Grid Tech

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 ...

The inverter is an electronic device or circuitry that changes direct current (DC) to alternating current (AC). In short, the Inverter is a DC-AC converter. It can be seen as an application for DC chopper. We can classify inverters into single-phase inverters and 3-phase inverters. We will see some inverter circuits and how they act. 1. Single Phase Inverter: Half Bridge, Full Bridge Half Bridge 1-1. Half-bridge inverter circuit 1-2 Half-bridge inverter graph  In figure 1-1, we can see the Half-bridge circuit. In this circuit, there are two rules of triggering: First, because of KVL, T1 and T2 can not be on at the same time. Second, KCL is satisfied by D1 and D2.  A pair of a diode and a transistor acts like a switch. So In figure 1-2, if SW1 (T1 and D1) is on for the time duration 0<t<T/2, then V_o is V_s/2. On the other hand,  if SW2 (T2 and D2) is on for the time duration T/2<t<T, then V_o is V_s/2. Assuming that it's a highly indu...

 A voltage converter is an electric power converter that changes the voltage of an electrical power source. On this page, I am going to talk about the DC-DC converter. In the DC-DC converter, there are 3 types. 1. Step-down(Buck) converter: Where the output voltage of the converter is lower than the input voltage. In a buck converter, there are two types of modes. Continuous conduction mode(CCM) and Discontinuous conduction mode(DCM). During CCM(Mode 1), while switch S is on, the voltage of the load is conducted as V_s. During DCM(Mode 2), while switch S is off, any current doesn't flow.  V_a=F(t_on, f_s) is a linear function. t_on is the on pulse width. Controlling t_on is known as PWM control. f_s is the switching frequency.  Low current ripple(by adding inductor) This is a buck converter which provides a low current ripple by adding an inductor on load.  Low voltage ripple(by adding capacitor) This is a buck converter which provides lo...

EV means "Electric Vehicles", which use one or more electric motors or traction motors for propulsion. In this poster, there will be a description about the history of electric vehicles and their current infrastructure. History of Electric Vehicle   Electric car built by  Thomas Parker , photo from 1895    In 1827, Hungarian priest, Ányos Jedlik, started electric power. After that year, he used an electric motive motor to power his small car. It had been developed and upgraded more and more.  Finally, in America, in the early 1900s, the first mass-produced electric vehicles appeared. But It had more disadvantages than advantages compared to a combustion engine vehicle which appeared later. The high cost, low speed, and short-range battery problem were the main problems of EV in comparison to a combustion engine vehicle.  But, in the 21st century, demand for alternative fuel instead of oil has been increasing. By the help of the trend, the import...