Switching Modulation Method of Inverter

There are many switching modulation methods of inverters such as square wave modulation and PWM(pulse width modulation). Square wave modulation is the method of only controlling its frequency, not controlling the magnitude of output voltage. However, PWM controls the magnitude of output voltage as well as its frequency. For this, the pulse is produced to generate the fundamental voltage which is the same voltage and frequency as a reference voltage by on and off switching. Moreover, there are also many methods in PWM. SPWM is one of many ways to do PWM.

Fig.1 Square wave modulation and PWM control

SPWM(Sinusoidal PWM)

Fig 2. 3 Phase Inverter Circuit

Fig 3. SPWM

SPWM is a modulation method using sinusoidal pulse. As seen in Fig 3 (a), a carrier wave(triangle wave) is produced. Comparing it with the reference wave, in this case, it works like: carrier wave > reference wave, then Sa(switcing) is on and in another case, Sa is off. So Van is generated depending on Sa. The way how it works is called SPWM.

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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 ...

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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 ...

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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 ...

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Grid Tech

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