TERM PAPER ON

CONTROL SYSTEMS IN REFRIGERATION AND AIR

CONDITIONING

SUBMITTED TO: SUBMITTED BY:

Mr. VIJAY SHANKAR AJAY KUMAR

SECTION: B4801

ROLLNO: 25

REG. NO.: 10805661

CONTENTS

INTRODUCTION

REFERIGERATION SYSTEM

TRENDS IN REFRIGERATORS

AIR CONDITIONER SYSTEM

ENERGY EFFICIENCY POWER FACTOR CORRECTION (PFC)

HIGH-VOLTAGE ISOLATION

INTEGRATION HOME NETWORK

POWER MANAGEMENT INDUCTION MOTOR CONTROLLER

TEMPERATURE CONTROL SYSTEM

DEFROST CONTROLLER SYSTEM

TESTING THE TECHNOLOGY

MOISTURE AND THE HUMIDITY CONTROLLER

DUCT CONTROLLER

ELECTRONIC CONTROLLER

INTRODUCTION

REFERIGERATION SYSTEM

Today’s refrigerators are more energy efficient, are quieter, and are smarter than the ones developed in years past. Texas Instruments has developed products to meet the challenges and requirements for these new sophisticated systems.

Energy Efficiency: Home appliance (a.k.a. white goods) motors are often oversized to account for the load torque changes and transients. Scalar techniques for control can result in inefficient systems and noisy operation. This, in turn, leads to a mediocre energy efficiency that hovers in the 40% to 50% range. By implementing the control system with TI’s digital signal controllers, designers are able to implement smaller, quieter motors with energy efficiency as high as 85% - 90%. A high efficiency is necessary to receive a stamp of approval from a governing body such as the US Environmental Protection Agency and Department of Energy ENERGY STAR rating.

High-Voltage Isolation: For larger, higher-performance products where reliability and motor-control accuracy are key concerns, TI offers isolation products that block high voltage, isolate grounds, and prevent noise currents from entering the local ground and interfering with or damaging sensitive circuitry.

TRENDS IN REFRIGERATORS:

A home mesh network consisting of home appliances, audio/video equipment, HVAC system, lighting fixtures, etc connected wirelessly and controlled via a remote control sounds futuristic but can be done. Manufacturers can develop tomorrow’s products that communicate with each other by creating intelligent home networks such that, for example, a wash load is completed and a message be displayed on your TV, or LCD display on your refrigerator or remote control.

Does not require line-of-sight Has an increased range such that one can remotely control any device from anywhere

in the home

Allows for two-way communication

Refrigerators have separate systems that are responsible for different features. However, not all refrigerators have all systems. To look for information about the operation of your refrigerator, click one of these topics:

Automatic defrost Cooling Temperature control Lighting Icemaker Ice and water dispenser Door seals and hinges

The defrost heater is similar to the burners on an electric stove. It's located just beneath the cooling coils, which are concealed behind a panel in the freezer compartment. The heater gets hot. And, because it's close to the cooling coils, any ice or frost build-up melts. As the frost and ice melt, the resulting water drips into a trough. The trough is connected to a tube that drains the water into a shallow pan at the bottom of the refrigerator. The water is then evaporated by a fan that blows warm air from the compressor motor over the pan and out the front of the refrigerator.

COOLING

You'll more quickly understand refrigerator cooling systems if you think of their action as, removing heat from the air in the refrigerator" rather than "cooling the air in the refrigerator. All residential refrigerators work on the same principal for cooling. They all have:

A Compressor A Condenser A Metering Device (Capillary Tube) An Evaporator

TEMPERATURE CONTROL SYSTEM

All refrigerators have a thermostat to maintain the proper temperature. These are usually very simple devices. When the refrigerator reaches the set temperature, the thermostat interrupts the electricity flow to the compressor, which stops cooling.

LIGHTING

Refrigerators with internal lighting normally have only one functional component--the switch--which is usually a white push-button mounted inside the refrigerator near the door. When the refrigerator door closes, the door pushes the switch to turn the light off. When the door opens, the button automatically pops back out to turn on the light. The light bulb itself is usually a standard appliance bulb.

ICEMAKER

The ice maker is a small appliance within a freezer. It's usually independent of the other systems of the refrigerator. Ice maker systems have two basic functional components: the icemaker itself and the water fill valve. The ice maker sends a signal to the water fill valve (normally located on the outside back of the refrigerator, near the bottom) to open and let water into the ice maker tray. The amount of water is determined by a cam and switch within the ice maker control panel. The icemaker sends the signal to open the water valve for a certain length of time (7-10 seconds) then stops the signal. While the ice maker is dumping the cubes into a holding bin, a metal wire similar to a coat hanger swings up to let the cubes drop below it. When the cubes have dropped, the wire comes back down. If the holding bin is full of ice, the wire cannot come all the way back down, which stops further production of ice.

DOOR SEALS AND HINGES

All refrigerator/freezer doors have a seal--a rubber-like gasket attached to the door. Usually white, almond, black, or brown, the seal's job is to keep the cool air inside the refrigerator and the room air out. The seal is lined with a magnet that runs its length and width. The magnet helps to hold the door closed and create a tight seal. The screws that hold the seal to the door also hold the door liner in and help to "square" the door. The hinges allow the door to swing open. Some hinges also assist the door in closing. For the door to close properly, the hinges must be correctly adjusted.

AIR CONDITIONER SYSTEM

Heating, ventilation, and air conditioning (HVAC) systems are becoming more sophisticated as manufacturers design features into the product that make them more reliable, quieter, more efficient, and with a higher comfort level in ambient temperature.

ENERGY EFFICIENCY:

Digital signal controller systems save energy. Since most air conditioners operate with a light load, an inverter-controlled air conditioner can adjust the compressor motor speed for a light load by changing the frequency. This allows designers to use a high-efficiency compressor motor in the outdoor unit of the air conditioner.

POWER FACTOR CORRECTION (PFC):

PFC is a technique of counteracting the undesirable effects of electric loads that create a power factor that is less than

PFC is needed because of the continuous transients and surge currents exhibited by the electric motor, and it is also used to boost the rectified mains voltage up to 300 V to 450 V, which is then used to power the 3-phase inverters which ultimately operate the electric motor. With TI products, PFC can be performed externally with a separate integrated circuit or it can be done in the digital signal controller eliminating the need for a separate external PFC controller.

HIGH-VOLTAGE ISOLATION:

For larger, higher-performance systems where reliability and motor-control accuracy are key concerns, TI offers isolation products that block high voltage, isolate grounds, and prevent noise currents from entering the local ground and interfering with or damaging sensitive circuitry.

INTEGRATION:

Texas Instruments provides fully-integrated solutions such as the digital signal controllers (for digital motor control, PFC, and other system functions), and relay drivers that provide up

to 8 channels, zero-volt detection, and 5 V linear regulation for 5 V logic that may reside on the board.

HOME NETWORK:

A home mesh network consisting of home appliances, audio/video equipment, HVAC system, lighting fixtures, etc connected wirelessly and controlled via a remote control is possible today with the products. TI provides customers with industry-leading compliant solutions and a broad range of proprietary RF-ICs that enable innovative low-power RF applications. HVAC and thermostat (or indoor controller unit) manufacturers can develop products that wirelessly communicate with each other. Furthermore, temperature settings can be controlled via a remote control unit. With low-power wireless solutions from TI, home owners will benefit from a universal remote control that:

Does not require line-of-sight

Has an increased range such that one can remotely control any device from anywhere in the home.

Allows for two-way communication.

POWER MANAGEMENT:

Offline 24 V power supply lines are typically available in most homes. TI offers buck controllers and linear regulators that convert this offline voltage to something the microcontroller on the thermostat or indoor controller unit can use either 3.3 V or 1.8 V typically.

INDUCTION MOTOR CONTROLLER

The use of PI controllers for speed control of induction machine drives is characterized by an overshoot during tracking mode and a poor load disturbance rejection. This is mainly caused by the fact that the complexity of the system does not allow the gains of the PI controller to exceed a certain low value. At starting mode the high value of the error is amplified across the PI controller provoking high variations in the command torque. If the gains of the controller exceed a certain value, the variations in the command torque become too high and will destabilize the system.

To overcome this problem we propose the use of a limiter ahead of the PI controller. This limiter causes the speed error to be maintained within the saturation limits provoking, when appropriately chosen, smooth variations in the command torque even when the PI controller gains are very high.In this paper, a new approach to control the speed of an indirect field oriented induction machine drive using a classical PI controller is proposed. Its simulated input – output non linear relationship is then learned off – line using a feed – forward linear network with one hidden layer.The simulation of the system using either the modified PI controller or the learned neural network controller shows promising results. The motor reaches the reference speed rapidly and without overshoot, step commands are tracked with almost zero steady state error and no overshoot, load disturbances are rapidly rejected and variations of some of the motor parameters are fairly well dealt with.Induction motor drive, Field orientation control, PI controller, Speed control

 With the apparition of the indirect field oriented control (FOC), induction machine drives are beginning to become a major candidate in high performance motion control applications. In

the complex machine dynamics, this decoupling technique permits independent control of the torque and the field.

PID classical controllers find some difficulties in dealing with the detuning problem. The complexity of the system does not allow the gains of the PID controllers to exceed a certain value causing the controller to deal very poorly with the detuning problem. At starting mode the high value of the error is amplified across the PI controller provoking high variations in the command torque which will destabilizes the system for high controller gains values. To overcome this problem we propose to use a limiter at the input of the controller in order to allow the system to accept high values of the PID controller gains.

In this paper an original PI based controller for speed adjustment of an indirect field oriented voltage fed induction machine drive is presented.

It’s simulated input-output non linear relationship is then learned offline using an appropriate neural network in order to realise a robust neural controller.

  rotor stator and mutual inductance

rotor and stator resistance

T* torque command

  rotor flux component command

J rotor inertia referred to motor shaft

B viscous friction coefficient

P number of pole pairs

  stator electrical angle

  electrical synchronous speed

  electrical rotor speed

  rotor speed

  slip speed

  speed error

  direct and quadrature component of stator voltage command

phase voltage

PROPOSED ORIGINAL CONTROLLER STRUCTURE

 Fig.1 gives the block diagram structure of a voltage fed induction motor speed control using indirect field oriented command scheme. To replace the controller used in this structure we propose the original PI based controller presented by fig. 2.

 

Fig. 1. Indirect field orientation control block diagram

Fig. 2. Proposed PI based controller structure

DEFROST CONTROLLER SYSTEM

Refrigerators are appliances where demand for both energy conservation and user functionality is increasing. Looking for new ways to improve energy efficiency in refrigerators is an important task that should not be ignored.

One area where refrigerators can improve is in the defrosting systems. Many refrigerator/freezer systems are capable of automatic defrosting. In freezers, as the coils that cool the air reach low temperatures, the humidity in the air condenses and freezes on the coils, building up frost. As coils accumulate this frost, it becomes more difficult for them to cool the air inside the freezer. This effect forces the freezer system to stay on for longer periods of time to keep the space cold.

This is why defrost systems are installed. In a typical application, a defrost system has a timer, a heater, and a terminator. At certain intervals, the timer turns off the condenser that is used to cool the system and turns on the heater, which heats up the coils to melt the frost. The terminator can be a thermostat that turns off the heater once the temperature rises to a certain

level, or it can be another timer that turns it off after a certain time. Unfortunately, this kind of temperature cycling is not optimal for food preservation and, therefore, should be kept at a minimum.

These cycles also consume a large amount of energy by heating up the coils and then cooling them back down. Many companies have developed proprietary systems for adaptive defrost control, and several patents exist on the subject. However, there is no accurate measurement of how much frost may be present, so a freezer may try to defrost itself when in fact there is no frost on the coils.

The change in the field creates a “capacitor” between the driving electrode and the object within the field, each forming a “plate” that holds the electric charge. The voltage measured on the capacitor is an inverse function of the capacitance between the electrode being measured, the surrounding electrodes, and other objects in the electric field surrounding the electrode. Increasing the capacitance results in decreasing voltage.

Visual representation of e-field sensor

Block diagram of defrost system with e-field sensor.

Measurements were then taken on the e-field sensor as the freezer was turned on with no items inside. Results showed a change in the electric field as the temperature in the freezer decreased and, to a smaller extent, as frost formed on the sides of the wall of the refrigerator where the plates were placed.

A metal ring electrode was then placed around the pipe that feeds the cooling coil to create a measurement point. The pipe was straight and smooth, and frost built up at this point at the same rate as the entire cooling coil. Measurements taken in this test showed a change in the capacitive field as frost built up on the coil (see Figure 3). The tests showed that as frost built up on the coil, the e-field sensor’s output voltage changed. Further tests showed that when the freezer temperature returned to room temperature, the e-field sensor returned to its initial readings. By monitoring the output voltage, the adaptive defrost system can better control defrost temperature cycling to improve cooling performance and energy efficiency.

Picture of third test setup and e-field input voltages.

MOISTURE AND THE HUMIDITY CONTROLLER

A minimum amount of condensation is normal, especially during higher humidity conditions. If you live in a humid area, it is normal for your refrigerator to have a certain amount of humidity on the freezer or refrigerator.

Humid room air causes moisture to build, especially when the doors are opened often. Avoid excess moisture build-up by minimizing door openings. Get all items out at one time, keep food organized, and close the door as soon as possible.

Improper sealing of the gaskets on the refrigerator or freezer doors could also cause humidity to form. Check the seal around the outside doors and the freezer door to make sure nothing is obstructing the gasket seal.

If condensation continues, adjust the temperature control colder to reduce the humidity.

Moisture may also collect on the centre mullion (divider between the freezer and refrigerator compartments) and the refrigerator cabinet flanges during periods of high humidity. Wipe surfaces dry as needed. Moisture on the vertical hinged seal (divider between the two refrigerator doors) may also occur during periods of high humidity.

 

Energy Saver option (On select French-door models) 

The refrigerator uses more energy when the Energy Saver option has been turned off because a heater in the vertical mullion is running to help reduce moisture. The Energy Saver feature turns off the vertical mullion heater.

To use the Energy Saver option: 

Press the control to On to save energy when the environment is less humid. Press the control to Off when the environment is warm and more humid, or if

moisture is noticed on the vertical mullion.

DUCT CONTROLLER

The present invention relates to a dual duct control system for use in an environmental control system. The dual duct control system is preferably utilized in a dual duct VAV box. The control system advantageously receives room temperature values, mixed air flow values, and positions the actuators in response to temperature values and flow values. The dual duct

control system preferably executes a shower algorithm implemented in software to position the actuators. The shower algorithm provides a scheme for incrementally adjusting the hot and cold air flow set points for the VAV box so the internal environment reaches a comfortable temperature within a minimum amount of time.

ELECTRONIC CONTROLLERThe limit switch is found only on frost-free refrigerators and freezers. Its function is to keep the defrost heating element from exceeding certain set temperatures. If a refrigerator has lots of frost in the freezer compartment, the problem may be the limit switch. However, other components -- the evaporator fan, the defrost timer, and the defrost heater -- can cause the same problem. Check these for malfunctions, as detailed below. If these parts are in working condition, the problem is most likely in the limit switch.

Thermostat controls regulate the temperature of the refrigerator and freezer. Remove the control panel to reach the controls.

REFERENCES:

http://www.repairclinic.com/Refrigerator-How-Things-Work

http://hbd.org/mtippin/tempcont.html

http://www.essortment.com/refrigerator-problem-repair-fix-refrigerator-temperature- control-11776.html

http://www.instructables.com/id/Temperature-Controlled-Freezer/

http://www.acmehowto.com/howto/appliance/refrigerator/check/tempcontrol.php

http://www.breworganic.com/refrigeratortemperaturecontroller.aspx