Cassiano Rech

Hybrid Multilevel Converters: Unified Analysis and Design Considerations

The concept of hybrid multilevel converters has been generalized for different arrangements of direct-current voltage levels, modulation strategies, topologies of series-connected cells, and/or semiconductor technologies to optimize the power processing of the overall system. Therefore, a given number of levels can be synthesized by several multilevel configurations, significantly increasing flexibility and complexity in the design of hybrid multilevel converters. However, a generalized design methodology to define the main parameters of these topologies for distinct design criteria has not yet been presented. To overcome this lack, this paper presents a comparative analysis among various hybrid multilevel topologies, and it proposes some design considerations for distinct applications. Consequently, this paper constitutes a useful basis for defining an adequate hybrid arrangement for any application

Comparison of digital control techniques with repetitive integral action for low cost PWM inverters

This paper presents a comparison among digital control techniques with repetitive integral action applied to voltage-source PWM inverters. As a result of the repetitive integral action, these digital control schemes can reduce steady-state errors and distortions caused by unknown periodic disturbances, which usually result from the input source and output load. Moreover, these digital control schemes measure only the output voltage, decreasing the amount of sensors and the overall system cost. The control laws, stability analysis, common and distinguishing features of these control algorithms are discussed. Experimental results from a PWM inverter (110 V/sub RMS/, 1 kVA) controlled by a low cost microcontroller are presented to demonstrate the control techniques performance under different load conditions, output filters and command strategies.

Analysis and Design of a New High-Efficiency Bidirectional Integrated ZVT PWM Converter for DC-Bus and Battery-Bank Interface

This paper proposes a high-efficiency bidirectional integrated zero-voltage transition (iZVT) pulsewidth-modulation (PWM) converter for dc-bus and battery-bank interface. The proposed converter can operate as battery charger when the utility is within its acceptable voltage range and can supply energy to critical loads when the utility fails. The converter practically eliminates both low- and high-frequency current ripple on the batteries, thus maximizing battery life without penalizing the volume of the converter. Moreover, soft switching of all switches is achieved using the proposed integrated auxiliary commutation circuit (iACC). Just one iACC is used to provide soft-switching conditions for the three converters that compose the system: the preregulator (boost), the battery charger (bidirectional converter operating as a buck), and the backup converter (bidirectional converter operating as a boost). This auxiliary circuit has few components and low reactive energy, increasing the systems overall efficiency. Experimental results based on a 580-W prototype are presented to validate the analysis and the proposed design procedure and to demonstrate the performance of the proposed approach

Comparison of Neutral-Point-Clamped, Symmetrical, and Hybrid Asymmetrical Multilevel Inverters

This paper presents a comparison of three topologies of multilevel inverters applied to drive an induction motor of 500 kVA/4.16 kV rating. The multilevel inverters analyzed are the following: a neutral-point-clamped inverter, a symmetrical cascaded multilevel inverter, and a hybrid asymmetrical cascaded multilevel inverter. The performance indexes used in the comparison are total harmonic distortion, first-order distortion factor, second-order distortion factor, common-mode voltage, semiconductor power loss distribution, and heat-sink volume. The multilevel inverters are designed to present 99% efficiency at the nominal operating point, and the aforementioned performance indexes are compared for distinct values of amplitude modulation depth.

Generalized Carrier-Based Modulation Strategy for Cascaded Multilevel Converters Operating Under Fault Conditions

This paper proposes a simple modulation approach for symmetrical and asymmetrical cascaded multilevel converters, suitable for operation under normal and fault conditions. Initially, the set of all possible converter common-mode voltages for linear operation is derived, considering the status of each converter cell. It is demonstrated that the methods previously described in the literature belong to the derived set. By properly selecting the common-mode voltage, the entire converter voltage synthesis capability can be achieved under any fault condition. The proposed modulation approach has been applied for both symmetrical and asymmetrical cascaded multilevel converters. Simulation and experimental results show the effectiveness of the proposed modulation approach and validate the theoretical analysis.

Analysis and comparison of hybrid multilevel voltage source inverters

This paper analyzes different hybrid multilevel inverters for high-power applications. With these hybrid topologies, it is possible to minimize the number of series-connected inverters for a given number of levels and, consequently, to reduce the THD of output voltage. Moreover, this paper develops a comparison among different hybrid multilevel inverters, especially between binary and trinary hybrid multilevel inverters. Several points are discussed, taking into account number of levels, spectral performance and power processing of hybrid multilevel inverters. Finally, a design procedure to obtain the number of H-bridge cells and DC voltage source of each cell for a given number of levels is proposed, so that few H-bridge cells synthesize a voltage waveform with a large number of levels, in order to minimize the circulating energy among cells.

Analysis and design of a repetitive predictive-PID controller for PWM inverters

This paper presents a predictive PID controller including a feedforward control and a repetitive controller for UPS applications. This digital control scheme can minimize periodic distortions resulted from nonlinear cyclic loads. Design procedure and stability analysis of the control scheme are discussed. Simulation and experimental results for a single-phase PWM inverter (110 V/sub RMS/, 1 kVA) controlled by a low cost microcontroller are presented to demonstrate the performance of the proposed control approach under periodic load disturbances.

Reduced-Order Model and Control Approach for the Boost Converter With a Voltage Multiplier Cell

The boost converter with a voltage multiplier cell allows the static gain extension by means of the switching capacitor technique, reducing the duty cycle needed to achieve the same voltage gain when compared to the conventional boost converter. However, the modeling of this converter is complex and requires the use of advanced techniques due to the resonant inductor. Thus, this paper aims to present a reduced-order model of this converter without the resonant energy exchange between the capacitors, so that the state-space averaging technique can be applied assuming small ripple in the state variables. In addition, this paper presents the design of a control system for the boost converter with a voltage multiplier cell. The adopted strategy employs an inner loop to control the input current and an outer loop for the output voltage regulation. Extensive analysis based on simulations and an experimental prototype demonstrate that the proposed modeling, although simplified, is sufficient for an adequate control system design, ensuring good voltage regulation, and fast transient responses.

Impact of Hybrid Multilevel Modulation Strategies on Input and Output Harmonic Performances

This paper presents a detailed analysis of the impact of a hybrid multilevel modulation strategy on the harmonic content of the input currents and output voltages. Advantages and limitations of this modulation strategy are first discussed from the load point of view. This paper also proposes a new modulation strategy for hybrid multilevel inverters which can be used with asymmetrical multipulse connection of uncontrolled rectifiers to improve the input harmonic performance of adjustable-speed drives at every operating point. This new modulation strategy maintains the original capability to synthesize output voltages with reduced harmonic distortion and makes it possible to eliminate undesirable low-frequency harmonics from input currents in all operating ranges, even when the series-connected cells process distinct active power levels

Integrated Full-Bridge-Forward DC–DC Converter for a Residential Microgrid Application

This paper proposes a novel integrated converter topology for interfacing between the energy storage system and the dc bus for a residential microgrid application. The proposed integrated full-bridge-forward dc–dc converter presents the following features: low number of active devices compared to the converters usually applied to similar applications, low input and output current ripple, high voltage ratio, bidirectional power flow, and galvanic isolation. A double-ended forward converter with particularities such as no extra transformer demagnetizing circuit is originated from the integration process. This converter is approached in detail in this paper, including three different clamping circuits which are analyzed and compared. The structure, principle of operation, analysis, transformer design methodology, comparison with the dual active bridge converter, and experimental results of the proposed topology are presented.