Vital Component in Photovoltaic Inverter "Inductors"

Inductor is the key component in photovoltaic inverters. The selection and installation of inductors have a direct impact on the reliability of the inverter.

What is Inductor ?

Inductor, converts the electrical energy into magnetic energy for storage. The inductor has similar structured as transformer, but has only one coil winding. An inductor has inductance which prevents the current changes. If there is no current flow, it will attempt to block the current when the circuit is closed. If the inductor has current, it will try to keep the current when the circuit is disconnected. Inductors are also known as CHOKE, reactor, and dynamic reactor.

Inside a conductor

Inductors are generally composed of frame, coil winding, magnetic core or iron core, shielding cover, packaging material, etc. A frame that covers a coil. The enameled wire is wrapped around the support, and then the magnetic core or copper or iron core is put into the cavity of the support to improve its inductance. Coil winding refers to a group of coils with specified functions, which can be divided into single layer and multi-layer. Core materials mainly include silicon steel sheet, permo alloy, ferrite, amorphous, metal magnetic powder core, etc.

What is the role of inductor in inverter?

In a photovoltaic inverter, there are usually 3 kinds of inductors, ac-dc common-mode inductor, booster inductor and filter inductor. The booster inductor and filter inductor are both power inductors and heating devices. Common mode inductor mainly plays the role of EMI filtering, on the one hand to filter out the interference of external common mode electromagnetic to the inverter, on the other hand to suppress the inverter itself not to send out electromagnetic interference, to avoid affecting the normal work of the grid and other equipment in the same electromagnetic environment.

Photovoltaic component is a DC source, it won't produce electromagnetic interference, some inverter manufacturers cancel the inverter dc EMI common-mode inductor for cost control purpose, in fact, as the inverter power switch device speed is very high, it will produce larger commonmode interference electric current, if there is no dc EMI common-mode inductor, the interference current signal will spread to the dc cable and component, the component will work like an antenna, produce electromagnetic interference, affect the normal use of home appliance equipment surrounding the inverter, such as television, radio and other equipment.

In order to improve power generation and optimize system design, series inverters are generally of two-stage structure, a wide input voltage range, with single-phase of 70-550v and three-phase of 200-1000v. Upper level BOOST booster, to configure the BOOST inductor, lower level inverter circuit, to configure the filter inductance, BOOST inductor and filter inductance is power inductors, from the perspective of working current, power inductors throughout its work within the period of relatively large ripple current and high working temperature, the dc bias characteristics of inductance of power demand is high, particularly at high temperature, thus for high power dc bias characteristics of inductance requirement (especially at high temperature), on the one hand, to improve power inductors corresponding ferrite materials of high temperature Bs (saturation magnetic flux density; On the other hand, the iron loss of the power inductor should be reduced, because the loss of the power inductor can account for 20% to 40% of the loss of the photovoltaic system.

Topology of PV Inverter

How to reduce inductor loss in pv inverter?

Iron loss is mainly determined by the characteristics of magnetic materials. In order to reduce iron loss, it is necessary to optimize the selection of materials with good high-frequency loss characteristics. The relationship between the loss of magnetic materials: ferrite < amorphous < ferrosilicon aluminum < ferrosilicon < pure iron powder core. Among all kinds of magnetic materials, iron, silicon and aluminum magnetic powder cores have distributed air gap, large saturation magnetic induction intensity, wide constant magnetic permeability, high Curie temperature, extremely low loss at high frequency, nearly zero magnetostrictive coefficient, and moderate price, making them the best choice for photovoltaic inverter power inductors.

Sendust cores advantages: reasonbale cost, better than molybdenum permo alloy/high magnetic flux and composite alloy; Lower loss, better than iron powder core; Higher saturation, better than gap ferrite; Near zero magnetostriction, better than iron core; No heat aging phenomenon, better than iron powder core; Soft saturation, better than ferrite and composite alloy.

Sendust cores disadvantages:like all powder metallurgy materials, sendust cores also need binder, compared with silicon steel sheet, there is aging cracking, capacity loss at high temperature, large current noise and other shortcomings, in order to overcome these shortcomings, generally adopt inductance pouring process.

What are the advantages of patented inductance pouring technology?

Inductance pouring: it is divided into several processes, such as aluminum profile assembly, inductance assembling, initial measurement, thermal conductivity silica gel pouring, curing, final measurement, and overall package wiring harness finishing, which increases the material cost by more than 30% and the labor cost by 50%.The inductor installed as a whole is installed behind the inverter. Compared with the inductor installed inside the inverter,

There are three advantages:

1. The thermal conductivity of air is 0.023w /mk, the thermal conductivity of aluminum is 160w /mk, and the thermal conductivity of silica gel is about 1.2w /mk. The inductance of the grouting process is equivalent to the expansion of heat dissipation area by 3-4 times, and the heat dissipation speed is increased by more than 10 times.

2. Since inductance is the second heating component of the inverter, inductance and PCBA board are installed separately, heat will be directly distributed to the outside, and the internal temperature of the inverter will not be increased. Avoid inverter other components such as capacitor, chip, sensor temperature rise and performance is affected, reduce the life.

3. By using the silicone and aluminum shell double seal, can reduce the noise of the inductor. The inductor is fixed on the inverter frame, which can reduce the vibration of the inverter during transportation and installation.

Inductor is the key component in photovoltaic inverters. The selection and installation of inductors have a direct impact on the reliability of the inverter. Tiger Magnetics insists on adopting patented inductor gluing technology to ensure the long-term reliable and stable operation of the inverter in its life cycle, thus guaranteeing the protection of the majority of customers' photovoltaic power stations.

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