Grid Tech

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 Simulation 1

 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 S

Voltage Source Inverter  Voltage source Inverter is a device that converts power from a DC constant voltage source into AC form by switching behavior. The output voltage has a switching waveform and the output current has AC form. It is classified into two inverters: square wave inverter and PWM inverter. Fig 2. Voltage Source Inverter 2 Fig 1. Voltage Source Inverter 1 It consists of 3 pairs of 2 switching components. Depending on the switching condition, input and output voltage are determined. In order to prevent short circuit accident, switching component works in a commensurate way. 1. 3 Phase 2-Level Inverter Fig 3. General Circuit of 3 phase 2-level inverter Fig 3 is a common circuit of an 3 phase 2-level inverter. Line voltage has 3 level form which is +Vdc, 0, and -Vdc, The detail about this inverter is explained in one of my past posts titled as "Inverter: Single Phase Inverter and 3 Phase Inverter"  2. 3 Phase 3-Level Invert

 Nowadays about 70% of all electricity in industry is used for providing electromotive force by driving electric motor. The beginning of development in electric motor is originated from discovery of Electromagnetic Induction by Michael Faraday. Fig 1. Classification of Motor Motor is largely categorized by 2 parts : AC motor and DC motor. In fact, between these two types, there is also Brushless DC motor(BLDCM). It cannot be considered as a typical motor but we will figure it out later, not now.  DC motor is divided into 2 types : Separatly Excited and Self Excited. It depends on how it makes Excitation power in order to generate magnetic flux in field coil of a stator.  AC motor is also divided into 2 types : Synchronous motor and Induction motor. It is not presented in diagram but Synchronous motor can be divided by 3 types : Permanent magnet, Wound Field and Reluctance. And in Permanent magnet. we use semiconductor, which is so important. So we will figure

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

0. Induction Motor   The induction motor is invented by the scientist Nikola Tesla and it is the most common motor type even today (Around 90%). About 50% of global electric power consumption is due to induction motors. The induction motor has basically two main parts: Stator and Rotor. 1) Stator: Stationary Part The stator is the stationary part of an induction motor like Fig 1-2. It is made up of various stampings with slots to carry 3 phase windings. The windings are geometrically divided 120 degrees separated. It does not require DC current to run the machine. 1. Induction Motor 2) Rotor: Rotating Part 2. :Various Rotors   The rotor is the rotating part of the induction motor. The rotor is simply a collection of conducting bars short-circuited by end rings. Its rotation is because of the interaction between the windings and magnetic fields producing a torque around the rotor's axis. There are many kinds of rotors: Squirrel-cage rotor, Wou