Pure Sine Wave Inverter VS Modified Wave DC-AC Inverter

Pure sine wave inverters generally use PWM inverter, and some even add multi-step inverter, which has a complex structure, but the output waveform is good, and it is suitable for inductive and capacity loads. Modified wave inverters generally use square wave inverter, and a few add stepped inverters, which are simple in structure, but the output waveform is poor, and is not suitable for inductive and capacity loads.

Pure sine wave inverters are suitable for inductive, capacitive, and resistive loads, while modified wave inverters are only suitable for resistive loads. If the modified wave inverter is used in an inductive electrical appliance, it will emit a lot of noise and cause a lot of loss to the electrical appliance.

Modified sine wave inverter can be applied to mobile phones, laptops, televisions, video cameras, CD players, various chargers, car refrigerators, game consoles, DVD players, and power tools. It is also widely used as a backup power supply for tourism or field operations, and can also solve the electricity problem in remote areas with power shortage. It has become a supporting inverter power supply for wind power generation and solar photovoltaic projects, and can also be used as a backup power supply for industrial and mining enterprises and hospitals.

Corrective sine wave inverters should avoid "inductive loads". In layman's terms, it refers to high-power electrical products made by applying the principle of electromagnetic induction, such as motors, compressors, relays, fluorescent lamps and so on. These products require a much larger (about 5-7 times) start-up current than is required to maintain normal operation. For example, a refrigerator that consumes about 150 watts of power during normal operation can have a starting power of more than 1,000 watts. In addition, because the inductive load will generate a back electromotive force voltage at the moment when the power is turned on or disconnected, the peak value of this voltage is far greater than the voltage value that the vehicle inverter can bear, which can easily cause the instantaneous overload of the vehicle inverter and affect the service life of the inverter.

When measuring the AC output of a quasi-sine wave (modified sine wave) on-board inverter using a common multimeter, the displayed voltage is about 20 V lower than that of 220 volts.

Problems arise when operating precision equipment, and high-frequency interference can also be caused to communication equipment.

The square wave inverter outputs a poor quality square wave alternating current, and its positive and negative maximums are generated almost simultaneously, which has a drastic unstable effect on the load and the inverter itself. At the same time, its load capacity is poor, only 40-60% of the rated load, and cannot carry inductive loads. If the load is too large, the third harmonic component contained in the square wave current will increase the capacitive current flowing into the load, and in severe cases, the power filter capacitor of the load will be damaged.

In view of the above shortcomings, in recent years, there has been a modified sine wave (or modified sine wave, quasi-sine wave, simulated sine wave, etc.) inverter, and its output waveform has a time interval from the positive maximum to the negative maximum, and the use effect has been improved, but the waveform of the modified sine wave is still composed of broken lines, which still belongs to the square wave category, and the continuity is not good, and there is a dead zone (the waveform is shown in the "Modified Sine Wave Waveform Diagram"). Modified sine wave inverters generally use non-isolated coupling circuits, while pure sine wave inverters use isolated coupling circuit design. The price also varies widely. Modified sine wave switching inverter power supply, not only eliminates the cumbersome power frequency transformer, but also greatly improves the inverter efficiency by 90%.

The modified sine wave switching inverter power supply uses PWM pulse width modulation to generate the corrected wave output, which greatly reduces the power loss of the system due to the use of special intelligent circuit and high-power FET in the inverter process. And the soft start function is added, which effectively ensures the reliability of the inverter. If the requirements for power quality are not very high, and it can meet the needs of most electrical equipment, but it still has 20% harmonic distortion, there will be problems in the operation of precision equipment, and it will also cause high-frequency interference to communication equipment.

A coil load is called an inductive load, a capacitive load is called a capacitive load, and a purely resistive load is called a resistive load. For example, electric motors are inductive loads, capacitors are capacitive loads, electric furnace resistance wires, incandescent lamps, iodine dock lights, etc. are resistive loads. In the electrical or electronics industry, the definition of load impedance characteristics can be divided into pure resistive, inductive and capacitive types. It is called resistive, perceptual and capacitive. The characteristics of some loads in DC circuits are: Resistive loads: The relationship between current and voltage complies with the basic European regulation I=U/R. Inductive load: An electric current can flow, but the current lags behind the voltage, and energy can be stored in the inductor.