Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
1995-12-12
2001-08-21
Salata, Jonathan (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C361S023000
Reexamination Certificate
active
06278256
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electric vehicle control system, and more particularly to an electric vehicle control system which controls a permanent magnet synchronous motor for driving an electric vehicle.
2. Description of the Related Art
In order to run an AC motor driven electric vehicle controlled by variable voltage variable frequency inverters (“inverters”) smoothly, the electric vehicle control system should be designed in such a way that even if, by chance, an inverter should malfunction, it is possible to continue driving the electric vehicle by opening the malfunctioning part.
In general, a 3-phase induction motor is typically used as an electric vehicle drive motor. However, recently an electric vehicle has been developed which is driven by permanent magnet synchronous motors (“PM motors”) supplied respectively with 3-phase AC power from inverters. PM motors can be broadly divided into two types. The first type are PM motors having a surface magnet structure in which permanent magnets are attached to the rotor surface of the motor. The second type are PM motor having a buried magnet structure in which permanent magnets are buried inside the rotor. PM motors are superior in maintainability, controllability and ability to withstand the environment, and are capable of being operated with high efficiency and high power factor as compared to other types of motors. Therefore, PM motors possess desirable characteristics and features as electric vehicle drive motors.
FIG. 2
is a schematic diagram of a prior art electric vehicle control system which controls one PM motor
5
with one inverter
3
. DC power collected from an overhead power line (not illustrated) via a pantograph
1
passes through a line breaker
2
which switches the current ON and OFF. The DC power is, then, converted to a variable voltage variable frequency AC power by the inverter
3
, and is supplied to the PM motor
5
. A control device
4
receives information P from sensors (not illustrated) mounted in inverter
3
and information R, such as a speed of revolution and an angle of rotation of PM motor
5
. Then, based on information R, control device
4
calculates an inverter frequency and a motor voltage, and outputs these as a control signal C. Inverter
3
is controlled based on this control signal C. Inverter
3
is composed of self-turn-off semiconductor devices
3
a
-
3
f
(“semiconductor devices”), such as GTO thyristors or IGBTs, which are capable of being controlled by control signal C from control device
4
so as to be placed conductive or non-conductive states with predetermined timing. Diodes
31
are respectively connected in an antiparallel fashion with the self-turn-off semiconductor devices
3
a
-
3
f.
FIG. 3
is a drawing showing the operation in the prior art electric vehicle control system shown in
FIG. 2
when semiconductor device
3
a
of semiconductor devices
3
a
-
3
f
malfunctions so as to be in a state of constant conduction. When semiconductor device
3
a
is in a conduction malfunction state, inverter
3
cannot supply 3-phase AC power to PM motor
5
. When control device
4
detects the conduction malfunction of semiconductor device
3
a
via information P from sensors mounted in inverter
3
, control device
4
outputs an opening instruction al to line breaker
2
. Therefore, the operation of inverter
3
is stopped by placing the line breaker
2
into an open state. In this case, generally, the electric vehicle continues to be operated with 3-phase AC power supplied to other PM motors
5
from other fault-free electric vehicle control systems, respectively. However, when the electric vehicle continues to be operated, the rotor of PM motor
5
connected to malfunctioning inverter
3
continues to rotate. Since PM motor
5
is composed of permanent magnets, a magnetic flux is generated inside PM motor
5
, even when AC power is not supplied from inverter
3
, and PM motor
5
operates as a generator. At this time, if all of semiconductor devices
3
a
-
3
f
are in a fault-free state, the system is designed such that the current does not continue to flow from PM motor
5
. However, when semiconductor devices
3
a
has a conduction malfunction, short-circuit currents flow between the phases of PM motor
5
via the routes shown by the arrows in FIG.
3
. Therefore, a problem arises that, if the electric vehicle continues to be operated in this state, it may result in PM motor
5
burning out through overcurrent and overheating due to the short-circuit currents.
In a prior art electric vehicle control system such as described above, when any semiconductor device of an inverter has a conduction malfunction, the power supply from the overhead supply line side to the malfimctioning inverter is cut off by the line breaker and the electric vehicle continues to be operated by other fault-free electric vehicle control systems.
However, short-circuit currents continue flow in the PM motor via the malfunctioning inverter. As a result, there arises the problem of burn-out of the PM motor. Therefore, the problem arises that the operation of the electric vehicle itself cannot be continued, and thus commercial operation thereof will be hindered.
SUMMARY OF THE INVENTION
Accordingly, one object of this invention is to provide an electric vehicle control system which can continue the operation of the electric vehicle even in a case when an inverter of the electric vehicle control system is in a malfunction state.
Another object of this invention is to provide an electric vehicle control system which, even in a case when an inverter of the electric vehicle control system is in a malfunction state, can protect the malfunctioning inverter and a PM motor connected to the malfunctioning inverter for driving the electric vehicle.
Still another object of this invention is to provide an electric vehicle control system which can prevent unnecessary current from flowing into the inverter when at least one of the inverters is stopped by an operating instruction during the electric vehicle operation.
These and other objects of this invention can be achieved by providing an electric vehicle control system for controlling an electric vehicle. The electric vehicle control system includes an inverter adapted to receive DC power from an overhead power line for converting the DC power into three-phase AC power, a permanent magnetic synchronous motor connected to receive the three-phase AC power from the inverter for driving the electric vehicle, a control device for generating an opening signal based on one of a malfunction signal of the inverter and an operating instruction, and an opening device connected to receive the opening signal from the control device for opening the connection between the inverter and the permanent magnetic synchronous motor.
In another aspect of the present invention, when an inverter is malfunctioning or when the operation of an inverter is stopped via an operating instruction, the permanent magnet synchronous motor connected to that inverter can be electrically opened. Therefore, the operation of the electric vehicle can be continued by other electric vehicle control systems. Thus, interference with commercial operation can be prevented. Also, the sum of the 3-phase currents is always zero. Therefore, even by providing opening devices in at least two phase output lines out of three phase output lines, current can be prevented from flowing in the remaining one phase.
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patent: 4-4
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Salata Jonathan
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