reducing conducted transients in automotive windshield wiper motors

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Reducing Conducted Transients in Automotive Windshield Wiper Motors Robert Langdorf, Shuvra Das, Mohan Krishnan University of Detroit Mercy

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Reducing Conducted Transients in Automotive Windshield Wiper Motors. Robert Langdorf, Shuvra Das, Mohan Krishnan University of Detroit Mercy. Project Objectives. Study the causes of conducted transients and develop a low-cost design solution to reduce them - PowerPoint PPT Presentation

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Page 1: Reducing Conducted Transients in Automotive Windshield Wiper Motors

Reducing Conducted Transients in Automotive Windshield Wiper Motors

Robert Langdorf, Shuvra Das, Mohan Krishnan

University of Detroit Mercy

Page 2: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-02972

Project Objectives

Study the causes of conducted transients and develop a low-cost design solution to reduce them

Apply knowledge and skills obtained during other university coursework

Gain additional understanding of automotive motors and their electrical/mechanical interrelationships

Page 3: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-02973

Problem Description

When an electric motor is switched off, a large amount of energy (measured as a negative voltage) can be emitted to the main power net and can often be damaging to other devices.

For current design motor, transient emissions of >200V are possible. Customers desire no more than 100V (even less for some customers).

Page 4: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-02974

Design Considerations

Cost (there is already a very costly solution using varistors)

Packaging/Space Constraints Use of standard components

Effects on Other Electrical Requirements Other Conducted Emissions (radio

interference) Conducted Immunity Radiated Emissions

Effect on Motor Performance

Page 5: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-02975

Problem-Solving Approach

1. Create a working circuit model2. Perform some hand calculations on the

2nd-order system3. Perform PSPICE simulation4. Apply DOE principles to find optimum

solutions using PSPICE, Minitab & Excel5. Build and test physical samples to

validate results

Page 6: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-02976

Background InformationThe current design:

Capacitors

Inductors

Terminal Connections to Cover Assembly

Printed Wiring Board

Page 7: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-02977

The active components during a “switch-off” function are:– Two 0.47 F Capacitors– Two 5 H Inductor Coils– Motor (including inherent induction properties)

Background Information

Page 8: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-02978

Background InformationThe circuit used for simulation and analysis:

Page 9: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-02979

Assumptions

The high speed part of the circuit was neglected - there is no current flowing through it.

Relay was assumed to have a switching time of 0.5s. (Ford spec is <1s)

Motor armature inductance was measured at approximately 970 H.

Motor resistance, including armature and brushes was measured at approximately 0.5, but was assumed lower due to magnetic effects.

Page 10: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029710

Assumptions, cont..

The rotational load on the motor (~10Nm) was accounted for with a 25 resistance from motor ground to source ground.

There are 2 different grounds in the system

Line resistance was assumed to be 1.25 between each side of the power source and the motor brush card terminals.

Note: these two assumptions were derived empirically by changing values until a solution was found that approximates the result of a typical experiment.

Page 11: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029711

Comparison of solution to test resultProduction part test result:

Page 12: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029712

Comparison of solution to test resultPSPICE Result:

Time

0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0msV(Vout)

-400V

-200V

0V

200V

Page 13: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029713

Comparison of solution to test result

The previous voltage responses exhibit: Voltage peaks of similar magnitude Similar dampening characteristics

Page 14: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029714

Ground-to-ground issueFor a production motor, the motor ground to source ground was captured:

Page 15: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029715

Ground-to-ground issueThe PSPICE model produces a similar result:

Time

0s 0.5ms 1.0ms 1.5ms 2.0ms- V(Vmg)

-80V

-40V

0V

40V

80V

Page 16: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029716

Hand Calculations

Hand calculations were done using the same model as used in PSPICE.

The following calculation is done to find the approximate magnitude of the negative transient spike

Finding the decay takes considerably more calculation

Page 17: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029717

Steady State SolutionCurrent through motor at t=0 is 4.737Avc1 = 7.588V, vc2 = 5.921V

Page 18: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029718

Initial conditionsdi/dt = 9.184 A/s at t = 0+

Page 19: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029719

2nd Order Differential Equation

The following equation can be derived:

dt

di

Li

LCdt

di

L

R

dt

id LR

RmR

25.2612

2

The following parameters can be calculated:

57.1782

L

R 9.465941

0 LC

Page 20: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029720

2nd Order Differential Equation

The response is underdamped and the natural frequency can be expressed as:

6.46954220 d

The natural response can be expressed as:

tBtAeti ddt

n sincos)(

Page 21: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029721

2nd Order Differential EquationThe forced response, which will be neglected for now, is

expressed as:

dt

di

Lti L

f

25.26)(

This is neglected because I do not have an expression for iL related to iR

The parameters A & B in the natural response equation are calculated by applying the initial conditions:

737.4A 018.0B

Page 22: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029722

2nd Order Differential EquationThe expression for current with all of the

constants applied becomes:

ttedttiC

tv tt

RC 6.46594cos65.16.46594sin76.216)(1

)( 57.178

01

The expression for voltage across the capacitor C1 becomes:

tteti tR 6.46594sin018.06.46594cos737.4)( 57.178

Page 23: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029723

2nd Order Differential Equation Solution

Plot of voltage across C1 versus time:Voltage across capacitor based on hand calculation

-214.2 V @ 32s

-250

-200

-150

-100

-50

0

50

100

150

200

250

0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012

Time (s)

Vo

ltag

e (V

)

Page 24: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029724

Simulation ResultPSPICE Result:

V = -219.2 V @ t = 23.5 s

Time

0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0msV(Vout)

-400V

-200V

0V

200V

Page 25: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029725

Experimental Design

Comment on inductors, L1 & L2: Changing the values of the external inductors

has very minimal effect on the transient solution. Inductors in series simply add and these 5mH coils are negligible compared to the 970mH motor inductance.

These coils only will significantly effect the RFI filtering.

For the purpose of these experiments, the coils will be left unchanged.

Page 26: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029726

Experimental Design

Using PSPICE & Minitab, a DOE was performed, modifying only the values of the capacitors, C1 & C2.

Each capacitor was simulated at 5 levels: 0.047F, 0.1F, 0.47F, 1F, 4.7F

Page 27: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029727

Experimental Design

Using Minitab’s response surface feature, regression equations were formulated to help solve for the expected minimum and maximum peak voltages

Page 28: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029728

Main Effect Plots

Page 29: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029729

Main Effect Plots

Page 30: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029730

Interaction Plots

Page 31: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029731

Interaction Plots

Page 32: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029732

Regression Equations

Minimum voltage peak:

Maximum voltage peak:

Note: C2 is insignificant in the min. voltage equation and the interaction C1xC2 is insignificant in both equations.

211 1.1061.6014.561 CCV

222

211 5.243.1459.1068.6051.435 CCCCV

Page 33: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029733

Regression Solution

This yields as an optimum solution: C1 = 1.18F, C2 = 2.97 F Vmin = 0V, Vmax = 84.7V

When tested in PSPICE, the result is: Vmin = 145.5V, Vmax = 122.7V

?????This means there must be some other

relationship – try using the log of the capacitance values

Page 34: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029734

Log Regression Equations

Minimum voltage peak:

Maximum voltage peak:

Note: C2 is insignificant in the min. voltage equation and the C2

2 is insignificant in both equations.

212

121 loglog3.45log4.174log5.51log0.1855.83 CCCCCV

2122

211 loglog8.18log1.19log9.171log0.1746.144 CCCCCV

Page 35: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029735

Log Regression Solution

This yields as an optimum solution (with minimum peak-to-peak voltage): C1 = 3.81 F, C2 = 4.7 F

Vmin = -85.6V, Vmax = 51.8V

When tested in PSPICE, the result is: Vmin = -86.6V, Vmax = 65.5V

This is a much better model!!!

Page 36: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029736

Log Regression Solution

Based on feedback from the supplier, it is not recommended to pursue use of 4.7F capacitors due to the high cost of materials. 3.3F capacitors are relatively less expensive.

Using 3.3F as a limit, the log regression model is re-optimized to yield: C1 = 3.3 F, C2 = 3.3 F Vmin = -90.4V, Vmax = 49.0V

PSPICE yields: Vmin = -93.8V, Vmax = 64.4V

Page 37: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029737

Other Possible SolutionsSeveral other possible solutions exist to fix the transient

spike problem: Bridge capacitor (Y-type) Voltage suppressor Diode

These devices are placed in the circuit in this location:

Since these are much more capable of fixing the problem than only capacitors, the capacitance used in conjunction with these items can be reduced (thereby reducing cost).

Page 38: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029738

Experimental Design #2

Another designed experiment was run to simulate the effects of the various solutions: No change Bridge capacitor (0.47F) Voltage Suppressor (Vishay TPSMA27A) Diode (D1N4184 from PSPICE library)

Each option was run at 3 levels of matched C1 & C2 (matched may be better to suppress RFI): 0.47F, 0.047F, 4.7nF

Page 39: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029739

Dotplots of PSPICE Results

D1

N4

14

8

TP

SM

A2

7a

0.4

7

No

ne

0

-1000

-2000

C3

Min

Dotplots of Min by C3(group means are indicated by lines)

Page 40: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029740

Dotplots of PSPICE Results

D1

N4

14

8

TP

SM

A2

7a

0.4

7

No

ne

2000

1000

0

C3

Ma

xDotplots of Max by C3

(group means are indicated by lines)

Page 41: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029741

Analysis of Dotplots

It is evident from these plots that one of the recommended solutions may have a major impact.

Data means for each solution: None - min = -974.2, max = 829.8 0.47F Cap - min = -188.4, max = 175.6 TPSMA27A - min = -30.1, max =

1.0 D1N4148 - min = -3.7, max = 0.5

Page 42: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029742

PSPICE Result for 0.47mF Bridge Capacitor

Time

0s 0.5ms 1.0ms 1.5ms 2.0msV(Vout)

-200V

-100V

0V

100V

200V

Page 43: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029743

PSPICE Result for Voltage Suppressor

Time

0s 0.5ms 1.0ms 1.5ms 2.0msV(Vout)

-30V

-20V

-10V

0V

10V

Page 44: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029744

PSPICE Result for Diode

Time

0s 0.5ms 1.0ms 1.5ms 2.0msV(Vout)

-4.0V

0V

4.0V

8.0V

Page 45: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029745

Motor Build and Test Plan2 sets of parts have been built and tested:

Motors with the current capacitors (3x3 full factorial DOE)

C1 = 0.47F, 1F, 3.3F C2 = 0.47F, 1F, 3.3F

Motors with smaller capacitors and 2 of the voltage reduction solutions previously mentioned (3x2 full factorial):

C1 & C2 = 0.47F, 0.047F, 4.7nF C3 = 0.47F bridge capacitor, TPSMA30A Voltage

Suppressor

Page 46: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029746

Comments on Build Plan

Cost is a serious consideration: 0.047F ~ $0.025 0.47F ~ $0.046 1F ~ $0.092 3.3F ~ $0.13 TPSMA30A ~ $0.16 Diode ~ too expensive to

seriously consider

Page 47: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029747

Motor Test Plan

All motors were subjected to CE 410 (conducted emissions)

DOE principles are applied to analyze testing results

They will also be subjected to CE 420 (RFI emissions). However, timing did not allow such testing to be completed during the scope of this project

Page 48: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029748

Test ResultsFollowing shows how Minitab outputs

analysis results:

General Linear Model: Min versus C1, C2Factor Type Levels Values C1 fixed 3 0.47 1.00 3.30C2 fixed 3 0.47 1.00 3.30Analysis of Variance for Min, using Adjusted SS for TestsSource DF Seq SS Adj SS Adj MS F PC1 2 1980.0 1980.0 990.0 2.21 0.138C2 2 16958.5 16958.5 8479.3 18.96 0.000C1*C2 4 3101.1 3101.1 775.3 1.73 0.187Error 18 8050.3 8050.3 447.2Total 26 30090.0

P = 0 translates to virtually 100% confidence that the factor is significant.

Page 49: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029749

Test Results – Experiment #1

Assumptions of normality, independence of the testing order, constant variance and independence from other variables are deemed adequate based on analysis of residuals.

For the minimum peak voltage: The value of C1 is ~86% significant The value of C2 is 100% significant The interaction is ~81% significant

The effect plots (next slide) show that the optimum condition is when both capacitors are 3.3 F, similar to the simulation results.

Page 50: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029750

Test Results – Experiment #1Optimum Settings at C1, C2 = 3.30

Page 51: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029751

Test Results – Experiment #1

For the maximum peak voltage: The value of C1 is 100% significant The value of C2 is ~80% significant The interaction is ~99.4% significant

The effect plots (next slide) show that the optimum condition is when both capacitors are 3.3 F, similar to the simulation results.

Page 52: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029752

Test Results – Experiment #1Optimum Settings at C1, C2 = 3.30

Page 53: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029753

Test Results – Experiment #1

Using the optimum settings from this experiment (C1 & C2 are 3.3 F): The negative peak is about -110V The maximum peak is about +50V

Compared to the current capacitor design: Negative peak ≈ -200V Positive peak ≈ +85V This is a significant improvement

Page 54: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029754

Test Results – Experiment #2

Assumptions of normality, independence of the testing order, constant variance and independence from other variables are deemed adequate based on analysis of residuals.

For the minimum peak voltage: The effect of the matched capacitors is not

statistically significant. The effect of the suppression device is 100% The interaction effect is ~93% significant.

Based on the effect plots (next slide), the ideal solution is the combination of 4.7 nF capacitors and the voltage suppressor.

Page 55: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029755

Test Results – Experiment #2

Optimum Settings at C3 = TPSMA30A & C1C2 = 0.0047

Page 56: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029756

Test Results – Experiment #2

For the maximum peak voltage: The effect of the matched capacitors is

~92% significant The effect of the voltage suppression

devices is 100% significant The interaction is ~97% significant

The effect plots (next slide), show that the optimum solution is the combination of 4.7 nF capacitors and the voltage suppressor, similar to the simulation results.

Page 57: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029757

Test Results – Experiment #2Optimum Settings at C1C2 = 0.0047 & C3 = TPSMA30A

Page 58: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029758

Test Results – Experiment #2

Based on analysis, the overall optimal solution includes: Matched Smaller Capacitors ~4.7nF Vishay Voltage Suppressor (TPSMA30A or similar)

Using these optimum settings: The negative peak is ~ -90V The maximum peak is ~ +15V.

Compared to the current capacitor design: Negative Peak ≈ -200V Positive peak ≈ +85V This is a significant improvement, even better than the

optimized design as determined in Experiment #1.

Page 59: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029759

Conclusion

Cost comparison: Optimal solution

3 x $0.025 + $0.16 $0.235 per motor. Current cost

3 x $0.046 $0.138 per motor Varistor solution

$0.38 per motor

Page 60: Reducing Conducted Transients in Automotive Windshield Wiper Motors

SAE 2006-01-029760

Conclusion

Questions