Saad Ul Hasan

A Comprehensive Study on Equivalent Modulation Waveforms of the SVM Sequence for Three-Level Inverters

According to the number of segments, the space vector modulation (SVM) can divide into conventional SVM sequence (CSVMS) and special SVM sequence (SSVMS). It is well known that SVM can be equivalently realized by carrier-based pulse width modulation (CBPWM) with a zero component injection in both two-level and three-level inverters. For eight segment CSVMS in three-level inverters, many papers have ever got the injected zero component equation. But similar approach does not work for SSVMS, which has more than eight segments, e.g., 10, 12, or 14. What more, the accurate injected zero component has never been achieved so far. To solve above problems, therefore, a generated decomposition method of modulation wave has been proposed in this paper. By strict theoretical derivation, the same correlation can be extended to SSVMS and the corresponding zero component expression can be acquired. Based on this method, this paper puts a lot attention on the essential feature explanation, mathematical proof, and gives a detailed process to get the zero component equation, using it can realize SSVMS by CBPWM. The simulation and experimental results illustrate that the generated decomposition method of modulation wave is correct, and the unified theory of CBPWM and SVM is verified.

A quasi-periodic modulation strategy to mitigate EMI for a GaN-based quasi-Z-source DC-DC converter

Wide-bandgap (WBG) switching devices, such as gallium nitride (GaN), enable switching at high frequencies with low rise and fall times. This provides advantages such as high power density and compact size, however a potential unwanted side-effect is increased electromagnetic interference (EMI) because of large transient currents. A novel quasi-periodic modulation scheme is described for voltage-fed quasi-Z-source (qZS) DC-DC converters which substantially reduces the peak EMI. The driver logic required is simple and generic, and therefore adaptable to all modulation schemes proposed to date for isolated qZS DC-DC converters. Various experimental results verify the effectiveness of the proposed strategy in terms of voltage gain, efficiency and EMI suppression.

An Aperiodic Modulation Method to Mitigate Electromagnetic Interference in Impedance Source DC–DC Converters

Rapid voltage and current transitions in switched-mode power converter circuits generate electromagnetic interference (EMI) which may interfere with other electronic systems. High-speed (e.g., wide bandgap) switching devices can improve circuit efficiency and compactness, but may increase the bandwidth of the interference generated. The peak interference is concentrated at harmonics of the fundamental switching frequency, and so may be reduced by modulating the converter switching frequency. However, converter topologies incorporating more than one switching device may not be suited to modulation of the switching frequency, and coordinated modulation of other pulse parameters is required to suppress interference. A relatively simple implementation of a hybrid pulse modulation technique is presented to suppress EMI in a quasi-Z-source converter comprising an impedance-source network and GaN-based H-bridge switching circuit. The technique uses two anharmonically related periodic signals to generate a modulated sawtooth carrier, which in turn generates coordinated switching pulses aperiodically modulated in position and width within a constant switching period. Experimental results demonstrated 10 dB suppression of the peak interference with negligible impact upon the converters efficiency or output voltage. The proposed pulse modulation technique and its method of implementation are generic, and are expected to be widely applicable to other switched-mode dc–dc power converters.

A new PWM Shoot-through control for voltage-fed quasi-z-source DC/DC converters

This paper presents a new shoot-through control method applicable for an impedance source galvanically isolated DC/DC converter. In impedance source converters, the introduction of shoot-through states increases the switching speed of H-bridge switches about two to three times the switching frequency. This approach reduces the switching transient of all switches of inverters by commutating them once in a switching cycle. The shoot-through states are generated by alternatively switching the single leg of the inverter whereas, in baseline modulation approach, all the switches are turned on during shoot-through states. This method decreases the switching loss of front-end converters and independent controllability of active and shoot through states. This modulation technique is applied and validated to a voltage-feed Quasi-Z source isolated DC-DC converter with a voltage doubling rectifier.

An FPGA-based aperiodic modulation strategy for EMI suppression in quasi-Z-source DC-DC converters

The adoption of wide-bandgap (WBG) switching devices in switching power converters provides several advantages, such as high power density, compact size and high efficiency, however a potential side-effect is the increased electromagnetic interference (EMI) due to high-speed switching transients. This paper presents an aperiodic modulation technique to suppress EMI in H-bridge based switched-mode power converters. A generic framework for the generation of an aperiodic carrier signal is demonstrated which can be extended and flexibly applied in other power converters. The aperiodic modulation strategy is programmed in a MATLAB Simulink environment and implemented using a field-programmable gate array (FPGA). The efficacy of the proposed aperiodic modulation was tested on a quasi-Z-source DC-DC converter, and a 10 dB suppression in the peak conducted EMI emissions was demonstrated.

Aperiodic pulse-modulation technique to reduce peak EMI in impedance-source DC-DC converters

The use of wide-bandgap (WBG) devices in power converters provides several advantages in terms of efficiency, power density and low cooling requirements. However, a potential unwanted side-effect is the increased electromagnetic interference (EMI) noise, the basis of which is the high di/dt and dv/dt realized by the characteristic sharp rise and fall switching offered by the WBG power switches. To suppress the EMI, this paper presents a generic framework for the generation of an aperiodic carrier signal, which can be extended to drive multiple switched power converters. The aperiodic modulation scheme is implemented in a MATLAB Simulink environment and realized on a field-programmable gate array (FPGA) development board through an auto-code generation feature offered by a hardware description language (HDL) coder. Finally, the efficacy of the proposed aperiodic modulation methodology has been tested on a quasi-Z-source DC-DC converter. A 9 dB suppression in the peak conducted EMI emissions was demonstrated with no adverse impact on the voltage gain and efficiency of the power converter.

A new PWM shoot-through control technique to reduce switching losses in impendance source DC/DC converters

A simplified shoot-through pulse width modulation (PWM) technique is presented for reducing switching losses in impedance source DC-DC converters. The proposed PWM method alternates shoot-through state conduction in each leg of the H-bridge, thereby increasing controllability of the converter, reducing the number of switching transients, and reducing the dynamic loss of the converter through soft-switching. The proposed modulation method was verified using a GaN-based quasi-Z-source DC-DC converter. This method demonstrates better performance at low load and with high switching frequency.

A wavelet frames + K-means based automatic method for lung area segmentation in multiple slices of CT scan

Computer assisted detection of lung nodules offers a more accurate method of nodule detection which leads to reliable diagnosis of lung cancer. Lung segmentation is a first step in the process of automatic detection of nodules. In this paper, we propose a wavelet packet frames based approach for effective lung segmentation. The proposed algorithm selects the optimal wavelet representation that is a collection of wavelet packet frames. The frames are subsequently used for clustering of coefficients using k-means clustering, which leads to the segmented lung region. The algorithm is tested on the one publicly available dataset containing 350 images and CT scan dataset of 5 local patients containing a total of 71 images. Accurate segmentation of lung is acquired with average difference in pixels from the ground truth being as low as 1.34±0.451. Furthermore, the proposed technique is fully automated and is capable of segmenting lung in multiple slices with no manual intervention or change in parameters.