AFE 정류기의 성능개선에 관한 연구

The THD(Total Harmonic Distortion) level of AFE rectifiers is relatively lower than DFE rectifiers in the AC output of a source unit and the power factor can be improved by controlling input currents. In addition, it makes output voltages similar to DC waveforms in a DC link. However there is a disadvantage that when the source voltage is unmeasurable precisely because of harmonics or noises in circuits, a phase angle of the source can not be detected accurately, therefore the control of the rectifier will be unstable. In this paper, the improved AFE rectifier which has the enhanced controller of a phase angle in the source unit is proposed and it also provides decoupling control by feeding forward interference factors to the synchronous rotating and axises. Consequently, the simulation demonstrated that the output waveform in the DC link of the improved AFE rectifier illustrates the reduced harmonics and the improved power factor.|AFE 정류기는 DFE 정류기에 비해서 교류전원 출력측의 총고조파왜형률이 낮고, 입력 전류가 제어가 가능하므로 역률이 향상된다. 또한, DC link단의 직류 출력 파형을 일정하게 유지 할 수 있다. 하지만 전원 전압이 고조파나 잡음으로 제대로 측정되지 않을 경우 전원 전압의 위상각이 정확하게 검출되지 않으므로 정류기 제어가 불안정해지는 단점이 있다. 본 논문에서는 제안하는 전원 전압 위상각 제어기를 이용한 개선된 AFE 정류기를 설계하였고, 동기회전좌표계로 변환된 축, 축 전류에 외란으로 영향을 주는 간섭성분을 전향보상하여 독립적으로 제어하였다. 개선된 AFE 정류기의 직류출력 파형개선, 전원 출력측의 고조파 저감 및 역률 개선 등의 응답특성이 우수함을 시뮬레이션의 결과로서 증명하였다.제 1 장 서 론 1 1.1 연구배경 1 1.2 연구내용 2 1.3 논문의 구성 3 제 2 장 선박의 전기추진시스템 4 2.1 전기추진시스템의 개요 및 전체구성 4 2.2 전기추진시스템의 세부구성 5 2.2.1 원동기와 발전기 5 2.2.2 전력변환장치 5 2.2.3 추진전동기 7 제 3 장 기존 전기추진시스템의 정류기 9 3.1 DFE 정류기 9 3.1.1 DFE 정류기의 구성 9 3.1.2 DFE 정류기의 직류출력과 전원 출력측의 고조파 발생정도 10 3.2 상천이변압기를 이용한 DFE 정류기 11 3.2.1 상천이변압기의 개요 11 3.2.2 12펄스 정류 12 3.2.3 18펄스, 24펄스 정류 14 3.2.4 상천이변압기를 이용한 DFE 정류기의 직류출력과 전원 출력측의 고조파 발생정도 17 3.3 AFE 정류기 18 3.3.1 AFE 정류기의 구성 18 3.3.2 AFE 정류기의 특징 19 3.3.3 AFE 정류기의 직류출력과 전원 출력측의 고조파 발생정도 23 3.4 기존 정류기의 고조파 비교 24 제 4 장 본 논문에서 제안하는 AFE 정류기 26 4.1 AFE 정류기의 수학적 모델링 26 4.2 개선된 전원 전압 위상각 제어기의 설계 27 4.2.1 좌표축 변환 27 4.2.2 제안하는 위상각 제어의 기본 원리 31 4.2.3 개선된 위상각 제어기의 설계 34 4.3 속도기전력 전향보상을 갖는 전류제어기 설계 37 4.4 DC link단 직류 출력전압 제어기 39 4.5 제안하는 AFE 정류기의 전체 제어회로 40 제 5 장 시뮬레이션 42 5.1 기존의 AFE 정류기 출력 44 5.2 제안하는 AFE 정류기 출력 48 5.3 제안하는 AFE 정류기를 활용한 전기추진시스템의 시뮬레이션 53 제 6 장 결 론 59 참고문헌 61Maste

Application of Modular Multilevel Converters (MMC) Using Phase-Shifted PWM and Selective Harmonic Elimination in Distribution Systems

Reducing the size and weight of a power electric system is a prodigious challenge to researchers as the development of the latest technologies emerge in the field of electrical engineering. A similar urge is there to develop a light-weight mobile power substation (MPS) to use in the electric power distribution systems during emergency conditions. This thesis proposes a power electronics based solution using the modular multilevel converter (MMC) topology to design the MPS system. The market-available power semiconductor devices are analyzed and suitable devices are selected to design the system. The phase-shifted pulse width modulation (PS-PWM) and selective harmonic elimination (SHE) switching algorithms are selected to modulate the MMC terminals. To validate the proposed techniques simulation files are built in MATLAB/SIMULINKTM. Simulation results are presented and analyzed to verify the theoretical claims. These simulation results prove the feasibility of designing the MPS system with the proposed techniques

A Study on Sensorless Control of Low Speed Range for Induction Motor

In order to detect the speed of an induction motor, a speed detector such as an encoder has been mainly used in the rotor, but a sensorless speed control method without a speed detector has been widely studied due to constraints such as installation environment, reliability, and price. In addition, most sensorless vector controls show a relatively good control result in the high speed region, but show a tendency of deterioration of control characteristics in the low speed region. In this paper, we propose a new control system by combining indirect vector control using spatial vector modulation with sensorless speed control using AFE rectifier and current error compensation. The AFE method can control harmonics included in the input power by actively controlling the input current of the AC power, and have the characteristics of making power excellent quality by controlling the power factor of the input voltage and current. In the sensorless speed control method using current error compensation, a stator voltage is applied to reduce the stator current difference between the induction motor and the modified model so that the speed of the induction motor follows the speed of the model. It is a method controlling the speed of induction motors indirectly by making the current difference between the induction motor and the mathematical model close to zero without controlling the speed directly. In this paper, an improved space vector modulation method in which less harmonics are included in current and torque than conventional hysteresis control and triangular wave comparison modulation, switching cycle is reduced by 1/2 compared to conventional space vector modulation. And the computational structure is so simple that it can be easily implemented in low-cost controllers. In addition, this study focuses on the practicality of robustness against parameter variation and dynamic characteristics improvement from very low speed to low speed, which is a problem of the conventional sensorless speed control algorithm. In order to verify the applicability of the proposed algorithm and system, the response characteristics of the indirect vector control using the modified SVPWM using the AFE rectifier and the 2.2[kW] induction motor were analyzed through computer simulation and experiments. As a result, It is confirmed that the excellent input current is supplied and the speed response and load characteristics of the induction motor are excellent even in the extremely low speed range and the low speed range.|유도전동기의 속도를 검출하기 위해서는 회전자에 엔코더 등의 속도 검출기가 주로 사용되어 왔지만 설치환경, 신뢰성 그리고 가격 등의 제약으로 인하여 속도검출기가 없는 센서리스 속도제어 방식이 폭 넓게 연구되고 있다. 또한, 대부분의 센서리스 벡터제어는 고속영역에서 비교적 양호한 제어 결과를 얻을 수 있지만 저속영역에서는 제어특성이 저하하는 경향을 보여 주었다. 본 논문에서는 AFE 정류기와 전류오차보상법을 이용한 센서리스 속도제어법에 공간벡터변조방식을 이용한 간접벡터제어를 결합하여 새로운 제어시스템을 제안하였다. AFE 방법은 교류전원의 입력전류를 능동적으로 제어하여 입력 전압과 전류에 포함된 고조파를 감소시킬 수 있고 입력전원의 역률을 제어하여 전력의 품질을 향상시키는 특성을 가진다. 전류오차보상에 의한 센서리스 속도제어법은 유도전동기와 수식모델의 고정자 전류차이가 감소하는 방향으로 고정자 전압을 인가함으로써 유도전동기의 속도가 설정치인 모델의 속도를 추종하도록 하는 방식으로 직접 속도를 제어하지 않고 실제 유도전동기와 수식모델의 전류차이를 0에 가깝게 함으로써 간접적으로 유도전동기의 속도를 제어하는 방법이다. 본 논문에서는 기존의 히스테리시스 제어와 삼각파 비교 변조 방식에 비하여 전류와 토크에 포함된 고조파가 적고 기존의 공간벡터변조방식보다 스위칭 주기가 1/2로 감소하여 스위칭 손실이 감소되며, 계산시간을 크게 줄일 수 있어 연산 구조가 매우 간단하기 때문에 저가의 제어기에서도 손쉽게 구현이 가능한 개선된 공간벡터변조법을 적용하여 전류제어를 수행하였다. 또한, 기존의 센서리스 속도제어 알고리즘의 문제점인 극저속에서부터 저속영역에 이르기까지의 동특성 개선과 파라메타 변동에 대해서도 강인성을 가지는 실용성에 초점을 맞추어 연구를 수행하였다. 제안된 알고리즘과 시스템의 적용 가능성을 확인하기 위해서 AFE 정류기와 2.2[kW] 유도전동기를 사용하여 개선된 SVPWM을 적용한 간접벡터제어의 응답특성을 컴퓨터 시뮬레이션과 실험을 통하여 분석한 결과, 고조파가 적은 우수한 입력전류가 공급되어 극저속영역과 저속영역에서 유도전동기의 속도응답 및 부하특성이 양호함을 확인하였다.목 차 목차 ⅰ 그림목차 ⅳ 표목차 ⅶ Abstract ⅷ 기호 및 약어 ⅻ 1. 서 론 1 1.1 연구배경 및 동향 1 1.2 연구 목적 3 1.3 논문의 구성 4 2. 유도전동기 제어방법 6 2.1 직접토크제어 6 2.1.1 직접토크제어 알고리즘 6 2.1.2 직접토크제어의 기본 개념과 이론 8 2.2 벡터제어 14 2.2.1 직접벡터제어 15 2.2.2 간접벡터제어 18 3. AFE 정류기와 Inverter 전류 제어 방식 23 3.1 히스테리시스 제어 23 3.2 삼각파 비교 전류 제어 26 3.3 공간 벡터 전압 변조 방식 30 3.3.1 공간 벡터 변조 기법의 원리 32 3.3.2 대칭 공간 벡터 변조 방식 37 3.4 개선된 공간 벡터 전압 변조 방식 41 3.4.1 공간 벡터 변조 패턴 41 4. 유도전동기 센서리스 속도제어 방식 49 4.1 속도추정기에 의한 방식 49 4.2 모델기준적응제어에 의한 방식 51 4.3 신경회로망을 이용한 방식 53 4.4 고주파 신호주입을 이용한 방식 57 4.5 칼만필터를 이용한 방식 60 4.6 슬롯고조파 분석을 이용한 방식 62 4.7 상태궤환 선형화 기법을 이용한 방식 64 4.8 유도전동기 센서리스 속도제어 방식 비교 69 5. 제안하는 전류오차보상에 의한 센서리스 속도제어 71 5.1 이론적 배경 71 5.2 제어 알고리즘 및 특징 78 6. 컴퓨터 시뮬레이션 81 6.1 속도검출기가 있는 유도전동기 속도제어 83 6.2 제안하는 센서리스 유도전동기 속도제어 89 6.3 시뮬레이션 결과 검토 96 7. 실험장치의 구성과 실험결과 97 7.1 전력변환시스템의 제어회로 구성 97 7.1.1 마이크로프로세서 98 7.1.2 인터페이스 99 7.1.3 게이트 드라이브 102 7.1.4 부하 인가 장치 104 7.2 실험결과 및 검토 104 8. 결 론 115 참고문헌 118Docto

Low capacitance cascaded H-bridge StatCom

The application of Cascaded H-Bridge (CHB) multilevel converter StatCom is well established in the industry. In a conventional CHB StatCom, low frequency ripple on the dc side is limited to 10% by utilizing large capacitance. Having a smaller capaci-tance is advantageous because the system will be smaller, cheaper, and more reliable. However, reducing the capacitors will increase the ripple’s magnitude and causes problems such as, control and filtering issues, and high voltage stress on the semicon-ductors. In this thesis, the next generation of CHB StatCom i.e. Low Capacitance StatCom (LC-StatCom) is developed which is able to operate with ripple magnitudes close to the theoretical limit (smallest capacitors’ size). A feed-forward filtering scheme is developed that is able to effectively filter out large ripples without imposing any delay to the control loop and facilitates design of higher bandwidth capacitors’ voltage controllers. A decoupling theory which outlines requirements for completely decoupling the individual capacitors’ voltage controller from the rest of the control system is introduced. The decoupled control system has a linear cluster capacitors’ voltage controller which is essential for operation of the LC-StatCom The proposed LC-StatCom utilizes this linearity to have a variable capacitors’ voltage reference in order to limit the maximum voltage stress on the semiconductors. The proposed LC-StatCom and innovative solutions are evaluated by simulation and experimental case studies. It is shown that the LC-StatCom can achieve 80% reduction in the capacitors’ size, improve current quality, and reduce the maximum voltage stress on the semiconductors com-pared to a conventional StatCom. The LC-StatCom has a reduced operating area in the inductive region compared to conventional StatComs. In this thesis, to overcome this drawback, a hybrid LC-StatCom that utilizes a series thyristor bypassed inductor is developed. The compensated LC-StatCom developed in this thesis, provides approxi-mately 75% reduction in overall energy storage capacity of passive components

Enhanced decoupling current scheme with selective harmonic elimination pulse width modulation for cascaded multilevel inverter based static synchronous compensator

This dissertation is dedicated to a comprehensive study and performance analysis of the transformer-less Multilevel Cascaded H-bridge Inverter (MCHI) based STATic synchronous COMpensator (STATCOM). Among the shunt-connected Flexible AC Transmission System (FACTS) controllers, STATCOM has shown extensive feasibility and effectiveness in solving a wide range of power quality problems. By referring to the literature reviews, MCHI with separated DC capacitors is certainly the most versatile power inverter topology for STATCOM applications. However, due to the ill-defined transfer functions, complex control schemes and formulations were emerged to achieve a low-switching frequency high-bandwidth power control. As a result, adequate controller parameters were generally obtained by using trial and error method, which were practically ineffective and time-consuming. In this dissertation, the STATCOM is controlled to provide reactive power (VAR) compensation at the Point of Common Coupling (PCC) under different loading conditions. The goal of this work is to enhance the performance of the STATCOM with the associated proposed control scheme in achieving high dynamic response, improving transient performance, and producing high-quality output voltage waveform. To evaluate the superiority of the proposed control scheme, intensive simulation studies and numerous experiments are conducted accordingly, where a very good match between the simulation results and the experimental results is achieved in all cases and documented in this dissertation

Model predictive control for advanced multilevel power converters in smart-grid applications

In the coming decades, electrical energy networks will gradually change from a traditional passive network into an active bidirectional one using concepts such as these associated with the smart grid. Power electronics will play an important role in these changes. The inherent ability to control power flow and respond to highly dynamic network will be vital. Modular power electronics structures which can be reconfigured for a variety of applications promote economies of scale and technical advantages such as redundancy. The control of the energy flow through these converters has been much researched over the last 20 years. This thesis presents novel control concepts for such a structure, focusing mainly on the control of a Cascaded H-Bridge converter, configured to function as a solid state substation. The work considers the derivation and application of Dead Beat and Model Predictive controllers for this application and scrutinises the technical advantages and potential application issues of these methodologies. Moreover an improvement to the standard Model Predictive Control algorithm that include an intrinsic modulation scheme inside the controller and named Modulated Model Predictive Control is introduced. Detailed technical work is supported by Matlab/Simulink model based simulations and validated by experimental work on two converter platforms, considering both ideal and non-ideal electrical network conditions

Model predictive control for advanced multilevel power converters in smart-grid applications

In the coming decades, electrical energy networks will gradually change from a traditional passive network into an active bidirectional one using concepts such as these associated with the smart grid. Power electronics will play an important role in these changes. The inherent ability to control power flow and respond to highly dynamic network will be vital. Modular power electronics structures which can be reconfigured for a variety of applications promote economies of scale and technical advantages such as redundancy. The control of the energy flow through these converters has been much researched over the last 20 years. This thesis presents novel control concepts for such a structure, focusing mainly on the control of a Cascaded H-Bridge converter, configured to function as a solid state substation. The work considers the derivation and application of Dead Beat and Model Predictive controllers for this application and scrutinises the technical advantages and potential application issues of these methodologies. Moreover an improvement to the standard Model Predictive Control algorithm that include an intrinsic modulation scheme inside the controller and named Modulated Model Predictive Control is introduced. Detailed technical work is supported by Matlab/Simulink model based simulations and validated by experimental work on two converter platforms, considering both ideal and non-ideal electrical network conditions