Essay: Modernization of traditional scalar V/f speed control technique of IM drives

ABSTRACT:
This thesis elaborates the modernization of traditional scalar V/f speed control technique of IM drives. In this proposed system, concept of scalar V/f control technique is kept intact though the mere change is done in the equipments used. Equipments are selected so that the required operation will be done very sophisticatedly in no time. The proposed system consists of 1ph source connected to IPM module, DSP TMS320F2812 and induction motor of 0.75 KW whose output is sensed by the eQEP sensor. The experimental results are taken for the motor under loading and unloading condition. Thus, concluded the stability of V/f ratio of the suggested system. Thus, it assures the effectiveness of the system. So, the proposed system is less complicated, cost effective and highly efficient and ultimately, reliable than the system used earlier for this type of control. The simulation results and hardware results are included in this thesis.
Keywords: Scalar V/f control, IPM module (Intelligent Power Module), DSP TMS320F2812, IM(induction motor), V/f ratio, eQEP sensor.
CHAPTER 1: INTRODUCTION
Now-a-days, induction motors are used in all commercial use, that is, in industries as the induction motors are easy to construct and are without any mechanical contacts such as brushes as that of DC motor which eliminate frequent maintenance. Also, its speed control and traction is easy than other means. It can be controlled either by microprocessor or Digital Signal Processor. Its construction is robust than DC. The electric component used for the speed control is called as the electric drives.
Today, IM are highly demanded in industries. More than 1 IM are used in single industries and for its speed control, basic scalar V/f control technique is used. So, there is a need for its operation to be optimized. It has the major disadvantage is that its output changes if load is applied to it which causes the wear and tear of the motor as well as the complete setup. Hence, it is not preferable to use it for the high precision system. So, numerous advancements were done in the techniques to enhance the speed control. But its complexity increased and also the cost of the system. So, to avoid this, there was a need of one advanced solution which will easily control the speed in loaded conditions, majorly, and does not increases the cost and complexity.
Types of speed control of IM:
scalar control: V/f control
vector control: DTC, FOC etc
Basics of scalar V/f control:
The synchronous speed of induction is-
Ns=120*f/P
Where,
Ns is the synch.speed
F is the supply frequency
P is the staor poles
When 3 phase ac supply is given to the stator of induction motor, then alternating voltage is generated in it which produces the magnetic field in the rotor. To match stator flux speed rotor rotates in the same direction but with some less speed, this speed is called as base speed Nb and the flux speed is called as synchronous speed Ns. the difference between Ns and Nb is the slip which is directly proportional to load but inversely proportional to speed.
% slip= (Ns-Nb)/Ns*100
Where,
Sync and base Speeds are in RPM.
 
Now,
Stator vtg α stator flux * angular velocity
V α K* 2Bf
K α V/f
 
This is the V/f concept.
ADVANTAGES OF TRADITIONAL SCALAR V/f :
Not complicated.
Easy to implement
Cost effective
Disadvantages of the trsditional scalar V/f control:
Slow operation
Cannot be used for low frequencies or in high speed operations
Suitable for only low and medium speed and precision operation
Less efficient than FOC or DTC which comes under vector control technique.
 
 
 
CHAPTER 2:LITERATURE SURVEY
Mainly three papers were referred:
A New Simplified V/f Control of Induction Motor for Precise Speed Operation.
In this paper the output was observed at specific constraint ie, at cut off freq. equal to 0.
Paper proposed simple construction with high performance index at the constraints decided.
Limitation:
It does not show the correct results to the values set other than that of 1.
At low frequencies system output disturbs.
 
Sensorless Closed Loop V/F Control Of Medium- Voltage High- Power Induction Motor With Synchronized Space Vector PWM
Space vector technique is used.
Based on yhe formulaes and simulation results conclusion were obtained.
Voltage booster technique is used to keep V/f constant.
Sub harmonics,even and triplen harmonics were removed.
Limitation:
Voltage to be boosted is difficult to determine.
Complex system.
A Novel Stator Flux Oriented V/F Control Method In Sensorless Induction Motor Drives For Accuracy Improvement And Oscillation Suppression
Oscillation suppression, slip frequency compensation, stator resistance compensation is used.
Harmonics are reduced in greater extend.
Limitation:
System is complicated.
Control parameter should be designed sophisticatedly to keep the system stable.
 
 
 
 
 
CHAPTER 3:METHODOLOGY
All the compensation techniques used in earlier methods are replaced by the use of DSP KIT TMS320F2812 [1],[2],[3]and[7]. In this kit, the programs are stored and implemented in accordance with the load applied. So, it performs to provide the desired quantity in very less time. This enhances the system operation. It does it so by comparing the output speed with the reference speed and finally, providing the desired parameter to establish the balance between output and reference. All the need of compensations is hence, eliminated. So we can say that this is the brain of the system of the as it performs all algorithms in it.
 
 
Fig.1 block diagram of the proposed system.
 
Above fig.1. is the absolute system with the power circuit , driver and controller circuit. This system consists of 1ph power supply, IMP module, DSP kit, IM, eQEP sensor. DSP TMS320F2812 comes under the category of driver and controller circuit as it is giving its output to the input of IPM and finally, to the IM. IPM module comes under the controlling category as it controls the over current, over voltages also the special feature is thermal protection in the system. it consisting of IGBT panels which will be triggered by the controlling pulses from DSP kit. It works for the protection of complete system so can be called as the heart of the complete prposed system. this module smartly performs according to the pulses provided by the DSP kit. so this is Intelligent Power Module.
Here, sensors are used to sensed the output of the IM. In this system, special type of sensor is used that is, eQEP sensor. Electronic Quadrature Encoder Pulse detects the reduced speed and gives that to the DSP kit. also, DSO is used to verify the system pulses.
 
 
CHAPTER 4: TOOLS/PLATFORM
Basically, it consist of
Software: CCStudio v3.3 and MATLAB10 32bit.
Hardware: the power supply, auto trsnsformer, IMP module, DSP kit TMS320F2812, Induction Motor, eQEP sensor, computer.
Now,
Software:
MATLAB is used to construct and verify the output of simulations.
CCS v3.3 is used to check the hardware implimeneted results. To perform this system, this setup is required. here, we can see the output of IM under load and no load conditions. Speed can be verified here.
Hardware:
Here,
IPM module:
Source
IM
Sensor
DSP TMS320F2812
Computer
emulator
Source:
1 phase, AC source, 50 hz supply is given to the system via auto-transformer. Auto transformer is used to set up the required dc voltage at the IPM module.
IPM module:
It is Intelligent Power Module which consists of 6 IGBTs connected as shown in fig 2. The front panel consisting of over voltage protection relay(capacitor). It can be turn on and off by switching MCB at the left top corner. On the left bottom coner supply 1 ph is to be given. Top consist of connection ports for the DSP 64 and 32 pins repectively. On right top corner we can observe the Vdc to be setup for the system. bottom right hand corner pins are meant for the 3 phase supply produced by the IGBTs according to the output conditions. So, it acts as inverter in this system.
Here IGBTs are used of the ratings- 1200V, 20A.
 
fig 2. Fornt panel of IPM
 
Induction Motor:
Induction motor is the asynchronous motor which is having stator ad rotor. Here we are using 1HP otor ie. 0.75 KW. Its lowest speed is 300 rpm and max speed is 1415 rpm.
Specifications Rating
Stator poles 4
HP rating 1 hp
Current rating 1.8 A
Rated speed 1415 rpm
Power factor 0.8
 
Here motor is connected to the output of IPM module viz. receiving the 3 phase supply. So according to the triggering by dsp kit it will get the output voltage managed to the desired level. Load is connected to IM.
 
DSP TMS 320F2812:
Here, emulator is connected in between the computer and DSP kit for the interfacing. Programs are stored in DSP by writting it in computer. Here, c2000 family is used. It has 32 pin and 64 pin for the analog to digital conversion and the pulse production for the IGBTs. it is then connected to the IMP module. Following fig.3. shows the DSP TMS320F2812.
 
fig.3 actual DSP TMS320F2812
to turn on DSP kit, switch is provided at the top . The DSP kit used in this system consists of 2 ports: At the top left corner, one for PWM signal (64 pin port) other for the ADC Feedback path (32 pin port). One display is provided for the display of execution of the program. For decrement, increment and reset, the switches are provided at the right side bottom corner. Programming can be done by CCSv3.3.
This kit provides 60 million instruction per second to execute on it. It is used to compare and modulate. Emulator is connected to interface it with the computer for programming purpose. C or C++ language can be used for the programming purpose.
Operating speed: 150 Mhz
Program /data memory : 256 kb RAM
For the PWM generation, it has some features.
It has 2 event managers: EVA and EVB they are identical to each other. Sub components as:
Interrupt logic: gives priority to interrupts while performance
General-Purpose (GP) Timers: counts the pulses. 2 for EVA (1,2) and 2 for EVB(3,4) [T1CON]
Full- Compare Units: for the comparision of the pulses [ COMCONA] and [COMCONB]
Programmable Deadband Generator: this is special feature. Two components must not short circuit. So this sub component is present to prevent from short circuiting.[DBTCONA] and [DBTCONB]
PWM Waveform Generation: generates the PWM according to the output conditions.
Double Update PWM Mode : new changed PWM is obtained by comparing the output speed.
Capture Unit: capture the output and keep it close to required.
Quadrature – Encoder Pulse (QEP) Circuit: for sensing the output of eQEP sensor
Sensor: eQEP
This is the special sensor which detects the speed by counting the dark and white band on it.when it is turn on,it starts the counting. When it completes 1 min then it counts the resemblance. If the starting point and end point is same then the speed is same. But if not, then it will calculate the diffence by comparing with the reference value, and gives output signal to the DSP kit. this sensor gives the speed in RPM. Folling fig. 4 . shows the dark and white band for the measurement of speed.
 
fig.4 eQEP sensor
CHAPTER 5:DESIGN AND IMPLEMENTATION
Connections should be done properly. Then, turn ON the PC hving the programs in it. Turn on the DSP. Interface correctly. Now, turn on the supply to the system. Adjust 300V Vdc by observing it in the IPM module. This process should done gradually. Observe DSP. It shows “SERIAL MODE”. By using toggle switch adjust the set speed and by using reser switch reset the DSP. Then turn on MCB of IPM module.
Steps to measure the speed:
Double click on setup CC Studiov3.3
My system
System configuration:
Family: C28XX
Platform: xds100usb
Select R2812XDS100USB emulator
Select
Add
Save and quit
Click yes
Files: right click on :project
Open project
F drives
Ac motor 2812 ADC
Sincl_2812 (for close loop)
Sincl.pjt (project file)
Select
Debug : sincl.pjb
On screen go to debug
Select connect
Ascii code will be generate automatically
Source file: isr for generation for pwm
Rebuilt all
Built complete
File
Load program
Debug folder
Sincl.out
Open
Debug on screen
Run
Take the reading after increasing the dc link voltage to 300V.
Motor will run.
Motor will start running with the base speed. Take reading for no load first. Then apply some load observe the changes. It can be observed that within some seconds the system restors the set value. So, this is done by the DSP and Sensor. Sensor will sense the reduced output and give it to the DSP kit. DSP kit will follow the algorithm are according to that give pulses to the IGBTs . IGBT on IPM module will be triggered and gives the output to the IM. IM will run by taking that increased voltage and thus, maintains the speed.
 
 
 
 
 
 
 
 
CHAPTER 6: RESULTS AND CONCLUSION
Probes are connected in between port 1 and 4. DIGITAL SIGNAL OSCILLOSCOPE is used to see this waveform.
 
Fig.5. pulses of IGBT 1 and IGBT 4
 
Fig.6 IGBT 3 and IGBT 6 pulses
 
 
Fig.7 waveform of IGBT1 and IGBT6
.
 
 
Fig.8 pulses of IGBT 3 IGBT4
 
These are the triggering pulses used for the triggering of IGBTs in the IPM module. DSO is used to take this snapshots. Deadband can be observed.
 
Fig.9 output of matlab simulation
TABLE 1: UNLOADED CONDITION
Stator voltage
(V) fref
(Hz) frun
(Hz) Set speed
(RPM) Run speed
(RPM) V/f set V/f run
87.98 10.60 10.60 300 300 8.30 8.3
147.22 17.7 17.7 502 502 8.29 8.29
161.30 19.4 19.3 550 549 8.29 8.30
234.92 28.3 28.2 801 800 8.30 8.30
293.239 35.33 35.33 1000 1000 8.30 8.30
 
 
 
 
 
 
TABLE 2: LOADED CONDITION
Stator voltage
(V) fref
(Hz) frun
(Hz) Set speed
(RPM) Run speed
(RPM) V/f set V/f run
87.98 10.60 10.60 300 300 8.30 8.3
147.22 17.7 17.7 502 502 8.29 8.29
161.30 19.4 19.3 550 549 8.29 8.30
234.92 28.3 28.2 801 800 8.30 8.30
293.239 35.33 35.33 1000 1000 8.30 8.30
 
CONCLUSION:
From above, table 1 and table 2 proves that the set speed and run speed are almost same during loading and unloading condition which is keeping the V/f ratio also constant. This is achieved by the fast processing device DSP TMS320F2812. It processes the samples fast and gives the triggering to the IGBT module. It triggers and gives the output to the IM. So, the system assures precision, reliability, and the efficiency. This Modern V/f control for Closed loop Operation of Induction Motor Drives by using DSP TMS320F2812 technique can be used for the motors having the ratings upto 3 HP.
 
 
 
 
 
 
 
 
CHAPTER 7:FUTURE SCOPE
This method can be established on the kits where instead of IGBT CMOS is used. Then system will response faster than this method. If the design parameter is designed so sophisticatedly then it can be work for high speed operation.