Discharge device

Abstract

To provide a discharge device capable of preventing a thermal destruction of a resistor and realizing an improvement of reliability.SOLUTION: A power conversion device 1 comprises: a discharging part that contains a first discharge resistance circuit that has a first resistance R1 and a first switch SW1, a second discharge resistance circuit that is parallely connected to the first discharge resistance circuit, and includes a second resistance R2 and a second switch SW2 that are serially connected each other, and a third switch SW3 that is arranged so that the first resistance R1 and the second resistance R2 are serially connected; and a discharge device 6 that includes a voltage measurement part 7 that measures a voltage of a smooth capacitor 5, and a switching control part 8 that performs a switching control of the discharging part. The switching control part serially connects the first resistance R1 and the second resistance R2 in the case where the voltage at a discharge start of the smooth capacitor 5 is a predetermined threshold value or larger, and parallely connects the first resistance R1 and the second resistance R2 in the case where the voltage at the discharge start of the smooth capacitor 5 is the predetermined threshold value or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a discharge device. [Background technology]

[0002] In an inverter having multiple resistors, there is a concern that as the voltage increases, a high voltage is applied to the discharge resistor immediately after the start of discharge, causing a large current to flow in. To solve this problem, for example, Patent Document 1 below describes a technology in which two active discharge resistors having different resistance values ​​are connected in parallel, and discharge is first performed using only the resistor with the larger resistance value, and then halfway through, the other resistor is also used to perform discharge. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-41363 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the technology described in Patent Document 1, the discharge reaches a predetermined voltage within a certain time, but since the discharge is performed using one resistor immediately after the start of the discharge, the voltage applied to the resistor is high and may exceed the energy capacity of the resistor. In view of this, the object of the present invention is to provide a discharge device that prevents thermal destruction of resistors and improves reliability. [Means for solving the problem]

[0005] A discharge device for a smoothing capacitor included in a power conversion device, the discharge device including a first discharge resistance circuit connected in parallel to the smoothing capacitor and having a first resistor and a first switch connected in series to each other, a second discharge resistance circuit connected in parallel to the first discharge resistance circuit and having a second resistor and a second switch connected in series to each other, and a third switch arranged so that the first resistor and the second resistor are connected in series to each other, a voltage measurement unit that measures the voltage of the smoothing capacitor, and a switching control unit that performs switching control of the discharge unit, wherein the switching control unit connects the first resistor and the second resistor in series when the voltage at the start of discharging of the smoothing capacitor is equal to or higher than a predetermined threshold, and connects the first resistor and the second resistor in parallel when the voltage at the start of discharging of the smoothing capacitor is equal to or lower than the predetermined threshold. Effect of the Invention

[0006] According to the present invention, it is possible to provide a discharge device which prevents thermal destruction of resistors and improves reliability. [Brief description of the drawings]

[0007] [Figure 1] 1 is an electrical circuit diagram of a discharge device according to an embodiment of the present invention; [Diagram 2] Variations [Diagram 3] A table explaining the on / off state of the switches for each connection in the discharge circuit in Figure 2 [Figure 4] FIG. 2 is an explanatory diagram of a duty ratio of a power conversion device according to an embodiment of the present invention. [Diagram 5] 1 is an illustration of the cumulative discharge energy for a first resistor according to an embodiment of the present invention; [Figure 6] 1 is an illustration of the cumulative discharge energy for a second resistor according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and appropriate omissions and simplifications have been made for clarity of explanation. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0009] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0010] (First embodiment and overall configuration) (Figure 1) The power conversion device 1 is connected to a battery 4 and a motor 2, converts DC power input from the battery 4 into AC power, and outputs the three-phase AC power to the motor 2. The power conversion device 1 has a semiconductor module 3, a smoothing capacitor 5, a plurality of switches SW1 to SW3, and a plurality of resistors R1 and R2.

[0011] The power conversion device 1 has a first discharge resistance circuit and a second discharge resistance circuit as a discharge section. The first discharge resistance circuit is composed of a first resistor R1 and a first switch SW1, and is connected in parallel to the smoothing capacitor 5. In the first discharge circuit, when the first switch SW1 is turned on, the first resistor R1 and the first switch SW1 are connected in series.

[0012] The second discharge resistance circuit is composed of a second resistor R2 and a second switch SW2, and is connected in parallel to the first discharge resistance circuit. In the second discharge resistance circuit, when the second switch SW2 is turned on, the second resistor R2 and the second switch SW2 are connected in series.

[0013] In the power conversion device 1, the third switch SW3 is arranged to connect the connection point between the first resistor R1 and the first switch SW1 in the first discharge resistance circuit and the connection point between the second resistor R2 and the second switch SW2 in the second discharge resistance circuit to each other. When the first switch SW1 and the second switch SW2 are turned off and the third switch SW3 is turned on, the first resistor R1 and the second resistor R2 are connected in series.

[0014] The power conversion device 1 is provided with a discharge device 6 in order to control the first discharge resistance circuit and the second discharge resistance circuit. The discharge device 6 has a voltage measurement unit 7 and a switching control unit 8. The voltage measurement unit 7 measures the voltage when the smoothing capacitor 5 is discharged. The switching control unit 8 performs switching control of a plurality of switches SW1 to SW3.

[0015] In the rapid discharge (PWM discharge) performed to prevent the application of a high voltage to the smoothing capacitor 5, it is necessary to reduce the voltage of the smoothing capacitor 5 to a certain voltage or less within a specified time. For example, such a discharge condition is a discharge in which the voltage of the smoothing capacitor 5 at the start of discharge is 1200V and this voltage is reduced to 60V or less within 2 seconds.

[0016] By controlling the on / off of at least one of the first switch SW1 and the second switch SW2 in the series connection so as to satisfy such discharge conditions, the applied voltage is divided by the first resistor R1 and the second resistor R2, preventing a high voltage from being applied to each resistor, and suppressing the peak power.

[0017] The first resistor R1 and the second resistor R2 are connected in series, and when the voltage at the start of discharging of the smoothing capacitor 5 falls below a predetermined threshold, the switching control unit 8 turns the third switch SW3 OFF and turns the first switch SW1 and the second switch SW2 ON, thereby switching the connection of the first resistor R1 and the second resistor R2 from a series connection to a parallel connection.

[0018] By connecting the first resistor R1 and the second resistor R2 in parallel, when the voltage falls below a predetermined threshold and is low, a voltage can be applied to the first resistor R1 and the second resistor R2 to increase the voltage, while suppressing a decrease in the discharge rate without exceeding the energy tolerance of the first resistor R1 and the second resistor R2, thereby preventing thermal destruction of the resistors.

[0019] (Modification) (Fig. 2, Fig. 3) The discharge resistance circuit includes a plurality of switches SW1 to SW3 and a plurality of resistors R1 and R2, and the first discharge resistance circuit may further include a fourth switch SW4, and the second discharge resistance circuit may further include a fifth switch SW5. The fourth switch SW4 has one end connected to the first resistor R1 and the other end connected to the connection point of the first switch SW1 and the third switch SW3. The fifth switch SW5 has one end connected to the second resistor R2 and the other end connected to the negative electrode of the smoothing capacitor 5.

[0020] As shown in Fig. 3, the switches SW1 to SW5 are off during discharge standby. During series connection and discharge of the first resistor R1 and the second resistor R2, the switching control unit 8 turns on the third switch SW3, the fourth switch SW4, and the fifth switch SW5, and turns off the first switch SW1 and the second switch SW2. During parallel connection and discharge of the first resistor R1 and the second resistor R2, the switching control unit 8 turns on the first switch SW1 to the fourth switch SW4, and turns off the fifth switch SW5. With this configuration, the voltage applied to the switches can be divided.

[0021] In the case of parallel connection, the same effect can be achieved by controlling the on / off of at least one of the first switch SW1 and the fourth switch SW4, and at least one of the second switch SW2 and the fifth switch SW5.

[0022] In the above configuration of the present invention, two discharge resistors are used, but three or more discharge resistors may be used. When there are three discharge resistors, the effect of the present invention can be realized by always connecting one of the three resistors in parallel. When there are three discharge resistors, the effect of the present invention can be realized by switching from an initial state in which the three resistors are connected in series to a state in which one parallel connection and two series connections are mixed, and finally connecting the three resistors in parallel.

[0023] In addition, when there are four discharge resistors, the effects of the present invention can be achieved by initially connecting the four resistors in series, then mixing two resistors in parallel and two resistors in series, and finally connecting the four resistors in parallel.

[0024] (Figs. 4 to 6) Fig. 4 is a diagram showing the change in duty over time of the first resistor R1 and the second resistor R2, Fig. 5 is a diagram showing the change in accumulated discharge energy over time of the first resistor R1, and Fig. 6 is a diagram showing the change in accumulated discharge energy over time of the second resistor R2. First, a description will be given of the calculation of the duty ratio relating to the relationship between the duty ratio during rapid discharge of the smoothing capacitor 5 and switching of the resistor connection according to the embodiment described above.

[0025] When the voltage of the smoothing capacitor 5 is equal to or higher than a predetermined voltage, the two discharge resistors are connected in series and discharge begins, and when the voltage subsequently drops below the predetermined voltage, the two discharge resistors are switched to a parallel connection and the voltage increases. In other words, it is necessary to set a duty ratio for discharging to a predetermined voltage or lower within a certain time by switching between series and parallel connections so as not to exceed the energy tolerance of the first resistor R1 and the second resistor R2.

[0026] The formula for calculating such a duty ratio D is, for example, D=(T(t)-E(t)) / (R[I(t)])^2Δt. Note that T(t) represents the energy tolerance of the discharge resistor after t seconds have elapsed since the start of discharge. E(t) represents the accumulated discharge energy after t seconds have elapsed since the start of discharge. R represents the resistance value of the discharge resistor. I(t) represents the current flowing through the discharge resistor after t seconds have elapsed since the start of discharge. Δt represents the time per period of PWM discharge.

[0027] By setting the duty ratio calculated in this way, when the voltage at the start of discharging of the smoothing capacitor 5 is equal to or higher than a predetermined threshold, the switching control unit 8 controls on / off of at least one of the third switch SW3, the fourth switch SW4, and the fifth switch SW5 so that the upper limit of the energy consumed by the first resistor R1 or the second resistor R2 is not exceeded, and the discharge can be performed in the shortest time according to the energy tolerance of each of the first resistor R1 and the second resistor R2. In addition, since there is no need to restrict the magnitude of the resistance values ​​of the first resistor R1 and the second resistor R2, the design is easy. In addition, providing the first resistor R1 and the second resistor R2 with the same resistance value can contribute to cost reduction.

[0028] Incidentally, the energy tolerance T(t) may not be the actual tolerance (actual value), and an arbitrary margin (offset) may be provided to improve reliability.

[0029] The cumulative discharge energy and duty ratio associated with the first resistor R1 and the second resistor R2 will be described with reference to Figs. 4 to 6. As shown in Fig. 5, immediately after the start of discharge, the cumulative discharge energy (Energy1) quickly follows the energy tolerance curve (Tolerance1) of the first resistor R1. This behavior occurs because the duty ratio is set to 100% as shown in Fig. 4. After this, the graph of the cumulative discharge energy is limited so as not to exceed the tolerance curve.

[0030] Comparing the behavior of the accumulated discharge energy of the first resistor R1 in Figure 5 and the second resistor R2 in Figure 6, the accumulated discharge energy (Energy2) of the second resistor R2 moves faster along the energy tolerance curve (Tolerance2). On the other hand, the accumulated discharge energy of the first resistor R1 moves fastest along the energy tolerance curve (Tolerance1) after parallel connection.

[0031] As shown in Figure 4, immediately after switching from series to parallel connection (after 1.2 seconds), the duty ratio of the first resistor (Resistor1) becomes 100% so as to align it with the energy tolerance curve as quickly as possible, and then increases monotonically from a certain duty, while the duty ratio of the other resistor, the second resistor (Resistor2), increases monotonically from a certain duty. Ultimately, the duty ratios of both the first resistor R1 and the second resistor R2 become 100%. This difference between the first resistor R1 and the second resistor R2 is due to the difference in resistance value and energy tolerance between the first resistor R1 and the second resistor R2.

[0032] As shown in Figure 5, the instantaneous power consumption (Power1) in the first resistor R1 is the same immediately after the start of discharge as it is after switching to parallel connection. In other words, by connecting the resistors in series in the discharge circuit under high voltage conditions immediately after the start of discharge, the effect of suppressing peak power is achieved.

[0033] If the resistance values ​​of the first resistor R1 and the second resistor R2 match the energy tolerance curve, the behavior of the first resistor R1 and the second resistor R2, including the duty (see Figure 4), will be the same. Therefore, there is no need to intentionally prepare resistors with different resistance values, and the discharge resistor can be applied without restrictions on the magnitude of the resistance value. In addition, if the first resistor R1 and the second resistor R2 are the same, there is a cost advantage and design efficiency can be expected.

[0034] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0035] (1) A discharge device 6 for a smoothing capacitor 5 included in a power conversion device 1 includes a discharge section including a first discharge resistance circuit having a first resistor R1 and a first switch SW1 connected in parallel to the smoothing capacitor 5 and connected in series to each other, a second discharge resistance circuit having a second resistor R2 and a second switch SW2 connected in parallel to the first discharge resistance circuit and connected in series to each other, and a third switch SW3 arranged so that the first resistor R1 and the second resistor R2 are connected in series to each other, a voltage measurement section 7 for measuring the voltage of the smoothing capacitor 5, and a switching control section 8 for controlling the switching of the discharge section, in which the switching control section 8 connects the first resistor R1 and the second resistor R2 in series when the voltage at the start of discharge of the smoothing capacitor 5 is equal to or higher than a predetermined threshold, and connects the first resistor R1 and the second resistor R2 in parallel when the voltage at the start of discharge of the smoothing capacitor 5 is equal to or lower than the predetermined threshold. In this way, a discharge device 6 can be provided that prevents thermal destruction of resistors and improves reliability.

[0036] (2) When the voltage at the start of discharge of the smoothing capacitor 5 is equal to or higher than a predetermined threshold, the switching control unit 8 turns off the first switch SW1 and the second switch SW2 and turns on the third switch SW3 to connect the first resistor R1 and the second resistor R2 in series, and when the voltage at the start of discharge of the smoothing capacitor 5 is equal to or lower than the predetermined threshold, the switching control unit 8 turns on the first switch SW1 and the second switch SW2 and turns off the third switch SW3 to connect the first resistor R1 and the second resistor R2 in parallel. In this way, it is possible to suppress a decrease in the discharge rate without exceeding the energy tolerance of the first resistor R1 and the second resistor R2, and to prevent thermal destruction of the resistors.

[0037] (3) The first discharge resistance circuit has a fourth switch SW4 having one end connected to the first resistor R1 and the other end connected to the connection point of the first switch SW1 and the third switch SW3, and the second discharge resistance circuit has a fifth switch SW5 having one end connected to the second resistor R2 and the other end connected to the negative electrode of the smoothing capacitor 5. In this way, the voltage applied to the switches can be divided.

[0038] (4) When the voltage at the start of discharge of the smoothing capacitor 5 is equal to or higher than a predetermined threshold, the switching control unit 8 turns off the first switch SW1 and the second switch SW2 and turns on the third switch SW3, the fourth switch SW4, and the fifth switch SW5 to connect the first resistor R1 and the second resistor R2 in series, and when the voltage at the start of discharge of the smoothing capacitor 5 is equal to or lower than a predetermined threshold, the switching control unit 8 turns on the first switch SW1, the second switch SW2, the fourth switch SW4, and the fifth switch SW5 and turns off the third switch SW3 to connect the first resistor R1 and the second resistor R2 in parallel. In this way, the voltage applied to the switches during discharge can be divided while preventing thermal destruction of the resistors.

[0039] (5) When the voltage at the start of discharging of the smoothing capacitor 5 is equal to or higher than a predetermined threshold, the switching control unit 8 controls on / off of at least one of the third switch SW3, the fourth switch SW4, and the fifth switch SW5 so as not to exceed the upper limit of the energy consumed by the first resistor R1 or the second resistor R2. In this way, the fastest discharge can be achieved without exceeding the energy tolerance by using the set duty ratio.

[0040] The present invention is not limited to the above-described embodiment, and various modifications and other configurations can be combined without departing from the spirit of the present invention. Furthermore, the present invention is not limited to those having all of the configurations described in the above-described embodiment, and includes those in which some of the configurations are omitted. [Explanation of symbols]

[0041] 1 Power conversion device 2 Motors 3. Semiconductor Module 4 Battery 5 Smoothing capacitor 6 Discharge device 7 Voltage measurement section 8 Switching control section R1 First resistor R2 2nd resistor SW1 First switch SW2 Second switch SW3 3rd switch SW4 4th switch SW5 5th switch

Claims

1. A discharge device for a smoothing capacitor included in a power conversion device, a discharge section including a first discharge resistance circuit connected in parallel to the smoothing capacitor and having a first resistor and a first switch connected in series with each other, a second discharge resistance circuit connected in parallel to the first discharge resistance circuit and having a second resistor and a second switch connected in series with each other, and a third switch arranged so that the first resistor and the second resistor are connected in series with each other; A voltage measuring unit that measures a voltage of the smoothing capacitor; A switching control unit that controls switching of the discharge unit, The switching control unit connects the first resistor and the second resistor in series when a voltage at the start of discharging of the smoothing capacitor is equal to or higher than a predetermined threshold, and connects the first resistor and the second resistor in parallel when a voltage at the start of discharging of the smoothing capacitor is equal to or lower than a predetermined threshold. Discharge device.

2. The switching control unit is When a voltage at the start of discharging of the smoothing capacitor is equal to or higher than a predetermined threshold, the first switch and the second switch are turned off and the third switch is turned on to connect the first resistor and the second resistor in series, When the voltage at the start of discharging of the smoothing capacitor is equal to or lower than a predetermined threshold, the first switch and the second switch are turned on and the third switch is turned off, thereby connecting the first resistor and the second resistor in parallel. The discharge device according to claim 1 .

3. the first discharge resistor circuit has a fourth switch having one end connected to the first resistor and the other end connected to a connection point of the first switch and the third switch; The second discharge resistor circuit has a fifth switch having one end connected to the second resistor and the other end connected to the negative electrode of the smoothing capacitor. The discharge device according to claim 1 .

4. The switching control unit is when the voltage at the start of discharging of the smoothing capacitor is equal to or higher than a predetermined threshold value, the first switch and the second switch are turned off, and the third switch, the fourth switch, and the fifth switch are turned on, thereby connecting the first resistor and the second resistor in series; When the voltage at the start of discharging of the smoothing capacitor is equal to or lower than a predetermined threshold, the first switch, the second switch, the fourth switch, and the fifth switch are turned on and the third switch is turned off, thereby connecting the first resistor and the second resistor in parallel. The discharge device according to claim 3.

5. The switching control unit is When the voltage at the start of discharging of the smoothing capacitor is equal to or higher than a predetermined threshold value, at least one of the third switch, the fourth switch, and the fifth switch is on / off controlled so that the energy consumed by the first resistor or the second resistor does not exceed an upper limit value. The discharge device according to claim 3.

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