DC motor drive assembly including integrated charger/controller/regenerator circuit

A drive assembly comprises a DC electric motor and an integrated charger/controller/regenerator which includes a power module, a step-up module and a control circuit. The input of the power module is connected to an electric power source during charging, and to the DC motor during regenerative braking. The input of the step-up module is connected to the power module, and the output is connected to the battery. The control circuit includes a switch, and has three modes of operation: driving, regenerative braking and charging. During driving, the switch connects the battery to the power module input and the power module output to the DC motor. During regenerative braking, the switch connects the DC motor to the power module input and the power module output to the step-up module input, and the step-up module output charges the battery. During charging, the switch connects the power module output to the step-up module input, and the step-up module output charges the battery.

BACKGROUND OF THE INVENTION 
This invention relates generally to drive assemblies including a DC motor, 
battery and charger, and, more particularly, to such a drive assembly 
which includes an integrated electronic charger/controller/regenerator. 
Conventional battery operated motors utilize separate battery chargers and 
motor controller circuits. Although these circuits may utilize similar 
components, the controller and the charger are not operated at the same 
time. Separate chargers and controllers increase the number of components, 
cost, size, and weight which is especially critical in the design of 
electrically powered vehicles. 
Recently, integrated battery charger and motor controllers have been 
developed. Exemplary of such devices are those illustrated in Ripple U.S. 
Pat. Nos. 4,920,475 and 5,099,186, Slicker U.S. Pat. No. 4,491,768 and 
Coconi U.S. Pat. No. 5,341,075. The integrated charger/controllers of 
these patents are directed to single phase battery chargers and polyphase 
AC electric motor controllers. In comparison to a single phase DC motor, a 
polyphase AC motor requires a relatively more complex device to generate 
the rotating magnetic field which operates the motor. Moreover, polyphase 
AC motor controllers should not be used to drive single phase DC motors. 
Conventional high voltage AC drive systems require battery voltages in 
excess of 162 VDC (115 VAC) or 325 VDC (230 VAC) in order to operate 
effectively. However, this high voltage potential creates a high 
capacitance and requires added insulation to decrease stray capacitance 
(leakage). Moreover, higher voltage potential inherently increases the 
risk of shock hazard injuries to operators. Furthermore, high voltage 
systems require many battery cells in combination to operate effectively. 
However, the practice of connecting many cells in combination generally 
places greater stress on individual cells and amplifies minor differences 
in internal resistance which together may cause both capacity losses and 
premature failure of the overall drive system. 
In addition, it is often desirable to provide for the regeneration of the 
power during braking of DC motors in order to increase the range of 
battery powered electric vehicles in which DC motors are employed. During 
regenerative braking, the direction of the flow of electrical power from 
the battery to the DC motor during driving is reversed by either 
maintaining the direction of current flow constant while reversing the 
voltage polarity, or by reversing the direction of current flow while 
maintaining the polarity of the voltage. Conventional integrated 
charger/controllers utilize separate electronic circuits such as free 
wheel diodes and bridge circuits to enable regeneration. 
Accordingly, it is an object of the present invention to provide a novel 
electric drive assembly for vehicles which include an integrated battery 
charger, DC motor controller, and regenerator circuit during braking. 
It is also an object to provide such a drive assembly which utilizes a low 
power battery and a single phase DC electric motor. 
Another object is to provide such a drive assembly which is relatively 
simple in construction and reliable in operation. 
A further object is to provide a novel method for charging a battery and 
controlling a DC electric motor for driving a vehicle. 
SUMMARY OF THE INVENTION 
It has now been found that the foregoing and related objects may be readily 
attained in a drive assembly comprising a DC electric motor and an 
integrated charger/controller/regenerator for controlling the DC electric 
motor in a drive mode of operation, for charging a battery in a 
regenerative braking mode of operation, and for connection to an electric 
power source for charging the battery in a charge mode of operation. The 
integrated charger/controller/regenerator includes a power module, step-up 
module and control circuit. The input of the power module is connected to 
an electric power source during the charge mode of operation, and to the 
DC motor during the regenerative braking mode of operation. The power 
module includes a transformer to reduce the input voltage of the power 
source during the charge mode of operation. 
The input of the step-up module is connected to the power module, and the 
output is connected to the battery. The control circuit includes switch 
means having three modes of operation: driving, regenerative braking and 
charging. During driving, the switch means connects the battery to the 
input of the power module and the output of the power module to the DC 
motor to control the DC motor. During regenerative braking, the switch 
means connects the DC motor to the input of the power module and the 
output of the power module to the input of the step-up module, and the 
output of the step-up module is connected to the battery to charge it. 
During charging, the input of the power module is connected to the 
electric power source, and the switch means connects the output of the 
power module to the input of the step-up module, and the output of the 
step-up module is connected to the battery to charge it. 
Preferably, the step-up module includes the transformer, a transistor, and 
diode, the transistor being connected in parallel with the diode and 
connected in series with the transformer. Generally, the power module also 
includes another transistor connected in parallel with both the diode and 
the transistor of the step-up module, and the other transistor controls 
the DC current output of the DC motor during the regenerative braking mode 
of operation. 
Desirably, the power module includes the transistor of the step-up module 
which is closed, and the other transistor is pulse width modulated to 
control the DC current output of the DC motor during the regenerative 
braking mode of operation. 
Preferably, the power module is a programmable pulse width modulated 
converter having power transistors and a parallel/series switching system 
which connects the power transistors in series during the charge mode of 
operation. These power transistors rectify the AC current input to the DC 
current output of the power module and the parallel/series switching 
system connects the power transistors in parallel during the drive mode of 
operation to control the associated DC motor. 
Desirably the power module includes another diode connected in parallel 
with the other transistor, and the control circuit pulse width modulates 
the transistor of the step-up module to periodically short circuit the 
transformer to allow current to flow through the other diode and charge 
the battery during the charge mode of operation. 
Preferably, the control circuit pulse width modulates the other transistor 
and closes the transistor of said step-up module to periodically short 
circuit the DC motor to reverse the direction of the current to charge the 
battery during the regenerative braking mode of operation. 
Generally, the transformer is a toroidal transformer, and the voltage of 
the output of the step-up module is not greater than 100 volts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning first to FIG. 1, this block diagram illustrates a drive assembly 
embodying the present invention as comprised of a DC motor 24 which 
derives power through a power controller 10 from a battery 26. The power 
controller 10 also channels power from an electric power source 12, which 
may be either AC or DC, to the battery 26 through a step-up converter 11. 
The integrated charger/controller/regenerator has three modes of 
operation: (1) a charge mode as indicated by the solid arrows; (2) a drive 
mode as indicated by the dashed arrows; and (3) a regenerative braking 
mode as indicated by the dash-dot arrows in FIG. 1. 
During the charge mode of operation, the input of the power controller 10 
is connected to either a DC or an AC electric power source 12 and the 
output of the power controller 10 supplies DC current. If an AC power 
source is used, the power controller 10 rectifies the AC current input to 
produce a DC current output; if a DC power source is used, the DC current 
would flow unrectified through the power controller 10. The voltage of the 
DC current from the power controller 10 is then raised by a step-up 
converter 11 to a voltage level which slightly exceeds the voltage rating 
of the battery 26, which is below 100 volts. 
Once the battery 26 is sufficiently charged, the drive mode may commence 
during which the DC current from battery 26 is controlled by the power 
controller 10 to supply a single phase DC voltage to drive the DC motor 
24. 
During the regenerative braking mode, the power controller 10 in 
conjunction with the step-up converter 11 reverses the flow of current 
from the DC motor 24 while maintaining the polarity of the voltage to 
charge the battery 26. 
Thus, the integrated power charger/controller/regenerator performs the 
functions of voltage conversion during the charge mode of operation, 
voltage regulation during the drive mode of operation, and regenerative 
braking during the regenerative braking mode of operation. 
Turning next to FIG. 2, therein schematically illustrated is the circuitry 
of the integrated charger/controller/regenerator of the present invention 
during the charge mode of operation. The AC power source 13 is connected 
to the primary winding 30 of the voltage transformer 28, and the voltage 
of the AC power source 13 is lowered through the secondary winding 32 of 
the voltage transformer 28. The transformer 28 isolates the AC power 
source 13 from the battery 26 to reduce the potential of a hazardous 
shock. Moreover, the voltage transformer 28 is a toroidal transformer 
whose size is substantially reduced compared to conventional transformers 
because it utilizes the existing charge control circuitry to decrease the 
duty cycle, thus allowing the toroidal transformer 28 to charge at higher 
power levels than rated without overheating. 
The transformer 28 lowers the voltage of the AC power source 13 
significantly to reduce capacitance losses and shock hazard. The AC power 
source 13 current is rectified by the power transistors 14 which are 
connected in series during the charge mode of operation. The power 
controller 10 includes a programmable pulse width modulator (PWM) which, 
in turn, includes the power transistors 14, a microprocessor control 
circuit 16, a power transistor 18 with an intrinsic diode 22, a power 
transistor with an intrinsic diode 20, and electronic switch S1. 
During the charge mode of operation, the battery 26 is connected to the DC 
output of the step-up converter 11. The rectified voltage output of 
transistors 14 is then raised to the charging voltage level for the 
battery 26 by the step-up converter 11. The step-up converter 11 includes 
the power transistor 19 connected in parallel to the diode 20 and utilizes 
the inherent inductance of the transformer 28. The transformer 28 
eliminates the need for an additional inductor and is also smaller and 
lighter than a conventional inductor. 
The switching transistor 19 is connected in parallel to the diode 20, and 
the two are a part of the same transistor. During the charge mode of 
operation, the pulse Width Modulated (PWM) microprocessor control circuit 
16 pulse width modulates the switching transistor 19 to periodically short 
circuit the transformer 28 to allow the current to flow through the diode 
22 to charge the battery 26. 
Turning next to FIG. 3, the schematic circuit diagram shows the integrated 
charger/controller/regenerator of the present invention during the drive 
mode of operation. The pulse Width Modulated (PWM) microprocessor pulse 
width modulates the power transistor 19 and opens the power transistor 18 
during the drive mode of operation. The switch S1 is closed to connect the 
DC battery 26 to the power transistor 19 which provides a controlled 
voltage output to drive the motor 24. 
The regenerative mode of operation is also illustrated in FIG. 3. During 
this mode, the PWM microprocessor control circuit 16 closes the switching 
transistor 19 while pulse width modulating the power transistor 18 to 
periodically short-circuit the DC motor 24 and reverse the direction of 
the current while maintaining the polarity of the voltage to charge the 
battery 26 and brake the DC motor 24. 
Illustrated in FIG. 4 is an alternative embodiment of the integrated 
charger/controller/regenerator of the present invention which utilizes 
diodes 40 connected in a series bridge configuration in place of the high 
power switching transistors 14 of the PWM circuit to rectify the reduced 
voltage of the AC power input. 
The programmable PWM of the integrated charger/controller circuit allows 
the programming of various charging characteristics for charging batteries 
having a variety of characteristics. Accordingly, each battery may utilize 
a proprietary charging algorithm. In addition, the PWM may also be used as 
a pulse charger to increase the battery cycle life, or to quick charge the 
battery. 
In comparison to conventional polyphase AC charger/controllers, the 
charger/controller/regenerator of the present invention requires about 
two-thirds less components and enables a corresponding cost advantage. 
Thus, it can be seen from the foregoing detailed description and attached 
drawings that the drive assembly of the present invention includes an 
integrated charger/controller/regenerator which eliminates redundant 
components of separate chargers and controllers and thereby achieves 
savings in terms of cost, weight ahd space. It also enables efficient use 
of low power batteries and single phase DC motors.