JP2003134694A - Uninterruptible power supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interruptible power supply system which uses a bidirectional inverter connected with a transformer for detecting voltage in which an overcurrent is prevented from flowing to the transformer when power is supplied to a load from a three-phase AC power supply. SOLUTION: Between a three-phase AC power supply 1 and a load 2, a DC power supply 3, a bidirectional inverter 4, and a transformer 7 are provided in parallel. The inverter 4 is composed of three pairs of half-bridge type switching circuits 12 whose virtual neutral point has an electric potential at an intermediate point of a direct current divided into two by a capacitor and an inverter control circuit 15 for controlling operation of the switching circuit 12. The secondary side of the transformer 7 is connected to the circuit 15 and the neutral point on the primary side is connected to the virtual neutral point. When the three-phase AC power supply 1 is abnormal, power is supplied by the DC power supply 3. A switch 16 is provided to a circuit connecting the virtual neutral point and the neutral point on the primary side of the transformer 7. The switch is turned OFF when power is supplied by the three-phase AC power supply and ON when power is supplied by the DC power supply.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-phase AC power source connected to a DC power source in parallel via a bidirectional inverter.
If an abnormality occurs in the phase AC power supply, the DC power supply
The present invention relates to an uninterruptible power supply for supplying AC power of a single phase. 2. Description of the Related Art FIG. 3 is a block diagram of an uninterruptible power supply using a bidirectional inverter. 3, reference numeral 1 denotes a three-phase commercial power supply (AC power supply), reference numeral 2 denotes a load, and reference numeral 3 denotes a storage battery (DC power supply). AC power is supplied to the load 2. 4 is a bidirectional inverter, 5
Is a current transformer for detecting the output current, and 6 is a switch for preventing power from being supplied from the bidirectional inverter 4 to the commercial power supply 1 when the commercial power supply 1 becomes abnormal. It is configured to detect this when it occurs and to operate immediately. Reference numeral 7 denotes a transformer for detecting a voltage in the voltage control mode in the power supply from the storage battery 3. The bidirectional inverter 4 in this uninterruptible power supply has a circuit configuration shown in FIG. In FIG. 4, reference numeral 11 denotes an AC ripple absorbing circuit in which capacitors C ₁ and C ₂ are connected in series, and an intermediate point of which is a virtual neutral point of three phases. Numeral 12 indicates that the DC power source 3 is connected to _two capacitors C ₁ and C ₂ .
Divided intermediate switching circuit constituted by a semiconductor element Tr ₁ to Tr ₆ three pairs of half-bridge type in which a virtual neutral point potential, 13 is a current transformer for inverter current detection of the output of the switching circuit 12 is there. Reference numeral 14 denotes a low-pass filter for shaping an inverter output waveform mainly in the voltage control mode. Reference numeral 15 denotes an inverter control circuit, which generates a signal for controlling the on / off of the semiconductor elements Tr _{1 to} Tr ₆ of the switching circuit 12, and outputs a signal from a voltage detection circuit by a voltage detection transformer 7 in a voltage control mode. Receiving the signal
In an internal reference sine wave generation circuit described later, the semiconductor elements Tr _{1 to} T ₁ of the switching circuit 12 are compared with a reference signal.
for controlling the driving of the r _6. In the current control mode, the signals from the current transformers 5 and 13 are detected by an internal current detection circuit described later, and the semiconductor of the switching circuit 12 is controlled so that the signal synthesized by the synthesis circuit follows the reference sine wave. element Tr ₁ ~T
for controlling the driving of the r _6. That is, in the conventional uninterruptible power supply, the commercial power supply 1 is used normally, and when the commercial power supply 1 operates normally, the phase of the input current by the switching circuit 12 is changed to the power factor of 1 regardless of the phase and the waveform of the output current of the inverter. And so that the waveform becomes a sine wave. When the commercial power supply 1 is abnormal, the commercial power supply 1 is disconnected, and the inverter controls the output voltage and the voltage waveform with the power from the storage battery 3.
In the voltage control mode, the primary neutral point of the voltage detecting transformer 7 is connected to the virtual neutral point of the connection point of the capacitors C ₁ and C ₂ constituting the AC ripple absorbing circuit 11 and instantaneously. Waveform control is controlled by an inter-phase voltage. Next, an example of a block circuit of the inverter control circuit 15 is shown in FIG. 5, and an outline of the above-described operation will be described.
The AC input abnormality detection circuit 21 is connected to the commercial power supply 1 and determines whether or not the voltage and frequency of the commercial power supply 1 are normal based on the AC input voltage, and sends a signal to the synchronization circuit 22 if normal. If abnormal, a signal for stopping the current control is transmitted. If normal, the synchronizing circuit 22 generates signals for three phases synchronized with the AC input,
Send a signal to The reference sine wave generation circuit 23 generates a sine wave synchronized with the AC input, becomes a reference waveform for current control,
The actual current of each phase is controlled to follow this reference sine wave. On the other hand, the amplitude of the reference sine wave is determined by controlling the DC voltage. That is, the DC voltage detection circuit 24
Detects the DC voltage of the storage battery 3 and controls the DC voltage to maintain a constant value. The DC voltage detected by the DC voltage detection circuit 24 is input to an error amplifier 25, and is compared and amplified with a reference voltage of the error amplifier 25 to control the amplitude of the reference sine wave in the reference sine wave generation circuit 23. It becomes. That is, if the DC voltage increases, the input current is reduced by reducing the amplitude of the reference sine wave, and if the load current is constant, the current flowing from the AC input to the storage battery 3 through the switching circuit 12 decreases, and the DC current decreases. The voltage will drop. The current detection circuit 26 adjusts the phase of the output current (load current) detected by the current transformer 5 and the level of the inverter current detected by the current transformer 13. In the combining circuit 27, the output current and the inverter current are added and regarded as an input current. This is for stabilizing the operation by including the current of the low-pass filter 14 in the inverter current. In the next error amplifying circuit 28, the combining circuit 27
Is compared with the input sine wave from the reference sine wave generation circuit 23 to obtain an error signal with respect to the current waveform and current value. The modulation circuit 29 converts this error signal into PWM
(Pulse Width Modulation) A circuit that performs modulation, and switches the triangular wave generated by the triangular wave generation circuit 30 and the error signal by a comparator. The PWM waveform obtained here is connected to the upper and lower semiconductor elements Tr _{1 to} Tr _{6 of the} switching circuit 12.
(Generally, IGBTs or FETs are used). The drive circuit 32 converts the signal from the signal distribution circuit 31 into power so that the semiconductor elements Tr _{1 to} Tr ₆ of the switching circuit 12 can be driven. Triangular wave generation circuit 30
Receives a three-phase integer multiple frequency signal from the synchronization circuit 22 and converts it into a triangular wave. This frequency becomes the PWM frequency. Note that a reference sine wave generation circuit 23, a current detection circuit 26, a synthesis circuit 27, an error amplification circuit 28, a modulation circuit 29, a signal distribution circuit 31, and a drive circuit 32 surrounded by a chain line are provided corresponding to each phase. The AC input abnormality detection circuit 21, synchronization circuit 22, DC voltage detection circuit 24, error amplifier 25, and triangular wave generation circuit 30 are provided in common for each phase. When the AC input abnormality detection circuit 21 detects an abnormality in the commercial power supply 1, the detection signal is input to a microcomputer (not shown) and the switch S
By operating W _{1 to} SW ₃ , a circuit on the dotted line side is formed.
The operation of the switch SW _1, the synchronization circuit 22 creates a 3-phase signal synchronized with the signal from the oscillation circuit 33 corresponding to the AC input, it sends a signal to the reference sine wave generating circuit 23. The operation of the switch SW ₂ which is switched at the same time also signals for controlling the amplitude of the reference sine wave, transformer 7
Based on the AC output voltage signal input from the secondary side of
The signal is sent to the reference sine wave generation circuit 23 via the AC output detection circuit 34 and the error amplification circuit 35. The reference sine wave from the reference sine wave generation circuit 23 and the AC output voltage signal input from the secondary side of the transformer 7 are compared and amplified by an error amplifier 36, and the obtained error signal is modulated. As a PWM waveform, the semiconductor element Tr ₁ of the switching circuit 12 is operated by the same operation as described above.
It is intended to control the on and off of ~Tr _6. As described above, in the conventional three-phase uninterruptible power supply, in the voltage control mode when the commercial power supply 1 has an abnormality, the AC ripple absorbing circuit 11 Capacitors C ₁ . Considers the connection point C ₂ (the middle point) and the neutral point of the 3-phase, and controls the line voltage by the waveform control each phase voltage instantaneously. On the other hand, in the current control mode, since the current of each phase is controlled, when the current of each phase is in an unbalanced state, the inter-phase voltage is equal among the three phases due to the line impedance of each phase. Disappears. If the voltage is not equal, the neutral point of the primary side of the voltage detecting transformer 7 is forcibly connected to the capacitors C ₁ . When connected to a virtual neutral point to make with C _2, trans 7
The excitation current on the primary side is not canceled out by three phases, and an unexpectedly large excitation current flows. The transformer 7 for detecting voltage in the conventional three-phase uninterruptible power supply generally has a capacity of about several watts, so that the current on the primary side is about 30 mA.
Therefore, in the voltage control mode, an abnormal current does not flow because the voltages of the three phases are balanced. However, in the current control mode, the impedance of each phase is controlled by controlling the current of each phase individually. The interphase voltage becomes unbalanced. As a result, a difference occurs in the voltage applied to the primary winding of the voltage detecting transformer 7, and an excessive exciting current of 30 mA or more flows through the primary winding, and
There is a problem that a winding having a current capacity of about 0 mA is burned. The present invention prevents the above-mentioned excessive current from flowing through the primary winding of the voltage detecting transformer 7 even in the above-described current control mode. According to the present invention, there is provided an uninterruptible power supply device comprising a DC power supply, and an intermediate potential obtained by dividing the DC power supply into two parts by a capacitor in parallel between a three-phase AC power supply and a load. A bidirectional inverter including a half-bridge type three-pair switching circuit having a virtual neutral point and an inverter control circuit for controlling the operation of the switching circuit; a secondary side connected to the inverter control circuit; A transformer for detecting the voltage of each phase to which a primary neutral point is connected at a point is provided, and when an abnormality occurs in the three-phase AC power supply, power supply to the load is performed from the three-phase AC power supply. In an uninterruptible power supply device switched to a DC power supply, a semiconductor switch is provided in a connection circuit between the virtual neutral point and the primary-side neutral point of the transformer, and When the power supply is supplied from the three-phase AC power supply, the semiconductor switch is turned off. When an abnormality occurs in the three-phase AC power supply and the power supply to the load is switched to the supply from the DC power supply, the semiconductor switch is turned off. The control means for turning on is provided. FIG. 1 is a circuit diagram of an uninterruptible power supply according to the present invention. The same parts as in FIG. 4 showing a conventional uninterruptible power supply are indicated by the same symbols. As is clear from FIG. 1, the uninterruptible power supply according to the present invention includes an AC ripple absorbing circuit 11 of a bidirectional inverter 4 connected to a DC power supply 3.
And a virtual neutral point, which is a connection point between the capacitors C ₁ and C ₂ constituting the circuit, and a primary neutral point of the voltage detecting transformer 7 whose secondary side is connected to the inverter control circuit 15. When the switch 16 is provided and the power is supplied from the commercial power supply 1 to the load 2, the semiconductor switch 16
When the power supply to the load 2 is switched to the supply from the DC power supply 3 due to an abnormality in the commercial power supply 1, the semiconductor switch 16 is turned on (conduction). . That is, as shown in the flow chart of the control state shown in FIG. 2, when the commercial power supply 1 changes from the normal state to the abnormal state and the AC input abnormality detection circuit 21 detects it, the microcomputer shown in FIG.
By operating W _{1 to} SW ₃ , the operation of the bidirectional inverter 4 is switched from the current control mode to the voltage control mode, and the semiconductor switch 16 is turned from off to on (conducting) state, so that the primary of the voltage detecting transformer 7 By setting the side neutral point to the same potential as the virtual neutral point which is the connection point of the capacitors C ₁ and C ₂ , instantaneous waveform control by the inter-phase voltage is enabled. Further, when the commercial power supply 1 is restored to the normal state, the switch back SW ₁ to SW ₃ to the solid line inoperative, the switching to the current control mode bidirectional inverter 4 from the voltage control mode, the semiconductor switch 16 is turned off (non-conducting) and the primary neutral point of the transformer 7 for voltage detection is separated from the virtual neutral point, so that the primary neutral point of the transformer 7 becomes free and automatically becomes 3 It moves to the neutral point of the phase so that unbalanced current does not flow. When an abnormality occurs in the commercial power supply 1, the AC input abnormality detection circuit 21 shown in FIG. 5 detects the abnormality, and by this detection, the power supply to the load 2 of the commercial power supply 1 is cut off by the switch 6 and turned on ( This is for controlling the semiconductor switch 16 in the (conductive) state to the off (non-conductive) state. As described in detail above, in the conventional uninterruptible power supply, in the voltage control mode in which the power supply to the load is switched to the DC power supply due to the abnormality of the three-phase AC power supply, The virtual neutral point divided into two by the capacitor of the AC ripple absorption circuit is connected to the primary neutral point of the transformer for voltage detection. Therefore, in the current control mode in which power is supplied from the three-phase AC power supply to the load, when the inter-phase voltage is in an unbalanced state, the primary winding of the voltage detection transformer is switched from the primary neutral point. The present invention has solved the problem that an excessive exciting current flows through the windings and burns the windings, thereby stabilizing the uninterruptible power supply and improving the reliability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of a main part of an uninterruptible power supply using a bidirectional inverter according to the present invention. FIG. 2 is a flowchart showing a timing of switching from a current control mode to a voltage control mode and a timing of a semiconductor switch according to the present invention. FIG. 3 is a block circuit diagram showing a general circuit configuration of an uninterruptible power supply using a bidirectional inverter. FIG. 4 is a circuit diagram showing an example of a main part of a conventional uninterruptible power supply using a bidirectional inverter. FIG. 5 is a block circuit diagram showing an example of an inverter control circuit of a bidirectional inverter used in the uninterruptible power supply. [Description of Signs] 1 Three-phase commercial power supply 2 Load 3 Storage battery 4 Bidirectional inverter 5, 13 Current transformer 6 Switch 7 Transformer for voltage detection 11 AC ripple absorption circuit 12 Switching circuit 14 Low-pass filter 15 Inverter control circuit 16 Semiconductor Switch 21 AC input abnormality detection circuit 22 Synchronization circuit 23 Reference sine wave 24 DC voltage detection circuit 25, 28, 35, 36 Error amplification circuit 26 Current detection circuit 27 Synthesis circuit 29 Modulation circuit 30 Triangular wave generation circuit 31 Signal distribution circuit 32 Drive circuit 33 Oscillation circuit 34 AC output detection circuit

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Atsushi Miyasaka             480 Toyohira, Chino-shi, Nagano Shinano Electric Stock             Inside the Chino factory (72) Inventor Yuki Tanaka             480 Toyohira, Chino-shi, Nagano Shinano Electric Stock             Inside the Chino factory F term (reference) 5G015 FA02 GA08 HA16 JA24 JA32                       JA34 JA35 JA52                 5H007 AA05 AA17 BB05 CA01 CB04                       CB05 CC03 CC09 CC23 DA03                       DA06 DB01 DC02 DC04 DC05                       EA04 FA02 FA03 FA14 FA19                       GA06 GA09

Claims (1)

1. A half-bridge type in which a DC power supply and an intermediate potential obtained by dividing the DC power supply into two parts by a capacitor are set as a virtual neutral point in parallel between a three-phase AC power supply and a load. A bidirectional inverter comprising a switching circuit of three pairs and an inverter control circuit for controlling the operation of the switching circuit; a secondary side connected to the inverter control circuit and a primary side neutral point connected to the virtual neutral point And a transformer for detecting the voltage of each phase is provided, and when an abnormality occurs in the three-phase AC power supply, the power supply to the load is switched from the three-phase AC power supply to the DC power supply. In the power failure power supply device, a semiconductor switch is provided in a connection circuit between the virtual neutral point and the primary neutral point of the transformer, and power is supplied to a load from the three-phase AC power supply. When the semiconductor switch is turned off, control means for turning on the semiconductor switch is provided when the power supply to the load is switched to the supply from the DC power supply when an abnormality occurs in the three-phase AC power supply. Uninterruptible power supply.