JP2012170200A - Load control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reconcile capacitor miniaturization and motor drive efficiency improvement.SOLUTION: An inverter comprising a bridge connection of IGBTs 51-56 and a smoothing capacitor 57 are arranged in parallel across a DC power supply. A communication arbitrating microcomputer 10 and power semiconductor driving microcomputers 15 instruct (S106-S118) a switching rate adjustment circuit 30 for adjusting the switching rate of switching signals controlling the IGBTs 51-56 to slow the switching rate of the switching signals with increasing temperature of the smoothing capacitor 57 estimated from a signal output from a temperature sensor 57a for outputting a signal depending on the temperature of the smoothing capacitor 57.

Description

  The present invention relates to a load control device.

  2. Description of the Related Art Conventionally, in a motor drive device that drives a vehicle drive motor of an electric vehicle by an inverter, an inverter configured by bridge-connecting switching elements is arranged between DC power supplies, and the switching element on the upper arm side and the lower arm are arranged according to a PWM signal. The arm-side switching element is complementarily turned on / off.

  In such a device, since an inductance component exists in the battery or the DC power supply line, a capacitor (for example, a film capacitor) having excellent high frequency characteristics between the DC power supplies is suppressed in order to suppress a surge voltage generated when the switching element of the inverter is turned on / off. ) Must be provided.

  However, when a motor for driving a vehicle is actually driven by a motor control device including such an inverter, a phenomenon occurs in which the capacitor generates heat. Since the capacitor rapidly deteriorates as the temperature rises, it is necessary to increase the capacity of the capacitor or to provide a cooler for the capacitor. For this reason, it will result in the enlargement of an apparatus.

  Therefore, paying attention to the fact that the ripple current flows through the smoothing capacitor as the inverter switching signal is switched on and off, and when the inverter output increases, the ripple current also increases and the amount of heat generated by the capacitor also increases. Smoothing capacitor when the inverter output is large by operating in the rectangular wave mode with few switching times and operating in the PWM mode that can drive the motor efficiently when the output of the inverter is small and the heat generation of the capacitor is small There is one that suppresses the temperature rise (see, for example, Patent Document 1).

JP 2008-154431 A

  However, the apparatus described in Patent Document 1 suppresses the temperature rise of the smoothing capacitor in a situation where the temperature of the smoothing capacitor further rises even when the motor is driven in the rectangular wave mode. This makes it difficult to reduce the size of the smoothing capacitor.

  Moreover, the apparatus as described in the said patent document 1 cannot suppress the temperature rise of a smoothing capacitor in the PWM mode which can drive a motor efficiently. For this reason, there exists a problem that efficiency is not good.

  The present invention has been made in view of the above problems, and an object thereof is to achieve both reduction in the size of a capacitor and improvement in motor drive efficiency.

  In order to achieve the above object, an invention according to claim 1 is an inverter arranged between a DC power supply and having a plurality of switching elements (51 to 56) bridge-connected, and a smoothing capacitor arranged between the DC power supplies. (57), temperature detection means (57a) for outputting a signal corresponding to the temperature of the smoothing capacitor (57), and switching speed adjustment for adjusting the switching speed of the switching signal for controlling the plurality of switching elements (51 to 56) The switching speed adjustment circuit (30) so that the switching speed of the switching signal becomes slower as the temperature of the circuit (30) and the smoothing capacitor (57) estimated based on the signal output from the temperature detection means (57a) becomes higher. And a speed adjustment instruction means (S106 to S118) for instructing.

  According to such a configuration, the switching speed adjustment circuit (such that the switching speed of the switching signal becomes slower as the temperature of the smoothing capacitor (57) estimated based on the signal output from the temperature detection means (57a) becomes higher. 30). That is, regardless of the operation mode such as the PWM mode and the rectangular wave mode, the higher the smoothing capacitor temperature, the slower the switching speed of the switching signal, and the temperature rise of the smoothing capacitor is suppressed. Therefore, even when the motor is driven in the rectangular wave mode and the temperature of the smoothing capacitor further increases, the temperature of the smoothing capacitor can be suppressed, and the smoothing capacitor can be downsized. Even in the PWM mode, the higher the smoothing capacitor temperature, the slower the switching speed of the switching signal and the temperature rise of the smoothing capacitor is suppressed, so that the motor drive efficiency can be improved.

  Further, in the invention according to claim 2, the switching speed adjustment circuit (30) changes the resistance value of the gate resistance connected to each gate of the plurality of switching elements (51 to 56) step by step. The switching speed is adjusted stepwise, and the speed adjustment instruction means (S106 to S118) instructs the switching speed adjustment circuit so that the switching speed of the switching signal decreases stepwise. Yes.

  As described above, the switching speed adjustment circuit (30) changes the resistance value of the gate resistance connected to each gate of the plurality of switching elements (51 to 56) stepwise to change the switching speed of the switching signal stepwise. The speed adjustment instructing means (S106 to S118) can instruct the switching speed adjusting circuit so that the switching speed of the switching signal is gradually reduced.

  Further, as in the third aspect of the invention, the temperature detecting means (57a) is constituted by the temperature detecting element incorporated in the smoothing capacitor, so that the temperature of the smoothing capacitor can be estimated with high accuracy.

  According to a fourth aspect of the present invention, the temperature detection means (57a) includes a temperature detection element incorporated in each of the plurality of switching elements, a temperature detection element that detects the temperature of a load connected to the inverter, It can also be configured by any one of current sensors that detect a current flowing through a load connected to the inverter.

  In the invention according to claim 5, a diode (51a to 56a) is connected to each of the plurality of switching elements (51 to 56) in parallel with the switching element. A recovery current flowing through the diode (51a to 56a) during ON switching of (51 to 56) and means for reducing the frequency thereof are provided.

  According to such a configuration, it is possible to reduce the recovery current and the frequency that the diodes (51a to 56a) flow when the switching elements (51 to 56) are turned on, and to suppress the temperature rise of the smoothing capacitor.

  According to a sixth aspect of the present invention, the inverter includes three series circuits (51 and 52, 53 and 54, 55 and 56) formed by connecting the switching elements on the upper arm side and the switching elements on the lower arm side in series. The recovery current reducing means has a snubber capacitor (59) connected in parallel with three series circuits (51 and 52, 53 and 54, 55 and 56). It is characterized by.

  In this way, the diodes (51a to 56a) are turned on when the switching elements (51 to 56) are turned on by the snubber capacitor (59) connected in parallel with the three series circuits (51 and 52, 53 and 54, 55 and 56). ) Can be reduced from flowing into the smoothing capacitor.

  The invention according to claim 7 is a means for reducing the recovery current and its frequency, wherein the first end is connected to the power supply line of the DC power supply and the other end is connected to one end of the snubber capacitor (59). And the second inductor (58b) having one end connected to the ground line of the DC power source and the other end connected to the other end of the snubber capacitor (59). .

  In this way, one end is connected to the power supply line of the DC power supply, the other end is connected to one end of the snubber capacitor (59), one end is connected to the ground line of the DC power supply, and the other By providing the second inductor (58b) whose end is connected to the other end of the snubber capacitor (59), the recovery current and the frequency that the diode (51a-56a) flows when the switching element (51-56) is turned on Can be reduced.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a figure which shows the whole structure of the load control apparatus which concerns on one Embodiment of this invention. It is a figure which shows the detail of the A section in FIG. It is an example of the measurement waveform of the ripple current which flows into a smoothing capacitor. It is a figure which shows the ESR characteristic of a smoothing capacitor. It is a flowchart of the microcomputer for communication arbitration, and the microcomputer for power semiconductors. It is the figure which showed the temperature characteristic of the smoothing capacitor at the time of changing the switching speed of a switching signal. It is the figure which showed the relationship between the presence or absence of a snubber capacitor, and the temperature characteristic of a smoothing capacitor. It is the figure which showed the relationship between the presence or absence of an inductance, and a recovery current.

  FIG. 1 shows the overall configuration of a load control apparatus according to an embodiment of the present invention. The load control device 1 is connected to a DC power source (battery) 2 and a three-phase high-voltage AC motor 3 as a load. The motor 3 is used as a power source for traveling the vehicle.

  The load control device 1 includes a communication arbitration microcomputer 10, six power semiconductor drive microcomputers 15, six switching speed adjustment circuits (referred to as SW speed adjustment circuits in the figure) 30, an insulated gate transistor (hereinafter, IGBT). 5) to 56, a smoothing capacitor 57, inductances 58a and 58b, a snubber capacitor 59, and an MG-ECU 60. The IGBTs 51 to 56 include diodes 51a to 56a connected in parallel, respectively. Further, the smoothing capacitor 57 includes a temperature sensor 57 a that outputs a signal corresponding to the temperature of the smoothing capacitor 57. Specifically, the temperature sensor 57a is configured by a thermistor.

  The smoothing capacitor 57 is provided between the DC power supplies for suppressing a surge voltage generated when the IGBTs 51 to 56 are turned on and off, and for reducing a voltage fluctuation of the DC power supply. As the smoothing capacitor 57, a ceramic capacitor, a film capacitor, or the like is used.

  Snubber capacitor 59 is formed of a ceramic capacitor, and is connected in parallel with an inverter formed of IGBTs 51 to 56.

  One end of the inductance 58 a is connected to the power supply line of the DC power supply, and the other end is connected to one end of the snubber capacitor 59.

  One end of the inductance 58 b is connected to the ground line of the DC power supply, and the other end is connected to the other end of the snubber capacitor 59.

  The snubber capacitor 59 and the inductances 58a and 58b are provided to make it difficult for the recovery current flowing through the diodes (51a to 56a) to flow into the smoothing capacitor when the IGBTs 51 to 56 described later are turned on, and to reduce the frequency of the recovery current. ing.

  The load control device 1 is configured to input a sine wave PWM signal to the gates of the IGBTs 51 to 56 and PWM drive the motor 3, and input an overmodulation PWM signal to the gates of the IGBTs 51 to 56. And a rectangular wave control mode in which a rectangular wave signal is input to the gates of the IGBTs 51 to 56 to drive the motor 3 to a rectangular wave.

  The communication arbitration microcomputer 10 is for communicating with the MG-ECU 60. The communication arbitration microcomputer 10 includes a voltage detection circuit (not shown) that detects a voltage between terminals of the DC power supply 2, and notifies the MG-ECU 60 of the voltage between terminals of the DC power supply 2 detected by the voltage detection circuit. It is like that. The MG-ECU 60 determines an operation mode (corresponding to a control mode) for optimally driving the motor 3 based on the voltage between terminals of the DC power supply 2 notified from the communication arbitration microcomputer 10. The communication arbitration microcomputer 10 is notified of information for specifying the operation mode.

  In addition, a signal from the thermistor 57a is input to the MG-ECU 60. The MG-ECU 60 estimates the temperature of the smoothing capacitor 57 based on the signal input from the thermistor 57a, and determines the optimum speed degree (low speed, medium speed, high speed) of the switching signal for switching the inverter based on this. The switch arbitration microcomputer 10 is notified of switch speed specifying information indicating the determined speed.

  Upon receiving information for specifying the operation mode from the MG-ECU 60, the communication arbitration microcomputer 10 specifies the switching speed value of the signal input to the gate of each IGBT 51 to 56 suitable for the operation mode, and drives each power semiconductor. Is notified to the microcomputer 15.

  The power semiconductor drive microcomputer 15 controls the switching speed adjustment circuit 30 according to the switching speed value notified from the communication arbitration microcomputer 10.

  The switching speed adjustment circuit 30 is a circuit for adjusting the rising speed and falling speed of the voltage applied to each gate of the IGBTs 51 to 56. The switching speed adjustment circuit 30 will also be described in detail later.

  The IGBTs 51 to 56 are configured as three-phase inverters. In this embodiment, the IGBT 51 is the U-phase upper arm, the IGBT 52 is the U-phase lower arm, the IGBT 53 is the V-phase upper arm, the IGBT 54 is the V-phase lower arm, the IGBT 55 is the W-phase upper arm, and the IGBT 56 is the W-phase. It is a lower arm.

  The MG-ECU 60 includes a microcomputer 67. As described above, the microcomputer 67 determines an operation mode for optimally driving the motor 3 based on the voltage across the terminals of the DC power supply 2 notified from the communication arbitration microcomputer 10, and indicates the determined operation mode. A process of notifying information to the communication arbitration microcomputer 10 is performed.

  The microcomputer 67 is over-modulated when the voltage between the terminals of the DC power supply 2 is a high voltage (for example, about 700 V) and when the voltage between the terminals of the DC power supply 2 is an intermediate voltage (for example, about 600 V). In the PWM control mode, when the voltage between the terminals of the DC power supply 2 is a low voltage (for example, about 500 V), the operation mode is determined so that the rectangular wave control mode is set.

  FIG. 2 shows the details of part A in FIG. In this figure, a switching speed adjustment circuit 30, a semiconductor drive microcomputer 15 and an IGBT 51 are shown.

  The switching speed adjustment circuit 30 includes a level shift circuit 31, a resistor 301, and speed adjustment circuits 32-35.

  A switching signal corresponding to an operation mode is input to the level shift circuit 31 from the semiconductor drive microcomputer 15 via the switch terminal SW.

  The level shift circuit 31 outputs a voltage obtained by shifting the voltage level (for example, 5 V) of the switching signal to a constant voltage range (for example, 0 V to 30 V) input via the input terminal IN.

  The speed adjustment circuits 32 and 33 are circuits for adjusting the rise of the waveform of the gate voltage of the IGBT 51, and the speed adjustment circuits 34 and 35 are circuits for adjusting the fall of the waveform of the gate voltage of the IGBT 51. .

  The speed adjustment circuit 32 includes resistors 321 and 322, a capacitor 323, a diode 324, and an N-channel MOS transistor 325.

  Similarly, the speed adjustment circuit 33 includes resistors 331 and 332, a capacitor 333, a diode 334, and an N-channel MOS transistor 335.

  The resistor 321 in the speed adjustment circuit 32 and the resistor 331 in the speed adjustment circuit 33 are connected in parallel with the resistor 301.

  By turning on or off the transistor 325 in the speed adjustment circuit 32 and the transistor 335 in the speed adjustment circuit 33, the combined resistance including the resistor 301, the resistor 321 in the speed adjustment circuit 32, and the resistor 331 in the speed adjustment circuit 33 is changed. The gate resistance of the IGBT 51 is changed. Note that as the resistance value of the combined resistor composed of the resistor 301, the resistor 321 and the resistor 331 increases, the rise of the waveform of the gate voltage of the IGBT 51 becomes gentler.

  The speed adjustment circuit 34 includes resistors 341 and 342, a capacitor 343, a diode 344, and an N-channel MOS transistor 345.

  Similarly, the speed adjustment circuit 35 includes resistors 351 and 352, a capacitor 353, a diode 354, and an N-channel MOS transistor 355.

  The diode 354 in the speed adjustment circuit 35 and the diode 344 in the speed adjustment circuit 34 are connected in the opposite direction to the diodes 324 and 334 in the speed adjustment circuits 32 and 33.

  By turning on or off the transistor 345 in the speed adjustment circuit 34 and the transistor 355 in the speed adjustment circuit 35, the combined resistance composed of the resistor 301, the resistor 341, and the resistor 351 changes, and the gate resistance of the IGBT 51 changes. ing. Note that the fall of the waveform of the gate voltage of the IGBT 51 becomes gentler as the resistance value of the combined resistor including the resistor 301, the resistor 341, and the resistor 351 increases.

  By the way, as a result of experiments and the like, the present inventors have found that the main factor of heat generation of the smoothing capacitor is a high-frequency current component caused by the recovery current included in the ripple current, and the low frequency component does not significantly affect the heat generation of the smoothing capacitor. I found out.

  Note that the recovery current is changed from a state in which a switching signal input to each of the gates of the IGBTs 51 to 56 is changed from OFF to ON, and currents are flowing through the diodes 51a to 56a connected in parallel to the IGBTs 51 to 56. This is a current that is generated when no current flows in the circuit.

  Hereinafter, the relationship between the recovery current and the heat generation of the smoothing capacitor will be described. FIG. 3 shows an example of a measurement waveform of the ripple current flowing through the smoothing capacitor 57. (B) in FIG. 3 is an enlarged view of (1) in FIG. FIG. 3B shows a pulse current having a frequency component in the several MHz band and a pulse current having a frequency component in the tens of kHz band.

  In this example, the ripple current flowing through the smoothing capacitor 57 is roughly divided into two types of pulse currents of several MHz band and tens of kHz band. Among these pulse currents, a pulse current of several MHz band is a current component due to the recovery current. The recovery current component has a very large value of about several hundred amperes, although the current flowing time is short compared to other pulse currents.

Here, the calorific value of the smoothing capacitor can be represented by the amount of power consumed by the smoothing capacitor. That is, it can be calculated as (heat generation amount of the smoothing capacitor) = (current flowing through the smoothing capacitor) ² × (series equivalent resistance). Note that the resistance value of the series equivalent resistance ESR (Equivalent Series Resistance) changes according to the frequency of the current flowing through the smoothing capacitor.

  FIG. 4 shows the ESR characteristics of the smoothing capacitor. In the example of this figure, the ESR at the time of ten and several kHz is about 1 m ohm (Ω), and the ESR at the time of several MHz is about 30 m ohm (Ω). Thus, the series equivalent resistance ESR of the smoothing capacitor increases as the frequency increases.

  In other words, when the peak value of the current value is small and the frequency of the current flowing into the smoothing capacitor is low, the amount of heat generated by the smoothing capacitor is small, but the peak value of the current value is large and the current flowing into the smoothing capacitor is small. It can be seen that when the frequency is high, the amount of heat generated by the smoothing capacitor increases significantly.

  Therefore, by reducing the high-frequency recovery current component that has a large peak current value and a large series equivalent resistance ESR, it is possible to significantly suppress the heat generation of the smoothing capacitor.

  As described above, it has been found that the main factor of the heat generation of the smoothing capacitor is a high-frequency component resulting from the recovery current included in the ripple current.

  Therefore, the load control device 1 estimates the temperature of the smoothing capacitor 57 based on a signal output from the thermistor 57a that detects the temperature of the smoothing capacitor 57, and controls the IGBTs 51 to 56 as the temperature of the smoothing capacitor 57 increases. The switching speed adjustment circuit 30 is instructed to slow down the switching speed of the switching signal to reduce the recovery current peak value and suppress the temperature rise of the smoothing capacitor 57.

  Next, processing of the communication arbitration microcomputer 10 will be described with reference to FIG. Here, the processing of the communication arbitration microcomputer 10 and the power semiconductor microcomputer 15 will be described. When power is supplied from the low-voltage battery, the communication arbitration microcomputer 10 and the power semiconductor microcomputer 15 are activated to perform the processing shown in FIG. Here, description will be made assuming that the inverter is operated in the sine wave PWM control mode.

  First, the MG-ECU 60 estimates the temperature of the smoothing capacitor 57 based on the signal output from the temperature sensor 57 (S100).

  The MG-ECU 60 determines the optimum switching speed degree (low speed, medium speed, high speed) of the switching signal input to the gates of the IGBTs 51 to 56 based on this temperature information, and specifies the switch speed indicating the determined speed degree. Information (SW speed specifying information) is notified to the communication arbitration microcomputer 10. In this embodiment, when the temperature of the smoothing capacitor 57 is less than 70 ° C., the speed is high, when the temperature of the smoothing capacitor 57 is 70 ° C. or more, and when the temperature is less than 90 ° C., the temperature is 90 ° C. or more. In the case of, the degree of switching speed is determined so as to be low.

  When receiving the switch speed specifying information (S104), the communication arbitration microcomputer 10 determines the switch speed based on the switch speed specifying information (S106).

  Here, when the estimated temperature of the smoothing capacitor 57 is less than 70 ° C. and it is determined that the degree of the switching speed is high based on the switch speed specifying information, the gate resistance of the high switching speed is determined. A combination is specified (S108). Here, the control signal instructing the switching speed adjustment circuit 30 is specified so that the resistance values of the gate resistors of the IGBTs 51 to 56 are reduced. Specifically, in the switching speed adjustment circuit 30 shown in FIG. 2, the transistor 325 of the speed adjustment circuit 32 and the transistor 335 of the speed adjustment circuit 33 are turned on in order to make the rising speed of the switching signal steep. In order to specify the logic levels of the Cnt2 terminal and the Cnt3 terminal, and to make the falling speed of the switching signal steep, the transistor 345 of the speed adjustment circuit 34 and the transistor 355 of the speed adjustment circuit 35 are respectively turned on. The logic levels of the Cnt4 terminal and the Cnt5 terminal are specified.

  In this case, the resistance value of the gate resistance of the IGBTs 51 to 56 at the rising edge of the switching signal is the resistance value of the combined resistance in which the resistor 301, the resistor 321 of the speed adjustment circuit 32, and the resistor 331 of the speed adjustment circuit 33 are connected in parallel. It becomes. Further, the resistance value of the gate resistance of the IGBTs 51 to 56 at the falling edge of the switching signal is the resistance value of the combined resistance in which the resistance 301, the resistance 341 of the speed adjustment circuit 34, and the resistance 351 of the speed adjustment circuit 35 are connected in parallel. It becomes.

  Next, the switching speed adjustment circuit 30 is instructed to increase the switching speed (S110). Specifically, a control signal is output to the Cnt2 terminal to Cnt4 terminal so as to achieve the logic level specified in S108. Thereby, the rising speed and falling speed of the switching signal input to each gate of the IGBTs 51 to 56 are increased. In addition, since the switching loss of IGBT51-56 is reduced by speeding up the switching speed of a switching signal in this way, an inverter can be driven efficiently.

  Next, the temperature of the smoothing capacitor 57 rises, and the estimated temperature of the smoothing capacitor 57 is 70 ° C. or higher and lower than 90 ° C. In S106, the degree of switching speed is determined based on the switch speed specifying information. If it is determined that the speed is medium, a combination of gate resistances is selected so that the switching speed is medium (S112). Here, the control signal instructing the switching speed adjustment circuit 30 is specified so that the resistance values of the gate resistances of the IGBTs 51 to 56 become an intermediate value. Specifically, in the switching speed adjustment circuit 30 shown in FIG. 2, the transistor 325 of the speed adjustment circuit 32 is turned on and the transistor 335 of the speed adjustment circuit 33 is turned off in order to make the rising speed of the switching signal medium. As described above, the logic levels of the Cnt2 terminal and the Cnt3 terminal are specified, and the transistor 345 of the speed adjustment circuit 34 is turned on and the transistor 355 of the speed adjustment circuit 35 is turned off in order to make the falling speed of the switching signal medium. The logic levels of the Cnt4 terminal and the Cnt5 terminal are specified.

  In this case, the resistance value of the gate resistance of the IGBTs 51 to 56 at the rising edge of the switching signal is the resistance value of the combined resistance in which the resistor 301 and the resistor 321 of the speed adjustment circuit 32 are connected in parallel. Further, the resistance value of the gate resistance of the IGBTs 51 to 56 when the switching signal falls is the resistance value of the combined resistance in which the resistor 301 and the resistor 341 of the speed adjustment circuit 34 are connected in parallel.

  Next, the switching speed adjustment circuit 30 is instructed so that the switching speed becomes a medium speed (S114). Specifically, a control signal is output to the Cnt2 terminal to Cnt4 terminal so as to achieve the logic level specified in S112. Thereby, the rising speed and falling speed of the switching signal input to each gate of the IGBTs 51 to 56 are respectively medium speed. In this way, heat generation of the smoothing capacitor 57 is suppressed by setting the switching speed of the switching signal to a medium speed.

  Further, the temperature of the smoothing capacitor 57 rises, and the estimated temperature of the smoothing capacitor 57 becomes 90 ° C. or higher. In S106, it is determined that the degree of switching speed is low based on the switch speed specifying information. In such a case, a combination of gate resistances that makes the switching speed low is specified (S116). Here, the control signal instructing the switching speed adjustment circuit 30 is specified so that the resistance values of the gate resistors of the IGBTs 51 to 56 are increased. Specifically, in the switching speed adjustment circuit 30 shown in FIG. 2, the transistor 325 of the speed adjustment circuit 32 and the transistor 335 of the speed adjustment circuit 33 are turned off in order to reduce the rising speed of the switching signal. In order to specify the logic levels of the Cnt2 terminal and the Cnt3 terminal and to lower the falling speed of the switching signal, the transistor 345 of the speed adjustment circuit 34 and the transistor 355 of the speed adjustment circuit 35 are turned off, respectively. The logic levels of the terminal and the Cnt5 terminal are specified.

  In this case, the resistance value of the gate resistance of the IGBTs 51 to 56 when the switching signal rises is equal to the resistance 301, and the resistance value of the gate resistance of the IGBTs 51 to 56 when the switching signal falls is also equal to the resistance 301. Become.

  Next, the switching speed adjustment circuit 30 is instructed to reduce the switching speed (S118). Specifically, a control signal is output to the Cnt2 terminal to Cnt4 terminal so that the logic level specified in S116 is obtained. As a result, the rising speed and falling speed of the switching signal input to each gate of the IGBTs 51 to 56 are low. Note that heat generation of the smoothing capacitor 57 is suppressed by reducing the switching speed of the switching signal in this way.

  If the temperature of the smoothing capacitor 57 decreases, the estimated temperature of the smoothing capacitor 57 becomes less than 90 ° C., and it is determined in S106 that the degree of switching speed is medium based on the switch speed specifying information, A combination of gate resistors that makes the switching speed medium speed is specified (S112), and the switching speed adjustment circuit is instructed to make the switching speed medium speed (S114).

  By repeating the above processing, when the temperature of the smoothing capacitor 57 increases, the switching speed adjustment circuit 30 is instructed to slow down the switching speed of the switching signal. Since the switching speed adjustment circuit 30 is instructed to increase the switching speed of the switching signal when the temperature of the inverter decreases, the switching loss of the inverter can be reduced, that is, the load can be driven efficiently. .

  Therefore, it is not necessary to increase the size of the capacitor or increase the cooling capacity in order to suppress the temperature rise of the smoothing capacitor.

  Further, the temperature rise of the smoothing capacitor 57 can be suppressed regardless of the operation modes such as the PWM control mode and the rectangular wave mode.

  FIG. 6 shows the temperature characteristics of the smoothing capacitor 57 when the switching speed of the switching signal is changed. The recovery current decreases as the switching speed of the switching signal is decreased. FIG. 6 shows the temperature characteristics of the smoothing capacitor 57 when the peak value of the recovery current is 450 amperes, 550 amperes, and 700 amperes. As shown in the figure, it can be seen that the temperature rise of the smoothing capacitor is suppressed as the peak value of the recovery current becomes smaller.

  Next, the difference in temperature characteristics of the smoothing capacitor depending on the presence or absence of the snubber capacitor 59 will be described. FIG. 7 shows the presence / absence of the snubber capacitor 59 and the temperature characteristics of the smoothing capacitor.

  As shown in the figure, when the snubber capacitor 59 is present, the temperature rise of the smoothing capacitor 57 is suppressed more than when the snubber capacitor 59 is not present. This is because the recovery current flowing through the smoothing capacitor 57 is reduced by the snubber capacitor 59.

  FIG. 8 shows simulation waveforms of the recovery current flowing through the smoothing capacitor when the inductances 58a and 58b are not provided and when the inductances 58a and 58b are provided. (A) shows the case where the inductances 58a and 58b are not provided, and (b) shows the case where the inductances 58a and 58b are provided.

  As shown in FIGS. 8A and 8B, the waveform of the recovery current flowing through the capacitor is higher when the inductances 58a and 58b are provided than when the inductances 58a and 58b are not provided. The component is low and the waveform is dull. This is because the high-frequency recovery current is less likely to flow into the smoothing capacitor 57 due to the inductances 58a and 58b.

  Thus, by providing the snubber capacitor 59 and the inductances 58a and 58b, it is possible to further suppress the heat generation of the smoothing capacitor 57.

  According to the configuration described above, the switching speed adjustment circuit 30 is instructed so that the switching speed of the switching signal becomes slower as the temperature of the smoothing capacitor 57 estimated based on the signal output from the temperature sensor 57a becomes higher. That is, regardless of the operation mode such as the PWM mode and the rectangular wave mode, the higher the smoothing capacitor temperature, the slower the switching speed of the switching signal, and the temperature rise of the smoothing capacitor is suppressed. Therefore, even when the motor is driven in the rectangular wave mode and the temperature of the smoothing capacitor further increases, the temperature of the smoothing capacitor can be suppressed, and the smoothing capacitor can be downsized. Even in the PWM mode, the higher the smoothing capacitor temperature, the slower the switching speed of the switching signal and the temperature rise of the smoothing capacitor is suppressed, so that the motor drive efficiency can be improved.

  Further, the means for reducing the high-frequency component current caused by the recovery current flowing through the diodes 51a to 56a when the IGBTs 51 to 56 are turned on is less likely to flow into the smoothing capacitor, thereby further suppressing the temperature rise of the smoothing capacitor. Can do.

  Here, a snubber capacitor 59 is provided as means for reducing the high-frequency component current, and this snubber capacitor 59 reduces the high-frequency component current caused by the recovery current that the diodes 51a to 56a flow when the IGBTs 51 to 56 are turned on. It is possible.

  One end is connected to the power line of the DC power supply, the other end is connected to one end of the snubber capacitor 59, one end is connected to the ground line of the DC power supply, and the other end is connected to the snubber capacitor 59. By providing the second inductor 58b connected to the other end, it is possible to reduce the flow of the high-frequency component current caused by the recovery current flowing through the diodes 51a to 56a into the smoothing capacitor when the IGBTs 51 to 56 are turned on.

  In addition, this invention is not limited to the said embodiment, Based on the meaning of this invention, it can implement with a various form.

  For example, in the above embodiment, the sine wave PWM control mode is set when the voltage between the terminals of the DC power supply 2 is high, and the rectangular wave control mode is set when the voltage between the terminals of the DC power supply 2 is low. The switching of the operation mode is an example. For example, when the estimated temperature of the smoothing capacitor 27 is low, the PWM control mode is selected. As the estimated temperature of the smoothing capacitor 27 increases, the duty of the switching signal increases. When the estimated temperature of the smoothing capacitor 27 exceeds a threshold value, the operation mode may be switched so that the rectangular wave control mode is set. Moreover, you may comprise so that an operation mode may be switched according to various conditions other than the voltage between terminals of DC power supply 2. FIG.

  Moreover, in the said embodiment, although the structure which drives the three-phase high voltage alternating current motor 3 as a load was shown, it is not limited to such a load.

  Moreover, in the said embodiment, although the temperature sensor 57a which detects the temperature of a smoothing capacitor directly was used as a temperature detection means, for example, the temperature sensor incorporated in each of IGBT51-56, the temperature which detects the temperature of the motor 3 The temperature of the smoothing capacitor may be estimated from the sensor. Further, the temperature of the smoothing capacitor may be estimated from the output of a current sensor that detects the current flowing through the motor 3.

  In the above embodiment, the switching speed adjustment circuit 30 is configured to adjust the switching speed of the switching signal in stages by changing the resistance values of the gate resistors connected to the gates of the IGBTs 51 to 56 in stages. The switching speed adjustment circuit 30 is instructed so that the switching speed of the switching signal is gradually decreased (S106 to S118). For example, the resistance value of the gate resistor connected to each gate of the IGBTs 51 to 56 The switching speed adjustment circuit 30 is configured to linearly adjust the switching speed of the switching signal by linearly changing the switching signal, and the switching speed adjustment circuit 30 is instructed to linearly slow the switching speed of the switching signal. (S106 to S118) may be configured.

DESCRIPTION OF SYMBOLS 1 Load control apparatus 2 DC power supply 3 Motor 10 Communication arbitration microcomputer 15 Power semiconductor drive microcomputer 30 Switching speed adjustment circuit 51-56 IGBT
57 Smoothing capacitor 58a, 58b Inductance 59 Snubber capacitor 60 MG-ECU

Claims (7)

An inverter that is arranged between the DC power sources and that bridge-connects a plurality of switching elements (51 to 56);
A smoothing capacitor (57) disposed between the DC power sources;
Temperature detecting means (57a) for outputting a signal corresponding to the temperature of the smoothing capacitor (57);
A switching speed adjustment circuit (30) for adjusting a switching speed of a switching signal for controlling the plurality of switching elements (51 to 56);
Instructs the switching speed adjustment circuit (30) so that the switching speed of the switching signal becomes slower as the temperature of the smoothing capacitor (57) estimated based on the signal output from the temperature detecting means (57a) becomes higher. And a speed adjustment instruction means (S106 to S118) for performing the load control. The switching speed adjusting circuit (30) adjusts the switching speed of the switching signal stepwise by changing stepwise the resistance value of the gate resistance connected to each gate of the plurality of switching elements (51 to 56). Is supposed to
The load control apparatus according to claim 1, wherein the speed adjustment instruction means (S106 to S118) instructs the switching speed adjustment circuit so that a switching speed of the switching signal is decreased in a stepwise manner.   The load control device according to claim 1 or 2, wherein the temperature detection means (57a) comprises a temperature detection element built in the smoothing capacitor.   The temperature detection means (57a) includes a temperature detection element incorporated in each of the plurality of switching elements, a temperature detection element for detecting a temperature of a load connected to the inverter, and a current flowing through the load connected to the inverter The load control device according to claim 1, wherein the load control device is configured by any one of current sensors for detecting the current. A diode (51a-56a) is connected to each of the plurality of switching elements (51-56) in parallel with the switching element,
A means for reducing a recovery current flowing through the diodes (51a to 56a) when the switching elements (51 to 56) are ON-switched and a frequency between the DC power sources is provided. 4. The load control device according to any one of 4. The inverter is configured by connecting in parallel three series circuits (51 and 52, 53 and 54, 55 and 56) formed by connecting upper arm side switching elements and lower arm side switching elements in series.
The recovery current and its frequency reduction means comprise a snubber capacitor (59) connected in parallel with the three series circuits (51 and 52, 53 and 54, 55 and 56). Item 6. The load control device according to Item 5. A first inductor (58a) having one end connected to a power supply line of the DC power supply and the other end connected to one end of the snubber capacitor (59);
The second inductor (58b) having one end connected to the ground line of the DC power supply and the other end connected to the other end of the snubber capacitor (59). Load control device.

Images