JP4378226B2 - Uninterruptible power supply system - Google Patents

Description

  The present invention relates to an uninterruptible power supply system, and more particularly, to a system in which a plurality of uninterruptible power supply devices are operated in parallel to prevent a circulating current when an AC power supply and a capacitor are shared.

  FIG. 7 is a circuit diagram of a conventional uninterruptible power supply system in which two uninterruptible power supply devices are connected in parallel and shares an AC power supply and a storage battery. The two uninterruptible power supply devices 2A and 2B are connected in parallel with the AC power source 1 and connected to the storage battery 4, and the storage battery 4 is charged by the uninterruptible power supply devices 2A and 2B, respectively. The components of the uninterruptible power supply 2A are a PWM (pulse width modulation) converter 9A, an inverter 10A, and rectifier elements 11A and 12A. The components of the PWM converter 9A are AC reactors 51A and 52A, a smoothing capacitor 8A for absorbing high-frequency ripple current connected between the positive and negative electrodes of the DC output terminal, transistors 911A to 914A, and diodes 921A to 924A. Further, the uninterruptible power supply 2B has the same configuration as the uninterruptible power supply 2A, and the same parts are denoted by the reference numeral B instead of the reference numeral A in the same numerals.

  The PWM converters 9A and 9B are well-known PWM converters having a control circuit that suppresses higher harmonics of the AC input current and improves the input power factor than conventional diode rectifiers, and are pulse width modulation control type converters.

  Next, the operation will be described. In FIG. 7, converters 9A and 9B always supply DC power to inverters 10A and 10B via rectifying elements 11A, 12A, 11B, and 12B and float storage battery 4 during input power reception. Inverters 10A and 10B convert this DC power into AC power and supply AC power to the load. At the time of an input power failure, the function of the uninterruptible power supply is maintained by supplying DC power from the storage battery 4 to the inverters 10A and 10B.

  Next, among the circulating currents generated by the time difference between the generation of pulses for driving on / off of the transistors 911A to 914A and the corresponding transistors 911B to 914B, the flow of the circulating current using the storage battery 4 as a power source is, for example, the transistor 911A on In the state where the transistor 912A is off, the transistor 911B is off, and the transistor 912B is on, the path is storage battery 4-transistor 911A-AC reactor 51A-AC reactor 51B-transistor 912B-storage battery 4. This circulating current is blocked by the rectifying element 11A or 12B.

In the state where the transistor 911A is on, the transistor 912A is off, the transistor 911B is on, and the transistor 912B is off, the energy stored in the AC reactors 51A and 51B is used as a power source, and the transistor 911A-AC reactor 51A-AC reactor 51B-diode 921B-transistor The route is 911A. This circulating current is blocked by the rectifying element 11A.
By blocking these circulating currents, it is possible to prevent biasing of the AC reactor and increased loss of the transistors and diodes.

JP-A-5-308777

A conventional uninterruptible power supply system that operates in parallel with a shared AC battery and storage battery is configured as described above, so that a large current to be supplied to the inverter must be passed through the rectifier to prevent circulating current. A large-sized element that can be used is required, and cooling components for this element are also required, so that the apparatus is large and expensive.
The present invention has been made to solve the above-described problems. It is an object of the present invention to obtain a low-cost uninterruptible power supply system that can continue operation even when a load is regenerated while preventing circulating current. Objective.

An uninterruptible power supply system according to the present invention includes a converter control circuit that controls on / off of a switching element, a converter that converts AC input into DC power, and an inverter that converts DC power output from the converter into AC power. In an uninterruptible power supply system having a plurality of uninterruptible power supply devices connected to a common alternating current input and a storage battery, respectively. When each current sensor is provided and the circulating current circulating between a plurality of uninterruptible power supply devices is obtained from the sum of the output signals of the current sensors, and when the circulating current flows out to the AC input side due to the polarity of the circulating current , turns off the converter switching element through which the circulating current flowing out, the circulating current is AC input When flowing from, the converter of a switching element through which the circulating current flowing turns off is obtained so as to prevent the circulation currents.

  In addition, current sensors are respectively provided at the positive and negative electrodes of the DC output terminal of the converter, and a circulating current circulating between a plurality of uninterruptible power supply devices is obtained from the sum of output signals of the current sensors so that the circulating current decreases. Further, the switching element of the converter is controlled to be turned on / off.

  Furthermore, current sensors are provided in all phases of the AC input section of the converter, and a circulating current circulating between a plurality of uninterruptible power supply devices is obtained from the sum of output signals of the current sensors so that the circulating current decreases. The switching element of the converter is controlled to be turned on / off.

According to the uninterruptible power supply system of the present invention, a current sensor is provided at each of the positive and negative electrodes of the DC output end of the converter, and the circulating current circulating between the plurality of uninterruptible power supply devices is calculated from the sum of the output signals of the current sensors. When the circulating current flows out to the AC input side due to the polarity of the circulating current , the switching element of the converter through which the circulating current flows out is turned off, and when the circulating current flows from the AC input side Since the switching element of the converter that passes the circulating current flowing in is turned off to prevent the circulating current, a large rectifying element and its cooling parts are not required, and the uninterruptible power supply system can be reduced in size. The operation can be continued even if the load is regenerated while reducing the cost and preventing the circulating current.

  In addition, current sensors are respectively provided at the positive and negative electrodes of the DC output terminal of the converter, and a circulating current circulating between a plurality of uninterruptible power supply devices is obtained from the sum of output signals of the current sensors so that the circulating current decreases. In addition, since the switching elements of the converter are controlled to be turned on and off, a large rectifying element and its cooling parts are unnecessary, the uninterruptible power supply system can be reduced in size and cost, and circulating current can be prevented. However, the operation can be continued even if the load is regenerated.

  Furthermore, current sensors are provided in all phases of the AC input section of the converter, and a circulating current circulating between a plurality of uninterruptible power supply devices is obtained from the sum of output signals of the current sensors so that the circulating current decreases. Because the switching element of the converter is controlled to be turned on and off, a large rectifying element and its cooling parts are not required, the uninterruptible power supply system can be reduced in size and cost, and the circulating current can be prevented. Even if the load is regenerated, the operation can be continued.

Embodiment 1 FIG.
1 is a circuit diagram showing an uninterruptible power supply system according to Embodiment 1 of the present invention. In the figure, the same reference numerals as those in FIG. 7 denote the same or corresponding parts. The same shall apply hereinafter. 21A is the uninterruptible power supply according to Embodiment 1, 601A is a current sensor that is provided at the positive electrode of the DC output end of the converter 9A and detects the current on the positive electrode side, and the direction flowing out from the converter 9A is the positive direction. . A current sensor 602A is provided at the negative electrode of the DC output end of the converter 9A and detects a current on the negative electrode side. Like the current sensor 601A, the direction flowing out from the converter 9A is a positive direction.
Reference numeral 611A denotes a current sensor that detects an input current from the AC power source 1 to the converter 9A. The uninterruptible power supply 21B also has the same configuration as the uninterruptible power supply 21A, and the same parts are denoted by the reference numerals B instead of the reference numerals A.

  FIG. 2 is a converter control block diagram of the first embodiment. In the figure, 71A is a control circuit of a general PWM converter, and outputs an on / off gate command to the transistors 911A to 914A so that the input power factor becomes 100%. Explaining this operation, the current command generation circuit 711A generates a sine wave current command with an input power factor of 100%, and the deviation between this current command and the output signal (detected current) of the current sensor 611A is the current control circuit. Input to 712A. The current control circuit 712A outputs a PWM command to the known PWM modulation circuits 713A and 714A so that the current deviation decreases according to the magnitude of the current deviation, and the PWM modulation circuits 713A and 714A are connected to the transistors 911A to 914A. Outputs on / off command. In this way, the control circuit of the PWM converter controls the input power factor to 100%.

The first embodiment is characterized in that on / off commands output from the PWM modulation circuits 713A and 714A are output to the transistors 911A to 914A via the AND circuits 723A to 726A, which will be described below.
In FIG. 2, 721A and 722A are positive / negative determination circuits for determining the polarities of the currents detected by the current sensors 601A and 602A, respectively. The positive / negative determination circuit 721A outputs HIGH when the polarity of the current is positive. When LOW, LOW is output. The positive / negative determination circuit 722A outputs LOW when the polarity of the current is positive and outputs HIGH when the current is negative. The uninterruptible power supply 21B has the same configuration as that of the uninterruptible power supply 21A, and the same part has the same converter control circuit 71B in which the reference numeral B is added to the same numeral instead of the reference numeral A.

  Next, the operation will be described. In FIG. 1, when the transistor 911A is on, the transistor 912A is off, the transistor 911B is off, and the transistor 912B is on, the storage battery 4 is used as a power source, and the storage battery 4-transistor 911A-AC reactor 51A-AC reactor 51B-transistor 912B-storage battery 4 path. Thus, a circulating current that circulates between the uninterruptible power supply devices 21A and 21B flows. This circulating current is detected by the current sensor 601A. In the PWM converter control circuit diagram of FIG. 2, since this detected current is determined to be negative by the positive / negative determining circuit 721A, the input of the AND circuit 723A becomes LOW and is turned on. An off command is output to the transistor 911A. Further, the circulating current is also detected by the current sensor 602B. When the sign A is changed to B in the PWM converter control of FIG. 2, the circulating current detected by the current sensor 602B is determined to be positive by the positive / negative determining circuit 722B. Therefore, the input of the AND circuit 724B becomes LOW, and an off command is output to the transistor 912B that has been turned on. This blocks circulating current through transistor 911A and transistor 912B.

In FIG. 1, when the transistor 911A is on, the transistor 912A is off, the transistor 911B is on, and the transistor 912B is off, the energy stored in the AC reactors 51A and 51B is used as a power source, and the transistor 911A-AC reactor 51A-AC reactor 51B-diode. A circulating current that circulates between the uninterruptible power supply devices 21A and 21B flows through the path 921B-transistor 911A. This circulating current is detected by the current sensor 601A. In the PWM converter control circuit of FIG. 2, since this detected current is determined to be negative by the positive / negative determining circuit 721A, the input of the AND circuit 723A is LOW and turned on. An off command is output to the transistor 911A.
As described above, since the circulating current is detected and the PWM converter control circuit outputs an on / off command to the transistor so as to block the circulating current, a large rectifying element and its cooling parts are unnecessary. Thus, the uninterruptible power supply system can be reduced in size and cost.

Embodiment 2. FIG.
In the first embodiment, the case where the circulating current is detected in the direction of the current at the DC output terminal and the transistor of the converter is turned on / off so as to prevent the circulating current has been described. However, power is regenerated to the load of the inverter. When a device to be connected is connected, this regenerative current is determined as a circulating current, and therefore there is a problem that the uninterruptible power supply system cannot continue operation when the load is regenerated.

  In the second embodiment, a method for solving the above problem will be described. In FIG. 1 described in the first embodiment, when the circulating current does not flow, the direct current output from the PWM converter 9A passes through the current sensor 601A and is supplied to the inverter 10A or the storage battery 4 and then all the current. Since it returns to the PWM converter 9A through the sensor 602A, the sum of the detection currents of the current sensors 601A and 602A becomes zero. Even if a regenerative load is connected to the inverter, the sum of the detected currents is similarly zero. That is, when the circulating current is flowing, the sum of the detected currents of the current sensors 601A and 602A is not zero because of the current component that circulates between the uninterruptible power supply devices 21A and 21B.

FIG. 3 is a PWM converter control block diagram of the second embodiment. The sum of the currents detected by the current sensors 601A and 602A is obtained and used as the circulating current. This circulating current is a zero-phase current component of the AC input current of the uninterruptible power supply 21A, and 731A is a zero-phase current outflow detection circuit that outputs LOW when it is detected that this zero-phase current has flowed out to the AC side. is there. That is, when the circulating current obtained from the sum of the detected currents becomes negative, LOW is output, the inputs of the AND circuits 723A and 725A become LOW, and an off command is output to the transistors 911A and 913A through which the circulating current flows out. The Thus, the zero-phase current flowing out to the AC side of PWM converter 9A in FIG. 1 is blocked by diodes 921A and 923A.

In FIG. 3, reference numeral 732A denotes a zero-phase current inflow detection circuit that outputs LOW when it detects that a zero-phase current has flowed in, and is obtained from the sum of the detected currents. Since the LOW is output when the circulating current circulating between the uninterruptible power supply devices 21A and 21B becomes positive, the inputs of the AND circuits 724A and 726A become LOW, and the transistors 912A and 914A through which the circulating current flows are supplied . An off command is output. Thereby, the zero-phase current flowing from the AC side of PWM converter 9A in FIG. 1 is blocked by diodes 922A and 924A.

Although the determination that the zero-phase current outflow detection circuit 731A and the zero-phase current inflow detection circuit 732A detect the zero-phase current has been described as a positive / negative sign, the zero-phase current that can be tolerated by the uninterruptible power supply (for example, 1 of the rated current) (About 3%) may be used as the determination value.
The above configuration eliminates the need for a large rectifying element and its cooling parts, reduces the cost of the uninterruptible power supply system, and continues operation even when the load is regenerated while preventing circulating current. can do.

Embodiment 3 FIG.
In the second embodiment, the case where the zero-phase current outflow detection circuit 731A and the zero-phase current inflow detection circuit 732A are used to turn off the transistor to block the circulating current has been described. In the third embodiment, the circulating current is suppressed and controlled. The method to do is described.
FIG. 4 is a block diagram of converter control according to the third embodiment. As shown in the figure, a circulating current control amplifier 74A is newly provided, and the sum of the output of the circulating current control amplifier 74A and the current control circuit 712A is input to the PWM modulation circuits 713A and 714A. The circulating current control amplifier 74A receives the circulating current obtained from the sum of the detection currents of the current sensors 601A and 602A described in the second embodiment, and the circulating current control amplifier 74A performs PWM modulation according to the inputted circulating current. A signal is output to the circuits 713A and 714A so that the circulating current decreases.

For example, if the circulating current is positive, the zero-phase current flows in. Therefore, the circulating current control amplifier 74A has a longer on-time of the transistors 911A and 913A through which the circulating current flows out to the AC side, and the circulating current flowing in from the AC side. A command is output to PWM modulation circuits 713A and 714A so that the on-time of transistors 912A and 914A through which the current passes is shortened. As a result, the current flowing through AC reactors 51A and 52A increases from converter 9A toward AC power supply 1, and the inflowing zero-phase current decreases.
On the other hand, if the circulating current is negative, the zero-phase current flows out. Therefore, the circulating current control amplifier 74A shortens the ON time of the transistors 911A and 913A through which the circulating current flows out to the AC side, and flows from the AC side. A command is output to the PWM modulation circuits 713A and 714A so that the on-time of the transistors 912A and 914A through which the circulating current passes is increased, and the flowing out zero-phase current is reduced.
With the above configuration, a large rectifying element and its cooling parts are unnecessary, and the operation can be continued even when the load is regenerated while preventing the circulating current.

Embodiment 4 FIG.
In the third embodiment, the case where the current sensors 601A and 602A, 601B and 602B are provided at the DC output terminal to suppress and control the circulating current has been described. FIG. 5 is a circuit diagram showing the uninterruptible power supply system of the fourth embodiment. As shown in FIG. 5, a current sensor is not provided at the DC output end, and the uninterruptible power supply 22A of the fourth embodiment is newly provided with a current sensor 612A at the AC input portion of the PWM converter 9A. 22B describes a case where a current sensor 612B is provided in the AC input section of the PWM converter 9B.

FIG. 6 is a PWM converter control block diagram of the fourth embodiment. The output of the current sensor 611A is used for PWM converter control, and at the same time, used for obtaining the circulating current. The sum of the current sensor 611A and the current sensor 612A is zero-phase current component of the AC input current of the uninterruptible power supply 22A, that is, the circulating current circulating between the uninterruptible power supply 22A and 22B. The circulating current suppression control similar to that of the third embodiment can be performed by inputting the circulating current thus obtained to the circulating current control amplifier 74A. Note that the current sensors 611A and 612A may be arranged between the AC reactors 51A and 52A and the AC power supply 1 instead of the arrangement shown in FIG. The arrangement of the current sensors 611B and 612B may be similarly changed.

  The above configuration eliminates the need for a large rectifying element and its cooling parts, reduces the cost of the uninterruptible power supply system, and continues operation even when the load is regenerated while preventing circulating current. can do.

It is a circuit diagram which shows the uninterruptible power supply system of Embodiment 1 of this invention. FIG. 3 is a block diagram of converter control according to the first embodiment. FIG. 6 is a converter control block diagram of a second embodiment. FIG. 10 is a converter control block diagram of a third embodiment. FIG. 6 is a circuit diagram showing an uninterruptible power supply system according to a fourth embodiment. FIG. 10 is a converter control block diagram of a fourth embodiment. It is a circuit diagram of the conventional uninterruptible power supply system which shares an alternating current power supply and a storage battery.

Explanation of symbols

1 AC power supply 2A, 2B, 21A, 21B, 22A, 22B Uninterruptible power supply 4 Storage battery 8A, 8B Smoothing capacitor 9A, 9B Converter 10A, 10B Inverter 11A, 12A, 11B, 12B Rectifier element 51A, 52A, 51B, 52B AC Reactor 71A, 71B Converter control circuit 74A Circulating current control amplifier 601A, 602A, 601B, 602B Current sensor 611A, 611B Current sensor 612A, 612B Current sensor 711A Current command generation circuit 712A Current control circuit 713A, 714A PWM modulation circuit 721A, 722A , 722B Positive / negative determination circuits 723A to 726A, 724B AND circuit 731A Zero phase current outflow detection circuit 732A Zero phase current inflow detection circuits 911A to 914A, 911B to 914B Transistors 21A~924A, 921B~924B diode.

Claims (3)

A plurality of converters having a converter control circuit for controlling on / off of the switching element, which converts AC input into DC power, and inverters that convert DC power output from the converter into AC power. And an uninterruptible power supply system having a plurality of uninterruptible power supplies connected to a common AC input and storage battery, respectively,
A current sensor is provided at each of the positive and negative electrodes of the DC output terminal of the converter, and from the sum of the output signals of the current sensor, a circulating current that circulates between the plurality of uninterruptible power supply devices is obtained, and by the polarity of the circulating current, When the circulating current flows out to the AC input side, the switching element of the converter that passes the flowing circulating current is turned off, and when the circulating current flows from the AC input side, the circulating current that flows in is passed through. An uninterruptible power supply system characterized in that the switching element of the converter is turned off to prevent the circulating current. A plurality of converters having a converter control circuit for controlling on / off of the switching element, which converts AC input into DC power, and inverters that convert DC power output from the converter into AC power. And an uninterruptible power supply system having a plurality of uninterruptible power supplies connected to a common AC input and storage battery, respectively,
A current sensor is provided at each of the positive and negative electrodes of the DC output terminal of the converter, and from the sum of the output signals of the current sensor, a circulating current that circulates between the plurality of uninterruptible power supply devices is obtained, and by the polarity of the circulating current, When the circulating current flows out to the AC input side, the conduction time of the switching element of the converter through which the circulating current flowing out is made shorter than the conduction time of the switching element of the converter through which the circulating current flows in,
When the circulating current flows from the AC input side, the conduction time of the converter switching element that passes the circulating current flowing in is shorter than the conduction time of the converter switching element that passes the circulating current flowing out,
An uninterruptible power supply system characterized by controlling the circulating current to decrease . A plurality of converters having a converter control circuit for controlling on / off of the switching element, which converts AC input into DC power, and inverters that convert DC power output from the converter into AC power. And an uninterruptible power supply system having a plurality of uninterruptible power supplies connected to a common AC input and storage battery, respectively,
Current sensors are provided in all phases of the AC input section of the converter, and a circulating current circulating between the plurality of uninterruptible power supply devices is obtained from the sum of output signals of the current sensors, and the circulating current is supplied to the AC input side. When flowing out, the conduction time of the converter switching element through which the circulating current flowing out is made shorter than the conduction time of the converter switching element through the circulating current flowing in,
When the circulating current flows from the AC input side, the conduction time of the converter switching element that passes the circulating current flowing in is shorter than the conduction time of the converter switching element that passes the circulating current flowing out,
An uninterruptible power supply system characterized by controlling the circulating current to decrease .

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