JP2021158896A - Power conversion device - Google Patents

Abstract

To provide a power conversion device whose size and cost can be reduced.SOLUTION: A power conversion device 100 includes: a rectification circuit 101 for converting AC power to DC power; a current-limiting resistor 102 for suppressing inrush current in turning on power; a thyristor 103 or a separation device 110; a regenerative brake circuit 105 that operates in a regeneration state; an inverse conversion circuit 106 for converting DC power to AC power; and a control unit 111. In the regeneration state, the current-limiting resistor 102 is separated from the rectification circuit 101 and plays a role of a brake resistor.SELECTED DRAWING: Figure 3

Description

The present invention relates to a power converter.

The power conversion device is a device capable of changing the commercial power supply frequency by converting an AC voltage into a DC voltage and reconverting it into an AC voltage. When the power converter is used to control the rotation speed of an induction motor, for example, the rotation speed estimated from the frequency output from the power conversion device is slower than the actual rotation speed of the motor (hereinafter referred to as the regenerative state). Can occur. In this state, since the induction motor becomes an induction generator, the device receives the regenerative energy and raises the DC voltage thereof.

If the DC section voltage exceeds the permissible range of the device, a general power conversion device determines that the DC section overvoltage is abnormal and stops its output. This regenerative energy increases as the speed difference described above increases. That is, an overvoltage abnormality is likely to occur when the slope of the speed change (particularly during deceleration) is large or the moment of inertia of the load machine connected to the induction motor is large.

However, in actual use of the power converter, there are many cases where the performance is required to be the limit or higher that is not judged to be abnormal. In such a case, the power converter itself cannot receive the regenerated energy, so when it detects that the DC voltage exceeds a certain value, the resistor (braking resistor) connected to the inside or outside of the power converter There is a function that consumes regenerative energy as heat.

Patent Document 1 describes the regenerative resistance on the regenerative power processing circuit and the braking resistance on the braking power processing circuit in a motor control device including an inverter bridge circuit that converts a DC power supply into an AC power supply and supplies and controls it to the motor. A method for reducing the size or cost of a dual-purpose device is disclosed.

JP 2012-196143

Patent Document 1 adds a resistor on the circuit that can be used for both purposes to process the energy received by the device during regeneration and braking. However, a resistor usually used in such an application has a high capacity and requires a large mounting area on a substrate or a space for installation, which poses a big problem in terms of miniaturization.

In addition, the power converter generally has a resistor (current limiting resistor) that suppresses the inrush current when the power is turned on. As for the braking resistor and the current limiting resistor, a resistor with a large rated capacity is selected because of its role. These resistors have large dimensional values and require a large space in the power converter or control panel.

If a braking resistor is built in in addition to the current limiting resistor that is essential for the power converter, the basic performance of the power converter can be expected to improve, but the external dimensions of the power converter itself will inevitably increase. Further, when the braking resistor is connected to the outside, a space for installing the braking resistor is required in addition to the power conversion device itself, which imposes a burden and cost on the customer who designs the board.

Patent Document 1 does not give consideration to miniaturization and cost reduction of a power conversion device including a braking resistor in addition to a current limiting resistor.

An object of the present invention is to provide a power conversion device capable of miniaturization and cost reduction.

A preferred example of the present invention is a rectifier circuit that converts AC power into DC power.
A current limiting resistor that suppresses the inrush current when the power is turned on, a thyristor or contactor, a regenerative braking circuit that operates in a regenerative state, an inverse conversion circuit that converts the DC power into the AC power, and a control unit. Have and
In the regenerative state,
The current limiting resistor is a power conversion device that is separated from the rectifier circuit and acts as a braking resistor.

According to the present invention, it is possible to reduce the size and cost.

It is a figure which shows the structure of the power conversion apparatus as a 1st comparative example. It is a figure which shows the structure of the power conversion apparatus as a 2nd comparative example. It is a figure which shows the structure of the power conversion apparatus in Example 1. FIG. It is a figure which shows the structure of the power conversion apparatus in Example 2. FIG.

First, in order to facilitate the understanding of the present invention, a comparative example of the power conversion device 100, which is an industrial device, will be described.

FIG. 1 is a diagram showing a basic configuration of a power conversion device 100 as a first comparative example. The power conversion device 100 receives AC power, converts the received AC power into DC power by a rectifying circuit, and controls the rotation of the motor by reconverting the DC power into AC power.

The power conversion device 100 includes a rectifier circuit 101, a current limiting resistor 102, a thyristor (or contactor) 103, an electrolytic capacitor 104, a regenerative braking circuit 105, and a reverse conversion circuit 106.

The rectifier circuit 101 receives the three-phase AC power AC via the input terminals R, S, and T. The rectifier circuit 101 composed of a plurality of diodes performs full-wave rectification on the received AC power and converts it into DC power. The inrush current generated by the sudden voltage fluctuation immediately after the power is turned on is suppressed by the current limiting resistor 102. The DC power that has passed through the current limiting resistor 102 is smoothed by the electrolytic capacitor 104 and supplied to the inverse conversion circuit 106. When this power is turned on, the control power supply also rises at the same time, power is supplied to the thyristor 103, the thyristor 103 operates, and the current flowing through the current limiting resistor 102 changes the flow path to the thyristor 103.

The inverse conversion circuit 106 that receives the DC power reconverts the DC power into AC power and supplies the DC power to the motor M from the output terminals U, V, and W to drive the motor M. The rotation speed of the motor M can be controlled by changing the frequency of the AC power to an arbitrary value.

As described above, the power conversion device 100 supplies and drives electric power having an arbitrary frequency to the motor, but when the frequency of the supplied AC power suddenly changes or the inertial moment of the device or object connected to the motor is large. , A state may occur in which the rotation speed of the motor brought about by the frequency output by the power converter 100 is faster than the actual rotation speed of the motor.

In this regenerative state, the motor becomes a generator, and the power converter 100 receives electric power in the form of regenerative energy. The DC power section voltage (hereinafter, DC voltage) of the power conversion device 100 that has received the regenerated energy rises, and depending on the amount of energy, the power conversion device 100 determines that the power conversion device 100 is abnormal due to the overvoltage.

The regenerative braking circuit 105 operates when the DC voltage exceeds a certain value in order to prevent the power conversion device 100 from determining that it is abnormal. When the power converter 100 detects an increase in the DC voltage, the DC voltage is pulsed to the braking resistor 107 connected to the terminal RB and the terminal P on the regenerative braking circuit in FIG. 2 showing the second comparative example. It starts to take. As a result, excess energy is consumed as heat and the rise in DC voltage is suppressed.

Both the current limiting resistor 102 and the braking resistor 107 have a role of consuming excess energy as heat to protect the circuit and the like. The operation timing of the former is only when the former is started, while the latter is the case where the regenerative state is mainly caused by the deceleration operation of the motor.

When the braking resistor detects that the DC voltage exceeds a certain value, it consumes regenerative energy as heat. In addition, the current limiting resistor suppresses the inrush current when the power is turned on. In this embodiment, one resistor is configured to serve as two types of resistors, a current limiting resistor and a braking resistor, whose operation timings are completely different.

According to the first embodiment, even if the power converter 100 receives energy that normally requires a braking resistor, it can be consumed as heat by the built-in resistor. It has the effect of improving the basic performance of the power conversion device 100 itself and the effect of reducing the installation area as a system by eliminating the need to use an external device.

The details of the first embodiment will be described with reference to FIG. FIG. 3 is a diagram showing the configuration of the power conversion device 100 in the first embodiment. The power conversion device 100 includes a rectifying circuit 101 that converts AC power into DC power, a current limiting resistor 102 that suppresses an inrush current when the power is turned on, a thyristor (or contactor) 103, a disconnection device 110, an electrolytic capacitor 104, and a diode. A regenerative braking circuit 105 that has a diode and operates in a regenerative state, an inverse conversion circuit 106 that converts DC power into AC power, and a control circuit (control unit) 111 that controls a power conversion device 100 are provided. The control circuit includes a CPU (Central Processing Unit) such as a microcomputer, and executes control of the thyristor (or contactor) 103 and control of disconnection of the disconnection device 110.

In the first embodiment, the terminal RB for connecting the braking resistor 107 to the outside is branched and connected to the rectifier circuit 101 side of the current limiting resistor, and a switch or the like is further connected to the rectifier circuit 101 side from the connection portion. , B contact disconnection device 110 is attached. In parallel with the thyristor 103, the disconnection device 110 and the current limiting resistor 102 are connected from the rectifier circuit 101 side. Further, both the side of the current limiting resistor 102 connected to the rectifier circuit 101 and the side connected to the reverse conversion circuit 106 (output side of the power conversion device) are connected to the regenerative braking circuit 105. The terminal PD and the terminal P are connected by an electric wire, and elements can be connected as needed.

In the configurations shown in FIGS. 1 and 2, the braking resistor 107 was indispensable when operating the regenerative braking circuit 105, but in the power conversion device 100 in the present embodiment shown in FIG. 3, the branch destination of the terminal RB is branched. The current limiting resistor 102 existing in the above can also serve as a braking resistor in the regenerative state.

However, if the two points are simply connected, a serious accident may occur due to a short circuit of the DC power unit when the regenerative braking circuit 105 operates.

Therefore, a b-contact disconnection device 110 is prepared, and the control circuit 111 controls the thyristor 103 so as to allow the thyristor 103 to conduct. The control circuit 111 separates the device 110 from the conductive state (not disconnected state) to the disconnected state so as to cut off the primary side of the current limiting resistor 102 and the rectifier circuit 101 at the same time as the control or with a slight delay. Control.

According to the first embodiment, when a plurality of high-power resistors are required, it is possible to make a single resistor have a plurality of functions by appropriately separating the required moments. In addition, since it has a function as a braking resistance, it increases the regenerative energy withstand capacity of the power conversion device and improves basic performance such as shortening the motor deceleration time. Further, it contributes to miniaturization and cost reduction of the entire system including the power conversion device having a configuration that does not require an external braking resistor.

In the first embodiment, the current limiting resistor 102 was always connected to the regenerative braking circuit 105. However, if the disconnection device 110 connected between the rectifier circuit 101 and the current limiting resistor 102 does not operate normally in the disconnected state for some reason, or the current limiting resistor is not used as a braking resistor and is external. The configuration of the second embodiment is a configuration in consideration of an application in which only the braking resistor prepared in the above is used.

In this embodiment, another second disconnection device 120 is added between the current limiting resistor 102 and the regenerative braking circuit 105.

The details of this embodiment will be described with reference to FIG. FIG. 4 is a diagram showing a circuit configuration of the power conversion device 100 according to the second embodiment. In the second embodiment, the disconnection device 110, the current detector 121, and the current limiting resistor 102 are connected in parallel with the thyristor 103 from the rectifier circuit side. The description of the same configuration as that of the first embodiment will be omitted.

The operation of the second disconnection device 120 can be performed in any of the cases where the disconnection device 110 is malfunctioning and in any case. A current detector 121 is added to the subsequent stage (inverse conversion circuit side) of the disconnection device 110 to detect a malfunction of the disconnection device 110. When the current is confirmed by the current detector 121 despite the situation where the thyristor 103 is conductive and the disconnection device 110 should operate, the control circuit 111 activates the second disconnection device 120 and controls the disconnection state. Then, the current limiting resistor 102 is cut off from the regenerative braking circuit 105.

Further, regarding the operating state of the second disconnection device 120, it is possible to select a warning without stopping the operation of the device and an error detection for stopping the operation on the operation screen of the power conversion device 100.

In FIG. 4, an example in which the current detector 121 is used is shown, but the voltage detection that detects the voltage of the electrolytic capacitor 104 connected to the DC bus 130 on the positive side and the DC bus 131 on the negative side instead of the current detector 121. You may arrange the vessel. If the voltage does not change despite the situation where the thyristor 103 is conductive and the disconnection device 110 should operate, it is considered that the disconnection device 110 is malfunctioning in the same situation as the current is flowing, so that the control circuit 111 , The second disconnection device 120 is activated, the disconnection state is controlled, and the current limiting resistor 102 is interrupted from the regenerative braking circuit 105.

According to the second embodiment, the malfunction of the disconnection device 110 is detected, and the second disconnection device 120 operates to disconnect the current limiting resistor 102 from the regenerative braking circuit 105, so that the DC power unit is short-circuited. You can avoid serious accidents.

101 ... Rectifier circuit 102 ... Current limiting resistor 103 ... Thyristor 104 ... Electrolytic capacitor 105 ... Regenerative braking circuit 106 ... Reverse conversion circuit 110 ... Detachment device 111 ... Control Circuit 120 ... Second disconnection device

Claims (7)

A rectifier circuit that converts AC power to DC power,
A current limiting resistor that suppresses the inrush current when the power is turned on,
With a thyristor or contactor,
A regenerative braking circuit that operates in a regenerative state,
An inverse conversion circuit that converts the DC power into the AC power,
Has a control unit
In the regenerative state,
The current limiting resistor is a power conversion device that is separated from the rectifier circuit and acts as a braking resistor. In the power conversion device according to claim 1,
The current limiting resistor and the disconnecting device are connected in parallel with the thyristor or contactor.
A power conversion device in which the rectifier circuit side and the reverse conversion circuit side of the current limiting resistor are connected to the regenerative braking circuit. In the power conversion device according to claim 2,
The control unit
When allowing continuity of the thyristor or contactor,
From the unseparated state to the detached state,
A power conversion device that controls the disconnection device. In the power conversion device according to claim 1,
The current limiting resistor, the disconnector, and the current detector are connected in parallel with the thyristor or contactor.
A power conversion device including a second disconnection device between the current limiting resistor and the regenerative braking circuit. In the power conversion device according to claim 4,
The control unit
A power conversion device that controls the second disconnection device to a detached state when the current detector detects a current while the thyristor is conducting. In the power conversion device according to claim 1,
The regenerative braking circuit
A power converter having a diode and a transistor. In the power conversion device according to claim 4,
Instead of the current detector, a voltage detector for detecting the voltage of a capacitor connected between the positive side and the negative side of the DC bus is provided.
The control unit
A power conversion device that controls the second disconnection device to a detached state when the voltage of the voltage detector does not change when the thyristor or the contactor is conducting.

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