JPS5845275B2 - Switching method between regenerative braking and dynamic braking for DC motors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for switching between regenerative braking and dynamic braking for a DC motor, and particularly to a method for smoothly switching between regenerative braking and dynamic braking.

Control technology for DC motors using thyristor choppers has been widely used in the field of electric railways, and regenerative braking is usually used for braking.

However, in DC electric railways that use rectifier substations, regenerative braking cannot be performed if there is no running vehicle that can absorb regenerative power in the same section as the regenerative vehicle. Can not.

Relying on mechanical braking every time regenerative braking expires will increase wear on the brake shoes, requiring maintenance.

As a countermeasure to this problem, a method is used in which when regenerative braking fails, the vehicle switches to dynamic braking.

FIG. 1 is a circuit diagram showing a typical example of a conventional embodiment that switches between regenerative braking and dynamic braking as described above.

PG is a pantograph, SL, S2 is a breaker, Ijl
p L2 beam handle, C is a capacitor, D is a diode, R□, R2 are resistors, T is a thyristor, CH is a chopper, M is a motor armature, F is a field, and OVD is an overvoltage detector.

When there is a sufficient regenerative power absorption load, the power generated by the armature M energized by the on/off operation of the chopper OH is returned to the DC power source through the pantograph PG.

In a range where the speed during regenerative braking is higher than the rated speed of the motor, a resistor R2 is inserted in series with the motor circuit to prevent overcurrent from flowing.

That is, in a chopper electric train, since it is usually not a good idea to provide a speed generator for control, it is common to control the short circuit of the series resistor R2 based on the voltage relationship.

At this time, as is well known from Japanese Patent Application Laid-Open No. 51-42918, when the power supply voltage and the motor generated voltage satisfy a predetermined relationship, if the series resistor R2 is short-circuited, ideal regeneration efficiency can be obtained. Desired regeneration efficiency cannot be obtained if fluctuations in power supply voltage are ignored.

For this reason, it is common to detect the voltage of the filter capacitor C as a value equivalent to the power supply voltage.

If there is no load to absorb regenerative power during regenerative braking, the regenerative current can flow to the DC power source through the pantograph PG, and the power generated by the armature M increases the voltage of the capacitor C.

When the voltage of the capacitor C exceeds a certain limit value, an overvoltage detector OVD detects this, ignites the thyristor T, and connects the resistor R1 as a regenerative power absorption load.

As mentioned above, in the high speed range of the motor, the resistor R2 is inserted in series with the motor, but as the speed of the motor decreases, the potential difference across the capacitor C (hereinafter referred to as capacitor voltage and its value is E).

)E and the voltage generated by armature M (the value is assumed to be E).

) When the difference from EM exceeds a certain value, that is, when E −E is insufficient, the resistor R2 is short-circuited by the breaker S2 to ensure the regenerated power to the DC power supply. There is.

However, when there is no load to absorb the regenerated power, the capacitor voltage EC increases even in the high speed range, so equation (1) is satisfied, and the resistor R2 is shorted, causing the motor current to become excessive. , the tendency of the electric motor to flashover increases.

Furthermore, even if the load that absorbs regenerative power recovers and returns to regenerative braking after that, the same overcurrent condition as above will appear because resistor R2 is short-circuited despite the high speed range. Therefore, unless some method is taken to reduce the motor current, stable braking force cannot be obtained.

As described above, the conventional method of switching between regenerative braking and dynamic braking for a DC motor has the disadvantage that the braking operation is unstable because the resistor R2 is short-circuited in the high speed range.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a method that always ensures stable braking force even when switching from regenerative braking to dynamic braking and returning to regenerative braking at Xt.

The feature of the present invention is that when there is no load to absorb regenerated power, a command is given by the output signal of the detector,
By removing the short-circuit condition of the resistor connected in series with the motor, it prevents overcurrent during dynamic braking at high speeds.
Regenerative braking is about stabilizing the braking force.

FIG. 2 is a diagram showing an embodiment of the present invention, where VD is a voltage detector, ME is a storage element, and AND is an AND gate, one of whose input terminals satisfies the condition of equation (1). When the signal is input, the signal is being input.

Other symbols are the same as those in FIG.

The output of the overvoltage detector OVD is input to the storage element ME,
The output signal is ANDed at the same time as breaker S1 is opened.
Since 'O' is input to the other input terminal of the gate, even if the signal ''1' is input to the one input terminal, the circuit breaker S2 is not turned on and the series resistor R2
remains connected and becomes 1.

Further, the memory of this memory element ME is cleared by a signal when the voltage detector VD detects that the DC power source is capable of accepting regeneration.

As a result, even if the resistor R2 is disconnected from the DC power supply during regenerative braking at high speeds and an overvoltage occurs, the resistor R2 will not be short-circuited, and therefore, even when switching to dynamic braking, no overcurrent will occur. A switch is made from regenerative braking to stable dynamic braking.

Further, even when returning from dynamic braking to regenerative braking, there is no overcurrent due to the presence of the resistor R2, so this switching is also performed smoothly.

Next, the present invention will be explained in comparison with a conventional example using current characteristic diagrams.

FIG. 3 is a diagram showing the motor speed as the horizontal axis and the motor current as the vertical axis.

In the figure, OR1 shows the waveform when resistor R2 is short-circuited, and CR2 shows the waveform when R2 is inserted.

As in the conventional example, when the speed is high and the resistor R2 is short-circuited, constant current control by the chopper during dynamic braking becomes impossible, and the motor current changes as 1 → 2 → 3 → 4, resulting in the above-mentioned change. This can lead to overcurrent and flashover of the motor.

FIG. 4 is a diagram showing temporal changes in motor current during braking.

T1 and T3 indicate the period of regenerative braking, and T2 indicates the period of dynamic braking.

Current change during dynamic braking: The symbols 1A→2A→3A→4A correspond to the positions 1→2→3→4 in FIG.

The current change shown in Figure 4 from 4A to 5A to 6A is when R2 in the conventional example is short-circuited and the dynamic braking returns to regenerative braking at high speed.In this case, the motor generated voltage is high. Therefore, the current becomes excessive, so the characteristics are shown when measures are taken to suppress this.

In the case of the present invention, as shown in FIG. 3, the flow is not like 1 → 2 → 3 → 4 as in the conventional example, but the constant current control by the chopper is continued, so the flow becomes like 1 → 4, and the 4th In the figure, it changes like a solid line, such as from 1A to 4A.

Furthermore, when returning from dynamic braking to regenerative braking, R2 is inserted, so the transition becomes P4→P6 (solid line part).

Fig. 5 shows another embodiment of the present invention, which differs from Fig. 2 in that a method using a current detector 4 is adopted instead of detecting the voltage of the DC power source as a method for detecting failure of regenerative braking. This is what is happening.

Insufficient regenerative load is detected by detecting that the current regenerated in the DC power supply actually decreases, and the short-circuit condition of resistor R2 is canceled.

Note that the method for detecting insufficient regenerative load can be realized by methods other than those shown in FIGS. 2 and 5.

As described above, according to the present invention, it is possible to smoothly switch between regenerative braking and dynamic braking of a DC motor.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional device, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a comparison diagram between the conventional example and the system according to the present invention based on dynamic braking speed-current characteristics, and Fig. 4 The figure is a comparison diagram of the present invention and a conventional example in which the motor current is electrified at the time of regulation, and FIG. 5 is a circuit diagram showing another embodiment of the present invention. S1# S2... Breaker, Ll, L2... Reactor, D... Diode, C... Capacitor, R1
t R2...Resistor, T...Thyristor, CH...
・Chopper, M...DC motor, OVD...overvoltage detector, VD...voltage detector, ME...memory element,
AND...AND gate, CD...current detector.

Claims (1)

[Claims] 1. A DC motor that operates as a generator, a chopper that constitutes a self-excitation circuit of this DC motor, a diode that regenerates the energy generated by the DC motor to a DC power source when the chopper is turned off, and the self-excitation circuit of the DC motor. a series resistor inserted in series in the circuit and short-circuited at a relatively low speed based on the relationship between the power supply voltage and the motor voltage; and a regeneration failure detection means responsive to the power supply voltage exceeding a predetermined value; For a braking control device for a DC motor including a thyristor that causes the generated energy to be consumed in a dynamic braking resistor in response to the operation of the detection means, A method for switching between regenerative braking and dynamic braking for DC motors with means to prevent short circuits.