JP3279712B2 - Uninterruptible power system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an uninterruptible power supply comprising a rectifier, an inverter and a storage battery, and more particularly to a plurality of uninterruptible power supplies in which the output of a rectifier is directly connected to a common storage battery. The present invention relates to an uninterruptible power supply having a control function for balancing output currents of rectifiers.

[0002]

2. Description of the Related Art In a stationary type uninterruptible power supply device composed of semiconductor elements, a plurality of uninterruptible power supply devices are often installed to improve parallel reliability in order to improve reliability as a power supply. FIG. 4 is a block diagram showing an example of a conventional parallel system of a plurality of uninterruptible power supply devices and a control device therefor. In the uninterruptible power supply having a configuration in which a DC bus of each device is directly connected to a commonly provided storage battery. 1 shows a parallel system of power supply devices. In the figure, 1 is an input AC power supply such as a commercial power supply, 2 is a storage battery, 3 is a DC bus, 4 is a load, 5 is an AC output bus, 11, 21, ..., N1 is a rectifier having a function of charging the storage battery 2, 12 .22, N2 is the inverter, 1
N3 are switches for inputting the output of the inverter to the AC bus 5 and disconnecting it, 14, 24,.
4 is a DC current transformer, 10, 20, and N0 are Units 1 and 2,
.. Shows the control circuits of the rectifiers 11, 21,. Since the internal configurations of the rectifier control circuits 10, 20,..., N0 are all the same, the rectifier control circuit of the first unit will be described as a representative, and 101 will keep the output voltage of the rectifier 11 (corresponding to the voltage of the DC bus 3) constant. The constant voltage control circuit 102 does not operate when the output current of the rectifier 11 is equal to or less than the rated current. However, when a current exceeding the rated current flows, the constant voltage control circuit 102 controls the current to be equal to or less than a predetermined limit current. A constant current control circuit for limiting the output level of the circuit 101, and a transfer device 103 for determining the firing phase of the rectifier 11 according to the output of the constant voltage control circuit 101. The inverters 12, 22,... N2 are controlled by a control circuit (not shown).
The output voltage and phase are controlled so that each unit matches,
The balance of the output current is maintained.

[0003]

On the other hand, the rectifiers 11, 21,... N1 directly connected to the storage battery 2 by the DC bus 3 are controlled at a constant voltage by the operation of the rectifier control circuits 10, 20,. However, for example, the constant voltage control circuit 1 of the first unit
The voltage setting of 01 is a constant voltage control circuit 201,.
If the voltage is slightly higher than the voltage setting of 01, a feedback signal for constant voltage control is obtained from the common bus 3 for each unit, so that the constant voltage control circuits 201,.
Is the rectifier 2 of the other unit due to the action of the closed loop control.
There is a possibility that the operation will be performed to reduce the output voltage of 1,... N1. If such an operation occurs, the inverter 12,
22... DC current supplied to N2 and storage battery 2 is shared only by rectifier 11.

The above phenomenon is caused by the constant current control circuit 10
.., N03 are eliminated to some extent.
For example, assuming N = 3, the load 4 is 200% with respect to the capacity of each device 100% (a load rating that does not hinder even if one unit stops).
In the case of (1), if the limiting current of the constant current control circuits 103, 203 and 303 is set to 120% of the rated value, the rectifier with the highest voltage setting of the constant voltage control circuit is 120% and the rectifier with the second highest voltage is 80% DC. As a result, the output currents of the rectifiers of the three devices are 120%, 80%, and 0%. If the load 4 is equal to or less than 120%, only one rectifier is shared as described above.

In any case, the rectifiers 11, 21,... N
1, the degree of sharing of the output current is poor, and the tendency is stronger as the load is lighter, and when the apparatus is operated for a long period of time, unbalance occurs in each apparatus in terms of reliability and life, which is not preferable. .

As a control device for solving the above problems,
A control device as shown in FIG. 5 (only shown for the first machine) is conceivable. That is, there is a configuration in which the output level of the constant voltage control circuit 122 is limited in order to reduce the output current deviation by the output of the current deviation detection circuit 121 that detects the deviation of the output current of each rectifier.

However, in the configuration as shown in FIG. 5, it is necessary to transmit and receive signals between the parallel units, and the complexity increases as the number of parallel operation units increases, and it is not easy to adjust the balance. Also, since the loop that controls the output current deviation forms a kind of closed loop, the operation tends to become unstable unless the coordination between the closed loop of the constant voltage control and the response is good. Also, it is not easy to adjust the response.

An object of the present invention has been made in view of the above points. In a plurality of uninterruptible power supplies in which the outputs of rectifiers are directly connected to a common storage battery, the output currents of the rectifiers regardless of the size of the load are determined. Is to provide an uninterruptible power supply that can easily balance the power.

[0009]

[Means for Solving the Problems] SUMMARY OF THE INVENTION
Rectifier with voltage and current control as described in
And the DC output of the rectifier to AC
It is composed of an inverter that has the function of controlling voltage and current.
The DC output of the rectifier to a common storage batteryConnectionBe done
And the AC output of the inverter is
In the uninterruptible power supply connected in a row, the power supply of the rectifier
Current reference of the inverterWith output current
Effective current componentBy providing means for changing according to
Is achieved.

Further, the object is to provide a rectifier having a voltage and current control function and an inverter having a function of controlling an AC output voltage and current while converting a DC output of the rectifier into AC. In the uninterruptible power supply, wherein the DC output of the rectifier is connected to a common storage battery and the AC output of the inverter is connected in parallel via a common bus, the current reference of the current control means of the rectifier is operated in parallel. This can also be achieved by providing a means for changing the effective output current of the inverter according to the effective current reference of the current control means .

[0011]

According to the first aspect of the present invention, since each inverter controlled in parallel operation has its load current balanced by the parallel operation control function, the effective current component of the output current of each inverter is reduced. By detecting and providing this detection signal as a current reference signal for each rectifier, each rectifier can share the current in a balanced state regardless of the size of the load.

Furthermore, according to the second aspect of the present invention, since the load currents of the respective inverters controlled in parallel operation are balanced by the parallel operation control function, the current control circuit of each inverter is effective. If a signal corresponding to the current reference is given as a current reference signal of each rectifier, each rectifier can share the current in a balanced state regardless of the size of the load.

[0013]

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, components having the same reference numerals as those in FIG. 4 have the same functions as those in FIG. 3, and a description thereof will be omitted. In the figure, 15, 15,... N5 are CTs for detecting the output current of each inverter, and control circuits 18, 2 for each rectifier.
, N8 have the same internal configuration and the control circuits 19, 29,... N9 of each inverter have the same internal configuration. Each internal configuration will be described on behalf of the first unit. 1
31 is a constant current control circuit that operates in the same manner as 102 in FIG. 4, 141 is a parallel control circuit that controls the output current of the inverter 12 so as to be balanced with another unit, and 142 is an inverter detected by CT15. 12, an effective component (a component having the same phase as the output voltage) is detected and supplied to the parallel control circuit, and a signal is sent to the constant current control circuit 131 in accordance with the output current effective component to change its operation level. This is an effective current detection circuit to be applied.

Next, the operation of the uninterruptible power supply of the present invention configured as described above will be described. The inverter 12 is controlled in parallel operation by the operation of the parallel control circuit 141 so that the output current is balanced with that of the other inverters. The operation principle of this parallel operation control is described in, for example, Japanese Patent No. 1215332, "Inverter. This is a well-known technique such as "parallel operation device of the motor", and the detailed description thereof is omitted here.

The output current of the inverter 12 is determined by the apparent power (KVA) of the load, but the output current of the rectifier is determined by the active power (KW) of the load.
An effective component of the output current of the inverter 12 detected via the inverter 15 is detected by an effective current detection circuit 142, and the operation level of the constant current control circuit 131 of the rectifier 11 is controlled in accordance with the detected output. .

The characteristics of the operation level correction of the constant current control circuit 131 are set, for example, as shown in FIG. In FIG. 2, the horizontal axis represents the effective component of the inverter output current, and the vertical axis represents the operating level of the constant current control circuit 131. The active component of the inverter output current is 100%, and the operating level is 105%.
(5% corresponds to the charging current for the storage battery 2). For example, if the load factor is 80% of the rated capacity and the load power factor is 90%, the operation level is 80 × 0.9 + 5 = 7.
7%.

In this way, according to the effective component of the output current of the inverters that are controlled in parallel operation so as to be balanced,
By controlling the output current of the rectifier, the output current of the rectifier is controlled to be indirectly balanced regardless of the size of the load. The charging current of the storage battery 2 can also be limited to an appropriate level. Further, since it is not necessary to exchange signals between the devices, a simple configuration can be achieved even when the number of parallel devices increases.

In the embodiment shown in FIG. 1, the operation level of the constant current control circuit of the rectifier is corrected in accordance with the effective component of the output current of the inverter controlled in parallel operation. The correction may be made according to the effective current reference inside the parallel control circuit 142 for current control.

FIG. 3 shows the details of the parallel operation control circuit 142 including the effective current reference 151.
Is a current reference that outputs a reference level corresponding to the load current and the number of parallel operation units, 152 is an active current reference that extracts only the active component of the current reference 151, and 153 detects a deviation between the output current active component and the active current reference. Current deviation detection circuit, 15
4 is a phase control circuit for controlling the output phase of the inverter according to the current deviation, and 155 is a voltage control circuit. The output of the effective current reference 152 is supplied to the constant current control circuit 131 for correcting the operation level. Can be

In recent years, a PWM converter using a self-extinguishing element such as GTO or IGBT has been used as a rectifier to improve input power factor and reduce input harmonics. Since the input power factor is controlled to be 1.0, the present invention can be applied by replacing the rectifier output current control of FIG. 1 with the input current control.

[0021]

As described above, according to the first aspect of the present invention, the load currents of the respective inverters controlled in parallel operation are balanced by the parallel operation control function. Since the effective current component of the output current of each inverter is detected and this detection signal is given as a current reference signal of each rectifier, each rectifier shares the current in a balanced state regardless of the size of the load. be able to.

Furthermore, according to the second aspect of the present invention, the load current of each inverter controlled in parallel operation is balanced by the parallel operation control function. If a signal corresponding to the effective current reference of the control circuit is given as a current reference signal of each rectifier,
Each rectifier can share the current in a balanced state regardless of the size of the load.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a characteristic curve diagram showing a characteristic example of an operation level correction of the constant current control circuit of FIG. 1;

FIG. 3 is a detailed view of a parallel control circuit for explaining another embodiment of the present invention.

FIG. 4 is a block diagram showing an embodiment of a conventional parallel system of uninterruptible power supply devices and a control device thereof.

FIG. 5 is a block diagram showing another embodiment of a conventional parallel system of uninterruptible power supply devices and a control device thereof.

[Explanation of symbols]

1 ... AC input power supply 2
… Storage battery 3… DC bus 4
... Load 5 ... AC output bus 11,21 ~ N1
... Rectifiers 12,22-N2 ... AC filters 13,23-N3
... Switches 14, 24 to N4 ... DC current transformers 15, 25 to N5
... current transformers 18, 28 to N8 ... rectifier control circuits 19, 29 to N9
... Inverter control circuit 101 ... Constant voltage control circuit 103
… Transfer device 131… Constant current control circuit 141
… Parallel control circuit 142… Active current detection circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H02J 3/00-5/00 H02J 9/00-9/08

Claims (2)

(57) [Claims] A rectifier having a voltage and current control function;
The rectifier is configured by an inverter having a function of controlling the AC output voltage and current while converting the DC output of the rectifier into AC,
In an uninterruptible power supply in which the DC output of the rectifier is connected to a common storage battery and the AC output of the inverter is connected in parallel via a common bus, the current reference of the current control means of the rectifier is set to the output current of the inverter. An uninterruptible power supply device comprising means for changing the current in accordance with the effective current component . 2. A rectifier having a voltage and current control function.
The rectifier is configured by an inverter having a function of controlling the AC output voltage and current while converting the DC output of the rectifier into AC,
In an uninterruptible power supply in which a DC output of the rectifier is connected to a common storage battery and an AC output of the inverter is connected in parallel via a common bus, the current reference of the current control means of the rectifier is operated in parallel. An uninterruptible power supply device comprising: means for changing the effective output current of an inverter according to an effective current reference of a current control means for balancing the effective current.