Rajapandian Ayyanar

Pwm control of dual active bridge: Comprehensive analysis and experimental verification

The dual active bridge (DAB) topology is ideally suited for high power dc-dc conversion. This paper presents a comprehensive analysis and experimental results with PWM control of the DAB. The PWM control is in addition to phase shift modulation between the two H-bridges. The analysis includes PWM of one bridge at a time and of both bridges simultaneously. In the latter, five distinct modes arise based on the choice of PWM and load condition. The possibilities are analyzed for optimizing power density and efficiency for low load operation. An optimum PWM scheme is proposed that extends the soft-switching range, reduces rms and peak currents at low loads, and results in significant size reduction of the transformer. Experimental results are presented with a 10 kW prototype.

A DC–DC Multiport-Converter-Based Solid-State Transformer Integrating Distributed Generation and Storage

The Solid-state transformer (SST) has been proposed by researchers to replace the regular distribution transformer in the future smart grid. The SST provides ports for the integration of storage and distributed generation (DG), e.g., photovoltaic (PV), and enables the implementation of power quality features. This paper proposes a SST topology based on a quad-active-bridge (QAB) converter which not only provides isolation for the load, but also for DG and storage. A gyrator-based average model is developed for a general multiactive-bridge (MAB) converter, and expressions to determine the power rating of the MAB ports are derived. These results are then applied to analyze the QAB converter. For the control of the dc-dc stage of the proposed QAB-based SST integrating PV and battery, a technique that accounts for the cross-coupling characteristics of the QAB converter in order to improve the regulation of the high-voltage-dc link is introduced. This is done by transferring the disturbances onto the battery. The control loops are designed using single-input single-output techniques with different bandwidths. The dynamic performance of the control strategy is verified through extensive simulation and experimental results.

Space-Vector-Based Hybrid Pulsewidth Modulation Techniques for Reduced Harmonic Distortion and Switching Loss

Novel switching sequences can be employed in space-vector-based pulsewidth modulation (PWM) of voltage source inverters. Different switching sequences are evaluated and compared in terms of inverter switching loss. A hybrid PWM technique named minimum switching loss PWM is proposed, which reduces the inverter switching loss compared to conventional space vector PWM (CSVPWM) and discontinuous PWM techniques at a given average switching frequency. Further, four space-vector-based hybrid PWM techniques are proposed that reduce line current distortion as well as switching loss in motor drives, compared to CSVPWM. Theoretical and experimental results are presented.

Optimal Variable Switching Frequency Scheme for Reducing Switching Loss in Single-Phase Inverters Based on Time-Domain Ripple Analysis

The choice of switching frequency for pulsewidth modulation single-phase inverters, such as those used in grid-connected photovoltaic application, is usually a tradeoff between reducing the total harmonic distortion (THD) and reducing the switching loss. This paper discusses an approach to minimize the switching loss while meeting a given THD requirement using variable switching frequency schemes (switching schemes with the switching frequency varying within a fundamental period). An optimal switching scheme is proposed based on time-domain current ripple analysis and the calculus of variations. The analysis shows that, to meet the same THD requirement, the optimal scheme has a significant saving on switching loss, compared to the fixed switching frequency scheme and the hysteresis control scheme, in addition to other benefits such as reduced peak switching loss and a spread spectrum of the current harmonics. The optimal scheme has been implemented in a prototype and the experimental results have verified the theoretical analysis. Also, a straightforward design method for designing filter inductors for single-phase converters is provided based on the time-domain current ripple analysis.

Advanced bus-clamping PWM techniques based on space vector approach

Conventional space vector pulsewidth modulation (CSVPWM) employs conventional switching sequence, which divides the zero vector time equally between the two zero states in every subcycle. Existing bus-clamping PWM (BCPWM) techniques employ clamping sequences, which use only one zero state in a subcycle. This paper deals with a special type of switching sequences, termed here as “double-switching clamping sequences,” which use only one zero state and apply an active vector twice in a subcycle. The present work brings out a class of bus-clamping PWM techniques, which employ such sequences. It is shown analytically as well as experimentally that the proposed BCPWM techniques result in reduced harmonic distortion in the line currents over CSVPWM as well as existing BCPWM techniques at high modulation indices for a given average switching frequency of FSW. At high modulation indices, the dominant harmonic components in the line voltages are around 2 FSW with the proposed BCPWM techniques, while the dominant components are around FSW and 1.5 FSW, respectively, with CSVPWM and existing BCPWM techniques. The proposed techniques also reduce the inverter switching losses at high power factors over CSVPWM and existing BCPWM techniques.

Reduction of Torque Ripple in Induction Motor Drives Using an Advanced Hybrid PWM Technique

A voltage source inverter-fed induction motor produces a pulsating torque due to application of nonsinusoidal voltages. Torque pulsation is strongly influenced by the pulsewidth modulation (PWM) method employed. Conventional space vector PWM (CSVPWM) is known to result in less torque ripple than sine-triangle PWM. This paper aims at further reduction in the pulsating torque by employing advanced bus-clamping switching sequences, which apply an active vector twice in a subcycle. This paper proposes a hybrid PWM technique which employs such advanced bus-clamping sequences in conjunction with a conventional switching sequence. The proposed hybrid PWM technique is shown to reduce the torque ripple considerably over CSVPWM along with a marginal reduction in current ripple.

PWM control of dual active bridge: comprehensive analysis and experimental verification

The dual-active-bridge (DAB) topology is ideally suited for high-power dc-dc conversion, especially when bidirectional power transfer is required. However, it has the drawback of high circulating currents and hard switching at light loads, if wide variation in input and output is expected. To address these issues, this paper presents a comprehensive analysis and experimental results with pulsewidth-modulation (PWM) control of the DAB. The PWM control is in addition to phase-shift modulation between the two H-bridges. The analysis addresses PWM of one bridge at a time and of both bridges simultaneously. In the latter, five distinct modes arise based on the choice of PWM and load condition. The possibilities are analyzed for optimizing power density and efficiency for low-load operation. Finally, a composite scheme combining single and dual PWM is proposed that extends the soft-switching range down to zero-load condition, reduces rms and peak currents, and results in significant size reduction of the transformer. Experimental results are presented with a 10-kW prototype.

A novel full-bridge DC-DC converter for battery charging using secondary-side control combines soft switching over the full load range and low magnetics requirement

A novel full-bridge DC-DC configuration with a tapped transformer and secondary side control is proposed. It achieves zero-voltage switching for the primary side switches and zero-current switching for the secondary side switches, under all operating conditions. The conduction losses are significantly lower than those in the conventional soft-switching DC-DC converters. Due to superior filter waveforms, the filter requirements, both at the input and at the output, are significantly reduced. The features of the proposed converter are compared with those for the conventional phase-modulated full-bridge DC-DC converters. The proposed configuration is ideally suited for the AC-DC stage of high-power battery-charging applications with a power-factor-corrected preregulator. Analytical and experimental results on a 500 W/100 kHz prototype are presented.

Hybrid Interleaved Space Vector PWM for Ripple Reduction in Modular Converters

This paper addresses the problem of optimizing space vector PWM (SVM) for interleaved, parallel-connected, three-phase voltage source converters to reduce total harmonic distortion (THD) of the total line current. A systematic approach is presented for designing hybrid SVM schemes involving multiple sequences, including those based on active state division, and different phase shifts to reduce current ripple. First, the effect of different phase shifts on the current ripple is investigated and it is shown that using standard phase shifts yields performance close to optimal. Second, a zone-division plot is generated based on all sequence-phase shift combinations. The plot shows spatial regions within a sector where a certain sequence-phase shift combination results in the lowest rms current ripple in one switching period, and thus represents the optimal hybrid scheme. Lastly, simplified, easy-to-implement quasi-optimal SVM schemes are derived from the zone-division plot based on specific application requirements, and their performances are compared with the optimal scheme. The application of the proposed approach to a two-converter case is discussed in detail. A simple, quasi-optimal SVM scheme is proposed for grid-connected applications with analytical and experimental results confirming significant reduction in current THD. Finally, extension to three- and four-converter cases is discussed.

A Photovoltaic Array Transformer-Less Inverter With Film Capacitors and Silicon Carbide Transistors

A new photovoltaic (PV) array power converter circuit is presented. This inverter is a transformer-less topology with grounded PV array and only film capacitors. The motivations are to reduce circuit complexity, eliminate leakage ground currents, and improve reliability. The use of silicon carbide (SiC) transistors is the key enabling technology for this particular circuit to attain reasonable (>97%) efficiency. Some background about the challenges of ground currents and power decoupling to be addressed is first discussed. The proposed solution of a bidirectional buck boost converter, dynamically varying dc link, and half-bridge inverters is then presented along with details on the basic functionality. Some aspects of selecting passive components for the circuit are discussed. The average dynamic model and control system are then presented. Finally, simulation and experiment results are shown demonstrating that the proposed topology is a viable solution.