Stability challenges and solutions in current-mode controlled power electronic converters

This dissertation focuses on stability issues in single-staged and multi-staged current controlled power electronic converters. Most current-mode control (CMC) approaches suffer from sub-harmonic oscillations. An external ramp is usually added to solve this problem. However, to guarantee stability this ramp has to be designed for the worst possible case which consequently over damps the response. Adaptive slope compensation (ASC) methods are the solution for this problem. In paper 1 of this dissertation, first three ASC methods will be investigated and analyzed through their small signal models. Then, through simulation analyses and experimental test of a variable-input voltage converter the results will be validated. Two of the methods studies in the first paper are peak CMC methods and the last one is called the projected cross point control (PCPC) approach. This method is relatively new. Therefore, a detailed discussion of the principles of operation of PCPC will be presented in paper 2. In addition, the small signal model of PCPC is developed and discussed through simulation and experimental analyses in the second paper of this dissertation. Peak, average, and hysteresis CMC schemes are used for comparison. In paper 3, the stability issues which arise in multistage converters will be addressed. A solid state transformer (SST) as an example of a multistage converter will be studied. A comprehensive small signal modeling will be conducted which helps for stability analysis of SST. Time domain simulations in Computer Aided Design software (PSCAD) are presented which validates the frequency domain analysis --Abstract, page iv

Screening of three common mtDNA mutations among subjects with autosomal recessive non-syndromic hearing loss in Sistan va Baluchestan province, Iran

Background: Non-syndromic hearing loss may be induced by mutations in both nuclear and mitochondrial genes. Mutations in mtDNA are present in less than 1% of the children with pre-lingual deafness but are more prevalent later. Most of the molecular defects responsible for mitochondrial disorder, associated with hearing loss may be induced by mutations in the 12SrRNA and tRNA genes. This aim of this study was to investigate the frequency of three common mtDNA mutations including A1555G, A3243G and A7445G in a cohort of autosomal recessive non-syndromic hearing loss (ARNSHL) subjects in Sistan va Baluchestan province. Material and Methods: In this descriptive- experimental based study, a total of 110. ARNSHL subjects from Sistan va Baluchestan province were investigated for three common mtDNA mutations using PCR-RFLP procedure. The possible mutations were confirmed by direct sequencing. Results: None of the A1555G and A7445G mutations were detected in this study. However, we found one sample to carry A3243G mutation (0.9%). Moreover abolishing a MTTL1 restriction site close to A3243G mutation revealed a G3316A allelic variant in 0.9% of patients studied. Conclusion: This study showed that mtDNA mutations are responsible for less than 1% of pre-lingual ARNSHL associated subjects. The present study will improve the genetic counseling of hearing impaired patients in Sistan va Baluchestan province, Iran

Modified Projected Cross Point Control - A Large Signal Analysis

Modified projected cross point control (PCPC) is introduced and discussed in this paper. Compared to the existing PCPC method, the hardware implementation of the proposed modified method is simpler. This modified PCPC method benefits from the advantages of traditional fixed- and variable-frequency current mode control approaches. For instance, as argued in this paper, while modified PCPC is a fixed-frequency approach, it is stable for the entire range of the duty cycle similar to the variable-frequency hysteresis current mode control scheme. Other advantages and large-signal characteristics of modified PCPC are discussed by comparing it with the well-known peak and average current mode control methods

Modified Projected Cross Point Control - A Small Signal Analysis

In this paper, the small-signal analysis of the modified projected cross point control (PCPC) method is investigated. Modified PCPC is a new current-mode control approach which benefits from several advantages over common current-mode control methods such as peak current-mode control (PCMC) and average current-mode control (ACMC). Followed by the small-signal analysis, different small-signal transfer functions for this method are obtained. To prove the significant superiority of the modified PCPC controller, the small-signal properties of this novel method are compared with those of the PCMC and ACMC approaches

Modeling and Analysis of Projected Cross Point Control-A New Current-Mode-Control Approach

This paper features the projected cross point control (PCPC) approach which is a recent current-mode control (CMC) technique. PCPC benefits from several advantages including fixed switching frequency, wide stability range, high current loop gain, improved audio susceptibility, and simpler design procedure. An introduction of its principles of operation is followed by detailed discussions about its stability and dynamic response. This paper then describes the development of the small-signal model of PCPC and derives transfer functions, such as current loop gain, audio susceptibility, and output impedance. Finally, simulations and experimental results are presented. Peak, average, and hysteresis CMC schemes are used for comparison

Power Factor Correction Using Projected Cross Point Control (PCPC)

Projected cross point control (PCPC) is a new current-mode control approach which has been recently introduced. The PCPC method benefits from the advantages of traditional fixed-frequency and variable-frequency current-mode control methods. For instance, while PCPC is a fixed-frequency approach, it is stable for the entire range of the duty cycle similar to the variable-frequency hysteresis current-mode control (HCMC) scheme. In this paper, PCPC is used as the control strategy in a power factor correction (PFC) application. The results are compared with PFC methods based on the peak current-mode control (PCMC) and average current-mode control (ACMC) techniques

A Generalized Capacitor Voltage Balancing Scheme for Flying Capacitor Multilevel Converters

Multilevel power electronic converters are the converter of choice in medium-voltage applications due to their reduced switch voltage stress, better harmonic performance, and lower switching losses. Although it has received little attention, the flying-capacitor multilevel converter has a distinct advantage in terms of its ease of capacitor voltage balancing. A number of techniques have been presented in the literature for capacitor voltage balancing, some relying on self-balancing properties. However, self balancing cannot guarantee balancing of capacitor voltages in practical applications. Other researchers present closed-loop control schemes which force voltage balancing of capacitors. In this paper, a new closed loop control scheme is proposed which regulates the capacitor voltages for a multilevel flying capacitor converter. The proposed scheme is based on the converter equations and involves implementing simple rules. In particular, multiple duty cycles are defined and modulated in direct response to the capacitor voltages. Through simulation, the method is shown to work on four, eight and nine-level flying capacitor inverters

Hysteresis-Based Control of a Single-Phase Multilevel Flying Capacitor Active Rectifier

The deployment of a single-phase, multilevel flying capacitor converter as a 1.5-kW active rectifier is discussed in this paper. The challenges associated with this approach include providing unity power factor, regulating the dc output voltage, and maintaining balanced voltages across the flying capacitors. In such applications, the input current is usually controlled via a reference-frame-based control approach. Here, a different approach, which is based on the hysteresis current-mode control scheme, is applied. The simulation and experimental results for both reference-frame-based and hysteresis-based controllers are presented and compared. The results show that the hysteresis-based method exhibits a tighter regulation of the input current and offers easier hardware implementation

Capacitor Voltage Regulation and Pre-Charge Routine for a Flying Capacitor Active Rectifier

In this paper, a research is carried out on a single-phase flying capacitor active rectifier. In order to regulate the voltage of the flying capacitors, a method based on redundant state selection is developed that generates an offline switching table. In addition, an online process is introduced that, by using the offline table, reduces the total number of switching events in the converter which leads to a reduction of switching losses. This method can be used for a flying capacitor converter with any number of levels. Furthermore, in order to control the inrush current during the start-up procedure and avoid extra voltage and current stresses for active switches and capacitors, a pre-charge routine for the flying capacitors is proposed. Experimental results demonstrate the benefits of the new concepts

A New Control Strategy for a Class of Multiple-Input DC-DC Converters

This paper proposes a new control scheme for a class of multi-input dc-dc power converters. The new control method is based on coupling the signals from independent control loops of conventional controller for a multi-port converter. In this paper, the non-restricted double input buck converter is introduced. The properties of this converter and its steady-state equations along with its small-signal model are reviewed. Next, the conventional control method is reviewed and the new control method is introduced based on coupling the voltage and current loops from the conventional controller. Then, the small-signal model of the converter with the new control method is analyzed and the converter transfer functions are derived. Finally, the converter transfer functions are used to find the output impedance of the converter in order to compare the performance of the new controller with the conventional controllers. Simulation results are provided to verify the results predicted by the small signal analysis