Electric vehicle control system

Abstract: 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 recieve 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 an 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.

Description: 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. In order to smoothly run an AC motor driven electric vehicle controlled by variable voltage variable frequency inverters (hereafter stated as "inverters"), the electric vehicle control system should be composed in such a way that even if, by any chance, an inverter should malfunction, it is possible to continue driving the electric vehicle by swiftly opening the malfunctioning part. In general, a three-phase induction motor is typical for an electric vehicle drive motor. For example, a control system for an electric vehicle having a three-phase induction motor is shown in EP-A-0588628. However, recently an electric vehicle has been developed which is driven by permanent magnet synchronous motors (hereafter stated as "PM motors"). supplied respectively with 3-phase AC powers from inverters. PM motors can be broadly divided into two types. These are a PM motor having the surface magnet structure in which permanent magnets are attached to the rotor surface of the motor, and a PM motor having the 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. Therefore, PM motors possess desirable characteristics and features as electric vehicle drive motors. Figure 2 is a schematic diagram of a prior art electric vehicle control system which controls one PM motor by one inverter. 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 an inverter 3, and is supplied to a PM motor 5. A control device 4 receives an information P from sensors (not illustrated) mounted in inverter 3 and an 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 3a - 3f. The self-turn-off semiconductor devices mentioned here are, for instance, GTO thyristors or IGBTs, and are semiconductor devices which are capable of being controlled by control signal C from control device 4 in the conductive and non-conductive states at any timing. Diodes 31 are respectively connected in anti-parallel with self-turn-off semiconductor devices (hereafter stated as "semiconductor devices") 3a - 3f. Figure 3 is a drawing showing the operation in the prior art electric vehicle control system shown in Figure 2 when semiconductor device 3a out of semiconductor devices 3a - 3f which compose inverter 3 has malfunctioned and has become in a state of constant conduction. When semiconductor device 3a becomes in conduction malfunction state, inverter 3 cannot supply 3-phase AC power to PM motor 5. When control device 4 detects this conduction malfunction of semiconductor device 3a by information P from sensors mounted in inverter 3, control device 4 outputs an opening instruction a1 for line breaker 2. Therefore, the operation of inverter 3 is caused ta stop by putting line breaker 2 into the open state. In this case, generally, the electric vehicle continues to be operated by supplying 3-phase AC powers to other PM motors 5 from other fault-free electric vehicle control systems, respectively. However, when the electric vehicle continues operation, the rotor of PM motor 5 connected to inverter 3 in malfunction state continues to rotate. Since PM motor 5 is composed of permanent magnets, a magnetic flux is generated inside PM motor 5 even in the state in which AC power is not supplied from inverter 3, and PM motor 5 operates as a generator. At this time, if all of semiconductor devices 3a - 3f are in a fault-free state, it is designed such that the current does not continue to flow from PM motor 5. However, when semiconductor devices 3a has a conduction malfunction, short-circuit currents flow between the phases of PM motor 5 by the routes shown by the arrows in Figure 3. Therefore, the 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, even if, by any chance, any semiconductor device which composes an inverter has a conduction malfunction and the power supply from the overhead supply line side to the malfunctioning inverter is cut off by-the line breaker, the electric vehicle continues to be operated by other fault-free electric vehicle control systems. Therefore, short-circuit currents will 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. 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 becomes in 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 becomes in 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 the 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. Accordingly the present invention provides an electric vehicle control system for controlling an electric vehicle, comprising the features of claim 1. When using the above composition, in the case of an inverter malfunctioning or when the operation of an inverter is caused to stop by an outer operating instruction, the permanent magnet synchronous motor connected to that inverter only 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 three-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. BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Figure 1 is a schematic diagram showing an electric vehicle control system according to an embodiment of this invention; Figure 2 is a schematic diagram showing a prior art electric vehicle control system; and Figure 3 is a drawing to illustrate the operation of the electric vehicle control system shown in Figure 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, the embodiments of this invention will be described below. Figure 1 is a schematic diagram showing an electric vehicle control system according to an embodiment of this invention. In Figure 1, DC power collected from the overhead power line (not illustrated) via pantograph 1 passes through line breaker 2 which switches the current ON and OFF. Then, the DC power is converted to variable voltage variable frequency AC power by inverter 3, and is supplied to PM motor 5. A control device 4A 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 4A calculates the inverter frequency and the motor voltage, and outputs these as control signal C. Inverter 3 is controlled based on this control signal C. Inverter 3 is composed of semiconductor devices 3a - 3f and diodes 31 respectively connected in anti-parallel with semiconductor devices 3a - 3f. Contrary to the prior art shown in Figure 2, PM motor 5 is not directly connected to the 3-phase AC output terminals of inverter 3 via the three phase output lines U, V and W. Contactors 6a and 6b are respectively connected to the output lines of two phases, for example output lines U and W, out of the three phase output lines U, V and W. Contactors 6a and 6b are normally closed. They are operated to open by an opening instruction (described later) from control device 4A. If any one, or multiple, semiconductor devices of semiconductor devices 3a - 3f which compose inverter 3 become in conduction malfunction state, PM motor 5 operates as a generator, even in the state when there is no power supply from inverter 3, as described above. One example of detecting conduction malfunction of semiconductor devices 3a - 3f is described below. Sensors (not illustrated) are respectively mounted for semiconductor devices 3a - 3f. Each sensor detects the voltage between the anode and cathode of one of semiconductor devices 3a - 3f, respectively. Sensors send these detected voltages as information P to control device 4A. Control device 4A receives information P, and judges whether or not the detected voltages are zero voltages during when gate-off signals are applied to semiconductor devices 3a - 3f, respectively. When the detected voltage of any one of semiconductor devices 3a - 3f is zero voltages, control device 4A determines that such semiconductor device is in conduction malfunction state. When control device 4A detects a conduction malfunction of semiconductor devices 3a - 3f by information P from sensors mounted in inverter 3, control device 4A outputs opening instruction al for line breaker 2 and an opening instruction a2 for contactors 6a and 6b. Then, line breaker 2 opens. Furthermore, 3-phase output lines U and W between inverter 3 and PM motor 5 are respectively opened by contactors 6a and 6b. Therefore, the flow of short-circuit currents between the phases of PM motor 5 can be prevented. In this embodiment, contactors 6a and 6b are respectively provided in 3-phase lines U and W between inverter 3 and PM motor 5. This is because, as the sum of 3-phase currents is always zero, if the output lines U and W of two phases out of the 3-phase output lines U, V and W are respectively opened by contactors 6a and 6b, current does not flow in the remaining one phase output line V either. That is to say, the output lines of at least two phases out of the 3-phase output lines U, V and W may be opened. Therefore, it goes without saying that even opening devices such as contactors are provided in all the 3-phase output lines U, V and W, the same effect as in this embodiment will be obtained. Therefore, when using this embodiment, even in a case when one or more of semiconductor devices 3a - 3f which compose inverter 3 malfunction, it is possible electrically to open only PM motor 5 which is driven by malfunctioning inverter 3. Therefore, the electric vehicle can continue to be operated by other fault-free electric vehicle control systems. Furthermore, malfunctioning inverter 3 and PM motor 5 connected to malfunctioning inverter 3 can be protected from burning out and so on. Also, contactors 6a and 6b have been used as the devices for opening 3-phase output lines U, V and W which connect PM motor 5 and inverter 3. However, the same effect can be expected by substituting non-contact systems which use semiconductor devices for contactors 6a and 6b or by substituting overcurrent fuses for contactors 6a and 6b. In the above-described embodiment, contactors 6a and 6b are respectively connected to the output lines of two phases U and W. This invention is not limited to this embodiment. Instead, it is possible to provide contactors 6a and 6b in two lines U and W inside PM motor 5. Furthermore, in this embodiment, the case of electric vehicle in which one PM motor 5 is controlled by one inverter 3 has been described. But, this invention is not limited to this embodiment. This invention is related to individual PM motor. Therefore, this invention is applied to a control system for an electric vehicle in which multiple PM motors are controlled by one inverter. In this case, the same effect can be obtained by providing opening devices for respective PM motors. Also, in the above-described embodiment, opening the opening devices has only been described for the case of inverter 3 malfunctioning. However, this invention is not limited to this embodiment. This invention is also applied to the case when inverter 3 is stopped during electric vehicle operation, such as during coasting operation, by an operating instruction (not illustrated). This invention is also applied to the case when some of the electric vehicle control systems are stopped by an operating instruction (not illustrated) when there is comparatively little acceleration or deceleration. In these cases, the effect that the flow of unnecessary current into inverter 3 is prevented can be expected. When using this invention as described above, it is possible 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 becomes in malfunction state. Furthermore, it is possible to provide an electric vehicle control system which, even in a case when an inverter of the electric vehicle control system becomes in malfunction state, can protect the malfunctioning inverter and a PM motor connected to the malfunctioning inverter for driving the electric vehicle. It is also possibie to provide an electric vehicle control system which can prevent the 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. Obviously, numerous modifications and variations of the present invention are possible in light of the above - teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims: An electric vehicle control system for controlling an electric vehicle, comprising: an inverter (13) adapted to receive DC power from an overhead power line for converting said DC power into three-phase AC power said inverter including a plurality of semiconductor devices each having a respective sensor configured to detect the voltage across it; and an AC motor connected to receive said three-phase AC power from said inverter (13) for driving said electric vehicle; characterised in that: said AC motor is a permanent magnet synchronous motor (5) ; control means (4A) for generating an opening signal (a1, a2) based on a malfunction signal (P) of said inverter or an operating instruction when one of said plurality of sensors detects zero voltage across one of said semiconductor devices while said permanent magnet synchronous motor (5) continues to rotate; and switch means (6a, 6b) connected to receive said opening signal (a2) from said control means (4a) for opening the connection between said inverter (3) and said permanent magnet synchronous motor (5) so as to cut off a short-circuit current generated from said permanent magnet synchronous motor (5) by operation of said electric vehicle. The electric vehicle control system according to claim 1, wherein: said inverter is composed of three-phase bridge-connected self-turn-off semiconductor devices (3a-3f) ; said plurality of sensors detects conduction states of said self-turn-off semiconductor devices, respectively, and outputs a plurality of said conduction states as conduction information; said control means (4a) is connected to said sensors for receiving said conduction information and judges whether any one of said self-turn-off semiconductor devices is in a conduction malfunction state based on said conduction states detected by said sensors, and outputs said malfunction signal of said inverter when any one of said self-turn-off semiconductor devices is judged to be in a conduction malfunction state. An electric vehicle control system according to claim 1: wherein three-phase output terminals of said inverter are connected to three-phase input terminals of said permanent magnet synchronous motor through three-phase output lines (U, V, W); said switch means includes at least two opening devices (6a, 6b) provided in at least two phase output lines (U,W) out of said three-phase output lines, respectively; and said opening devices are opened by said opening signal (a2) from said control means, thereby opening the connection between said inverter and said permanent magnet synchronous motor. An electric vehicle control system according to claim 1, wherein: three-phase output terminals of said inverter are connected to three-phase input terminals (U, V, W) of said permanent magnet synchronous motor; said switch means includes at least two opening devices provided in at least two phase input lines inside of said permanent magnet synchronous motor; and said opening devices are opened by said opening signal from said control means, thereby opening the connection between said inverter and said permanent magnet synchronous motor. An electric vehicle control system according to claim 1, wherein: said control means generates said opening signal when said control means receives said operating instruction for stopping said inverter while said electric vehicle is in coasting operation; and said switch means opens the connection between said inverter and said permanent magnet synchronous motor based on said opening signal from said control means, thereby opening the connection between said inverter and said permanent magnet synchronous motor. An electric vehicle control system according to claim 1: wherein said electric vehicle is composed of a plurality of said electric vehicle control systems; and wherein each of said control means of a first group of said electric vehicle control systems generates said opening signal when said control means receives said operating instruction for stopping said inverter while said electric vehicle is in operation and little acceleration or deceleration is necessary; each of said control means of a second group of said electric vehicle control systems does not generate said opening signal during when said electric vehicle is in operation and little acceleration or deceleration is necessary; each of said switch means of said first group of said electric vehicle control systems opens the connection between said inverter and said permanent magnet synchronous motor based on said opening signal from said control means, thereby opening the connection between said inverter and said permanent magnet synchronous motor; and each of said switch means of said second group of said electric vehicle control systems maintains the connection between said inverter and said permanent magnet synchronous motor.

Inventors: AOYAMA IKUYA, AOYAMA, IKUYA, Aoyama, Ikuya, c/o Toshiba Corp.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1995
Main classification: B60L9
IPC codes: B60L3, H02P27, B60L9