An adjustable speed motor that does not trip ground fault interrupters (GFI s)

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1 An adjustable speed motor that does not trip ground fault interrupters Presented by DynaMotors, Inc. 1

2 Background Inverters that drive induction motors, brushless dc motors and switched reluctance motors can produce ground fault currents that cause GFI to trip 2

3 Typical 1 and 3 Phase Input PWM Motor Drive Inverters 3

4 Background Inverters that drive induction motors, brushless dc motors and switched reluctance motors can produce ground fault currents that cause GFI to trip Cabling between drive inverters and motors can conduct common-mode energy to the motor stator windings which will generate ground currents. 4

5 Background 5

6 Background Inverters that drive induction motors, brushless dc motors and switched reluctance motors can produce ground fault currents that cause GFI to trip Cabling between drive inverters and motors can conduct common-mode energy to the motor stator windings which will generate ground currents. An example of the ground current produced by a typical PWM motor drive with a 230Vac output and a 10kHz carrier frequency follows here: 6

7 Background 7

8 Background The ground currents generated in the example are about 1.3 Amperes peak with a duration of 1 usec resulting in an average current over a half cycle of one phase of about 26 mamps. Adding the ground current from the other two phases will increase the current. 8

9 Background The ground currents generated in the example are about 1.3 Amperes peak with a duration of 1 usec resulting in an average current over a half cycle of one phase of about 26 mamps. Adding the ground current from the other two phases will increase the current. The ground currents exceed the Class A GFI device tripping specification of 4 to 6 mamps. Even the Class B GFI trip current specification of 20 mamps is exceeded. 9

10 Background The ground currents generated in the example are about 1.3 Amperes peak with a duration of 1 usec resulting in an average current over a half cycle of one phase of about 26 mamps. Adding the ground current from the other two phases will increase the current. The ground currents exceed the Class A GFI device tripping specification of 4 to 6 mamps. Even the Class B GFI trip current specification of 20 mamps is exceeded. The conclusion is that this drive and motor will trip a GFI. 10

11 Background The ground currents generated in the example are about 1.3 Amperes peak with a duration of 1 usec resulting in an average current over a half cycle of one phase of about 26 mamps. Adding the ground current from the other two phases will increase the current. The ground currents exceed the Class A GFI device tripping specification of 4 to 6 mamps. Even the Class B GFI trip current specification of 20 mamps is exceeded. The conclusion is that this drive and motor will trip a GFI. Tests of typical commercial PWM drives and motors were conducted to determine if this conclusion is justified. 11

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13 There are several ways to eliminate the generation of ground currents. One way is to use VFDs that have linear sine wave outputs this is a rather inefficient solution but will work. 13

14 There are several ways to eliminate the generation of ground currents. One way is to use VFDs that have linear sine wave outputs this is a rather inefficient solution but will work. Another solution is to use a brushless repulsion motor. 14

15 There are several ways to eliminate the generation of ground currents. One way is to use VFDs that have linear sine wave outputs this is a rather inefficient solution but will work. Another solution is to use a brushless repulsion motor. The brushless repulsion motor is a variable speed motor that uses a stator winding that is connected directly to the ac mains, this implies that there is no fast rising, high frequency voltages being applied to the stator coils. 15

16 There are several ways to eliminate the generation of ground currents. One way is to use VFDs that have linear sine wave outputs this is a rather inefficient solution but will work. Another solution is to use a brushless repulsion motor. The brushless repulsion motor is a variable speed motor that uses a stator winding that is connected directly to the ac mains, this implies that there is no fast rising, high frequency voltages being applied to the stator coils. The brushless repulsion motor is also constructed with the control devices built into the motor frame. 16

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18 Construction of a Brushless Repulsion Motor 18

19 Simplified image of a Brushless Repulsion Motor Armature coil is open Armature coil is shorted 19

20 Flux pattern in 4 pole Brushless Repulsion Motor 20

21 View of FET switches and heat sink 21

22 Armature PC board view of photo sensors 22

23 View of control board and IR emitters 23

24 View of motor interior 24

25 Conclusions The adjustable speed brushless repulsion motor eliminates the need for high frequency PWM drive inverters that produce radiated and conducted energy and high frequency commonmode currents. 25

26 Conclusions The adjustable speed brushless repulsion motor eliminates the need for high frequency PWM drive inverters that produce radiated and conducted energy and high frequency commonmode currents. The problem of common-mode currents is eliminated because all the power switching is done in a closed space on the armature. 26

27 Conclusions The adjustable speed brushless repulsion motor eliminates the need for high frequency PWM drive inverters that produce radiated and conducted energy and high frequency commonmode currents. The problem of common-mode currents is eliminated because all the switching is done in a closed space on the armature. The filtering requirement for the input power line is reduced. 27

28 Conclusions The adjustable speed brushless repulsion motor eliminates the need for high frequency PWM drive inverters that produce radiated and conducted energy and high frequency common-mode currents. The problem of common-mode currents is eliminated because all the switching is done in a closed space on the armature. The filtering requirement for the input power line is reduced. No filtering is needed for the space between the controller and the armature. 28

29 Patents Dynamotor technology is protected by the US patents listed below. 5,424,625 Brushless Repulsion Motor 5,491,398 Brushless Repulsion Motor 5,686,805 Brushless Repulsion Motor 5,936,374 Brushless Repulsion Motor 6,049,187 Speed Control for Brushless Repulsion Motor 6,108,488 Speed Control for Brushless Repulsion Motor 6,321,032 Brushless Repulsion Motor 29

30 References Michigan Municipal Workers Compensation Fund Ground Fault Circuit Interrupters 9 D 1 2D2C Electrical Safety and Energy Ground Fault Circuit Interrupter (GFCI) G,Skibinski, D,Dahl, K.Pierce, R.Freed and DGilbert/, Installation Considerations for Multi Motor AC Drives and Filters Used in Metal Industry Applications / IEEE J.Erdman, R.J.Kerkman,D.Schlegel and G.Skinbinski, Effect of PWM Inverters on AC Motor Bearing Currents and Shaft Voltages, Allen Bradley Drives Div.,IEEE APEC Dallas, TX March, 1995 D.Busse, J.Erdman, R.J.Kerkman,D.Schlegel and G.Skinbinski, System Electrical Parameters and Their Effects on Bearing Currents, Allen Bradley Drives Div., IEEE APEC San Jose, CA March, 1996 OSHA, 29 CFR (b)(1)(ii), Ground fault circuit interrupters 30

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