JPH09252581A - Operation of uninterruptive power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen noise of an uninterruptive power supply at the time when a power inverter is stopped and only a power rectifier is operated or at the time of light-load operation. SOLUTION: At the time of the stoppage of a power inverter 3 or at the time of light-load operation, an UPS control circuit 6 detects such an operating condition and then sends a signal for switching a carrier frequency of a power rectifier 2 to an analog switch and thereby the uninterruptive power supply device is operated with a different carrier frequency of the power rectifier 2. The carrier frequency of the power rectifier 2 at the time of the stoppage of the power inverter 3 and at the time of light-load operation is set higher than that at the rated operation. By this method, noise from an AC reactor, etc., can be lessened and noise of the uninterruptive power supply device can be lessened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating an uninterruptible power supply, and more particularly to a method of operating an uninterruptible power supply capable of reducing noise.

[0002]

2. Description of the Related Art An uninterruptible power supply device is described, for example, in "All about power electronics" published by OHM. The uninterruptible power supply is composed of a rectifier, a storage battery and an inverter. A PWM converter and a PWM inverter are generally adopted as the rectifier and the inverter, respectively. Moreover, as a switching device used for a forward converter and an inverse converter of an uninterruptible power supply, an IGBT is often used in many cases. IGBT
Is used, a carrier frequency of about 2 kHz to 10 kHz is used.

[0003]

In the above prior art, since the carrier frequency is set to a frequency in the audible range of 2 to 10 kHz, there is a problem that noise of the AC reactor is noisy.

In order to reduce the noise caused by the carrier frequency, the carrier frequency may be set to a frequency outside the audible range for humans. However, if the carrier frequency is increased, the switching device in the forward converter and the inverse converter will be used. However, there is a problem in that the loss becomes large and the efficiency remarkably decreases.
In addition, in the uninterruptible power supply, when the load device is stopped at night, the operating method is generally such that, for economical reasons, the reverse converter is stopped and only the forward converter is operated to charge the storage battery. In this case, the noise of the uninterruptible power supply often becomes a problem during nighttime when devices other than the uninterruptible power supply are stopped, rather than during daytime when the load device is operating.

An object of the present invention is to provide a method of operating an uninterruptible power supply for reducing noise in a specific operating state of the uninterruptible power supply (during light load operation or when the inverse converter is stopped). It is in.

[0006]

In order to achieve the above object, in the present invention, when the inverse converter is stopped and only the forward converter is operated or at the time of light load operation, the carrier frequency is set to be lower than that at the time of rated operation. Set it to a high frequency (a frequency outside the human audible range).

According to this operating method, when the inverse converter is stopped and only the forward converter is operated, or at the time of light load operation, the operation is performed at a carrier frequency outside the audible range of humans, so that noise from the AC reactor, etc. And the noise of the uninterruptible power supply can be reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. The uninterruptible power supply (UPS) 7 includes a forward converter 2, an inverse converter 3, a storage battery 4, a forward converter 2 and an inverse converter 3.
And a UPS control circuit 6 for controlling. The forward converter 2 converts an AC voltage supplied from the AC power supply 1 into a DC voltage and outputs the DC voltage. The output of the forward converter 2 has an inverse converter 3 and
The storage battery 4 is connected. The inverse converter 3 is the forward converter 2
Alternatively, the DC voltage from the storage battery 4 is converted into an AC voltage and supplied to the load device 5.

During normal operation, the forward converter 2 is controlled by a predetermined carrier frequency to supply DC power to the reverse converter 3 and charge the storage battery 4. The inverse converter 3 converts DC power into AC power and supplies it to the load device 5. When the load device 5 is stopped and the reverse converter 3 is stopped at night, a holiday, etc., and only the forward converter 2 is operated to charge the storage battery 4, the forward converter 2 sends a stop signal of the reverse converter 3 to UPS. By detecting with the control circuit 6, the carrier frequency is switched to a higher carrier frequency than that in the normal operation to operate.

An example of a carrier frequency switching method when the inverse converter 3 is stopped will be described with reference to FIG. The forward converter 2 is a PWM control type three-phase bridge converter, and its main circuit is composed of a capacitor 9 installed at an input end, an AC reactor 10, IGBTs 11A to 11F and diodes 12A to 12F connected in antiparallel thereto, and a direct current. Smoothing capacitor 1
3 is comprised.

The operation of the control circuit of this main circuit will be described.
First, the difference between the feedback of the voltage across the DC smoothing capacitor 13 and the output reference voltage 14 is amplified by the operational amplifier 15. This output and the outputs of the synchronous sine wave generating means 16A to 16C that generate a sine wave synchronized with the AC voltage are multiplied by the multipliers 17A to 17A.
17C, and the difference between the output of the multipliers 17A to 17C and the feedback of the AC input current by the current transformers 18A to 18C is amplified by the operational amplifiers 19A to 19C. The outputs of the operational amplifiers 19A to 19C and the output of either the first triangular wave generating means 20 or the second triangular wave generating means 21 selected by the analog switch 23 are compared with the comparators 22A to 22A.
2C, and the IGBT driving means 8 drives the IGBTs 11A to 11F by the outputs (PWM signals) of the comparators 22A to 22C.

For example, when the feedback of the voltage across the DC smoothing capacitor 13 is higher than the output reference voltage 14, the multiplier 1
Since the outputs of 7A to 17C are reduced and controlled so as to reduce the input current, the voltage across the DC smoothing capacitor 13 is lowered and kept to match the output reference voltage 14. Further, the outputs of the multipliers 17A to 17C and the current transformer 18 synchronized with the input AC voltage by the operational amplifiers 19A to 19C.
Since the AC input currents from A to 18C are controlled to match each other, the input current is kept in a sine wave and the input power factor is kept at 1.0. As the triangular wave generating means at this time, the first triangular wave generating means 20 (for example, carrier frequency: 5 kHz) depends on the operating state of the uninterruptible power supply.
Alternatively, either the second triangular wave generating means 21 (for example, carrier frequency: 20 kHz) is used. The analog switch 23 has an inverse converter operation signal 24 from the UPS control device 7.
Thus, when the inverse converter 3 is in operation, the inverse converter operation signal 24 is transmitted and the first triangular wave generating means 20 side is turned on, and when the inverse converter 3 is stopped, the inverse converter operation signal 24 is not transmitted, The one triangular wave generating means 20 side is turned off and the second triangular wave generating means 21 side is turned on. Therefore, when the inverse converter 3 is in operation, the first triangular wave generating means 20 is selected and noise of 5 kHz is generated from the AC reactor 10. However, when the inverse converter 3 is stopped, the second triangular wave generating means 21 is selected. ,
Since the carrier frequency is 20 kHz, which is out of the audible range, noise is eliminated. This uninterruptible power supply is designed for cooling based on the loss generated during rated operation. When the inverse converter 3 is stopped, this loss is significantly reduced, so even if the carrier frequency is increased, only a smaller loss than the loss during rated operation occurs, and the noise of the uninterruptible power supply unit does not increase without increasing the cooling device. Reduction can be realized.

Next, a second embodiment will be described with reference to FIG. The main circuit of the forward converter 2 has the same configuration as that of FIG. 2, and the control circuit configuration is basically the same as that of FIG. 2, but the carrier frequency switching conditions are different. The inverse converter 3 is a PWM control type three-phase bridge inverter, and the main circuit is an IGBT26.
A to 26F and diodes 27A to 27 connected in anti-parallel thereto
F and a DC smoothing capacitor 25.
Explaining the operation of the control circuit of the inverse converter 3, the output voltage of the inverse converter 3 is transformed by the transformer 28, and the difference between this voltage and the outputs of the reference sine wave generators 30A to 30C is calculated by the operational amplifiers 31A to 31C. Amplify with. Operational amplifier 31A to 31C
And the output of either the first triangular wave generating means 20 or the second triangular wave generating means 21 selected by the analog switch 23 are compared by the comparators 32A to 32C,
IGB by the output (PWM signal) of the comparators 32A to 32C
The T drive means 33 drives the IGBTs 26A to 26F. The carrier frequency is switched by inputting the output current value of the inverse converter 3 which has been transformed by the current transformers 29A and 29B to a switching signal generator 34 which generates a switching signal, and by the output of the switching signal generator 34, an analog signal is output. The switch 23 is switched. The switching signal generator 34 is a hysteresis comparator that determines that the output current of the inverse converter 3 has reached a certain level or higher.

The operation will be specifically described with reference to FIGS. 4 and 5. FIG. 4 shows the operation of the switching signal generator 34, the operation of the analog switch 23, and the change of the carrier frequency with respect to the change of the output current of the inverse converter 3.
In this figure, first, the output current of the inverse converter 3 is 20% of the rated value.
When it exceeds, the output of the switching signal generator 34 becomes H, and the switching signal is sent to the analog switch 23. Then, the analog switch 23 is switched to the first triangular wave generating means 20 side, and the forward converter 2 operates at a carrier frequency of 5 kHz. Next, when the output current of the inverse converter 3 becomes 10% or less of the rated value, the output of the switching signal generator 34 becomes L, and the switching signal is sent to the analog switch 23. Then, the analog switch 23 switches from the first triangular wave generating means 20 side to the second triangular wave generating means 21 side, and the forward converter 2 operates at a carrier frequency of 20 kHz. Here, the switching signal generator 34 is a device having a hysteresis characteristic as shown in FIG. 5, and becomes H when the output current of the inverse converter 3 exceeds 20% of the rating, and the output current of the inverse converter 3 becomes 10% of rating
When it becomes the following, it operates to become L. Switching signal generator 3
The reason why 4 has a hysteresis characteristic is to prevent chattering of the analog switch 23 due to a change in the output current of the inverse converter 3.

When the above operating method is used, when the entire system including the load device is operated and the noise of the entire system is noisy, the uninterruptible power supply also makes a lot of noise, but the load except for the important load that cannot turn off the power supply. When the entire system becomes quiet by stopping the equipment, the noise of the uninterruptible power supply can be reduced, so that the noise of the uninterruptible power supply in the system is not noticed.

As described above, in addition to the carrier frequency used during the rated operation of the uninterruptible power supply, another carrier frequency (frequency higher than the carrier frequency used during the rated operation) is prepared and By switching between these two carrier frequencies depending on the operating condition,
It is possible to reduce the noise of the uninterruptible power supply in a limited operating state.

[0017]

According to the present invention, since the carrier frequency can be increased when the inverse converter is stopped and only the forward converter is operated or when the load is light, the noise from the AC reactor 10 is reduced. There is an effect of reducing.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an embodiment of a carrier frequency switching circuit of a forward converter.

FIG. 3 is a diagram showing a configuration of another embodiment of a carrier frequency switching circuit.

FIG. 4 is a diagram showing details of a carrier frequency switching signal in FIG.

5 is a diagram showing an operation of a switching signal generator 25 in FIG.

[Explanation of Codes] 1 ... AC power source, 2 ... Forward converter, 3 ... Inverter converter, 4 ... Storage battery, 5 ... Load device, 6 ... UPS control circuit, 7 ... Uninterruptible power supply device, 8, 33 ... IGBT drive Means, 9 ... Capacitor, 10 ... AC reactor, 11A-11F, 26A-
26F ... IGBT, 12A-12F, 27A-27F ...
Diodes, 13, 25 ... DC smoothing capacitors, 14
... Output reference voltage, 15, 19A to 19C, 31A to 31
C ... Operational amplifier, 16A-16C ... Synchronous sine wave generating means, 17A-17C ... Multiplier, 18A-18C, 29A,
29B ... Current transformer, 20, 21 ... Triangular wave generating means, 22A
22C, 32A to 32C ... Comparator, 23 ... Analog switch, 24 ... Inverse converter operation signal, 28 ... Transformer, 30
A to 30C ... Reference sine wave generator, 34 ... Switching signal generator.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hideaki Kunisada 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory

Claims (3)

[Claims] 1. A forward converter for converting an AC voltage into a DC voltage,
In a method of operating an uninterruptible power supply device that includes a storage battery charged by the DC voltage, and an inverse converter that converts the DC voltage into an AC voltage and outputs the AC voltage, when operating the inverse converter, the order When the carrier frequency of the converter is set to the first carrier frequency, the inverse converter is stopped, and only the forward converter is operated to charge the storage battery, the carrier frequency of the forward converter is set to the second carrier frequency. A method of operating an uninterruptible power supply, characterized by setting to. 2. A forward converter for converting an AC voltage into a DC voltage,
In the uninterruptible power supply device including a storage battery charged by the DC voltage, and an inverse converter that converts the DC voltage to an AC voltage and outputs the AC voltage, when the uninterruptible power supply device is in a rated operation, the carrier frequency of the forward converter. Is set to the first carrier frequency, and when the load is operated at a load equal to or less than a predetermined ratio with respect to the rated operation, the carrier frequency of the forward converter is set to the second carrier frequency. How to operate the device. 3. The method for operating an uninterruptible power supply according to claim 1, wherein the second carrier frequency is higher than the first carrier frequency.