A FREQUENCY CONTROL METHOD FOR REGULATING WIRELESS POWER TO IMPLANTABLE DEVICES
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
science projects buddy
Active In SP
**

Posts: 278
Joined: Dec 2010
#1
18-12-2010, 08:50 PM


A FREQUENCY CONTROL METHOD FOR REGULATING WIRELESS POWER TO IMPLANTABLE DEVICES
Presented By:
Jyothis.R
S7 ECE
College Of Engineering, Trivandrum
2007-11 batch


.ppt   A FREQUENCY CONTROL METHOD FOR REGULATING WIRELESS POWER1.ppt (Size: 896.5 KB / Downloads: 64)

CONTENTS
Objectives
Need for Wireless Power Supply (WPS)
Architecture of WPS
Circuit Diagram of WPS
Analysis of Frequency Control
Switched Capacitor Control
Conclusion
References
OBJECTIVES
Study the architecture of WPS
Analysis of power flow against frequency
Presents a method to regulate the power by adjusting resonant frequency
WHY WPS?
Supply energy for indefinite period
Avoids risk of infection
No reliability problems
WPS WORKING
Use magnetic field for energy transfer
High frequency ac current produced in primary coil
Secondary coil gets power by electro magnetic induction

CLOSELY COUPLED WPS
NEED FOR POWER REGULATION

Power varies due to loose coupling
Power transfer depends on match b/w resonant frequencies
Coupling conditions varies because of day-to-day activities
Power variation causes tissue heating & device damage

ARCHITECTURE OF WPS
Primary coil placed outside & driven by push pull converter
Secondary coil implanted under the skin
Coupling coefficient varies in the range 0.1 - 0.3

EXTERNAL PRIMARY
IMPLANTABLE SECONDARY
ANALYSIS OF POWER FLOW AGAINST FREQUENCY
CURRENT & VOLTAGE WAVEFORMS


Relationship between frequency & power
Relationship between phase & frequency
ZERO LOAD CONDITION
F1 & F2 are boundary frequencies to maintain constant output
Operation between F1 & F2 causes high power dissipation
Operate at frequency under F1 or over F2
Contd..
SWITCHED CAPACITOR FREQUENCY CONTROL
Capacitors at the input port of resonant tank are controlled by hard switching of MOSFETS
Frequency variation can’t be smooth
Causes switching losses
Produces surge current ,that may damage the device

ALTERNATIVE
Variable capacitance controlled by soft switching a capacitor with varied duty cycle
No destructive surge current
Less switching losses
Frequency range is determined by total capacitance
PUSH- PULL RESONANT CONVERTER
PHASE CONTROL METHOD
WAVE FORMS

CONCLUSION
Discussed power regulation method based on frequency control
Relationship between power & frequency derived
Explained phase control method to vary frequency
REFERENCES
H. Maki, Y. Yonezawa, E. Harada, and I. Ninomiya, “An implantable telemetry system powered by a capacitor having high capacitance,” in Proc. 20th Annu. Int. Conf. IEEE Eng. Med. Biol. Soc., Oct. 2008, vol. 4, pp. 1943–1946.
A. S. Berson, “Magnetic control and powering of surgically implanted instrumentation,” IEEE Trans. Magn., vol. MAG-19, no. 5, pp. 2157–2161, Sep. 2008.
R. S. Sanders and M. T. Lee, “Implantable pacemakers,” Proc. IEEE, vol. 84, no. 3, pp. 480–486, Mar. 2008.


Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion
Reply
science projects buddy
Active In SP
**

Posts: 278
Joined: Dec 2010
#2
18-12-2010, 09:54 PM

A FREQUENCY CONTROL METHOD FOR REGULATING WIRELESS POWER TO IMPLANTABLE DEVICES
Submitted By:
Sreesyam k
S7 AE
Roll no.65


.doc   A FREQUENCY CONTROL METHOD FOR REGULATING WIRELESS POWER TO IMPLANTABLE DEVICES.doc (Size: 280 KB / Downloads: 47)

ABSTRACT

This paper presents a method to regulate the power transferred over a wireless link by adjusting the resonant operating frequency of the primary converter. A significant advantage of this method is that effective power regulation is maintained under variations in load, coupling and circuit parameters. This is particularly important when the wireless supply is used to power implanted medical devices where substantial coupling variations between internal and external systems is expected. . A frequency control method is proposed for regulating the operating frequency of the WP supply .The operating frequency is changed dynamically by altering the effective tuning capacitance through soft switched phase control A switched-capacitor method of varying the effective resonant capacitance of the primary power converter is proposed and developed. This method offers dynamic control of the operating frequency of the WP supply while retaining low switching losses and smooth frequency variations. A thorough analysis of the proposed system has been undertaken, and experimental results verify its functionality.


INTRODUCTION
IMPLANTABLE biomedical devices have found applications in a wide range of areas, including pacemakers, cochlear implants, physiological monitoring devices, drug infusion devices, functional electrical stimulators (FES), left ventricular assist devices (LVAD), and artificial hearts. The traditional approach to supplying power to these devices is implantable batteries and percutaneous links. However, any battery has a limited energy storage and life span, and percutaneous links are susceptible to infection and reliability problems. Wireless power (WP) supplies offer the opportunity to provide power for indefinite periods without the risk of infection from a percutaneous lead.

A WP supply making use of magnetic fields for energy transfer will consist of a primary (external) power circuit and a secondary implantable power pick-up. A primary converter employed in the primary station produces a high frequency alternating current flowing through an external coil (track), generating an alternating electromagnetic field. The presence of the time varying field within the secondary coil induces currents which can be converted to power an implanted device. A common characteristic associated with biomedical applications is loose coupling between the primary and secondary coils. Compensation for loose coupling can be achieved through the use of resonance circuits which enables the voltage (or current at the secondary to boost up to useful levels even in the presence f low coupling coefficients. The ability to achieve power transfer is dependent on the match between the resonant frequency of the primary with the resonant frequency of the secondary. In applications such as cochlear implants the external coil can be fitted to the skin on the scale in a consistent manner and the coupling coefficient is repeatable. However, for high power applications, such as LVADs, the size of WP systems dictate that they must be located in soft tissue locations where the coupling conditions are likely to vary not only between patients, but from day-to-day activities such as posture changes and fitting. Although some efforts have been made to provide consistent coupling, these can lead to skin irritation and lesions. This work presents a method of regulating power which is robust to variations in coupling.
3

ARCHITECTURE OF WP SUPPLY
High power implantable devices such as LVADs and artificial hearts require up to 10–30 W of power. The primary coil is placed outside of a patient, driven by a converter power from a portable battery. The secondary power pick-up coil is implanted under the skin, facing the primary coil. Typically the coupling coefficient of such a system will be within the range of 0.1–0.3 and the distance between the external and internal coils is less than 3cm . A current-fed push–pull resonant converter is employed at the primary side due to its advantages of high efficiency, low harmonics and small physical size . The primary track (coil) is represented by an inductor , which connects to a constant capacitor C and a variable capacitor in parallel, forming a resonant tank. The operating frequency of the WP supply is equal to the push–pull converter zero-voltage-switching (ZVS) frequency .


where ,T and are the initial phase angle, the quality factor and the time constant of the resonant tank. It can be seen from that the operating frequency is dependent on the capacitance.

The secondary pick-up coil is represented by Ls , it is parallel tuned with capacitor Ct. The voltage induced in the pick-up coil can be boosted up according to the designed boost-up-factor of the resonant circuit . Using air core windings for the primary and secondary coils reduces weight and temperature rise by eliminating core losses. The dc inductor Ldc is to maintain the continuous current flow through the rectifier, making power transfer from ac to dc side smooth and uninterrupted It is complicated to determine an optimal operating frequency of a WP supply, because there are many factors that need to beconsidered—including physical size, power efficiency ,power capacity, electromagnetic interference (EMI), tissue heating ,and ZVS operation.
4

CIRCUIT DIAGRAM


.
External primary





Implantable Secondary
5
ANALYSIS OF PO
WER FLOW AGAINST FREQUENCY

To design a WP supply based on frequency control, it is necessary to analyze the relationship between the power follow and the operating frequency of the system. It is also necessary to determine the range in frequencies required to allow for load, coupling and circuit parameter variations.


Thevenin equivalent of parallel tuned pick up circuit






The ac voltage source Voc represents the open circuit voltage induced in the pick-up coil. The output dc voltage Vdc is supplied to the load. For maximum power transfer purpose, the dc inductance Ldc is normally designed to be larger than a value determined by equation given below to ensure the continuation of the dc current under the steady-state conditions . This also means that the input current Iac of the rectifier is in the shape of a square waveform having an approximate constant magnitude of Idc



6

as seen by the inductor in the pick-up. Neglecting harmonics the current Iac appears as a sinusoidal waveform with the peak value of ,being the amplitude of the fundamental component of the Fourier series. The current Iac and voltage Vac are in phase because the diodes of the rectifier conduct only when forward voltages are applied. Specifying the pdhase angle difference between voltages to be , as shown in Fig. The phasor of the current can be determined by (3). In addition, the amplitude of is governed by the output dc voltage
according to (4). This indicates that the voltage will remain constant as the pick-up output voltage is maintained constant at Vdc

Under steady-state conditions, the following equation can be
obtained using the relationship

Iac = IL - Ic
7



Power deliverd to the load




Where K is a constant called boost Up Factor

The power will vary with frequency . This shows the basis for using the control of frequency to achieve regulation of power. In addition, it can be seen that controlling the primary frequency can also compensate for the errors and variations of the circuit parameters

8
RELATION SHIP BETWEEN FREQUENCY AND POWER






Graph illustrates the steady-state relationship between the power flow and the operating frequency , It can be seen that the shape of the relationship between and is parabolic with a maximum power occurring at the natural resonant frequency f0

As a comparison, the power transfer for a reduced value of boost-up-factor is also shown in Fig. The maximum power for the boost-up-factor K’ is obtained at the same full tuning frequency , but the magnitude of the peak is less. However, the curve for has a wider frequency range, from F1’to F2’ shown in Fig. This indicates that the WP supply with a higher boost-up-factor needs more accurate frequency control with a higher resolution to achieve equivalent power regulation than a system with a lower boost-up-factor.

9
RELATIONSHIP BETWEEN FREQUENCY AND PHASE





Fig shows the relationship between the phase angle and the operating frequency . It can be seen that the phase angle moves from to while the frequency varies from the boundary F1 toF2 . Actually, the phase angle is the power transfer angle of the pick-up. If K is constant, varying the frequency changes the power transfer angle, so that the power
delivered in the pick-up is changed. When the system operates at the full tuning frequency for maximum power transfer, the phase angle is equal to F1and F2 are the minimum andmaximum frequencies for maintaining the constant output dc

10



SWITCHED CAPACITOR CONTROL




As discussed earlier, the primary frequency can be varied by changing the effective capacitance of the primary resonant tank. A direct on–off control of a capacitor bank has been developed for changing resonant capacitance. A number of capacitors are placed at the input port of the resonant tank, and they are controlled to be in and out by direct hard switching of semiconductor devices such as MOSFETs . Because changing the capacitance is implemented by hard switching in one of a number of capacitors in discrete steps, the frequency can not be smoothly varied. Moreover, the hard switching of the capacitors can cause larger switching losses, and resultant surge currents can damage the switching devices. The step size can be reduced and the frequency variation range can be increased by having more capacitors and switching devices, but the system size, cost and reliability would be compromised.




To reduce the power losses and achieve smooth variations of the frequency, a new method to change the resonant capacitance is proposed and implemented. A variable capacitance is controlled by soft switching a capacitor with a varied duty cycle.
This means that the effective capacitance of a capacitor is controlled by changing the average charging and discharging period of the capacitor. Because soft switching can be achieved, there is no destructive surge current to damage the switching devices. A frequency variation range is only determined by the total capacitance rather than the number of capacitors.

11
PUSHPULL RESONANT CONVERTER




Fig.(a) shows the basic structure of the push–pull resonant converter with the implementation of the frequency control. Inductor (primary coil or track), fixed tuning capacitor , and switched capacitors C s1 and C s2 form the primary resonant tank. The main switches S1and S2 are switched on and off alternatively for half a resonant period. When the converter shown in Fig.(a) operates in the duration when S1 is on and S2 is off, its equivalent circuit is shown in Fig.(b). Capacitor C s1 is not involved due to grounding through the main switch S1 . Similarly, the capacitor C s2 will not be involved in the resonant tank when the converter operates in the duration when S2 is on and S1 is off.
12
PHASE CONTROL METHOD




Soft switching is important to ensure that destructive surge currents are not generated when switching the capacitor. This is achieved using the phase control method shown in Fig.Vsyn is the signal of the resonant voltage Vref is a reference dc voltage. Gate control signals Vgsw1 and Vgsw2 are generated by comparing Vref to Vsyn . Setting the voltageVref determines the duty cycle of the gate control signals. In a WP supply, Vref is a feedback signal from the secondary side representing the actual power demand of the load.



13


Fig. shows the waveforms of Vsyn ,Vgsw ,Ics1 and current flowing through the switched capacitor . The switching angle and duty cycle of the gate control signal are varied
in response to changes of Vref. At the beginning of switching on the current is seen to be negative. This means the current is flowing through the body diode of the switch . Neglecting
the voltage drop of the diode, zero voltage switching is achieved. If the capacitances are equal, the net effect of switching the two capacitances over a resonant period is equivalent
to that of switching one capacitor of value Cs1 using dual side switching. Then the equivalent capacitance is determined by the equation



Effective capacitance can vary from zero to Cs1 when switching angle varies from 0 to 90 .

The switching angle is determined by equation


From these relations ,it is clear that the operating frequency is a function of Vref .By substituting the value of Cs in terms of the switching angle in to the equation of power,the following relations are obtained.

It shows the relation between power flow and Vref which represents the power requirement of the load. Thus the power at secondary is regulated.
14

CONCLUSION






This paper has demonstrated a power regulation method based on controlling the frequency of a primary WP supply. It can achieve regulation in the presence of variations of multiple circuit parameters prevalent in the application of powering implantable medical devices.




The relationship between power delivered and primary operating frequency has been derived. It was shown that a larger boost-up-factor k requires a smaller frequency variation range for the full range of power flow control. Also, the maximum power transfer capacity is proportional to the boost-up-factor.The phase control method of implementing a variable capacitive element performs well in controlling the operating frequency of the push–pull resonant converter while maintaining full soft switching conditions. Experimental results have shown that the power delivered to the load can be regulated effectively under a wide variety of load requirements and reasonable circuit parameter variations.






REFERENCES







[1] Maki, Y. Yonezawa, E. Harada, and I. Ninomiya, “An implantable telemetry system powered by a capacitor having high capacitance,” in Proc. 20th Annu. Int. Conf. IEEE Eng. Med. Biol. Soc., Oct. 2008, vol. 4, pp. 1943–1946.




[2] A. S. Berson, “Magnetic control and powering of surgically implanted instrumentation,” IEEE Trans. Magn., vol. MAG-19, no. 5, pp. 2157–2161, Sep. 2008.




[3] R. S. Sanders and M. T. Lee, “Implantable pacemakers,” Proc. IEEE, vol. 84, no. 3, pp. 480–486, Mar. 2008.


Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion
Reply

Important Note..!

If you are not satisfied with above reply ,..Please

ASK HERE

So that we will collect data for you and will made reply to the request....OR try below "QUICK REPLY" box to add a reply to this page

Quick Reply
Message
Type your reply to this message here.


Image Verification
Please enter the text contained within the image into the text box below it. This process is used to prevent automated spam bots.
Image Verification
(case insensitive)

Possibly Related Threads...
Thread Author Replies Views Last Post
  detecting power grid synchronization failure jaseelati 2 385 20-05-2016, 12:28 PM
Last Post: Dhanabhagya
  WIRELESS MIROSERWER seminar ideas 2 690 09-04-2016, 12:35 PM
Last Post: mkaasees
  FLEXIBLE POWER ELECTRONIC TRANSFORMER seminar tips 2 1,627 05-07-2015, 09:58 AM
Last Post: tunhtutaye
  electronic diesel control edc pdf jaseelati 0 333 17-02-2015, 03:09 PM
Last Post: jaseelati
  wireless electricity transmission ppt jaseelati 0 337 09-02-2015, 02:38 PM
Last Post: jaseelati
  electronic power generator using transistor jaseelati 0 353 31-01-2015, 01:52 PM
Last Post: jaseelati
  floating power plant ppt jaseelati 0 360 31-01-2015, 12:49 PM
Last Post: jaseelati
  global wireless e-voting ppt jaseelati 0 334 23-01-2015, 04:19 PM
Last Post: jaseelati
  inductive power transfer ppt jaseelati 0 274 23-01-2015, 02:21 PM
Last Post: jaseelati
  high speed electronics devices ppt jaseelati 0 292 23-01-2015, 02:18 PM
Last Post: jaseelati