JPH04364357A - Method of protecting chopper - Google Patents

Abstract

PURPOSE:To prevent the increase of an input current and prevent the damage of parts by quickly discharging the capacitors connected between i/o terminals, when an overcurrent flows to the load of a step-up/down chopper circuit, and forcibly turning off the reverse checking thyristor connected in series to a power source. CONSTITUTION:When it detects the overcurrent of load 11 turns off a thyristor 15 for short circuit, the oscillating current by a capacitor 10 and a reactor 16 flows from the capacitor 10 and the terminal voltage VO of the capacitor 10 drops. Capacitors 3 and 4 are great in capacity and the terminal voltages VC1 and VC2 do not change suddenly. When the voltage VO of the capacitor 10 becomes zero, the voltage between the anode of a switching element 5 and the cathode element of a switching element 6 turns from normal voltage (VC1-VO +VC2) to VO+VL (VL = power source voltage). Voltage VO is applied to a reactor 2 with the polarity shown by the figure, and the input current flowing to the reactor 2 becomes zero quickly, and a reverse checking thyristor 14 is extinguished. Hereby, the increase of an input current is prevented.

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, that is, a step-up/step-down chopper device used in an auxiliary power source for electric vehicles.

0002

[Prior Art] Unexamined Japanese Patent Publication No. 3-82 proposed earlier by the present inventor
FIG. 3 shows a main circuit connection diagram of the buck-boost chopper device described in the No. 364 publication. This buck-boost chopper device includes a reverse blocking thyristor 14 connected in parallel with a charging resistor 13 between the positive and negative poles of a DC power supply 1, a first reactor 2, a first switching element 5, a second reactor 9, and a two switching elements 6 are connected in series, and 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, A first diode 7 is connected with its cathode side disposed at the cathode of the first switching element 5 and its anode side disposed at the connection point between the first and third capacitors 3 and 10, and the second switching element 6 The anode side is arranged at the anode of the third capacitor 10 and the cathode side is arranged at the connection point of the third and second capacitors 10 and 4, and the second diode 8 is connected, and the output is taken out from both ends of the third capacitor 10. It is. A detailed explanation of the operation of this buck-boost chopper device will be omitted, but the main feature of this circuit is that it can step up or step down the DC output voltage V0 across the third capacitor with respect to the input DC voltage VL. The polarity of the output voltage V0 is opposite to the polarity of the first and second capacitors 3 and 4.

In FIG. 3, 12 is a switch for disconnecting the device from the DC power supply, and a charging resistor 13 is connected to the switch 1.
This is to suppress a sudden large charging current to the first and second capacitors 3 and 4 when capacitor 2 is turned on (the third
(The 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 turned on when the first and second capacitors 3 and 4 are charged, shorting the charging resistor 13. It is something to do.

In the circuit shown in FIG. 3, by alternately turning on and off the first and second switching elements 5 and 6 and controlling their conductivity, the voltage across the third capacitor 10, which is the DC output voltage, can be adjusted. It is possible to keep V0 constant. When the input DC voltage is VL, the voltages VC1 and VC2 across the first and second capacitors 3 and 4 are expressed by the following equations. VC1=VC2=(VL +V0)/2

[0005]
In this circuit, when an overcurrent flows to the DC output side due to a cause on the load side, the current flowing through the first and second switching elements 5 and 6 also increases in proportion to the overcurrent, which exceeds the current interrupting ability of the switching elements. If this occurs, the switching element will be destroyed. In order to prevent this, when a current exceeding the breaking capacity flows, the switching elements 5 and 6 are prevented from breaking and remain in the on state. 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 As the current decreases, the current rapidly increases.

This large current will be interrupted by the switch 12, but the switch 12 is a high-speed one that starts the interruption operation early before the current becomes even larger and completes the interruption within a short time. Must. Furthermore, it is necessary to select switching elements 5 and 6 that can withstand the current until this interruption is completed.

[0007]

In the conventional protection method, it is necessary to increase the overcurrent withstand capacity of the switching elements 5 and 6 themselves, which necessitates the use of unnecessary large-capacity switching elements. Furthermore, since the large current is interrupted by the switch 12, the contacts of the switch are damaged, and cleaning them requires time and skill.

Furthermore, if the protection system of the substation, which is the DC power supply 1, and the breaking performance of the switch 12 are not well coordinated,
The drawback was that the substation would shut down first, affecting other healthy equipment.

The object of the present invention is to provide an excellent protection scheme that utilizes the operating characteristics of this circuit in order to eliminate the above-mentioned drawbacks.

0010

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

[0011]

[Operation] When the third capacitor charged to voltage V0 is rapidly discharged, the first and second capacitors 3 and 4
The voltage charged to [(VL +V0)/2] may be due to the use of large capacitors for each capacitor.
It doesn't change quickly. Therefore, 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 VC1 - V0 + VC2, and during normal operation VC1 -V0 +VC2=VL) becomes V0 +VL, and a voltage V0 is applied to the reactor 2 with 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 is naturally extinguished. By subsequently opening the switch without current, it becomes possible to reliably disconnect the chopper circuit from the DC power supply 1.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the 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 parts with the same functions as those in FIG. 3 are given the same reference numerals.

As a discharge means for the third capacitor 10,
Reactor 16 and thyristor 1 in parallel with capacitor 10
Connect the series circuit with 5. When the thyristor 15 is turned on during protection, the capacitor 10 and the reactor 16
An oscillating current flows from the capacitor 10 due to this, and is rapidly discharged, so that the voltage of the capacitor 10 becomes zero, and the reverse blocking thyristor 14 can be turned off as described above.

Another embodiment of the invention is shown in FIG. FIG. 2 shows a case where a voltage source inverter 17 (either single phase or three or more phases is acceptable) 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, when one or more of the series-connected switching elements (for example, GTU and GTX shown in FIG. 2) in the voltage source inverter 17 are simultaneously turned on during protection, the capacitor 1 An oscillating current flows between the capacitor 16 and the reactor 16, 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 18 at the moment when the protection operation starts is maintained (voltage source inverter 17 If the switching element is three-phase, two switching elements are conductive on the positive side and one on the negative side, or vice versa). For example, among the switching elements of the voltage source inverter in FIG.
Assuming that TU, GTV, and GTZ are conducting,
If these switching elements continue to conduct during protection, a DC voltage will be applied to the primary winding of the transformer 18, and the transformer core will rapidly reach magnetic saturation, resulting in low impedance (primary side leakage inductance). A large current flows from capacitor 10 causing capacitor 10 to rapidly discharge. In this case, the primary impedance at the time of saturation of the transformer plays the role of the reactor 16, so as shown in FIG.
The reactor 16 in is no longer necessary.

[0016]

According to the present invention, the reverse blocking thyristor on the input side is made non-conductive by rapidly discharging the charge stored in the capacitor 10, thereby ensuring that the chopper circuit is connected to the DC power source 1 during protection. can be separated from

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the 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 buck-boost chopper device to which the protection method of the present invention is applied.

[Explanation of symbols]

1 DC power supply 2 First reactor 3 First capacitor 4 Second capacitor 5 First switching element 6 Second switching element 7 First diode 8 Second diode 9 Second reactor 10 Third capacitor 11 Load 12 Switch 13 Charging resistance 14 Reverse blocking thyristor 15 Short circuit thyristor 16 Protective reactor 17 Voltage type inverter 18 AC transformer

Claims (4)

[Claims] Claim 1: A reverse blocking thyristor, a first reactor, a first switching element, a second reactor, and a second reactor, which are connected in parallel with a charging resistor between the positive and negative electrodes of a DC power supply.
switching elements are connected in series, and 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,
A first diode is connected by arranging the cathode side to the cathode of the first switching element and the anode side to the connection point of the first and third capacitors, and the anode side to the anode of the second switching element. , in a buck-boost chopper device in which the cathode side is arranged at the connection point of the third and second capacitors and the second diode is connected, and the output is taken out from both ends of the third capacitor, when the device operates abnormally, the A chopper protection system characterized in that the reverse blocking thyristor is forcibly turned off by rapidly discharging the charge of the capacitor No. 3. 2. A series circuit including a protective reactor and a short-circuit thyristor is connected in parallel with the third capacitor as means for rapidly discharging the charge of the third capacitor,
2. The chopper protection system according to claim 1, wherein the short circuit thyristor is turned on during protection. 3. A voltage source inverter connected as a load to both ends of the third capacitor, characterized in that during protection, all switching elements of the voltage source inverter are turned on to rapidly discharge the third capacitor. 2. The chopper protection system according to claim 1. 4. A voltage source inverter having an AC transformer on the output side is connected as a load to both ends of the third capacitor, wherein the voltage source inverter is maintained in the operating state at that moment during protection; Claim 1 characterized in that the third capacitor is rapidly discharged by energizing the AC transformer with DC current to bring it to magnetic saturation and making the primary winding of the transformer low impedance. The chopper protection method described.