CA1184243A - Electric motor speed controller and method - Google Patents
Electric motor speed controller and methodInfo
- Publication number
- CA1184243A CA1184243A CA000379655A CA379655A CA1184243A CA 1184243 A CA1184243 A CA 1184243A CA 000379655 A CA000379655 A CA 000379655A CA 379655 A CA379655 A CA 379655A CA 1184243 A CA1184243 A CA 1184243A
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- CA
- Canada
- Prior art keywords
- motor
- voltage
- circuit
- power
- transistor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P7/00—Arrangements for regulating or controlling the speed or torque of electric DC motors
- H02P7/06—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current
- H02P7/18—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power
- H02P7/24—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices
- H02P7/28—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices
- H02P7/285—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only
- H02P7/29—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only using pulse modulation
Abstract
ELECTRIC MOTOR SPEED CONTROLLER AND METHOD
Abstract of the Disclosure An electric motor speed controller circuit which comprises at least one power transistor in series between the motor and a power supply to form a power circuit such that current flows between the power supply and the motor through the transistor only when a signal current is supplied to the base of the transistor and which further comprises a control circuit for supplying a signal to the base of the transistor which signal is pulse width modulated so that the width of the pulse is proportional to the value of a variable resistance, inductance or capacitance of the speed control;
A method for controlling the speed of an electric motor which comprises varying the resistance, inductance or capacitance of a speed control and supplying a pulse width modulated signal current, having pulse widths proportional to the value of the varied resistance, capacitance or inductance, to the base of at least one power transistor to activate the transistor which is connected by its emitter and collector, as an electrical switch in series between the motor and a power supply;
A variable speed motor controlled by the speed controller circuit; and A vehicle powered by a motor controlled by the speed controller circuit.
Abstract of the Disclosure An electric motor speed controller circuit which comprises at least one power transistor in series between the motor and a power supply to form a power circuit such that current flows between the power supply and the motor through the transistor only when a signal current is supplied to the base of the transistor and which further comprises a control circuit for supplying a signal to the base of the transistor which signal is pulse width modulated so that the width of the pulse is proportional to the value of a variable resistance, inductance or capacitance of the speed control;
A method for controlling the speed of an electric motor which comprises varying the resistance, inductance or capacitance of a speed control and supplying a pulse width modulated signal current, having pulse widths proportional to the value of the varied resistance, capacitance or inductance, to the base of at least one power transistor to activate the transistor which is connected by its emitter and collector, as an electrical switch in series between the motor and a power supply;
A variable speed motor controlled by the speed controller circuit; and A vehicle powered by a motor controlled by the speed controller circuit.
Description
f~lECTRIC ~IOTO~ SPE~D CONTROLLF.R ~MD Mr.T~lOD
B~ G~OUND Ol Tlll~ INVf:~lTION
__ __ _ _ A) l~ield of the Invention ___ _ __ _~_ This invention relates to speed controllers for electric motors anc'l especially relates to speed controllers for electric motors, particularly series-field rnotors, used to dri-ve battery powered electric vehicles.
B) Ilistory of the I'rior Art In the prior art, motors, especially DC electric motors, were generally controlled by the use of an adjustable large current series resistance. This ~ethod of controlllng the speed of an electric rnotor, particularly those used to drive electric vehicles, has been generally unsatisEactory because torque and speed are almost completely interclependent. The interdependency results in very ~oor speed regulation. In addition, such resistance controllers are e~temely ineEficient c]ue to high dissipation of electrical energy through the controller resistance elements. This energy dissipation marlcedly reduces battery llfe and the allowab]e time between charges and also increases the minimum acceptable initial size, weight and cost o-f the battery.
~ urthermore, such controllers did not result in Eully proportional speed control since frequently the controllers had to be almost in the fully on position before sufficient torque could be developed to start an electric vehicle from a stopped position. The controller would then have to be backed ofi to reduce the torque after motion started. Such controllers therefore resulted in inconsistent non-uniform motor operation ~q givlng a "jerky" feel to the movernent oE a vehicle.
More recently, an attempt has been made to control the speed of an electric motor by placing a power transistor as an elec-tronic switch between the battery and the motor and ac~ivating the transistor by supplying pulses of curr~nt to the transistor base. In general, these pulses were of constant duration and the speed was controlled in only a few stages by chopping a current at only a few different speeds~ The resulting motor operation is non-uniEorm, and electrlcal energy ls wastecl slnce current ls supplied only at a Eew levels.
BRIEF DESCRIPTION OF T~IE INVENTION
In accordance wlth wlth the present lnventlon, there ls provlded an electrlc motor speed eontroller circuit which overcomes essentially all of the previously mentioned disadvantages of prior art controller circults. In particular, the electric motor speec] controller circuit, in accordance with the present invention, is interposed between the motor and a power supply sufficient to drive the motor~ The speed controller circuit comprises at least one power transistor connected through its emitter and collector in series between the motor and the power supply to form a power circuit such that current flows between the power supply and the motor through the transistor only when a signal current is supplied to the base of the transistor. The speed controller further comprlses a speed control whlch provldes a variable resistance, lnduc~ance or capacltance within a control circuit and a control circuit having a power requirement substantially lower than the power requirement to operate the motor which supplies pulses of a pulse width rnodulated signal current to the base of the power transistor, the i~idth of the pulse being proportional to the value of the variable resistance, inductance or capacitance of the speed control.
The invention Eurther comprises a method for controlling the speed of an electric motor. The method comprises varying the variable resistance, inductance or capacitance of a speed control; and supplying a pulse width modulated signal current, having pulse widths proportional to the value of the variable resistance, inductance, or capacitance, to the base of at least one power transistor to activate the transistor which is connected by its emitter and collector as an electrical switch in series between the motor and a power supply.
The invention further comprises a variable speed motor connected with and controlled by the electrical motor speed controller of the invention and an electrical vehicle powered by a motor controlled by the electric motor speed controller of the invention.
~RIEF DESCRIPTION OF THE DP~AWINGS
Figures 1, 2 and 3 are representative graphs showing the relationship between the EMF's of an elec-trical voltage proportional to the resistance, capacitance or inductance of a speed control, the electrical voltage of a comparison saw tooth wave generated by the control circuit and the electrical voltage of a pulse modulated output signal.
FiguLe ~ is a schematic diagram of a preferred embodiment of the electric motor speed controller of the invention.
Figure 5 is a schematic layout of a 1/~ mile test course.
Figure 6 is a power curve showing the power used by a golf car controlled with the solid state controller oE the invention as the golf car moves around the test course shown in Figure 5;
and Figure 7 is a power curve showing the same golf car as Figure 6 wherein a resistor controller is used as the golf car travels the test course of Figure 5.
DETAILED DESCRI~TION OF T~IE NVENTION
The electric motor controlled by the speed controller circuit oE the invention may be any electric motor but is usually a direct current (DC) electric motor which most often has a series-field.
The power supply is any power supply sufficient to drive the motor and for a DC motor is a DC power supply which may have a uniform or variable EMF. Usually the power supply is a battery of any suitable type including one or more packaged batt~ries in series or parallel. Suitable batteries include rechargeable batteries such as lead-acid batteries; nickel-cadminum batteries and the newer lithium-chloride batteries.
~ s previously discussed, the speed controller circuit comprises at least one power transistor connected through its emitter and collector in series between the motor and the power supply to form a power circuit such that the current flows through the transistor from the power supply to the motor only when a signal current is supplied to the base of the transistor.
The power transistor is a single transistor or coupled transistors which act as a single transistor. The po~Jer transistor is clesirably a bistable transistor, i.e., a transistor whose base currellt controls both on and oEE switching but ~mder certain circumstances may be a thyrister or in the case of an al-ternating current, a ~riac. Examples of power transistors are power Darlington connected transistors~ Examples of suitable particular transistors are Motorola's MJ11028 Darlington and ~C~'s Series SE~3570 through SK3582.
A plurality of such power transistors can be used in parallel to increase the current carrying capability oE the circuit.
The speed control, which is usually manually operated, i.e., operated by human action such as a footpedal or a hand operated accelerator, provides a variable resistance, inductance or capacitance within the control circuit. The speed control usually provides a -variable resistance within -the circuit by means of a rheostat.
The control circuit is designed to have a power requirement substantially lower than the power requirement to operate the motor. The control circuit usually requires less than 10 and preferably less than 5% of the power requirement of the motor.
The control circuit supplies pulses of a pulse width modulated signal current to the base of -the power transistor or transistors, the width of the pulse being proportional to the value of the variable resistance, inductance or capacitance of the speeci control.
Pulse width modulation (PWM) is a:Lso known as pulse duration modulation (PDM) or pulse length modulation (PL~I). In general, pulse width modulation is that modulation oE a signal at an essentially constant frequency where a time length or width of pulses of a constant EMF` signal are varied in relation to an input signal. The longer the width oE the modulation, the more current is supplied with the signal and the shorter the width of the mod1llation, the less current is supplied with the signal Mumerous methods are known to those skilled in the art for creating a pulse width modulated signal sincc the signals have been examined in the area of electronics communication and to a lesser extent in the area of electronic controllers in other applications (see references on page 1~-51 of the Electronics Engineers' Handbook edited by Donald G. Eink, published by McGraw-~lill, 1975).
In accordance with a preferred embodiment of the present invention, the control circuit comprises a means for generating a constant freq-uency electrical vol-tage wave Eorm biased so that the lowest voltage of the wave is greater than zero; a means Eor generating a voltage proportional to the-variable resistance, inductance or capacitance of the speed control and a means for comparing the voltage of the wave form with the generated proportional voltage and for outputing a pulse width modulated signal to the base of the power transistor when the gcnerated proportional voltage is greater than the voltage of the electrical wave -form. The constant frequency electrical voltage wave form is most desirable a saw tooth wave form so that the lengths of the outputted signal pulses are directly proportional to the generated proportional voltage, although other constant frequency wave forr~ls can be used so that other proportional relationships can be obtained between the generated proportional voltage ancl the lengths of the outputted signal pul~ses.
"E'roportional", as used herein, means having the sarne or constant ratio or a ratio which varies in accordance with a set mathematical function. In general, the proportional relationship, in accordance with the preEerred embodiment of the invention, is a direct proportion and optionally, a proportion which varies exponentially, logarithmically or trigonometrically.
Figure 1 of the drawings shows a graph of voltage against time for a generated constant Erequency saw tooth electrical voltage wave, (a), a voltage proportional to the variable resistance when the resistance is exceedingly high thus producing a proportional voltage (b) which is lower than the lowest voltage of the constant frequency electrical voltage wave (a) and the resulting outputted pulse width modulated wave ~c) which has no pulses (pulse width zero) since at no time is the generated proportional voltage greater than the voltage oE the constant frequency electrical voltage wave.
Figure 2 shows essentially the same curve as Figure 1 except that the proportional voltage (b) ~iS sometimes greater than and sometimes less than the voltage of constant frequency electrical voltage wave (a) which resul-ts in pulses (x) which are o-utputted to the base of the power transistor in original or amplified form, the length of pulse (x) representing the current flow to the base of the transistor. The width of pulse (x) of wave (c) is determined by the length of time that the propor-tional voltage is greater than the voltage of the constant frequency electrical voltage wave form. Figure 3 again shows essentially the same relationship except that generated proportional voltage (b) is always greater than the voltage of constant frequency electrical voltage wave form (a) thus the generated current pulses (x) of wave (c) have essentially merged into a constant high current flow to the base of the power transistor.
As can be see from these figures, the current flow to the base of the transistor is proportionally varied depending upon the proportional voltage which is generated in response to the resistance, inductance or capacitance of the speecl control thus the current flow to the base of the power transistor is also constantly varied in relationship to the variable resistance, inductance or capacitance and as a result, the current flow from the power source through the power transistor to the motor ls also constantly varied in relationship to the reslstance, inductance or capacitance of the speed control.
The speed control therefore varies the current flow to the motor thro-ugh the motor controller circuit and has essentially no effect upon the voltage applied to the motor during current pulses.
This desirable result is contrary to the results obtained using prior art electronic motor control circuits.
Optionally and desirably, means is provided for stopping available signal currents to the base of the power transistor when current through the power circuit is greater than a maximum desired level and for restoring available signal currents when the current -through the power circuit is again below the maximum L~ 3 desired level. Thls means is desirably present to prevent the power circuit from being overloaded. ~ny means known to those slcilled in the art ~or detecting current overload and shutting off a signal in response to such detection can be used. In a preEerred embodiment of the invention, a direct current E~I-E is selected which will decrease through an operational amplifier as current through a calibrated portion of the cable from a DC power supply increases. When the selected EM~ is reduced to a sufficiently lo~ level, another operational amplifier turns on which forces a third operational amplifier off which in turn clamps the generated voltage proportional to the variable resistance, inductance or capacitance to a le-vel below the lowest voltage of the saw tooth or triangular wave form. This results in no pulses being sent to the base oE the power transistor thus effectively stopping current Elow through the motor.
There is also optionally and desirably provided a means for stopping available signal currents to the base of the power transistor when battery voltage falls below the desired minimum voltage to drive the motor and means for restoring available signal currents when the battery voltage is again above the minimum desired voltage to drive the motor. Agaln, any means known to those skilled in the art for detecting voltage drop and for stopping a signal to the base of the transistor as a result of such detection can be used. In the preferred embodimen-t of the invention, an operational amplifier is caused to turn on if the voltage drops below a predetermined level. When the operational amplifier is on, the generated proportional voltage is again clamped below the lowest voltage level of the triangular wave form, again forcing the output to the base of the power transistor to be zero or at least too low to activate the transistor .
The same or similar circuits can also be used as failsafe mechanisms to turn ofE the power transistor when open circuit or short circuit conditions are detected.
The frequency of the saw tooth or triangular wave form and the frequency of the pulse width modulated signal is desirably selected to be compatible with motor operating characteristics.
The method oE the invention Eor controlling the speed oE an electric motor comprises varying the resistance, inductance or capcaci-tance of a speed control, preferably manually, and supplying a pulse width modulated signal current having pulse widths proportional to the value of the variable resistance, capacitance or inductance to the base of at least one power transistor to activa-te the transistor which is connnected by its emitter and collector as an electrical switch in series between the motor and the power supply.
The controller and method of the invention are more efficient and superior for controlling the speed of a DC motor and, when a triac is used as the power transistor, can even be more efficient in controlling the speed of an AC motor. The circuit does not have ~he power loss inherent in a control circuit using resistors or chopped pulses which are not pulse width modulated. Contrary to the results obtained with prior art controllers, the controller of the invention provides a variable current supply depending upon the current requirement of the motor in response to both motor characteristics and the variable resistance, inductance or capacitance of the speed control.
Further~ore, the pulse widths of the signal to the base of the power transistor or transistors can be made directly proportional to the variance in the resistance, inductance or capacitance of the speed control. The result is a smoothly operating motor which uses less current than was possible using prior art controller circuits and with less "jerk" of the motors in response to current surges provided by prior art controller circuits which "jerk" is undesirable for smooth operation, good motor performance and good motor wear.
A schematic diagram of a preferred controller circuit, in accordance with the invention, is set forth in Figure ~.
The schematic diagram of Figure 4 has been divided by dotted boxes into various circuit components for ease of explanation.
The dotted box represented by A is the power circuit wherein electric current from battery 10 passes through power transistors 12 to motor 14 through reversing SWitCtl 16. A free wheeling diode l~ is provided which provides a current path Eor electrical currents generated by motor rotation caused by coasting of the motor and apparatus connected to the motor.
Power transistors 12 act as electronic switches which are turned on by a sigrnal provided to transistor bases 12A~ A signal is a wave form which is pulse width modulated in proportion to a variable resistance which is manually altered as i-n the form of a rheostat represented within dotted box B of Figure 40 The rheostat, in the case of an electric vehicle, is usuall~ changed by means of a footpedal.
In order to generate the pulse width modulated signal, a saw tootl1 wave :Eorm is generated by means oE the circuit represented by dotted box C. The triangular shaped circuit components, through 8, as shown in Figure ~ are operational amplifiers which n1ay be discrete components or one or more may be combined in a single electronic package. The operational amplifiers used in accordance with the embodiment shown in Figure ~ are National quad operational amplifiers LM32~M wherein each triangle shown in Fi.gure 4 represents one-fourth of the quad operational amplifier package.
The frequency of the triangular or saw tooth wave form generated by a circuit enclosed by dotted box C can be altered by changing the values of resistance R1 and/or capacitance C1. The triangular wave form is offset from ground preferably by about 5.5 volts with a 13 volt peak to peak swing.
The circuit represented by dotted box D generates an EMF
which is directly proportional to the val.ue of rheostat 20. The signal from circuit D is provided to the circuit represented within dotted box E which compares the signal -from circuit D with the triangular wave form from circuit C. IE the voltage of the signal from circuit D is larger than the voltage of the triangular wave form from circuit C, a current pulse is input from circuit E to circuit F which amplifies the pulse and provides the amplified pulse to the bases of power transistors 12 which turns the power transistors on thus permitting c~1rrent to flow from battery 10 to motor 1~. As was previously explained, with respect to Figures 1, 2 and 3, the length of the current pulse to the bases of transistors 12 frorn circuits L and F is dependent upon the voltage of a signal from circuit D in response to the variable resistance of circuit B.
In the preferred embodiment shown in Figure 4, safety circuits are also provided. The circuits represented by the dotted boxes G and ~ shut down the signal to the bases 12A of power transistors 12 when current through the power circuit A is too high. Similarly, circuit I shuts down the signal to bases 12~ of power transistors 12 when a brownout or low voltage condition exists.
It is to be understood that the schematic diagram of ~igure 4 is only one of many possible circuit arrangements in accordance with the invention and even in the schematic diagram of Figure 4, circuit components, e.g., resistances, can be changed to balance the circuit for the characteristics of somewhat different motors, batteries, resistances, capacitors, speed controls, regulators, transistors diodes and operational ampliEiers. Differen-t but similar components may therefore be substit-uted in the circuit with corresponding appropriate changes in other components.
In addition, if desired, a capacitive or inductive reactance can be added in parallel with the pulse width modulated signal in any control circuit of the invention to create a smoother transition in signal EMF and/or current to the base of the power transistor or optionally, if the capacitance or inductance is large enough, the reactance may even be added in parallel with the power circuit. The motor windings themselves add a reasonably large inductance to the power circuit to smoothen changes in the signal.
~ controller circuit essentially as shown in Figure 4 was incorporated into a Melex golf car with total gross weight of 1,615 pounds (including the weight of the car). The golf car with the electric motor speed controller circuit of the present invention traveled over thirty miles with repeated dead stops followed with normal acceleration and at the end of the thirty miles, there was still sufficient charge in the batteries to keep driving the golf car.
In a test for normal operations, a Melex golf car, having a total gross weight of 1,493 pounds controlled with an electric motor speed controller circuit in accordance wi~h the invention, we able to travel thirty-six holes on a hilly golf course with less than 50% battery discharge~
In a comparative test, a Melex golf car, having a total gross weight of 1,615 pounds, was tested with a prior art resîstance motor controller and the motor speed controller circuit of the present invention around a one-fourt.h mile test course having the configuration set forth in Figure 5. The relative power requirement and power drain between the golf car with the controller of the present invention and the golf car with the resistor controller are set forth in Figures 6 and 7 respectively. The comparison of these Figures clearly shows that at various stops at positions 1, 2, 3 and 4, the current drain utilizing the electric motor speed controller of the invention is consistently less and furthermore, the top speed is higher than the golf car wherein the state of the art resistance controller is used.
14 * Trade Mar~.
~,,
B~ G~OUND Ol Tlll~ INVf:~lTION
__ __ _ _ A) l~ield of the Invention ___ _ __ _~_ This invention relates to speed controllers for electric motors anc'l especially relates to speed controllers for electric motors, particularly series-field rnotors, used to dri-ve battery powered electric vehicles.
B) Ilistory of the I'rior Art In the prior art, motors, especially DC electric motors, were generally controlled by the use of an adjustable large current series resistance. This ~ethod of controlllng the speed of an electric rnotor, particularly those used to drive electric vehicles, has been generally unsatisEactory because torque and speed are almost completely interclependent. The interdependency results in very ~oor speed regulation. In addition, such resistance controllers are e~temely ineEficient c]ue to high dissipation of electrical energy through the controller resistance elements. This energy dissipation marlcedly reduces battery llfe and the allowab]e time between charges and also increases the minimum acceptable initial size, weight and cost o-f the battery.
~ urthermore, such controllers did not result in Eully proportional speed control since frequently the controllers had to be almost in the fully on position before sufficient torque could be developed to start an electric vehicle from a stopped position. The controller would then have to be backed ofi to reduce the torque after motion started. Such controllers therefore resulted in inconsistent non-uniform motor operation ~q givlng a "jerky" feel to the movernent oE a vehicle.
More recently, an attempt has been made to control the speed of an electric motor by placing a power transistor as an elec-tronic switch between the battery and the motor and ac~ivating the transistor by supplying pulses of curr~nt to the transistor base. In general, these pulses were of constant duration and the speed was controlled in only a few stages by chopping a current at only a few different speeds~ The resulting motor operation is non-uniEorm, and electrlcal energy ls wastecl slnce current ls supplied only at a Eew levels.
BRIEF DESCRIPTION OF T~IE INVENTION
In accordance wlth wlth the present lnventlon, there ls provlded an electrlc motor speed eontroller circuit which overcomes essentially all of the previously mentioned disadvantages of prior art controller circults. In particular, the electric motor speec] controller circuit, in accordance with the present invention, is interposed between the motor and a power supply sufficient to drive the motor~ The speed controller circuit comprises at least one power transistor connected through its emitter and collector in series between the motor and the power supply to form a power circuit such that current flows between the power supply and the motor through the transistor only when a signal current is supplied to the base of the transistor. The speed controller further comprlses a speed control whlch provldes a variable resistance, lnduc~ance or capacltance within a control circuit and a control circuit having a power requirement substantially lower than the power requirement to operate the motor which supplies pulses of a pulse width rnodulated signal current to the base of the power transistor, the i~idth of the pulse being proportional to the value of the variable resistance, inductance or capacitance of the speed control.
The invention Eurther comprises a method for controlling the speed of an electric motor. The method comprises varying the variable resistance, inductance or capacitance of a speed control; and supplying a pulse width modulated signal current, having pulse widths proportional to the value of the variable resistance, inductance, or capacitance, to the base of at least one power transistor to activate the transistor which is connected by its emitter and collector as an electrical switch in series between the motor and a power supply.
The invention further comprises a variable speed motor connected with and controlled by the electrical motor speed controller of the invention and an electrical vehicle powered by a motor controlled by the electric motor speed controller of the invention.
~RIEF DESCRIPTION OF THE DP~AWINGS
Figures 1, 2 and 3 are representative graphs showing the relationship between the EMF's of an elec-trical voltage proportional to the resistance, capacitance or inductance of a speed control, the electrical voltage of a comparison saw tooth wave generated by the control circuit and the electrical voltage of a pulse modulated output signal.
FiguLe ~ is a schematic diagram of a preferred embodiment of the electric motor speed controller of the invention.
Figure 5 is a schematic layout of a 1/~ mile test course.
Figure 6 is a power curve showing the power used by a golf car controlled with the solid state controller oE the invention as the golf car moves around the test course shown in Figure 5;
and Figure 7 is a power curve showing the same golf car as Figure 6 wherein a resistor controller is used as the golf car travels the test course of Figure 5.
DETAILED DESCRI~TION OF T~IE NVENTION
The electric motor controlled by the speed controller circuit oE the invention may be any electric motor but is usually a direct current (DC) electric motor which most often has a series-field.
The power supply is any power supply sufficient to drive the motor and for a DC motor is a DC power supply which may have a uniform or variable EMF. Usually the power supply is a battery of any suitable type including one or more packaged batt~ries in series or parallel. Suitable batteries include rechargeable batteries such as lead-acid batteries; nickel-cadminum batteries and the newer lithium-chloride batteries.
~ s previously discussed, the speed controller circuit comprises at least one power transistor connected through its emitter and collector in series between the motor and the power supply to form a power circuit such that the current flows through the transistor from the power supply to the motor only when a signal current is supplied to the base of the transistor.
The power transistor is a single transistor or coupled transistors which act as a single transistor. The po~Jer transistor is clesirably a bistable transistor, i.e., a transistor whose base currellt controls both on and oEE switching but ~mder certain circumstances may be a thyrister or in the case of an al-ternating current, a ~riac. Examples of power transistors are power Darlington connected transistors~ Examples of suitable particular transistors are Motorola's MJ11028 Darlington and ~C~'s Series SE~3570 through SK3582.
A plurality of such power transistors can be used in parallel to increase the current carrying capability oE the circuit.
The speed control, which is usually manually operated, i.e., operated by human action such as a footpedal or a hand operated accelerator, provides a variable resistance, inductance or capacitance within the control circuit. The speed control usually provides a -variable resistance within -the circuit by means of a rheostat.
The control circuit is designed to have a power requirement substantially lower than the power requirement to operate the motor. The control circuit usually requires less than 10 and preferably less than 5% of the power requirement of the motor.
The control circuit supplies pulses of a pulse width modulated signal current to the base of -the power transistor or transistors, the width of the pulse being proportional to the value of the variable resistance, inductance or capacitance of the speeci control.
Pulse width modulation (PWM) is a:Lso known as pulse duration modulation (PDM) or pulse length modulation (PL~I). In general, pulse width modulation is that modulation oE a signal at an essentially constant frequency where a time length or width of pulses of a constant EMF` signal are varied in relation to an input signal. The longer the width oE the modulation, the more current is supplied with the signal and the shorter the width of the mod1llation, the less current is supplied with the signal Mumerous methods are known to those skilled in the art for creating a pulse width modulated signal sincc the signals have been examined in the area of electronics communication and to a lesser extent in the area of electronic controllers in other applications (see references on page 1~-51 of the Electronics Engineers' Handbook edited by Donald G. Eink, published by McGraw-~lill, 1975).
In accordance with a preferred embodiment of the present invention, the control circuit comprises a means for generating a constant freq-uency electrical vol-tage wave Eorm biased so that the lowest voltage of the wave is greater than zero; a means Eor generating a voltage proportional to the-variable resistance, inductance or capacitance of the speed control and a means for comparing the voltage of the wave form with the generated proportional voltage and for outputing a pulse width modulated signal to the base of the power transistor when the gcnerated proportional voltage is greater than the voltage of the electrical wave -form. The constant frequency electrical voltage wave form is most desirable a saw tooth wave form so that the lengths of the outputted signal pulses are directly proportional to the generated proportional voltage, although other constant frequency wave forr~ls can be used so that other proportional relationships can be obtained between the generated proportional voltage ancl the lengths of the outputted signal pul~ses.
"E'roportional", as used herein, means having the sarne or constant ratio or a ratio which varies in accordance with a set mathematical function. In general, the proportional relationship, in accordance with the preEerred embodiment of the invention, is a direct proportion and optionally, a proportion which varies exponentially, logarithmically or trigonometrically.
Figure 1 of the drawings shows a graph of voltage against time for a generated constant Erequency saw tooth electrical voltage wave, (a), a voltage proportional to the variable resistance when the resistance is exceedingly high thus producing a proportional voltage (b) which is lower than the lowest voltage of the constant frequency electrical voltage wave (a) and the resulting outputted pulse width modulated wave ~c) which has no pulses (pulse width zero) since at no time is the generated proportional voltage greater than the voltage oE the constant frequency electrical voltage wave.
Figure 2 shows essentially the same curve as Figure 1 except that the proportional voltage (b) ~iS sometimes greater than and sometimes less than the voltage of constant frequency electrical voltage wave (a) which resul-ts in pulses (x) which are o-utputted to the base of the power transistor in original or amplified form, the length of pulse (x) representing the current flow to the base of the transistor. The width of pulse (x) of wave (c) is determined by the length of time that the propor-tional voltage is greater than the voltage of the constant frequency electrical voltage wave form. Figure 3 again shows essentially the same relationship except that generated proportional voltage (b) is always greater than the voltage of constant frequency electrical voltage wave form (a) thus the generated current pulses (x) of wave (c) have essentially merged into a constant high current flow to the base of the power transistor.
As can be see from these figures, the current flow to the base of the transistor is proportionally varied depending upon the proportional voltage which is generated in response to the resistance, inductance or capacitance of the speecl control thus the current flow to the base of the power transistor is also constantly varied in relationship to the variable resistance, inductance or capacitance and as a result, the current flow from the power source through the power transistor to the motor ls also constantly varied in relationship to the reslstance, inductance or capacitance of the speed control.
The speed control therefore varies the current flow to the motor thro-ugh the motor controller circuit and has essentially no effect upon the voltage applied to the motor during current pulses.
This desirable result is contrary to the results obtained using prior art electronic motor control circuits.
Optionally and desirably, means is provided for stopping available signal currents to the base of the power transistor when current through the power circuit is greater than a maximum desired level and for restoring available signal currents when the current -through the power circuit is again below the maximum L~ 3 desired level. Thls means is desirably present to prevent the power circuit from being overloaded. ~ny means known to those slcilled in the art ~or detecting current overload and shutting off a signal in response to such detection can be used. In a preEerred embodiment of the invention, a direct current E~I-E is selected which will decrease through an operational amplifier as current through a calibrated portion of the cable from a DC power supply increases. When the selected EM~ is reduced to a sufficiently lo~ level, another operational amplifier turns on which forces a third operational amplifier off which in turn clamps the generated voltage proportional to the variable resistance, inductance or capacitance to a le-vel below the lowest voltage of the saw tooth or triangular wave form. This results in no pulses being sent to the base oE the power transistor thus effectively stopping current Elow through the motor.
There is also optionally and desirably provided a means for stopping available signal currents to the base of the power transistor when battery voltage falls below the desired minimum voltage to drive the motor and means for restoring available signal currents when the battery voltage is again above the minimum desired voltage to drive the motor. Agaln, any means known to those skilled in the art for detecting voltage drop and for stopping a signal to the base of the transistor as a result of such detection can be used. In the preferred embodimen-t of the invention, an operational amplifier is caused to turn on if the voltage drops below a predetermined level. When the operational amplifier is on, the generated proportional voltage is again clamped below the lowest voltage level of the triangular wave form, again forcing the output to the base of the power transistor to be zero or at least too low to activate the transistor .
The same or similar circuits can also be used as failsafe mechanisms to turn ofE the power transistor when open circuit or short circuit conditions are detected.
The frequency of the saw tooth or triangular wave form and the frequency of the pulse width modulated signal is desirably selected to be compatible with motor operating characteristics.
The method oE the invention Eor controlling the speed oE an electric motor comprises varying the resistance, inductance or capcaci-tance of a speed control, preferably manually, and supplying a pulse width modulated signal current having pulse widths proportional to the value of the variable resistance, capacitance or inductance to the base of at least one power transistor to activa-te the transistor which is connnected by its emitter and collector as an electrical switch in series between the motor and the power supply.
The controller and method of the invention are more efficient and superior for controlling the speed of a DC motor and, when a triac is used as the power transistor, can even be more efficient in controlling the speed of an AC motor. The circuit does not have ~he power loss inherent in a control circuit using resistors or chopped pulses which are not pulse width modulated. Contrary to the results obtained with prior art controllers, the controller of the invention provides a variable current supply depending upon the current requirement of the motor in response to both motor characteristics and the variable resistance, inductance or capacitance of the speed control.
Further~ore, the pulse widths of the signal to the base of the power transistor or transistors can be made directly proportional to the variance in the resistance, inductance or capacitance of the speed control. The result is a smoothly operating motor which uses less current than was possible using prior art controller circuits and with less "jerk" of the motors in response to current surges provided by prior art controller circuits which "jerk" is undesirable for smooth operation, good motor performance and good motor wear.
A schematic diagram of a preferred controller circuit, in accordance with the invention, is set forth in Figure ~.
The schematic diagram of Figure 4 has been divided by dotted boxes into various circuit components for ease of explanation.
The dotted box represented by A is the power circuit wherein electric current from battery 10 passes through power transistors 12 to motor 14 through reversing SWitCtl 16. A free wheeling diode l~ is provided which provides a current path Eor electrical currents generated by motor rotation caused by coasting of the motor and apparatus connected to the motor.
Power transistors 12 act as electronic switches which are turned on by a sigrnal provided to transistor bases 12A~ A signal is a wave form which is pulse width modulated in proportion to a variable resistance which is manually altered as i-n the form of a rheostat represented within dotted box B of Figure 40 The rheostat, in the case of an electric vehicle, is usuall~ changed by means of a footpedal.
In order to generate the pulse width modulated signal, a saw tootl1 wave :Eorm is generated by means oE the circuit represented by dotted box C. The triangular shaped circuit components, through 8, as shown in Figure ~ are operational amplifiers which n1ay be discrete components or one or more may be combined in a single electronic package. The operational amplifiers used in accordance with the embodiment shown in Figure ~ are National quad operational amplifiers LM32~M wherein each triangle shown in Fi.gure 4 represents one-fourth of the quad operational amplifier package.
The frequency of the triangular or saw tooth wave form generated by a circuit enclosed by dotted box C can be altered by changing the values of resistance R1 and/or capacitance C1. The triangular wave form is offset from ground preferably by about 5.5 volts with a 13 volt peak to peak swing.
The circuit represented by dotted box D generates an EMF
which is directly proportional to the val.ue of rheostat 20. The signal from circuit D is provided to the circuit represented within dotted box E which compares the signal -from circuit D with the triangular wave form from circuit C. IE the voltage of the signal from circuit D is larger than the voltage of the triangular wave form from circuit C, a current pulse is input from circuit E to circuit F which amplifies the pulse and provides the amplified pulse to the bases of power transistors 12 which turns the power transistors on thus permitting c~1rrent to flow from battery 10 to motor 1~. As was previously explained, with respect to Figures 1, 2 and 3, the length of the current pulse to the bases of transistors 12 frorn circuits L and F is dependent upon the voltage of a signal from circuit D in response to the variable resistance of circuit B.
In the preferred embodiment shown in Figure 4, safety circuits are also provided. The circuits represented by the dotted boxes G and ~ shut down the signal to the bases 12A of power transistors 12 when current through the power circuit A is too high. Similarly, circuit I shuts down the signal to bases 12~ of power transistors 12 when a brownout or low voltage condition exists.
It is to be understood that the schematic diagram of ~igure 4 is only one of many possible circuit arrangements in accordance with the invention and even in the schematic diagram of Figure 4, circuit components, e.g., resistances, can be changed to balance the circuit for the characteristics of somewhat different motors, batteries, resistances, capacitors, speed controls, regulators, transistors diodes and operational ampliEiers. Differen-t but similar components may therefore be substit-uted in the circuit with corresponding appropriate changes in other components.
In addition, if desired, a capacitive or inductive reactance can be added in parallel with the pulse width modulated signal in any control circuit of the invention to create a smoother transition in signal EMF and/or current to the base of the power transistor or optionally, if the capacitance or inductance is large enough, the reactance may even be added in parallel with the power circuit. The motor windings themselves add a reasonably large inductance to the power circuit to smoothen changes in the signal.
~ controller circuit essentially as shown in Figure 4 was incorporated into a Melex golf car with total gross weight of 1,615 pounds (including the weight of the car). The golf car with the electric motor speed controller circuit of the present invention traveled over thirty miles with repeated dead stops followed with normal acceleration and at the end of the thirty miles, there was still sufficient charge in the batteries to keep driving the golf car.
In a test for normal operations, a Melex golf car, having a total gross weight of 1,493 pounds controlled with an electric motor speed controller circuit in accordance wi~h the invention, we able to travel thirty-six holes on a hilly golf course with less than 50% battery discharge~
In a comparative test, a Melex golf car, having a total gross weight of 1,615 pounds, was tested with a prior art resîstance motor controller and the motor speed controller circuit of the present invention around a one-fourt.h mile test course having the configuration set forth in Figure 5. The relative power requirement and power drain between the golf car with the controller of the present invention and the golf car with the resistor controller are set forth in Figures 6 and 7 respectively. The comparison of these Figures clearly shows that at various stops at positions 1, 2, 3 and 4, the current drain utilizing the electric motor speed controller of the invention is consistently less and furthermore, the top speed is higher than the golf car wherein the state of the art resistance controller is used.
14 * Trade Mar~.
~,,
Claims (12)
1. A direct current electric motor speed controller circuit between the motor and a power supply sufficient to drive the motor which controller consists essentially of:
a) at least one power transistor connected through its emitter and collector in series between the motor and the power supply to form a power circuit such that current flows between the power supply and the motor through the transistor only when a signal current is supplied to the base of the transistor;
b) a speed control which provides a variable resistance, inductance or capacitance within a control circuit;
c) a control circuit having a power requirement substantially lower than the power requirement to operate the motor, said control circuit supplying pulses of a pulse width modulated signal current to the base of the power transistor, the width of the pulse being proportional to the value of the variable resistance, inductance or capacitance of the speed control, said control circuit comprising:
i) means for generating a constant frequency saw toothed electrical voltage wave form biased so that the lowest voltage of the wave is greater than zero;
ii) a means for generating a voltage proportional to the variable resistance, inductance or capacitance; and iii) a means for comparing the voltage of the saw toothed wave form with the generated proportional voltage and for outputing a direct current pulse width modulated signal to the base of the power transistor when the generated proportional voltage is greater than the voltage of the electrical wave form, the width of the pulses of said pulse width modulated signal being directly proportional to the generated proportional voltage;
d) means for stopping available signal currents to the base of the power transistor when current through the power circuit is greater than a maximum desired level and for restoring available signal currents when the current through the power circuit is again below the maximum desired level; and e) means for stopping available signal currents to the base of the power transistor when power supply voltage falls below the desired minimum voltage to drive the motor;
the means for generating a constant frequency saw toothed wave, the means for generating a proportional voltage, the means for comparing the voltage of the saw toothed wave form with the proportional voltage, the means for stopping available signal currents to the base of the power transistor when current through the power circuit is greater than a maximum desired level and the means for stopping available signal currents to the base of the power transistor when the power supply voltage falls below the desired minimum voltage to drive the motor each comprising at least a part of at least one integrated circuit.
a) at least one power transistor connected through its emitter and collector in series between the motor and the power supply to form a power circuit such that current flows between the power supply and the motor through the transistor only when a signal current is supplied to the base of the transistor;
b) a speed control which provides a variable resistance, inductance or capacitance within a control circuit;
c) a control circuit having a power requirement substantially lower than the power requirement to operate the motor, said control circuit supplying pulses of a pulse width modulated signal current to the base of the power transistor, the width of the pulse being proportional to the value of the variable resistance, inductance or capacitance of the speed control, said control circuit comprising:
i) means for generating a constant frequency saw toothed electrical voltage wave form biased so that the lowest voltage of the wave is greater than zero;
ii) a means for generating a voltage proportional to the variable resistance, inductance or capacitance; and iii) a means for comparing the voltage of the saw toothed wave form with the generated proportional voltage and for outputing a direct current pulse width modulated signal to the base of the power transistor when the generated proportional voltage is greater than the voltage of the electrical wave form, the width of the pulses of said pulse width modulated signal being directly proportional to the generated proportional voltage;
d) means for stopping available signal currents to the base of the power transistor when current through the power circuit is greater than a maximum desired level and for restoring available signal currents when the current through the power circuit is again below the maximum desired level; and e) means for stopping available signal currents to the base of the power transistor when power supply voltage falls below the desired minimum voltage to drive the motor;
the means for generating a constant frequency saw toothed wave, the means for generating a proportional voltage, the means for comparing the voltage of the saw toothed wave form with the proportional voltage, the means for stopping available signal currents to the base of the power transistor when current through the power circuit is greater than a maximum desired level and the means for stopping available signal currents to the base of the power transistor when the power supply voltage falls below the desired minimum voltage to drive the motor each comprising at least a part of at least one integrated circuit.
2. The motor controller circuit of Claim 1 wherein the speed control provides a variable resistance within the control circuit.
3. The motor controller circuit of Claim 1 wherein the speed control is manually operated to vary the resistance.
4. The motor controller circuit of Claim 1 wherein the outputed signal pulses are amplified before being transmitted to the base of the power transistor.
5. The motor controller circuit of Claim 1 wherein a control switch is provided between the power supply and the control circuit.
6. The motor controller circuit of Claim 1 wherein the power supply is a battery.
7. The motor controller circuit of Claim 1 wherein a reactance is provided in parallel with the motor.
8. A variable speed motor comprising a motor connected with and controlled by the electric motor speed controller circuit of Claim 1.
9. An electric vehicle powered by a motor controlled by the electric motor speed controller circuit of Claim 1.
10. The electric vehicle of Claim 9 wherein the vehicle is a golf cart.
11. The electric vehicle of Claim 9 wherein the vehicle is an electric automobile.
12. A method for controlling the speed of a direct current electric motor which consists essentially of:
a) varying a variable resistance, inductance or capacitance of a speed control;
b) providing a constant frequency saw toothed electrical voltage wave form biased so that the lowest voltage of the wave is greater than zero, utilizing at least a part of an integrated circuit;
c) providing a voltage proportional to the value of the variable resistance, inductance or capacitance, utilizing at least a part of an integrated circuit;
d) comparing the voltage of the saw toothed wave form with the voltage proportional to the resistance, inductance or capacitance, utilizing at least a part of an integrated circuit;
e) outputing a direct current pulse width modulated signal when the proportional voltage is greater than the voltage of the electrical voltage wave form; the width of the pulses of said pulse width modulated signal being directly proportional to the generated proportional voltage, utilizing at least a part of an integrated circuit;
f) supplying said pulse width modulated signal current, to the base of at least one power transistor to activate the transistor which is connected by its emitter and collector, as an electrical switch in series between the motor and a power supply;
g) stopping available signal currents to the base of the power transistor when current through the motor is greater than a maximum desired level and for restoring available signal currents when the current through the motor is again below the maximum desired level, utilizing at least a part of an integrated circuit; and h) stopping available signal currents to the base of the power transistor when battery voltage falls below the desired minimum voltage to drive the motor, utilizing at least a part of an integrated circuit.
a) varying a variable resistance, inductance or capacitance of a speed control;
b) providing a constant frequency saw toothed electrical voltage wave form biased so that the lowest voltage of the wave is greater than zero, utilizing at least a part of an integrated circuit;
c) providing a voltage proportional to the value of the variable resistance, inductance or capacitance, utilizing at least a part of an integrated circuit;
d) comparing the voltage of the saw toothed wave form with the voltage proportional to the resistance, inductance or capacitance, utilizing at least a part of an integrated circuit;
e) outputing a direct current pulse width modulated signal when the proportional voltage is greater than the voltage of the electrical voltage wave form; the width of the pulses of said pulse width modulated signal being directly proportional to the generated proportional voltage, utilizing at least a part of an integrated circuit;
f) supplying said pulse width modulated signal current, to the base of at least one power transistor to activate the transistor which is connected by its emitter and collector, as an electrical switch in series between the motor and a power supply;
g) stopping available signal currents to the base of the power transistor when current through the motor is greater than a maximum desired level and for restoring available signal currents when the current through the motor is again below the maximum desired level, utilizing at least a part of an integrated circuit; and h) stopping available signal currents to the base of the power transistor when battery voltage falls below the desired minimum voltage to drive the motor, utilizing at least a part of an integrated circuit.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US15934380A | 1980-06-13 | 1980-06-13 | |
| US159,343 | 1980-06-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1184243A true CA1184243A (en) | 1985-03-19 |
Family
ID=22572172
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000379655A Expired CA1184243A (en) | 1980-06-13 | 1981-06-12 | Electric motor speed controller and method |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5728586A (en) |
| CA (1) | CA1184243A (en) |
| DE (1) | DE3123358A1 (en) |
| FR (1) | FR2484733A1 (en) |
| GB (1) | GB2078029A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20160253957A1 (en) * | 2008-06-06 | 2016-09-01 | Sony Corporation | Scanning drive circuit and display device including the same |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3611884A1 (en) * | 1986-04-09 | 1987-10-22 | Fein C & E | Hand tool, especially a screwdriver, driven by a rechargeable battery (accumulator) |
| US7197390B2 (en) * | 2003-03-13 | 2007-03-27 | Wavecrest Laboratories Llc | Electric vehicle with adaptive cruise control system |
| CN102541104B (en) * | 2012-01-19 | 2013-06-12 | 金湖县华能机电有限公司 | Speed adjustable controller used for dried diet feeder |
| CN107623468A (en) * | 2017-09-29 | 2018-01-23 | 深圳市巴丁微电子有限公司 | A kind of motor control method and device based on FLL |
-
1981
- 1981-06-12 GB GB8118061A patent/GB2078029A/en not_active Withdrawn
- 1981-06-12 FR FR8111640A patent/FR2484733A1/en active Pending
- 1981-06-12 CA CA000379655A patent/CA1184243A/en not_active Expired
- 1981-06-12 DE DE19813123358 patent/DE3123358A1/en not_active Withdrawn
- 1981-06-12 JP JP9070281A patent/JPS5728586A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20160253957A1 (en) * | 2008-06-06 | 2016-09-01 | Sony Corporation | Scanning drive circuit and display device including the same |
| US9685110B2 (en) * | 2008-06-06 | 2017-06-20 | Sony Corporation | Scanning drive circuit and display device including the same |
| US9940876B2 (en) | 2008-06-06 | 2018-04-10 | Sony Corporation | Scanning drive circuit and display device including the same |
| US10741130B2 (en) | 2008-06-06 | 2020-08-11 | Sony Corporation | Scanning drive circuit and display device including the same |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3123358A1 (en) | 1983-01-05 |
| JPS5728586A (en) | 1982-02-16 |
| GB2078029A (en) | 1981-12-23 |
| FR2484733A1 (en) | 1981-12-18 |
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