In the mid-1800s, the competition between Nikola Tesla and Thomas Edison raged to determine whether alternating current (AC) or direct current (DC) would be the dominant format for electricity generation and distribution. Tesla won the race, and AC was defined as the most helpful format.
An inverter is required to convert direct current (DC) to usable alternating current (AC) at the voltage (V), current (A), and frequency (Hz). Most household appliances are run on AC (120V and 60Hz), and the grid power companies generate the majority of their power as AC.
The pros and cons of AC vs. DC were considered, and it was a close-run race, but ultimately the critical advantages of AC won out over DC.
- AC is simpler to produce than DC.
- AC is less expensive than DC to generate.
- AC systems have higher efficiency than DC, such as AC generators.
- The waste of power is negligible for AC during transmission.
- AC power can easily be converted into DC form.
Let’s look at why we need an inverter to turn stored chemical energy-derived direct current into more useful alternating current.
What Does An Inverter Do And Why?
An inverter converts the direct current (DC) from a battery or solar panel into alternating current (AC), which is easier to transmit over long distances and is the format of electrical power on which most electrical appliances and equipment are designed to run.
To understand how an inverter works, we must first understand the difference between direct current and alternating current. The chemical potential energy in a battery or solar panel directly causes electrons to flow from the negative terminal via a conductor to the positive terminal.
If we connect an Oscilloscope to the circuit, we will see a stable positive voltage line above the Zero Line on the scope screen. Now let’s assume that we could switch the polarity on the battery terminal around every one second. The graph on the Oscilloscope will now show a box-shaped standing wave on the scope screen.
The wave’s shape would be above the Zero line for one second and then switch to below the Zero line for the next one second. We will end up with an alternating square wave with a frequency of one Hertz (one per second).
We could run some AC motors with such a square alternating current, but the motor will not run very efficiently and generate a lot of noise. The wave shape is not harmonious like a pure sine-wave. In practice, the electrons in the conductor will be vibrating back and forth at a frequency of 1 Hz.
An inverter uses multiple switches called MOSFETs to switch the current direction back and forth and also a controller or Pulse Wave Modulator to change the frequency of the switching so that the square wave shape is converted into a smooth sine wave.
AC-powered appliances run best when the AC wave shape is as close as possible to a pure sine wave. If the wave shape is not smooth but angular and stepped, this is called Total Harmonic Distortion (THD), and it should be less than 7% for the AC power to allow the electrical components to run efficiently.
Good quality inverters are designed to convert DC to AC with less than 5% THD, better than the THD of grid power.
How Are Inverters Used In Everyday Applications?
The grid power is often disrupted due to electrical storms that cause voltage spikes to blow up power transmitters and other components on the power supply grid. We use inverter batteries to maintain AC power to critical electrical equipment such as computer systems, fridges, and other appliances.
An inverter battery system consists of a set of batteries (or battery bank) and an inverter/charger that will use grip power to charge and maintain the state of charge in the battery bank. When the grid power goes down, the inverter will switch on and convert the direct current supplied by the battery bank to an alternating current.
These systems are called uninterrupted power supplies (UPS) or inverter batteries. More recently, solar power generation has developed through photovoltaic cells that generate a direct electrical current when exposed to sunlight of sufficient intensity.
The DC generated by solar panels is great for charging large battery banks during the day when the sunlight is at its most intense. As the sunlight diminishes, the DC from the batteries can be converted to functional AC for use in household appliances.
Large solar arrays can also feed electrical power to the power grid, but the energy must be converted from DC to AC of the same voltage and frequency as the grid power system.
Can AC Be Turned Into DC And Why?
We need a rectifier to turn alternating current (AC) into direct current (DC). A rectifier does the reverse of an inverter by clipping and inverting the AC into a DC of constant voltage and current flow.
Rectifiers are pretty standard as we have some appliances like laptops powered by DC from a built-in battery. For example, the 120V 60Hz AC will be stepped down and rectified into 19V DC with a current strength of 74A for my laptop.
The square black box on your laptop power cord is the rectifier. Turning AC into DC is not 100% efficient, as evident by the heat generated in the rectifier housing.
Electrical DC motors are more energy-efficient and run quietly, making them ideal for ceiling fans and computer system cooling fans. Batteries cannot directly be charged with AC but require the AC first to be rectified to DC of the correct charge voltage and current strength to charge the batteries.
Using the best properties of AC and DC as dictated by the specific device or equipment to be powered, we need inverters and rectifiers to change the electrical power into the best format for the particular application.
When power is generated by solar panels or a battery as direct current, we need an inverter to convert it into AC for long-distance transmission of power to the AC devices that can run directly from the AC power.
We need to convert the AC power from the inverter or grid to be rectified to DC to recharge the battery for battery-powered devices.
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