JP2017121132A - Electric power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve suppression of switching noise without need for executing complicate control.SOLUTION: An electric power conversion system 1 includes: a plurality of switching elements 24 for inverting DC power into AC power by a switching operation; a plurality of gate resistors 22 connected with gates of the switching elements 24; a changer 23 for changing over whether or not each of the gate resistors 22 should be changed over to parallel connection; a current detector 12 for detecting a current value corresponding to a load current; and a current comparator 25 for determining changing-over of the changer 23 so that a combined resistance of the plurality of gate resistors 22 becomes larger as the current value is larger.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device that converts DC power into AC power.

  In the power electronics field, power converters that convert DC power to AC power by performing PWM (Pulse Width Modulation) control are widely used. Since the power conversion device that performs PWM control performs switching of the semiconductor switching element at high speed, high-frequency switching noise (ringing) is generated in the output power.

  Therefore, in order to reduce switching noise, an AC motor and a generator are connected to the output side of the power converter, and AC power not including switching noise is output from the generator, and the AC power is amplified by an amplifier. A technique for obtaining AC power that does not include switching noise is known (see, for example, Patent Document 1).

Japanese Patent Application No. 11-90041

  However, in the power conversion device disclosed in Patent Document 1, since it is necessary to connect an AC motor, a generator, and an amplifier to the output side of the power conversion device, the cost increases and the scale of the entire device increases. There was a problem.

  The objective of this invention made | formed in view of this situation is providing the power converter device which can reduce switching noise, without performing complicated control.

  In order to solve the above problems, a power conversion device according to the present invention is a power conversion device that supplies AC power converted from DC power to a load, and a plurality of switching elements that convert DC power into AC power by a switching operation. A plurality of gate resistors connected to the gate of the switching element, a switch for switching whether or not the gate resistors are connected in parallel, and a current value corresponding to a load current flowing through the load is detected. And a current comparator that determines switching of the switch so that a combined resistance of the plurality of gate resistors increases as the current value increases.

  Furthermore, in the power conversion device according to the present invention, a temperature detector that detects a temperature value corresponding to the temperature of the switching element, and when the temperature value exceeds a threshold value, a combined resistance of the plurality of gate resistors is And a switching adjuster for re-determining switching of the switch so as to be smaller than a value determined by the current comparator.

  According to the present invention, the switching noise can be reduced without performing complicated control by adjusting the switching speed according to the magnitude of the load current.

It is a block diagram which shows the structural example of the power converter device which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structural example of the power converter device which concerns on the 2nd Embodiment of this invention.

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

(First embodiment)
FIG. 1 is a block diagram illustrating a configuration example of a power conversion device according to the first embodiment of the present invention. The power conversion device 1 converts DC power generated by the DC power supply 10 into AC power. The AC power to be converted may be single-phase or three-phase, but in the present embodiment, the AC power to be converted will be described below as being converted to 3-phase AC power.

  1 includes a PWM signal control circuit 11, a current detector 12, an arm circuit 20 (a U-phase arm circuit 20-1, a V-phase arm circuit 20-2, and a W-phase arm). Circuit 20-3), which converts DC power input from the DC power supply 10 into AC power and supplies it to a load (not shown) such as a motor.

  The current detector 12 detects a value (hereinafter referred to as a current value) corresponding to a load current flowing through a load connected to the power conversion device 1 and outputs the detected value to the arm circuit 20. Here, the current value may be the value of the current that actually flows through the load, or may be a value that has a proportionality or correlation with the value of the current that actually flows through the load.

  Each arm circuit 20 includes a gate drive circuit 21 (upper arm gate drive circuit 21P and lower arm gate drive circuit 21N), a gate resistor group 22 (upper arm gate resistor group 22P, and lower arm gate). Resistor group 22N), switching device 23 (upper arm switching devices 23P-1 to 23P-x and lower arm switching devices 23N-1 to 23N-x), and switching element 24 (upper arm switching device 24P). , And a lower arm switching element 24N) and a current comparator 25. Since the configurations of the arm circuits 20-2 and 20-3 are the same as those of the arm circuit 20-1, only the arm circuit 20-1 is shown in FIG.

  The PWM signal control circuit 11 generates a PWM signal for controlling the on / off operation of the switching element 24 based on the current value input from the current detector 12 and outputs the PWM signal to the gate drive circuit 21.

  The gate drive circuit 21 generates a voltage to be applied to the gate of the switching element 24 based on the PWM signal input from the PWM signal control circuit 11 and outputs the voltage to the gate resistor group 22.

  The gate resistor group 22 includes a plurality of gate resistors. One terminal of each gate resistor is connected to the gate drive circuit 21, and the other terminal is connected to the gate of the switching element 24 or the switch 23. The

  The switching element 24 is a power semiconductor element such as an IGBT. The switching elements 24P and 24N perform a switching operation by PWM control so that when one is turned on, the other is turned off, and the DC power is converted into AC power by the switching operation.

  The current comparator 25 compares the current value input from the current detector 12 with a preset threshold value. A plurality of threshold values may be provided.

  When the switching speed of the switching element 24 is constant, the switching noise increases as the load current increases. Further, when the gate resistance value of the switching element 24 is increased, the gate current flowing through the gate is decreased, so that the switching speed is reduced, and as a result, switching noise can be reduced. Therefore, the current comparator 25 switches the switch 23 on and off according to the comparison result so that the combined resistance of the plurality of gate resistor groups 22 increases as the current value input from the current detector 12 increases. Determine (that is, determine which switch 23 is connected to or disconnected from the gate resistor group 22), and output switching information indicating the determination result to the switch 23.

  The switching device 23 is connected in series to one or more gate resistors in the gate resistor group 22 and is turned on / off based on the switching information input from the current comparator 25 to connect the gate resistors in parallel. Toggles whether or not. When the switch 23 is on, the gate resistor group 22 connected to the switch 23 is connected in parallel between the gate drive circuit 21 and the switching element 24. As the number of gate resistors connected in parallel increases, the combined resistance of the gate resistor group 22 decreases. On the other hand, when the number of gate resistors connected in parallel decreases, the combined resistance of the gate resistor group 22 increases.

  In general, a power conversion device includes a current detector 12 because it is necessary to detect an output current from the viewpoint of current control and overcurrent protection. The power conversion device 1 according to the present invention controls the switching speed using the current value detected by the current detector 12 included in the conventional power conversion device. Therefore, it is possible to easily adjust the switching speed and reduce the switching noise only by adding the switch 23 and the current comparator 25 as described above.

(Second Embodiment)
Next, a power conversion device 2 according to a second embodiment of the present invention will be described.

  FIG. 2 is a block diagram illustrating a configuration example of the power conversion device 2 according to the second embodiment. In the second embodiment, each arm circuit 20 includes a gate drive circuit 21 (upper arm gate drive circuit 21P and lower arm gate drive circuit 21N) and a gate resistor group 22 (upper arm gate resistor). Group 22P and lower arm gate resistor group 22N), switching device 23 (upper arm switching devices 23P-1 to 23P-x and lower arm switching devices 23N-1 to 23Nx), and switching elements 24 (upper arm switching element 24P and lower arm switching element 24N), a current comparator 25, a temperature detector 26, and a switching adjuster 27.

  The power conversion device 2 according to the second embodiment is different from the power conversion device 1 according to the first embodiment in that a temperature detector 26 and a switching adjuster 27 are further provided. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  The temperature detector 26 is attached near the base of the switching element 24, detects a value corresponding to the temperature of the switching element 24 (hereinafter referred to as a temperature value), and outputs it to the switching adjuster 27. Here, the temperature value may be an actual temperature, or a value having a proportional relationship or correlation with the actual temperature. The temperature detector 26 is a sensor such as a thermistor. When the temperature detector is used for protecting the temperature of the switching element 24 or when the switching element 24 is provided, it may be used.

  When the temperature value input from the temperature detector 26 exceeds a preset threshold value, the switching adjuster 27 reduces the combined resistance of the gate resistor group 22 to a value determined by the current comparator 25. As described above, the switching of the switching device 23 is determined again (that is, the number of switching devices 23 to be turned off determined by the current comparator 25 is reduced).

  When one or more gate signals in the gate resistor group 22 are disconnected by the switch 23 to reduce the switching speed of the switching element 24, the switching loss of the switching element 24 increases and the temperature rises. However, in the power conversion device 2 according to the present invention, since the temperature of the switching element 24 is monitored and the switching regulator 27 is added as described above, the switching speed is adjusted to reduce the switching noise while switching. It is possible to prevent the loss from increasing excessively.

  Although the above embodiment has been described as a representative example, it will be apparent to those skilled in the art that many changes and substitutions can be made within the spirit and scope of the invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments, and various modifications and changes can be made without departing from the scope of the claims. For example, a plurality of constituent blocks described in the embodiments can be combined into one, or one constituent block can be divided.

DESCRIPTION OF SYMBOLS 1 Power converter 10 DC power supply 11 PWM signal control circuit 12 Current detector 20 Arm circuit 21 Gate drive circuit 22 Gate resistor group 23 Switching device 24 Switching element 25 Current comparator 26 Temperature detector 27 Switching regulator

Claims (2)

A power conversion device that supplies alternating current power converted from direct current power to a load,
A plurality of switching elements that convert DC power into AC power by switching operation;
A plurality of gate resistors connected to the gate of the switching element;
A switch for switching whether or not to connect the gate resistors in parallel, and
A current detector for detecting a current value corresponding to a load current flowing through the load;
A current comparator that determines switching of the switch so that a combined resistance of the plurality of gate resistors increases as the current value increases;
A power conversion device comprising: A temperature detector for detecting a temperature value corresponding to the temperature of the switching element;
A switching regulator for redetermining switching of the switch so that the combined resistance of the plurality of gate resistors is less than the value determined by the current comparator if the temperature value exceeds a threshold;
The power converter according to claim 1, further comprising:

Images