JPH07241084A - Uninterruptible power supply - Google Patents

Abstract

PURPOSE:To eliminate the need of large and expensive resistors, switches, and the like by performing the phase control of current such that an undue charging current does not flow at the initial charging stage of a capacitor having high capacitance and performing the current control such that an undue discharge current does not flow at the time of perfect discharge clue to stoppage of operation. CONSTITUTION:An initial charge control circuit 10 for a capacitor C1 receives an AC power supply voltage V1, a signal V1z representative of the zero-cross point thereof, and a voltage Vdc between DC buses P, N and delivers drive signals S111, S121 individually to the thyristors THYs 11, 12 in a switch SW1 based on an initial charging command IC. An initial charge control circuit 20 delivers drive signals S211, S221 for the thyristors THYs 21, 22 in a switch SW2. Furthermore, a perfect discharge control circuit 30 delivers a drive signal to the thyristors THYs 11, 12 in order to control perfect discharge of the capacitor C1.

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 device having a converter and an inverter and having a large capacity capacitor in a DC circuit.

[0002]

2. Description of the Related Art Demand for an uninterruptible power supply tends to increase more and more in fields such as computer data processing and various control technologies. FIG. 5 shows an example of the main circuit configuration of such a conventional uninterruptible power supply.

The uninterruptible power supply circuit of FIG. 5 is basically a voltage from an AC power supply 1 to a converter CNV having a large-capacity capacitor C1 connected between DC output terminals, and an antiparallel diode connected to each arm. Type inverter INV
AC power is supplied to the load 5 via the. In the illustrated apparatus, an AC reactor ACL is connected between an AC power supply 1 and a converter CNV, and an insulating transformer TR is interposed between an inverter INV and a load 5. The converter CNV is a diode D in which high speed switching elements Q11 to Q14 are connected in antiparallel for each arm.
It is a bidirectional PWM converter composed of 11 to D14. The capacitor C1 connected between the output DC buses P and N of the converter CNV is a large capacity capacitor such as an electric double layer capacitor. The inverter INV is a PWM inverter composed of high-speed switching elements Q21 to Q24 in which diodes D21 to D24 are connected in antiparallel for each arm. A capacitor C2 is connected in parallel to the output end of the transformer TR, and an LC filter circuit is configured by the leakage reactance component of the insulating transformer TR and the capacitor C2, thereby removing the output harmonic pulse component of the inverter INV. ing. Note that the primary and secondary winding ratio of the transformer TR is 1: k.

A large charging current and a large discharging current can flow in the capacitor C1 because of its large capacity. A large charging current can flow at the time of initial charging, and a large discharging current can flow at the time of completely discharging the device for safety purposes when the device is completely stopped. In order to suppress such charging current and discharging current, in the device of FIG. 5, the parallel circuit of the initial charging resistor R1 and the short-circuiting contactor Ctt is connected in series to the AC reactor ACL, and the DC bus lines P and N are connected. A discharge resistor R2 is connected between the switch SW6 and the AC power source 1 and the transformer T.
Series switch SW2 including a pair of thyristors THY21 and THY22 connected in antiparallel with the output side of R
A bypass circuit 3 including is provided.

In the uninterruptible power supply configured as described above, during normal operation, the contactor Ctt is closed, the switch SW6 is opened, and the switch SW2 is opened to connect the converter CNV on the AC input side to the AC power supply 1 The voltage between the DC buses P and N, that is, the DC bus voltage Vdc, is boosted so as to be a predetermined value Vdc1 while controlling to obtain a sinusoidal current having a power factor of 1 synchronized with. On the other hand, the inverter INV receives the DC voltage Vdc and performs a voltage control sine wave PWM operation to generate a stable AC output Vo synchronized with the AC power supply 1. The unnecessary harmonic pulse component due to the high frequency switching at that time is removed by the leakage reactance of the transformer TR and the LC filter circuit by the capacitor C2, and a stable sine wave AC output can be supplied to the load 5.

Next, the case where the AC power supply 1 fails during the operation of the apparatus will be described. In this case, the energy stored in the capacitor C1 is temporarily used to drive the inverter I
The power supply to the load 5 is continued via the NV. Capacitor C
The DC voltage Vdc gradually decreases as the power is supplied from 1. When the voltage becomes equal to or lower than a certain limit voltage value Vdc2 determined from the winding ratio of the transformer TR, the output voltage Vo cannot be continuously maintained any more. Therefore, at the time when the DC voltage Vdc reaches the voltage value Vdc2. The apparatus is stopped, that is, the backup operation by the capacitor C1 is ended. The time from when the DC voltage Vdc reaches the limit voltage value Vdc2 from the initial voltage value Vdc1 is the power failure backup time Tb.

In the above case, Vdc1 = 400V,
Assuming that Vdc2 = 200V, the power supplied to the load 5 is 1 kW, and the device efficiency is 90%, the backup time Tb
The relationship between (s) and the capacitance C1 (F) of the capacitor C1 is as follows. (1/2) C1 × (400 ² −200 ² ) = (10 ³ /0.9)×Tb ∴C1 = 0.185 × Tb (F) (1) In the formula (1), the power failure backup time Tb = Tb =
If it is 60 (s), C1 = 1.11 (F).

At present, electric double layer capacitors of the several (F) class are in a practically feasible state.
By using it as the capacitor C1 in the uninterruptible power supply, the uninterruptible power supply having sufficient practicality can be configured.

On the other hand, the voltage of the capacitor C1 is zero (V) when the uninterruptible power supply of this type is used for the first time after assembling or when the apparatus is restarted after maintenance and inspection. If the full voltage is applied all at once, a large charging current will flow. Therefore, the capacitor C1 is charged via the initial charging resistor R1. For example, considering a 1 kVA class uninterruptible power supply, an AC power supply of 100 V (rm
s), DC voltage Vdc = 100 × 1.4 = 140
The contactor Ctt is kept open until it becomes (V). At this time, if R1 = 10Ω and C1 = 1 (F), the charging time constant C1 · R1 = 10 × 1 = 10 (s) initial current 100 (V) / 10 (Ω) = 10 (A) The power loss Ps during 10 (s) is Ps = 10 (Ω) × 10 ² (A) = 1 kW, and a charging resistor having a capacity almost equal to the device rating is required.

Thus, the device becomes large and expensive. Also, the initial charging time is required to be about 3 times or more of the above time constant, which is 30 (s) or more in this example. Further, at the time of maintenance or when the product is shipped after inspection at the factory, it is necessary to completely discharge the capacitor C1 in consideration of safety. At that time, it is possible to artificially cause a power failure and forcibly perform a backup operation to reduce the DC voltage from 400V to 200V. However, in this case, it is necessary to supply electric power to the load 5, and the time required for that depends on the size of the load. If the load happens to be light, as in the above example, it will take a considerably long time.

When discharging, the capacitor voltage is further increased to 2
The switch SW6 is closed to reduce the voltage from 00V to 0V, and the discharge resistor R2 is connected between the DC buses P and N. Similarly, at this time, if R2 = 10Ω, the initial discharge current = 200 (V) / 10 (Ω) = 20 (A), and the loss at that time is 10 (Ω) × 20 (A) ² = It is a very large value of 4 (kW). In addition, a discharge time of 5 to 6 times as long as the time constant of 10 (s) is required for complete discharge. Furthermore, the switch SW6 needs to be a DC200V / 20A class switch, which is very expensive.

As shown in FIG. 6, the initial charging resistance R
1 and the contactor Ctt for short circuit are moved to the DC busbars P and N, and the resistor R1 is connected in parallel with the contactor Ctt (connection between contacts b and c) or in parallel with the capacitor C1 (connection between contacts a and c). Switch SW to switch between
By providing 7, the switch SW6 and the resistor R2 in FIG. 5 can be omitted, and the initial charging resistor R1 can also serve as the discharging resistor. In the case of FIG. 6, the changeover switch SW7 is closed between b and c and the contactor Ctt is opened during the initial charge, and the changeover switch SW is opened during the discharge.
7 is switched so as to close between a and c. In this case as well, the resistor R1 needs to have a large capacity and an expensive value equal to or larger than the device capacity, and the changeover switch SW
7 also requires a large size of 20 (A) class.

[0013]

As described above, in a device having a large-capacity capacitor in a DC circuit, a resistor or a resistor provided for initial charging or discharging of the capacitor, which is not an essential function of the uninterruptible power supply, is provided. The switches are large and expensive, which hinders the overall construction of the device to be small and inexpensive.

Therefore, the present invention does not require a large and expensive resistor, switch, etc., uses components originally provided in the apparatus, and adds a relatively simple control circuit to perform initial charging or complete discharge. It is an object of the present invention to provide an uninterruptible power supply that can be easily realized and can be configured at a small size and at a low cost.

[0015]

In order to achieve the above object, the present invention provides a converter in which a large-capacity capacitor is connected between DC output terminals and a voltage in which an antiparallel diode is connected to each arm. In an uninterruptible power supply that supplies AC power to a load via a type inverter, an initial charge control unit that performs phase control of the current so that the charging current of the large capacity capacitor does not become excessive during initial charging of the large capacity capacitor. A complete discharge control means is provided for controlling the current so that the discharge current of the large-capacity capacitor does not become excessive when the large-capacity capacitor is completely discharged when the operation of the apparatus is stopped.

[0016]

According to the present invention, at the time of initial charging of the large capacity capacitor, the initial charge control means for controlling the phase of the current so that the charging current of the large capacity capacitor does not become excessive, and the large capacity capacitor due to the operation stop of the apparatus. By providing a complete discharge control means for controlling the current so that the discharge current of the large-capacity capacitor does not become excessive at the time of complete discharge, it does not require a large and expensive resistor or switch, and is originally provided in the device. By using parts and adding a relatively simple control circuit, initial charging and complete discharge can be easily realized, and a small and inexpensive uninterruptible power supply device can be configured.

[0017]

1 shows the main circuit configuration of an uninterruptible power supply unit constructed according to an embodiment of the present invention. In the main circuit of FIG. 1, the same circuit parts or portions as those of the device of FIG. 5 are designated by the same reference numerals, and their description will be omitted.

In the device of FIG. 1, in comparison with the device of FIG. 5, the switch SW6 and the discharge resistor R2 are omitted,
A switch SW1 including a pair of antiparallel connection thyristors THY11 and THY12 is provided instead of the charging resistor R1 and the contactor Ctt, and a switch SW3 is connected in series to the load 5.

FIG. 2 is a block diagram of a control device for controlling the main circuit of FIG.

To control the initial charging of the capacitor C1,
An AC power supply voltage (voltage of AC power supply 1) V1, a zero-cross signal V1z indicating a zero-cross point of the voltage V1, and a DC voltage (voltage between DC bus P and N) Vdc are input, and a high-order controller (not shown) is input. Initial charge instruction IC or initial charge instruction IC issued in response to operator's operation instruction
The thyristors THY11 and THY of the switch SW1 based on
First initial charge control circuit 10 for individually sending drive signals S111 and S121 to HY12, and switch S
A second initial charge control circuit 20 is provided which sends drive signals S211 and S221 individually to the thyristors THY21 and THY22 of W2. Similarly, the capacitor C1
Converter control circuit 100 that controls the current of the converter CNV during normal operation in order to perform complete discharge control of
On the other hand, a complete discharge command CD for reversing the phase of the current reference I1r by 180 ° to perform power regeneration control is input. To control the complete discharge of the capacitor C1, the AC power supply voltage V1, the zero-cross signal V1z, and the DC voltage Vdc are further input to individually drive signals to the thyristors THY11 and THY12 of the switch SW1 based on the complete discharge command CD. A first complete discharge control circuit 31 that sends out S112 and S122 is provided. In addition to the voltage control circuit 210 that sends the voltage command SI1 to the inverter INV to perform voltage control during normal operation, the inverter control circuit 200 that controls the inverter INV in the power regeneration mode uses a current reference I2r. A current control circuit 22 for sending a corresponding current command SI2 based on
0 is added so that the voltage control can be switched to the current control based on the complete discharge command CD. Further, the second complete discharge control for inputting the AC power supply voltage V1, the zero-cross signal V1z, and the DC voltage Vdc and sending drive signals S212 and S222 to the thyristors THY21 and THY22 of the switch SW2 based on the complete discharge command CD. A circuit 40 is provided, and the thyristors THY21 and THY22 are turned on during the above-described initial charge and complete discharge.
In order to avoid a situation in which a distorted wave is applied to the load 5 when it is turned off, the initial charge command IC and the complete discharge command CD
A SW3 control circuit 50 that sends an open command signal to the switch SW3 that is connected in series to the load 5 is provided.

As described above, in the initial charging of the uninterruptible power supply device including the main circuit and the control circuit shown in FIGS. 1 and 2, the AC power supply voltage V1 is in the positive half cycle period and V1> Vdc. When the thyristor THY11 of the switch SW1 is turned on in the section (see FIG. 3), current flows from the AC power supply 1 through the closed circuit of THY11 → D11 → C1 → D14 → AC power supply 1 to charge the capacitor C1. However, if the difference between the voltages V1 and Vdc is too large, an excessive current that cannot be blocked by the reactor ACL will flow. Therefore, reactor A
Based on the inductance of CL and the allowable current value of the circuit, an allowable value for the difference between the voltages V1 and Vdc is calculated and set in advance as the allowable width ΔV1. The voltage V1,
An example of waveforms of Vdc and allowable current i1 is shown. In the figure, the thyristor THY is set at point A where V1 = Vdc + ΔV1.
11 is turned on. The current i1 is assumed to be equal to or less than the current value allowed by the device. As is clear from the figure, there are basically two points where V1 = Vdc (X point and Y point).
However, here, the point (that is, the point Y) existing in the phase section of 90 ° to 180 ° of the power supply voltage V1 is used. Strictly speaking, the value of the tolerance ΔV1 changes depending on the value of the DC voltage Vdc, but in practice, a representative value (maximum value) may be used. Further, instead of the tolerance ΔV1, the time ΔT1 from the point A to the point Y of the power supply voltage V1 may be used. In that case, for example, the time Ty at the previous Y point
The time Ts corresponding to the point A may be determined (predicted) by subtracting the time ΔT1 from. Further, the value of the current i1 may be fed back to determine the timing Ta at which the thyristor THY11 is turned on by PI control, that is, the phase control may be performed.

When the power supply voltage V1 is in the negative half cycle period, an ON signal may be given to the thyristor THY12 at the time point -V1 = Vdc + ΔV1 (see the broken line of the voltage V1).

The drive signal S11 of the thyristors THY11 and THY12 of the switch SW1 at the time of initial charging described above.
1, S121 are waveforms corresponding to power supply voltages V1 and Vdc + ΔV1, and a waveform V1 indicating a zero cross point of the power supply voltage V1.
It is shown in FIG. 4 together with z (change at the zero cross point).

As described above, the thyristors THY11 and THY12 of the switch SW1 are controlled so that a charging current is passed through the capacitor C1 and the DC voltage Vdc is gradually increased to the initial value when the peak value of the power supply voltage V1 becomes almost equal. Is completed, and thereafter, thyristors THY11 and THY1
2 is constantly turned on, and the converter CNV is operated as a current control converter by the converter control circuit 100 to perform a boosting operation until reaching a predetermined DC voltage value.

The same operation as described above can be performed by using the switch SW2 of the bypass circuit 3 and the anti-parallel diodes D21 to D24 of the PWM inverter. In this case, assuming that the winding ratio of the transformer TR is 1: k, | V1 |
Thyristors THY21 and THY2 at the point / k> Vdc
It suffices to generate the drive signal of 2, and the concept is the same as that of the switch SW1. The charging current in this case is
For example, when the power supply voltage is in the positive half-wave section, THY21
→ TR → D21 → C1 → D24 → TR The charging current flows along the route. The initial charging is completed when the value of the DC voltage Vdc becomes substantially equal to the peak value / k of the power supply voltage V1. In the case of this embodiment, the inductance component of the transformer TR is used as the reactance means for the current block, but it is also equivalent to connect an independent inductance element in series to the primary side or the secondary side of the transformer TR.

Next, the complete discharge will be described. The converter CNV of FIG. 1 has an AC → DC or DC circuit configuration.
→ A bidirectional converter that can control the flow of AC and power. Therefore, in order to discharge the capacitor C1, DC in the opposite direction to the case of normal AC → DC is used.
→ AC, that is, it may be operated in the power regeneration mode. In this case, when Vdc> V1 peak value, it is possible to control the current of the power source regeneration without any problem, so the switch SW1
Should be kept on. Next, when the discharge of the capacitor C1 progresses and the peak value of Vdc <V1 is reached, unless the thyristors THY11 and THY12 are controlled according to the instantaneous value of the voltage V1, as in the case of initial charging during the period of V1> Vdc, the converter is charged. There is a risk of recharging the capacitor C1 via the CNV diode. In order to avoid this, in this embodiment, when the complete discharge is required, the converter CNV is operated in the regenerative mode, and at the same time, the switch SV is operated.
The drive signals S112 and S122 of W1 are set to Vdc> | V1
It suffices to send it only during the period |.

Similarly, power regeneration can be performed by using the inverter INV and the switch SW2 of the bypass circuit 3. Originally, the circuit configuration of the inverter INV is basically the same as that of the converter CNV, and this can also be basically operated as a bidirectional converter. However, normally, the inverter INV operates as a voltage control type inverter via the voltage control circuit 210 of the inverter control circuit 200, but when the capacitor C1 needs to be completely discharged, the operation mode is switched by the complete discharge command CD. Similarly to the converter CNV, the current control circuit 220 operates as a current control type inverter to perform power regeneration. In this case as well, it is necessary to turn on the switch SW2 of the bypass circuit 3 depending on the value of the DC voltage Vdc. In that case, only during the period of Vdc> | V1 | / k, the complete discharge control circuit 40 causes the ON drive signal S212 of the switch SW2,
It suffices to output S222. In the case of this method, even after the discharge of the capacitor C1 is almost completed, the switch SW
After turning off 2, the excitation component impedance of the transformer TR is used, and the combination of the switching elements Q21 and Q24 of the inverter INV or the switching element Q23,
It is possible to completely discharge by turning on either one of them in combination with Q22. This is because, even if the DC voltage Vdc is several V or less, the value of the capacitor C1 is large, so that the stored energy becomes a considerably large value.

As described above, according to this embodiment,
Initial charge of large-capacity capacitor C1 connected to DC circuit /
The complete discharge can be surely and quickly executed without using a large resistor or the like, by simply adding a relatively simple and inexpensive control circuit to the circuit components originally required for the uninterruptible power supply.

As described above, there are two types of initial charge / complete discharge, that is, the method using the converter CNV on the AC input side or the method using the inverter INV and the bypass circuit 3, respectively. It is possible to carry out by any of the methods, and it is also possible to use the two methods together, so that more rapid initial charge or complete discharge can be carried out.

The inverter INV and the bypass circuit 3
Switch SW2 of the bypass circuit 3 when using
However, since the operation is not the 180 ° energization type, the load may be adversely affected in some cases. In such a case, such an adverse effect can be avoided by disconnecting the load 5 by the switch SW3 during initial charge or complete discharge. Furthermore, the switch SW1 composed of a thyristor can be replaced with a mechanical contactor or the like. In that case, if a contactor with multiple poles is used, the contactor on the input side and the switch connected to the output side will be shared, and the converter on the input side will not be a bidirectional converter (full bridge), but one will be a diode. It is also possible to use a mixed bridge type converter configured by, and by doing so, a simpler and less expensive uninterruptible power supply device can be configured.

[0031]

As described above, according to the present invention, in an uninterruptible power supply device having a large-capacity capacitor in a DC circuit, without requiring a large and expensive resistor or the like,
The initial charge and complete discharge of the capacitor can be performed easily, inexpensively, and surely and quickly.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a main circuit configuration of an uninterruptible power supply according to the present invention.

FIG. 2 is a block diagram showing a configuration example of a control circuit of the uninterruptible power supply according to the present invention.

FIG. 3 is a waveform diagram for explaining the operation of an embodiment of the device of the present invention.

FIG. 4 is a timing chart for explaining the operation of the embodiment.

FIG. 5 is a circuit diagram showing an example of a main circuit configuration of a conventional uninterruptible power supply.

FIG. 6 is a circuit diagram showing a main part of another example of a main circuit configuration of a conventional uninterruptible power supply.

[Explanation of symbols]

1 AC power supply 3 Bypass circuit 5 Load CNV converter INV Inverter SW1, SW2, SW3 switch THY11, THY12, THY21, THY22 Thyristor C1 Large capacity capacitor 10, 20 Initial charge control circuit 30, 40 Full discharge control circuit 100 Converter control circuit 200 Inverter Control circuit

Claims (7)

[Claims] Claim: What is claimed is: 1. An AC power supply, a converter having a large-capacity capacitor connected between DC output terminals, and a voltage-type inverter having an anti-parallel diode connected to each arm.
In an uninterruptible power supply device that supplies alternating-current power to a load, initial charge control means that performs phase control of the current so that the charging current of the large-capacity capacitor does not become excessive at the initial charge of the large-capacity capacitor, and device operation stop And a complete discharge control means for controlling the current so that the discharge current of the large capacity capacitor does not become excessive when the large capacity capacitor is completely discharged. 2. The initial charge control means includes a first switch connected in series between the AC power supply and the converter, an instantaneous voltage value of the AC power supply, and a zero cross point of the instantaneous voltage value. The first initial charge control circuit for controlling ON / OFF of the first switch based on a responsive zero-cross signal and a DC voltage across the large-capacity capacitor. Uninterruptible power supply described. 3. A bypass circuit capable of connecting the AC power supply to an output terminal of the inverter via a second switch, an instantaneous voltage value of the AC power supply, and a zero value of the voltage instantaneous value. A second initial charge control circuit for controlling ON / OFF of the second switch based on a zero-cross signal responding to a cross point and a DC voltage across the large-capacity capacitor. Item 1. The uninterruptible power supply device according to item 1 or 2. 4. The regenerator capable of regenerative operation, wherein the converter comprises a diode having a controllable switching element connected in anti-parallel to each arm, and the complete discharge control means is provided between the AC power supply and the converter. A first switch connected in series to the control circuit, control means for operating the converter in a current regeneration mode, a voltage instantaneous value of the AC power supply, a zero-cross signal responding to a zero-cross point of the voltage instantaneous value, and 4. A first complete discharge control circuit for controlling ON / OFF of the first switch based on a DC voltage across the large-capacity capacitor, and the first complete-discharge control circuit according to claim 1. Uninterruptible power system. 5. A bypass circuit that connects the output terminal of the inverter to the AC power supply via a second switch, the complete discharge control means, a voltage instantaneous value of the AC power supply, and a zero voltage instantaneous value thereof. On / off of the inverter and the second switch is controlled based on a zero-cross signal responding to a cross point and a DC voltage across the large-capacity capacitor, and power regeneration is executed via the bypass circuit. The uninterruptible power supply according to claim 1, further comprising a second complete discharge control circuit. 6. The uninterruptible power supply device according to claim 3, further comprising a third switch, which is in series with the load and which is turned off in association with the second switch. 7. The uninterruptible power supply according to claim 2, wherein the converter is a controllable type, and the controllable converter substitutes for the function of the first switch.