Three-leg Inverter Research Articles

THREE-PHASE FOUR-WIRE PV-BASED SERIES HYBRID ACTIVE POWER FILTER FOR POWER QUALITY IMPROVEMENT

This paper proposes a photovoltaic (PV)-based three-phase four-wire (3P4W) series hybrid active power filter (SHAPF) it comprises of a series active power filter (SAPF) and an LC shunt passive filter. The proposed system eliminates both the current and voltage harmonics and compensates reactive power, neutral current and voltage interruption. A SAPF demands a source of energy for compensating the voltage sag/swell. This system introduces a new topology for SHAPF utilizes the PV with DC–DC boost converter as a source of DC power for SAPF. The compensation current reference evaluation is based on the twin formulation of the vectorial theory of electrical power theorem with fuzzy logic controller (FLC). The PV array/battery managed DC–DC boost converter is employed to step up the voltage to meet the DC bus voltage requirement of the three-leg voltage source inverter (VSI). The foremost benefit of the proposed system is that, it will provide uninterrupted compensation for the whole day. This system utilizes the renewable energy accordingly saves the energy and shares the load during the solar irradiation available. The simulation and experimental studies are carried out to validate the effectiveness of the proposed PV-SHAPF.

Comparative Study of Three Phase Four Wire Shunt Active Power Filter Topologies based Fuzzy Logic DC Bus Voltage Control

In this paper, a comparative study based fuzzy logic DC bus voltage control for three phase four wire shunt active power filter for two different inverter topologies, three-leg splitcapacitor topology (TLSC) and four-leg inverter (FLFB) are proposed. Identification of reference currents will be developed by classical extraction filters based on pq theory in the first section of the paper. DC-bus voltage control in three-phase four-wire shunt active filter is treated by a fuzzy logic control. A comparison of the proposed method against the conventional proportional integral is illustrated with two different inverter topologies through simulation results and a clear advantage of the fuzzy logic control can be observed. Moreover, the switching pattern of the inverter is generated by a modulated hysteresis current controller. All simulations have been realized in the same conditions so results can be compared with each other. The effectiveness of the proposed method is verified by MATLAB software.

Minimum signal modulation scheme based on a single carrier for interleaved operation of parallel phase legs in voltage source converters

Connecting legs in parallel is a common way to increase the output current of a power converter. Interleaving the carriers used to modulate the reference signals for each leg leads to a reduction in the output current ripple without resorting to increasing the switching frequency. A whole set of shifted carriers is required if interleaved pulse-width modulators (PWMs) are used. Implementing this by means of a digital signal processor (DSP) means that the higher the number of carriers, the higher the number of DSP timing resources required. Provided that the latter are usually limited, this could be a drawback when increasing the number of interleaved carriers. This study presents the implementation of a PWM scheme where all modulators use the same carrier offering the same results as if a set of n interleaved carriers were used. Since the proposed algorithm takes maximum benefit from the PWM units available in a DSP, a higher number of legs connected in parallel can be controlled without adding any external processing hardware. A MATLAB/Simulink model has been set up for simulation purposes. Selected experimental results obtained from a three-leg single-phase inverter are reported, confirming the effectiveness of the proposed implementation.

Single DC source three‐phase multilevel inverter using reduced number of switches

A novel pulse-width modulation-less three-phase multilevel DC–AC inverter using only one DC source is presented in this study. The proposed approach enables multilevel output to be realised by a few cascaded H-bridges and a three-leg inverter using minimum number of power switches. As an illustration, a 19-level three-phase inverter has been implemented based on cascading four H-bridges and a three-leg inverter. Switching strategy has been derived for the proposed inverter such that a three-phase power system with 19 output levels can be realised with proper capacitor voltage regulation and a single energy source. Only 22 power switches instead of 108 are required to achieve the objective. Experimental results are included to demonstrate the outstanding performance of the proposed inverter. Although only 50 Hz results are presented, the proposed inverter could be applied in aircraft systems by only changing the switching frequency.

Design and Control Scheme of Three-Phase Photovoltaic Grid-Connected Inverter

With the development of power electronics technology, a variety of unbalanced load are connected to the grid, causing the grid voltage imbalance and power quality decline, seriously affect the user's normal use. Traditional three-leg inverter can output three-phase symmetrical voltage in the case of three-phase symmetrical load. But it is difficult to output three-phase symmetrical voltage when the three-phase load is asymmetric. In order to solve the impact of unbalanced load on the power quality, the three-phase four-leg inverter which is obtained with the addition of a bridge arm on the basis of traditional three-leg inverter is adopted in this paper. Therefore, the three-phase symmetrical voltage can be acquired in the case of unbalanced load, at the same time, with the advantages of simple structure, small size, light weight, higher voltage utilization.

Characteristic of Induction Motor Drives Fed by Three Leg and Five Leg Inverters

This paper aims to compare the performance of three phase induction motor drives using Five Leg Inverter (FLI) and Three Leg Inverter (TLI) configurations. An Indirect Field Oriented Control (IFOC) method using a TLI is well established and incorporated for high performance speed drives in various industries. The FLI dual motor drive system on the other hand shows good workability in the independent control of two induction motor drives simultaneously. In this experiment, the IFOC method is utilized for both drive systems, and Space Vector Pulse Width Modulation (SVPWM) is used to generate pulses for both inverters. For the FLI, the Double Zero Sequence (DZS) Injection technique is used to generate the modulation signal. The complete experiment setup is done by using a DSpace 1103 controller board. The individual motor performances are analyzed using similar schemes, equipment setups and controller parameter values. The results show similar speed performance response capability between the single motor operation using a TLI system and the two motor operation using a FLI system based on the variable speed range either in forward or reverse operation. They also show similar load rejection abilities. However, the single motor with a TLI has a better power quality aspect such as ripple current and total harmonics distortion (THD).

Development and Application of the Two-Phase Orthogonal Power Supply for Electromagnetic Stirring

This paper presents a three-leg voltage-source inverter topology for two-phase orthogonal power supply used for driving electromagnetic stirring. Compared with the conventional two two-leg inverter, the three-leg structure reduced the loss of power module and switching. The improved structure has an inductor in series between two-phase orthogonal power supply and the common phase of electromagnetic stirring, which make it possible to apply deadbeat current control method to two-phase orthogonal power supply, thus the controller design is simplified, the current adjustment speed is enhanced, and the current waveform is improved. A control strategy with reactive power compensation is proposed for enhancing the utilization rate of a three-phase pulsewidth modulation (PWM) rectifier in two-phase power supply, which makes it possible that the three-phase PWM rectifier not only operating rectification status but also operating reactive power compensation status. Hence, the reactive compensation cost of enterprises will be decreased. At last, simulation and industrial application results are provided to verify the effectiveness of the proposed topology and control strategy.

Digital-Scalar PWM Approaches Applied to Four-Leg Voltage-Source Inverters

In this paper, we present two modulation schemes for generating unbalanced voltages by means of four-leg voltage-source inverters. The first modulation is an extended scheme of a digital-scalar pulsewidth modulation previously proposed for controlling three-leg inverters. The second one is based on the decomposition of the voltage reference signals into their symmetrical components. The schemes are compared theoretically by simulations and experimental results. As a consequence, we find out a total equivalence between the two modulations despite their different conceptions. The fundamentals of both techniques and a mathematical proof of their equivalence are unfolded. Also, the performances of the techniques with respect to the harmonic distortion and power switching loss are discussed. The results show that the techniques are effective.

Two Digital-scalar PWM Schemes for Generating  ree-phase Unbalanced Voltages

This paper presents two modulation approaches for generating unbalanced voltages by means of four-leg voltage source inverters (VSI). The first modulation is an extended scheme of a digital scalar pulse width modulation previously proposed for controlling three-leg inverters. The second one is based on the decomposition of the voltage reference signals into their symmetrical components. The schemes are compared theoretically, by simulations and by experimental results. As consequence, it is found out a total equivalence between the two modulations despite their different inspirations. The fundamentals of both techniques and a mathematical proof of their equality are unfolded. Also, the performance of the techniques with respect to the harmonic distortion and power switching loss are discussed. The results show that the techniques are effective.

Analysis and Simplification of Three-Dimensional Space Vector PWM for Three-Phase Four-Leg Inverters

The main objective of this paper is to simplify the implementation of continuous and discontinuous 3-D space vector pulsewidth modulations (SVPWMs). This paper analyzes the relationships, whether in or coordinates, between three-phase voltages and the following elements: the tetrahedron in which the reference vector resides, three adjacent active switching vectors (or three switching states), and their duration times. Based on the analysis, the calculation of the turn-on time of each switch in the actual implementation is simplified, and discontinuous PWM (DPWM) methods in three-leg inverters can be extended to four-leg inverters without the phase angle. In addition, two more DPWM methods that are peculiar to 3-D SVPWM are presented. This simplified algorithm does not use irrational operations or look-up tables, and it alleviates the computation burden of the processor. The simulation and experimental results are provided to validate the effectiveness of the proposed algorithm.

Adaptive pole-placement control of 4-leg voltage-source inverters for standalone photovoltaic systems

Three-leg inverters for photovoltaic systems have many disadvantages, especially when the load is unbalanced. These disadvantages are, for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the 4-leg inverter. Most papers dealing with 4-leg inverters suggest classic controllers, such as PI controller, for the system. However, the transient performance of the closed-loop system does not become acceptable. On the other hand, adaptive control of 4-leg inverters has not yet been discussed in the literature. This paper proposes pole-placement control strategy, via state feedback, for 4-leg voltage-source inverters to adjust the transient performance of the closed-loop system. In addition, a STR (self-tuner regulator) is introduced to guarantee the adaptive performance of the controller in the presence of time-variant RL loads. Simulation results validate the theoretical results and proposed control strategy.

A Constant DC Voltage Control Based Strategy for the Current Balancer in Single-Phase Three-Wire Secondary Distribution Systems

This paper deals with applying the constant dc voltage control based algorithm to the current balancer in single-phase three-wire secondary distribution systems. The power flows into a three-leg inverter, which performs the current balancer, are discussed, and then we show that only the reactive power flows into the three-leg inverter. This demonstrates that the required-capacity of the dc capacitor can be reduced as compared to that of the active power quality compensator used in the electrified railways. This reduced-capacity dc capacitor results in the rapid and stable balancing. The basic principle of the proposed method is discussed in detail, and then confirmed by digital computer simulation. Digital computer simulation results demonstrate that the balanced source currents with unity power factor are obtained remaining the unbalanced load currents conditions.

Performance Evaluation and Slip Regulation Control of an Asymmetrical Parameter Type Two-Phase Induction Motor Drive Using a Three-Leg Voltage Source Inverter

This paper presents a performance evaluation and a simple speed control method of an asymmetrical parameter type two-phase induction motor drive using a three-leg VSI (Voltage Source Inverter). The two-phase induction motor is adapted from an existing single-phase induction motor resulting in impedance unbalance between main and auxiliary windings. The unbalanced two-phase inverter outputs with orthogonal displacement based on a SPWM (Sinusoidal Pulse Width Modulation) method are controlled with appropriate amplitudes for improving the motor performance. Dynamic simulation of the proposed drive system is given. A simple speed controller based on a slip regulation method is designed. The overall system is implemented on a DSP (Digital Signal Processor) board. The validity of the proposed system is verified by simulation and experimental results.

Selective Compensation in Four-Wire Electric Systems Based on a New Equivalent Conductance Approach

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a new calculation method to obtain the reference currents for a selective shunt active power compensator (APC) with the capability of distinguishing between selective and global operating modes. This selective compensation operation is done through an identification of the current terms related to the physical phenomena that exist in electrical systems following a new equivalent conductance concept. Through this identification, this paper proposes the adequate set of reference currents that, used by a shunt APC (SAPC), achieve the selective cancellation of a desired nonefficient phenomenon. Furthermore, by combining the different current terms, it is possible to derive the sets of reference currents that allow the cancellation of a desired combination of nonefficient phenomena. By using these reference currents, a selective compensation feature is added to the SAPC control. An SAPC based on a three-phase three-leg inverter with a split dc bus has been implemented. The neutral wire of the electrical installation is connected to the midpoint of the dc bus, so the selective SAPC is able to work in four-wire electrical systems. The experimental results obtained demonstrate that the proposed selective compensation properly works in three-phase electrical systems with load-current unbalances, voltage asymmetries, and harmonic components. The electric quality is improved with the use of the proposed selective control based on this new equivalent conductance approach. </para>

New Control Method of Active Power Quality Compensator with Reduced-Capacity Three-Leg Inverter for Electrified Railways

This paper proposes a new control method for reducing the capacity of an active power quality compensator with a three-leg inverter used in electrified railways. In the proposed control method, the fundamental reactive and unbalanced-active components of the load currents are detected. The non-active and unbalanced-active components are compensated on the source side with the fundamental reactive power control. This reactive power control reduces the capacity of the three-leg inverter, which performs the active power quality compensator. The basic principle of the proposed control method is discussed in detail, and then confirmed by digital computer simulation using the PSIM software. A reduced-scale experimental model is constructed and tested. Experimental results demonstrate that the balanced sinusoidal source currents with the power factor of 0.9 are obtained, reducing the capacity of the three-leg inverter by 13% as compared to the already proposed control method.

Monolithic Systems Using Standard Three-Leg Inverter Supplying Independently Two Motors

This paper presents two series-connected motor-drive-system topologies. These configurations have been designed for applications in which it is necessary to control two motors independently by using a standard three-leg inverter. The systems will be referred to as monolithic systems, since the three-leg inverter and both machines have been considered as a part of the same product. The monolithic systems are seen as a potentially viable industrial solution for applications requiring one high-power (three-phase) machine and one low-power (single-phase) machine. Furthermore, this paper presents the following: 1) relevant characteristics of the systems; 2) pulsewidth-modulation techniques; 3) control strategies; 4) voltage and current analyses; 5) unconventional induction-machine design to improve the performance of the monolithic system; and 6) simulated and experimental results.

Realization of a Carrier-Based Unbalanced Output Space Vector PWM Strategy Using Analogue and Digital Techniques for Three-Leg Voltage Source Inverter Fed Two-Phase Induction Motors

Realization of a Carrier-Based Unbalanced Output Space Vector PWM Strategy Using Analogue and Digital Techniques for Three-Leg Voltage Source Inverter Fed Two-Phase Induction Motors

DC–AC Cascaded H-Bridge Multilevel Boost Inverter With No Inductors for Electric/Hybrid Electric Vehicle Applications

This paper presents a cascaded H-bridge multilevel boost inverter for electric vehicle (EV) and hybrid EV (HEV) applications implemented without the use of inductors. Currently available power inverter systems for HEVs use a dc-dc boost converter to boost the battery voltage for a traditional three-phase inverter. The present HEV traction drive inverters have low power density, are expensive, and have low efficiency because they need a bulky inductor. A cascaded H-bridge multilevel boost inverter design for EV and HEV applications implemented without the use of inductors is proposed in this paper. Traditionally, each H-bridge needs a dc power supply. The proposed design uses a standard three-leg inverter (one leg for each phase) and an H-bridge in series with each inverter leg which uses a capacitor as the dc power source. A fundamental switching scheme is used to do modulation control and to produce a five-level phase voltage. Experiments show that the proposed dc-ac cascaded H-bridge multilevel boost inverter can output a boosted ac voltage without the use of inductors.

Interleaving Controlled Three-Leg Electronic Ballast for Dual-HID-Lamps

This paper presents a novel electronic ballast for dual high-intensity-discharge (HID) lamps. The electronic ballast is composed of a boost preregulator to achieve high power factor and a three-leg inverter to drive two HID lamps. One leg of the inverter is operated at a low frequency with a 50% duty ratio to drive the HID lamps with low-frequency square-wave current in order to avoid acoustic resonance. The other two legs of the inverter are operated at a high frequency to modulate the lamp current with constant lamp power. Also, interleaving control is applied to the high-frequency legs to decrease the current stress on the low-frequency leg. To verify the feasibility of the proposed methodology, a laboratory prototype is implemented to drive two 35-W HID lamps. The overall efficiency of the proposed electronic ballast is about 90%.

Reduced Switch Count Multiple Three-Phase AC Machine Drive Systems

In this paper, two three-phase ac drive systems with reduced number of components, named configurations and , are investigated. Configuration uses multiple two-leg voltage source inverters in which all inverters share an extra-leg. Configuration also employs multiple two-leg inverters but in this case the inverters share the midpoint of a capacitor bank in the dc-link, instead. These configurations are compared to configuration that employs multiple three-leg inverters. The main characteristics of the machine drive systems are presented together with selected experimental results that demonstrate the feasibility of the proposed configurations.