JP4851183B2 - Capacitor input type rectifier circuit having overcurrent detection function and inverter device using the same - Google Patents

Description

  The present invention relates to a capacitor input type rectifier circuit that supplies current to a large current load and a small current load, and in particular, a rectifier circuit having a function capable of detecting an overcurrent state caused by an abnormality of a large current load without malfunctioning, And an inverter device using the same.

  A capacitor input type rectifier circuit in which a smoothing capacitor is connected to the output side of a rectifier circuit that converts AC power into DC power is widely used in various electric devices because of its simple circuit configuration. In such a capacitor input type rectifier circuit, in order to protect the rectifier element constituting the rectifier circuit and the circuit element constituting the load side circuit from overcurrent, an overcurrent state caused by load abnormality is detected and an alarm signal is generated. There is something to output.

  FIG. 5 is a circuit example of an inverter device in which a capacitor input type rectifier circuit having a function of detecting an overcurrent caused by such a load abnormality is employed in a DC power supply unit. The inverter device 51 converts AC power supplied from a commercial power source 52 into DC power by a capacitor input rectifier circuit 53, converts it to AC power having a predetermined frequency and a predetermined voltage by an inverter circuit 54, and converts the motor 55 into AC power. To supply.

  This capacitor input type rectifier circuit 53 supplies current to two loads of an inverter circuit 54 that requires a large current and a control circuit 56 that controls the switching operation of the inverter circuit 54. For this purpose, two input capacitors (smoothing capacitors) 57 and 58 are provided inside. A direct current including pulsation rectified by the rectifier circuit 59 is directly input to the first input capacitor 57. The current that has passed through the diode 60 connected to the output of the rectifier circuit 59 is input to the second input capacitor 58.

  A current is supplied from both ends of the first input capacitor 57 to the inverter circuit 54 as the first load, and a current is supplied from both ends of the second input capacitor 58 to the control circuit 56 as the second load. . The reason why the current is supplied to the control circuit 56 from the second input capacitor 58 separated by the diode 60 in this way is pulsated more than the voltage across the first input capacitor 57, although the current is small in the control circuit 56. This is to supply a smoothed voltage with a small amount of current.

  In such an inverter device 51, for example, when an overcurrent flows due to a short circuit accident in the motor 55, the rectifier element constituting the rectifier circuit 59 and the switching element constituting the inverter circuit 54 may be destroyed. In order to prevent this, an overcurrent detection circuit 61 for monitoring the current flowing from the capacitor input type rectifier circuit 53 to the inverter circuit 54 is attached, and the overcurrent is detected and notified to the control circuit 56. When the overcurrent detection circuit 61 outputs an overcurrent detection signal to the control circuit 56, the control circuit 56 turns off all the switching elements in the inverter circuit 54 and prevents the overcurrent from flowing. Thereby, the elements constituting the rectifier circuit 59 and the inverter circuit 54 are prevented from being destroyed by overcurrent.

  Since this overcurrent detection circuit 61 is intended to detect an overcurrent flowing through the inverter circuit 54, it is originally installed between the output terminal 64 of the capacitor input type rectifier circuit 53 and the input terminal 65 of the inverter circuit 54. Good. However, since a large current flows through the inverter circuit 54, an overcurrent detection circuit capable of detecting a large current is required when mounting at such a position. In order to avoid this, in the circuit of FIG. 5, the overcurrent detection circuit 61 is attached at a position where the charge / discharge current of the first input capacitor 57 can be detected. The charge / discharge current of the first input capacitor 57 is smaller than the current flowing through the inverter circuit 54. Therefore, if it is attached at such a position, a circuit for detecting a small current can be adopted as the overcurrent detection circuit 61.

  When an overcurrent flows through the inverter circuit 54 with the circuit configuration in which the overcurrent detection circuit 61 is attached to the location shown in FIG. 5, a large discharge current flows out from the first input capacitor 57 for a short time. . Therefore, if the magnitude of the discharge current is monitored, the occurrence of an overcurrent state can be detected. In order to detect an overcurrent state from the magnitude of the discharge current, the overcurrent detection circuit 61 is configured to detect only the discharge current of the first input capacitor 57 and not the charge current.

  By the way, when such an inverter device 51 is operating, a surge current may be placed on the commercial power source 52 due to lightning or other causes. Regulations such as IEC require that malfunctions due to lightning surges be prevented. The lightning surge placed on the commercial power source 52 is rectified by the rectifier circuit 59 to generate a direct current surge current. Then, the first and second input capacitors 57 and 58 are charged through a path indicated by arrows 66 and 67 in FIG. Lightning surge current is a waveform that rises quickly and has a short duration. For this reason, since it is hindered by the wiring and the inductance of the motor 55, only a small amount flows through the inverter circuit 54.

  The second input capacitor 58 is usually an electrolytic capacitor having a large capacity in order to increase the voltage smoothness. Electrolytic capacitors have poor frequency characteristics and high internal resistance. Therefore, the second input capacitor 58 is not charged to a high voltage due to the lightning surge current.

  On the other hand, a film capacitor having a relatively small capacity and good frequency characteristics may be used for the first input capacitor 57. An example is an inverter device called a capacitorless inverter device.

  If a capacitor having a small capacity and good frequency characteristics is used as the first input capacitor 57, the capacitor is charged to a high voltage by a lightning surge current. The electric charge charged in the first input capacitor 57 is discharged through the two paths 68 and 69 indicated by arrows in FIG. 6 when the lightning surge current stops. A path 68 is a path for charging the second input capacitor 58 having a low charging voltage, and a path 69 is a path for flowing through the inverter circuit 54 to be discharged. The overcurrent detection circuit 61 detects a current obtained by adding the currents passing through the two paths as a discharge current of the first input capacitor 57.

  In many cases, the second input capacitor 58 has a large capacity as described above. For this reason, the current for charging the second input capacitor 58 has a large value. When this charging current is large, the value of the discharge current of the first input capacitor 57 detected by the overcurrent detection circuit 61 also increases. When the value of the discharge current exceeds the overcurrent detection threshold of the overcurrent detection circuit 61, the overcurrent detection circuit 61 outputs an overcurrent detection signal. The overcurrent detection signal in this case is not due to an abnormality in the inverter circuit 54 or the motor 55 that is a load.

  As described above, in the conventional capacitor input rectifier circuit 53 with an overcurrent detection function as shown in FIGS. 5 and 6, when a surge current due to a lightning surge or the like flows even if there is no abnormality in the load circuit. There is a problem that an overcurrent detection signal is erroneously output.

  The present invention has been made to solve such problems of the prior art, and the problem is a capacitor input type rectifier circuit for supplying current to a large current load and a small current load, which is a lightning surge current. The present invention provides a rectifier circuit having a function capable of detecting only an overcurrent state caused by an abnormality of a large current load without malfunction, and an inverter device using the rectifier circuit.

The invention described in claim 1 for solving the above-described problem is a capacitor input type rectifier circuit for supplying current to a large current load and a small current load, the rectifier circuit (9) converting AC power into DC power. ), A first input capacitor (7) connected between the positive DC bus (12) and the negative DC bus (13) connected to the output terminal of the rectifier circuit, and the positive of the first input capacitor An overcurrent detection circuit (11) for detecting that the current flowing from the side terminal to the plus side DC bus exceeds a predetermined threshold and outputting an overcurrent detection signal; and a plus side terminal of the first input capacitor ( 16) and a negative input DC bus, and a second input capacitor (8) that is charged via a diode (10). The first input capacitor (7) is a film capacitor, Input Capacitor (8) is a first input capacitor frequency response is poor compared to the capacitor (7), for large current loads by supplying a current from the positive side DC bus line and the negative side DC bus, the small current load A capacitor input type rectifier circuit having an overcurrent detection function, wherein current is supplied from both ends of a second input capacitor.

  In the capacitor input type rectifier circuit having such a configuration, when an abnormality occurs in a large current load and an overcurrent flows, a large discharge current flows from the first input capacitor for a short time. Since the overcurrent detection circuit constantly monitors the discharge current of the first input capacitor, it can detect that the discharge current has exceeded a predetermined threshold value and output an overcurrent detection signal. In the case of this circuit configuration, the overcurrent detection circuit detects the discharge current of the first input capacitor, and the value of this discharge current is smaller than the current flowing through the large current load. Therefore, there is an advantage that a circuit component that detects a small current, such as a current transformer for small current, can be used in the current detection portion of the overcurrent detection circuit.

  In the case of this circuit configuration, when the first input capacitor is charged to a high voltage due to a surge current such as a lightning surge, the overcurrent detection circuit detects only the discharge current flowing through the large current load in the subsequent discharge process. The current discharged to the second input capacitor is not detected. Therefore, there is an effect that the overcurrent detection circuit is less likely to erroneously determine the discharge current caused by lightning surge or the like as the overcurrent caused by the abnormality of the large current load.

  The invention described in claim 2 provides an inverter circuit (4) as a large current load of the capacitor input type rectifier circuit according to claim 1, and a control device (6) for controlling the inverter circuit as a small current load. Connected and given an overcurrent detection signal output from the overcurrent detection circuit to the control device, and when the control device received the overcurrent detection signal, all the switching elements constituting the inverter circuit were turned off. This is an inverter device.

  The inverter device having such a configuration has the same effect as that of the first aspect of the invention. Further, when the overcurrent detection signal is output, the control device turns off all the switching elements constituting the inverter circuit and cuts off the current flowing through the load. Therefore, the circuit elements constituting the inverter circuit and the rectifier circuit are prevented from being destroyed by an overcurrent.

  Hereinafter, a capacitor input type rectifier circuit having an overcurrent detection function according to the present invention and an inverter device adopting the capacitor input type rectifier circuit in a DC power supply unit will be described with reference to the configuration diagram shown in FIG.

  The inverter device 1 of the present embodiment includes a capacitor input rectifier circuit 3 having an overcurrent detection function, an inverter circuit 4, and a control circuit 6 that controls the switching operation of the inverter circuit 4.

  The capacitor input type rectifier circuit 3 is a DC power supply circuit that converts AC power supplied from the commercial power supply 2 into DC power and supplies the DC power to the inverter circuit 4 and the control circuit 6. The inverter circuit 4 switches the DC power supplied from the capacitor input type rectifier circuit 3 to convert it into AC power, and supplies it to the motor 5 that is the load. Since the inverter circuit 4 is a circuit for driving the motor 5, a large amount of electric power is required for the drive. As the inverter circuit 4, for example, a known full bridge circuit configured by six switching elements as shown in FIG. 2 is used.

  The control circuit 6 is a so-called gate drive circuit that controls the ON / OFF timing of each switching element constituting the inverter circuit 4. The control circuit 6 controls the ON / OFF timing so that AC power of a predetermined frequency and a predetermined voltage is output from the inverter circuit 4. Although the control circuit 6 requires less power, it needs power with less voltage fluctuation because it needs to control the output frequency and output voltage of the inverter circuit 4 with high accuracy.

  The capacitor input type rectifier circuit 3 includes a rectifier circuit 9, a first input capacitor 7, a second input capacitor 8, a diode 10, and an overcurrent detection circuit 11. The rectifier circuit 9 is a bridge circuit composed of, for example, a diode, and rectifies AC power supplied from the commercial power supply 2 and converts it into DC power. A plus side DC bus 12 and a minus side DC bus 13 are connected to the output terminal of the rectifier circuit 9.

  The first input capacitor 7 is connected between the plus side DC bus 12 and the minus side DC bus 13. Between the positive terminal 16 and the negative DC bus 13 of the first input capacitor 7, a series circuit of the second input capacitor 8 and the diode 10 connects the second input capacitor 8 to the negative DC bus 13 side. Connected. The second input capacitor 8 is charged by the current through the diode 10.

  The overcurrent detection circuit 11 is attached to a wiring portion that connects the plus side DC bus 12 and the plus side terminal 16 of the first input capacitor 7. The overcurrent detection circuit 11 monitors the discharge current flowing from the plus side terminal 16 of the first input capacitor 7 toward the plus side DC bus 12 and when the value exceeds a predetermined threshold value, the overcurrent is detected. This circuit outputs a detection signal Vo. The overcurrent detection signal Vo is input to the control circuit 6. When receiving the overcurrent detection signal Vo, the control circuit 6 turns off all the switching elements constituting the inverter circuit 4 and stops the current supply to the motor 5.

  FIG. 3 is a configuration example of the overcurrent detection circuit 11. The overcurrent detection circuit 11 includes a current transformer 31, two diodes 32 and 33, a resistor 34, and a comparator 35. A diode 32 and a series circuit of a diode 33 and a resistor 34 are connected in parallel to the output terminal of the current transformer 31. When the discharge current I flows from the first input capacitor 7, the current flows through the diode 33 to the resistor 34, and a voltage proportional to the discharge current I is generated across the resistor 34. The voltage across the resistor 34 is input to the comparator 35 and compared with a predetermined threshold voltage Vref.

  When the voltage across the resistor 34 exceeds the threshold voltage Vref, the comparator 35 outputs an overcurrent detection signal Vo. When the charging current (−I) flows through the first input capacitor 7, the current detected by the current transformer 31 flows through the diode 32. At this time, since the current does not flow through the diode 33, the voltage across the resistor 34 becomes zero. With such a configuration, the overcurrent detection circuit 11 outputs the overcurrent detection signal Vo only when the discharge current I of the first input capacitor 7 exceeds a predetermined value.

  Next, the overall operation of the inverter device 1 will be described. In a normal operation state, AC power supplied from the commercial power source 2 is rectified by the rectifier circuit 9, and the pulsating DC current Ia as an output charges the first input capacitor 7 and the second input capacitor 8. At the same time, a current Id is supplied from the plus side DC bus 12 toward the inverter circuit 4. It is assumed that a current flowing in the direction of charging the first input capacitor 7 is Ib, and a current that charges the second input capacitor 8 through the diode 10 is Ic.

  Since the value of the current Id flowing through the inverter circuit 4 is large, the DC voltage between the plus side DC bus 12 and the minus side DC bus 13 cannot be sufficiently smoothed only by the first input capacitor 7. Therefore, the voltage, that is, the charging voltage of the first input capacitor 7 has a waveform including pulsation. The current Ib flowing into the first input capacitor 7 repeats reversal in positive and negative directions in synchronization with the voltage pulsation. The magnitude of the current Ib that repeats inversion positively and negatively is smaller than the current Id flowing through the inverter circuit 4. Therefore, the current transformer 31 of the overcurrent detection circuit 11 that monitors the magnitude of the discharge current (−Ib) of the first input capacitor 7 may be small in current capacity.

  The second input capacitor 8 is charged by the current Ic that has passed through the diode 10 only while the charging voltage is lower than the charging voltage of the first input capacitor 7. The capacity of the second input capacitor 8 is set to a large value in order to supply the control circuit 6 with a stable voltage with little pulsation. Therefore, the charging voltage of the second input capacitor 8 is a voltage close to the peak value of the charging voltage of the first input capacitor 7. The control circuit 6 receives the DC voltage with less pulsation and controls the inverter circuit 4 with high accuracy.

On the other hand, the inverter circuit 4 is supplied with a DC voltage having a large pulsation from between the plus-side DC bus 12 and the minus-side DC bus 13, switches it to an AC voltage, and supplies it to the motor 5. When a DC voltage having a large pulsation is switched and converted into an AC voltage, the amplitude of the output AC voltage usually has a pulsating waveform. However, in an inverter device called a capacitorless inverter, a value of a DC voltage including a supplied pulsation is detected, and the switching timing of the inverter circuit 4 is controlled based on the detected value, so that the amplitude is constant without being affected by the pulsation. Output AC voltage. In such an inverter device, a capacitor having a small capacity and good frequency characteristics is used as the first input capacitor 7 .

  The above is the normal operation of the inverter device 1. Next, a description will be given of a case where an overcurrent flows through the inverter circuit 4 due to an abnormality such as overload or short circuit in the motor 5. In this case, the current Id flowing through the inverter circuit 5 increases rapidly and an overcurrent flows. In order to supply the large overcurrent, the first input capacitor 7 is rapidly discharged, and a large discharge current (−Ib) is supplied to the positive side DC bus 12. The discharge current (−Ib) is constantly monitored by the overcurrent detection circuit 11.

  As described above, when the discharge current (-Ib) exceeds a predetermined threshold value, the overcurrent detection circuit 11 outputs an overcurrent detection signal Vo. The overcurrent detection signal Vo is sent to the control circuit 6, and the control circuit 6 receiving it turns off all the switching elements in the inverter circuit 4. As a result, the current supply to the motor 5 is stopped and the overcurrent is stopped. When the overcurrent is stopped, the switching element in the inverter circuit 4 and the rectifier element in the rectifier circuit 9 are prevented from being destroyed by the overcurrent.

  Next, a case where a surge voltage such as a lightning surge that is fast and short in duration is placed on the commercial power supply 2 will be described. The lightning surge voltage is also rectified by the rectifier circuit 9 to become a direct current surge current, and charges the first and second input capacitors 7 and 8 in the same manner as in a normal case. Since the lightning surge current has a fast waveform and a short duration, it is hindered by the wiring and the inductance of the motor 5. For this reason, only a small amount flows through the inverter circuit 4.

  The second input capacitor 8 is often an electrolytic capacitor having a large capacity in order to increase the smoothness. Electrolytic capacitors have poor frequency characteristics and high internal resistance. For this reason, the second input capacitor 8 is not charged to a high voltage by the lightning surge current.

On the other hand, the first input capacitor 7, there may be a good film capacitor frequency characteristic capacitance is relatively small is adopted. The capacitorless inverter device described above is an example. For this reason, the first input capacitor 7 is charged to a high voltage by the lightning surge current.

  In the inverter device 1 of the present embodiment, when the lightning surge current stops, the charge charged in the first input capacitor 7 is discharged through the two paths 21 and 22 indicated by arrows in FIG. The path 21 is a path for charging the second input capacitor 8 having a low charging voltage, and the path 22 is a path for flowing through the inverter circuit 4 and discharging. The discharge current flowing through the path 22 is detected as a discharge current by the overcurrent detection circuit 11, but the discharge current flowing through the path 21 is not detected by the overcurrent detection circuit 11.

  In the case of the conventional circuit described in “Background Art”, the charge charged in the first input capacitor 57 by the lightning surge current as shown in FIG. Discharge through. On the other hand, in the inverter device 1 shown in FIG. 1 and FIG. 4 of the present embodiment, the current discharged through the path 21 for charging the second input capacitor 8 is not detected by the overcurrent detection circuit 11, and the inverter circuit 4 Only the current of the path 22 that flows and discharges is detected by the overcurrent detection circuit 11. Therefore, the value of the discharge current detected by the overcurrent detection circuit 11 is smaller than that of the conventional circuit, and the possibility that the value exceeds the threshold value for determining the overcurrent is reduced.

  Thus, according to the inverter device 1 of the present embodiment, even if a lightning surge occurs, the overcurrent detection circuit 11 outputs an erroneous overcurrent signal indicating that the overcurrent is caused by a load abnormality. Can be eliminated. That is, there is an effect that the malfunction of the overcurrent detection circuit 11 due to the lightning surge can be prevented.

It is a lineblock diagram of inverter device 1 concerning one embodiment of the present invention. 3 is a configuration example of an inverter circuit 4. 2 is a configuration example of an overcurrent detection circuit 11. It is a figure explaining the path | route of the discharge current of the 1st input capacitor. FIG. 2 is a view corresponding to FIG. FIG. 5 is a view corresponding to FIG. 4 according to the prior art.

Explanation of symbols

  In the drawings, 1 is an inverter device, 3 is a capacitor input type rectifier circuit, 4 is an inverter circuit, 6 is a control device, 7 is a first input capacitor, 8 is a second input capacitor, 9 is a rectifier circuit, and 10 is a diode. , 11 is an overcurrent detection circuit, 12 is a positive DC bus, 13 is a negative DC bus, and 16 is a positive terminal.

Claims (2)

A capacitor input type rectifier circuit for supplying current to a large current load and a small current load,
A rectifier circuit (9) for converting AC power into DC power;
A first input capacitor (7) connected between a positive DC bus (12) and a negative DC bus (13) connected to the output terminal of the rectifier circuit;
An overcurrent detection circuit (11) for detecting that the current flowing from the plus side terminal (16) of the first input capacitor to the plus side DC bus exceeds a predetermined threshold and outputting an overcurrent detection signal When,
A second input capacitor (8) that is charged through a diode (10) from between the positive terminal of the first input capacitor and the negative DC bus;
The first input capacitor (7) is a film capacitor;
The second input capacitor (8) is a capacitor having poor frequency characteristics as compared with the first input capacitor (7),
The large current load is configured to supply current from the plus side DC bus and the minus side DC bus, and the small current load is configured to supply current from both ends of the second input capacitor. Capacitor input type rectifier circuit with overcurrent detection function.   An inverter circuit (4) is connected as the large current load of the capacitor input type rectifier circuit according to claim 1, and a control device (6) for controlling the inverter circuit as the small current load is connected. An overcurrent detection signal to be output is provided to the control device, and the control device is configured to turn off all switching elements constituting the inverter circuit when the overcurrent detection signal is received. Inverter device.

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