Introduction to Off-grid Solar Inverter

An off-grid solar inverter, also known as a power regulator and power regulator, is an indispensable part of a photovoltaic system. The main function of the photovoltaic off-grid solar inverter is to convert the direct current generated by the solar panel into the alternating current used by the home appliances. Through the full-bridge circuit, the SPWM processor is generally used to modulate, filter, boost, etc., to obtain a sinusoidal AC power that matches the lighting load frequency, rated voltage, etc. for the end user of the system. With the off-grid solar inverter, it is possible to use a DC battery to supply AC power to the appliance. Next, let's take a look at the introduction of an off-grid solar inverter.

Here is the content list:

• What is an off-grid solar inverter?

• Performance parameters of the off-grid solar inverter.

What is an off-grid solar inverter?

Solar AC power generation system is composed of solar panels, a charge controller, an off-grid solar inverter, and a battery; solar DC power generation system does not include an inverter. The process of converting AC power into DC power is called rectification, the circuit that completes the rectification function is called a rectifier circuit, and the device that realizes the rectification process is called a rectifier device or rectifier. Correspondingly, the process of converting DC power into AC power is called an inverter, the circuit that completes the inverter function is called an inverter circuit, and the device that realizes the inverter process is called inverter equipment or off-grid solar energy inverter.

The core of the inverter device is an inverter switch circuit, which is referred to as an inverter circuit for short. The circuit completes the inverter function by turning on and off the power electronic switch. The on-off of electronic switching devices requires certain pulses, and these pulses can be adjusted by changing the voltage signal. The circuits that generate and condition the pulses are often referred to as control circuits or control loops. The basic structure of the inverter device includes a protection circuit, an output circuit, an input circuit, an output circuit, and the like in addition to the above-mentioned inverter circuit and control circuit.

Performance parameters of the off-grid solar inverter.

There are many parameters and technical conditions that describe the performance of an off-grid solar inverter. Here we only briefly describe the technical parameters commonly used when evaluating an off-grid solar inverter. First, the operating environment conditions of the off-grid solar inverter, the normal operating conditions of the off-grid solar inverter: the altitude does not exceed 1000m, and the air temperature is 0～+40℃. Second, the DC input power supply conditions, the input DC voltage fluctuation range: ±15% of the rated voltage of the battery pack. 

Third, the rated output voltage, within the allowable fluctuation range of the specified input DC voltage, represents the rated voltage that the off-grid solar inverter should be able to output. The stable accuracy of the output rated voltage value is generally stipulated as follows: During steady-state operation, the voltage fluctuation range should be limited, for example, its deviation should not exceed ±3% or ±5% of the rated value. In the dynamic situation of load mutation or other interference factors, the output voltage deviation should not exceed ±8% or ±10% of the rated value. 

Fourth, the rated output frequency, the frequency of the output AC voltage of the off-grid solar inverter should be a relatively stable value, usually the power frequency 50Hz. The deviation under normal working conditions should be within ±1%. Fifth, the rated output current (or rated output capacity), which represents the rated output current of the off-grid solar inverter within the specified load power factor range. Some off-grid solar inverter products give the rated output capacity, expressed in VA or kVA. The rated capacity of the off-grid solar inverter is when the output power factor is 1 (ie pure resistive load), and the rated output voltage is the product of the rated output current.

Sixth, rated output efficiency, the efficiency of an off-grid solar inverter is the ratio of output power to input power under specified working conditions, expressed in %. The efficiency of the off-grid solar inverter at rated output capacity is full load efficiency, and the efficiency at 10% rated output capacity is low load efficiency. Seventh, the maximum harmonic content of off-grid solar inverter, sine wave off-grid solar inverter, under resistive load, the maximum harmonic content of the output voltage should be less than or equal to 10%. 

Eighth, the overload capacity of the off-grid solar inverter is the ability of the off-grid solar inverter to output more than the rated current value in a relatively short period under specified conditions. The overload capacity of the off-grid solar inverter should meet certain requirements under the specified load power factor. Ninth, the efficiency of the off-grid solar inverter is the ratio of the output active power of the off-grid solar inverter to the input active power (or DC power) under the rated output voltage, output current, and specified load power factor. The tenth is the load power factor, which characterizes the ability of an off-grid solar inverter to carry an inductive load or capacitive load. Under sine wave conditions, the load power factor is 0.7 to 0.9 (hysteresis), and the rated value is 0.9.

Eleventh, load asymmetry, under 10% asymmetric load, the asymmetry of the output voltage of the fixed frequency three-phase off-grid solar inverter should be less than or equal to 10%. Twelfth, the unbalance of the output voltage. Under normal working conditions, the unbalance of the three-phase voltage output by the off-grid solar inverter (the ratio of the reverse sequence component to the positive sequence component) should not exceed a specified value, generally expressed in % expressed, such as 5% or 8%. Thirteenth, starting characteristics, under normal working conditions, the off-grid solar inverter should be able to start normally for 5 consecutive times under full load and no-load operation conditions. 

Fourteenth, protection function, off-grid solar inverter should be set: short-circuit protection, over-current protection, over-temperature protection, over-voltage protection, under-voltage protection, and phase loss protection. Among them, the overvoltage protection means that for the off-grid solar inverter without voltage stabilization measures, there should be output overvoltage protection measures to prevent the negative cutoff from being damaged by the output overvoltage. Over-current protection refers to the over-current protection of the off-grid solar inverter, which should be able to act in time when the load is short-circuited or the current exceeds the allowable value, to prevent it from being damaged by the surge current. Fifteenth, interference and anti-interference, the off-grid solar inverter should be able to withstand electromagnetic interference in the general environment under the specified normal working conditions. The anti-interference performance and electromagnetic compatibility of the off-grid solar inverter shall comply with the relevant standards. 

Sixteenth, the off-grid solar inverter that is not frequently operated, monitored, and maintained should be ≤95db; the off-grid solar inverter that is frequently operated, monitored, and maintained should be ≤80db. Seventeenth, display, off-grid solar inverter should be equipped with data display of AC output voltage, output current, output frequency, and other parameters, as well as the signal display of input, live, power-on, and fault status. Eighteenth, communication function, the remote communication function allows users to check the running status of the machine and the stored data without going to the site. 

Nineteenth, the waveform distortion of the output voltage, when the output voltage of the off-grid solar inverter is sinusoidal, the maximum allowable waveform distortion (or harmonic content) should be specified. Usually expressed as the total waveform distortion of the output voltage, its value should not exceed 5% (single-phase output allows 10%). The twentieth, starting characteristic, characterizes the off-grid solar inverter's ability to start with load and its performance during dynamic operation. The off-grid solar inverter should be guaranteed to start reliably under rated load. Twenty-first, noise, transformers, filter inductors, electromagnetic switches, and fans in power electronic equipment will generate noise. When the off-grid solar inverter is running normally, its noise should not exceed 80dB, and the noise of a small off-grid solar inverter should not exceed 65 dB.

If you are interested in an off-grid solar inverter, you can contact us, our website is http://www.hinverter.com/, you are welcome, and look forward to cooperating with you.