In order to reach better results for pulse width modulation (PWM)-based methods,
the reference waveforms known as control laws have to be achieved with good
accuracy. In this paper, three control laws are created by considering the harmonic
components of modular multilevel converter (MMC) state variables to suppress the
circulating currents under nonlinear load variation. The first control law consists
of only the harmonic components of the MMC’s output currents and voltages.
Then, the second-order harmonic of circulating currents is also involved with both
upper and lower arm currents in order to attain the second control law. Since
circulating current suppression is the main aim of this work, the third control law
is formed by measuring all harmonic components of circulating currents which
impact on the arm currents as well. By making a comparison between the
switching signals generated by the three proposed control laws, it is verified that
the second-order harmonic of circulating currents can increase the switching
losses. In addition, the existence of all circulating current harmonics causes
distributed switching patterns, which is not suitable for the switches’ lifetime.
Each upper and lower arm has changeable capacitors, named “equivalent
submodule (SM) capacitors” in this paper. To further assess these capacitors,
eliminating the harmonic components of circulating currents provides fluctuations
with smaller magnitudes, as well as a smaller average value for the equivalent
capacitors. Moreover, the second-order harmonic has a dominant role that leads to
values higher than 3 F for equivalent capacitors. In comparison with the first and
second control laws, the use of the third control-law-based method will result in
very small circulating currents, since it is trying to control and eliminate all
harmonic components of the circulating currents. This result leads to very small
magnitudes for both the upper and lower arm currents, noticeably decreasing the
total MMC losses. All simulation results are verified using MATLAB software in the
SIMULINK environment.

제 1편 : SIMULINK 기본편

1.1 SIMULINK의 시작 1
블록의 연결 5
블록 파라미터의 설정 7
시뮬레이션 파라미터 (Configuration Parameters)의 설정 8
시뮬레이션의 수행 9
블록 파라미터의 표시 9
복수 데이터의 표시 11
2.2 동적 시뮬레이션 13
이차 미분방정식 17
선형 상태변수 모델 23
DC 모터의 시뮬레이션 24
함수 블록의 사용 29
차분방정식(difference equation)의 모델링 34
Subsystem(부시스템)의 구성 37

제 2편 : 연구논문

1. Introduction 42
2. The Modular Multilevel Converter (MMC) 43
3. Evaluation of the Proposed Control Laws 50
4. Accurate Sizing of the Equivalent SM Capacitors of the MMC
Arms 53
5. Simulation Results 56
6. Conclusions 63
7. References 65