Application of Perturbation Theory to Static Load Testing of Cylinder Loads

Application of Perturbation Theory to Static Load Testing of Cylinder Loads

1. Structure of Cylinder Loads

Cylinder loads are widely used for load testing of solar modules due to their ease of operation.

The structure of the cylinder load is as follows: 

In the figure, 1 is the cylinder or hydraulic cylinder, 2 is the solar module, 3 is the control system, 4 is the piston, 5 is the pulling pressure sensor, 6 is the suction cup, 7 is the air compressor, 8 is the inflating valve group, 9 is the flow control valve, 10 is the vacuum valve, and 11 is the vacuum generator.

The control method is as follows:

Turn on the air compressor, the control system controls the on-off condition of the inflatable valve group, the upper air port A on the cylinder inflates and the lower air port B deflates, the piston applies the pressure to the solar module downward through the suction cups, and the control system receives the magnitude of the pressure from the pull pressure sensor, and the control system controls the flow rate control valve so that the pressure reaches the target value.

2. Static overshoot phenomenon of cylinder load

However, in reality, due to the difference between the dynamic friction and static friction of the cylinder piston, especially after the deformation of the component, the verticality of the cylinder is affected, resulting in increased friction, the control value of the flow control valve can not be transferred in time to the pulling pressure sensor, the value of the pulling pressure sensor generates a serious hysteresis, the pulling pressure can not be correctly controlled, overshoot phenomenon occurs, or even damage to the component.

Examples are as follows:

The set value is 2400Pa, and the actual value jumps from 2330Pa, which is lower than 2400Pa, to about 2800Pa instantly, exceeding the standard requirement of ±100Pa.

3. Problem solving

Zealwe Tech adopts the control method of combining industrial controller and PLC, and uses the perturbation theory to remove the problem of lagging response of tensile pressure sensor due to cylinder friction.

Perturbation theory is commonly used for MPPT tracking in solar power plants. We applied this theory to the static load control of the cylinder load and achieved good results.

3.1 Perturbation theory

The perturbation-observation method based on the “mountain-climbing principle” is the main method, which takes scanning as the basis of perturbation, and the magnitude of the value of the adjacent two calculated tensile pressure values as the basis of judging the direction of the perturbation of the flow valve pressure, which is in fact a self-seeking optimal control process.

The program flow chart of the perturbation-observation method is shown below, UREF is the barometric pressure given signal, and △P is the barometric pressure perturbation step. Applying a certain magnitude of perturbation to UREF, the air pressure has a certain degree of change, which reacts to the pulling pressure and produces a change. If the pull pressure does not reach the target value, keep the perturbation direction unchanged in the next cycle, otherwise make the perturbation direction opposite to the current cycle.

3.2 Effect of the application of perturbation theory

Through the application of perturbation theory, the pressure can be precisely controlled, no more overshoot phenomenon, and the uniformity is controlled within 0.5%.

Introduction to the author Binwei Gu

With more than ten years of technical precipitation in the electrical industry, he has specialized in the R&D and application of photovoltaic technology in recent years. After joining Zealwe Tech, he is mainly responsible for the electrical design of PV physical testing equipment, and has successively completed the electrical design and debugging of equipment for crushing, hail, stripping, lead end and mechanical load.

During this period, he encountered a lot of problems and issues, through his own unremitting efforts and the support and help of the company team, and finally successfully solved these difficulties and problems.

There are many hardships along the way, but with the support of the team there is a constant flow of power to help me grow and move forward. I believe that our equipment will be more perfect, to provide customers with more quality service.

Zealwe Tech: PV Lab turnkey solution for IEC61215, IEC61730

Zealwe Tech Co., Ltd. was founded in May 2012, as a high-quality photovoltaic industry PV laboratory turnkey project and special test equipment suppliers, the products are mainly used in  module aging test. Our products are mainly applied to module aging test, including environmental chamber and power supply equipment, steady state light aging chamber, UV chamber, mechanical load test equipment, hail test equipment, etc. Covering all the equipments of IEC61215, IEC61730 and other photovoltaic module standards.

It has the qualification of Shanghai High-tech Enterprise, Specialized and Specialized New Enterprise, with 8 invention patents, 14 utility model patents and many software copyrights, and the enterprise credit reaches AAA grade.