invention may be employed in a single-phase or multi-phase applications.

Application of a multivariable feedback linearization scheme for rotor angle stability and voltage regulation of power systems

Abstract: This paper investigates the application of a nonlinear controller to the multi-input multi-output model of a system consisting of a hydraulic turbine and a synchronous generator. The controller proposed is based on a feedback linearization scheme. Its main goal is to control the rotor angle as well as the terminal voltage, to improve the system's stability and damping properties under large disturbances and to obtain good post-fault voltage regulation. The response of the system is simulated in the presence of a short-circuit at the terminal of the machine in two different configurations and compared to the performance of a standard IEEE type 1 voltage regulator, PSS and a PID speed regulator.

Adaptive repetitive control of PWM inverters for very low THD AC-voltage regulation with unknown loads

Abstract: An adaptive repetitive control scheme is proposed and applied to the control of a pulsewidth-modulated (PWM) inverter used in a high-performance AC power supply. The proposed control scheme can adaptively eliminate periodic distortions caused by unknown periodic load disturbances in an AC power supply. The proposed adaptive repetitive controller consists of a voltage regulator using state feedback control, a repetitive controller with tuning parameters and an adaptive controller with a recursive least-squares estimator (LSE). This adaptive repetitive controller designed for AC voltage regulation has been realized using a single-chip digital signal processor (DSP) TMS320C14 from Texas Instruments. Experimental verification has been carried out on a 2 kVA PWM inverter. Simulation and experimental results show that the DSP-based adaptive repetitive controller can achieve both good dynamic response and low total harmonic distortion (THD) under large-load disturbances and uncertainties.

Power line conditioner using cascade multilevel inverters for voltage regulation, reactive power correction, and harmonic filtering

Abstract: A power line conditioner using cascade multilevel inverter used for voltage regulation, reactive power (var) compensation and harmonic filtering, including the control schemes for operating the cascade inverter for voltage regulation and harmonic filtering in distribution systems. The cascade M-level inverter consists of (M-1)/2 H-bridges in which each bridge has its own separate DC source. This new inverter (1) can generate almost sinusoidal waveform voltage with only one time switching per line cycle, (2) can eliminate transformers of multipulse inverters used in the conventional static VAR compensators, and (3) makes possible direct connection to the 13.8 kV power distribution system in parallel and series without any transformer. In other words, the power line conditioner is much more efficient and more suitable to VAR compensation and harmonic filtering of distribution systems than traditional multipulse and pulse width modulation (PWM) inverters. It has been shown that the new inverter is specially suited for simultaneous VAR compensation and harmonic filtering.

Uninterruptable power supply

Abstract: Disclosed is an integrated uninterruptable power supply (UPS) for a computer powered by a commercial power supply. The uninterruptable power supply is operative to feed power from a normal power supply to a first load to be operated at a first DC voltage and a second DC voltage that is lower than the first DC voltage. If a characteristic of the normal power supply is deviated from a defined value, the UPS of the present invention will continue feeding power from a battery power supply to the first load. The uninterruptable power supply includes a power supply unit, having an output connected to the first load, for converting a voltage of the normal power supply to the first DC voltage and for outputting the same. The UPS also includes a first voltage converter having an input connected to the battery and an output connected to the first load, for converting an output voltage of the battery to the second DC voltage and for outputting the same. If the normal power supply is within the defined value, the first voltage converter waits in a no-load state.

WSCC voltage stability criteria, undervoltage load shedding strategy, and reactive power reserve monitoring methodology

Abstract: Engineers have long been struggling with developing voltage stability criteria for their systems. The development of the criteria becomes even more difficult if one attempts to apply the criteria to an entire region such as the one within Western Systems Coordinating Council (WSCC). The WSCC which is comprised of 86 member systems from the western region of North America (Canada, Mexico, and US) has developed strict voltage stability standards which must be complied with by all member systems. The purpose of this paper is to describe the WSCC system-wide voltage stability criteria, which are based on V-Q and P-V methodologies. A methodology for determining the proper mixture of static and dynamic reactive power source, an undervoltage load shedding strategy, and a reactive power reserve monitoring methodology are also discussed.

Volt/VAr control at distribution substations

Abstract: This paper proposes new methods to improve the performance of the current volt/VAr control schemes at distribution substations. The approach makes use of the new measurement and computer resources that are now available at the substations. The paper shows that new supervisory type control schemes can be developed to improve the performance of both the voltage regulator controllers and also the substation capacitor controllers that are used at the substations for volt/VAr control. The new voltage regulator controller makes use of the voltage drop characteristics of the feeders it regulates. The capacitor controller uses local real and reactive power measurements for power factor control at the substation.

Effects of nonsinusoidal voltage on the operation performance of a three-phase induction motor

Abstract: This paper uses a real load test to investigate the effects of each order of harmonic from 2 to 13 under various voltage distortion factors (VDF) on the performance of a three-phase induction motor. The investigation includes input current, power factor, efficiency, temperature rise and their impacts on the consumers and utility companies. Since the life span of the motors is dramatically affected by the temperature rise, a new derating factor is proposed in this paper. Besides, the impacts of harmonics on electricity energy, consumers and the life span of a motor are also discussed, respectively. Finally, it is strongly suggested that even order harmonics and harmonics having an order below 5 should be considered in related regulations of harmonics control and limits.

Control of energy optimized dynamic voltage restorer

Abstract: The dynamic voltage restorer (DVR) is a custom power device used for voltage compensation of sensitive loads against voltage disturbances in power distribution lines. This paper illustrates a correction technique, which draws a minimum amount of energy from the DVR during the process of compensation of a voltage sag or swell. Using the proposed method it can be shown that a particular disturbance can be corrected with less amount of storage energy compared to that of existing in-phase boosting method. The paper also discusses a multiloop feedback control method applicable for the DVR to obtain good dynamic performance.

Charge pump circuit adjustable in response to an external voltage source

Abstract: An integrated circuit detects the voltage level of the supply voltage to the integrated circuit. Circuity on the integrated circuit including the charge pump circuity adjusts to operate more effectively or efficiently at the voltage level of the supply voltage.

Effect of voltage sags on adjustable-speed drives: a critical evaluation and an approach to improve performance

Abstract: In this paper, a critical evaluation of the effect of voltage sags on adjustable-speed drives (ASDs) is presented. In particular, the DC-link voltage variation under voltage sag and its dependence on source impedance, DC-link inductance and output load is computed. It is shown that, for larger source impedance, the DC-link voltage variation under a voltage sag is also large and increases the susceptibility of an ASD and may result in a nuisance trip. The results from the analysis are plotted in per-unit quantities and serve as a design guide to assess ASD performance for a variety of sags. In order to improve the performance of ASDs, this paper proposes an integrated boost converter approach. This approach provides ride-through to critical ASD load during voltage sags without any additional energy storage device. Upon detection of a voltage sag, the boost converter operates with suitable duty ratio and maintains the DC-link voltage within acceptable limits. This prevents nuisance tripping and facilitates continuous operation of critical ASD load at rated torque. The proposed integrated boost converter does not introduce any additional semiconductors in the series path of the power flow and is low in cost. A commercially available 480 V 22 kVA ASD is modified with the integrated boost converter approach, and details are discussed. Analysis, simulation, and experimental performance of the ride-through approach are presented.

Shared-bus current sharing parallel connected current-mode DC to DC converters

Abstract: A power system consisting of parallel connected current-mode power converters combined with a voltage error signal on a shared-bus used in common for controlling all of the power stages for improved consistency, reliability, and performance in both transient and steady states. Near uniform current sharing is achievable without sacrificing the voltage regulation performance. The improved system offers faster settling time under step loads, consistent small signal characteristics and large signal responses regardless of mismatches of components values such as reference voltages, and reduced output impedance variations in magnitude and phase even during various modes of operation.

Design and implementation of an FPGA-based control IC for AC-voltage regulation

Abstract: This paper presents a field-programmable gate army (FPGA)-based control integrated circuit (IC) for controlling the pulsewidth modulation (PWM) inverters used in power conditioning systems for AC-voltage regulation. We also propose a multiple-loop control scheme for this PWM inverter control IC to achieve sinusoidal voltage regulation under large load variations. The control scheme is simple in architecture and thus facilitates realization of the proposed digital controller for the PWM inverter using the FPGA-based circuit design approach. Bit-length effect of the digital PWM inverter controller has also been examined in this paper. The designed PWM inverter control IC has been realized using a single FPGA XC4005 from Xilinx Inc., which can be used as a coprocessor with a general-purpose microprocessor in application of AC-voltage regulation. Owing to the high-speed nature of FPGA, the sampling frequency of the constructed IC can be raised up to the range that cannot be reached using a conventional digital controller based merely on microcontrollers or a digital signal processor (DSP). Experimental results show the designed PWM inverter control IC using the proposed control scheme can achieve good voltage regulation against large load variations.

Arrangement for decentralized supply of regenerative energy performs voltage regulation at combination point for controlled improvement of quality of electrical supply

Abstract: The arrangement regulates the voltage at a combination point for controlled electrical supply quality improvement. The arrangement for supplying power and the voltage regulator are in one unit. The regulator has arrangements for specifying a desired voltage spectrum at the combination point, diagnosing the state of the supply network and determining demand values of harmonics and/or a fundamental frequency reactive power to be compensated. The arrangement performs voltage regulation at a combination point for controlled improvement of the quality of the electrical supply. The arrangement for supplying power and the voltage regulator are contained in one unit. The regulator (17,20) has arrangements for specifying a desired voltage spectrum at the combination point, for diagnosing the state of the supply network and for determining demand values of harmonics to be compensated and/or a fundamental frequency reactive power to be compensated. Independent claims are also included for the following: a current converter.

Solar power generating device

Abstract: In order to obtain a solar power generating device capable of effectively using power generated by a solar cell, the virtual optimum operating voltage, the MPPT minimum voltage, the MPPT maximum voltage, and the low and high voltage change width switching voltages used when MPPT control is carried out are calculated on the basis of the output voltage of a solar panel immediately before the startup of the inverter circuit in the solar power generating device and the MPPT control is carried out on the basis of each of the calculated voltage values.

Method and apparatus for digital voltage regulation

Abstract: A digital voltage regulator has an input terminal (20) coupled to an input voltage source (12), an output terminal (22) coupled to a load (14), and a plurality of switching circuits (24) to alternately couple and decouple the input terminal (20) to the output terminal (22). An estimated current is calculated for each switching circuit (24), each estimated current representing a current passing through an inductor (34) associated with the switching circuit (24). A total desired output current to pass throught the inductor (34) is calculated which will maintain an output voltage at the output terminal (22) substantially constant. The switching circuits (24) are controlled based on the estimated current and the total desired output current so that a total current passing through the inductor (34) is approximately equal to the total desired output current.

Power feeding apparatus, power receiving apparatus, power transfer system, power transfer method, portable apparatus, and timepiece

Abstract: In a power feeding apparatus A 1 , a drive circuit 11 receives electrical power supplied from a power supply 10 and generates a driving signal V. In response to this, an actuator 12 vibrates, and this vibration is transmitted through vibration transmission members 14 and 20 to a converter 21 of a power receiving apparatus B 1 . The converter 21 includes a piezoelectric device. Accordingly, vibration is converted into voltage, thus generating an electromotive voltage Vg. The electromotive voltage Vg is rectified by a rectification circuit 23 , and a large-capacitance capacitor 24 is charged with rectified voltage. A clock circuit 25 receives power from the large-capacitance capacitor 24 and measures time.

Optimization of word-line booster circuits for low-voltage flash memories

Abstract: Two word-line booster circuits, which output a word-line voltage for reading dash memory data, are analyzed and optimized. A capacitor-switched booster circuit outputs a voltage higher than the supply voltage by switching the connection state of one of more boosting capacitors with the load capacitor from parallel to series. The optimum number of capacitors and capacitance per boosting capacitor are obtained as a function of the voltage ratio of the required high voltage to the supply voltage. The operation current consumed by the boosting operation is also analytically derived. In addition, another booster circuit-Dickson charge-pump circuit-is optimized under the condition to maximize the output current at a high word-line voltage. Characteristics of the booster circuits are compared, and the selection of booster circuit for low-voltage flash memory is discussed.

Common mode voltage reduction method modifying the distribution of zero voltage vector in PWM converter/inverter system

Abstract: This paper proposes a new space-vector pulsewidth modulation (PWM) strategy that can restrict the common-mode voltage within one-third of DC-bus voltage in a PWM converter/inverter system with the synchronization of the switching sequence. In this paper, the generation of the common-mode voltage pulse whose magnitude reaches two-thirds of DC-bus voltage is investigated and the elimination method of this voltage pulse is presented. The proposed method can be easily implemented in software and requires no extra hardware without degradation in control performance of PWM converter/inverter-fed AC motor drives.

Electrostatic precipitator slow pulse generating circuit

Abstract: An apparatus and method for generating slow rise-time, high voltage electrical pulses to a load, preferably using an existing transformer/rectifier set or power supply to charge an inversion or high voltage switching circuit to produce the pulsed voltage. An energy recovery circuit ( 100, 102 ) is used to return unused energy from the load ( 24 ) back to the means for producing pulsed voltage ( 110, 130 ). A load matching circuit ( 120 ) uses a blocking diode and a capacitor for charging the load. An additional blocking diode ( 32 ) inhibits load voltage discharge back through the slow pulse generating circuit. A transformer ( 20 ) can be used to step-up voltage from the inversion circuit, or high voltage switching circuit, to the load. One or more magnetic switch stages are used to transfer energy from the inversion circuit, or high voltage switching circuit, to the load matching circuit. A fire-on voltage controller ( 66 ) triggers the inversion or high voltage switching circuit.

Dual voltage electrical distribution system

Abstract: The invention is designed for vehicles having two electrical power supply systems and corresponding differentiated voltage level charges and two batteries operating at a first and a second voltage level. A bidirectional voltage converter cooperates with both systems whose input and output stages are galvanically insulated and include a switch. The batteries are connected to said input and output at a first and a second voltage level so that said bidirectional converter can provide a first reduced voltage mode and a second increased voltage mode . The passive components, e.g. the magnetic components and capacitances, of said stages have been chosen to provide an identical transitional behavior in both modes when a disruption occurs in the regulating system either in the charge or the input voltage.

Optimal power flow incorporating voltage collapse constraints

Abstract: The paper presents applications of optimization techniques to voltage collapse studies. First a "maximum distance to voltage collapse" algorithm that incorporates constraints on the current operating conditions is presented. Second, an optimal power flow formulation that incorporates voltage-stability criteria is proposed. The algorithms are tested on a 30-bus system using a standard power flow model, where the effect of limits on the maximum loading point is demonstrated.

Control strategy of an interleaved boost power factor correction converter

Abstract: Power factor correction interleaved boost converters provide a reduction of the inductor volume and weight when compared with the conventional PFC boost converter. However, to achieve these benefits, proper current sharing and current ripple minimization must be ensured. This paper proposes a controller based on the Lyapunov-likelihood control technique for interleaved boost converters (IBC) that ensures output voltage regulation and proper current share for each boost cell. In addition, a switching logic scheme for the IBC is developed to guarantee the input current ripple minimization. Extensive simulations are presented to demonstrate the performance of the proposed control and switching logic scheme.

The adverse effects of excitation system VAr and power factor controllers

Abstract: The trend toward automation of today's power stations has prompted an increased demand for excitation systems having voltage regulators with the ability to automatically regulate generator reactive power (VAr) output or power factor (PF). While not really a new type of control, automatic VAr and PF controllers are appearing in the specifications of more and more power plants and generator voltage regulators. This paper provides a functional description of voltage, VAr, and PF controllers and regulators, along with an example demonstrating the superior steady-state voltage support performance on a transmission system by regulating voltage, rather than VArs or PF. The paper concludes that VAr/PF controllers or regulators should generally not be specified or utilized on excitation controls for voltage supporting generator applications.

Energy supply circuit for a motor vehicle on-board electrical system having two voltage supply branches

Abstract: In an energy supply circuit for a motor vehicle on-board electrical system with two voltage supply branches at different voltage levels, the first voltage supply branch can be fed by way of an electric direct voltage converter by the second voltage supply branch and the second voltage supply branch can be fed by a generator. A multi-level controller W 3 with three voltage levels is provided whose first in/output is connected with the second voltage supply branch, whose second in/output is connected with the first voltage supply branch and whose third in/output is connected with the energy accumulator B 1 assigned to the first voltage supply branch.