Power Inverter Working Principle, Steps Explained
Power inverter working principle is based on three steps that include; supply-frequency control, voltage amplitude control, and DC-AC conversion.
This article discusses the working principle of power inverters, as follows;
1). Supply-Frequency Control (in explanation of the Power Inverter Working Principle)
The overall function of a power inverter is to convert electricity from one form to another, such as from DC to AC, or low-output voltage to high-output voltage . One of the key mechanisms by which it performs this function is by supply-frequency control.
Inverters increase the frequency of electric current that flows through their terminals, by any of various technical and electromagnetic mechanisms.
The most common way to increase frequency using an inverter, is by current-flow switching. Depending on the exact mechanism(s) involved, current-flow switching by a power inverter may be referred to by any of various terms, including sliding-mode control, which is based on rapid switching of current supply among multiple load phases .
Supply-frequency control is an important first-step in the working principle of power inverters, because it helps to control the speed of rotation of the induction motor(s) involved in electricity generation and/or transmission to the load .
When motor rotation is controlled, electricity supply mode can be altered in a flexible manner that meets the exact power requirements of the load at any point in time.
The manner in which a power inverter alters current supply frequency, depends on its current-switching rate, which is also known as its base frequency. It is very common for inverters to have a base frequency of around 50Hz, although some have frequencies that are lower or higher than this value.
When an inverter in installed into the current-supply chain of an electric circuit, the frequency of current modified by the inverter is usually equal or close to its base frequency.
It must be noted that a change in current frequency by an inverter, is equivalent to a change in voltage-frequency, as the latter is often mentioned instead of the former, in studies related to inverter technology.
The energy efficiency of supply-frequency modification by a power inverter may be affected by the resistance of flowing current to instantaneous switching, in a phenomenon that can be referred to as 'chattering'. The retarding impact and energy loss caused by chattering can be reduced by increasing the switching frequency of the inverter.
It must be noted that this chattering is different from occasional operating noises that come from inverters while they are being used.
Such noises may either be normal, or when excessive, may indicate other issues such as inefficient current input/output through the cables, low-capacity battery, or component malfunction.
Maintenance and noise suppression measures are generally recommendable to address (loud) operational inverter noises.
2). Supply-Voltage Amplitude Control
The amplitude of voltage is its maximum (or minimum) value in any electric circuit or system, which is usually represented as crests and troughs on a sinusoidal voltage wave.
Output voltage is controlled in an inverter by modifying or modulating the temporal with of voltage pulses; also known as the 'pulse width' (PW).
Pulse width is simply a measure of the elapsed time between the crest (highest point) and trough (lowest point) of the magnitude of voltage transmitted through a conductive medium.
The control of output voltage, of an inverter is called pulse width modulation (PWM), because it is simply a modification of voltage-flow magnitude and frequency .
By controlling voltage, inverters are able to effectively convert a DC current from a source, to usable AC current that is transmitted to a load.
This is especially needful for distributed energy resources management systems (DERMS) that rely significantly on stored energy, since energy storage in batteries and other systems generally favors DC as a storable form of power. Converting the stored energy from DC to AC form makes it suitable for microgrid (or conventional grid) transmission to electrical appliances .
Pulse width modulation (PWM) techniques in inverters  include;
1. Single Pulse Width Modulation
2. Multiple Pulse Width Modulation
3. Space Vector Pulse Width Modulation
4. Trapezoidal Pulse Width Modulation
5. Sinusoidal Pulse Width Modulation
6. Modified Sinusoidal Pulse Width Modulation
7. Selective Harmonic Elimination Pulse Width Modulation
8. Controlled Pulse Width Modulation
9. Harmonic Injection Modulation
10. Phase Displacement-Control Modulation
The methods of voltage control in inverters may be broadly categorized as; space vector, harmonic, and hysteresis voltage control, which cover all major techniques for the modification of voltage by inverters.
3). DC-AC Conversion (in explanation of the Power Inverter Working Principle)
The final step or outcome in the working principle of a power inverter is DC-AC conversion.
An inverter changes DC to AC by switching the frequency and amplitude of current in rapid, repetitive succession. The mode of switching may vary from one inverter to another, according to base frequency.
Asides DC to AC conversion, inverters also modify AC output voltage.
The working principle of a power inverter comprises of;
1. Supply-Frequency Control
2. Supply-Voltage Amplitude Control
3. DC-AC Conversion
1). Çakanel, A.; Utkin, V. (2016). "Frequency control of DC/AC inverter." 2016 IEEE XVII ROPEC, Ixtapa, Mexico. Available at: https://doi.org/10.1109/ROPEC.2016.7830632. (Accessed 14 March 2023).
2). Dwivedi, U. D. (2015). "A simple output voltage control scheme for single phase wavelet modulated inverters." Available at: https://doi.org/ 10.4314/ijest.v7i3.13S. (Accessed 14 March 2023).
3). Jang, D-H. (1994). "Voltage, frequency, and phase-difference angle control of PWM inverters-fed two-phase induction motors." IEEE Transactions on Power Electronics 9(4):377 - 383. Available at: https://doi.org/10.1109/63.318895. (Accessed 14 March 2023).
4). Mohsin, M. H.; Al-Shamaa, N. K. (2020). "DC-AC Inverter with Tap Changing Transformer." IOP Conference Series Materials Science and Engineering 671(1):012039. Available at: https://doi.org/10.1088/1757-899X/671/1/012039. (Accessed 14 March 2023).
5). Nguyen, T-T.; Yoo, H. J.; Kim, H-M.; Duc, H. N. (2018). "Direct Phase Angle and Voltage Amplitude Model Predictive Control of a Power Converter for Microgrid Applications." Energies 11(9):2254. Available at: https://doi.org/10.3390/en11092254. (Accessed 14 March 2023).
6). Rao, R. K.; Srinivas, P.; Kumar, M. (2014). "DESIGN AND ANALYSIS OF VARIOUS INVERTERS USING DIFFERENT PWM TECHNIQUES." Available at: https://bit.ly/3JERbc8. (Accessed 14 March 2023).