JP2016135056A - Brake resistance control apparatus and brake resistance control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain downsizing and reduction of cost in such a manner that an electrification current of a brake resistance control circuit can be set small.SOLUTION: A brake resistance control apparatus comprises: a brake resistor 9 which absorbs regenerative power from a motor 7 that is connected to an AC load side of an inverter 3; a brake resistance control circuit 8 that is provided between the brake resistor 9 and a DC intermediate circuit of the inverter 3 and controls a current flowing to the brake resistor 9; and temperature detection/control means 10 including functions by which a temperature of the brake resistor 9 is detected, control is performed to turn on the brake resistance control circuit 8 such that a current flows to the brake resistor 9 if the detected temperature is lower than a first preset temperature, and control is performed to turn off the brake resistance control circuit 8 if the detected temperature of the brake resistor 9 exceeds a second preset temperature that is higher than the first preset temperature.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a braking resistance control circuit that controls a current flowing through a braking resistor that absorbs regenerative power from an electric motor connected to a power converter (inverter), and is intended to reduce the size and cost of the braking resistance control circuit. Regarding technology.

  Generally, a power conversion device (inverter) for driving an electric motor is mounted with a braking resistance (DBR) for absorbing regenerative energy from the electric motor.

  An example of an inverter system provided with this braking resistance is shown in FIG. In FIG. 4, a three-phase AC power source 1 is connected to the AC side of the forward conversion unit 4 of the inverter 3 through a circuit breaker 2 for each phase.

  The inverter 3 includes a forward conversion unit 4 (diode rectifier) in which diodes are connected in a three-phase bridge, a capacitor 5 connected to a DC intermediate circuit (between the positive and negative ends of the forward conversion unit 4), and a DC side on both ends of the capacitor 5. And an inverter 6 connected in a three-phase bridge connection with semiconductor switching elements, and the three-phase AC side of the inverter 6 is connected to an electric motor 7.

  A braking resistor 9 is connected between the positive and negative ends of the forward conversion unit 4 (between both ends of the capacitor 5) via a braking resistance control circuit 8 (hereinafter referred to as a DBR control circuit in the drawing).

  The braking resistance control circuit 8 is usually a semiconductor switch such as an IGBT, and the semiconductor switch is controlled to be turned on / off. For example, when the DC intermediate voltage of the inverter 3, that is, the terminal voltage of the capacitor 5 exceeds the set value, when the semiconductor switch of the braking resistance control circuit 8 is turned on, a current flows through the braking resistor 9 and is accumulated in the capacitor 5. Electrical energy is discharged and consumed as thermal energy by the braking resistor 9.

  As a result, an increase in the DC voltage can be suppressed even under a situation where the DC voltage of the inverter 3 is increased by the regenerative power from the electric motor 7.

  Conventionally, a control device for an electric motor provided with a braking resistor has been proposed, for example, in Patent Document 1, and an elevator provided with a resistor that consumes regenerative power of the electric motor has been described in, for example, Patent Document 2. It was proposed.

Japanese Patent Laid-Open No. 10-225158 JP 2012-144357 A

  In the inverter system of FIG. 4, the relationship between the resistance value R of the braking resistor 9, the DC voltage V of the inverter 3, and the current I flowing through the braking resistor 9 is as follows:

V = IR
When the braking resistor 9 is used under a severe ambient environment such as an ambient temperature of −40 ° C. to + 60 ° C., the resistance value range becomes large in the case of an inexpensive stainless steel resistor or the like. Usually, the resistance value range is as large as about ± 8% based on room temperature (+ 20 ° C.).

  In a normal resistance element body, the resistance value of the braking resistor 9 decreases as the temperature decreases, and the resistance value increases as the temperature increases. That is, the current flowing through the braking resistance control circuit 8 increases as the resistance element body has a low temperature, and decreases as the temperature increases.

  The rated current of the braking resistance control circuit 8 is desired to be as small as possible in order to reduce cost and size, but is usually designed according to the maximum current in consideration of the range of resistance values. Therefore, there is a problem that the rated current of the braking resistance control circuit 8 has to be increased as the range of the resistance value is larger.

  The present invention solves the above-described problems, and an object of the present invention is to provide a braking resistance control device and method capable of setting the energization current of the braking resistance control circuit to be small and reducing the size and cost. There is.

The braking resistance control device according to claim 1 for solving the above-described problem is a braking resistor that absorbs regenerative power from an electric motor connected to the AC load side of the power converter,
A braking resistance control circuit that is provided between the braking resistance and a DC intermediate circuit of the power converter, and controls a current flowing through the braking resistance;
Temperature detecting / controlling means having a function of detecting the temperature of the braking resistance and turning on the braking resistance control circuit to flow a current through the braking resistance when the detected temperature falls below a first set temperature. It is characterized by having.

According to a third aspect of the present invention, there is provided a braking resistance control method according to a third aspect of the present invention, comprising: a braking resistor that absorbs regenerative power from an electric motor connected to the AC load side of the power converter; and a DC resistance intermediate circuit between the braking resistor and the power converter. A braking resistance control method in a device provided with a braking resistance control circuit for controlling a current flowing in the braking resistance,
Detecting the temperature of the braking resistor;
A step of turning on the braking resistance control circuit to flow a current through the braking resistance when the detected temperature falls below a first set temperature.

  According to the above configuration, since the current is supplied to the braking resistor by the on-control of the braking resistance control circuit by the temperature detecting / controlling means, the temperature of the braking resistor is maintained at the first set temperature or more, and the braking resistance is correspondingly increased. The resistance value range becomes smaller. For this reason, the resistance value of the braking resistance increases, and the current flowing through the braking resistance control circuit can be reduced. As a result, the energization current of the braking resistance control circuit can be set small, the cooling parts can be miniaturized, and the cost can be reduced.

  According to a second aspect of the present invention, there is provided the braking resistance control device according to the first aspect, wherein the temperature detection / control unit is configured such that the detected temperature of the braking resistance exceeds a second set temperature higher than the first set temperature. The brake resistance control circuit has a function of turning off when the brake resistance control circuit is turned on.

  According to a fourth aspect of the present invention, there is provided the braking resistance control method according to the third aspect, wherein when the detected temperature of the braking resistance exceeds a second set temperature higher than the first set temperature, the braking resistance control circuit is provided. It is further characterized by further comprising a step of controlling to turn off.

  According to the above configuration, the temperature of the braking resistor can be maintained between the first set temperature and the second set temperature, and the resistance value range of the braking resistor corresponds to the first set temperature. And a resistance value corresponding to the second set temperature. For this reason, the energization time of the braking resistance control circuit can be shortened by setting the first set temperature and the second set temperature so that the range of the resistance value of the braking resistance is reduced.

(1) According to the first to fourth aspects of the invention, the energization current of the braking resistance control circuit can be set small, thereby reducing the size of the braking resistance control circuit and reducing the cost.
(2) According to the second and fourth aspects of the present invention, the braking resistance control circuit is configured by setting the first set temperature and the second set temperature so that the range of the resistance value of the braking resistance is reduced. Can be shortened.

The block diagram of the inverter system provided with the braking resistance by one example of embodiment of this invention. The flowchart which shows an example of the braking resistance control process in one embodiment of this invention. The flowchart which shows transition of the control timing and resistance temperature of the braking resistance control circuit in one embodiment of this invention. The block diagram which shows an example of the inverter system provided with the conventional braking resistance.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In this embodiment, for example, in the inverter system of FIG. 4, a resistor that is inexpensive and has a large resistance value dependence on temperature is applied as a braking resistor. For example, in the inverter system of FIG. Is maintained within a certain range, and the resistance value range of the braking resistance during system operation is reduced.

  1, the same parts as those in FIG. 4 are denoted by the same reference numerals.

  10 detects the temperature of the braking resistor 9, and when the detected temperature falls below a certain temperature (first set temperature), the braking resistor control circuit 8 (semiconductor switch) is turned on to control the braking resistor 9. This is a temperature detection / control means for supplying current.

  As an example, the temperature detection / control unit 10 performs braking based on a temperature sensor such as a thermistor provided in the vicinity of the element of the braking resistor 9 or a resistance value of the thermistor that changes in accordance with the temperature detected by the thermistor. And a circuit for creating an on / off control signal for the resistance control circuit 8.

  As another example of the temperature detection / control means 10, a temperature switch such as a thermostat is provided in the vicinity of the element of the braking resistor 9 or in the vicinity thereof, and the semiconductor of the braking resistance control circuit 8 is determined by an on / off output signal of the temperature switch. The switch is configured to be turned on / off.

  When the temperature of the braking resistor 9 falls below a certain temperature (first set temperature), the temperature detection / control means 10 controls the braking resistance control circuit 8 to turn on the current from the forward conversion unit 4 to the braking resistor 9. The temperature of the braking resistor 9 is raised.

  By periodically performing such an operation, the temperature of the braking resistor 9 can always be maintained at a certain value or higher, the range of the resistance value of the braking resistor 9 can be reduced, and the resistance value can be increased.

  Therefore, since the energization current of the braking resistance control circuit 8 can be set smaller than the conventional one, it becomes possible to reduce the size of the cooling parts and the like and to reduce the cost.

  Next, an example of the braking resistance control process performed by the temperature detection / control unit 10 will be described with reference to the flowchart of FIG. 2 and the time chart of FIG.

  The lower part of FIG. 3 shows the control timing of the braking resistance control circuit 8, the upper part shows the transition of the resistance temperature of the braking resistor 9, “Temperature L level” is a preset first set temperature, and “Temperature H level”. Represents a second set temperature set higher than the first set temperature.

  First, in step S1 of FIG. 2, it is determined whether or not the resistance temperature of the braking resistor 9 has decreased below the L level. If it has decreased, the braking resistance control circuit 8 (semiconductor switch) is turned on in step S2. During the ON period of the braking resistance control circuit 8, a current is passed through the braking resistor 9, so that the resistance temperature rises as shown in FIG.

  Next, in step S3, it is determined whether or not the resistance temperature of the braking resistor 9 has exceeded the H level. If it has exceeded, the braking resistance control circuit 8 (the semiconductor switch) is turned off in step S4. During the OFF period of the braking resistance control circuit 8, the resistance temperature decreases with the ambient temperature as shown in FIG.

  Then, by repeatedly performing the processes of steps S1 to S4, the temperature of the braking resistor 9 can be maintained between the L level (first set temperature) and the H level (second set temperature). The range of the resistance value of the resistor 9 can be limited between a resistance value corresponding to the temperature L level and a resistance value corresponding to the temperature H level.

  As described above, since the resistance value can be kept high by keeping the temperature of the braking resistor 9 high and the range of the resistance value can be reduced, the energization current of the braking resistance control circuit 8 is set to be smaller than the conventional one. As a result, the braking resistance control circuit 8 can be reduced in size and cost.

  In addition, as can be seen from the temperature transition of the braking resistor 9 in FIG. 3, the temperature increase due to current energization (the ON period of the braking resistance control circuit 8) is usually higher than the temperature decrease of the braking resistor 9 due to the ambient temperature. The change is steep. Therefore, the energization time of the braking resistance control circuit 8 is short.

  Further, if the difference between the temperature L level and the temperature H level is set to be small so that the range of the resistance value of the braking resistor 9 is reduced, the energization time of the braking resistance control circuit 8 can be further shortened.

  The temperature detection control means 10 is not limited to the above embodiment, and may be configured to be provided in the braking resistance control circuit 8. For example, only the temperature sensor of the temperature detection / control unit 10 may be provided in or near the braking resistor 9, and a circuit for generating an on / off control signal for the braking resistance control circuit 8 may be provided in the braking resistance control circuit 8. .

  The present invention is particularly effective when used in winter and in low-temperature areas.

DESCRIPTION OF SYMBOLS 1 ... Three-phase alternating current power supply 2 ... Circuit breaker 3 ... Inverter 4 ... Forward conversion part 5 ... Capacitor 6 ... Reverse conversion part 7 ... Electric motor 8 ... Braking resistance control circuit 9 ... Braking resistance 10 ... Temperature detection and control means

Claims (4)

A braking resistor that absorbs regenerative power from the motor connected to the AC load side of the power converter,
A braking resistance control circuit that is provided between the braking resistance and a DC intermediate circuit of the power converter, and controls a current flowing through the braking resistance;
Temperature detecting / controlling means having a function of detecting the temperature of the braking resistance and turning on the braking resistance control circuit to flow a current through the braking resistance when the detected temperature falls below a first set temperature. When,
A braking resistance control device comprising:   The temperature detection / control unit has a function of turning off the braking resistance control circuit when a detected temperature of the braking resistance exceeds a second set temperature higher than the first set temperature. The braking resistance control device according to claim 1. A braking resistor that absorbs regenerative power from an electric motor connected to the AC load side of the power converter, and a braking resistor that is provided between the braking resistor and a DC intermediate circuit of the power converter, and controls the current flowing through the braking resistor A braking resistance control method in a device comprising a control circuit,
Detecting the temperature of the braking resistor;
When the detected temperature is lower than a first set temperature, turning on the braking resistance control circuit to pass a current through the braking resistance;
A braking resistance control method comprising:   The step of turning off the braking resistance control circuit when the detected temperature of the braking resistance exceeds a second set temperature that is higher than the first set temperature. Braking resistance control method.

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