CONTROLLER-INTEGRATED MOTOR PUMP

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a controller-integrated motor pump, and more particularly to a controller-integrated motor pump in which a control unit for controlling a motor based on vector control is integrally incorporated.

2. Description of the Related Art

A motor pump is a pump having a motor as a drive source of the pump. The motor pump is used for various applications. For example, the motor pump is used as a water supply unit for supplying water to a building. Operation of the motor is controlled by a control unit having an inverter. The inverter is configured to increase or decrease a rotational speed of the motor by changing frequency of current supplied to the motor. Vector control, which can provide torque control with excellent response, is known as a motor control method. This vector control is a technique in which the motor current is resolved into a torque current component and an excitation current component and these current components are controlled independently.

However, since an induction motor is used as the pump driving motor, distributed winding, which is provided in the induction motor, could limit downsizing of the motor and reduction in amount of conductive wire used. Consequently, it has been difficult to make the whole motor pump compact and to achieve the integral structure. Furthermore, the induction motor requires supply of excitation energy, which poses a problem in terms of efficiency improvement.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a high-efficiency controller-integrated motor pump.

One aspect of the present invention for achieving the above object is to provide a controller-integrated motor pump. The motor pump includes: a pump; a motor configured to drive the pump; a control unit configured to control the motor; and a discharge-side pressure measuring device configured to measure pressure of fluid at a discharge side of the pump, wherein the control unit is mounted on a motor casing of the motor, wherein the pump includes an impeller secured to a rotational shaft of the motor, and a pump casing in which the impeller is housed, wherein the control unit includes an inverter configured to produce alternating-current power having a frequency within a band that includes frequencies more than or equal to a commercial frequency, a pump controller configured to produce a torque command value for controlling operation of the pump, and a vector controller configured to determine a voltage command value for the inverter based on the torque command value, and wherein the motor has a rotor having a plurality of permanent magnets.

In a preferred aspect of the present invention, the pump controller is configured to perform estimated terminal pressure constant control operation in which a target pressure is calculated such that terminal pressure at an outlet of the fluid pressurized by the pump is kept substantially constant regardless of a discharge flow rate of the pump.

In a preferred aspect of the present invention, the control unit further includes a current detector configured to measure three-phase currents to be supplied from the inverter to the motor. The vector controller includes a three-to-two phase converter configured to convert the three-phase currents into an excitation current and a torque current on a two-phase rotating reference frame, a command converter configured to convert the torque command value into an excitation current command value and a torque current command value, a current controller configured to calculate a d-axis voltage command value for reducing a deviation between the excitation current and the excitation current command value to zero and to calculate a q-axis voltage command value for reducing a deviation between the torque current and the torque current command value to zero, a two-to-three phase converter configured to convert the d-axis voltage command value and the q-axis voltage command value into three-phase voltage command values on a three-phase stationary reference frame, and a phase calculator configured to calculate an angular frequency and a phase of the rotor.

In a preferred aspect of the present invention, the motor is an interior permanent magnet motor in which the plurality of permanent magnets are embedded in the rotor.

In a preferred aspect of the present invention, the control unit further includes: an electric power calculator configured to calculate an electric power input to the motor and to calculate an electric power input to the inverter; an electric power integrator configured to integrate values of the electric power calculated by the electric power calculator to determine electric energy per unit time; and an electric energy display device configured to display the electric energy.

In a preferred aspect of the present invention, the control unit further includes: a carbon dioxide emission calculator configured to calculate an amount of carbon dioxide emission based on the electric energy; and a carbon dioxide emission display device configured to display the amount of carbon dioxide emission.

In a preferred aspect of the present invention, the pump controller includes a memory configured to store a relationship between discharge flow rate and discharge pressure of the pump for maintaining the terminal pressure substantially constant, and the pump controller is configured to calculate the torque command value such that the pressure of the fluid, measured by the discharge-side pressure measuring device, coincides with pressure corresponding to an actual flow rate in accordance with the relationship.

In a preferred aspect of the present invention, the pump controller is configured to perform discharge pressure constant control for maintaining constant discharge pressure of the pump.

According to the present invention, because the permanent magnets compensate for the excitation, the energy for the excitation is not necessary. As a result, the efficiency is improved.

Moreover, because concentrated winding is employed as stator winding, a volume of the winding in its entirety and end winding can be small. As a result, copper loss is reduced and the efficiency is thus improved. Further, the motor can be made compact.

Furthermore, because the variable speed operation in the range of not less than the commercial frequency, in addition to the range of less than the commercial frequency, is performed by the vector control, high efficiency operation suitable for load (e.g., discharge pressure) can be realized.

Further, the following effects can be obtained by using the interior permanent magnet motor. Because the permanent magnets are disposed in the rotor, mechanical strength can be secured. In particular, it is possible to reliably prevent the permanent magnets from scattering. Furthermore, because a reluctance torque can be utilized, torque characteristic is improved. Because a magnetic circuit exhibits large saliency, a position of a magnetic pole of the stator can be detected easily. Therefore, sensorless control can be performed more easily.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a controller-integrated motor pump according to an embodiment of the present invention;

FIG. 2 is a side view of the motor pump shown in FIG. 1;

FIG. 3 is a schematic cross-sectional view of a motor shown in FIG. 1;

FIG. 4 is a block diagram showing a structure of the control unit;

FIG. 5 is a schematic view of a structure in which the motor pump according to the embodiment is applied to a water supply unit;

FIG. 6 is a diagram showing operating characteristic curve for illustrating estimated terminal pressure constant control;

FIG. 7 is a diagram showing table data indicating relationship between rotational speed and total head of the pump at a predetermined flow rate of the pump;

FIG. 8 is a diagram illustrating operating points of the pump;

FIG. 9 is a Q-H curve diagram showing the principle of detecting a shut-off operation state;

FIG. 10 is a flow diagram for detecting the shut-off operation state;

FIG. 11 is a Q-H curve diagram showing another method of detecting the shut-off operation state of the pump;

FIG. 12A through FIG. 12C are diagrams illustrating the principle of measurement of real power according to a digital sampling method; and

FIG. 13 is a diagram illustrating the principle of measurement of real power according to a summation average method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A controller-integrated motor pump, in which a control unit for a motor pump is integrally incorporated, according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing a controller-integrated motor pump according to an embodiment of the present invention, and FIG. 2 is a side view of the motor pump shown in FIG. 1. As shown in FIG. 1 and FIG. 2, the controller-integrated motor pump is a pump apparatus having a control unit 3 mounted on a motor 2. This motor pump has an integral structure in which a pump 1, the motor 2, and the control unit 3 are integrally assembled. The pomp 1 has an impeller 7 secured to a rotational shaft 5 of the motor 2. The impeller 7 is arranged in a volute chamber 11 formed by a pump casing 10. The pump casing 10 has a suction opening 10a and a discharge opening 10b which are in fluid communication with the volute chamber 11. As the impeller 7 is rotated by the motor 2, a liquid (e.g., water) is introduced into the volute chamber 11 through the suction opening 10a, pressurized in the volute chamber 11, and discharged through the discharge opening 10b. A mechanical seal 8 is provided between the impeller 7 and the motor 2 to thereby prevent the liquid from entering the motor 2.

A suction-side pressure sensor 14 for measuring suction-side pressure of the liquid is provided in fluid communication with the suction opening 10a of the pump casing 10. A check valve 15 is coupled to the discharge opening 10b, and a discharge-side pressure sensor 16 is coupled to a discharge side of the check valve 15. This discharge-side pressure sensor 16 is a sensor for measuring the pressure of the liquid at the discharge side of the pump 1. Output signals of the suction-side pressure sensor 14 and the discharge-side pressure sensor 16 are sent to the control unit 3 through signal lines (not shown in the drawings).

The control unit 3 is fixed to an outer surface of a motor casing 12. The control unit 3 is configured to control currents supplied to the motor 2 based on the output signal of the discharge-side pressure sensor 16. A power line inlet 13 is provided on a lower portion of the control unit 3. Power lines from an input power supply (e.g., a commercial power supply) and the above-described signal lines from the pressure sensors 14 and 16 are led into the control unit 3 through the power line inlet 13.

FIG. 3 is a schematic cross-sectional view of the motor 2 shown in FIG. 1. The motor 2 has a rotor 2a and a stator 2b, which are housed in the motor casing 12. The rotor 2a is secured to the rotational shaft 5, and the stator 2b is secured to an inner circumferential surface of the motor casing 12, The rotor 2a has a plurality of permanent magnets 20 embedded therein. The stator 2b is configured to produce a revolving magnetic field by the currents supplied from the control unit 3, so that the rotor 2 a and the rotational shaft 5 are rotated by the revolving magnetic field.

FIG. 4 is a block diagram showing a structure of the control unit 3. The control unit 3 includes an inverter 25 configured to produce voltages to be supplied to the motor 2, a pump controller 30 configured to control operation of the pump 1 according to a predetermined control mode, and a vector controller 40 configured to determine voltage command values for the inverter 25. The pump controller 30 produces a torque command value τ* for allowing discharge-side pressure of the pump 1 to reach a predetermined target pressure. The vector controller 40 receives the torque command value τ* and determines the voltage command values for the inverter 25 using a known vector control method. The inverter 25 generates alternating-current power according to the voltage command values from the vector controller 40.

The control mode of the pump controller 30 is determined depending on application of the motor pump. For example, control modes in the case of using the motor pump as the water supply unit include estimated terminal pressure constant control, discharge pressure constant control, low flow rate stop control, differential pressure constant control, and discharge flow rate constant control. These control modes will be described later.

Next, the vector controller 40 will be described in detail. Three-phase currents Iu, Iv, and Iw, which are supplied from the inverter 25 to the motor 2, are measured by a current detector 42, and the measured values thereof are sent to a three-to-two phase converter 45. This three-to-two phase converter 45 is configured to convert the three-phase currents Iu, Iv, and Iw on a three-phase stationary reference frame (u-v-w axes) into two-phase currents Iα and Iβ on a two-phase stationary reference frame (α-β axes) and further convert the two-phase currents Iα and Iβ into two-phase currents on a two-phase rotating reference frame (d-q axes), i.e., an excitation current Id and a torque current Iq.

The torque command value τ* is input to a command converter 47, where the torque command value τ* is converted into an excitation current command value Id* and a torque current command value Iq*. An excitation current setting device 48 is coupled to the command converter 47. This excitation current setting device 43 is an input device for specifying the excitation current command value Id*. This excitation current command value Id* is determined depending on characteristics of the motor 2. For example, a no-load current of the motor 2 may be used as a set value of the excitation current. The command converter 47 is coupled to a memory 49 in which constants of the motor 2 (i.e., fixed values, such as R and L, that depend on the motor 2) are stored. The constants are input into the memory 49 through a non-illustrated input device. The memory 49 may he incorporated in the command converter 47. The command converter 47 calculates the torque current command value Iq* from the constants of the motor 2 stored in the memory 49 and the excitation current command value Id* that has been set through the excitation current setting device 48. This calculation can be performed using a known method as disclosed in Japanese laid-open patent publication No. H09-9700.

The constants of the motor 2 can be obtained from a motor specification sheet, a motor inspection record sheet, or the like. Instead of manually inputting the known constants into the input device, the control unit 3 may have an auto-tuning function to automatically measure the constants of the motor 2 from the operation results of the motor 2 when driving it in a predetermined operation pattern. More specifically, a rated voltage and a rated frequency of the motor 2 are input to an initial value input device 50, variable voltages within a rated range are applied from the inverter 25 to the motor 2, the motor constants are calculated under various conditions (voltage/frequency), and the motor constants obtained are stored in the memory 49.

The torque current Iq converted by the three-to-two phase converter 45 and the torque current command value Iq* converted by the command converter 47 are input to a phase calculator 52, which determines an angular frequency ω and a phase θ of the rotor 2a of the motor 2. More specifically, the torque current Iq and the torque current command value Iq* are input to a subtracter 53 of the phase calculator 52, where a deviation between the torque current Iq and the torque current command value Iq* is calculated. This deviation is input to an integrator (PI controller) 54, which outputs the angular frequency ω of the rotor 2a. This angular frequency co obtained is further input to an integrator 55, which outputs the phase θ of the rotor 2a.

The excitation current command value Id*, the torque current command value Iq*, the excitation current Id, the torque current Iq, and the angular frequency ω are input to a current controller 58. This current controller 58 produces a d-axis voltage command value Vd* and a q-axis voltage command value Vq* which allow the excitation current Id and the torque current Iq to follow the excitation current command value Id* and the torque current command value Iq*, respectively. Specifically, the current controller 58 calculates the d-axis voltage command value Vd* that can reduce a deviation between the excitation current Id and the excitation current command value Id* to zero, and further calculates the q-axis voltage command value Vq* that can reduce a deviation between the torque current Iq and the torque current command value Iq* to zero.

The voltage command values Vd* and Vq* and the phase θ are input to a two-to-three phase converter 59, where the voltage command values Vd* and Vq* are converted into the three-phase voltage command values Vu*, Vv*, and Vw* (u-phase, v-phase, and w-phase). More specifically, the voltage command values Vd* and Vq* on the two-phase rotating reference frame (d-q axes) are converted into voltage command values Vα* and Vβ* on the two-phase stationary reference frame (α-β axes). The voltage command values Vα* and Vβ* are further converted into the three-phase voltage command values Vu*, Vv*, and Vw* on the three-phase stationary reference frame (u-v-w axes). The three-phase voltage command values Vu*, Vv*, and Vw* obtained are input to a drive circuit 26 of the inverter 25. In this manner, the vector controller 40 resolves the three-phase currents, which are supplied to the motor 2, into the torque current component and the excitation current component and controls these current components separately.

The inverter 25 receives the voltage command values Vu*, Vv*, and Vw* and produces alternating-current power having a frequency within a band including frequencies that are not less than the commercial frequency. The inverter 25 further includes an AC/DC converter 27 for converting alternating currents, which are supplied from the input power supply (e.g., the commercial power supply), into direct currents and a DC/AC converter 28 for further converting the direct currents into alternating currents. The drive circuit 26 of the inverter 25 controls the DC/AC converter 28 according to a voltage control method, such as PAM method or PWM method, whereby the DC/AC converter 28 produces three-phase power in accordance with the voltage command values Vu*, Vv*, and Vw*. This three-phase power is applied to the motor 2. Because the inverter 25 produces the alternating-current power in the wide frequency band including the range of not less than the commercial frequency in addition to the range of less than the commercial frequency, high efficiency operation suitable for load (e.g., discharge pressure) can be realized.

The above-described torque command value τ* is produced in the pump controller 30. This torque command value τ* varies depending on the control mode of the pump controller 30. For example, in the case where the pump controller 30 is configured to perform the discharge pressure constant control, a subtractor 32 calculates a deviation between a measurement value of the discharge-side pressure sensor 16 (i.e., the actual pressure at the discharge side of the pump 1) and a preset target pressure, a PI controller

33 calculates a target rotational speed that can reduce the deviation to zero, a subtractor

34 calculates a deviation between the target rotational speed and a current rotational speed determined from the angular frequency ω, and the PI controller 35 calculates the torque command value τ* that can reduce the deviation to zero.

FIG. 5 is a schematic view of a structure in which the motor pump according to the above-described embodiment is applied to a water supply unit. As shown in FIG. 5, the pressure sensor 14 is disposed at the suction side of the pump 1, so that the suction-side pressure of the pump 1 is measured by the pressure sensor 14. A flow switch 19 is provided downstream of the check valve 15, and the pressure sensor 16 and a pressure tank 18 are disposed downstream of the flow switch 19. The pressure sensor 16 measures the discharge-side pressure of the pump 1 (i.e., back pressure applied to the water supply unit).

The check valve 15 is a valve for preventing backflow of water when the pump 1 is stopped. The flow switch 19 is a flow rate detector for detecting that a flow rate of the water discharged from the pump 1 is reduced to a predetermined value. The pressure sensor 14 is a water-pressure measuring device for measuring the pressure at the suction side of the pump 1. The pressure tank 18 is a pressure-retaining container for retaining the discharge-side pressure while the pump 1 is stopped.

The flow switch 19, the pressure sensor 14, and the pressure sensor 16 are coupled to the control unit 3 through the signal lines. When the flow switch 19 detects that the flow rate of the water is reduced to the predetermined value, the control unit 3 performs a low flow rate stop operation. Specifically, the control unit 3 raises the operation speed of the pump 1 temporarily until the discharge-side pressure reaches a predetermined stop pressure, and then stops the operation of the pump 1. On the other hand, when the discharge-side pressure is reduced to a predetermined starting pressure, the control unit 3 starts the operation of the pump 1.

In the motor pump used as the water supply unit, the pump 1 is operated at variable speeds by the inverter 25 based on the output signal of the pressure sensor 16. Typically, the discharge pressure constant control or the estimated terminal pressure constant control is performed in the water supply unit. The discharge pressure constant control is a control method in which the operation speed of the pump 1 is controlled such that the pressure signal (i.e., the discharge pressure of the pump 1), measured by the pressure sensor 16, coincides with a preset target pressure. The estimated terminal pressure constant control is a control method for maintaining constant water pressure at a terminal water outlet by changing the target pressure in accordance with a pipeline resistance.

The estimated terminal pressure constant control will be describe with reference to FIG. 6 showing a diagram of operating characteristic curve. In FIG. 6, a horizontal axis represents flow rate of water, a vertical axis represents head (which may hereinafter be referred to as “pressure”), and curve Nx represents operating characteristic of the pump under a condition that the rotational speed of the pump 1 is constant. A resistance curve R represents the pipeline resistance from the pump 1 to the terminal water outlet (e.g., faucet) which varies depending on the flow rate of water. The resistance curve R shows a relationship between the discharge flow rate and the discharge pressure of the pump 1 for maintaining the terminal pressure substantially constant. This resistance curve R is stored in a memory 38 of the pump controller 30.

In the estimated terminal pressure constant control, the rotational speed of the pump 1 is controlled in consideration of the pipeline resistance (indicated by the resistance curve R) that varies depending on the flow rate of the water used. Specifically, the rotational speed of the pump 1 is controlled based on the measurement value of the pressure sensor 16 such that the discharge pressure of the pump 1 varies along the resistance curve R. In the pump controller 30, the subtractor 32 (see FIG. 4) calculates a deviation between the measurement value of the discharge-side pressure sensor 16 and the target pressure determined by the flow rate Q and the resistance curve R, the PI controller 33 calculates a target rotational speed that can reduce the deviation to zero, the subtractor 34 calculates a deviation between the target rotational speed and a current rotational speed, and the PI controller 35 calculates the torque command value τ* that can reduce the deviation to zero. The flow rate Q can be determined from the rotational speed of the pump 1 indirectly.

In the example shown in FIG. 6, the rotational speed of the pump 1 is controlled between Na (which is a rotational speed for achieving a target estimated terminal pressure when the flow rate is maximum) and Nb (which is a rotational speed for achieving the target estimated terminal pressure when the flow rate is zero). For example, at a flow rate Q1, the pump 1 is operated at a rotational speed Nc. A symbol Pa in FIG. 6 represents the discharge pressure of the pump 1 necessary for achieving the target estimated terminal pressure when the flow rate is maximum, and a symbol Pb represents the discharge pressure of the pump 1 necessary for achieving the target estimated terminal pressure when the flow rate is zero.

In the estimated terminal pressure constant control, the discharge flow rate of the pump 1 is estimated from the rotational speed of the pump 1, and the target pressure corresponding to each flow rate is determined. However, the relationship between the rotational speed and the discharge flow rate of the pump 1 varies depending on the suction-side pressure of the pump 1. Consequently, when the suction-side pressure of the pump 1 fluctuates, an accurate discharge flow rate cannot be estimated. Thus, the pump controller 30 is configured to compensate for the estimated discharge flow rate based on the suction-side pressure of the pump 1 measured by the suction-side pressure sensor 14.

The control modes of the pump operation performed by the pump controller 30 include the discharge pressure constant control, the estimated terminal pressure constant control, the differential pressure constant control, and the discharge flow rate constant control. These control modes are designated from a control mode setting device 37 to the pump controller 30. User can select a desired control mode through the control mode setting device 37.

The differential pressure constant control is a control method for maintaining a constant differential pressure between the suction-side pressure and the discharge-side pressure of the pump 1. In this control, a non-illustrated subtracter calculates the differential pressure between the suction-side pressure measured by the suction-side pressure sensor 14 and the discharge-side pressure measured by the discharge-side pressure sensor 16, the subtracter 32 calculates a deviation between the differential pressure and a preset target differential pressure, the PI controller 33 calculates a target rotational speed that can reduce the deviation to zero, the subtractor 34 calculates a deviation between the target rotational speed and the current rotational speed, and the PI controller 35 calculates the torque command value τ* that can reduce the deviation to zero.

The discharge flow rate constant control is a control method for maintaining a constant discharge flow rate of the pump 1. This discharge flow rate constant control will be described with reference to FIG. 7 and FIG. 8. As an initial step, a table data indicating a relationship between the rotational speed N and the total head is obtained under a condition that the discharge flow rate of the pump 1 is fixed to a target flow rate Q1. FIG. 7 shows the table data obtained. This table data, indicating the relationship between the rotational speed N and the total head of the pump 1, can be obtained from actual measurement. Specifically, the table data is obtained by measuring the total head when the pump 1 is operated at several rotational speeds under the condition that the discharge flow rate is fixed to Q1. FIG. 8 is a graph showing the relationship between the discharge flow rate and the discharge pressure of the pump 1. For simplifying the explanation, the suction-side pressure is assumed to be zero. When the suction-side pressure is zero (i.e., the measurement value of the suction-side pressure sensor 14 is zero), the discharge pressure is equal to the total head.

In FIG. 8, a symbol SC represents a system curve determined from resistance and loss of a system. When the rotational speed of the pump 1 is N2, an operating point of the pump 1 is an intersection point A of the operating characteristic curve at the rotational speed N2 and the system curve SC. Under the condition that the suction-side pressure is zero, the discharge pressure at the operating point A indicates the total head (actual total head). On the other hand, in the table data shown in FIG. 7, when the rotational speed of the pump 1 is N2, the total head (target total head) is PB. Thus, the rotational speed of the pump 1 is increased or decreased such that the deviation between the actual total head and the target total head on the table data at the corresponding rotational speed becomes zero. Specifically, the subtractor 32 (see FIG. 4) calculates the deviation between the actual total head and the target total head on the table data, the PI controller 33 calculates a target rotational speed that can reduce the deviation to zero, the subtractor 34 calculates a deviation between the target rotational speed and the current rotational speed, and the PI controller 35 calculates the torque command value τ* that can reduce the deviation to zero.

According to this control method of the pump 1, the discharge flow rate can be kept constant without providing a constant flow valve at the discharge side of the pump 1. Moreover, because the pump 1 can be operated in such a manner that the discharge pressure of the pump 1 agrees with the load used, i.e., the system curve SC, it is possible to solve a problem of difficulty in adjustment of the discharge pressure of the pump 1 caused by large pressure loss at the constant flow rate valve. Therefore, optimum operation can be realized. For example, when the system curve is as indicated by a dotted line SC in FIG. 8, the pump 1 is operated at an intersection point C.

The pump controller 30 further has a data table of a relationship between the rotational speed and corresponding shut-off pressure (or no-discharge pressure) of the pump 1. This data table is created by measuring the rotational speed of the pump 1 and the shut-off pressure while gradually increasing the rotational speed of the pump 1 in a shut-off state that is established by closing a valve (not shown) located at the discharge side of the pump 1. The shut-off pressure can be measured by the discharge-side pressure sensor 16. The data table obtained is stored in the memory 38 of the pump controller 30. The characteristic curve of the pump 1 to be used is often known in advance. In such a case, the data table of the rotational speed and the shut-off pressure of the pump 1 may be produced from the known characteristic curve, and the data table thus obtained may be stored in the memory 38 of the pump controller 30. The water supply unit further requires other control items, e.g., data of the rotational speed of the pump and the corresponding shut-off pressure for use in the estimated terminal pressure constant control. Therefore, such data table, which is prepared separately, may be used.

FIG. 9 is a Q-H curve diagram showing the principle of detecting the shut-off operation state. In FIG. 9, the current operating point is defined by a discharge-side pressure P and a flow rate Q. In this operating point, the rotational speed of the pump 1 is N+ and the shut-off pressure corresponding to the rotational speed N+ is P+. As can be seen from the figure, in a normal flow rate, the measured pressure P at the operating point is necessarily smaller than the shut-off pressure P+ corresponding to the rotational speed N+. That is, the relationship between the pressure P and the shut-off pressure P+ is P+>P.

On the other hand, when the discharge-side pressure P is constant and the flow rate Q becomes almost zero, the pump enters the so-called shut-off operation state (or no-discharge operation state). Since the check valve 15 is a one-way valve, the pressure downstream of the check valve 15 may be slightly higher than the target pressure. In such a case, the measured pressure exceeds the target pressure. Therefore, a deceleration command is issued to the pump 1. However, in the shut-off operation state, the discharge-side pressure is not decreased below the target pressure even when the pump speed is decreased, because the discharge-side pressure is retained by the check valve 15. Therefore, the shut-off pressure P− when the rotational speed is reduced to N− is smaller than the measured pressure P. That is, the relationship between the pressure P and the shut-off pressure P− is P>P−. From this relationship, it is possible to detect a complete shut-off operation state in which the flow rate of water discharged is zero.

FIG. 10 is a flow diagram for detecting the shut-off operation state described above. First, the relation between the current discharge-side pressure P measured by the pressure sensor 16 and the pump shut-off pressure Px corresponding to the current rotational speed is judged. As shown in FIG. 9, when the current flow rate of water is Q and the discharge-side pressure measured is P, the shut-off pressure P+ corresponding to the current rotational speed N+ is larger than the current pressure P measured. Therefore, it is judged that the pump 1 is not in the shut-off operation state, and the normal operation is continued. In contrast, when the flow rate Q becomes zero and the shut-off operation state is established, the discharge-side pressure is retained by the check valve 15 and is therefore not decreased to the target pressure P. In this case, the deceleration command is issued to the pump 1 in order to lower the discharge-side pressure of the pump 1, so that the rotational speed of the pump 1 is decreased. As a result, the shut-off pressure Px corresponding to the rotational speed becomes smaller than the pressure P (i.e., P>Px). This state is judged to be the shut-off operation state, and the low flow rate stop operation is performed. It is preferable to detect this state for a predetermined period of time by a timer or the like and to judge that the pump has entered the shut-off operation state from the fact that this state has been continued.

FIG. 11 is a Q-H curve diagram showing another method of detecting the shut-off operation state of the pump 1. In this detection method, when the rotational speed of the pump 1 is reduced to HzB that corresponds to a target pressure PB at the shut-off operation, the pump controller 30 reduces the rotational speed of the pump 1 to a rotational speed slightly lower than the rotational speed HzB (e.g., HzB−1 Hz). In this state, the pump controller 30 monitors for a predetermine time whether or not the pressure measured by the discharge-side pressure sensor 16 is reduced below a predetermined value (e.g., PB−1 m). If the pressure is not lowered, then it is judged that the pump is in the shut-off operation state because the check valve 15 does not allow the pressure measured by the discharge-side pressure sensor 16 to vary even when the rotational speed of the pump 1 is decreased. Then, the low flow rate stop operation of the pump 1 is performed. In this low flow rate stop operation, the rotational speed is increased to HzB′ for a certain period of time so as to raise the discharge pressure by several meters (e.g., +3 m) with respect to the pressure PB at the detection point of the shut-off operation, and then the pump 1 is stopped. On the other hand, if the pressure measured by the pressure sensor 16 is decreased as a result of the reduced speed operation of the pump 1, the normal operation is continued because the pump 1 is not in the complete shut-off operation state.

In the low flow rate stop operation, a pressure-accumulating operation is performed by increasing the discharge pressure up to PB+3 m. If the rotational speed of the pump 1 is increased beyond the corresponding shut-off operation speed HzB′ by 1 Hz or more during the low flow rate stop operation, the operation of the pump 1 is returned to the normal operation. Typically, in the low flow rate stop operation, the pump 1 is operated at the rotational speed HzB′ that corresponds to the target pressure (PB+3 m). However, if the flow rate of water is increased during the low flow rate stop operation, it is judged that the shut-off operation state is ended. In this case, the pump 1 is returned to the normal operation from the low flow rate stop operation.

Referring back to FIG. 4, a power consumption display function of the control unit 3 will be described. The control unit 3 has an electric power calculator 61, as shown in FIG. 4. This electric power calculator 61 has an inverter input power calculator 61A configured to calculate electric power input to the inverter 25 and a motor input power calculator 61B configured to calculate electric power input to the motor 2. The input side of the inverter 25 is coupled to a commercial AC power supply that supplies three-phase power of 200V with 50 Hz or 60 Hz, and the output side of the inverter 25 is coupled to the motor 2. The inverter 25 supplies the alternating-current (AC) power having desired frequency and voltage to the motor 2. The three-phase power from the input power supply is input to the AC/DC converter 27, which converts the three-phase power into direct-current power. A current and a voltage of the direct-current (DC) power are measured by a current detector 63 and a voltage detector 64. The current and the voltage measured are input to the inverter input power calculator 61A, where the power is calculated.

The currents and interphase voltages, to be input to the motor 2, are measured by the current detector 42 and a voltage detector 43. At least two phase of the three-phase currents and voltages are measured. The measured values of the currents and voltages are input to the motor input power calculator 61B, which calculates a real power supplied to the motor 2 from the measured values of the currents and voltages.

FIG. 12A through FIG. 12C are diagrams illustrating the principle of measurement of the real power according to a digital sampling method. Specifically, FIG. 12A shows sampling results of voltage waveform obtained from the output values of the voltage detector 43. Similarly, FIG. 12B shows sampling results of current waveform obtained from the output values of the current detector 42. In general, the real power is obtained by integrating instantaneous electric power (which is the product of instantaneous values of voltage and current) and dividing the resulting integrated value by a cycle T. An

$P = \frac{1}{T} \int_{0}^{T} e (t) \times i (t) \partial t \equiv \frac{1}{T} \sum_{k = 1}^{k = T / Δ t} e (k) \times i (k) \times Δ t$

where e(t) is an instantaneous value of voltage at a time off, i(t) is an instantaneous value of current at the time of t, e(k) is an instantaneous value of voltage in k-th sampling, i(k) is an instantaneous value of current in k-th sampling, and T is a cycle.

As can be seen from the right-hand side of the above approximate equation, the real power is determined by dividing the sum (over one cycle) of strips of the instantaneous electric power by the cycle T. Each strip of the instantaneous electric power has a width defined by a sampling interval At. The number of strips in one cycle is k that is determined by T/Δt. The motor input power calculator 61B executes the calculation of the above equation approximately as it is to thereby measure the power according to the digital sampling method. In actual practice, in order to increase measuring accuracy, a time for measuring the waveform is often set to be longer than one cycle. Typically, the sampling interval At is set to several tens of microseconds, and the reciprocal of At is a sampling frequency. The above equation expresses the real power per one phase. Therefore, the real power in the three phases is triple the real power given by the above equation.

FIG. 13 is a diagram illustrating the principle of measurement of the real power according to a summation average method. A symbol (a) in FIG. 13 shows voltage input waveform and current input waveform which are the outputs of the voltage detector 43 and the current detector 42. The real power is given by integrating the product of instantaneous values of voltage and current with respect to time over one cycle (or n cycles) and dividing the resulting integrated value by the cycle. An equation for

$Real Power = \frac{1}{T} \int_{0}^{2 π} V (t) \times i (t) \partial t = \frac{1}{nT} \int_{0}^{2 n π} V (t) \times i (t) \partial t$

where V(t) is an instantaneous value of voltage at a time of t, i(t) is an instantaneous value of current at the time of t, n is integer, and T is a cycle.

It is necessary to accurately sample the input waveforms of the voltage and the current for one cycle (or n cycles). In this method, in order to realize accurate sampling, the sampling interval is synchronized with the cycle of the input waveforms of the voltage and the current using zero crossing signals that are based on the input waveform of the current, as shown in a symbol (b) in FIG. 13. The real power is obtained by calculating an average of the product of instantaneous values of voltage and current in an effective sampling interval using an approximate equation of the above equation. When the input waveform of the current is small, the waveform of the voltage is used as the basis of the

$Real Power = \frac{1}{N} \sum_{k = 1}^{k = N} v (k) \times i (k)$

where v(k) is an instantaneous value of voltage in k-th sampling, i(k) is an instantaneous value of current in k-th sampling, and N is the number of samplings in synchronization with input cycle.

The electric power calculator 61 adds the power determined by the inverter input power calculator 61A and the power determined by the motor input power calculator 61B together and stores the resulting value of the power in a memory (now shown) provided therein. The power value calculated by the electric power calculator 61 is input to an electric power integrator 66. This electric power integrator 66 is capable of calculating electric energy per unit time (kWh) by integrating the power values, which are stored one after another in the memory, at predetermined time intervals to determine an integrated value per unit time. The electric energy per unit time (kWh) thus calculated is output to an electric energy display device 67. This electric energy display device 67 displays the electric energy per unit time (kWh).

The electric energy (kWh) calculated by the electric power integrator 66 is input to an electricity rate calculator 68 and a carbon dioxide emission calculator 73. An electricity rate memory 70 is coupled to the electricity rate calculator 68, and an electricity rate input device 71 is coupled to the electricity rate memory 70. The electricity rate input device 71 is an input unit, such as numeric keypad, through which an electricity rate per unit electric energy can be input. Since the electricity rate per unit electric energy varies from one electric power company to another, the electricity rate per unit electric energy provided by an electric power company used is set by a user through the electricity rate input device 71. The electricity rate per unit electric energy that has been input through the electricity rate input device 71 is stored in the electricity rate memory 70. The electricity rate calculator 68 calculates the electricity rate by multiplying the electricity rate per unit electric energy stored in the electricity rate memory 70 by the electric energy (kWh) calculated by the electric power integrator 66. The electricity rate obtained by the electricity rate calculator 68 is sent to an electricity rate display device 69, where the electricity rate is displayed. A difference may exist between a basic rate and a nighttime rate. In such a case, a cumulative electric energy at nighttime and a cumulative electric energy at daytime may be stored separately using a clock function provided in the electricity rate calculator 68, so that the electricity rates for the respective time zones can be calculated.

A carbon dioxide emission factor memory 74 for storing a carbon dioxide emission factor therein is coupled to the carbon dioxide emission calculator 73. Further, a carbon dioxide emission factor input device 75 for inputting the carbon dioxide emission factor is coupled to the carbon dioxide emission factor memory 74. The carbon dioxide emission factor is a factor for calculating an amount of carbon dioxide emission from an electric power consumption of an electrical appliance. The unit of the carbon dioxide emission factor is t-CO₂/kWh, which means the amount of carbon dioxide emission (ton) per unit electric energy (kWh). This factor varies from one electric power company to another, and also varies from year to year. The carbon dioxide emission factor is announced annually by each electric power company.

When the user inputs the carbon dioxide emission factor into the carbon dioxide emission factor input device 75, the carbon dioxide emission factor is stored in the carbon dioxide emission factor memory 74. The carbon dioxide emission calculator 73 calculates the amount of carbon dioxide emission per unit time from the carbon dioxide emission factor and the electric energy calculated by the electric power integrator 66. The amount of carbon dioxide emission is sent to a carbon dioxide emission display device 76, which displays the amount of carbon dioxide emission calculated.

It should be noted that the motor pump according to the present invention is not limited to the embodiments described above and is not limited to the examples in the drawings. Moreover, various modifications may be made within the scope of the present invention.

CONTROLLER-INTEGRATED MOTOR PUMP

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