JPH0145281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device against abnormal current flowing when a main motor of an electric vehicle using a chopper is reverse excited.

The method of controlling the speed of a DC series motor using a chopper has many features such as reducing power consumption and maintenance costs and improving ride comfort, and is rapidly being put into practical use. To take advantage of these features, a regenerative braking function has been added.

FIG. 1 shows the basic circuit of a regenerative brake circuit for a DC electric vehicle using a chopper. In Figure 1, PAN is a pantograph, LB ₁ and LB ₂ are breakers,
HB ₁ and HB ₂ are high speed flow reducers, HB ₁ R and HB ₂ R are flow reduction resistors connected across each high speed flow reducer,
FL is the filter reactor, FC is the filter capacitor, A is the armature of a DC series motor, F is the main motor field winding, MSL is the main smoothing reactor,
CH is a power supply, FWD is a freewheeling diode, CHR is an auxiliary charging resistor, and PEXD is a pre-excitation device. Also, the items within the broken line will be explained later, but PEXR is a pre-excitation confirmation current relay, and BRD is a reverse current blocking diode. Furthermore, inside Chiyotupa CH, MCRF
is the main thyristor, ACRF is the auxiliary thyristor,
ANL is an anode reactor that also serves as a commutating reactor, and CMC is a commutating capacitor. The operation of a regenerative braking circuit using such a Chiyotsupa CH has already been introduced extensively, so I will briefly explain it here. That is, during braking, if the chopper CH is on, the main current flows from one end of the traction motor armature A to LB ₂ -F-
MSL-ANL-MCRF-HB ₂ flows to the other end of the traction motor armature A, and if the chopper CH is off, the main current flows from the above-mentioned one end of the traction motor armature A to LB ₂ -F −MSL−FWD−FL−HB ₁
−LB ₁ −PAN− External load (not shown) − Ground −
It flows through HB ₂ - to the other end of the main motor armature A, and applies regenerative braking to the electric vehicle. In the above-described state, the reverse current blocking diode BRD within the broken line in FIG. 1 is shown for convenience of explanation to be described later, but it is not actually provided and will be ignored.

Conventionally, it has been common practice to pre-excite the traction motor field winding F in order to easily and smoothly cause the traction motor voltage to rise at the initial stage of braking. Moreover, if the preliminary excitation circuit were to fail, the traction motor would be excited in the opposite direction for the following reasons, and since the traction motor is a DC series motor, a self-excitation phenomenon would occur, and this self-excitation phenomenon would be abnormal. There was a possibility that it would grow and eventually destroy the traction motor. In other words, (1) Since there is no induced voltage in the main motor armature A, the charge in the commutator capacitor CMC is discharged in the direction of the dashed-dotted arrow in Figure 1 by firing the auxiliary thyristor ACRF. is configured.

(2) The main thyristor MCRF is fired before the auxiliary thyristor ACRF, but at that time the auxiliary thyristor ACRF is turned off and the armature voltage is also zero, so the main thyristor MCRF
No current flows and the arc goes out.

(3) Recent chopper thyristors use reverse conduction thyristors as shown in FIG. 1, so they do not have the function of blocking reverse current. Originally, even if a reverse blocking thyristor was used, a diode (not shown) was installed in anti-parallel with the main thyristor MCRF in order to switch at high speed, so this problem is common to all chips.

In this way, an overcurrent will flow to the main motor, but in the case of reverse excitation, an even worse condition is that the current capacity of the diode area of the main thyristor MCRF is designed to be smaller than the thyristor area (for a thyristor area of 400A). diode area
(usually around 150A), the main thyristor MCRF is more likely to be destroyed than a forward overcurrent, and the damage will be greater.

In order to protect the main motor and thyristor from such phenomena, conventional methods have been to operate the chopper after detecting that the pre-excitation current has flowed, or to install a diode in the main current circuit mentioned above to prevent reverse current from flowing. I used to put . That is, in these methods the pre-excitation confirmation current relay PEXR
and reverse current blocking diode BRD are required.
The drawback was that the device was large and expensive.

This invention attempts to eliminate the above-mentioned drawbacks by improving the commutation failure detector installed in the chopper.

The chip that performs regenerative brake control has the first
In order to protect the main motor from commutation failure of the chopper in a closed circuit as shown in the figure, that is, from overcurrent in the forward direction, a commutation failure detector CFD as shown in Figure 2 is usually installed.
is installed to force the high speed flow reducer HB ₂ to trip. That is, rather than tripping due to the overcurrent detection mechanism of the high speed current reducer HB ₂ itself,
If commutation fails, the high-speed current reducer HB ₂ is immediately tripped to shorten the time until the circuit breaks and suppress the growth of fault current.

The commutation failure detector CFD shown in Figure 2 is connected to the main current path of the chopper CH and the main thyristor MCRF.
a current transformer 1 that picks up the main current flowing through the
A DCCT circuit 2 that instantly responds to the current picked up by the current transformer 1 and outputs a positive or negative output; and a current detector that outputs an output in response only to the positive output from the DCCT circuit 2. For example, it has a comparator 3. The commutation failure detector CFD also has a main current off period setting circuit 4 which is activated by an off pulse from an off pulse generating circuit to set an off period during which no main current flows. The outputs of the current detector 3 and main current off period setting circuit 4 are applied to each input terminal of an AND circuit 5.

Figure 3 shows the commutation failure detector CFD shown in Figure 2.
This is a time chart to explain the operation of
Now, when an on-pulse P1 as shown in FIG. 3A is applied to the gate of the main thyristor MCRF,
This main thyristor MCRF is turned on and the chopper CH is turned on, so the main current flows through the main thyristor MCRF as explained for the regenerative brake circuit in Fig. 1 and as shown by A in Fig. 3C.
MCRF in the forward direction (in the direction of the solid arrow in Figure 2)
flows to This main current is picked up by a current transformer 1 and then supplied to a DCCT circuit 2. This DCCT
Circuit 2 produces a positive output at its output terminal O ₁ in response to a forward main current (solid arrow), as shown in FIG. In response to this positive output, the current detector 3 produces an output as indicated by A' in FIG. 3D. This output is applied to the AND circuit 5, but as shown in FIG. 3E, since there is no output from the main current off period setting circuit 4, the AND circuit 5 does not produce any output. Commutation failure detector CFD therefore produces no output as shown in FIG. 3F.

Next, in order to turn off Chiyotupa CH, see Figure 3B.
When the off-pulse P2 as shown in FIG. increases as shown in .
Thereafter, the main current flows in the opposite direction (in the direction of the dotted arrow in FIG. 2) as shown by C in FIG. 3C to discharge the commutating capacitor CMC charged with the opposite polarity. In other words, a reverse current flows to turn off MCRF and ACRF, and while this reverse current flows, MCRF and ACRF are reverse biased and turned off. In response to this reverse current
The DCCT circuit 2 produces an output of negative polarity at its output terminal _O1 , but since the current detector 3 responds only to the output of positive polarity as described above, any output as shown by C' in FIG. will not occur. When the main current becomes zero as shown by D in Figure 3C, the current detector 3 does not produce an output as shown by D' in Figure 3D. Third
Even if the output is generated as shown in Figure E, the AND circuit 5
produces no output. However, after the off-pulse P3 shown in FIG. 3B is applied, more precisely, after the commutation time during which the reverse current flows, the main current in the forward direction flows through the main thyristor MCRF, as shown by E in FIG. 3C. If so, consider this as a commutation failure and install a commutation failure detector.
CFD detects. That is, in response to the forward main current shown by E in FIG. 3C, the current detector 3 produces an output shown by H' in FIG.
and the main current off period setting circuit 4
Since the output shown in Figure E is generated and applied to the AND circuit 5, the commutation failure detector
CFD produces the commutation failure detection output shown in Figure 3F,
The trip coil of the high speed flow reducer _HB2 is then energized to trip the high speed flow reducer _HB2 .

This invention attempts to protect against reverse current by using the above-mentioned commutation failure detector.

By the way, to describe the characteristics of the DCCT circuit 2 shown in FIG. 4, when the main current flows from the forward direction to the reverse direction after the current off period as shown in FIG. 5A, the output of the DCCT circuit 2 is , if the main current is in the forward direction as shown by F in Fig. 5A, then it will be shown by F' in Fig. 5B accordingly,
On the other hand, if the main current goes in the opposite direction as shown by R in Fig. 5A, the main current will change depending on the current until the time T ₁ when the current transformer core is saturated due to the characteristics of the current transformer core of the DCCT circuit. The waveform becomes as shown by R' in FIG. 5B, and thereafter becomes a waveform R'' that pulsates in synchronization with the half cycle of the AC current of the DCCT circuit shown in FIG.

Therefore, the DCCT circuit 2 is usually F in FIG. 5A.
Since a main current in the forward direction shown by is passed and a positive output shown by F' in FIG. 5B is produced, the iron core is biased in the corresponding direction. Therefore, when a reverse current flows, there is always a period during which a negative polarity output shown in FIG. 5B is output until the iron core is saturated in the reverse direction. As is clear from the configuration of the DCCT circuit shown in FIG. 4, the maximum value of this negative polarity output is the forward voltage drop of the rectifier diodes, which is approximately 1.0 to 2.0V since two diodes are connected in series.

Therefore, by configuring a commutation failure detector that can detect this negative polarity output due to reverse current, it is possible to quickly detect abnormal current due to reverse excitation and destroy the main motor or thyristor, which is the object of the present invention. This means that overcurrent can be suppressed.
In addition, in the present invention, the commutation/reversal current period in FIG. 3 is the output of the current detector 3, but it is possible to secure a sufficient time between the output of the main current OFF period setting circuit 4 and the output of the main current off period setting circuit 4. Therefore, there will be no false positives. Furthermore, since the output of the main current off period setting circuit 4 is guaranteed at least once during the time T ₁ in FIG. 5 (the chopper frequency is generally greater than twice the commercial frequency), T ₁ can be detected within a time period of FIG. 6 shows a portion of an embodiment of a commutation failure detector that can also utilize negative polarity output. This embodiment is obtained by adding a portion surrounded by a dashed line to the DCCT circuit 2 shown in FIG. 4. If you explain in detail,
The output terminal O ₁ of the DCCT circuit 2 is connected to the current detector 3 of FIG. 2 via a first diode D ₁ connected in a direction in which a positive polarity output is energized. The connection point between the output terminal O ₁ and the anode of the diode D ₁ is connected to one input terminal of the amplifier A via an input resistor IR. A feedback resistor FR is connected between this input terminal of amplifier A and the output terminal of amplifier A. The other input terminal of the amplifier A is grounded together with the output terminal O ₂ of the DCCT circuit 2. The output terminal of amplifier A is a second diode connected with the same polarity as diode _D1 .
Connected to current detector 3 via diode _D2 . The operational amplifier OA, consisting of the amplifier A, the input resistor IR and the feedback resistor FR, converts the negative polarity output at the output terminal O ₁ into an output of the same magnitude but opposite polarity, ie, a positive polarity output. With such a configuration, in response to the main forward current,
The positive polarity output produced at the output terminal O ₁ of the DCCT circuit 2 is not only applied to the current detector 3 through the first diode D ₁ , but also the negative polarity output produced at the output terminal O ₁ in response to the reverse current. The output is also polarized by the operational amplifier OA and then applied to the current detector ₃ through the second diode D2, so the commutation failure detector CFD detects either the forward main current or the reverse main current, that is, the reverse current. It will also operate in response.

Next, the operation of an embodiment of the present invention in which the circuit shown in FIG. 6 is used in the DCCT circuit 2 portion shown in FIG. 2 will be described. FIG. 7 is a time chart for explaining the operation during normal operation and when commutation failure is detected.
All operations are the same as in the case of FIG. However, as explained in FIG. 6, the output of the DCCT circuit 2 becomes positive and is input to the current detector 3 in either the direction of the detected main current or in the reverse direction. Output is also generated during the reverse current period shown by C in FIG. 7C, as shown by A'' in D.
When the main current becomes zero as shown by D in FIG. 7C, the current detector 3
does not produce an output, so even if the main current off period setting circuit 4 produces an output as shown in FIG. 7E, the AND circuit 5 does not produce an output. That is, the commutation failure detector CFD does not produce a detection output in the case of instantaneous reverse current during normal commutation.

Figure 8 also shows how to detect when the preliminary excitation device PEXD shown in Figure 1 does not function properly at the initial stage of regenerative braking and causes reverse excitation of the traction motor as explained in the conventional problem section. This is a time chart for explaining the operation when That is, since there is no induced voltage in the main motor armature A when switching to regenerative braking, no current flows through the main thyristor MCRF even if the on-pulse indicated by P1 in FIG. 8A is applied to the gate of the main thyristor MCRF ( The main thyristor MCRF is turned off), and then an off pulse indicated by P2 in FIG. 8B is applied to the gate of the auxiliary thyristor ACRF, and the auxiliary thyristor
When ACRF is ignited, the initially charged commutating capacitor CMC is discharged in the direction of the dashed-dotted line arrow in Figure 1, and the main motor, the DC series motor, is excited in the opposite direction. A self-excitation phenomenon occurs within the main thyristor.
Figure 8C through the reverse diode section of MCRF.
A reverse divergence current will flow inside, as shown by F. Further, the output of the DCCT circuit 2 becomes the positive polarity and is input to the current detector 3 as explained in FIG. arise. In the commutation failure detector CFD shown in FIG. 2, the output of the current detector 3 is applied to the AND circuit 5, and the main current off period setting circuit 4 outputs the output shown in FIG. 8E. Since the voltage is generated and applied to the AND circuit ₅ , the detection output shown in FIG.

Note that the waveforms indicated by broken lines in FIGS. 8C and 8D show the normal state, and are convected with the normal state waveforms in FIGS. 7C and 7D.

As described above, in this invention, one polarity converter that converts the negative polarity output from the DCCT circuit to the positive polarity output is added to the commutation failure detector that originally detects commutation failure of the chopper. This suppresses the overcurrent that flows when the traction motor is reversely excited, and prevents damage to the traction motor and thyristor.

[Brief explanation of drawings]

Figure 1 is a basic circuit diagram of a regenerative brake circuit for an electric vehicle using a chopper, Figure 2 is a functional block diagram of a commutation failure detector, and Figure 3 is the operation of the commutation failure detector shown in Figure 2. Fig. 4 is a circuit diagram showing an example of the DCCT circuit, Fig. 5 is an output waveform diagram of the DCCT circuit shown in Fig. 4,
FIG. 6 is a circuit diagram showing a part of a commutation failure detector used in an embodiment of the present invention, and FIGS.
The figure is a time chart for explaining the operation of the commutation failure detector in one embodiment of the present invention. In the diagram, A is the traction motor armature, HB ₂ is the high-speed current reducer, CH is the chopper, CFD is the commutation failure detector,
2 is a DCCT circuit, 3 is a current detector, D ₁ and D ₂ are diodes, and OA is an operational amplifier.

Claims (1)

[Scope of Claims] 1. An electric vehicle in which the speed of a DC series-wound motor as a main motor is controlled by a chopper having a reverse conduction function, and also has a regenerative brake control function, wherein the chopper is controlled in a forward direction or a reverse direction during braking. a current detection circuit that generates outputs of positive polarity and negative polarity in response to the main current flowing through the chopper, a detector that responds only to the positive output from the current detection circuit, and a main current that does not flow through the chopper. The current detection circuit comprises a main current off period setting circuit that sets an off period, and a commutation failure detector that generates an output based on a logical sum of both outputs of the main current off period setting circuit and the detector. a first diode connected in a direction to conduct the positive output between the circuit and the detector; and a conversion circuit connected in parallel with the first diode to convert the negative output into a positive output. An electric vehicle protection device characterized by being provided with. 2. The electric vehicle protection device according to claim 1, wherein the conversion circuit comprises a series circuit of an operational amplifier and a second diode having the same polarity as the first diode.