KR20060018703A - Inrush protection circuit and its method for inverter - Google Patents

Abstract

The present invention relates to an inrush current prevention circuit and a prevention method of an inverter. In the case of an inverter using a three-phase AC power source, an inrush current is generated during initial charging as a high power is applied and a capacitor having a high capacity is used. A first relay connected in series with a neutral wire of a phase alternating current power source to open and close the connection of the neutral wire, and a second relay connected in series to a negative terminal of the rectifier of the inverter to open and close a connection between the rectifier and a negative terminal of the DC link terminal Since the inrush current prevention circuit and the prevention method of the inverter including the relay do not need to use an expensive magnetic switch, it is possible to implement a circuit that prevents the inrush current from being applied during the initial charging of the inverter at low cost.

Inverter, rectifier, DC link stage, relay

Description

Inrush protection circuit and its method for inverter             

1 is a circuit diagram of an inrush current prevention of a conventional inverter.

2 is an inrush current prevention circuit diagram of an inverter according to the present invention.

3 is a flowchart of a first embodiment of a method for preventing inrush current of an inverter according to the present invention.

4 is a flowchart of a second embodiment of a method for preventing inrush current of an inverter according to the present invention.

<Explanation of symbols on main parts of the drawings>

10: 3-phase power source 20: first relay

30: second relay 60: rectifier

70: DC link stage

The present invention relates to an inrush current prevention circuit and a prevention method of an inverter. More specifically, an inverter generated by a high voltage and a high capacity capacitor by the three-phase AC power in an inverter operated by applying a three-phase four-wire AC power. An inrush current prevention circuit and a prevention method of an inverter capable of interrupting inrush current during charging by using a low-cost relay.

In general, an inverter is a device for outputting an AC power of a variable voltage and a variable frequency by receiving a DC power, the DC power is generally used to rectify the three-phase AC power of a fixed voltage magnitude and frequency.

The three-phase AC power is converted into DC power by a rectifier composed of a plurality of diodes, and the DC power half-wave rectified by the rectifier is charged by a DC link stage composed of a plurality of capacitors. Output as negative.

However, the general three-phase AC power source generally has a size of 220V and the phase difference of each phase is 120 degrees, so the line voltage of the three-phase AC power source is about 380 degrees, and the capacity of the capacitor increases according to the high voltage. This causes inrush current during initial charging.

Therefore, in order to prevent the inrush current as described above, the inrush current prevention circuit is implemented in the inverter, a general inrush current prevention circuit will be described in detail with reference to FIG.

1 is a circuit diagram of an inrush current prevention of a conventional inverter. The inrush current prevention circuit of the inverter according to FIG. 1 is driven by a three-phase alternating current power source 1, wherein each phase of the three-phase alternating current power source is E1, E2, E3, and N is a neutral wire.

In addition, the inrush current prevention circuit includes a first switch (2) and a second switch (3) for controlling the application of the power, a magnet switch (4) for detecting the magnet to perform the on / off operation, and Rectifier 6 consisting of a shunt resistor 5 connected in series to the first switch 2, a plurality of diodes for rectifying the AC power applied from the three-phase AC power supply 1, and the rectifier 6 And a DC link stage 7 composed of a plurality of capacitors which receive the half-wave rectification and perform a charging operation so as to smooth the half-wave rectification outputted therefrom.

In addition, the inverter includes a main control unit (not shown) for controlling the first switch 2 and the second switch 3 to be opened and closed automatically according to a predetermined condition.

Hereinafter, the operation of the inrush current preventing circuit of the general inverter configured as described above will be described.

Initially, since both the first switch 2 and the second switch 3 are in the off state, the three-phase AC power source 1 cannot be applied to the DC link terminal 7, and when the power source is initially applied, the first switch ( 2) is activated and is turned on.

When the first switch 2 is turned on, the E1 power of the three-phase AC power source 1 is applied to the rectifying unit 6 through the first switch 2 and the shunt resistor 5, and the E3 power source is a magnet. It is connected and applied directly to the rectifying part 6 irrespective of the switch 4.

Accordingly, a line voltage between the voltages E1 and E3 of the three-phase AC power source 1 is applied to the rectifying unit 6. The initial charging current applied to the rectifying unit 6 and the DC link terminal 7 by the line voltage is applied. To limit, connect the shunt resistor (5) in series with the first switch (2).

When the capacitor of the DC link stage 7 starts charging by the initial charging current, and the voltage of the DC link stage caused by the charging becomes higher than or equal to a predetermined voltage, the first switch 2 is turned off and the second switch 3 ) And the magnet switch 4 are turned on.

Accordingly, each phase E1, E2, E3 of the three-phase AC power source 1 is applied to the rectifier 6, and the DC link unit 7 performs a steady state charging operation.

However, the conventional inrush current prevention circuit that can prevent the inrush current excessively generated initial charging current, the implementation cost is increased and the volume is increased by using a magnetic switch to perform the above operation Occurred, and expensive shunt resistance had to be used, resulting in an additional cost increase.

The present invention has been made to solve the above problems of the prior art, it is possible to implement a low-cost circuit that can prevent the inrush current excessively generated initial charging current without the need for using an expensive magnetic switch, the circuit An inrush current prevention circuit and a prevention method of an inverter that can reduce the space required for implementation are provided.

According to the inrush current prevention circuit of the inverter according to the present invention for solving the above problems, in the inverter driven by a three-phase four-wire AC power source rectifier comprising a plurality of diodes for rectifying the AC power source to the DC power source, The DC power supply for charging a predetermined DC voltage by the DC power applied from the rectifying unit, and the AC power supply so that a voltage between the power supply terminal of the AC power supply and the neutral terminal is applied to the DC link power during initial charging of the DC link power; The rectifier and the DC are connected in series with the neutral wire of the first relay to open and close the connection of the neutral wire, and the line voltage between the power terminal of the AC power supply is applied to the DC link terminal for the steady state charging of the DC link terminal. It is connected to the connection of the link terminal is composed of a second relay for opening and closing the connection of the rectifier and the DC link terminal.

In addition, according to the method for preventing the inrush current of the inverter according to the present invention, since the first relay connected to the neutral wire of the three-phase four-wire AC power is turned on, and the first relay is turned on in the first step, Accordingly, the voltage between the power terminal and the neutral terminal of the AC power is applied to the DC link terminal, so that the DC link terminal starts initial charging, and the initial voltage V charged to the DC link terminal in the second stage. Is determined to be greater than the existing set voltage (V1), and if the initial voltage (V) charged in the DC link stage is greater than the existing set voltage (V1), the DC link stage. The second relay is turned on so that the voltage between the power terminals of the AC power is applied to the DC link terminal for the steady state charging.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the inrush current prevention circuit and prevention method of the inverter according to the present invention, the basic operation of the device used in the same manner as in the prior art is as described above, and thus a detailed description thereof will be omitted.

2 is an inrush current prevention circuit diagram of an inverter according to the present invention. As shown in FIG. 2, the inverter uses a three-phase four-wire AC power supply 10 as a driving power supply. The terminals E1, E2, and E3 of each power supply are 220V and have a phase difference of 120 degrees.

In addition, the inrush current prevention circuit of the inverter according to the present invention receives a predetermined DC voltage by the rectifying unit 60 receives the AC power source 10 and rectifies it to DC, and the DC power rectified by the rectifying unit 60. The first relay 20 and the second relay to turn on / off the connection of the circuit to control the DC link stage 70 and the AC power supply 10 is applied to the DC link stage 70 It further comprises 30.

Prior to the operation of the inverter, the first relay 20 and the second relay 30 are turned off so that the AC power source 10 does not have a path to the DC link terminal 70. 20 is connected.

When the first relay 20 is connected, power terminals E1, E2, and E3 are applied to the DC link terminal 70 through the point A, and the phase voltage and the neutral line N are applied to the DC link terminal 70. Voltage is applied. That is, when the phase voltage of the AC power supply is 220V, the voltage between the phase voltage and the neutral line N is also 220V.

Therefore, the voltage applied to the DC link stage 70 in the initial charging step as described above is 220V lower than 380V in this case, the overcurrent is not applied. Therefore, the shunt resistor value for limiting the overcurrent applied to the DC link stage may be used as a small one or the shunt resistor may not be used depending on the capacitor capacity.

By the initial charging of the inverter as described above, the DC link stage is charged to the same degree as when it is charged by applying a single-phase 220V power, in the case of this embodiment is generally initially charged to a value of about DC 300V.

After the DC link stage 70 is charged to about 300V by initial charging, even though 380V power is applied by the AC power source 10, the voltage difference between the applied power source and the initially charged power source is not large. The charging current value due to the voltage difference is also not large.

Therefore, when the pre-charged voltage (V) is compared with the previously set voltage (V1) for the steady-state charging after the initial charge of the DC link stage 70, the steady-state charging when the pre-charged voltage (V) is large Without going through the step, it is determined that a predetermined time has elapsed since the initial charging is started, and when it is determined that the predetermined time has elapsed, it is possible to enter a steady state charging step.

When the DC link stage 70 is initially charged by the above-described method, it is possible to prevent an excessive current from occurring inrush current flowing to the DC link stage 70, and when the initial charging step is completed. The first relay 20 is turned off and the second relay 30 is turned on to start the steady state charging step.

On the other hand, according to the present invention, even in the steady state charging step, it is possible to prevent the application of overcurrent without turning off the first relay 20, which is the second relay 30 in the state in which the first relay 20 is turned on. This is because a voltage of 220V is applied to the DC link terminal 70 even though the current is turned on, so that an overcurrent is not applied.

In the steady state charging step in which the first relay 20 is turned off and the second relay 30 is turned on, all three phases E1, E2, and E3 of the AC power supply 10 are connected to the DC link stage 70. ) And a path to the DC link terminal 70 through points A and B, and the line voltage of the three-phase AC power source 10 is applied to the DC link terminal 70. In particular, the inverter to which the present invention is applied In case of inverter for BLDC motor, the current input in steady state is set to less than 20A.

In addition, when the second relay 30 is turned on, almost no voltage is applied to both ends of the second relay 30, and the DC link terminal 70 even when the second relay 30 is turned off. The voltage applied to both ends of the second relay 30 also decreases in magnitude due to the voltage value initially charged at).

Therefore, as described above, the first relay 20 and the second relay 30 applied to the inrush current prevention circuit of the inverter of the present invention may be implemented using a low power general power on / off switch, thus initially charging. There is an advantage that it is possible to implement a circuit that blocks the inrush current of the city at low cost.

3 is a flowchart of a first embodiment of a method for preventing inrush current of an inverter according to the present invention.

In the first step, a first relay connected to a neutral wire of a three-phase four-wire AC power source is converted to an on state (S1), and a shunt resistor may be connected to the first relay in series.

In the second step, as the first relay is turned on in the first step, a voltage between the power terminal and the neutral terminal of the AC power is applied to the DC link terminal, and the DC link terminal starts initial charging (S2).

Further, in the second step, since the power applied to the DC link terminal is a voltage between the power terminal and the neutral terminal of the three-phase AC power supply, the magnitude of the power is smaller than the line voltage, and thus the connection configuration of the shunt resistor is omitted. The first relay may also use an inexpensive general power on / off switch.

In the third step, the DC link terminal voltage V by the initial charging in the second step is measured (S3) and compared with the previously set voltage V1 to determine whether the value is larger (S4).

In the fourth step, when the measured voltage V is determined to be greater than the existing set voltage V1 in the third step, the second relay is turned on so that the line voltage of the three-phase AC power is applied to the DC link terminal. Allow the DC link stage to perform steady-state charging.

In addition, the fourth step may further include a step of turning off the first relay (S5, S6).

As described above, even though the line voltage of the three-phase AC power is applied to the DC link stage after the DC link stage is charged by the initial charging, the charged current value due to the voltage difference is not large. It is possible to enter the steady state charging stage when the initial charging stage has elapsed for a certain time without comparing with the set voltage.

According to the second embodiment of the inrush current prevention method of the inverter according to the present invention as described above, after the first and second steps of the first relay ON (S11) and the initial charging start of the DC link stage (S12), the first embodiment The third step and the third step of determining whether the DC link stage starts initial charging or whether a predetermined time T has elapsed the previously set time T1 (S13, S14). If the DC link stage determines that the initial charging time (T) exceeds the existing set time (T1) by turning on the second relay so that the line voltage of the three-phase AC power source is applied to the DC link stage, It can be replaced by the fourth step of performing the steady state charging operation (S15, S16).

As described above, the inrush current prevention circuit and the prevention method of the inverter according to the present invention have been described with reference to the illustrated drawings, but the present invention is not limited by the embodiments and drawings disclosed herein, and the technical spirit of the present invention Application is possible by those skilled in the art within the scope of protection.

The inrush current prevention circuit and the prevention method of the inverter configured as described above can prevent the inrush current excessively generated by the initial charging current by using an inexpensive general power on / off switch without using an expensive magnetic switch. As a result, the space required for the circuit implementation can be reduced.

Claims (7)

A rectifier comprising a plurality of diodes for rectifying the AC power to a DC power in an inverter driven by a three-phase four-wire AC power source; A DC link stage for charging a predetermined DC voltage by a DC power applied from the rectifying unit; A first relay connected in series with the neutral wire of the AC power source to open and close the connection of the neutral wire such that a voltage between the power terminal of the AC power source and the neutral wire terminal is applied to the DC link end when the DC link terminal is initially charged; It is connected to the connection of the rectifier and the DC link terminal to open and close the connection between the rectifier and the DC link terminal so that the line voltage between the power terminal of the AC power supply is applied to the DC link terminal for the steady state charging of the DC link terminal. Inrush current prevention circuit of the inverter, characterized in that the second relay. The method of claim 1, The inrush current prevention circuit of the inverter further comprises a shunt resistor connected in series with the first relay. The method of claim 1, Wherein the first relay or the second relay is a general power on / off switch. A first step of turning on a first relay connected to the neutral wire of the three-phase four-wire AC power source; A second step in which the voltage between the power terminal and the neutral terminal of the AC power source is applied to the DC link terminal as the first relay is turned on in the first step, and the DC link terminal starts initial charging; A third step of determining whether an initial voltage V charged in the DC link terminal is greater than an existing set voltage V1 in a second step; In the third step, when the initial voltage V charged in the DC link terminal is greater than the existing set voltage V1, the voltage between the power terminals of the AC power source is applied to the DC link terminal for the steady state charging of the DC link terminal. 4. A method for preventing inrush current of an inverter, comprising four steps of turning on the second relay to be applied. A first step of turning on a first relay connected to the neutral wire of the three-phase four-wire AC power source; A second step in which the voltage between the power terminal and the neutral terminal of the AC power source is applied to the DC link terminal as the first relay is turned on in the first step, and the DC link terminal starts initial charging; A third step of determining whether a time elapsed after the DC link stage starts initial charging in a second step has elapsed from a previously set time T1; In the third step, when it is determined that the elapsed time T after the initial start of the DC link stage begins to exceed the preset time T1, the AC power supply terminal for the steady state charging of the DC link stage 4. A method of preventing inrush current of an inverter, comprising four steps of turning on a second relay so that a voltage between the terminals is applied to the DC link stage. The method according to claim 4 or 5, The second step is to limit the amount of initial charging current applied to the DC link stage by the shunt resistor connected in series with the first relay. The method according to claim 4 or 5, The fourth step further comprises the step of turning off the first relay.

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