WO1996027942A1

WO1996027942A1 - Improved dc motor controller and method

Info

Publication number: WO1996027942A1
Application number: PCT/US1996/003095
Authority: WO
Inventors: Stephen F. Post; Andrew J. Shepard; Peter D. Andriola
Original assignee: Curtis Instruments, Inc.
Priority date: 1995-03-06
Filing date: 1996-03-06
Publication date: 1996-09-12
Also published as: AU5136296A

Abstract

In one embodiment, a controller (20) for a direct current permanent magnet motor (22) driven by current supplied from a battery (26), the controller including: apparatus (34) to adjust a duty cycle signal based on the level of the current and a programmed model representing one or more characteristics of the controller (20), the battery (26), and/or the motor (22). In another aspect, a controller (20) for an electric motor (22), the controller (20) including: apparatus (44, 34) to sense voltages on terminals to the motor (22) and to shut off electric power to the motor (22) if the level of the voltages of the terminals is not within a specified margin. In a further aspect, a controller (20) for controlling an electric motor (22), the controller (20) including: apparatus (34) to select one of at least two different groups of independently selectable parameter values (40), other than a motor speed parameter, representing conditions which affect vehicle performance and to adjust motor drive signals depending on the group of parameters selected. In an additional aspect, a control and operation status indication system (Fig. 3) for an electric vehicle, including: apparatus (80) to detect closing of a momentary contact switch (84) having common power wiring with a condition indicator (88). Additionally, a controller (20) for a direct current permanent magnet motor (22) to drive an electric vehicle, which controller (20) limits the speed of the vehicle when the controller (20) is in an 'off' condition. Further, there is provided a motor control system (20, 48) to indicate when speed of an electric vehicle is decreasing. Moreover, a thermally and electrically efficient semiconductor/capacitor/heatsink assembly (102) is provided.

Description

Improved DC Motor Controller and Method

Technical Field

The present invention relates to motor controllers generally and, more particularly, but not by way of limitation, to a novel motor controller for direct current permanent magnetic motors.

Background Art

Direct current (DC) permanent magnet (PM) motors are used in a variety of applications, for example, in mobility aids, such as wheelchairs and three-wheel scooters, and in industrial vehicles, such as forklift trucks.

In such a motor, the back electromotive force (EMF) generated by the motor is proportional to the motor's speed and the terminal voltage of the motor is equal to the back EMF and the voltage developed across the motor armature's impedance. Speed control in drive mode is normally accomplished by a method known as "IR compensation". In this technique, the voltage applied to the motor is increased in proportion to the current drawn, in order to compensate for the resistive losses in the armature. A disadvantage of such conventional method of speed control is that an accurate estimate of the resistance between the motor terminals is required. This becomes inaccurate at low speeds because of the non- linear voltage-current characteristic of the brushes. Additionally, there are secondary effects between the low power section of the motor controller and the motor for which there is no compensation. in convenitonal motor controllers, shorts across the motor terminals are either not protected against, resulting in destruction of the controller, or are protected by expensive and complex current sensing devices. No protection is provided for shorting of internal power semiconductors, which can cause unsafe operation or even destruction of the motor.

A conventional controller for such a motor has, at best, one or more selectable speed ranges which determine only the static effect of the throttle on the motor's speed. Most common is to have high and low speed ranges. In the case of a controller powering a mobility aid vehicle, for example, these ranges could be used for outdoor and indoor operation, respectively. However, for most applications, including those noted above, in addition to having a choice of speed ranges for indoor/outdoor use, other variables may include heavy/light loads, confined/open spaces, and positive or negative grades. The simple choice of two speed ranges does not adequately compensate for these and other variables.

It is common to have a control panel for a vehicle powered by a DC PM motor contain both momentary switches for operating the controller and associated LED indicators for displaying the controller's response to the operator. This configuration has a significant cost impact on the vehicle because it requires separate wiring for both the switch and the indicator.

A disadvantage with conventionally controlled vehicles is presented if they are required to be pushed, when it is necessary to do so, for example, when the battery is dead. A serious problem can occur if the vehicle is pushed too fast or if it rolls uncontrolled down an incline, as property and/or persons inside or outside the vehicle can be in jeopardy as well as the possibility of damage to the vehicle itself. Another disadvantage of conventional motor controllers is that the brake light on the vehicle is lighted only in response to a switch or other means responsive to the throttle being released. Thus, the brake light is not lit when a vehicle is slowed considerably under throttle control, which can create a dangerous condition.

It is also desirable for the power semiconductors and associated capacitors and heatsink in a motor controller to be optimally arranged thermally and electrically, with the semiconductors in intimate contact with the heatsink and with the semiconductors and capacitors closely disposed.

Accordingly, it is a principal object of the present invention to provide improved means and method for controlling the speed of a DC PM motor.

An additional object of the invention is to provide protection against internal power device failures and shorts in the external motor circuit. Another object of the invention is to provide means and method for controlling a DC PM motor which compensate for a variety of operating conditions.

Yet a further object of the invention is to reduce the cost of wiring a vehicle control panel. It is an additional object of the invention to provide means and method to prevent a disabled DC PM powered vehicle from being pushed, or rolling, too fast.

It is another object of the invention to provide a motor controller which will cause a brake light to be lighted when the vehicle slows for a selected length of time.

It is a further object of the invention to provide a motor controller in which the power semiconductors and associated capacitors and heatsink optimally arranged thermally and electrically. Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.

Disclosure of Invention

The present invention achieves the above objects, among others, by providing, in one preferred embodiment, a controller for a direct current permanent magnet motor driven by current supplied from a battery, said controller comprising: means to provide a duty cycle signal to motor driving means coupled to said motor; means to sense current drawn by said motor and provide an indication of the level thereof; and means to receive said indication of the level of said current and to adjust said duty cycle signal based on said level of said current and a programmed model representing one or more characteristics of said controller, said battery, and/or said motor. In another aspect of the invention, there is provided a controller for an electric motor, said controller comprising: means to sense voltages on terminals to said motor and to provide an indication of the level thereof; and means to receive said indication of said level of said voltages and to shut off electric power to said motor if said level of said voltages of said terminals is not within a specified margin from either terminal voltage while said controller is actively driving said motor terminals. In a further aspect of the invention, there is provided a controller for controlling an electric motor, said controller comprising: means to provide drive signals to said motor; means to select one of at least two different groups of independently selectable parameter values, other than a motor speed parameter, said parameters representing conditions which affect vehicle performance; and means to adjust said drive signals depending on the group of parameters selected. In an additional aspect of the invention, there is provided a control and operation status indication system for an electric vehicle, comprising: momentary contact switch, closing of which said switch affects operation of said vehicle; indicating means to indicate a condition effected by momentary said closing or not of said switch; said switch and said indicating means sharing common power wiring; means to sense said closing or not of said switch and to control activation or deactivation of said indicating means in response thereto; and means to continuously and rapidly deactivate said indicating means and to sense the condition of said switch during times said indicating means is deactivated. An additional aspect of the invention is to provide a controller for a direct current permanent magnet motor to drive an electric vehicle, said controller to limit the speed of said vehicle when said controller is in an "off" condition, said controller comprising: means to sense voltage produced by generator action of said motor by the rotation thereof when said motor is not being powered by electricity, and to provide an indication of the level of said voltage; and means to sense said indication of said level of said voltage and to short circuit said motor to provide braking if said level of said voltage exceeds a predetermined limit. In another aspect of the invention, there is provided a motor control system to indicate when speed of an electric vehicle is decreasing, said system comprising: means to control speed of said vehicle; throttle means to provide speed request signals to said means to control; visual stop indicating means electrically connected to said means to control; and said means to control to cause said brake light to be illuminated if said means to control attempts to decelerate said vehicle for more than a predetermined interval of time. In a further aspect of the invention, there is provided a semiconductor/capacitor/heatsink assembly, comprising: an inverted generally Pl-shaped heatsink member having two flanges extending horizontally outwardly therefrom near the upper edges of vertical, parallel, spaced apart walls of said member, said walls defining therebetween an open channel; a plurality of capacitors disposed in said channel; and plurality of vertically disposed semiconductors clamped to outside surfaces of said walls.

Brief Description of Drawings

Understanding of the present invention and the various aspects thereof will be facilitated by reference to the accompanying drawing figures, submitted for purposes of illustration only and not intended to define the scope of the invention, on which:

Figure 1 is a block diagram of a DC PM motor controller according to the present invention.

Figure 2 is a block diagram of the main control circuitry of the controller.

Figure 3 is a block/schematic diagram showing an arrangement for reducing the cost of control panel wiring. Figure 4 is a table showing an example of multiple mode variables according to the present invention.

Figure 5 is an isometric view of a power circuit board for a motor controller having a semiconductor/capacitor/heatsink arrangement according to the present invention. Figure 6 is a side elevational view, partially in cross-section, of the power circuit board of Figure 5.

Figure 7 is a bottom plan view, looking up, partially cut-away, of the power circuit board of Figure 5. Best Mode for Carrying Out the Invention

Although various aspects of the present invention are described with reference to the operation and control of DC PM motors, other aspects of the invention are applicable, as well, to other types of electric motors or to electric vehicles generally and it is intended that the description and appended claims are to be so interpreted.

Reference should now be made to the drawing figures, on which similar or identical elements are given consistent identifying numerals throughout the various figures thereof, and on which parenthetical references to figure numbers direct the reader to the view(s) on which the element(s) being described is (are) best seen, although the element(s) may be seen also on other views.

Figure 1 illustrates a DC PM motor controller constructed according to the present invention, generally indicated by the reference numeral 20, connected to control a DC PM motor 22 linked to a load 24 which load may be assumed, for illustrative purposes only, to be one of the mobility aid or industrial vehicles noted above (not shown). Power for motor 22 is provided by a battery 26. Controller 20 includes a throttle input 30 to conventional throttle processing circuitry 32 which provides a speed request to main control circuitry 34. Main control circuitry 34 provides drive signals to power stage circuitry 36, comprising a semiconductor bridge, which, in turn, provides drive power from battery 26 to motor 22.

Throttle processing circuitry 32 also receives acceleration, deceleration, and maximum speed inputs from multi-mode circuitry 40, the latter receiving a mode select input 41 and also providing IR coefficient and current limit inputs to main control circuitry 34. Main control circuitry 34 also receives a current sense input from power stage circuitry 36, inputs from output fault sense circuitry 42 and motor voltage sense circuitry 44, the latter two elements being connected to the output of the power stage circuitry, and an input from battery voltage sense circuitry 46. Main control circuitry 34 provides an output to a brake light 48.

Figure 2 illustrates drive signals generation circuitry 50 which is the portion of main control circuitry 34 which provides drive signals to power stage circuitry 36, the drive signals being duty cycle, direction, and open bridge, the latter being a command to turn off the semiconductors in the power stage. According to the present invention, inputs to drive signals generation circuitry 50 include output fault sense 42, battery voltage sense 46 (both Figure 1), a control circuit model 54, and outputs from speed control circuitry 52. Speed control circuitry receives current sense, temperature sense, and IR coefficient inputs and includes: a conventional IR compensation section 60; a programmed circuit model section 62 which models the characteristics of battery voltage changes, power stage switching delay times, power stage voltage drop, and all other delays in the system; and a programmed brush model section 64 which models the characteristics of motor brush voltage drop.

Referring now to Figure 3, a microprocessor 80 is coupled to an input circuit 82 which senses the closing of a momentary contact switch 84. Microprocessor 80 controls an LED driver 86 to turn on or turn off an LED 88. A conductor 90 is shown in broken lines to indicate that it would otherwise be present in a conventional control panel (not shown). Also, in such a conventional control panel, conductors 92 would be absent and switch 84 and LED 88 would be independently wired.

The operation of the foregoing elements of the present invention will now be described. Improved speed control is provided by sections 60, 62, and 64 in speed control circuitry 52 (Figure 2) receiving current sense information from power stage circuitry 36 and, through the programmed models in the speed control circuitry, causing bridge drive signals generator to vary its duty cycle output. It has been found that this arrangement provides superior speed control compared to the conventional method of simply varying duty cycle in proportion to the current drawn. In addition to conventional current limiting in controller 20, protection is also provided against shorted power devices and full or partial shorts across the terminals of motor 22 (Figure 1). Such shorts could be induced by insulation failure or failure of the motor brushes. This additional protection is provided by output fault sense circuitry 42 (Figure 1) detecting combinations of voltage levels at the connection terminals of motor 22 that could not be present under operation in the absence of a motor or controller failure and shutting the controller off in their presence. Any voltage on the motor terminals not within a specified margin from either battery terminal voltage while the controller is actively driving the motor terminals is considered a fault and causes drive signals generation circuitry 50 (Figure 2) to provide an open bridge signal to power stage circuitry 36 (Figure 1).

Multiple mode operation allows selection of several sets of multiple parameters which affect the static and dynamic response of controller 20 (Figure 1) to both throttle and load changes to compensate for different handling conditions of a vehicle under various circumstances. Each set consists of an independently selectable value for parameters such as acceleration rate, deceleration rate, maximum forward throttle request, amount of IR compensation, load, load position, and current limit. Figure 4 illustrates, qualitatively, how these parameters might be adjusted for four exemplary modes. The table is not intended to be inclusive and many other modes are possible for these and other vehicles and any other parameters which affect handling of a vehicle could be added. Selection of the particular mode is by operator input to multi-mode circuitry 40 (Figure 1) from operator operated mode select 41.

Referring now to Figure 3, momentary contact switch 84 may, for example, be a switch for one of three different inputs: mode, direction, and power on/off. LED 88 is on or off, depending on the control condition. In order to eliminate conductor 90 and to share a common conductor 94, LED is continuously and rapidly turned off (if it is on) by LED driver 86 and the condition of switch 84 is sensed during the off time. The duration of shutoff time for LED 88 is less than the operator's response time and the shutoff cycle rapid enough that a closing of switch 84 will not go undetected. The shutoff time of LED 88 is also short enough that any flickering of the LED will go unnoticed by the operator.

Controller 20 (Figure 1) permits a vehicle to be pushed safely when it is necessary to do so. When the vehicle is pushed, the rotation of PM motor 22 produces a voltage by generator action which is sensed by motor voltage sense 44 and transmitted to main control circuitry 34. This voltage is used to power controller 20 and is also an indication of the speed of the vehicle. When the speed becomes excessive, main control circuitry 34 causes power stage circuitry 36 to short motor 22 to provide braking. Because of the inertia of the vehicle, this procedure results in smooth control of the vehicle's velocity.

To provide an indication that a vehicle is slowing prior to the time throttle 30 (Figure 1) is released, whenever controller 20 attempts to decelerate the vehicle for more than 0.5 second, main control circuitry 34 causes brake light 48 to be lighted, thus providing an indication to others behind the vehicle that the vehicle is slowing and may be preparing to stop.

Referring now to Figures 5-7, there is illustrated a power circuit board 100 for a motor controller, having mounted thereon a semiconductor/capacitor/heatsink assembly, the motor controller being generally indicated by the reference numeral 102 and being constructed according to the present invention. Power circuit board 100 is a two-layer board and assembly 102 is optimally arranged both thermally and electrically therefor, but is also optimally arranged thermally for any number of board layers.

Assembly 102 includes an inverted generally PI- shaped heatsink member 120 having flanges 122 and 124 extending outwardly therefrom near the upper edges of vertical, parallel, spaced apart walls 130 and 132 defining therebetween an open channel 134. A plurality of capacitors, as at 138, is disposed in channel 134. Heatsink 120 is attached to circuit board 100 by means of a plurality of screws, as at 136 (Figures 6 and 7). A plurality of vertically disposed semiconductors, as at 140, is clamped to the outside surfaces of walls 130 and 132 by means of a plurality of vertical spring clamps, as at 142. Each spring clamp 142 is secured in place by means of tabs, as at 144, formed at the lower edges of the spring clamps and inserted into correspondingly configured openings, as at 146 (Figure 6), defined in circuit board 100, and by the distal ends of fingers, as at 148 (Figures 5 and 6) inserted into grooves 150 and 152 (Figure 6) defined in the lower surfaces of flanges 122 and 124, respectively. A plurality of vertical threaded holes, as at 160 (Figures 5 and 6) is defined in the upper surface of heatsink 120 for the mounting of assembly 102, with attached circuit board 100, to a suitable surface. A thermally conductive, electrically insulating fabric 152 (Figure 6) is disposed between semiconductors 142 and walls 130 and 132. Heatsink 120 may be formed from an aluminum extrusion and given an anodized surface.

So arranged, each set of paralleled semiconductors 142 is physically adjacent two battery planes on one side of circuit board 100 and two motor connection planes on the other side of the board, with capacitors 138 disposed between the sets of paralleled semiconductors 142. This arrangement results in the minimum possible electrical resistance and inductance in the semiconductor-capacitor current path and provides excellent heat dissipation from semiconductors 142. The shape of heatsink 120 allows a minimal thermal impedance path between semiconductors 140 and the upper, mounting surface of the heatsink. The present invention also contemplates within the scope thereof other semiconductor arrangements, such as interleaving the sets of paralleled parts, that utilize the same physical arrangement of heatsink 120, semiconductors 140, and capacitors 138.

It will thus be seen that the objects set forth above, among those elucidated in, or made apparent from, the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown on the accompanying drawing figures shall be interpreted as illustrative only and not in a limiting sense. it is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Claims

1. A controller for a direct current permanent magnet motor driven by current supplied from a battery, said controller comprising:

(a) means to provide a duty cycle signal to motor driving means coupled to said motor;

(b) means to sense current drawn by said motor and provide an indication of the level thereof; and

(c) means to receive said indication of the level of said current and to adjust said duty cycle signal based on said level of said current and a programmed model representing one or more characteristics of said controller, said battery, and/or said motor.

2. A controller, as defined in Claim 1, wherein: said one or more characteristics is (are) selected from the group consisting of: battery voltage changes, power stage switching delay times, motor brush drop, and power stage voltage drops.

3. A method of controlling a direct current permanent magnet motor driven by current supplied from a battery, said method comprising:

(a) providing a duty cycle signal to motor driving means coupled to said motor;

(b) sensing current drawn by said motor and provide an indication of the level thereof; and

(c) receiving said indication of the level of said current and adjusting said duty cycle signal based on said level of said current and a programmed model representing one or more characteristics of said controller, said battery, and/or said motor.

4. A method, as defined in Claim 3, wherein: said one or more characteristics is (are) selected from the group consisting of: battery voltage changes, power stage switching delay times, motor brush drop, and power stage voltage drops.

5. A controller for an electric motor, said controller comprising:

(a) means to sense voltages on terminals to said motor and to provide an indication of the level thereof; and

(b) means to receive said indication of said level of said voltages and to shut off electric power to said motor if said level of said voltages of said terminals is not within a specified margin from either terminal voltage while said controller is actively driving said motor terminals.

6. A method of controlling for an electric motor, said method comprising:

(a) sensing voltages on terminals to said motor and providing an indication of the level

5 thereof; and

(b) receiving said indication of said level of said voltages and shutting off electric power to said motor if said level of said voltages of said terminals is not within a specified

!0 margin from either terminal voltage while said controller is actively driving said motor terminals.

7. A controller for controlling an electric 15 motor, said controller comprising:

(a) means to provide drive signals to said motor;

(b) means to select one of at least two different groups of independently selectable parameter values, other than a motor speed parameter, 0 said parameters representing conditions which affect vehicle performance; and

(c) means to adjust said drive signals depending on the group of parameters selected.

5 8. A controller, as defined in Claim 7, wherein: said parameters are one or more parameters selected from the group consisting of: acceleration rate, deceleration rate, maximum throttle request, amount of IR compensation, current limit, load, and load position. 0

5

9. A method of controlling an electric motor, said controller comprising:

(a) providing drive signals to said motor;

(b) selecting one of at least two different groups of independently selectable parameter values, other than a motor speed parameter, said parameters representing conditions which affect vehicle performance; and

(c) adjusting said drive signals depending on the group of parameters selected.

10. A method, as defined in Claim 9, wherein: said parameters are one or more parameters selected from the group consisting of: acceleration rate, deceleration rate, maximum throttle request, amount of IR compensation, current limit, load, and load position.

11. A control and operation status indication system for an electric vehicle, comprising: (a) a momentary contact switch, closing of which said switch affects operation of said vehicle; (b) indicating means to indicate a condition effected by momentary said closing or not of said switch; (c) said switch and said indicating means sharing common power wiring;

(d) means to sense said closing or not of said switch and to control activation or deactivation of said indicating means in response thereto; and

(e) means to continuously and rapidly deactivate said indicating means and to sense the condition of said switch during times said indicating means is deactivated.

12. A method of controlling and indicating operation status of an electric vehicle, comprising:

(a) providing a momentary contact switch, closing of which said switch affects operation of said vehicle;

(b) providing indicating means to indicate a condition effected by momentary said closing or not of said switch;

(c) providing said switch and said indicating means sharing common wiring;

(d) sensing said closing or not of said switch and controlling activation or deactivation of said indicating means in response thereto; and

(e) continuously and rapidly deactivating said indicating means and sensing the condition of said switch during times said indicating means is deactivated.

13. A controller for a direct current permanent magnet motor to drive an electric vehicle, said controller to limit the speed of said vehicle when said controller is in an "off" condition, said controller comprising:

(a) means to sense voltage produced by generator action of said motor by the rotation thereof when said motor is not being powered by electricity, and to provide an indication of the level of said voltage; and

(b) means to sense said indication of said level of said voltage and to short circuit said motor to provide braking if said level of said voltage exceeds a predetermined limit.

14. A method of controlling a direct current permanent magnet motor to drive an electric vehicle, said method to limit the speed of said vehicle when the motor controller is in an "off" condition, said method comprising:

(a) sensing voltage produced by generator action of said motor by the rotation thereof when said motor is not being powered by electricity, and providing an indication of the level of said voltage; and

(b) sense said indication of said level of said voltage and short circuiting said motor to provide braking if said level of said voltage exceeds a predetermined limit.

15. A motor control system to indicate when speed of an electric vehicle is decreasing, said system comprising:

(a) means to control speed of said vehicle; (b) throttle means to provide speed request signals to said means to control;

(c) visual stop indicating means electrically connected to said means to control; and

(d) said means to control to cause said visual stop indicating means to be illuminated if said means to control attempts to decelerate said vehicle for more than a predetermined interval of time when said means to control is receiving a said speed request signal from said throttle means.

16. A method of indicating when speed of an electric vehicle is decreasing, said method comprising:

(a) providing means to control said speed of said vehicle in response to speed request signals from throttle means;

(b) providing a brake light; and

(c) causing said brake light to be illuminated if said means to control attempts to decelerate said vehicle for more than a predetermined interval of time.

17. A semiconductor/capacitor/heatsink assembly, comprising:

(a) an inverted generally Pi-shaped heatsink member having two flanges extending horizontally outwardly therefrom near the upper edges of vertical, parallel, spaced apart walls of said member, said walls defining therebetween an open channel; (b) a plurality of capacitors disposed in said channel; and (c) plurality of vertically disposed semiconductors clamped to outside surfaces of said walls.

18. A method of providing a semiconductor/capacitor/heatsink assembly, comprising:

(a) providing an inverted generally Pi-shaped heatsink member having two flanges extending horizontally outwardly therefrom near the upper edges of vertical, parallel, spaced apart walls of said member, said walls defining therebetween an open channel;

(b) providing a plurality of capacitors disposed in said channel; and

(c) providing a plurality of vertically disposed semiconductors clamped to outside surfaces of said walls.