This thesis/project/dissertation has been reviewed for 508 compliance.

To request enhancements,

please email [email protected]. SIMULATION OF VARIABLE FREQUENCY DRIVE PUMP FOR STORM WATER

CONTROL

A Project

Presented to the faculty of the Department of Electrical and Electronic Engineering

California State University, Sacramento

Submitted in partial satisfaction of the requirements for the degree of

MASTER OF SCIENCE

in

Electrical and Electronic Engineering

by

Muhammad Faisal Saeed

SPRING 2017

© 2017

Muhammad Faisal Saeed

ALL RIGHTS RESERVED

ii

SIMULATION OF VARIABLE FREQUENCY DRIVE PUMP FOR STORM WATER

CONTROL

A Project

by

Muhammad Faisal Saeed

Approved by:

______, Committee Chair Fethi Belkhouche, Ph.D.

______, Second Reader Tracy Toups, Ph.D.

______Date

iii

Student: Muhammad Faisal Saeed

I certify that this student has met the requirements for format contained in the University format manual, and that this project is suitable for shelving in the Library and credit is to be awarded for the project.

______, Graduate Coordinator ______Preetham Kumar, Ph.D. Date

Department of Electrical and Electronic Engineering

iv

Abstract

of

SIMULATION OF VARIABLE FREQUENCY DRIVE PUMP FOR STORM WATER

CONTROL

by

Muhammad Faisal Saeed

The project focuses on the application of variable frequency drives for storm water pump stations. Multiple pumps are activated according to the water level in the storage box. The multiple starts of the regular based pumps at full speed cause the pumps to consume high inrush current. This problem can be solved by using variable frequency drives.

Simulink is used in this project to show that the variable frequency drive based storm water pump stations consume less electrical energy and thus improve pump efficiently as compared to the constant speed pump stations [1].

Approved by:

______, Committee Chair Fethi Belkhouche, Ph.D.

______Date

v

ACKNOWLEDGEMENTS

This project is finished successfully through the help and support from the following people: my advisors, parents and friends. I would like to extend my sincere thanks to all of them.

I am highly indebted to Prof. Fethi Belchouche and Prof. Tracy Toups for their guidance and encouragement. Prof. Fethi Belchouche offered great help on academic knowledge, laboratory platform, project organization, and guidance of this paper. At the same time, I would like to thank Dr. Tracy Toups for being my second advisor and giving me so much valuable supervision and advice on this project, especially for his great guidance of

MATLAB simulation.

Finally, I would like to thank my parents and friends, who provided me support at any time.

The accomplishment of the project would not have been possible without them.

vi

TABLE OF CONTENTS Page

Acknowledgements ...... vii

List of Tables ...... xi

List of Figures ...... xii

Chapter

1. INTRODUCTION ………………………………………………………………. 1

1.1 Components of storm water pump station ...... 1

1.2 Variable frequency drive...... 4

1.3 Soft starter ...... 5

1.4 Pump……………………………………………………………………...... 5

2. PUMP STATION COMPONENT CHARACTERISTICS ...... 6

2.1 Dimensions of mechanical components...... 6

2.2 Pump characteristics ...... 6

2.3 Variable frequency drive characteristics ...... 10

3. PUMP STATION CONTROL SCHEMES ...... 12

3.1 Constant speed (float switch based) control ...... 12

3.2 Variable frequency drive based control ...... 14

4. PERFORMANCE CRITERIA...... 18

4.1 Total energy consumption...... 18

4.2 Water transportation efficiency...... 18

vii

4.3 Pump efficiency ...... 19

4.4 Water transportation time ...... 20

5. SIMULINK COMPONENTS ...... 21

5.1 Electrical power source and measurement ...... 21

5.2 Variable frequency drive and motor settings ...... 21

5.3 Centrifugal pump settings ...... 24

5.4 Water reservoir boxes settings ...... 25

5.5 Miscellaneous mechanical components ...... 29

5.6 Mechanical sensors ...... 30

5.7 Control system components ...... 32

5.8 Measurement block ...... 40

6. SIMULATION SETUP ...... 45

6.1 Simulation of storm water ...... 45

6.2 Simulation time ...... 46

6.3 Simulation solver ...... 46

6.4 Water level setting ...... 47

7. SIMULATION RESULTS AND COMPARISON ...... 49

7.1 Wet well water level ...... 49

7.2 Electrical energy consumption ...... 51

7.3 Pump efficiency ...... 53

7.4 Overall performance comparison ...... 57

viii

8. CONCLUSION ...... 57

8.1 Electrical energy consumption ...... 57

8.2 Pump efficiency ...... 57

8.3 Water transportation time ...... 58

References ...... 59

ix

LIST OF TABLES Tables Page

1. Typical dimensions of pump house mechanical devices .………………………6

2. Head pump curves with motor speed and flow ………………………………...8

3. Brake horsepower pump curves with motor speed and flow…………………...9

4. Pump stations electrical energy consumption’ comparison …………….……..53

5. Pump stations performance’ comparison ……………………………………...56

x

LIST OF FIGURES Figures Page

1. Typical pump house …….………………………….….……………………….3

2. Variable frequency drive……. ………………………………………………. ..4

3. Head pump curves ……………………………………………………….….….7

4. Brake horsepower pump curves…………………………………………...... 9

5. Higher-level schematics of DTC VFD …...………….……………………...... 11

6. Level based control ……….…………….…………………………………...... 13

7. Level based control ……….…………….…………………………………...... 15

8. Electrical power supply and measurements ………..………………………...... 21

9. DTC AC4 Simulink drive model …………………..………………………...... 22

10. DTC AC4 Simulink drive model parameters …………….……………………23

11. Centrifugal pump model ……………………………………..………………...24

12. Centrifugal pump parameters ……………….………………………………....25

13. Water reservoirs in storm water system …..……………………………….…..26

14. Water reservoir ports in simulink…………...... 27

15. Wet well tab settings in Simulink …..……...... 28

16. Discharge box tab settings in Simulink……………………………...... 28

17. Discharge pipe symbol in Simulink …………..…………………………….....29

18. Discharge pipe tab settings in Simulink ……………..……………………...... 29

19. Discharge pipe vertical tab settings in Simulink ……..………………………..30 xi

20. Discharge pipe check valve in Simulink …………..………………………..30

21. Ideal torque sensor in Simulink …………………………..………………....31

22. Flow sensor in Simulink …………...………………..……………………....31

23. Pressure sensor in Simulink ……………………….……….……………...... 31

24. Liquid level sensor in Simulink …….………………….……..…………...... 32

25. Constant speed control block ……………….…………….………………....33

26. Constant speed control block composition....………………..…………...... 34

27. Variable speed control block………………...... 35

28. Composition of variable speed control block………...... 36

29. Speed controller block in Simulink …………………………………...... 37

30. Level to speed converter block in Simulink …….………………………...... 38

31. Variable speed pump …………...…………..……………...……..39

32. Measurements block in Simulink ……………………..…..……..……...…..40

33. Measurements block composition in Simulink…..……………………...... 41

34. Pump efficiency calculation block composition in Simulink ………...…...... 42

35. Pump electrical energy calculation block composition ……….……...…...... 44

36. Rain level simulation using gate valve ……………….……..…………...... 45

37. Simulation time ……………………………...... 46

38. Power GUI block ……………………………………...... 46

39. Mechanical solver block ……………….……………………………...... 47

40. Constant speed pump station wet well water level …………………….….....49

xii

41. Variable speed pump station wet well water level …………………….…….....50

42. Constant speed pump station electrical energy consumption .…..……………...51

43. Variable speed pump station electrical energy consumption …………....…...... 52

44. Constant speed pump station pumps’ efficiency ……………………….……....54

xiii

1

CHAPTER 1

INTRODUCTION

Storm water pump stations are essential to avoid flooding and other losses in major roads and highways. They pump storm water from the highways to the nearby canals and levees.

Currently, the California Department of Transportation operate more than 350 storm water pump stations located at major highways and roads throughout the state.

1.1 Components of storm water pump station

In general, storm water pump stations consist of the following major components:

1. Storage Box

2. Discharge Box

3. Wet Well

4. Pumps & Motors

5. Control Room

These components are shown in figure 1 and described below.

1.1.1 Storage box

Storage boxes are vaults under the freeways or roads where water is accumulated through various gutters. Water remains in the storage box if it does not exceed the specific level.

2

1.1.2 Discharge box

Discharge boxes are the vaults usually located over a certain height above the freeway.

Water is finally pumped into the discharge box. From there water goes into the nearest canals or field through gravity. The pump outlet pipe is also located in the discharge box.

1.1.3 Wet well

Wet wells are the areas on the side of the road that contain the pumps and motor assembly

with a level-detecting device. Most of the time, when water level rises above a certain level,

the pumps get started and water is pumped out to the discharge box.

1.1.4 Pumps & motors

The pumps and motors are located in the wet well. The pumps run at specific rpm

(revolutions per minute) or with different speeds if the motors are fed through variable

frequency drives.

1.1.5 Control room

The control room is often located above the wet well. It contains all power and control

wiring for the motors and the pumps. The maintenance person can take over the automatic

operation of the pumps from the control room.

3

Figure 1. Typical pump house (Courtesy of CALTRANS)

4

1.2 Variable frequency drive

A variable-frequency drive (VFD) is a type of adjustable-speed drive used in electro- mechanical drive systems to control AC motor speed and torque by varying motor input frequency and [2]. The change in frequency is directly proportional to the change in AC speed as given by the following equation:

120 f Nm = s (1) P where

Nm = Mechanical speed of the induction motor f = Electrical frequency of the induction motor

P = Number of poles s= slip

One of the common variable frequency drives is shown in figure 2.

In this project, we will use the method to control the speed of the pump.

Figure 2. Variable frequency drive

5

1.3 Soft starter

A motor soft starter is a device used with AC electrical motors to temporarily reduce the

AC frequency of the motor during start-up to decrease the in rush current. After a specific time, the motor achieves its full speed [3]. Variable speed drives can change the speed of the motors at any time. Soft starters only reduce the speed of the motor during the start-up.

1.4 Pump

A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action. Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift, displacement, and gravity pumps [4].

Generally, the following two kinds of pumps are used in industry:

 Centrifugal Pumps

 Positive Displacement Pumps

For the storm water pump stations, centrifugal pumps are used, as storm water pump stations do not require constant flow for a given rpm. Moreover, centrifugal pumps have a wider pump curve, which is essential for variable speed pumping.

6

CHAPTER 2

PUMP STATION COMPONENT CHARACTERISTICS

For our simulation, we are considering a pump house that has the following dimensions for the wet well, discharge pipe and storage box.

2.1 Dimensions of mechanical components

Mechanical Component Height (ft) Cross-Sectional Area (ft2)

Wet Well 20 78.5

Storage Box 30 10 Discharge Pipes for Pump #1 and Pump #2 10 7.065

Table 1. Typical dimensions of pump house mechanical devices

2.2 Pump characteristics

The two pumps used in the simulation have the following characteristics:

2.2.1 Head pump curve:

Head is expressed in units of height such as meters or feet. The static head of a pump is the maximum height (pressure) it can deliver. The head of the pump varies with the flow and the input frequency of the motor as shown in figure 3.

7

Figure 3. Head pump curves (Courtesy of FLYGT)

8

The values of the head pump curves can be shown in the following table:

Freq Flow 40 Hz 45 Hz 50 Hz 55 Hz 60 Hz

0 gpm 26.4 ft 32.6 ft 41.5 ft 50 ft 60 ft

400 gpm 20.5 ft 27 ft 34 ft 42 ft 51 ft

800 gpm 15.8 ft 21.2 ft 27.5 ft 34.5 ft 42.5 ft

1200 gpm 11 ft 15.8 ft 21.5 ft 28 ft 35.5 ft

1600 gpm 5 ft 9.5 ft 15 ft 21 ft 28 ft

2000 gpm N/A N/A 8 ft 13.5 ft 20 ft

Table 2. Head pump curves with motor speed and flow

Note that the pump curves are given in frequencies instead of rpm. The frequencies will be converted to rpm when inputting values in Simulink. The values of flow in gpm (gallons per minute) shown under the column of 60 Hz will be used for constant speed applications.

2.2.2 Brake horsepower pump curve:

The brake horsepower of the pump also varies with the flow in gpm (gallons per minute) and the input frequency of the motor as shown in figure 4.

9

Figure 4. Brake horsepower pump curves (Courtesy of FLYGT)

The values of the head pump curves are shown in the following table.

Freq Flow 40 Hz 45 Hz 50 Hz 55 Hz 60 Hz

0 gpm 4.2 HP 6 HP 8.2 HP 11 HP 14.5 HP

400 gpm 4 HP 6.1 HP 8 HP 10.7 HP 14 HP

800 gpm 4.2 HP 6 HP 8.2 HP 10.8 HP 14.2 HP

1200 gpm 4.4 HP 6 HP 8.5 HP 11 HP 14.5 HP

1600 gpm 4.0 HP 6 HP 8.2 HP 11 HP 14.8 HP

2000 gpm N/A N/A 7.8 HP 10.8 HP 14.2 HP

Table 3. Brake horsepower pump curves with motor speed and flow

10

Just like in head pump curves, the brake horsepower pump curves are also given in

frequencies instead of rpm. The frequencies will be converted to rpm when inputting values

in Simulink. The values of flow in gpm shown under the column of 60 Hz will be used for

constant speed applications

2.3 Variable frequency drive characteristics

The variable frequency drive used in our simulation will vary the electrical frequency of

the AC induction motor from 40 Hz to 60 Hz. The required set point will be calculated

through the control system as shown in the next chapter. Note that the VFD will be rated

at 230V, 60 Hz. There are 4 main techniques used by variable frequency drives for

controlling the AC induction motors:

1. Six step voltage source inverter

2. Six step vector PWM (pulse width modulation) voltage source inverter

3. Field oriented control inverter

4. Direct torque control inverter.

2.3.1 Direct torque control inverter:

Direct torque Control (DTC) is one method used in variable frequency drives to control the torque (and thus the speed) of three-phase AC electric motors. This involves calculating an estimate of the motor's magnetic flux and torque based on the measured voltage and current of the motor [5]. The higher level schematics of Direct

Torque Control VFD is shown in figure 5.

11

Figure 5. Higher-level schematics of DTC VFD

2.4 Induction motor characteristics:

The electrical characteristics of the induction motors used in our simulations are :

Number of Voltage Phase Frequency Horsepower poles

220 V 3 60 Hz 4 15

12

CHAPTER 3

PUMP STATION CONTROL SCHEMES

Different control schemes are used to start the pumps when needed. In this chapter, two

different control schemes are presented to determine the number of pumps that are

activated when the water level in the wet well exceeds specific levels.

For our simulation, we are considering the following two control scenarios for duplex

control pump station:

1. Constant Speed (Float switch based) Control

2. Variable Frequency Drive based Control

Both of the above mentioned control schemes will be explained in the following sections.

3.1 Constant speed (float switch based) control

The constant speed pumping will have the following features:

3.1.1 Level based control:

For constant speed technique, we define the two pumps as lead pump and lag pump. Lead

pump is activated before lag pump. We can also divide the wet well into following four levels as shown in figure 6.

1. Lead Pump On

2. Lead Pump Off

3. Lag Pump On

4. Lag Pump Off

13

The control scheme based on the above mentioned four reference levels is:

 The lead pump will not come on if the water level in the wet well is less than the

level of the lead pump on. If the water level exceeds the level of lead pump on but

remains lower than the level of the lag pump on, the lead pump gets started and

remains on until the water level becomes lower than the lead pump off level.

 If the water level exceeds the lag pump on level, both pumps will be activated and

remain on until the water level becomes lower than the lag pump off level.

Lag On

Lead On

Lag Off

Lead Off

Figure 6. Level based control

14

3.1.2 Time based pump alternation:

Since running the same pump for a longer interval creates mechanical stress, pump alternation is crucial. The pump alternation in the scheme proposed here will be based on time. When the water level is less than the lag pump on level, the pumps start alternating after the specific time period.

3.2 Variable frequency drive based control

The variable speed pumping will have the following features:

3.2.1 Level based control:

For variable frequency drive technique, we define the following three levels for the wet well:

5. Low reference level

6. High reference level

7. High high reference level

The control scheme based on the above mentioned three reference levels is:

 Pumps will not come on if water level in the wet well is less the than the low

reference level. If the water level is between the high and low reference level, one

pump will start pumping with minimum speed and after some times, the other pump

will come on while the lead pump will turn off.

15

 If the water level is between the high reference level and the high high reference

level, the pumps will come on alternatively where the speed of the lead pump will

be proportional to the difference between the high and high high reference levels.

If the water level is more than the high high reference levels, both pumps will remain

on with their maximum speed until the water gets lower than the high high reference

level. Figure 7 explains the level based control feature.

High high

High

Low

Figure 7. Level based control

16

3.2.2 Pump speed control:

According to the variable speed pumping control scheme, when the water level is between low and high high reference level, the speed of the lead pump will be proportional to the difference of the level between high and high high reference level.

The closed loop speed control can be derived from the following equations:

Level ErrorLead = Storage Level − Low Reference Level (2)

Level ErrorLag = Storage Level − High Reference Level (3)

The water level errors are then passed to the equation that converts the water level into the speed by simply mapping the level errors to the speed ranges of the variable frequency drives linearly.

SpeedMax − SpeedMin Speed Error Slope = (4) Lead High Reference Level − Low Reference Level

Speed Error Lead = Speed Error Slope Lead × Level ErrorLead + SpeedMin (5)

Similarly, the equations for lag pump are:

17

SpeedMax − SpeedMin Speed Error Slope = (6) Lag High High Reference Level − High Reference Level

Speed Error Lag = Speed Error Slope Lag × Level ErrorLag + SpeedMin (7)

3.2.2 Time based pump alternation:

Since running the same pump for a longer interval creates mechanical stress, pump

alternation is crucial. The pump alternation in the scheme proposed here will be based on

time and it will follow the steps as shown below. When the water level is lower than the

High high reference level, the pumps start alternating after the specific time period such that they exchange their speed set points.

18

CHAPTER 4

PERFORMANCE CRITERIA

The following performance criteria have been used in our simulation of duplex control pump station:

1. Total Energy Consumption

2. Water Transportation Efficiency

3. Pump Efficiency

4. Water Transportation Time

Each criterion is explained below.

4.1 Total energy consumption

The total energy consumption identifies the total electric energy (kWh) consumed by the main electric supply for both variable frequency drives. Since Simulink only measures electric power, the electrical energy can be calculated as shown below

n (8) Electrical EnergykWh = ∑ PowerkW × ∆푡 i=0

4.2 Water transportation efficiency

In addition to the total energy consumption, another factor that plays an important role in determining the system efficiency is the water transportation efficiency which can be defined as:

19

Electrical EnergykWh Efficiency Water = (9) Water TransportedGallons

4.3 Pump efficiency

In addition to the total energy consumption, another factor that plays an important role in determining the system efficiency is the water transportation efficiency which can be defined as:

WHP Efficiency = (10) Pump BHP

where

WHP = Water horsepower

BHP = Brake horsepower

Water horsepower is the power exerted by the pump and is defined as:

Q gal × ∆PPump_psi WHP = min (11) 1715 where 1715 is a conversion factor to convert the power to imperial units.

Brake horsepower on the other hand refers to the input power needed at the pump shaft, it can be defined as:

TN.m × ωr rad/s BHP = (12) 746

20

4.4 Water transportation time

Water Transportation time is defined as the time it takes the pump system to reduce the water level of the wet well below low reference level. Even though the time it takes the pumps to reduce the water level is not as important as the other factors mentioned above, this factor should not be ignored.

21

CHAPTER 5

SIMULINK COMPONENTS

This chapter explains the components used in our Simulink simulation.

5.1 Electrical power source and measurement

In our simulation, we are assuming 220V, 3 phase, 60 Hz power supply as shown in figure 8.

Figure 8. Electrical power supply and measurements

Also note that the electrical power supply is passing through the three phase VI measurement block that will be used for active power and energy measurement.

5.2 Variable frequency drive and motor settings

As discussed before, the “direct torque control” technique has been used in our drives which means that we are taking feedback from the motor about the motor speed. In

22

Simulink, the direct torque control VFD is known as AC4 drive. The inputs and outputs of the AC4 variable frequency drive are shown in figure 9.

Figure 9. DTC AC4 Simulink drive model

5.2.1 Variable frequency drive ports:

The AC4 model has the following inputs:

 SP_ The speed set point in rpm.

 3 phase AC voltage A, B and C.

The AC4 model has the following outputs:

 S mechanical port. Note that in our simulation, this port will be connected to the

pump.

5.2.2 Variable frequency drive tab settings:

The AC4 VFD model in Simulink has the following settings as shown in figure 10.

23

Figure 10. DTC AC4 Simulink drive model parameters

24

5.3 Centrifugal pump settings

The centrifugal pump in Simulink is shown in figure 11.

Figure 11. Centrifugal pump model

5.3.1 Centrifugal pump ports:

The centrifugal pumps used in our simulation have the following ports:

 Port S will be connected to the mechanical input of the variable frequency drive

 Port T is the reference port for the storm water. Water will be pumped from T.

 Port P is the other mechanical port. Water will be pumped from port T to port P.

Note that the difference in pressure at ports P and T will create the required head for the storm water.

25

5.3.2 Centrifugal pump tab settings:

In the figure below, the pump curve values as noted in table #2 and table #3 are shown in the red block in figure 12:

Figure 12. Centrifugal pump parameters

Note that the values for pressure differential have been converted from the static head (as defined in section 2.2.1) in feet to psi using the following relationship:

푝푠푖 = 푃0.433 × ℎ푒푎푑푓푒푒푡

5.4 Water reservoir boxes settings

As mentioned before, there are three water reservoirs used in our simulation, the storage box, wet well and discharge box. These above mentioned water reservoirs are shown in figure 13.

26

Figure 13. Water reservoirs in storm water system

27

5.4.2 Water reservoir boxes ports:

These reservoirs have the following ports as shown in figure 14:

Port A and Port B: The hydraulic ports. The volume of the box rises if the liquid flows into these ports.

Port V: This port is used for measuring the volume or length of the hydraulic fluid inside the box.

Figure 14. Water reservoir ports in Simulink

5.4.3 Water reservoir boxes tab settings:

The dimensions of the reservoirs as noted in chapter 2 are shown in figure 15 and figure

16.

28

Figure 15. Wet well tab settings in Simulink

Figure 16. Discharge box tab settings in Simulink

29

5.5 Miscellaneous mechanical components

The other mechanical components used in the simulation are:

5.5.1 Discharge pipe:

Figure 17. Discharge pipe symbol in Simulink

The discharge pipe has the following settings for both pumps as shown in figure 18 and figure 19.

Figure 18. Discharge pipe tab settings in Simulink

30

Figure 19. Discharge pipe vertical tab settings in Simulink

5.5.2 Check valve:

In order to keep storm water from falling back to the wet well when the pumps are stopped, check valves are used as shown in figure 20.

Figure 20. Discharge pipe check valve in Simulink

5.6 Mechanical sensors

The mechanical sensors used in the simulation are:

5.6.1 Torque sensor:

In order to record and measure the torque to be delivered from the motors to the pumps, the ideal torque sensors have been used as shown in figure 21.

31

Figure 21. Ideal torque sensor in Simulink

5.6.2 Flow sensor:

In order to record and measure the liquid flow from each pump, flow sensors are used as shown in figure 22.

Figure 22. Flow sensor in Simulink

5.6.3 Pressure sensor:

In order to record and measure the difference in pressure between two ports, pressure sensors are used as shown in figure 23.

Figure 23. Pressure sensor in Simulink

32

5.6.4 Liquid level sensor:

In order to record and measure the liquid level at the wet well, liquid level sensor is used as shown in figure 24.

Figure 24. Liquid level sensor in Simulink

It should be noted that PS Simulink convertor gives liquid quantity in volume (ft3 ) and therefore, conversion to liquid level in feet is performed by dividing the volume by the cross sectional area.

5.7 Control system components

There are two main types of control schemes discussed in this project:

1. Constant Speed Control (Float Switch based)

2. Variable Speed Control (Variable Frequency Drive based)

5.1.1 Constant speed control:

The constant speed control block is shown in figure 25.

33

Figure 25. Constant speed control block

The constant speed control block does not have the speed controller since the speed of the pumps remain the same. However, the control blocks do include the pump alternator as shown in figure 26.

34

Figure 26. Constant speed control block composition

35

5.7.2 Variable speed control:

The variable speed control block is shown in figure 27.

Figure 27. Variable speed control block

The control system block is composed of the following two blocks.

 Speed controller

 Pump alternator

These blocks are shown below in figure 28.

36

Figure 28. Composition of variable speed control block

37

These two blocks are further explained below.

5.7.2.1 Speed controller:

Implementing the equations described in section 3.2.2, the speed controller block diagram is shown in figure 29 and figure 30.

Figure 29. Speed controller block in Simulink

38

Figure 30. Level to speed converter block in Simulink

39

5.7.2.2 Pump alternator:

Using JK flip flop, the pump alternator implemented is shown in figure 31.

Figure 31. Variable speed pump alternator

40

5.8 Measurement block

The measurement block used in simulation is shown in figure 32.

Figure 32. Measurements block in Simulink

41

As shown, for each pump motor set, the torque, pump speed, flow and pressure are measured. The measurements block is shown in figure 33.

Figure 33. Measurements block composition in Simulink

42

As seen in the block diagram, there are two additional blocks that are measuring the pump

efficiency and the electrical power consumption. These sub blocks are explained further

below.

5.8.1 Pump efficiency calculator:

Implementing equations 10, 11 and 12 from section 4.3, the pump efficiency calculator is shown in figure 34.

43

Figure 34. Pump efficiency calculation block composition in Simulink

44

5.8.2 Pump electrical energy calculator:

The Simulink blocks implementing the electrical energy calculations are shown in figure

35.

Figure 35. Pump electrical energy calculation block composition

45

CHAPTER 6

SIMULATION SETUP

This chapter shows the simulation setup for the duplex control pump station that will be used.

6.1 Simulation of storm water

To simulate storm water, the following block diagram has been used using storage tank and the gate valve as shown in figure 36.

Figure 36. Rain level simulation using gate valve

Note that for the simulation of both pump stations, the gate valve will open at 5 seconds and close at 20 seconds.

46

6.2 Simulation time

In order to simulate real life situations, we need to simulate the storm water pump station for more than 200 seconds. In this case, time has been set to 250 seconds as shown in figure

37.

Figure 37. Simulation time

6.3 Simulation solver

For power system blocks, discrete solver has been used with simulation a sample time of

0.001 seconds as shown in figure 38.

Figure 38. Power GUI block

For mechanical and hydraulic components, the sample time has been set to be the same to avoid errors as shown in figure 39.

47

Figure 39. Mechanical solver block

6.4 Water level setting

The water level references for both types of pump station are defined below:

6.4.1 Constant speed pump station water levels:

The reference water levels for two pumps are defined below for constant speed pump station:

Lead pump on: 5 feet

Lead pump off: 3 feet

Lag pump on: 8 feet

Lead pump off: 4 feet

48

6.4.2 Variable speed pump station water levels:

The reference water levels for two pumps are defined below for variable speed pump station:

Low reference level: 3 feet

High reference level: 5 feet

High high reference level: 10 feet

49

CHAPTER 7

SIMULATION RESULTS AND COMPARISON

This chapter presents the simulation results related to float switch based constant speed

storm water pump station. At the end of the chapter, the performance of both pump stations

will be compared with respect to electrical energy consumption, pump efficiency and

transportation time.

7.1 Wet well water level

The graph in figure 40 shows the water level in the wet well for constant speed storm water pump station.

Figure 40. Constant speed pump station wet well water level

50

For pumping station with variable speed drive, the wet well water level is shown in figure

41.

Figure 41. Variable speed pump station wet well water level

As described before, the gate valve for rain simulation opens at 5 seconds and closes after

20 seconds. Pumps for both stations are activated as soon as the water level reaches 5 feet.

If you compare the figures above, it can be concluded that the pump station with constant speed pumps the water out faster (190 sec) as compared to the variable speed pumping

(265 sec) because the speed of constant speed mode is set to the highest level. On the other

51 hand, for variable speed pumping, the speed of the motor gets lower as the water level goes down.

7.2 Electrical energy consumption

Both pump stations are simulated such that they transport equal amount of storm water from the wet well to the discharge box. So we can see which pump station takes less amount of electrical energy for carrying the same amount of work.

For constant speed pump station, the values are shown in figure 42.

Figure 42. Constant speed pump station electrical energy consumption

52

Similarly, for the variable speed pumping, the values are shown in figure 43.

Figure 43. Variable speed pump station electrical energy consumption

The comparison of electrical energy consumption for both pump plants is given in table 4.

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Pump Station Type

Constant Speed Pump Variable Speed Pump Station Station

Total Water Transported 5723 gal 5723 gal

Total Energy Consumed 0.3565 kWh 0.3164 kWh

Gallons per kWh 16,500 18,900

Table 4. Pump stations electrical energy consumption’ comparison

7.3 Pump efficiency

Pump efficiency is another important factor explained in section 4.3. The greater the pump efficiency, the lower the wear and tear on pump. For constant speed pump house, the pump efficiency for both pumps is shown in figure 42.

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Figure 44. Constant speed pump station pumps’ efficiency

As seen from the pump efficiency graph, the maximum efficiency for the pumps is around

85%. At the end when the water level starts dropping, the pump efficiency becomes less than 80%. It can be explained by the fact that for constant speed applications, the motors

55 are run at their maximum speed which also increases the dynamic head of the pumps that makes the pumps exert more pressure.

As seen from the graph above, the variable speed pumps efficiency reaches 99% when the water level is quite higher and the constant speed pump efficiency only reaches 85%. When the water level starts dropping, the pumps efficiencies also start dropping to less than 80% much like the same situation in constant speed.

7.4 Overall performance comparison

In order to summarize the performance comparison of both pump stations with different control schemes, a table is drawn below that compares water transportation time, pump efficiency, water efficiency and electrical energy consumption:

56

Pump Station Type

Constant Speed Pump Variable Speed Pump Station Station

Total Water Transported 5723 gal 5723 gal

Total Energy Consumed 0.3565 kWh 0.3164 kWh

Water Transportation 𝑔푎푙 𝑔푎푙 16,500 18,900 Efficiency 푘푊ℎ 푘푊ℎ Water Transportation Total 190 sec 265 sec Time

Max Pump Efficiency 85% 99%

Table 5. Pump stations performance’ comparison

Both pump stations transport the same volume of storm water from the wet well to the discharge box but they have differences in the performance criteria. Constant speed pump station performs better when it comes to water transportation time because of constant maximum speed. However, it does not perform well in the other performance criteria.

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CHAPTER 8

CONCLUSION

Two pump stations have been simulated using two different control schemes. One pump station used the conventional constant speed control using different reference levels for lead and lag pumps. The other pump station used variable speed pumping and different reference levels for both pumps. The simulation results can be summarized under the following headings.

8.1 Electrical energy consumption

The pumps controlled by variable frequency drives consume less electrical energy because they reduce the speed of the pump motor when the water level is not so high. Secondly, the pumps operate near the maximum efficiency point that makes the pumps consume less amount of energy. On the other hand, the constant speed pumps consume more energy to pump the same amount of water since they do not operate near the maximum efficiency point because of no change in speed.

8.2 Pump efficiency

The variable frequency driven pumps have better efficiency at each point as compared to the constant speed pumps. Since variable frequency drive pumps can change their speed with the change in water column of the well, they operate near the maximum efficiency

58 point. Constant speed pumps, on the other hand, keep deviating from the maximum efficiency point as the water column starts decreasing.

8.3 Water transportation time

This is the only performance criteria where constant speed pumps perform better as comparted to the variable speed pumps. Since the constant speed pumps work at their maximum speed, they transport the storm water faster as compared to the variable speed pumps that reduce their speed with the decrease of water column.

59

REFERENCES

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2011.

[2] Campbell, Sylvester J. (1987). Solid-State AC Motor Controls. New York: Marcel

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[3] Siskind, Charles S. (1963). Electrical Control Systems in Industry. New York:

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[4] Pump classifications, [online].

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