JPH06121461A - Method of protecting parallel operation of uninterruptive power unit - Google Patents

Abstract

PURPOSE:To provide a highly reliable protection method which can reduce the drop of the power efficiency in parallel operation of an uninterruptive power unit. CONSTITUTION:At parallel redundant operation of an uninterruptive power unit, each arm of an inverter 5 is provided with fuses 22u-22z, and if it detects a short circuit 10, it cuts off a faulty uninterruptive power unit from a sound parallel operation apparatus by turning off a changeover circuit by this detection signal, and also, turning on or turning off the switching elements 18u, 18y, 18w, 18y, and 18z of the U, V, W, Y and Z phases excluding the short-circuit arm of, for example, X phase with proper timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a parallel operation protection system for an uninterruptible power supply.

[0002]

2. Description of the Related Art A parallel redundant operation system of a plurality of uninterruptible power supply units is adopted for electric equipment which has a large capacity and is not allowed to have a momentary power failure.

FIG. 5 shows a parallel redundant operation system of a conventional uninterruptible power supply, which includes uninterruptible power supplies USP1 to USP1.
The outputs of the USP3 are connected at the connection points 12 and supply AC power to the load 14 via the main switch 13. Further, each uninterruptible power supply converts AC power from the commercial power supply 1 into DC by the rectifier circuit 2, removes ripples by the DC filter circuit 4, and then supplies the same to the inverter 5. In the inverter 5, the DC power is converted into AC power of a predetermined frequency and voltage based on the output signal of the control circuit 10, the AC filter circuit 6 removes the harmonic components, and the changeover switch circuit 7 and the changeover circuit 8 are used. AC power is supplied to the load 14.

In FIG. 5, 11 is a voltage detector for detecting the output voltage of the inverter 5, 9 is a storage battery for supplying DC power when the commercial side is out of power, and 3 is DC power from the storage battery 9 at the time of power failure. It is a switch circuit that is turned on.

FIG. 6 shows a circuit configuration of the inverter 5 and the DC filter 6, 15 is a current detector, 16 is a capacitor, 17 is a fuse, 18u to 18z are power transistors which are switching elements, and 19 is a commutation diode. Therefore, the inverter 5 is formed by these. 20
Is a reactor, and 21 is a capacitor circuit, which form the AC filter 6.

In the operating system of the uninterruptible power supply system shown in FIG. 5, for example, when a failure that cannot be operated in parallel occurs in the uninterruptible power supply system USP1 side, the uninterruptible power supply system USP1 must be promptly disconnected. Other healthy USP2 and USP3 also cause a failure due to the failure cause, and the power supply system goes down in the worst state. In order to prevent this, when a failure in which parallel operation is no longer possible occurs on the USP1 side, a reverse bias is applied to the changeover switch circuit 7 by the forced commutation method to immediately disconnect the failed machine (USP1) from parallel operation. I need to do it.

As a failure of the uninterruptible power supply system in which parallel operation cannot be continued, a short circuit failure of the element of the inverter 5 shown in FIG. 6 is considered. This will be described below.

Now, assuming that the element 18x deteriorates during normal operation,
It is assumed that a failure that causes a short-circuit state occurs due to a random failure (such a power transistor element generally causes a short-circuit failure). Then, when the U phase is on, the X is originally
The phase must be off, but because it is short-circuited, the anode of the DC electrolytic capacitor 16 → U → X → the cathode of the DC electrolytic capacitor 16 and the current I flow, and the current is detected by the current detector 15. By detecting the element short-circuit fault, the faulty machine is disconnected from the parallel state by the method described above.

[0009]

The changeover switch circuit 7 was necessary for the parallel redundant operation system, but it is necessary to use an expensive semiconductor switch element as the changeover switch element, and a failure of the changeover switch circuit 7 is considered. Therefore, the reliability is low and the power efficiency is reduced by the amount of the changeover switch circuit 7.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide a highly reliable protection system capable of reducing a decrease in power efficiency during parallel operation of uninterruptible power supplies. is there.

[0011]

In order to achieve the above object, the present invention uses a switching circuit to convert DC power obtained by converting AC power of an AC power supply or DC power of a battery into AC power by an inverter and through a switching circuit. In a system in which a plurality of uninterruptible power supplies for supplying a load are connected in parallel, each arm of the inverter is provided with a short-circuit current protection element, and it is detected that a switching element constituting the inverter has a short-circuit fault and the switching The circuit is turned off, and the switching elements of the arms other than the short-circuited arm are turned on and off at appropriate timing.

[0012]

[Operation] When the switching element of the inverter is short-circuited and broken, a short-circuit current flows. This short-circuit current is detected, the switching circuit is turned off by this detection signal, and switching elements other than the short-circuit arm are on / off controlled and protected at appropriate timing, and the short-circuit current of the arm provided in the short-circuit arm is protected. Cut off.

[0013]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 shows a circuit configuration of an inverter in a parallel operation protection system for an uninterruptible power supply according to an embodiment of the present invention. In the present embodiment, as shown in FIG. 2, the conventionally used changeover switch circuit is omitted, and as shown in FIG. 1, the power transistors 18u to 18z, which are the switching elements of each arm, are connected to the fuses 22u to 2z, respectively.
Connect 2z in series.

If the X-phase power transistor 18x is damaged in a short-circuited state, a short-circuit current I ₀ flows in the loop of the anode of the capacitor 16 → U-phase → X-phase → the cathode of the capacitor 16, and this current I _{When the} current detector 15 detects ₀ , the switching operation of the inverter 5 is immediately stopped. The switching circuit 8 on the output side is turned off by the failure signal of the current detector 15 to disconnect the failed machine.

However, 10 to 20, 30 m are required for this separation.
Generally, it takes a long time to separate s. At this time, the fuses 22u, which are inserted in the shorted arm,
22x is designed so as not to be sufficiently blown out in a normal normal operating state, and therefore will not be blown out even when this short circuit occurs.

Therefore, the X-phase power transistor 18x
There are short-circuited, and the current from the other healthy machine for switching circuit 8 is not turned off immediately until blowing the fuse 21x, or fuse 21y, until blowing both 21z, cross current I ₁ or I ₂ flows. Since this cross current is limited only to the reactor 20 of the AC filter circuit 6, it has a current value equivalent to 20 times the rated current.
For this reason, when such a current flows from the sound machine, the protection circuit of the sound machine operates, which eventually causes the system to go down.

Therefore, the feature of this embodiment is that
When damage to the switching elements is detected by the discharge current from the capacitor 16 due to the failure of the switching elements of the inverter 5, the switching circuit 8 is turned off and all switching elements are protected for a predetermined period (dead time) in order to protect the elements of the sound arm. ) Just turn it off. After a predetermined period after all the switching elements are turned off, the switching elements of each phase of U, V and W are turned on. The ON period of these switching elements is set to an appropriate time τ of about 100 ms. After that, after a dead time for preventing arm short circuit of a sound phase of 20 to 30 ms, the switching elements of the X, Y, and Z phases are turned on for an appropriate time τ. This time chart is shown in FIG.

That is, as shown in FIG. 3, when an X-phase short-circuit fault occurs at time t ₁ , the arm short-circuit current level becomes I.
_Ascend to ₀₁ . A failure is detected at time t ₂ after the failure occurs at time t ₂ , the U, V, W, Y and Z phases are turned off, and the U, V, W phases are turned on at time t ₃ after time T _3. To do.
As a result, the arm short circuit level becomes I ₀₂ , and the U phase and X
Phase fuses 18u and 18x are blown. The U, V, and W phases are turned off at time t ₄ after the time period T ₄ = τ from time t ₃ .

[0020] and from time t ₄ to select the Y phase and Z phase at time t ₅ after the period T _5, then turned off at time t ₆ after the period T _6.

In FIG. 3, a period T ₁ is a normal operation period before a failure occurs, T ₂ is a section from failure occurrence to failure detection, and T ₃ and T ₅ are U, V, W, Y and Z phases. Is an off period (dead time) for preventing arm short circuit due to storage time and hole time of the transistor. Further, the period T ₄ is an ON section of the U, V, W phase switching elements, and the period T ₆ is an ON section of the X, Y, Z phase switching elements. In this case, the X phase is short-circuited, At T ₄ , both fuses 18u and 18x are blown.

When the power transistor 18x is damaged,
A short-circuit current I ₀ flows from the capacitor 16 and the two fuses 18u and 18x can be blown at the same time. Since the two fuses can be blown, the switching circuit 8 is turned off. What I have to add here is
When the switching elements on the U, V, W phases and the X, Y, Z phases are turned on at the same time, the above-mentioned cross current flows from the sound machine, but the current value is such that the switching on time τ is short. Moreover, since it is through the reactor 20 of the AC filter circuit 6, the value is not a value that operates the protection circuit of the sound machine.

Next, a protection system for an uninterruptible power supply according to another embodiment of the present invention will be described.

In the present embodiment, in the circuit configurations of FIGS. 1 and 2, when the damage of the switching element is detected as described above, the following operation is performed.

(1) The switching circuit 8 shown in FIG. 2 is turned off.

(2) In order to protect the switching elements of the sound arm of the inverter 5 shown in FIG. 1, all the switching elements are turned off for a certain section (dead time).

(3) At the same time when the switching circuit 8 is turned off, the U-phase switching element is turned on. The ON time of this switching element is an appropriate time τ of about 100 ms or less.

(4) The V phase is turned on by τ similarly to the above item (3).

(5) Only the W phase is turned on.

(6) Turn on only the X phase.

(7) Turn on only the Y phase.

(8) Turn on only the Z phase.

The switching elements are turned on in this order. This time chart is shown in FIG.

For example, if the X-phase switching element is damaged, a short-circuit current I ₀ flows from the capacitor 16, and two fuses 22u and 22x can be blown at the same time. Since the two fuses 22u and 22x can be blown at the same time, a cross current flows from the sound machine until the switching circuit 8 is turned off.

It should be mentioned here that, for example, when the X-phase switching element is damaged, the Y-phase (or Z-phase) is turned on before the U-phase. As shown in FIG. 1, the cross current I ₁ or I ₂ flows, but the current value is such that the ON time τ of the switching element is short and the reactor 2 of the AC filter circuit 6 has a short time.
Since 0 is used, the value is not a value that activates the protection circuit of the sound machine.

As shown in FIG. 4, when an X-phase short-circuit fault occurs at time t ₁ , the arm short-circuit current level rises to I ₀₁ . U when the fault at time t ₂ after the period T ₂ from the failure is detected, V, W, Y, to turn off the Z-phase current. At time t ₃ after the period T ₃ to turn on the power transistor 18u of the U phase is X-phase arm series arm, the period T ₄ = tau
It turns off at time t ₄ after to turn on the power transistor 18v of V phase. Next, at time t ₅ , the V-phase power transistor 18v is turned off, and at the same time, the W-phase power transistor 18w is turned on and turned off at time t ₆ . After that, the power transistors 18y and 18z
Turn on and off.

According to each of the above-mentioned embodiments, since the changeover switch circuit which has been used conventionally is omitted to perform protection for the parallel redundant operation, the problem caused by using the changeover switch circuit is solved. Also, there is no reduction in power efficiency and reliability is improved.

[0038]

As described above, according to the present invention, in the parallel redundant operation of the uninterruptible power supply, a short-circuit current protection element such as a fuse is provided in each arm of the inverter, and when a short-circuit current is detected, this detection signal is used. Since the switching circuit is turned off and the switching elements of the arms other than the short-circuit arm are turned on / off at appropriate timing, high performance and high reliability protection can be achieved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an inverter used in a parallel operation protection system for an uninterruptible power supply according to an embodiment of the present invention.

FIG. 2 is a block diagram of a parallel operation protection system for an uninterruptible power supply according to an embodiment of the present invention.

FIG. 3 is an operation waveform diagram of a switching element of an inverter in a parallel operation protection system for an uninterruptible power supply according to an embodiment of the present invention.

FIG. 4 is an operation waveform diagram of a switching element of an inverter in a parallel operation protection system for an uninterruptible power supply according to another embodiment of the present invention.

FIG. 5 is a block diagram of a conventional parallel operation protection system for an uninterruptible power supply.

FIG. 6 is a circuit diagram of an inverter used in a parallel operation protection system for a conventional uninterruptible power supply.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... Rectifier circuit 3 ... Switch circuit 4 ... DC filter 5 ... Inverter 6 ... AC filter 8 ... Switching circuit 14 ... Load 15 ... Current detector 16 ... Capacitors 18u-18z ... Power transistors 22u-22z ... Fuse USP1 ~ USP3 ... Uninterruptible power supply

Claims (2)

[Claims] 1. A plurality of uninterruptible power supply devices connected in parallel to each other, wherein direct current power obtained by converting alternating current power of an alternating current power supply or direct current power of a battery is converted into alternating current power by an inverter and supplied to a load through a switching circuit. In the system, a short-circuit current protection element is provided in each arm of the inverter, the short-circuit failure of a switching element forming the inverter is detected, and the switching circuit is turned off, and switching of all arms of the inverter is performed. Turn off the elements, and then turn off the switching elements of all the arms on the opposite side of the arm to which the switching element that caused the short-circuit failure to the load is connected, and then turn on the switching elements of the remaining arms on the short-circuited side. A parallel operation protection system for uninterruptible power supplies, which is characterized by: 2. A plurality of uninterruptible power supply devices connected in parallel, wherein direct current power obtained by converting alternating current power of an alternating current power supply or direct current power of a battery is converted into alternating current power by an inverter and supplied to a load through a switching circuit. In the system, a short-circuit current protection element is provided in each arm of the inverter, the short-circuit failure of a switching element forming the inverter is detected, and the switching circuit is turned off, and switching of all arms of the inverter is performed. Turn off the element, and then turn off all the switching elements of the arms on the opposite side of the arm to which the switching element that caused the short-circuit failure to the load is connected, and then turn off the switching elements of the remaining arms on the short-circuited side. A parallel operation protection system for uninterruptible power supplies characterized by turning on.