Thermal design for the photovoltaic inverter

  Photovoltaic inverter is a very critical device for photovoltaic systems. The main role of the photovoltaic system is to turn the DC electricity generated by photovoltaic components into AC power. In addition, the inverter also undertakes the detection of components, power grid, cable operation status, communication and communication with the outside world, system security management and other important functions.In the photovoltaic industry standard NB32004-2013, the inverter has more than 100 strict technical parameters, and the photovoltaic system can't get the certificate until each parameter is qualified.

  A new inverter, from design to mass production, it takes more than two years to launch. In addition to over loaded voltage protection, the inverter also has many functions such as leakage current control, cooling control, thermal Design, electromagnetic compatibility, harmonic suppression, efficiency control, etc., need to invest a lot of resources to develop and test.

  1. Why should the inverter dissipate heat

  In the winter season, many people are worried about whether the inverter would be frozen. In fact, there are few inverters that are frozen. The most critical problem with the inverter is the problem of overheating. The BCC reports that most of the current failure of most electronic products is due to the bad cooling system, but the reliability of electronic devices is very sensitive to temperature. For every 1 degree increase in device temperature from the 70-80 degree level, reliability decreases by 5%.Too high temperature will shorten the inverter life and affect the reliability of the inverter.

  2, several methods of inverter cooling

The cooling system accounts for about 15% of the inverter's hardware cost, it mainly includes radiators, cooling fans, thermal grease and other materials, at present, there are two main types of inverter cooling modes: one is natural cooling, the other is forced air cooling.

  (1) Natural cooling

  This cooling method refers to the purpose of achieving local cooling to the surrounding environment without using any external auxiliary energy, which usually contains three main heat transfer methods: heat conduction, convection and radiation, of which Displaying flow of natural and flowing methods, natural cooling is often applicable to low power devices and components with low temperature control requirements and low heat flow density of device, as well as sealing or densely assembled devices. Under the circumstances of other cooling technology. At present, most manufacturers can use natural cooling in single phase inverters and three phase inverters below 30kW. A small number of manufacturers' 100kW three -phase inverters can also use natural cooling solution.

（2) Forced air cooling

  This cooling method for is to use the device to create a air flow such as fan and other compulsory devices, so as to take away the heat generated by the device. This method is a simple and excellent. If the space between the components in the component is suitable for air flow or is suitable for installing a local radiator, you can use this cooling method as much as possible. To improve the thermal performance, we need to increase the heat dissipation area and produce a relatively large air flow on the heat dissipation surface. Increasing the heat dissipation area on the surface of the radiator to improve the cooling performance of electronic components, it has been widely used in many industries. The project is mainly used to expand the heat dissipation area on the surface of the radiator to achieve the purpose of strengthening heat transfer. The selection of the radiator itself has a direct relationship with its cooling performance. At present, the material of the radiator is mainly made of copper or aluminum.

  （3) Comparison of two cooling methods

  Natural cooling method without fans, so it has low noise, but slow cooling efficiency, generally used for low-power inverters, forced air cooling should be configured with fans, it has some noise, but fast cooling efficiency, generally used for high-power inverters, in medium-power cluster inverters, both methods are available.

 Through the comparison of the cooling performance of the group -type inverter, it is found that in the group -type inverter above the 50kW power level, forced air cooling is better than the natural cooling, the internal capacitor of the inverter, IGBT and other key components. the temperature can decrease about 20 ° C which can ensure the efficient work of the inverter, and the temperature of the inverter using a natural cooling method the temperature will increase rapidly, and the working performance would be impacted.Forced air cooling uses high -speed fans and medium -speed fans. Using high -speed fans can reduce the volume and weight of the radiator, but it will increase noise, the fan life is relatively short. At low power, the fan does not turn, and the fan runs at low speed at the medium power. In fact, the inverter's full power running time is not much, so the life of the fan can be very long.