Water pump operation method, water pump control device, air compression system

Abstract

This invention provides a method for operating a water pump, a control device for a water pump, and an air compression system that enable highly efficient operation of water pumps used in applications where pressure is constantly changing. [Solution] A method for operating a water pump 16 that supplies water into a compression tank 12 in order to compress the air in the compression tank 12, wherein the rotational speed of the water pump 16 is controlled so that the efficiency of the water pump 16 is maximized regardless of the increase in the air pressure, thereby increasing the air pressure to a target value.

Description

Technical Field

[0001] The present invention relates to an operation method of a water pump suitable for supplying water to a region with a large pressure change such as a compressed air tank of air, a control device of the water pump, and a pneumatic compression system provided with the same.

Background Art

[0002] Conventionally, water pumps used for pumping water and the like are known. A common method of boosting pressure by a water pump is to operate at a constant pressure not exceeding the pump rated pressure and supply a constant flow rate.

[0003] On the other hand, an air compression device that compresses air (for example, refer to Patent Document 1), and CAES (Compressed Air Energy Storage) technology that stores electrical energy as compressed air are known.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Regarding the CAES technology described above, the patent applicant has developed an isothermal air compression system that compresses air isothermally. This system comprises a compression tank capable of storing a mixture of water and air, a water tank for storing water, and a water pump for supplying water from the water tank to the compression tank. The system isothermally compresses the air in the compression tank by raising the water level in the compression tank with the water supplied by the water pump (water piston). Thus, this system uses a water pump in the water-assisted air pressurization process. In normal processes, including water pumping, water pumps are rarely used with variable pressure except during transient states such as startup and shutdown, but in this system, the water pump's pressure changes are constant. If the rotational speed (rotational speed) of this water pump is fixed, the following problems (1) and (2) arise.

[0006] (1) If the rotation speed is reduced, the water flow rate will be insufficient when the air pressure is high, and the required pressure will not be reached. (2) To avoid the above (1), the rotation speed can be increased, but if the air pressure is low, the water flow rate will be excessive, so the water flow rate must be restricted by a throttle valve or other means (or restricted by the piping) to prevent the water pump from being overloaded, which will result in significant losses.

[0007] To solve these problems, there was a need to operate water pumps efficiently under conditions where pressure fluctuations are constant.

[0008] The present invention has been made in view of the above, and aims to provide a method for operating a water pump, a control device for a water pump, and an air compression system that can operate a water pump used in applications where the pressure is constantly changing with high efficiency. [Means for solving the problem]

[0009] To solve the above-mentioned problems and achieve the objective, the water pump operation method according to the present invention is a method for operating a water pump that supplies water into a compression tank in order to compress the air in the compression tank, characterized in that the rotational speed of the water pump is controlled so that the efficiency of the water pump is maximized regardless of the increase in the air pressure, thereby increasing the air pressure to a target value.

[0010] Another operating method according to the present invention is an operating method for a water pump that supplies water into a compression tank to compress air in the compression tank, characterized in that the rotational speed of the water pump is controlled so that the efficiency of the water pump is optimized regardless of the increase in air pressure, based on the amount of power and time required for the water pump to pressurize the air and a weight corresponding to the relative importance between the amount of power and time set in advance, thereby increasing the air pressure to a target value.

[0011] Furthermore, another operating method according to the present invention is characterized in that, in the invention described above, the rotational speed of the water pump is set based on the detected value of the water pump pressure or the detected value of the air pressure and the difference between the detected value and the set value of the water flow rate, and the water pump is controlled based on this rotational speed.

[0012] Furthermore, the water pump control device according to the present invention is a water pump control device that supplies water into a compression tank to compress air in the compression tank, and is characterized in that it controls the rotational speed of the water pump so that the efficiency of the water pump is maximized regardless of the increase in the air pressure, thereby increasing the air pressure to a target value.

[0013] Furthermore, another control device according to the present invention is a control device for a water pump that supplies water into a compression tank to compress the air in the compression tank, characterized in that it controls the rotational speed of the water pump so that the efficiency of the water pump is optimized regardless of the increase in air pressure, based on the amount of power and time required for the water pump to pressurize the air and a weight corresponding to the relative importance between the amount of power and time set in advance, thereby increasing the air pressure to a target value.

[0014] Furthermore, another control device according to the present invention is characterized in that, in the above-described invention, the rotational speed of the water pump is set based on the detected value of the water pump pressure or the detected value of the air pressure and the difference between the detected value and the set value of the water flow rate, and the water pump is controlled based on this rotational speed.

[0015] Furthermore, the air compression system according to the present invention is characterized by comprising a compression tank, a water pump that supplies water into the compression tank to compress the air in the compression tank, and a control device for the water pump described above. [Effects of the Invention]

[0016] According to the water pump operation method of the present invention, a water pump is operated by supplying water into a compression tank to compress air in the compression tank, and the rotational speed of the water pump is controlled so that the efficiency of the water pump is maximized regardless of the increase in the air pressure, thereby raising the air pressure to a target value. This method has the effect of enabling highly efficient operation of a water pump used in applications where the pressure is constantly changing.

[0017] Furthermore, according to another operating method of the present invention, in an operating method for a water pump that supplies water into a compression tank to compress the air in the compression tank, the rotational speed of the water pump is controlled so that the efficiency of the water pump is optimized regardless of the increase in air pressure, based on the amount of power and time required for the water pump to pressurize the air and a weight corresponding to the relative importance between the amount of power and time set in advance, thereby raising the air pressure to a target value. This has the effect of enabling operation that can be adapted to the conditions of a water pump used in applications where the pressure is constantly changing.

[0018] Furthermore, according to another operating method of the present invention, the rotation speed of the water pump is set based on the detected value of the water pump pressure or the detected value of the air pressure, and the difference between the detected value and the set value of the water flow rate, and the water pump is controlled based on this rotation speed. By controlling the rotation speed according to the pressure and flow rate, it is possible to avoid a sudden decrease in flow rate when the pressure rises, and it is possible to continue supplying water at a predetermined flow rate without large fluctuations in flow rate.

[0019] Furthermore, the water pump control device according to the present invention is a water pump control device that supplies water into a compression tank to compress the air in the compression tank, and controls the rotational speed of the water pump so that the efficiency of the water pump is maximized regardless of the increase in the air pressure, thereby raising the air pressure to a target value, and thus has the effect of enabling highly efficient operation of a water pump used in applications where the pressure is constantly changing.

[0020] According to another control device of the present invention, it is a control device for a water pump that supplies water into the compression tank to compress the air in the compression tank. Based on the required power consumption and required time of the water pump for increasing the pressure of the air, and the weight according to the relative importance between the preset required power consumption and required time, the rotational speed of the water pump is controlled so that the efficiency of the water pump becomes optimal regardless of the increase in the pressure of the air, and the pressure of the air is increased to the target value. Therefore, it is possible to achieve an operation according to the situation of the water pump used in applications where the pressure always changes.

[0021] According to another control device of the present invention, based on the detected value of the pressure of the water pump or the detected value of the pressure of the air, and the difference between the detected value of the flow rate of the water and the set value, the rotational speed of the water pump is set, and based on this rotational speed, the water pump is controlled. Therefore, by controlling the rotational speed according to the pressure and flow rate, it is possible to avoid a rapid decrease in the flow rate when the pressure increases, and it is possible to continue water supply at a predetermined flow rate so that the flow rate does not fluctuate greatly.

[0022] According to the air compression system of the present invention, it includes a compression tank, a water pump that supplies water into the compression tank to compress the air in the compression tank, and the control device for the water pump described above. Therefore, it is possible to operate the water pump used in the air compression system with high efficiency.

Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a schematic configuration diagram showing an embodiment of an operation method of a water pump, a control device of the water pump, and an air compression system according to the present invention. [Figure 2] FIG. 2 is a diagram showing an example of a characteristic curve of a water pump and a rotational speed control curve at optimal efficiency. [Figure 3] FIG. 3 is a diagram showing an example of the relationship between rotational speed, flow rate, and pressure. [Figure 4] FIG. 4 is a diagram showing an example of the relationship between pressure and rotational speed. [Modes for carrying out the invention]

[0024] The following describes in detail, with reference to the drawings, embodiments of the water pump operation method, water pump control device, and air compression system according to the present invention. However, the present invention is not limited to these embodiments.

[0025] As shown in Figure 1, the air compression system 10 according to an embodiment of the present invention comprises a compression tank 12 capable of storing a mixture of water and air, a water tank 14 for storing water, a water pump 16, and a control device 18. The system is used to isothermally compress the air in the compression tank 12 by raising the water level in the compression tank 12 with water supplied from the water pump 16 (water piston).

[0026] The water pump 16 supplies water from the water tank 14 to the compression tank 12 and is installed in the piping 20 connecting the compression tank 12 and the water tank 14. The water pump 16 is driven by a motor 22. When the motor 22 drives the water pump 16, it can pump water from the water tank 14 and send it to the compression tank 12 via the piping 20. The water pump 16 does not pump water against the head, but rather pumps water to compress the air inside the compression tank 12. Therefore, the pressure inside the compression tank 12 increases with the water being pumped, depending on the volume inside the tank. When the water pump is used to pump water to the upper reservoir in pumped-storage hydroelectric power generation, the volume of water in the upper reservoir is usually large, and the water level fluctuation is small relative to the total head, so the pressure fluctuation is small.

[0027] A butterfly-type valve 24 is provided in the piping 20 on the outlet side of the water pump 16. The valve 24 can also limit the amount of water pumped by the water pump 16 and prevent overload operation.

[0028] This air compression system 10 further includes a pressure sensor 26 for detecting the pressure inside the compression tank 12, a pressure sensor 28 for detecting the pressure of the water pump 16, a flow sensor 30 for detecting the flow rate of the water pump 16, and a rotational speed sensor 32 for detecting the rotational speed of the water pump 16. The pressure detection values ​​detected by the pressure sensors 26 and 28, the flow detection values ​​detected by the flow sensor 30, and the rotational speed detection values ​​detected by the rotational speed sensor 32 are transmitted to the control device 18.

[0029] The control device 18 controls the water pump 16 by controlling the rotational speed (rotational rate) of the motor 22 via an inverter. The only parameter that can be directly changed when supplying water with the water pump 16 is the rotational speed of the water pump 16. By changing and controlling the rotational speed of the water pump 16, the flow rate of the water pump 16 and the pressure in the compression tank 12 are indirectly controlled. Specifically, in order to improve responsiveness, the control device 18 sets the rotational speed of the water pump 16 using pressure and flow rate as parameters, and controls the water pump 16 to operate at the set rotational speed. Details of this control method will be described later.

[0030] This air compression system 10 includes a hydroelectric power generation device 34 that generates hydroelectric power using water pressurized with compressed air. The hydroelectric power generation device 34 has a branch pipe 36 that branches off from piping 20 near the compression tank 12 and connects to a water tank 14, a water turbine 38 installed in the middle of the branch pipe 36, a generator 40 that generates electricity by the rotation of the water turbine 38, and a butterfly-type valve 42 installed in the branch pipe 36, and generates hydroelectric power using water supplied from the compression tank 12 to the water turbine 38 via piping 20 and branch pipe 36. Note that the hydroelectric power generation device 34 is not essential to the present invention and can be omitted.

[0031] (Embodiment 1) Next, Embodiment 1 of the control device 18 will be described. In Embodiment 1, the control device is configured to always set the rotational speed at which the energy efficiency of the water pump 16 is maximized in relation to the pressure, and to drive the water pump 16 at this rotational speed. This control considers only the amount of power required from the amount of power and time required for the water pump 16 to pressurize the air.

[0032] Figure 2 shows an example of a characteristic curve for a water pump. Note that the numerical values ​​for each data point in the figure are examples only and do not restrict the actual numerical range. The horizontal axis represents the flow rate of the water pump, and the vertical axis represents the pressure head. Curve group A shows the relationship between flow rate and pressure when the rotational speed of the water pump is changed to 36%, 98%, and 100%. Curve group B shows the constant efficiency curve of the water pump. Curve C represents a line connecting the operating points where the efficiency of the water pump is highest, along the rotational speed, and can be called the rotational speed control operating curve at optimal efficiency (hereinafter referred to as the optimal speed increase line). As can be seen from curve group A, when the pressure is increased while keeping the rotational speed of the water pump constant, the flow rate decreases sharply as the pressure increases. To avoid this, it is necessary to control the rotational speed according to the pressure.

[0033] Figure 3 shows an example of operating the water pump 16 while sequentially changing its rotational speed (rotational speed), and plotting the measured flow rate and pressure. The horizontal axis represents the flow rate of the water pump 16, and the vertical axis represents the air pressure in the compression tank 12. The optimal speed increase line (curve C) from Figure 2 is superimposed on Figure 3, and optimal operation can be achieved by operating the water pump 16 at the intersection point (marked with a circle in Figure 3) of the rotational speed (rotational speed) curve and the optimal speed increase line in relation to the pressure.

[0034] Figure 4 shows an example plotting the relationship between pressure (marked with a circle in Figure 3) and rotational speed. From the regression line or other approximation lines obtained from this plot, the value of rotational speed (rotational speed) in relation to pressure can be approximately determined. The pressure is determined by the operation of the air compression system 10. The rotational speed is set according to the pressure value so that the efficiency of the water pump 16 is always at its maximum, regardless of pressure increases. The pressure value can be either the pressure detected by the water pump 16 or the pressure detected inside the compression tank 12.

[0035] An example of an approximate formula for calculating the rotational speed set value in relation to pressure while improving responsiveness is shown in equation (1) below. WP.REV.SET is the rotational speed set value of the water pump 16, and WP.PM.PRE is the pressure detected value of the water pump 16. ΔF is the difference between the flow rate detected value WP.FM.PRE and the flow rate set value WP.FM.SET of the water pump 16, where ΔF = WP.FM.PRE - WP.FM.SET. C1, C2, C p , C i is a constant, and t is time.

[0036]

number

[0037] The two right-hand terms on the right-hand side of equation (1) represent the flow rate control elements by PI control. The flow rate is actively controlled by flow rate feedback control, which incorporates the detected flow rate value as a parameter. Note that flow rate control is not limited to linear control such as PI control, and other control methods may be used. Also, the approximation formula for calculating the rotational speed set value is not limited to equation (1), and other approximation formulas may be used.

[0038] The control device 18 controls the water pump 16 based on the calculated rotational speed setting value. When using equation (1), when the pressure rises, control is performed to increase the rotational speed.

[0039] In this way, by constantly setting the rotational speed that maximizes the efficiency of the water pump 16 in relation to the pressure, and controlling the rotational speed according to the pressure and flow rate, it becomes possible to avoid a sudden decrease in flow rate when the pressure rises, and to continue supplying water at a predetermined flow rate range without large fluctuations in flow rate. This allows the air pressure to be raised to the target value. Furthermore, the water pump 16, which is used in applications where the pressure is constantly changing, can be operated with high efficiency. This contributes to reducing energy consumption.

[0040] (Embodiment 2) Next, Embodiment 2 using the control device 18 will be described. In Embodiment 2, considering the power consumption and time required for the water pump 16 to pressurize the air, the control device always sets a rotational speed that balances maximizing the energy efficiency of the water pump 16 with reducing the required time, and drives the water pump 16 at this rotational speed.

[0041] In the above embodiment 1, if the water pump 16 is operated at a rotational speed along the optimal speed increase line, for example, it is possible to operate it at maximum efficiency at all times. However, depending on the actual operating conditions, there may be cases where it is desirable to shorten the operating time even if the efficiency is slightly reduced. For example, this may be the case when it is desired to supply high-pressure air in a short time without increasing the size of the compression tank 12, etc.

[0042] Since improving efficiency and reducing required time are trade-offs, an index E defined by equation (2) below is introduced to enable operation according to the situation, and the water pump 16 is controlled based on index E. The first term on the right-hand side of the value E is the efficiency element term, and the second term on the right-hand side is the time element term. A smaller index E is desirable for the process. In other words, it is desirable for the power required to be small and the required time to be short. α and β in equation (2) are weights, and are numerical values ​​in the range of 0 to 1 that satisfy the relationship in equation (3) below.

[0043]

number

number

[0044] The required power is the amount of power the water pump is expected to need to raise the air pressure from the reference pressure to a predetermined pressure. The rated power is the rated power of the specified water pump 16. The required time is the expected time required for the water pump 16 to supply water and raise the air pressure from the reference pressure to a predetermined pressure. The rated pressurization time is the rated pressurization time of the specified water pump 16. In equation (2), the required power is normalized by the rated power and the required time is normalized by the rated pressurization time, but the rated power and rated pressurization time may be any power and time, respectively.

[0045] α and β are pre-set values ​​that represent the relative importance between the amount of power required and the time required. α and β can be arbitrarily set depending on the operating conditions. When α > β, it means that the amount of power required is given relatively more importance, and when α < β, it means that the time required is given relatively more importance. When α = 1, the control system prioritizes only the amount of power required and ignores the time required, and when β = 1, the control system prioritizes only the time required and ignores the amount of power required.

[0046] The control device 18 calculates index E from the set α, β, required power, rated power, required time, and required boosting time, and sets the rotational speed based on α, β, efficiency element term, and time element term. The above equation (1) can be used to calculate the rotational speed setting value. The control device 18 controls the water pump 16 based on this rotational speed.

[0047] For example, if α=1 and only the efficiency element term is considered, the rotational speed is set using the same optimal acceleration curve as in Embodiment 1 above, so that the efficiency of the water pump 16 is maximized regardless of the pressure increase. On the other hand, if β=1 and only the time element term is considered, the rotational speed is set so that the required time for the water pump 16 is minimized, regardless of the pressure increase, ignoring the efficiency of the water pump 16. In this case, for example, operation can be achieved by operating the water pump 16 at the intersection of the curve of rotational speed (revolutions per minute) and a first straight line obtained by moving the reference straight line (corresponding to the optimal acceleration curve) connecting the circles in Figure 3 by a predetermined amount to the right. It is desirable to set the optimal position for the shortest required time by trial and error with different amounts of movement in prior operation. In the example in Figure 3, the further to the right the reference straight line connecting the circles is shifted, the shorter the required time becomes, but the lower the efficiency. Therefore, to prioritize the required time, shift to the right; to prioritize efficiency, shift to the left.

[0048] When α≠1 and β≠1, the rotational speed is set so that the efficiency of the water pump 16 is optimized regardless of the pressure increase, and the required time is minimized, by considering both the efficiency and time elements. In this case, for example, a second straight line is set between the reference straight line and the first straight line when β=1, and the water pump 16 is operated at the intersection of the second straight line and the rotational speed (rotational speed) curve. It is desirable to determine the optimal position of this second straight line by trying different positions for each combination of α and β during prior operation.

[0049] In this way, by constantly setting a rotational speed that balances the maximization of energy efficiency and the reduction of operating time of the water pump 16 according to the importance of the required power and time, and controlling the water pump 16, it is possible to operate the water pump 16 according to the conditions of applications where the pressure is constantly changing.

[0050] As described above, the water pump operation method according to the present invention is a method for operating a water pump that supplies water into a compression tank to compress the air in the compression tank, and controls the rotational speed of the water pump so that the efficiency of the water pump is maximized regardless of the increase in the air pressure, thereby raising the air pressure to a target value. This makes it possible to operate a water pump used in applications where the pressure is constantly changing with high efficiency.

[0051] Furthermore, according to another operating method of the present invention, in an operating method for a water pump that supplies water into a compression tank to compress air in the compression tank, the rotational speed of the water pump is controlled so that the efficiency of the water pump is optimized regardless of the increase in air pressure, based on the amount of power and time required for the water pump to pressurize the air and a weight corresponding to the relative importance between the amount of power and time set in advance, thereby raising the air pressure to a target value. This makes it possible to operate the water pump according to the conditions of applications where the pressure is constantly changing.

[0052] Furthermore, according to another operating method of the present invention, the rotation speed of the water pump is set based on the detected value of the water pump pressure or the detected value of the air pressure, and the difference between the detected value and the set value of the water flow rate, and the water pump is controlled based on this rotation speed. By controlling the rotation speed according to the pressure and flow rate, it is possible to avoid a sudden decrease in flow rate when the pressure rises, and to continue supplying water at a predetermined flow rate without large fluctuations in flow rate.

[0053] Furthermore, according to the water pump control device of the present invention, a water pump control device that supplies water into a compression tank to compress air in the compression tank controls the rotational speed of the water pump so that the efficiency of the water pump is maximized regardless of the increase in the air pressure, thereby raising the air pressure to a target value, and thus enabling highly efficient operation of a water pump used in applications where the pressure is constantly changing.

[0054] Furthermore, according to another control device of the present invention, a control device for a water pump that supplies water into a compression tank to compress air in the tank controls the rotational speed of the water pump so that the efficiency of the water pump is optimized regardless of the increase in air pressure, based on the amount of power and time required for the water pump to pressurize the air and a weight corresponding to the relative importance between the amount of power and time set in advance, thereby raising the air pressure to a target value. This enables operation according to the conditions of a water pump used in applications where the pressure is constantly changing.

[0055] Furthermore, according to another control device of the present invention, the rotation speed of the water pump is set based on the detected value of the water pump pressure or the detected value of the air pressure, and the difference between the detected value and the set value of the water flow rate, and the water pump is controlled based on this rotation speed. By controlling the rotation speed according to the pressure and flow rate, it is possible to avoid a sudden decrease in flow rate when the pressure rises, and to continue supplying water at a predetermined flow rate without large fluctuations in flow rate.

[0056] Furthermore, the air compression system according to the present invention includes a compression tank, a water pump that supplies water into the compression tank to compress the air in the compression tank, and a control device for the water pump described above, so that the water pump used in the air compression system can be operated with high efficiency. [Industrial applicability]

[0057] As described above, the water pump operating method, water pump control device, and air compression system according to the present invention are useful for water pumps used in applications where the pressure is constantly changing, and are particularly suitable for operating the water pump with high stability. [Explanation of Symbols]

[0058] 10 Air Compression System 12 Compression Tank 14 Water Tanks 16 Water pumps 18 Control device 20 Piping 22 motors 24,42 valves 26,28 Pressure Sensor 30 Flow Sensor 32 Rotation speed sensor 34 Hydroelectric power plants 36 Branch pipes 38 Waterwheels 40 Generators

Claims

1. A method for operating a water pump that supplies water into a compression tank in order to compress the air inside the compression tank, A method for operating a water pump, characterized by controlling the rotational speed of the water pump so that the efficiency of the water pump is maximized regardless of the increase in air pressure, thereby increasing the air pressure to a target value.

2. A method for operating a water pump that supplies water into a compression tank in order to compress the air inside the compression tank, A method for operating a water pump, characterized in that the rotational speed of the water pump is controlled so that the efficiency of the water pump is optimized regardless of the increase in air pressure, based on the amount of power and time required for the water pump to pressurize the air, and a weight corresponding to the relative importance between the amount of power and time set in advance, thereby increasing the air pressure to a target value.

3. A method for operating a water pump according to claim 1 or 2, characterized in that the rotation speed of the water pump is set based on the detected value of the water pump pressure or the detected value of the air pressure and the difference between the detected value of the water flow rate and a set value, and the water pump is controlled based on this rotation speed.

4. A control device for a water pump that supplies water into a compression tank in order to compress the air inside the compression tank, A water pump control device characterized by controlling the rotational speed of the water pump so that the efficiency of the water pump is maximized regardless of the increase in air pressure, thereby increasing the air pressure to a target value.

5. A control device for a water pump that supplies water into a compression tank in order to compress the air inside the compression tank, A water pump control device characterized by controlling the rotational speed of the water pump so that the efficiency of the water pump is optimized regardless of the increase in air pressure, based on the amount of power and time required for the water pump to pressurize the air, and a weight corresponding to the relative importance between the amount of power and time set in advance, thereby increasing the air pressure to a target value.

6. The water pump control device according to claim 4, characterized in that the rotation speed of the water pump is set based on the detected value of the water pump pressure or the detected value of the air pressure and the difference between the detected value of the water flow rate and a set value, and the water pump is controlled based on this rotation speed.

7. An air compression system comprising a compression tank, a water pump that supplies water into the compression tank to compress the air in the compression tank, and a control device for the water pump according to claim 4 or 5.

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