FI126051B - Method for optimizing valve position and pump speed in a valve system with PID control without using external signals - Google Patents

Description

Method for Optimizing Valve Position and Pump Speed in a PID Control Valve System Without Using External Signals

Reference to relevant applications

The present application claims a benefit for Advance Patent Application Serial No. 60 / 780,547, filed March 8, 2006, the disclosure of which is incorporated herein by reference. The application also relates to and claims a benefit under Patent Application Serial No. 11/636 355 (05GI003US / 911-2.24-2), filed December 8, 2006, entitled "Method for determining pump flow without the use of traditional sensors," and Patent Application Serial No. 11/601 373 (05GI002 / 911-2.22-2), entitled "Method and Apparatus for Pump Protection Without the Use of Traditional Sensors", filed November 17, 2006, the entirety of which is also incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a pump, including a centrifugal pump, and more particularly to a method and apparatus for optimizing valve position and pump speed in a PID control valve system without the use of external signals.

2. Brief Description of the Prior Art

Other similar devices and their shortcomings are as follows: PCT WO 2005/064167 A1, entitled "Quantitative Measurement", by Witzel, Rolf et al., Discloses a methodology using a calibrated power / pressure versus flow versus velocity. Calibrated data is stored and compared to current values to determine pump flow. While this technique is capable of monitoring pump power and differential pressure values to predict flow from a calibrated pump curve at different speeds, it is unable to search for optimal pump speed and valve position in the PID control valve system.

U.S. Patent No. 6,591,697 to Henyan, entitled "Method for Determining Pump Flow Rates Using Motor Torque Measurements," discloses a method of explaining torque and velocity versus pump flow rate and the ability to control pump flow using a Variable Frequency Drive (VF). adjust the speed of the centrifugal pump. While this technique is capable of monitoring the torque-to-velocity versus pump flow rate and can control the pump flow using a frequency drive (VFD) to control the centrifugal pump speed, it is unable to find the optimum pump speed and valve position in the PID control valve.

U.S. Patent No. 6,464,464 B2 to Sabin et al., Entitled "Apparatus and Method for Controlling a Pump System", discloses a methodology that explains a control and pump protection algorithm, uses a VFD to control the flow, pressure, or speed of a centrifugal pump. While this technique is capable of controlling flow or pressure through a PID control loop embedded in a frequency drive (VFD) using feedback from an external transmitter, it cannot search for optimal speed and control valve position in the PID control valve system.

Summary of the Invention

In a broader sense, the present invention provides a method according to independent claim 9 and an apparatus according to independent claim 1 for determining flow reference data as a function of motor parameters such as speed, torque or power, or for controlling a centrifugal mixer or centrifugal compressor in a PID control valve system. The apparatus may take the form of a controller or other process device suitable for controlling the operation of a controller.

In fact, the present invention overcomes the drawbacks of the above-mentioned prior art pumping system devices that use a PI D control valve to log process to control a process where input of valve data / positioning or other external signals is undesirable. The algorithm of the present invention applies flow comparison information that can be mathematically determined as a function of various pump and motor parameters such as speed, torque or power, or from calibrated flow curves stored in an estimator, or from an external flow reference such as a flow meter.

Embodiments of the present invention may include one or more of the following: When the PI D control valve i i i has reached a constant condition at its constant, the calculated flow value may be stored and compared to the current flow value acquired after the frequency drive has decreased at frequency (velocity). For pressure control applications, the valve position can be optimized if the current flow is within the range of 90 to 110% of the flow of the best pump efficiency at the current speed. The final check can be performed for a fully open control valve state by increasing the pump speed by a set amount and comparing the current flow value with the stored flow rate, and if no flow increase is achieved, the valve position is optimized. If the controller has already reached its optimized state and if either the actual engine torque increases by 5% or more, or the actual flow increases by 5% or more over a delay period, the valve optimization process can be restarted at maximum speed. Alternatively, if the controller has already reached its optimized state and if either the actual engine torque is reduced by 5% or more, or the actual flow is reduced by 5% or more, the valve optimization process can be restarted at the current operating point. An additional fully open valve check may be provided by the user if the actual torque variation of the engine is 2% or more but less than 5% of the optimized state for the response delay period and if the condition is true and actual flow is greater than the optimized flow value can be restarted at maximum speed. Further, the position of the valve may be optimized just before the rate threshold, where the flow condition of the algorithm is no longer true, or just before the minimum speed is reached if the flow condition is still true, alone or in combination with one or more of the above features.

Description of the drawing

Figure 1 is a block diagram of a basic pump system according to the present invention.

Figure 2 is a flowchart of the basic steps performed by the controller shown in Figure 1 in accordance with the present invention.

Fig. 3 is a block diagram of the controller shown in Fig. 1 having one or more modules configured to perform the basic steps shown in Fig. 2.

Figure 4 shows a flow chart of a process variable set in accordance with the present invention.

Figure 5 shows a flow diagram of the constant pressure control applications of the present invention.

Detailed Description of the Invention

Figure 1 illustrates the basic pump system of the present invention, generally designated by reference numeral 2, having a controller 4, a motor 6 and a pump 8. In use, and according to the present invention, the controller 4 provides flow reference data as a function of various pump and motor parameters or power, or from calibrated flow curves stored in the estimator (not shown), or from an external flow reference such as a flow meter (not shown), and the use of flow reference data to adjust pump 8, consistent with and illustrated herein.

Figure 2 illustrates, by way of example, a flowchart generally designated 10, showing the basic steps 10a and 10b of the pump flow determining algorithm, which may be implemented by the controller 4 of the present invention. . The flow determining algorithm may be embedded in a frequency drive or a programmable logic controller, such as controller 4 of Figure 1, in connection with the above.

Figure 3: Controller 4

Figure 3 shows the basic modules 4a, 4b, 4c of the controller 4. Many types and types of controllers and control modules for controlling pumps are known in the art. Based on their understanding of such known controllers and control modules, one skilled in the art would be able to implement control modules such as 4a, 4b and configure them to perform functionality consistent with that described, including determining flow reference data as a function of various pump and motor parameters calibrated flow curves stored in the estimator (not shown), or an external flow reference such as a flow meter (not shown), and the use of flow comparison data to adjust pump 8, as shown in Figure 1 and described above, in accordance with the present invention. The estimator, and / or the flow meter may be included in, or be part of, said one or more modules 4a, 4b, or any combination thereof.

For example, the functionality of modules 4a, 4b may be implemented using hardware, software, silicon software, or a combination thereof, although the scope of the invention is not intended to be limited to any particular embodiment thereof. In a typical software implementation, such a module would be one or more microprocessor-based architectures having a microprocessor, random access memory (RAM), read only memory (ROM), input / output devices, and combining control, data, and address buses. One skilled in the art would be able to program such a microprocessor-based implementation to perform the functionality described herein without undue experimentation. The scope of the invention is not intended to be limited to any particular implementation using known technology or to be developed in the future.

Controller 4 has other controller modules 4c known in the art which do not form part of the underlying invention and are not described in detail herein. Other control modules 4c may, for example, include such an estimator and / or such a flow meter. Such estimators for recording flow curves and / or flow meters for providing external reference data are further known in the art and are not described in detail herein. Furthermore, the scope of the invention is not intended to be limited to any particular type or quality of the known or to be developed in the future. Embodiments are shown, in which also the estimator and / or the flowmeter are included, or form part thereof, in said one or more control modules 4a, 4b.

Engine 6 and pump 8

The motor 6 and pump 8 are known in the art and are not described in detail here. In addition, the scope of the invention is not intended to be limited to any particular type or quality known to it or to be developed in the future. Still further, the scope of the invention is also intended to include the use of the technique of the present invention in controlling the operation of a centrifugal pump, centrifugal mixer, centrifugal fan or centrifugal compressor.

Implementation

Today, there are many processes that operate with a fixed speed centrifugal pump control valve in combination with a PID controller. In the arrangement, the control valve is throttled to maintain the process reference using feedback from the external process transmitter and PID logic of the DCS (Distributed Control System), PLC (Programmable Logic Controller), or other loop control device. In many cases, the pump is oversized and the cost of throttling the valve can be high in terms of energy consumption. In addition, if the fixed speed pump is used further away from its best efficiency flow, the radial and axial loads of the pump will increase. These higher loads can adversely affect the life of bearings and gaskets and serve to reduce system reliability, which can lead to unplanned maintenance of equipment. Unscheduled maintenance costs include equipment repairs, production interruptions, and / or environmental cleanup.

Thus, it is advantageous to use a system in which the pump speed can be reduced so that valve throttling is minimized and the pump can operate as close as possible to its best efficiency flow.

Many users want the benefits of lower operating costs and greater system reliability, but do not want to make any changes to their control logic or provide external inputs. The invention solves this by using a Variable Speed Controller (VFD) and control logic in an effort to optimize both pump speed and control valve position without any changes to the external control logic of the control valve. The invention also seeks to accomplish this without using external inputs. The logic is as follows: VFD inputs to logic include: - maximum pump speed, - minimum pump speed, - motor torque, and - motor power.

In one form, the logic applies computed flow data that can be mathematically determined from various pump and motor parameters such as speed, torque or power, or from calibrated flow curves stored in the estimator. In practice, however, this logic could be pursued using some controller operating parameter that has a direct or quasi-linear relationship to the flow of the pump. In addition, while logic emphasizes functionality without any external process signal, a direct flow reading (from a flow meter) could also be used. The logic can be incorporated into either a Frequency Drive (VFD) or a Programmable Logic Controller (PLC).

Figure 4 shows a flow chart generally designated 50 for a process variable set to constant flow control, and Figure 5 is for constant pressure control applications.

There are three steps to the valve optimization process:

Step 1 - The pump system starts up and steps to maximum speed. A check is made to ensure that the pump is not operating at zero flow - a potentially hazardous condition. If enabled at zero flow, the user can optionally shut down (close) the unit or send a warning to the operator. If flow is detected, the process moves to the next step after waiting for one minute for the PID control valve to respond.

Step 2 - The valve optimization process begins when the PID control valve has reached the maximum pump speed setpoint, after a one minute delay period. The current flow value is stored as Q1. Follow-up pump is gradually decelerated by user adjustable speed increments at user adjustable stepping speed. When the (user adjustable) response delay has occurred to allow the control valve to reset the setpoint, a check is provided to compare the current flow to Q1. If the flow is constant (constant flow only) or the flow is increased or equal (constant pressure only), the rate reduction is iterated until either the pump minimum speed is reached or the flow is reduced (constant flow only). If the flow is reduced, the logic slightly increases the speed by a 1/4 speed increment until the current flow is equal to or greater than the flow Q1 before proceeding to step 3. This is important in applications with high static elevation. In pressure control applications, a check is made to see if the actual flow in the range is 90 to 110% of the best efficiency flow, the flow value is less than Q1, or the minimum speed is reached before proceeding to step 3.

Step 3 - The purpose of step 3 is to make sure that the control valve is not fully open. If the condition is "green", the pump speed and valve position are considered optimized. If the change in engine torque or flow is> + 5% over the optimized values over a response delay, it is determined that an increase in the reference has occurred and the valve optimization process is restarted at maximum speed. If the change in motor torque or flow is> + 5% of optimized torque or flow, it is determined that the setpoint has been reduced and the valve optimization process begins at step 2. In some applications, the user can increase the setpoint when the control valve is almost open. This may not cause the following> 5% change in engine torque. The condition is available for the user to select a feature to check for a fully open valve condition if engine torque has changed> +2% (but less than 5%).

It should also be noted that while the logic presented here uses calculated flow values, the flow could also be replaced by torque or power values. The logic constantly checks for dry running, minimum flow (flow too low) or run modes (flow too high) via the calculated flow value and either warns the user or closes the unit and sets the alarm to zero or automatically resets the unit (if configured) via pum red protection logic, filed in U.S. Patent Application Serial No. 60 / 780,529 (05GI002 / 911-2.22-1) filed March 8, 2006, and in Regular Patent Application No. 11/601 373 (05GI002 / 911-2.22-2), filed November 17, 2006 , both of which are referred to herein.

Other possible applications

Existing systems that use a control valve where the reference value is achieved by throttling the valve, normally at a fixed engine speed. The logic embedded in the VFD or PLC would allow optimization of pump speed and control valve position, reducing operating costs and increasing system reliability.

Scope of the Invention

It should be understood, unless otherwise stated, that some of the features, features, alternatives, or modifications described herein with respect to a particular embodiment may also be applied, utilized or incorporated with another embodiment described herein. In addition, the drawings herein are not drawn to scale.

While the invention has been described and illustrated in connection with exemplary embodiments thereof, the foregoing and various other additions and deletions may be provided without departing from the spirit and scope of the present invention.

Claims (16)

A control unit comprising at least one or more modules configured to determine flow reference data as a function of such various pump and motor parameters, such as speed, torque or power, or from calibrated flow curves stored in a rating device, or from an external flow reference such as a flow meter, characterized in that the control unit comprises at least one module configured for use of flow reference data to control a centrifugal pump driven by a controllable frequency drive, a centrifugal fan, a centrifugal mixer or a centrifugal compressor in a PID control system, which control unit, when the valve system's PID control valve has reached its steady state normal state, stores the calculated flow value and is compared with the current flow value obtained after the adjustable frequency drive has decreased in frequency (speed). A control unit according to claim 1, wherein the valve position is optimized just before the speed threshold, where an algorithm's flow condition is no longer true. Control unit according to claim 1, wherein the position of the valve is optimized just before the minimum rotation speed is reached, if the flow condition is still true. Control unit according to claim 1, wherein in pressure control applications the valve position is optimized if the current flow is in the range 90-110% of the pump's best efficiency flow at the current speed. The control unit of claim 1, wherein the final check is performed for a fully open control valve condition by increasing the pump speed by a specified amount and comparing the current flow value with the stored flow value, and if an increase in flow is not present, the valve position is optimized. A control unit according to claim 1, wherein, if the control unit has already achieved its optimized state, and if either the actual torque of the motor is increased at least 5% or the actual flow increases at least 5%, for a longer time than a delay period, a process which optimizes the valve again at maximal rotation speed. The control unit according to claim 1, wherein, if the control unit has already achieved its optimized state, and if either the actual torque of the motor decreases at least 5%, or the actual flow decreases at least 5%, the process which optimizes the valve is started again at the current operating point. 8. A control unit according to claim 1, wherein an additional inspection of a fully open valve is carried out at the choice of the user, if the change in the actual torque of the engine is at least 2% and at most 5% of the optimized condition during a response delay period, and if this condition is true and the actual flow is greater than the optimized flow value after the change in speed increase, the optimization process is restarted at maximum rotation speed. The method comprising steps in which flow reference data is determined as a function of such various pump and motor parameters as speed, torque or power, or from calibrated flow curves stored in a rating device, or from an external flow reference such as a flow meter, characterized in that flow reference data for controlling a centrifugal pump, a centrifugal fan driven by an adjustable frequency drive, a centrifugal mixer or a centrifugal compressor in a PID control valve system, in which the control unit, when the valve system's PID control valve, has reached its steady state, is normally controlled and is compared with the current flow value, which has been obtained after the adjustable frequency drive has dropped in frequency (speed). The method of claim 9, wherein the valve position is optimized just before the velocity threshold, where an algorithm's flow condition is no longer true. A method according to claim 9, wherein the position of the valve is optimized just before the minimum rotation speed is reached, if the flow condition is still true. The method of claim 9, wherein in pressure control applications, the valve position is optimized if current flow is in the range of 90-110% of the pump's best efficiency flow at current speed. The method of claim 9, wherein the final check is performed for a fully open control valve condition by increasing the pump speed by a specified amount and comparing the current flow value with the stored flow value, and if an increase in flow is not present, the valve position is optimized. A method according to claim 9, wherein, if the control unit has already achieved its optimized state, and if either the actual torque of the motor increases at least 5%, or the actual flow increases at least 5%, for a longer period than a delay period, the process which optimizes the valve again at maximum rotational speed. The method of claim 9, wherein, if the control unit has already achieved its optimized state, and if either the actual torque of the motor decreases by at least 5%, or the actual flow decreases by at least 5%, the process which optimizes the valve is started again at the current operating point. The method of claim 9, wherein an additional examination of a fully open valve is selected by the user, if the change in the actual torque of the motor is at least 2% and at most 5% of the optimized state during a response delay period, and if this condition is true. and the actual flow is greater than the optimized flow value after the change in velocity increase, the optimization process is restarted at maximum rotation speed.