기본 콘텐츠로 건너뛰기

Harmonics

What is harmonics?

When we think about harmonics, we can easily come up with harmony in music, which means the composition of individual sounds. What about electrical power? In an electrical power system, a harmonic is a voltage or current at multiple of the fundamental frequency of the system. Then, What is the fundamental frequency? Before we discuss harmonics, we should know what the fundamental frequency is. Maybe you know the relationship between voltage, current, and resistor, for example, V=IR. Assume that there is a system where a DC voltage supply and a resistor are connected in serial. Then, if the voltage is AC, the current is AC.  And It's totally because of the resistor in this system. That is, the resistor is linear. So in this system, we have one voltage sine wave and one current sine wave. And they can be called a fundamental frequency wave.


Fig.1



















What if the resistor is replaced with other components which is non-linear? The current will not be a complete sine wave such as the complex waveform in Fig.1. Why does it happen?? It's because of harmonics. Harmonics mean unwanted higher frequencies that superimposed on the fundamental waveform creating a distorted wave pattern. Harmonic frequencies in the power grid are one of the causes of power quality problems. Harmonics in power systems result in increased heating in the equipment and conductors, misfiring in variable speed drives and torque pulsations in motors. So we should know and take care of it.
 As I said, harmonics have a higher frequency than the fundamental one. More exactly, their frequency is multiple times as the fundamental one.
Fig.2







As fig 2 is illustrated, the fundamental wave is the first harmonic and there is the second one, the third one, and so on.

Fig.3














Interestingly, in fig 3, frequency response, you can notice that magnitude depends on its frequency. In this graph, the fundamental frequency seems to be 200 Hz. As the frequency is going higher like 400, 600 Hz, ..., its magnitude is getting lower. That makes sense because we can think like as speed goes up, power is lower and its whole power remains.


라벨:

댓글

댓글 쓰기

이 블로그의 인기 게시물

NPC Inverter and Psim Simulation

1. 3-Level NPC Type Inverter Fig 1. 3-Level NPC Type Inverter Fig 2, Switching  Fig 1 is 3-Level NPC Type Inverter and Fig 2 indicates how it works.  Fig 2 indicates how each switch is activated. There are 3 switching states which are called P, O, N. In each state, the output voltage becomes +V_dc/2, 0, -V_dc/2. Fig 3. Switching Mode  Left in Fig 3 indicates circuits when positive voltage and the right one is for negative voltage. Let's check how it works! Considering P switching state in positive voltage, S1 and S2 are on, and S3 and S4 are off. So we can ignore the circuit below. As a result, the output voltage is +V_dc/2. In the same way, you can see how the rest works. 2. Control Fig 4, SPWM  In Fig 4, we can see how SPWM works. The offset voltage is applied to control the circuit. The common value for offset voltage is 0. It makes the reference polarity voltage and the reference phase voltage same. 3. Circuit Fig 5. Circuit for Psim ...
댓글 쓰기
자세한 내용 보기

What is Energy Storage System (ESS) and its role in Grid?

Energy Storage System (ESS)  Methods of generating electricity by renewable energy such as wind power and solar power, rather than the methods by conventional power plants are becoming important  both politically and technically not only in Korea but also around the world. In the case of Korea, the importance of renewable energy is emphasized as the country pushes for the "2050 carbon neutrality" policy. However, there are certainly drawbacks to renewable energy. Wind power and solar power are the representative sources of renewable energy. Wind power generators are affected by wind speed, and photovoltaic  generators by solar radiation. Because of this inherent nature of renewable energy, the amount of power output from renewable energy is highly volatile. Many studies to reduce this volatility  are going on , and in this post, we will first learn about ESS and how it is typically utilized to decrease bad natures of renewable energy and eventually to help stabilize ...
댓글 쓰기
자세한 내용 보기