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Pure Sine Wave vs. Modified Sine Wave Inverters

Power inverters can be mainly divided into two types according to waveforms: pure sine wave inverter and modified sine wave inverter. In fact, there is also another type - square wave inverters, the earliest type of inverters which is seldom seen now.

Waveforms of power inverterPure sine wave inverter

Pure sine wave inverters output the true sine wave AC power which is the same as or even better than the power grid we use every day since there is no electromagnetic pollution. Pure sine wave inverters, with high efficiency, stable sine wave output and high frequency technology, are suitable for all kinds of loads without harms, which can not only power any common electrical equipment (including phone, heater, etc.), but also run the sensitive electronics or appliances (like microwave, fridge, etc.).

In summary, pure sine wave inverters provide high-quality AC, which can drive any kind of loads including resistive load and inductive load, and pure sine wave inverters have the highest conversion efficiency and the lowest loss, but they have higher technical requirements and costs than modified sine wave inverters.

Pure sine wave power inverter

Modified sine wave inverter

Modified sine wave (or corrective sine wave, quasi-sine, simulated sine wave, etc.) inverters have a time interval between their output waveforms from maximum positive value to maximum negative value, which improves their use effect. However, the modified sine wave is still composed of broken lines, which belong to the category of square waves, with poor continuity and blind zones.

Modified sine wave inverters should avoid powering inductive load. The inductive load refers to the high-power electrical products produced by the principle of electromagnetic induction, such as motors, compressors, relays, fluorescent lamps and so on, which require a much larger start-up current (about 5-7 times) than the current required to maintain normal operation. For example, a refrigerator that consumes about 150 watts of power in normal operation can start up with a power of more than 1000 watts. In addition, since the inductive load will produce counter electromotive force voltage at the moment of power on or off, and the peak of this voltage is much larger than that of inverters, which can easily cause the instantaneous overload of inverters and affect the service life of inverters.

Modified sine wave power inverter

If the demand for power quality is not very high, modified sine wave power inverters can still meet the needs of most electrical equipment. However, the modified sine wave inverters has 20% harmonic distortion, so there are still some problems in the operation of precision equipment and it can cause high-frequency interference to communication equipment. But modified sine wave inverters are much cheaper pure sine wave inverters.

Square wave inverter

Square wave inverters, which output square wave AC with poor quality, almost produce the maximum positive value to the maximum negative value simultaneously, thus causing severe instability to the load and the inverters themselves. At the same time, square wave inverters have poor load capacity, which is only 40-60% of the rated load, and they can not carry inductive load, because excessive load may make the third harmonic component in the square wave current increase the capacitive current flowing into the load, even seriously damage the power filter capacitance of the load. In addition, square wave inverters are made of simple multivibrators with the technology of the 1950s. Now the square wave inverters can hardly find in the market.

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