JPH072006B2 - Chopper protection method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter used in an auxiliary power source for an electric vehicle, that is, a step-up / down chopper device.

[0002]

2. Description of the Related Art JP-A-3-82364 proposed by the present inventor
Fig. 3 shows the main circuit connection diagram of the buck-boost chopper device described in Japanese Patent Publication No.
Shown in. This step-up / down chopper device includes a reverse blocking thyristor 14 connected in parallel with a charging resistor 13 between a positive electrode and a negative electrode of a DC power supply 1, a first reactor 2, a first switching element 5, a second reactor 9 and a second reactor 9. 2 switching elements 6
Are connected in series, and the first, third and second capacitors 3, 10 and 4 are connected in series between the anode of the first switching element 5 and the cathode of the second switching element 6, and the first switching The cathode of the element 5 is arranged on the cathode side, the anode side is arranged at the connection point of the first and third capacitors 3 and 10 to connect the first diode 7, and the anode of the second switching element 6 is arranged on the anode side. Is connected to the second diode 8 by arranging the cathode side at the connection point between the third and second capacitors 10 and 4, and the output is taken out from both ends of the third capacitor 10. A detailed description of the operation of this step-up / down chopper device is omitted,
The main feature of the circuit is that the DC output voltage V ₀ across the third capacitor can be stepped up or down with respect to the input DC voltage V _L , and the polarity of the output voltage V ₀ is the first. And the polarities of the second capacitors 3 and 4 are opposite.

In FIG. 3, reference numeral 12 is a switch for disconnecting the device from the DC power source, and charging resistor 13 is a large charging current for the first and second capacitors 3 and 4 when the switch 12 is turned on. (The third capacitor 10 is not charged in the opposite direction to the polarity shown in FIG. 3 by a parallel diode (not shown)), and the reverse blocking thyristor 14 is provided with the first and second capacitors 3, 4 When is charged, it turns on and shorts the charging resistor 13.

By alternately turning on and off the first and second switching elements 5 and 6 in the circuit of FIG. 3 and controlling the conduction rate thereof, the voltage across the third capacitor 10 which is a DC output voltage. It is possible to keep V ₀ constant.
When the input DC voltage is V _L , the voltages V _C1 and V _C2 across the first and second capacitors 3 and 4 are given by the following equations. V _C1 = V _C2 = (V _L + V ₀ ) / 2

In this circuit, when an overcurrent flows on the DC output side due to the load side, the currents flowing through the first and second switching elements 5 and 6 also increase in proportion to it.
When it exceeds the current cutoff capability of the switching element, the switching element is destroyed. In order to prevent this, when a current having a breaking capacity or more flows, the breaking of the switching elements 5 and 6 is blocked and the ON state is continued. As a result, a current flows in the path of DC power supply 1 → switch 12 → reverse blocking thyristor 14 → reactor 2 → switching element 5 → reactor 9 → switching element 6 → DC power supply, and the inductance due to magnetic saturation of the iron cores of reactors 2 and 9 The current rapidly decreases to a large current.

This large current is cut off by the switch 12, but the switch 12 is of a high speed type which starts the breaking operation early before the current becomes larger and completes the breaking within a short time. Must. Further, as the switching elements 5 and 6, it is necessary to select ones that can withstand the current until the interruption is completed.

[0007]

In the conventional protection method, the overcurrent withstanding capability of the switching elements 5 and 6 must be increased, and an unnecessarily large-capacity switching element must be used. Further, since a large current is cut off by the switch 12, the contact of the switch is damaged and it takes time and skill to clean it.

Furthermore, if the protection system for the substation, which is the DC power source 1, and the breaking performance of the switch 12 are not well coordinated, the substation will shut off first, affecting other healthy equipment. There was a drawback that caused it.

It is an object of the present invention to provide an excellent protection scheme which takes advantage of the operational characteristics of this circuit in order to overcome the above mentioned drawbacks.

[0010]

[Means for Solving the Problem] When a problem such as a load overcurrent or a DC output overvoltage occurs, the electric charge charged in the third capacitor 10 is rapidly discharged.

[0011]

When the third capacitor charged to the voltage V ₀ is rapidly discharged, the voltage [(V _L + V ₀ ) / 2] charged to the first and second capacitors 3 and 4 is discharged to each capacitor. It does not change rapidly because it uses a large capacity. Accordingly, when the third capacitor 10 is discharged and the voltage of the capacitor 10 becomes zero, the voltage between the anode of the switching element 5 and the cathode of the switching element 6 (this is V _C1 −V ₀ + V _C2 Time is V _C1 −
V ₀ + V _C2 = V _L ) becomes V ₀ + V _L , and the voltage V ₀ is applied to the reactor 2 in the polarity shown in FIG. Therefore, the current flowing through the reactor 2, that is, the DC input current rapidly decreases to zero, and the reverse blocking thyristor 14 spontaneously extinguishes the arc. After this, by opening the switch without current,
The chopper circuit can be reliably disconnected from the DC power supply 1.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a chopper protection system according to the present invention will be described with reference to the drawings. FIG. 1 shows a step-up / down chopper device to which a protection system according to the present invention is applied, and those having the same functions as those in FIG. 3 are designated by the same reference numerals.

As a discharging means of the third capacitor 10, a series circuit of a reactor 16 and a thyristor 15 is connected in parallel with the capacitor 10. When the thyristor 15 is turned on during protection, an oscillating current due to the capacitor 10 and the reactor 16 flows from the capacitor 10 and discharges rapidly
The voltage of 10 becomes zero, and as described above, the reverse blocking thyristor 14
Can be turned off.

Another embodiment of the present invention is shown in FIG. FIG. 2 shows a case where a voltage source inverter 17 (single-phase or three-phase or more) is connected as a DC load, and an AC transformer 18 may be connected to the AC output side of the voltage source inverter 17. In FIG. 2, a switching element group connected in series in the voltage source inverter 17 at the time of protection (for example, shown in FIG. 2).
When one or more of GTU and GTX) are turned on at the same time, an oscillating current between the capacitor 10 and the reactor 16 flows as in the case of FIG. 1 and the voltage of the capacitor 10 can be made zero.

Further, when the transformer 18 is connected to the AC side of the voltage source inverter 17, the operating state of each switching element of the voltage source inverter is maintained at the moment the protection operation starts (the voltage source inverter 17). Is three phases, two on the positive side, one on the negative side, or vice versa,
Either switching element is conducting). Figure 2
Among the switching elements of the voltage source inverter of GTU, G
Assuming that the TV and GTZ are conducting, if these switching elements are kept conducting during protection, the transformer
A DC voltage is applied to the primary winding of the transformer 18, the iron core of the transformer is rapidly magnetically saturated, and the impedance becomes low (primary side leakage inductance), and a large current flows from the capacitor 10 to rapidly discharge the capacitor 10. in this case,
When the transformer is saturated, the primary impedance is reactor 16
, The reactor 16 in FIG. 2 is unnecessary.

[0016]

According to the present invention, the reverse charge blocking thyristor on the input side is made non-conducting by rapidly discharging the charged electric charge of the capacitor 10, so that the chopper circuit can reliably operate the DC power supply 1 during protection. Can be separated from.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a protection method of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the protection method of the present invention.

FIG. 3 is a main circuit diagram of a step-up / down chopper device to which the protection method of the present invention is applied.

[Explanation of symbols]

 1 DC power supply 2 1st reactor 3 1st capacitor 4 2nd capacitor 5 1st switching element 6 2nd switching element 7 1st diode 8 2nd diode 9 2nd reactor 10 3rd capacitor 11 Load 12 Switch 13 Charge resistance 14 Reverse blocking thyristor 15 Short circuit thyristor 16 Protective reactor 17 Voltage source inverter 18 AC transformer

Claims (4)

[Claims] 1. A reverse blocking thyristor connected in parallel with a charging resistor between a positive electrode and a negative electrode of a DC power supply, a first reactor, a first switching element, a second reactor and a second switching element are connected in series. , First, third, and second capacitors are connected in series between the anode of the first switching element and the cathode of the second switching element, and the cathode side is connected to the cathode of the first switching element.
The anode side is arranged at the connection point of the first and third capacitors to connect the first diode, the anode side is connected to the anode of the second switching element, and the cathode is connected to the connection point of the third and second capacitors. In the step-up / down chopper device which arranges the side and connects the second diode, and takes out the output from both ends of the third capacitor, by rapidly discharging the electric charge of the third capacitor during abnormal operation of the device, A protection method for a chopper, characterized in that the reverse blocking thyristor is forcibly turned off. 2. A series circuit of a protective reactor and a short-circuit thyristor is connected in parallel with the third capacitor as a means for rapidly discharging the electric charge of the third capacitor, and the short-circuit thyristor is turned on at the time of protection. The chopper protection system according to claim 1, wherein: 3. A voltage-source inverter connected as a load to both ends of the third capacitor, all switching elements of the voltage-source inverter being turned on at the time of protection to rapidly discharge the third capacitor. The chopper protection system according to claim 1. 4. A voltage source inverter having an AC transformer on the output side is connected to both ends of the third capacitor as a load, and the voltage source inverter is maintained in an operating state at that moment during protection. 3. A third capacitor is rapidly discharged by causing a direct current demagnetization of the alternating current transformer to reach magnetic saturation and making the primary winding of the transformer low impedance.
Chopper protection method described.