Variable speed pumping systems

A variable speed pumping system includes a generator motor including a frequency converter, in which the variable speed pumping system, in the pumping mode, supply a power command to the generator motor to perform power control, and the power control correction signal generator adds a value obtained by multiplying a signal based on a difference between the power input command and an actual power input measured by a power detector in the pumping mode by a constant gain to a signal based on the deviation and inputs the added value to an integration control element to generate the power control correction signal based on an output signal of the integration control element.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. § 371 of International Patent Application No. PCT/JP2020/005199, filed on Feb. 10, 2020, the entire disclosure of which Application is incorporated by reference herein.

FIELD

The present invention relates to a variable speed pumping system, and particularly relates to a variable speed pumping system that enables an operation in which a power input monotonously and quickly follows a power input command to be close to the power input command in response to the power input command when a difference occurs between the power input command and an actual power input at a rotational speed according to a rotational speed command based on the power input command in a pumping mode, for example, when a deviation is generated by the influence of the pump turbine performance conversion error with respect to the rotational speed command, an increase in loss due to aging of the devices of the variable speed pumping system, or occurrence of a difference in a power input PMof each variable speed pumping system due to uneven flow distribution to each variable speed pumping system at the channel branch and an uneven input PPrequired by the pump turbine while a plurality of variable speed pumping systems shares the water conduit and/or the iron pipe conduit and/or the water discharge channel.

BACKGROUND

In contrast to a pumping mode of a variable speed pumping system, in a method in which a pump turbine is in charge of guide vane divergence control according to a power command and a head and a generator motor is in charge of power control to directly follow the power, including acceleration and deceleration to a rotational speed command based on a pumping power input command from the outside, a power response having relatively good followability to a change in a pumping power input command is obtained. Meanwhile, since a power control correction signal generator performs speed control to match the rotational speed with the rotational speed command, a control value corresponding to a difference between the power input command and the power input is accumulated in an integration control element in the power control correction signal generator until the rotational speed based on the power input command matches the rotational speed, and it is inevitable that a difference between the power input command and the actual power input is generated in a steady operation state in constant input command operation.

In a conventional variable speed pumping system, since a difference between a power input command and an actual power input in an operation in response to a rotational speed command based on the pumping power input command has not been considered, it has been inevitable that a difference between the power input command and the actual power input in an operation in response to a rotational speed command based on a pumping power input command is generated by the influence of the pump turbine performance conversion error with respect to the rotational speed command, an increase in loss due to aging of the devices of the variable speed pumping system, or occurrence of a difference in a power input PMof each variable speed pumping system due to uneven flow distribution to each variable speed pumping system at the channel branch and an uneven input PPrequired by the pump turbine while a plurality of variable speed pumping systems shares the water conduit and/or the iron pipe conduit and/or the water discharge channel.

Patent Literature 1 discloses a method in which a power control correction signal generator performs speed control to match a rotational speed with a rotational speed command in a pumping mode of a variable speed pumping system.

FIG.3is a diagram of a configuration of a variable speed pumping system disclosed in Patent Literature 1. InFIG.3, a power system is denoted by 1. A generator motor is denoted by 2. The generator motor2rotationally drives a pump turbine4directly connected to a rotor. The generator motor2is supplied with an alternating-current (AC) excitation current adjusted by a power frequency converter3to a predetermined frequency according to a rotational speed N of the generator motor2, and the generator motor2receives the alternating-current power having the same frequency, as that of the power system1to perform variable speed operation.

A speed detector is denoted by 5. The speed detector5measures the rotational speed N of the rotor and transmits a speed signal.

A rotational speed function generator for a power input command is denoted by 12. The rotational speed function generator12outputs an optimum rotational speed command NOPTbased on a rotational speed function set by a power input command POand a static head signal HST.

A subtractor is denoted by 18. The subtractor18outputs a difference between the optimum rotational speed command NOPTfrom the rotational speed function generator12and the rotational speed. N indicated by the speed signal from the speed detector5as a speed deviation signal.

A guide vane divergence function generator is denoted by 13. The guide vane divergence function generator13outputs a guide vane divergence command YOPTbased on a guide vane divergence function set according to the power input command POand the static head signal HST.

A guide vane controller is denoted by 9. The guide vane controller9controls the guide vane divergence of the pump turbine4in response to the guide vane divergence command YOPTfrom the guide vane divergence function generator13.

A power control correction signal generator is denoted by 16. The power control correction signal generator16receives the speed deviation signal from the subtractor18and outputs a power control correction signal c by the function described later in detail with reference to the drawing showing a configuration example of the power control correction signal generator16of a variable speed pumping system inFIG.4.

An adder is denoted by 19. The adder19adds the power control correction signal c from the power control correction signal generator16and the power input command POand outputs it.

A power detector is denoted by 6. The power detector6measures a power input from the power system1to the generator motor2and outputs a measured value PM. Hereinafter, PMis referred to as a power input.

A subtractor is denoted by 20. The subtractor20subtracts the power input PMfrom the power detector6from the output signal of the adder19and outputs it.

A power controller is denoted by 7. The power controller7outputs, in response to the output signal of the subtractor20, a set frequency command of the AC excitation current according to the rotational speed N of the generator motor2to the power frequency converter3.

FIG.4is a diagram showing a configuration example of the power control correction signal generator16of the variable speed pumping system shown inFIG.3. Note that the subtractor18shown inFIG.3is also shown inFIG.4for convenience.

The power control correction signal generator16includes a multiplier30, a multiplier31that is a proportional control element, an integration control element32, a differential control element33, an adder34, an upper/lower limit value limiter function35, and a multiplier36.

The multiplier30multiplies a speed deviation signal (NOPT−N) output from the subtractor18by a gain 1/N0and outputs a dimensionless rotational speed deviation signal unitized per rated rotational speed N0.

The multiplier31is a proportional control function of the proportional control element of the power control correction signal generator16and outputs a signal obtained by multiplying the dimensionless rotational speed deviation signal (NOPT−N)/N0output from the multiplier30by a proportional gain KPN.

The integration control element32performs integration by multiplying, the dimensionless rotational speed deviation signal (NOPT−N)/N0output from the multiplier30by an integration gain KIN.

The differential control element33performs inexact differential by multiplying the dimensionless rotational speed deviation signal (NOPT−N)/N0output from the multiplier30by a differential gain KDNand outputs the value.

The adder34adds the output value of the multiplier31, the output value of the integration control element32, and the output value of the differential control element33and outputs it.

The upper/lower limit value limiter function35outputs a dimensionless power control correction signal value in which the output value of the adder34is limited to a predetermined upper/lower limit value in a range of −1.0 to 1.0.

The multiplier36multiplies the dimensionless power control correction signal value output from the upper/lower limit value limiter function35by the maximum power input PMAXof the generator motor2as a gain and outputs a power control correction signal ε that is the output value of the power control correction signal generator16.

According to the variable speed pumping system disclosed in Patent Literature 1 having the configuration as shown inFIGS.3and4, as described in lines 15 to 20 on page 6 in Patent Literature 1, PM=PP, and PO=PP=PM=PO+ε if an error of the rotational speed function generator12is ignored, and the power control correction signal P eventually set to zero. As described above, the actual input PMcan be controlled according to the power input command POfrom the outside. Note that, in the above description of Patent Literature 1, input PPrequested by the pump=power input PMis satisfied since the generated losses of the generator motor2, the power frequency converter3, and the like are also ignored.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2550089 B

SUMMARY

Technical Problem

However, when the error of the rotational speed function generator12is generated by, for example, the influence of the pump turbine performance conversion error with respect to a rotational speed command, an increase in loss due to aging of the devices of the variable speed pumping system, or occurrence of a difference in a power input PMof each variable speed pumping system due to uneven flow distribution to each variable speed pumping system at the channel branch and an uneven input PPrequired by the pump turbine while a plurality of variable speed pumping systems shares the water conduit and/or the iron pipe conduit and/or the water discharge channel, power input command PO−power input PM=ε≠0 even if an optimum rotational speed command NOPTfrom the rotational speed function generator12and the speed signal from the speed detector5match with each other to be NOPT−N=0, which causes a state in which a dimensionless power control correction signal value corresponding to the power control correction signal ε is accumulated in the integration control element32in the power control correction signal generator16, and a state of power input command PO≠ power input PMcan possibly continue to occur.

FIG.5is a diagram showing an example of response analysis during input command change in a certain variable speed pumping system in which the configuration example of the power control correction signal generator16ofFIG.4is app led to the variable speed pumping system ofFIG.3while an error of the rotational speed function generator12occurs.FIG.5shows analysis results of power input command PO/maximum power input. PMAX, power input. PM/maximum power input PMAX, optimum rotational speed command NOPT/rated rotational speed N0, and rotational speed N/rated rotational speed. N0when power input command PO/maximum power input value PMAXis sequentially changed stepwise from approximately 0.72 to 0.81 to 0.91 to 1.0.

FIG.5shows that optimum rotational speed command NOPT/rated rotational speed N0and rotational speed N/rated rotational speed N0substantially match with each other in each step, but also shows that power input command PO/maximum power input PMAXand power input PM/maximum power input PMAXindicate a slight difference in each step, and that the state of power input command PO≠power input PMcontinuously occurs as described above.

The present invention has been made in view of the above, and a purpose of the present invention is to provide a variable speed pumping system that enables an operation in which a power input monotonously and quickly follows a power input command to be close to the power input command in response to the power input command in a situation where a difference occurs between the power input command and an actual power input at a rotational speed according to a rotational speed command based on the power input command.

Solution to Problem

According to an aspect of the present invention, in order to solve the problems and achieve the purpose, there is provided a variable speed pumping system including: a generator motor including a frequency converter and a primary side synchronously connected to a commercial power system although a rotor rotates at a variable speed; and a pump turbine directly connected to the rotor of the generator motor and configured to drive the generator motor in a power generation mode and to be driven by the generator motor in a pumping mode, wherein the variable speed pumping system is configured to, in the pumping mode, input to a power controller a value obtained by subtracting an actual power input from a value obtained by adding a power input command to a power control correction signal calculated by a power control correction signal generator based on a deviation between a rotational speed of the rotor and a rotational speed command calculated based on the power input command and supply a power command to the generator motor to perform power control, and the power control correction signal generator is configured to add a value obtained by multiplying a signal based on a difference between the power input command and an actual power input measured by a power detector in the pumping mode by a constant gain to a signal based on the deviation and input the added value to an integration control element to generate the power control correction signal based on an output signal of the integration control element.

Advantageous Effects of Invention

A variable speed pumping system according to the present invention has an effect of preventing a deviation from occurring between a power input command and an actual power input in a pumping mode.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of a variable speed pumping system according to the present invention be described in detail with reference to the drawings. Note that the present invention is not limited by the embodiment.

First Embodiment

The overall configuration of a variable speed pumping system according to the present invention is similar to that of a conventional variable speed pumping system shown inFIG.3. The variable speed pumping system according to the present invention differs from the conventional variable speed pumping system in a power control correction signal generator. That is, the variable speed pumping system according to the present invention has a configuration in which a power control correction signal generator16of the conventional variable speed pumping system shown inFIG.3is replaced with a power control correction signal generator161shown inFIG.1. Therefore, the power control correction signal generator161will be described below.

FIG.1is a diagram showing a configuration example of the power control correction signal generator161of the variable speed pumping system according to the present invention. InFIG.1, the same reference signs as those inFIGS.3and4used to describe the conventional example denote the same or corresponding parts. The parts denoted by the same reference signs as those inFIGS.3and4will not be described.

The power control correction signal generator161shown inFIG.1has a configuration in which an adder43is added to the input unit of the integration control element32of the power control correction signal generator16of the conventional variable speed pumping system shown inFIG.4, a subtractor40subtracts and outputs a power input PM, which is the output of the power detector6, and a power input command PO, a multiplier41multiplies the output value of the subtractor40by 1/PMAXas a gain to make it dimensionless with a maximum power input PMAXand outputs it, a multiplier42multiplies the output value of the multiplier41by a control gain K and outputs it, and an adder43adds a dimensionless rotational speed deviation signal (NOPT−N)/N0output from the multiplier30to the value output from the multiplier42, and an integration control element32receives the value output from the adder43.

In the power control correction signal generator161, even if a difference between an optimum rotational speed command NOPT, which is the speed deviation signal from the subtractor18, and a speed signal N from the speed detector5becomes zero and the output signal (NOPT−N)/N0of the multiplier30becomes zero, the output (PO−PM)/PMAX×K of the multiplier42is added to the output signal (NOPT−N)/N0of the multiplier30by the adder43and input to the integration control element32if the power input command PO(the output signal of the subtractor40)−power input P is not zero. Therefore, the dimensionless power control correction signal value in the integration control element32is sequentially corrected with a value proportional to (PO−PM), and the power control correction signal c that is the output signal of the power control correction signal generator161is also sequentially corrected with a value proportional to (PO-PM) until (PO−PM) reaches zero. Furthermore, since the rotational speed N is changed by correcting the power control correction signal s, which is the output signal of the power control correction signal generator161, by the output (PO-PM)/PMAX×K from the multiplier42, optimum rotational speed command NOPT(output signal of the subtractor18) rotational speed. N is also chanced, and is input to the multiplier31, which is a proportional control element of the power control correction signal generator161, and the integration control element.32to affect the power control correction signal ε. However, power input command PO-power input PMis controlled to be zero in a steady state by feedback by (PO−PM)/PMAX×K through the subtractor40, the multiplier41, and the multiplier42.

FIG.2is an example of response analysis during input command change in a certain variable speed pumping system in which the configuration example of the power control correction signal generator161shown inFIG.1is applied instead of the power control correction signal generator16shown inFIG.4in the same condition as that in the example of the response analysis during the input command in the certain variable speed pumping system in which the configuration example of the power control correction signal generator16shown inFIG.4is applied in the variable speed pumping system shown inFIG.3while the error of the rotational speed function generator12occurs as shown inFIG.5.FIG.2, similarly toFIG.5, shows analysis results of power input command PO/maximum power input PMAX, power input PM/maximum power input PMAx, optimum rotational speed command NOPT/rated rotational speed N0, and rotational speed N/rated rotational speed N0when power input command PO/maximum power input value PMAxis sequentially changed stepwise from approximately 0.72 to 0.81 to 0.91 to 1.0.

FIG.2shows that optimum rotational speed command NOPT/rated rotational speed N0and rotational speed N/rated rotational speed N0indicate a slight difference in each step unlikeFIG.5, but also shows that power input command PO/maximum power input value PMAXand power input PM/maximum power input value PMAXsubstantially match with each other in each step, and that the state of power input command PO=the power input PMis substantially achieved.

As described above, it is possible for the power control correction signal generator161according to the present embodiment to prevent the state of power input command PO≠power input PMfrom continuously occurring, when a difference occurs between the power input command POand the actual power input PMat the rotational speed according to the rotational speed command based on the power input command POby adding a value obtained by multiplying a signal based on a difference between the power input command POand the actual power input PMmeasured by the power detector6by a constant gain to a signal based on a difference between the optimum rotational speed command NOPT, which is an input signal of the power control correction signal generator161, and the rotational speed. N of the rotor, inputting the added signal to the integration control element32provided in the power control correction signal generator161, and performing monotonous and prompt following control in response to the power input command of the actual power input of the generator motor2. That is, it is possible to substantially achieve the state of power input command PO=power input PMas the normal state.

REFERENCE SIGNS LIST