Search

Cascaded H-bridge drives require using a significant-size capacitor on each cell to deal with the oscillatory power generated by the H-bridge inverter in the DC-link. This results in a bulky cell with reduced reliability due to the circulating second harmonic current through the DC-link capacitors. In this article, a control strategy based on a finite control set model predictive control and a proportional-resonant controller is proposed to compensate for the oscillatory power required by the H-bridge inverter through the cell's input rectifier. With the proposed strategy, a DC-link second harmonic free operation is achieved, allowing for the possibility of reducing the capacitor size and, in consequence, the cell dimensions. The feasibility of the proposed control scheme is verified by experimental results in one cell of a cascade H-bridge inverter achieving an operation with a capacitance 141 times smaller than required by conventional control approaches for the same voltage ripple. [ABSTRACT FROM AUTHOR]

This paper presents the implementation of a predictive control scheme for an indirect matrix converter. The control scheme selects the switching state that minimizes the reactive power and the error in the output currents according to their reference values. This is accomplished by using a prediction horizon of one sample time and a very intuitive control law. Experimental results with a 6.8-kVA indirect matrix converter prototype are provided in order to validate the proposed control scheme. The converter uses standard digital signal processor operating at a sampling frequency of 20 [micro]s. It is shown that the idea of controlling this converter topology with a predictive approach can be implemented simply and input currents with unity power factor and a total harmonic distortion lower than 5% can be obtained. Index Terms--AC motor drives, current control, predictive control.

The analysis of a multicell topology that is implemented with single-phase nonregenerative cells under an unbalanced ac mains is presented. The study shows that the topology naturally compensates most of the voltage unbalance; for instance, for a 100% voltage unbalance in the ac mains, just 32% reaches the load. For critical applications, a feedforward control technique is proposed in order to compensate the remaining unbalance at the load side. The resulting topology, in combination with the proposed strategy, reduces near to zero the load fundamental voltage unbalance, while the input current unbalance and distortion are also improved. A theoretical analysis that is based on symmetrical components and the experimental results confirm the theoretical considerations. Index Terms--AC-AC power conversion, insulated-gate bipolar transistor, multicell single-phase topology, multilevel system, power electronics, variable-speed drives.

This paper proposes a simple linear feedback-based control technique that ensures zero-neutral-point (NP) potential in three-level voltage-source inverters. The technique works even under dynamic load conditions and enables the decoupled control of the direct and in-quadrature load currents. The technique is based on the relative-gain-array (RGA) approach, which has been successfully used in the control of chemical-engineering processes. The resulting scheme allows the use of outer control loops to set the direct and in-quadrature load currents as required for the specific application (e.g., adjustable speed drives). Experimental results prove the theoretical considerations and show the simplicity of the proposed control scheme. Index Terms--Decoupling of systems, inverters, MIMO systems, multilevel systems.

Multicell power circuit topologies have proved to be an effective alternative to medium-voltage ac drives. The main advantage is the improved power quality at both the ac system and the motor sides. However, several drawbacks are present in these configurations, such as a lack of sustained regenerative operating mode, uncontrolled input reactive power, and a large second current harmonic that is injected by the load into the dc link of each cell, which leads to a bulky electrolytic capacitor. This paper proposes to replace the input diode-based front-end rectifier with an active front-end rectifier in all cells of the topology and a novel control strategy in order to overcome the aforementioned drawbacks. In fact, the active front-end rectifier allows the topology to regenerate and the control strategy handles the reactive input power and reduces the large second current harmonic from the dc-link capacitor, thus reducing its size. These features are achieved without any penalties in the quality of both the ac input current and the motor voltage waveforms. Experimental results confirm the theoretical considerations. Index Terms--Energy storage reduction, multilevel converter, regenerative cell.

New regulations impose more stringent limits on current harmonics injected by power converters that are achieved with pulsewidth-modulated (PWM) rectifiers. In addition, several applications demand the capability of power regeneration to the power supply. This paper presents the state of the art in the field of regenerative rectifiers with reduced input harmonics and improved power factor. Regenerative rectifiers are able to deliver energy back from the dc side to the ac power supply. Topologies for single- and three-phase power supplies are considered with their corresponding control strategies. Special attention is given to the application of voltage- and current-source PWM rectifiers in different processes with a power range from a few kilowatts up to several megawatts. This paper shows that PWM regenerative rectifiers are a highly developed and mature technology with a wide industrial acceptance. Index Terms--High power factor, power electronics, rectifier, regeneration.

This paper presents the performance analysis of a hybrid filter composed of passive and active filters connected in series. The analysis is done by evaluating the influence of passive filter parameters variations and the effects that different active power filter's gain have in the compensation performance of the hybrid scheme. The compensation performance is quantified by evaluating the attenuation factor in a power distribution system energizing high-power nonlinear loads compensated with passive filters and then improved with the connection of a series active power filter. Finally, compensation characteristics of the hybrid topology are tested on a 10-kVA experimental setup. Index Terms--Active power filter, current harmonics, power factor, power filter, reactive power.

A high-performance single-stage UPS system for single-phase ac power supply systems is presented. The topology generates a trapezoidal-shaped load voltage that is synchronized with the ac supply, therefore, a small tic-link capacitor is required. This feature leads to a high-input power factor (0.94 at nominal voltage), and due to the single-stage structure, high efficiency (93% at nominal voltage) is also achieved. Moreover, in both cases the supply current spectrum presents low-order harmonics, all of which satisfy IEC 555. The high performance is validated using both resistive (linear) and diode RC (nonlinear) loads. The dynamic performance of the UPS system is also analyzed under different transient conditions. Specifically, the supply to battery, battery to supply transition, load transient, and supply/battery-voltage transients are performed. They show a transfer time of 500 [[micro]seconds] (from ac supply to battery) and over-voltages of at most 15%. The dynamic and static evaluations are performed on a 1-kVA UPS system. The design guidelines for the key components and control parameters are also included. Index Terms - AC mains synchronization, PWM inverter, single-phase single-stage conversion topology, trapezoidal-shaped ac output voltage, UPS.

Standard low- and medium-power induction motor drives are based on the pulsewidth modulation (PWM) voltage-source inverter fed from a diode rectifier. The dual topology, based on the current-source inverter]rectifier structure is used in medium- and high-power applications. This paper analyzes the existing motor drives based on current-source topologies and proposes a control strategy that addresses some of the drawbacks of this approach compared to the voltage-source approach. The proposed strategy features the following: 1) an on-line operated PWM inverter, using instantaneous output capacitor voltage control based on space-vector modulation and 2) an additional inverter modulation index control loop, ensuring constant inverter modulation index and minimum dc-link current operation. The resulting additional advantages include the following: 1) fixed and reduced motor voltage distortion; 2) minimized dc-bus inductor losses; 3) minimized switch conduction losses; and 4) elimination of motor circuit resonances. Experimental results based on a digital signal processor implementation are given. Index Terms - AC drive, pulsewidth modulation current-source rectifier/inverter, reduced losses.

An inverter configuration for high-power induction heating and melting applications is presented. The proposed inverter covers loads with quality factors up to 12, while featuring self-starting capabilities. This is achieved by properly distributing the compensated capacitor between the primary and the secondary of the matching transformer. The transient analysis of the configuration defines the maximum ratio of the primary and secondary capacitors, in order to assure self starting. On the other hand, the steady-state analysis defines the minimum ratio to limit the operating flux level of the matching transformer to a safe level. This paper identifies the sources of self-starting failures in the standard configuration and presents the transient and steady-state analyses toward a systematic procedure of components design for the proposed topology. Experimental results on a laboratory prototype to prove the theoretical considerations are also included. Index Terms - Induction heating, self-starting inverter, series-resonant inverter.

Pulsewidth modulated (PWM) current-source rectifiers (CSR), among other alternatives, offer marked improve. merits over thyristor line-commutated rectifiers as a source of variable dc power. Advantages include reduced line current harmonic distortion and complete displacement power factor control, including unity displacement power factor operation. However, due to nonlinearities of the PWM-CSR model, their control has usually been carried out using direct line current control in a three-phase stationary frame (abc). This paper proposes the application of a nonlinear control technique that introduces more flexibility in the control of the rectifier and results in a more straightforward approach to controller design. The proposed technique is based on a nonlinear state variable feedback approach in the rotating frame (dq). The approach allows the independent control of the two components of the line current (active and reactive) with the same dynamic performance, regardless of the operating point. The control strategy also eliminates the need for input damping resistors and rejects the effect of supply voltage variations. Furthermore, a space vector modulation (SVM) technique is used to maximize the supply voltage utilization. This paper includes a complete formulation of the system equations and a controller design procedure. Experimental results on a 2-kVA digital-signal-processor-controlled prototype confirm the validity of theoretical considerations. Index Terms - Current-source rectifier, decoupled control, dq rotating frame, input-output linearization, on-line control, pulsewidth modulated, space vector.

On-line pulsewidth modulation (PWM) pattern generators for current-source rectifiers and inverters offer a number of control advantages over off-line optimized patterns. However, when implemented using the principles which apply to voltage-source inverter PWM pattern generators, the switching frequency is equal to: 1) the carrier frequency in standard carrier-based implementations and 2) a function of the cycle frequency, sequence of space vectors, and selection of the zero space vector in space vector implementations. This paper shows that this frequency can be reduced to one-half of the respective frequencies. Two pattern generators are investigated: 1) an analog on-line carrier-based technique, namely, the modified dead-band technique and 2) a digital on-line space vector-based technique, where advantage is taken of the extra zero state available in current-source converters. It is shown that the switching frequency reduction is achieved with no penalty in the line current harmonic distortion. Moreover, a significant reduction of ac line current distortion is obtained with the modified dead-band technique for modulation indexes greater than 0.4. The principles of operation of the proposed schemes are explained. Experimental results on a 5-kVA current-source rectifier and a 5-kVA current-source inverter confirm the feasibility and features of the proposed pattern generators. Index Terms - Current-source converter, minimum switching frequency, on-line control, PWM.

This paper presents a unified approach for generating pulsewidth-modulated patterns for three-phase current-source rectifiers and inverters (CSR/Is) that provides unconstrained selective harmonic elimination and fundamental current control. The approach uses the chopping angles or gating patterns developed for voltage-source rectifiers and inverters in combination with a logic circuit to generate the gating patterns for CSR/Is. The circuit also includes naturally and symmetrically distributed shorting pulses. Thus, the approach avoids the hassle of positioning the shorting pulses and defining and solving a set of nonlinear equations dedicated to CSR/Is. Moreover, the approach can eliminate an even or odd arbitrary number of harmonics (e.g., fundamental current control and elimination of the 5th, 7th, and 11th harmonics). This is an improvement over existing techniques and a new approach to pattern generation. Simulated and experimental results for both static and dynamic operating conditions are presented in order to validate the effectiveness of the approach. Index Terms--Current source, selective harmonic elimination, three phase, voltage source.

Shunt-type static vat compensators have been shown to be an effective means of increasing the transmission capability of power systems and of increasing the power factor of industrial loads. This paper presents an alternative to the shunt connection consisting of a series-connected transformer-coupled pulsewidth modulation (PWM) inverter. The scheme consists of a current source inverter (CSI) fed from a self-controlled dc current bus and presents the following features: 1) instantaneous series injected voltage control through on-line PWM of the dc link current and 21 steady-state modulation index of the PWM pattern near unity through dc link current minimization. The first feature results in fast dynamic response, while the second feature ensures low and fixed injected voltage harmonic distortion and reduced steady-state compensator losses. Operation of the compensator and of the two-loop control scheme are presented. Simulation and experimental results on a 2-kVA laboratory prototype unit confirm the feasibility of the proposed var compensator structure. Index Terms - Current source inverter, modulation index control, series compensator, var compensation.

A single-stage power-factor-corrected pulsewidth modulation converter with extended load power range is presented. The topology is based on a zero-voltage zero-current-switched full-bridge (ZVZCS-FB) inverter. Steady-state analysis of the topology shows that by operating the LC load filter in discontinuous mode, the dc-link voltage remains bounded and independent of the load level. Therefore, the load power range can be further expanded, including the no-load operating condition. The analysis also shows that the extension of the load power range is achieved without any penalty in: 1) the input power factor (due to the input current waveshaping feature); 2) the converter efficiency (due to ZVZCS and the single-stage features): and 3) the load voltage quality (due to the high bandwidth of the phase control loop). Simulated and experimental results are included to show the feasibility of the proposed scheme. Index Terms - Discontinuous operating mode, full bridge, high switching frequency, phase control, power factor correction, zero voltage zero current.

Current-source-inverter-based uninterruptible power supplies and V/f-controlled induction motor drives require sensing of two or more load voltages in addition to the dc voltage sensors used for protection purposes. This paper proposes a digital-signal-processor (DSP)-based load voltage control scheme that requires only information provided by the dc-bus voltage sensor. Load voltage estimation is based on ac line voltage reconstruction by means of a recursive least-square error algorithm that uses the information available on the dc bus and knowledge of the pulsewidth modulation gating pattern. Thus, the system minimizes the transducer count and, therefore, enhances reliability and ruggedness. Experimental results show that the load voltage can be reconstructed and its rms value controlled for a wide range of operating conditions with errors of at most 4%. Moreover, the use of the space-vector modulation technique ensures a reduced load voltage harmonic distortion, which remains within the 5% range at nominal voltage and for all load conditions. The paper presents the DSP algorithms required for the operation of the system and key experimental results obtained on a three-phase 208-V 60-Hz 2-kVA prototype unit. Index Terms - Current-source inverter, space-vector pulsewidth modulation, voltage control, voltage reconstruction.

Objectives.: To produce recombinant single-chain antibodies from alpaca that will bind to the excreted-secreted (ES) Fasciola hepatica antigen with high affinity and specificity, so as to develop new diagnostic technologies of human and animal fascioliasis., Materials and Methods.: A gene bank of DNA of the variable dominions of heavy single-chain antibodies (VHH) has been created, based on mononuclear cells of peripheral blood of an alpaca immunized with the ES antigen of F. hepatica. The gene bank was screened with the ES antigen by differential phage display, selecting ten VHH that bind specifically to ES. The anti-ES VHH was cloned in an expression vector, the recombinant protein (VHH-ES1) of 15.3 kDa was produced by fermentation in E. coli and purified to homogeneity by affinity chromatography. The binding of VHH-ES1 to the ES antigen was evaluated by ELISA using VHH-ES1 as capture antibody, policlonal anti-ES serum of rabbit and conjugated rabbit anti IgG with radish peroxidase., Results.: A VHH that binds to the ES antigen (VHH-ES1) has been identified through differential phage display and produced by fermentation in E. coli; this corresponds to an antibody of the long-hinge IgG2 subclass. The binding of the VHH-ES1 antibody to the antigen shows linearity with respect to the concentration of ES in the 50-5,000 ng/mL range and the limit of detection value of the antigen is in the 30-170 ng/mL range of ES (R2=0.99)., Conclusions.: The VHH-ES1 binds with affinity and specificity to the ES antigen of F. hepatica and is a promissory antibody to be assessed for the development of new fascioliasis diagnostic technologies.