JP2010025042A - Pump flow rate estimating system and pump flow rate estimating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pump flow rate estimating system and a pump flow rate estimating method, for estimating a flow rate of a variable speed pump driven by variable voltage and a variable frequency power source controlled by delivery pressure constant control or estimated end pressure constant control, by an electric current and a speed of a driving electric motor and net generation pressure of the pump. <P>SOLUTION: This invention measures a primary current of an electric motor driven by the variable voltage and the variable frequency power source, determines a secondary current of the electric motor by vectorially subtracting a preset exciting current from the measured primary current, estimates torque of the electric motor by multiplying an electric motor torque factor, and further arithmetically operates output of the electric motor by multiplying this estimated torque by an electric motor speed. A flow rate of the pump is arithmetically operated and estimated with pump efficiency as a known value, by measuring pump pressure, by applying the principle that the arithmetically operated electric motor output is equal to shaft power of the pump. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In the present invention, the flow rate of a variable speed pump driven by a variable voltage and variable frequency power source controlled by a constant discharge pressure control or a constant estimated terminal pressure control, the current and speed of the drive motor, and the net of the pump. The present invention relates to a pump flow rate estimation system and a pump flow rate estimation method that are estimated based on generated pressure.

  Some systems for estimating the pump flow rate detect the flow rate of a pump driven by a variable voltage, variable frequency power supply without using a flow rate sensor. The pump flow rate estimation system detects the pressure and speed of the pump, and estimates and calculates from a quadratic approximate expression representing the pump head-flow rate characteristic. The pump flow rate estimation system needs to measure and determine each constant of a quadratic approximate expression representing the pump head-flow rate characteristic for each pump.

  Further, in principle, there is a problem that an error occurs in the estimated flow rate when an error occurs. In the pump flow rate estimation system, it is difficult to calculate and estimate an accurate flow rate particularly when the characteristics of the pump change due to aging. In this case, the pump head-flow rate characteristic of the pump was measured again, and it was necessary to correct each constant of the quadratic approximation based on the result.

As described above, the conventional flow rate estimation method based on the pump head-flow rate quadratic approximation formula causes an error in the flow rate estimation calculation result when the constant is set incorrectly at the initial stage of setting or when the constant changes due to secular change. There was a problem. The parallel pump flow rate estimation method described in Japanese Patent Application Laid-Open No. 2008-14230 estimates the total flow rate of a water supply system configured to operate a plurality of variable speed pumps driven by a variable voltage and variable frequency power supply in parallel. ing.
JP 2008-14230 A

  An object of the present invention is to provide a pump flow rate estimation system that calculates and estimates the pump flow rate based on the current and speed of a drive motor, the pump pressure, and the like in order to solve the problems in the conventional pump flow rate estimation system. And

  The pump flow rate estimation system of the present invention measures a primary current of an electric motor driven by a variable voltage / variable frequency power source, and subtracts a preset excitation current in a vector form from the measured primary current to Secondary current is obtained, the motor torque coefficient is multiplied to estimate the motor torque, and the estimated torque is multiplied by the motor speed to calculate the output of the motor. Here, the principle that the calculated motor output is equal to the shaft power of the pump is applied. That is, the pump pressure is measured from the relational expression of motor output = shaft power = (pump pressure × flow rate) / (pump efficiency), and the pump flow rate is calculated and estimated with the pump efficiency known.

  According to the present invention, compared to the conventional method of estimating the pump flow rate from the quadratic approximation expression representing the pump head-flow rate characteristics, the motor torque corresponding to the actual pump flow rate is detected and calculated. There is an advantage that it is not easily affected by errors in initial setting of constants in the head approximation formula or errors due to aging of the constants. For example, by comparing the flow rate detected by the conventional method with the flow rate detected by the pump flow rate estimation system of the present invention as needed, it is possible to detect the occurrence of an error due to a setting error or aging.

  According to the present invention, by changing the constant setting, the flow rate control or the estimated terminal pressure constant control can be performed more accurately than the conventional method.

  According to the present invention, it is possible to realize an inexpensive pump aging characteristic diagnosis function without using an expensive flow rate sensor by mounting the function in the pump controller in software.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an overall configuration diagram in the case where the flow rate estimation method of the present invention is applied to a water supply system with a constant discharge pressure control of a variable speed pump driven by a variable voltage and variable frequency power source. In FIG. 1, an accessory of a water supply system that is not necessary for explaining the present invention, for example, a check valve for preventing a reverse flow, a flow switch, a pressure tank, a pump bypass pipe, and the like prepared in the direct feed water supply system are omitted. .

  In FIG. 1, the pump 1 is driven by an inverter 21 and an electric motor 12. As shown in FIG. 1, the pump 1 has a water supply pipe connected to the discharge side via a check valve 2 and a cutoff valve 3. The suction side of the pump 1 is connected to a water main through a shutoff valve 4. The inverter 21 receives the inverter frequency command FS1 which is the output of the pressure control controller PCONT (constant discharge pressure control device) 31 of the pump 1 and controls the motor 12 with variable voltage and variable frequency.

  The pressure setting unit 31-3 sets a pump discharge pressure setting hS (p.u.), (= pump set discharge pressure HS (Mpa) / pump rated pressure HN (Mpa)). The discharge pressure setting hS (pu) set by the pressure setter 31-3 is obtained by a coefficient unit 31-4 in which the detection pressure Hi (Mpa) of the discharge pressure detector 11 of the pump 1 is set to 1 / HN. Compared with hi (pu).

  The comparison result is given to the PID or PI controller 31-1. The PID or PI controller 31-1 automatically adjusts the output frequency command FS (Hz) so that the error due to the comparison becomes small. The output frequency command FS is converted into an analog signal FS1 (Hz) by the D / A converter 31-2 to control the inverter 21. That is, the discharge pressure of the pump 1 detected by the discharge pressure detector 11 and the set value set by the pressure setter 31-3 constitute a discharge pressure constant control system by the inverter 21. SEQ 31-5 shows a known sequence control device prepared in an automatic water supply system.

  FIG. 2 is a block FLOWD in FIG. 1 and shows a flow rate calculation circuit of the present invention. In FIG. 2, the principle of flow rate detection when acceleration / deceleration torque is not considered will be described. The flow rate calculation circuit 41 receives the motor primary current I1 (A) from the inverter 21 in the form of a digital signal. This value is squared by the square calculator 41-1. An excitation current estimated value Im * (A) generated by an excitation current generator 41-2 described later is squared by a square calculator 41-3.

I1 ² (A) squared by the square calculator 41-1 subtracts Im * ² squared by the square calculator 41-3, and square root calculation is performed by the square root calculator 41-4. Thus, the estimated secondary current value I2 * (A) of the electric motor is obtained. That is, the secondary current of the motor 12 is changed from the primary current of the motor 12 supplied from the inverter 21 by the square calculator 41-1, the excitation current generator 41-2, the square calculator 41-3, and the square root calculator 41-4. Is estimated.

  The calculated secondary current estimated value I2 * (A) is divided by the rated secondary current I2N (A) by the coefficient unit 41-5 to convert the secondary current into p.u. The conversion result I2N by the coefficient multiplier 41-5 is converted into i2T (p.u.).

The motor speed is detected at the inverter command frequency FS (Hz) as an approximate value. The FS (Hz) received from the constant discharge pressure control device 31 is converted to fS (pu) by multiplying 1 / FN, (FN is the rated frequency (Hz)) by the coefficient unit 41-6. fS (pu) and i2T * (pu) are multiplied by a multiplier 41-7 to generate a motor output p0 (pu).

On the other hand, the flow rate calculation circuit 41 receives the discharge pressure Hi (MPa.) Of the pump 1 from the discharge pressure detector 11. When the changeover switch 41-15 is in a state where the terminals 1 and 2 are closed, the discharge pressure Hi gives a signal to the coefficient unit 41-16 in which 1 / HN is set. The divider 41-8 divides the previously obtained motor output p0 (pu) by the output hnet (pu) obtained by the coefficient unit 41-16. This results in a pump efficiency of 100
Estimated flow rate q0 * (pu) in%.

  The pump / efficiency generator 41-9 calculates the pump efficiency by the pump speed N (rpm), the pump net set pressure, HSnet (Mpa) (= HS-HSU) and the pump speed. In the present invention, hSnet (pu) in which HSnet is expressed by pu is applied, and an inverter frequency command is used as an approximate value of pump speed n (pu) (= pump speed N (rpm) / rated speed NR (rpm)). First, pu efficiency (= pump efficiency ηP / base pump efficiency ηbase) is generated by using fS (pu). The pump / efficiency generator 41-9 is configured to multiply the result by the base pump efficiency to generate the pump efficiency during operation. Details thereof will be described later.

  Therefore, when the frequency command fS (pu) is given as an approximate value of the pump speed and the net set pressure of the pump is given hSnet (pu), the pump / efficiency generator 41-9 responds to the operation state at that time. The pu pump efficiency is calculated, and the result is multiplied by the base efficiency ηbase of the pump to output ηP *. Therefore, the multiplier 41-10 calculates q0 * (p.u.) × ηP * to obtain the estimated flow rate q1 *. The coefficient unit 41-11 is a coefficient unit for matching the shaft power and the motor output 100% when the pump flow rate is 100% and the pump pressure is 100%.

  The estimated flow rate value q1 * obtained by multiplying the coefficient of the coefficient multiplier 41-11 is converted into an actual flow rate estimated value, q * (p.u.). That is, when the motor output is equal to the pump shaft power, the estimated flow rate q * (p.u.) of the pump can be obtained by the present invention described above. However, in the case of acceleration and deceleration of the pump, the motor output and the pump shaft power are not equal due to acceleration and deceleration torque.

  In the present invention, the motor model 41-12, the differential calculator 41-13, and the coefficient unit 41-14 calculate the acceleration / deceleration current Iα * from the frequency command FS of the inverter 21 to solve the above problem. The operation will be described later. Here, the exciting current generator 41-2 will be described. As is well known, the excitation current of the motor when it is controlled by a constant V / F inverter can be calculated by a T-type equivalent circuit if a motor equivalent circuit constant is given.

  FIG. 3 shows an example in which the torque and exciting current are calculated when the pump motor is operated with the frequency set. The excitation current shown in FIG. 3 is an example of calculating the torque and excitation current when the 1.6KW2P pump motor with a rated frequency of 60 Hz is operated with the frequency set to 60 Hz, 30 Hz, and 15 Hz. It is shown that when the operating frequency of the electric motor is 30 Hz or higher, the change in excitation current with respect to torque is small. Actually, in the pump discharge pressure constant control, the speed control range of the pump has a property of being as small as 1: 2 or less.

For example, consider a lift coefficient of 1.46, a flow coefficient of 0.46, and a lift-flow characteristic of 1.46n ² -0.46q ² . Where n: pump speed (pu) (n = pump speed N (rpm) / rated speed NR (rpm), q: pump flow rate (pu) (q = pump flow rate Qm ³ / min / rated flow rate QNm ³ / min With this pump, the pump speed control range at 1.00 pu pressure setting is very small from 1.00 pu to 0.828 pu, so the exciting current generator 41-2 can be easily made using this property. In other words, an approximate value of the excitation current can be generated by selecting the motor torque as the median value, creating a table of the excitation current against the frequency, and reading this table value according to the operating frequency at that time. be able to.

  Further, the accurate excitation current generator 41-2 can be realized as follows. Here, first, the speed torque characteristic of the pump is obtained from the second-order approximation expression of the pump head-flow rate, the efficiency characteristic of the pump, and its control method. For example, in the constant discharge pressure control, calculation can be performed as shown in FIG.

  FIG. 4 is a graph showing the relationship between pump speed (p.u.) and torque (p.u.). In FIG. 4, since the necessary torque with respect to the pump speed is obtained, the motor slip for generating the torque can be calculated from the T-type equivalent circuit. For example, in the example of FIG. 4, for n = 0.833, 0.917, and 1.00 p.u., the slips were 0.034, 0.076, and 0.118. Thus, if the slip with respect to a required torque can be calculated, the exciting current and torque in that point can be calculated.

  FIG. 5 shows the relationship between speed (p.u.), excitation current, and torque (p.u.). For the pressure setting of 1.00 p.u. in FIG. 4, the slip of the motor is calculated from the pump torque, and the excitation current is calculated. In FIG. 5, an approximate expression is applied to simplify the slip calculation. For this reason, it is shown that a slight error occurs between the pump torque and the motor torque. That is, if the excitation current generator 41-2 is configured so as to obtain an equation of an approximate straight line with respect to the frequency from the excitation current thus obtained and generate the excitation current according to the operation frequency, the excitation current generator 41-2 is configured more than the above method. Accurate excitation current can be set.

  This latter method is not limited to discharge pressure constant control. For example, in the case of the estimated terminal pressure constant control, it is obvious that the excitation current with respect to the frequency can be calculated in the same manner by calculating the relationship between the speed and the torque corresponding to the set target curve.

Next, the pump efficiency generator 41-9 will be described. It is known that the pu pump efficiency of a pump whose speed is controlled by an inverter is approximately expressed by the following equation.
Pump efficiency: ηP = -C1 (q / f) ² + C2 (q / f) + C3 ---- (1)
Where C1, C2, C3: constants determined by the pump
q: Flow rate (pu)
f: Inverter frequency (pu) = Inverter frequency F (Hz) / Inverter rated frequency FN (Hz)
In this case, the inverter frequency f (pu) when the discharge pressure constant control is performed is as follows. The lift-flow rate approximate expression and the pump net set pressure hSnet (pu) (= pump set pressure hS (pu) −pump suction pressure hSU ( pu)). Here, when hSU (pu) << hS (pu), hSnet (pu) ≈hS (pu) is set, and the calculation can be performed by the equation (2). Further, the variable (q / f) that determines the pu efficiency can be calculated by the equation (3).
f = ((h S + bq ² ) / a) ^1/2 ---- (2)
q / f = ^{[aq 2 / (hS + bq 2} ) ] ^1/2 ---- (3)
Where hS: pump set pressure (pu) = pump set pressure (Mpa) // pump rated pressure (Mpa)
a, b: Pump constant

  By substituting (q / f) in equation (3) into equation (1), p.u. pump efficiency can be calculated. Further, since the approximate value of the speed at this time is given by the equation (2), the p.u. efficiency of the pump performing the discharge pressure constant control can be calculated as shown in FIG. FIG. 6 is a graph showing the relationship between pump speed (p.u.) and efficiency (p.u.). The actual pump efficiency is obtained by multiplying this value by the base efficiency of the pump. That is, the pump efficiency generator 41-9 sets the pu pump efficiency obtained in this way in the form of a table or an approximate function, and corresponds to the net set pressure hSnet (pu) of the pump during the pump operation. The corresponding pu efficiency value is read from time to time according to the inverter frequency fS. This value is multiplied by the base efficiency ηbase (not shown) of the pump, and the actual pump efficiency is output.

The method for calculating the pump efficiency in the pump discharge pressure constant control has been described above. However, this method can, of course, be applied as the efficiency calculation method for the estimated terminal pressure constant control. Also in this case, if hSU (pu) << hS0 (pu), hSnet (pu) ≒ hS0 (pu) is set and (4), (5) instead of (2) and (3) Apply an expression.
f = [(HS0 + [(1 -hS0) + b] q ²⁾ / a] ^1/2 ---- (4)
q / f = [aq ² / (hS0 + [(1 -hS0) + b] q ^{2)] 1/2} ---- (5)
Where hS0: Minimum set pressure (pu) = Minimum set pressure HS0 (Mpa) / Pump rated pressure HN (Mpa)

  The changeover switch COS 41-15 has two sets of changeover contacts, 1-2, 1-3 and 4-5, 4-6. For example, in a water tank type water supply pump, the switching setting 41-15 is selected so that the contacts 1-2 and 4-5 are closed. Also, the pressure on the suction side of the pump is not negligible compared to the pressure generated by the pump. For example, in a direct feed water pump, the contacts 1-3 and 4-6 are selected to be closed. In this way, the problem is that the operating point of the pump changes when there is a suction side pressure. As a matter of course, when the suction side pressure of the water receiving tank type or the like can be ignored as compared with the pump generated pressure, the pressure detector 13 can be omitted and simplified.

  Next, a method for compensating acceleration / deceleration torque will be described. As is well known, the secondary current of the motor that flows during acceleration / deceleration is algebraically added to the pump load by the secondary current corresponding to the acceleration / deceleration torque. For this reason, when acceleration / deceleration torque compensation is not performed, only the method described above can be applied only as a method for estimating a flow rate after the end of acceleration / deceleration. Acceleration / deceleration torque compensation solves this problem. The motor model 41-12 gives an approximate transfer characteristic from the inverter frequency to the pump speed, and when the input is the inverter command frequency FS (Hz), the estimated pump speed N * (rpm) is obtained at the output. Is a transfer function. The differential calculator 41-13 obtains the acceleration / deceleration torque Tα * (Kg · m) by differentiating the estimated value N * (rpm) of the pump speed.

  The coefficient unit 41-14 converts the acceleration / deceleration torque Tα * that gives the reciprocal of the torque coefficient KT (Kg · m / A) into the acceleration / deceleration secondary current Iα * (A). Therefore, by subtracting the acceleration / deceleration secondary current I2α * (A) obtained here from the secondary current I2 * (A) as shown in the figure, the net secondary current I2 * corresponding to the pump shaft power is obtained. -I α * (A) can be calculated.

In the inverter drive system having a constant V / F, the following quadratic approximation formula is applied as a transfer function having the frequency command FS (Hz) as an input and the motor speed N (rpm) as an output.
N (s) / FS (s) = (KINV · (1 / KE)) / (TaTms2 + Tms + 1) ---- (6)
Where KINV = inverter voltage coefficient (V / Hz)
KE = Voltage coefficient (V / rpm)
Ta = equivalent armature time constant (sec)
Tm = mechanical time constant (sec) = [(GD2 / 375) · Ra] / (KT · KE)
GD ² = motor GD ² + pump GD ² (Kg · m ² )
KT = Torque coefficient (Kg · m / A)
Ra = equivalent armature resistance (Ω)
s = Laplace operator

In the motor model 41-12, the transfer function of the equation (6) is set. The output N by differentiating, that is, by multiplying the (GD ^2/375) s, the acceleration and deceleration torque is obtained are well known in the art. That is, the output of the differential calculator 41-13 is the acceleration / deceleration torque Tα (the acceleration torque has a positive sign and the deceleration torque has a negative sign).

  Next, the dynamic characteristic of the flow rate calculation estimation of the present invention in which the acceleration / deceleration torque compensation described above is performed will be described. FIG. 7 shows a flow rate estimation characteristic when the flow rate of the present invention is calculated and estimated in a pump system that performs constant discharge pressure control. In addition, the system resistance of the pump is intentionally increased from time 7.0 sec, the flow rate is decreased, and the following characteristic of the present invention is confirmed. From FIG. 7, it is confirmed that the estimated flow rate shows a characteristic close to the actual flow rate. The estimated flow rate is shown by changing the scale so that it can be easily compared with the actual flow rate.

  However, in this simulation, for the sake of simplicity, the efficiency of the pump efficiency generator 41-9 is fixed to the base efficiency, and the differential arithmetic operation unit 41-13 is added with a 10 msec primary delay for noise countermeasures. The first-order lag differential form is used for the simulation.

  From the above description, according to the present invention, it is shown that the flow rate can be estimated and calculated accurately, including during acceleration and deceleration of the pump. In the present invention, as an application thereof, the extremely simple case of displaying the flow rate on the flow rate display 51 and detecting the low flow rate is shown. The latter sets the low flow rate qmin with the low flow rate setting device 41-17, and when the flow rate falls below this value, the comparator 41-18 obtains a low flow rate detection signal q0 that is "1". To the sequence control circuit SEQ 31-5 to stop the pump.

  However, since the present invention is a method of calculating and estimating from the secondary current and speed of the motor corresponding to the actual flow rate and the actual pressure in principle, it is a constant compared to the conventional method of estimating the flow rate using the head approximation formula. There is an advantage that it is difficult to be influenced by flow calculation errors due to setting errors and errors. For this reason, many applications other than the above can be expected. As a simple example, although not shown in the figure, the estimated flow rate q * is squared, and this is multiplied by a coefficient Kq indicating pipe friction resistance, and the pressure setting is added to the minimum pump setting pressure hS0 (pu). For example, a constant control of the estimated end pressure can be established.

  Further, the flow rate can be controlled without a flow rate sensor. Alternatively, it is possible to construct a control for monitoring and correcting a flow rate calculation error by using it together with a conventional flow rate detection method based on a head approximation formula. In the description of the present invention, when the contacts 1-2 and 4-5 of the changeover switch 41-15 are selected to be closed, that is, the suction side pressure of the pump is sufficiently higher than the generated pressure of the pump. Small, that is, the net generated pressure of the pump can be approximated as hi (pu) ≈hnet (where hi (pu) = Hi / HN), and the net set pressure hSnet (pu) is hSU (pu ) ≪ In the case of hS (pu), the case where hSnet (pu) ≈hS (pu) can be set has been described.

  If the pump suction side pressure hSU (p.u.) Cannot be ignored, the pressure sensor 13 is installed on the pump suction side as described above. Then, the contacts 1-3 and 4-6 of the changeover switch 41-15 are selected. The net generated pressure of the pump is obtained by Hi (Mpa) −HSU (Mpa), and hnet (p.u.) Is calculated by the changeover switch 41-15 and the coefficient unit 41-16. On the other hand, the suction pressure HSU (Mpa) is converted into hSU (p.u.) by the coefficient unit 41-19.

  The set pressure hs (p.u.)-HSU (p.u.) Is selected by the contact 4-6 of the changeover switch 41-15 and is given to the pump efficiency generator 41-9 as hSnet (p.u.). In this way, the pump suction side pressure hSU (p.u.) Is configured so that no error is added to the flow rate estimation calculation even when the pump generated pressure cannot be ignored.

  The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the embodiments, and various designs can be made without departing from the matters described in the claims. It is possible to make changes. The blocks in the embodiments can be configured by known or well-known circuits.

1 is an overall configuration diagram when the flow rate estimation method of the present invention is applied to a water supply system with a constant discharge pressure control of a variable speed pump driven by a variable voltage and variable frequency power supply. (Example 1) The block FLOWD in FIG. 1 shows the flow rate calculation circuit of the present invention. It is the example which calculated the torque and excitation current at the time of setting a frequency about the motor for pumps, and operating. It is a figure showing the relationship between pump speed (p.u.) and torque (p.u.). It shows the relationship between speed (p.u.), excitation current, and torque (p.u.). It is a figure which shows the relationship between pump speed (p.u.) and efficiency (p.u.). In the pump system that performs constant discharge pressure control, the flow rate estimation characteristics when the flow rate of the present invention is calculated and estimated are confirmed by simulation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pump 2 ... Check valve 3, 4 ... Cutoff valve 11 ... Discharge pressure detector 12 ... Electric motor 13 ... Suction pressure detector 14 ... Discharge pressure detector 21 ... Inverter 31 ... Discharge pressure constant control device 41 ... Flow rate calculation circuit

Claims (5)

In a pump flow rate estimation system for estimating the flow rate of a variable speed pump driven using an electric motor controlled by a variable voltage / variable frequency power source,
Primary current detection means for detecting a primary current of the motor;
Excitation current setting means for setting the excitation current of the motor;
A secondary current calculation estimating means for calculating and estimating a secondary current by subtracting the excitation current set by the excitation current setting means in a vector from the primary current detected by the primary current detection means;
Torque estimation means for estimating the torque of the motor by multiplying the secondary current estimated by the secondary current calculation estimation means by the torque coefficient of the motor;
A motor output calculation estimating means for calculating and estimating the output of the motor by multiplying the torque estimated by the torque estimating means by the speed of the motor;
Applying the principle that the estimated motor output is equal to the shaft power of the pump, and separately dividing means for dividing the motor output by the detected net generated pressure of the pump;
Multiplying means for multiplying the value obtained by the dividing means by a preset efficiency of the pump;
The flow rate of the pump is estimated by comprising at least the pump flow rate estimation system. A transfer function calculating means for obtaining a transfer function from a variable voltage / variable frequency power source based on the motor torque estimated by the torque estimating means during acceleration or deceleration of the pump;
Based on the value calculated by the transfer function calculating means, an electric motor model mounted in the controller,
Differential operation means for differentiating with a differential time constant determined by the total inertia of the pump and the motor;
Net torque calculating means for subtracting acceleration torque or deceleration torque from the motor torque obtained by the torque estimating means to obtain a net torque;
A motor output calculating means for multiplying the net torque by a motor speed to obtain an output of the motor;
The pump flow rate estimation system according to claim 1, wherein the pump flow rate is calculated and estimated by providing at least.   3. The pump flow rate estimation system according to claim 1, wherein a frequency of the motor or a frequency command value of a variable voltage / variable frequency power source is used instead of the motor speed. In a pump flow rate estimation method for estimating a flow rate of a variable speed pump driven using an electric motor controlled by a variable voltage / variable frequency power source,
Pump based on the discharge pressure detected by the discharge pressure detector, the set value of the pressure setter, the frequency command value of the inverter, the primary current of the motor that drives the pump, and the value of the suction pressure detected by the suction pressure detector An estimated flow rate of the pump is calculated, and the constant discharge pressure control device is controlled based on the estimated flow rate of the pump.   5. The pump flow rate estimation method according to claim 4, wherein the calculated estimated flow rate of the pump is displayed on a flow rate display.

Images