Regarding variable-frequency speed control
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The last edit to this post was made by Bālínghòu de Hàozi on 2012-4-27 at 15:57. The project includes a methanol injection pump, and the amount of methanol injected each year varies (as determined by the process engineering team); in the PID control system, this pump is designated as a variable-frequency pump. The process engineering team says that it’s difficult to select an appropriate signal for frequency conversion (in previous projects, one of pressure, flow rate, or liquid level was generally used as the signal for frequency conversion). They are asking us in the electrical engineering team whether it’s possible to control the speed regulation based on the calculated annual amount of methanol to be injected. Is this feasible? Please provide some guidance
Yes, the PID control method of frequency converters can be used to meet the requirements mentioned by the poster；
The last edit to this post was made by Bālínghòu de Hàozi on 2012-4-27 at 18:22. Could you provide more detailed information? What exactly is the PID control method used in frequency converters, and how should we proceed with its use?
In fact, the amount of methanol injected is also reflected in changes in flow rate; therefore, flow rate regulation via frequency conversion is used to achieve this. For reference
I don’t know why, but the people in our engineering team say it’s difficult to obtain the flow rate signal
What the original poster said isn’t very clear. Frequency conversion can be controlled using PID based on feedback signals, but since you’re emphasizing empirical values here, fixed-frequency control is possible – the frequency output can be adjusted according to monthly or annual variations
I think that’s what is meant by ‘process control’. Based on process calculations, the amount of methanol to be injected changes from year to year; under normal conditions it remains relatively constant. Therefore, they hope to use the amount of methanol that can be calculated based on the existing parameters as a signal to control the speed (frequency) of the motor, rather than using an input signal from the pipelines on site to drive the frequency converter. I’m not sure whether the frequency converter is capable of doing this, so I’d like to ask everyone for their opinions
Two interpretations: In one approach, the production control of the process is entirely digital; the flow rate is regulated by electric proportional control valves to control the amount of methanol required during production. The digital model used to control this electric proportional control valve is also input into the water pump controller; the water pump controller module then calculates the amount of methanol required for actual production. Based on the operating characteristics of the water pump, it automatically adjusts the pump’s speed, thereby achieving digital control. Another approach: The process flow rate requirements are met by adjusting valves to satisfy the methanol demand of the production process. We usually use pressure-based parameters, but calculators can be used to compare previous flow rate data and production processes, thereby making adjustments for proportional control and fulfilling the process requirements more effectively.