Showing papers on "Three-phase published in 2003"

A comparative analysis of multiloop voltage regulation strategies for single and three-phase UPS systems

Abstract: Most of the many reported control algorithms for uninterruptible power supplies (UPSs) use either filter inductor or filter capacitor currents as feedback variables to regulate the output voltage. This paper explores the fundamental performance issues associated with the use of these quantities as feedback variables, with a view to determining their contribution to the transient system response and output harmonic compensation in any particular situation. A proportional plus resonant (P+resonant) compensator is then added into the outer voltage regulation loop to achieve zero steady error, to develop a high performance UPS control algorithm, which is applicable to both single-phase and three-phase systems. Theory, simulation, and experimental results are presented in the paper.

Genetic algorithm based design of the active damping for a LCL-filter three-phase active rectifier

Abstract: The use of a LCL-filter mitigates the switching ripple injected in the grid by a three-phase active rectifier. However stability problems could arise in the current control loop. In order to overcome them a damping resistor can be inserted, at the price of a reduction of the efficiency. On the contrary the use of the active damping seems really attractive but it is often limited by the use of more sensors respect to the standard control and by the complex tuning procedure. This paper introduces a new active damping method that does not need the use of more sensors and that can be tuned using genetic algorithms. It consists of adding a filter on the reference voltage for the converter's modulator. The tuning process of this filter is easily done, for a wide range of sampling frequencies, with the use of genetic algorithms. This method is used only for the optimum choice of the parameters of the filter and an on-line implementation is not needed. Thus the resulting active damping solution does not need new sensors or complex calculations. Moreover, in the paper particular attention is devoted to the dynamics of the system due to the introduction of the active damping.

Input-output linearization and zero-dynamics control of three-phase AC/DC voltage-source converters

Abstract: Nonlinear differential-geometric techniques are proposed for the design of a feedback controller for three-phase voltage-source pulsewidth modulation (PWM) AC/DC boost converters under a cascade control structure. The input-output linearizability of the system modeled in d-q synchronous reference frames is examined. The results lead to a decoupled d-q current control scheme. For the internal DC-bus voltage dynamics (zero dynamics), by considering the d-axis current command as control input and using a square transform on DC-bus voltage, it is shown that this remaining system contains an input memoryless nonlinearity of conic sector type and satisfies the conditions for a Lur'e plant. This suggests a new outer-loop control strategy to control the square of the DC output voltage, rather than DC output voltage itself, utilizing a simple proportional plus integral (PI) controller cascaded to the d-axis current loop. Since most results do not consider the control of zero dynamics, the strategy for the control of zero dynamics via cascade control structure may provide valuable insight for the design of input-output linearized systems in which zero dynamics contain some desired control variables. The absolute tracking concept for Lur'e plants is introduced to prove the global tracking capability with zero steady-state error of the voltage loop. The controlled PWM AC/DC converter has the features of global stability, fast (exponential) tracking of DC-bus voltage command with zero steady-state error, asymptotic rejection of load disturbance, robustness against parameter uncertainties and decoupled dynamical responses between d and q current loops. Also, measurement of load current is not required. All these features are confirmed via laboratory experiments on a 1.5 kVA PC-based controlled prototype.

A stable three-phase LCL-filter based active rectifier without damping

Abstract: Industrial-LCL-based grid converters using an active rectifier need to be designed in view of robustness, stability and high efficiency In this paper the design of an active rectifier that does not need damping whether passive or active is described This allows obtaining stability without the decrease of the efficiency typical for the passive damping methods or the increase of cost due to more sensors or more complex control algorithms that is typical for the active damping methods This has been achieved with a careful choice of sensor position and of the passive elements in the LCL-filter In fact if the current sensors are on the grid side, rather than on the converter side, the current loop is much more near to the stability Moreover, if the grid side inductance is a fraction of the converter side one, the current loop is again much more near to the stability Thus, with a proper design the system can be made stable at some switching frequencies even without any damping

Three-phase unity-power-factor star-connected switch (VIENNA) rectifier with unified constant-frequency integration control

Abstract: A unified constant-frequency integration (UCI) controller for a three-phase star-connected switch three-level rectifier (VIENNA) with unity-power-factor-correction is proposed. One of advantages of this rectifier is that the switch voltage stress is one half of the total output voltage. The proposed control approach is based on one-cycle control and features great simplicity and reliability: all three phases will be power factor corrected using one or two integrators with reset along with several flips-flops, comparators and logic and linear components. It does not require multipliers to scale the current reference according to the output power level as used in many other control approaches. In addition, the input voltage sensor is eliminated. It employs constant switching frequency modulation that is desirable for industrial applications. The proposed controller can operate by sensing either the inductor currents or the switching currents. If the switching currents are sensed, the cost is further reduced because switching currents are easier to sense comparing with inductor currents. The proposed approach is supported by experimental results.

Analysis of three-phase rectifiers with constant-voltage loads

Abstract: This work presents a quantitative analysis of the operating characteristics of three-phase diode bridge rectifiers with AC-side reactance and constant-voltage loads. We focus on the case where the AC-side currents vary continuously (continuous AC-side conduction mode). This operating mode is of particular importance in alternators and generators, for example. Simple approximate expressions are derived for the line and output current characteristics as well as the input power factor. Expressions describing the necessary operating conditions for continuous AC-side conduction are also developed. The derived analytical expressions are applied to practical examples and both simulations and experimental results are utilized to validate the analytical results. It is shown that the derived expressions are far more accurate than calculations based on traditional constant-current models.

Unified constant-frequency integration control of three-phase standard bridge boost rectifiers with power-factor correction

Abstract: In this paper, a three-phase six-switch standard boost rectifier with unity-power-factor correction is investigated. A general equation is derived that relates the input phase voltages, output DC voltage, and duty ratios of the switches in continuous conduction mode. Based on one of the solutions and using one-cycle control, a unified constant-frequency integration controller for PFC is proposed. For the standard bridge boost rectifier, a unity power factor and low total harmonic distortion can be realized in all three phases with a simple circuit that is composed of one integrator with reset along with several flips-flops, comparators, and some logic and linear components. It does not require multipliers and three-phase voltage sensors, which are required in many other control approaches. In addition, it employs constant-switching-frequency modulation that is desirable for industrial applications. The proposed control approach is simple and reliable. All findings are supported by experiments.

A novel doubly-fed induction wind generator control scheme for reactive power control and torque pulsation compensation under unbalanced grid voltage conditions

Abstract: Wind energy is often installed in rural, remote areas characterized by weak, unbalanced power transmission grids. In induction wind generators, unbalanced three phase stator voltages cause a number of problems, including overheating and stress on the mechanical components from torque pulsations. Therefore, beyond a certain amount of unbalance (for example 6%), induction wind generators are switched out of the network. In doubly-fed induction generators, control of rotor currents allows for adjustable speed operation and reactive power control. In addition, it is possible to control the rotor currents to correct for the problems caused by unbalanced stator voltages. This paper presents a novel controller design for a doubly-fed induction generator that provides adjustable speed and reactive power control while greatly reducing torque pulsations.

High-power galvanically isolated DC/DC converter topology for future automobiles

Abstract: This paper presents a 2 kW three-phase dual active bridge converter (DAB3) which converts power between 42 V and 300 V and is easily scalable up to 20 kW. The DAB3 has been selected for this application based on detailed simulations comparing different suitable topologies. The circuits investigated in this paper can operate in a soft-switching manner enabling a reduction in device switching losses and therewith an increase in switching frequency. Candidate topologies under investigation are the serial resonant converter (SR), the single-phase dual active bridge (DAB1) and the three phase dual active bridge (DAB3). Key-features are the galvanic isolation, reduced cooling costs, and the capability of transferring energy over a wide voltage range.

General steady-state analysis of three-phase self-excited induction generator feeding three-phase unbalanced load/single-phase load for stand-alone applications

Abstract: A general steady-state analysis of a three-phase self-excited induction generator (SEIG) feeding a three-phase unbalanced load or single-phase load is presented. Symmetrical component theory is used to obtain relevant performance equations through sequence quantities. While the analysis of the system is inherently complicated due to unbalance and magnetic saturation, valid simplifications incorporated in the equivalent circuit for both forward and backward fields result in manageable equations suitable for computer simulation. Suitable non-linear parameters are chosen corresponding to appropriate saturation levels. Using this technique a 7.5 kW, 415/240 V, four- pole, threephase induction motor operated as a SEIG is analysed tinder different unbalanced loads and compared with experimental results. The fcasibility of using three-phase machines for such unbalanced operations has been critically examined for stand-alone power generation.

A novel discrete control strategy for independent stabilization of parallel three-phase boost converters by combining space-vector modulation with variable-structure control

Abstract: We propose a discrete nonlinear controller, developed in a synchronous frame, for a parallel three-phase boost converter consisting of two modules. The basic idea, however, can be extended to a system with N modules. Each of the closed-loop power-converter modules operates asynchronously without any communication with the other modules. The controller stabilizes the currents on the dq-axes and limits the flow of the pure-zero sequence current. It combines the space-vector modulation scheme with a variable-structure control, thereby keeping the switching frequency constant and achieving satisfactory dynamic performance.

Motor drive control with a single current sensor using space vector technique

Abstract: A drive system for a three phase brushless AC motor is arranged to optimize the transistor switching pattern to improve power output whilst allowing current measurement in all of the phases using a single sensor. This is achieved by defining voltage demand vectors x where more than two states are required to meet a minimum state time requirement determined by the single sensor method, and calculating three or more state vectors which produce the demanded vector x whilst still allowing single current sensing. Various methods of optimising the PWM pattern so as to give maximum output whilst using single current sensing are also disclosed.

Analysis of the neutral conductor current in a three-phase supplied network with nonlinear single-phase loads

Abstract: This paper describes what factors (i.e., load and supply) have an important effect on the neutral conductor current. It is shown that an asymmetry up to 10/spl deg/ or an unbalance of 10% in the power supply has only a minor effect on the RMS value of the neutral conductor current. An unbalance in load conditions increases the neutral conductor current. Harmonics in the power supply voltage highly affect the RMS value of the neutral conductor current.

Analysis of the asymmetrical operation of dual three-phase induction machines

Abstract: The paper deals with the problem of the unbalanced current and power sharing in the dual three-phase induction machine supplied by a sinusoidal voltage source. In particular, the case discussed has two three-phase sets of full-pitch windings, spatially shifted by 30 electrical degrees with isolated neutrals. The unbalanced current sharing between the two winding sets is due to the not eliminable small system asymmetries. First, the machine model to compute the unbalances is presented; second, the analysis of the system asymmetries and their effects on the machine operation is discussed. Simulated and experimentally tested sinusoidal supply conditions are presented for a 10 kW dual-three phase induction machine prototype.

A simplified three-phase zero-current-transition inverter with three auxiliary switches

Abstract: Most existing three-phase soft-switching inverters with fewer than six auxiliary switches have fundamental drawbacks in performance. There exist a few soft-switching inverters with six auxiliary switches that can potentially achieve desirable performance, but are penalized with the high cost and large size associated with the auxiliary switches. This paper proposes a zero-current-transition (ZCT) inverter topology that requires only three auxiliary switches. Each phase of the proposed circuit employs one auxiliary switch and one LC resonant tank to assist switching transitions. With considerable reduction in device count, cost, and size, the proposed topology realizes zero-current turn-off for all main switches and auxiliary switches, and provides soft commutation for all diodes. Meanwhile, it requires no modification to normal pulsewidth modulated (PWM) algorithms. The operation principles, design and control guidelines, and an analysis using the state-plane technique are presented. Based on the proposed topology, a 50-kW three-phase prototype inverter has been developed for electric vehicle propulsions, and tested to the full power level with a closed-loop induction motor drive system. Experimental results on the 50-kW prototype are provided to verify the proposed concept in high-power AC adjustable speed drive applications.

Rotation drive control circuit of multiphases direct current motor and the start-up method thereof

Abstract: In start-up control of a motor in which currents are caused to flow through any two of three phase coils to detect the polarity of a voltage induced in each de-energized phase, thereby determining the corresponding energized phase at start-up thereof, based on the polarity of the detected induced voltage, the levels of induced voltages are detected in addition to the polarity of the induced voltage for the de-energized phase to thereby determine the relationship between the magnitudes thereof, and the energized phase at the start-up is determined based on the relationship of magnitude between the polarity of each induced voltage and the level thereof. In drive control of a multi-phase DC motor wherein a driver for allowing a drive current to flow through each coil is controlled by PWM control signals, and a sine wave-shaped current is caused to flow through each coil to thereby rotatably drive the motor, positive-phase and negative-phase signals are generated as triangular wave carrier signals for generating the PWM control signals, and the PWM control signal related to the corresponding phase coil of the respective phase coils, to which a voltage of an intermediate level is applied by the driver, is generated using a carrier signal opposite in phase to a triangular wave signal used to generate the PWM control signals for other phase coils.

A three-phase ZVS PWM DC/DC converter with asymmetrical duty cycle for high power applications

Abstract: This paper proposes the application of the asymmetrical duty cycle to the three-phase DC/DC PWM isolated converter. Thus soft commutation is achieved for a wide load range using the leakage inductance of the transformer and the intrinsic capacitance of the switches, as no additional semiconductor devices are needed. The resulting topology is characterized by an increase in the input current and output current frequency, by a factor of three compared to the full bridge converter, which reduces the filters size. In addition, the RMS current through the power components is lower, implying an improved thermal distribution of the losses. Besides, the three-phase transformer allows the reduction of the core size. In this paper, a mathematical analysis, the main waveforms, a design procedure as well as simulation and experimental results obtained in a prototype of 6 kW are presented.

Evaluation of 1200 V-Si-IGBTs and 1300 V-SiC-JFETs for application in three-phase very sparse matrix AC-AC converter systems

Abstract: In this paper based on experimental investigations of the power semiconductor switching behavior and on analytical calculations the conduction and switching losses of it three-phase very sparse AC-AC matrix converter (VSMC) supplying a permanent magnet synchronous motor are discussed in detail. There, 1200 V-Si-IGBTs/1200 V-Si-ultra-fast-recovery diodes and 1300 V-SiC-JFET/Si-MOSFET cascodes are employed for realizing the converter power circuit. The worst case operating conditions are identified and the efficiencies resulting in dependency of the switching frequency and load current amplitude are shown in graphical form. Furthermore, the operating range of the VSMC with respect to the maximum admissible junction temperature of the power semiconductors is determined. Finally, topics to be treated in the continuation of the research are discussed briefly.

Space vector modulation and control of a unidirectional three-phase/level/switch VIENNA I rectifier with LCL-type AC filter

Abstract: This paper presents a novel three-level space vector modulation method applied to a vector controlled VIENNA I rectifier with LCL-type AC filter. The principle modulation algorithm operation, basic assumptions and restrictions due to the main circuit are analysed in case of conventional L filter. Then the analysis is extended to include the LCL filter. On the basis of the key equations derived from the system examined, the vector control system is realised. The theoretical analysis of the proposed modulation technique and vector control system is verified by Simplorer and Matlab Simulink simulations, taking into consideration the total harmonic line current distortion, the losses in the active and passive components, delays and switching transients of the semiconductor devices. The rectifier system is designed to operate at a nominal DC link output power of 50 kW, DC link voltage 650 V and applied switching frequency 3.5 kHz. The LCL filter is designed so that the total harmonic line current distortion is 1% while the rectifier current distortion is 4%.

A high-power-factor, three-phase isolated AC-DC converter using high-frequency current injection

Abstract: A single-stage, three-phase AC-to-DC converter topology is proposed for high-frequency power supply applications. The principal features of the circuit include continuous current operation of the three AC input inductors, inherent shaping of the input currents, resulting in high power factor, a transformer isolated output, and only two active devices are required, both soft-switched. Resonant conversion techniques are used, and a high power factor is achieved by injecting high-frequency currents into the three-phase rectifier, producing a high frequency modulation of the rectifier input voltages. The current injection principle is explained and the system operation is confirmed by a combination of simulation and experimental results.

Three-phase bridge power block module type auxiliary resonant AC link snubber-assisted soft switching inverter for distributed AC power supply

Abstract: This paper presents a novel prototype of the three-phase power module bridge package type auxiliary resonant AC link snubber circuit for the three-phase voltage source type sinwave soft switching PWM inverter operating under instantaneous space voltage vector modulation scheme. The operating principle of a novel prototype resonant AC link snubber circuit in addition to unique features are described for current source load model during one switching period which is equivalent to the three-phase voltage source type inverter with LPF, along with its design approach based on the simulation data. The steady-state performance evaluations of space vector modulated three-phase voltage source type sinewave soft switching inverter incorporating a new prototype circuit of three-phase active auxiliary resonant AC link snubber is illustrated and discussed as compared with those of three-phase voltage source type sinewave hard switching PWM inverter with a space voltage vector modulation strategy. The power loss analysis and conventional efficiency estimation of the three-phase voltage source soft switching PWM inverter using IGBT power modules is actually evaluated and discussed on the basis of the conduction power losses based upon the measured v-i characteristics for in addition to all the switching power losses of IGBT with antiparallel diode.

Positive and negative sequence estimation for unbalanced voltage dips

Abstract: This paper proposes the use of a complex Kalman filter for the estimation of positive and negative sequences from three phase voltages. A complex voltage is obtained by applying the /spl alpha//spl beta/-transform followed by the dq-transform using a rotational operator. The algorithm for three phase voltages containing K harmonics is also given. In the conventional method, estimation of positive and negative sequences is performed through two steps: the magnitude and phase-angle in each individual phase of the voltages are first estimated and the symmetrical component transformation is then applied. The proposed method offers a direct estimation of the positive and negative sequences that may reduce the estimation errors. In addition, the proposed method has a reduced computational cost since the number of state variables is reduced to 2/3 as compared to that in the conventional method. An experiment was performed on measured three phase voltage data. Results have shown that the proposed method offers a good estimation.

Three-phase active harmonic rectifier (AHR) to improve utility input current THD in telecommunication power distribution system

Abstract: Modern telecommunication power supply systems have several parallel-connected switch-mode rectifiers to provide -48 V DC. A typical switch-mode rectifier configuration includes a three-phase diode rectifier followed by a DC-DC converter. Such a system draws significant harmonic currents for the utility, resulting in poor input power factor and high total harmonic distortion. In this paper, a three-phase active harmonic rectifier (AHR) scheme is proposed. In the AHR scheme, a diode rectifier module is replaced by a six-insulated-gate-bipolar-transistor pulsewidth-modulation rectifier to supply load harmonics as well as its own active power. Each DC-DC converter module is connected to a shared 48-V DC link. The AHR module together with parallel-connected switch-mode rectifiers is controlled to achieve clean input power characteristics. The VA ratings of the AHR scheme is compared with an active power filter approach. The control design is based on the synchronous reference frame approach. Analysis, simulation, and experimental results show that the AHR offers several advantages such as lower VA rating, better current control response, efficient use of the AHR DC link, small size, and stable DC-link voltage control.

Control implementation of a five-leg voltage-source-inverter supplying two three-phase induction machines

Abstract: A 5-leg inverter has already been proposed and simulated to supply to 3-phase induction machine in fault operation. This paper suggested a new control strategy for such a power structure. This specific pulse width modulation enables an experimental validation of the 5-leg inverter supplying both 3-phase induction machines. Independent behaviors of the machines are obtained.

Mitigation of noneliminated harmonics of SHEPWM three-level multipulse three-phase active front end converters with low switching frequency for meeting standard IEEE-519-92

Abstract: Three-level NPC active-front-end three-phase (3LAFE) converters can be applied to high-power medium voltage applications, with 4-quadrant unity-power-factor operation, allowing a broad range for power conversion systems, such as decentralized energy distribution and utilization. Switching losses and network interaction limit the operation of 3LAFE high-power converters, especially when GTO-converters are used. That is why, low switching frequency and reduced harmonic distortion are the main goals when using optimum pattern PWM where selective harmonic elimination modulation method (SHEPWM) is used. This paper introduces a simple method to choose a good operating point for two 3LAFE converters in a 12-pulse configuration based on the behavior of noneliminated harmonics by SHE method. A complete characterization is given as a base of SHE and the optimization criteria is fully explained.

Advanced modulation scheme for three-phase three-switch buck-type PWM rectifier preventing mains current distortion originating from sliding input filter capacitor voltage intersections

Abstract: Modulation schemes for three-phase three-switch buck-type PWM rectifiers where the switching state of one bridge leg is clamped within a /spl Pi//3-wide interval of the mains period do guarantee minimum switching losses as well as minimum input filter capacitor voltage ripple and minimum DC current ripple. However, as shown in this paper by a detailed analysis of the time behavior of the input filter capacitor voltages within a pulse period such modulation schemes are characterized by the occurrence of sliding intersections of the filter capacitor voltages which do cause input current distortion. An advanced modulation scheme is proposed which does prevent the input current distortion and does allow to maintain the optimum performance of conventional modulation schemes.

Micro-stepping control of a two-phase linear stepping motor with three-phase VSI inverter for high-speed applications

Abstract: This paper presents a synchronous frame current control scheme for micro-stepping a two-phase linear stepping motor drive using a three-phase voltage-source inverter. Because of the wide operating frequency, the frequency-dependent voltages are decoupled from the controller to reduce the current-following errors and preserve the dynamic characteristics as the frequency varies. A motor cogging force compensation scheme performed in the synchronous frame is proposed to reduce the positioning error and velocity ripple caused by the cogging force. A space-vector pulse width modulation scheme is used for motor voltage modulation. This scheme is based on the harmonic injection principle originally derived for three-phase motor drives. Good static and dynamic performance is obtained in the experimental verifications.

Active rectifier module for three-phase generators of vehicles

Abstract: The invention relates to a rectifier for rectifying alternating current into direct current, in which a three-phase generator comprises a three-phase stator winding (9). The phases (11, 12, 13) of the stator winding (9) are controlled by means of switching elements (15.1, 15.2; 16.1, 16.2; 17.1, 17.2) of a power circuit (8). The latter (8) is controlled by a control part (2), which comprises a regulator module (3, 55). The rectifier (1) comprises a control part (2) (control module), equipped with control connections (30) and a power circuit (8) (power module), which is controlled by said part, optionally provided with a cooling device (23, 24) and in which all the power conducting components (15.1, 15.2, 16.1, 16.2; 17.1, 17.2; 13) are configured as power MOS components (28) and integrated in a stacked construction (20).

Control system for canceling load unbalance of three-phase circuit

Abstract: A control system for canceling load unbalance of a three-phase circuit includes phase current detectors for detecting phase currents caused to flow through a secondary circuit of a current transformer provided in high voltage distribution lines, respectively, phase change-over switches through which phases of the high voltage distribution lines, and primary sides of distribution transformers provided across high and low voltage distribution lines are connected to each other, a control center for, when a magnitude of a zero-phase current detected by the zero-phase current detector is larger than a predetermined value, on the basis of the phase currents, respectively, out putting a control signal so that the load of the phase having a maximum current appearing therein is changed over to the phase having a minimum current recognized therein, and a phase change-over slave station for controlling the phase change-over for the phase change-over switches in accordance with the control signal.