JP5857189B2 - Inverter device - Google Patents

Description

  The present invention relates to an inverter device that includes a plurality of switching elements, converts DC power into AC having a desired frequency, and drives a load such as a motor.

  Conventionally, in a so-called inverter device that converts input power from a power source into alternating current of a desired frequency and is used for driving a motor or the like, a series circuit of two switching elements on the upstream side and the downstream side according to the application direction of the power source voltage is used. Two sets of switching circuits are common. IGBTs (insulated gate bipolar transistors), MOSFETs (a kind of field effect transistors), and the like are widely used as the upstream side, so-called upper arm switching elements, and the downstream side, so-called lower arm switching elements.

  As a characteristic of such a switching element, an IGBT device has a low efficiency at a low load, but has a relatively high efficiency at a high load and a high switching speed, while a MOSFET device has a low efficiency. The load is highly efficient, the load is relatively low, and the switching speed is high. Further, in general inverter circuits, most of the switching elements of the upper and lower arms of the switching circuit are composed of the same elements.

  On the other hand, as shown in Patent Document 1, in the case where two switching elements on the upstream side and the downstream side have at least one series circuit composed of MOSFETs, and one of them is an IGBT, High voltage and high current output due to the constant voltage between both terminals, and high frequency switching due to high MOSFET on / off speed, and low voltage and low current output. There has been proposed an inverter control circuit that improves the efficiency by utilizing the characteristic that the loss is small.

In the inverter circuit shown in Patent Document 2, the switching element of the upper arm of the switching circuit used for driving the DC motor is configured by IGBT or MOSFET, and the switching element of the lower arm is configured by bipolar transistor. It was. By using an IGBT or MOSFET capable of high-speed switching for the three phases of the upper arm of the switching circuit and using a bipolar transistor for the three phases of the lower arm, it is cheaper than using an IGBT or MOSFET for all six phases. And, compared to when using a bipolar transistor, it enables fine switching and chopping control, and furthermore, it is possible to perform control to eliminate electromagnetic noise when driving a DC motor and to reduce vibration due to resonance with peripheral mechanisms. The noise reduction was improved.

JP 2007-129848 A JP-A-7-31182

  In the case of an inverter device in which the upper and lower arms of such a switching circuit are configured with different types of switching elements, when driven with a normal switching pattern, the load balance on each switching element becomes uneven, In some cases, the load is concentrated on the switching element of this type, and the drive range is limited due to a temperature rise.

  In addition, since the conditions for increasing the efficiency of each switching element vary depending on the type of the switching element, it is difficult to maximize the efficiency in consideration of the characteristics of the switching element when driven by a normal switching pattern. It was.

  The present invention has been made in view of such a point, and an object of the present invention is to control driving of the switching element in an inverter device using different types of switching elements such as MOSFETs and IGBTs for the upper and lower arms, respectively. The purpose of this is to reduce the inverter circuit loss and improve the efficiency with high reliability under any load conditions.

The inverter apparatus according to the present invention, comprises a switching circuit including a plurality of upper and lower arms, and a control means for driving the switching circuit in the PWM modulation method, the inverter apparatus for outputting a sinusoidal voltage, the upper arm switching a switching element constituting the circuit, the switching elements constituting the lower arm switching circuit is composed of different types of switching devices, said control means, and the on-resistance of the switching elements constituting the lower arm side switching circuit, the Based on the condition for determining the magnitude relationship with the on-resistance of the switching element constituting the upper arm side switching circuit, the average output voltage of the sine wave voltage is lower than the intermediate voltage of the power supply voltage supplied to the switching circuit. or high voltage Lee, characterized in that shifting to the side A converter unit.

As a result, a low-loss, high-speed switching element is provided, and a high-efficiency inverter is always available , even under load conditions where the lower arm-side switching element is highly efficient and under load conditions where the upper-arm side switching element is highly efficient. A device is realized.

As described above, according to the present invention, a low-loss, high-speed switching element is provided, and an optimally efficient inverter device can be realized at any load condition.

Configuration diagram of the inverter device according to the first embodiment of the present invention. The characteristic diagram showing the characteristic of the switching element of the inverter device The timing chart showing an example of switching timing characteristics in the PWM modulation system of the inverter device The characteristic figure of an example which showed the characteristic of the electric energy which passes the switching element of the upper arm side and lower arm side in an inverter device The timing chart showing another example of the switching timing characteristics in the PWM modulation system of the inverter device The characteristic diagram of another example which showed the characteristic of the electric energy which passes the switching element of the upper arm side and lower arm side in an inverter apparatus similarly The characteristic diagram showing the switching characteristic of the output voltage with respect to the output current in the control means of the inverter device Timing chart showing switching timing characteristics in PWM modulation method of conventional inverter device

A first aspect of the present invention is a switching circuit composed of a plurality of upper and lower arms, the switching circuits and a control means for driving by the PWM modulation scheme, the inverter apparatus for outputting a sinusoidal voltage, the upper arm switching circuit a switching element forming, the switching elements constituting the lower arm switching circuit is composed of different types of switching devices, said control means, and the on-resistance of the switching elements constituting the lower arm side switching circuit, the upper arm The average output voltage of the sine wave voltage is lower or higher than the intermediate voltage of the power supply voltage supplied to the switching circuit based on the condition that determines the magnitude relationship with the on-resistance of the switching elements constituting the side switching circuit. inverter der, characterized in that shifting the voltage side .
As a result, a low-loss, high-speed switching element is provided, and a high-efficiency inverter is always available , even under load conditions where the lower arm-side switching element is highly efficient and under load conditions where the upper-arm side switching element is highly efficient. A device is realized.

In a second aspect of the invention, particularly in the first aspect of the invention, the control means is configured such that the on-resistance of the switching element constituting the lower arm side switching circuit is smaller than the on resistance of the switching element constituting the upper arm side switching circuit. In this condition, the average output voltage of the sine wave voltage is shifted to a lower voltage side than the intermediate voltage of the power supply voltage, and the on-resistance of the switching element constituting the upper arm side switching circuit is the lower arm side switching. The inverter device shifts an average output voltage of the sine wave voltage to a higher voltage side than an intermediate voltage of the power supply voltage under a condition of being smaller than an on-resistance of a switching element constituting the circuit .
Thus, low loss, a high speed switching element, even in the load conditions the lower arm switching element becomes high efficiency, even in the loading condition in which the switching elements of the upper arm becomes high efficiency, always high efficiency inverter A device is realized.

According to a third aspect of the invention, particularly in the second aspect of the invention, the control means further includes a current detection unit that detects an output current value, and the control unit detects the output current value detected by the current detection unit and the upper arm side switching. A comparison means for determining a magnitude relationship with a predetermined current value defined by a switching element that constitutes the circuit and the lower arm side switching circuit, and the control means is configured to determine the upper limit based on a determination result of the comparison means. This is an inverter device that determines the magnitude relationship between the on-resistance of the switching element that constitutes the arm-side switching circuit and the on-resistance of the switching element that constitutes the lower arm-side switching circuit .
As a result, a low-loss, high-speed switching element is provided, and the inverter device is always highly efficient even under load conditions in which the upper arm side switching element is highly efficient and in which the lower arm side switching element is highly efficient. Is realized.

In a fourth aspect of the invention, particularly in the third aspect of the invention, the control means shifts an average output voltage value of the sine wave voltage in accordance with the magnitude of the output current value detected by the current detection means. It is.
As a result, a low-loss, high-speed switching element is provided, and the inverter device is always highly efficient even under load conditions in which the upper arm side switching element is highly efficient and in which the lower arm side switching element is highly efficient. Is realized.

The fifth invention is an inverter device in which, in any one of the first to fourth inventions, the different types of switching elements constituting the upper arm side switching circuit and the lower arm side switching circuit are MOSFETs and IGBTs. .
As a result, an inverter device with high conversion efficiency is realized regardless of load conditions.

A sixth invention is an inverter device according to any one of the first to fourth inventions, wherein the different types of switching elements constituting the upper arm side switching circuit and the lower arm side switching circuit are GaN transistors and IGBTs. is there.
As a result, an inverter device with high conversion efficiency is realized regardless of load conditions.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a configuration diagram showing a detailed configuration in an embodiment of an inverter device according to the present invention. The AC power supplied from the AC power source 1 is temporarily converted to DC by the rectifier circuit 4 and the smoothing capacitor 5 and supplied to the inverter device 2. The inverter device 2 has a three-phase series circuit composed of switching elements on the upper arm side constituted by the switching elements 22 to 24 and switching elements 25 to 27 on the lower arm side. The interconnection point is connected to the motor 3 as a load.

  The control means 21 controls switching of the switching elements 22 to 27 so that the inverter device 2 outputs AC power that causes the motor 3 to rotate at a desired number of rotations. As a switching method, a general pulse width modulation (PWM) method in which the output voltage is controlled by the time width of the drive pulse of the element is used.

  Further, the control means 21 is provided with current detection means 28a and 28b for detecting the current flowing through the motor 3, and a switching pattern is configured by a control method for reducing loss described later based on the detected current value. And has a function of driving the switching elements 22 to 27.

  As the switching elements 22 to 24 on the upper arm side, IGBT (Insulated Gate Bipolar Transistor) semiconductor devices that are high-efficiency insulated gate bipolar transistors at high loads are used, and freewheeling diodes 22a to 24a are provided in parallel. On the other hand, as the switching elements 25 to 27 on the lower arm side, MOSFET semiconductor devices that can be switched at a higher speed than the upper arm and have high efficiency at low loads are used.

  In this MOSFET device, a diode is formed in the device because of its configuration, and therefore it is not necessary to provide a free-wheeling diode in parallel. By using switching elements with different characteristics for the upper arm and lower arm and using a drive system that matches each characteristic, it is possible to achieve high efficiency of the inverter control circuit with an inexpensive configuration. it can.

FIG. 2 is a characteristic diagram showing characteristics of the switching element used in the first embodiment of the inverter device according to the present invention. The voltage-current characteristic of IGBT which is a switching element used for an upper arm and MOSFET which is a switching element used for a lower arm is shown.

  The characteristic curve of the IGBT shows the relationship between the collector-emitter voltage Vce (sat) (ON voltage) and the collector current Ic when the IGBT is ON. In the IGBT, the larger the current, the smaller the increase in the voltage drop, which is the collector-emitter voltage Vce, and the slope of this characteristic curve consisting of the reciprocal of the resistance of the switching element becomes relatively large. The loss that occurs is reduced.

  On the other hand, regarding the characteristics of the MOSFET, the relationship between the voltage drop, which is the drain-source voltage Vds, and the drain current Id is as shown in the straight line shown in the figure. Since the slope of is substantially constant, the resistance of the element is constant regardless of the magnitude of the current.

  By superimposing the characteristics of these switching elements, it can be seen that in the case of a current smaller than the current I1 (voltage drop V1), the MOSFET has a smaller voltage drop than the IGBT, that is, the loss is small.

  On the contrary, when the current is larger than the current I1, the IGBT has a smaller voltage drop amount than the MOSFET, that is, the loss is small.

  Therefore, when the load current is smaller than I1, which is the changing point, the current flows through the MOSFET rather than the IGBT, and conversely when the load current is larger than I1, the current flows through the IGBT rather than the MOSFET. Loss per element tends to be reduced and efficiency tends to increase.

  FIG. 8 is a timing diagram showing switching timing characteristics in the PWM modulation method of the conventional inverter device. In the case of this PWM modulation method, a voltage is applied in a sine wave shape with respect to the phase angle of the rotor of the motor.

  The U-phase, V-phase, and W-phase output voltages are sine waves having a phase difference every 120 degrees. On the other hand, as shown in the figure, the magnitudes of carrier signals composed of triangular waves having a predetermined carrier frequency with respect to the sine wave voltage are compared. As a result of the comparison, when the output voltage is larger than the carrier signal, it is turned on by outputting a drive signal to the switching elements 22 to 24 of the upper arm, and conversely, the switching elements 25 to 27 of the lower arm are turned off.

  When the output voltage is lower than the carrier signal, the output is turned on by outputting a drive signal to the switching elements 25 to 27 on the lower arm, and the switching elements 22 to 24 on the upper arm are turned off. As a result, the drive waveforms of the switching elements of the U-phase upper arm, V-phase upper arm, W-phase upper arm, U-phase lower arm, V-phase lower arm, and W-phase lower arm shown on the lower side of the figure are output.

  FIG. 3 is a timing chart showing an example of switching timing characteristics of the PWM modulation method of the inverter device according to the first embodiment of the present invention.

  When the control means 21 controls the switching of the switching elements 22 to 27 according to the PWM modulation method and outputs a sine wave to the motor 3, the voltage output to the three phases (U phase, V phase, W phase) of the motor 3 is In a general inverter device, the average voltage is set to a voltage Vdc / 2 that is half the voltage of the DC portion of the inverter device, that is, the voltage across the smoothing capacitor 5, as shown in FIG. The sine wave that has been output.

  On the other hand, in the case of the inverter device 2 of the present invention, when the current value output to the motor 3 is low, it is set to a value lower than Vdc / 2 (in this case, Vdc / 8) as shown in FIG. Is done. Although the average voltage of the voltage output to the motor is lowered, the same line voltage as the waveform shown in FIG. 8 is applied to the line voltage applied between the terminals of the three-phase winding of the motor. The motor 3 performs the same operation. When the current flowing through the motor 3 is smaller than the current I1 shown in FIG. 2, it is possible to improve the efficiency of the inverter device by applying to the motor a voltage whose average voltage is reduced by this method.

  The principle will be described with reference to FIG. FIG. 4 is an example of a characteristic diagram showing a characteristic of electric energy passing through the switching elements on the upper arm side and the lower arm side of the inverter device according to Embodiment 1 of the present invention.

  As shown in FIG. 3, this characteristic diagram shows the amount of power passing through the switching elements on the upper arm side and the lower arm side when the average value of the output voltage of the inverter device 2 is set to a value lower than Vdc / 2. Show properties.

  When the average value of the output voltage is lower than Vdc / 2, the amount of power flowing to the lower arm switching elements 25 to 27 flows to the upper arm switching elements 22 to 24 for almost all average output voltage regions. Indicates that it is greater than the amount of power. This is because when the inverter device 2 is operated as described above, the on-time of the switching elements 25 to 27 of the lower arm, as seen from the driving waveform of the switching elements of FIG. Longer than the on-time. That is, since the average output voltage is low, the ON time of the switching elements 25 to 27 on the lower arm side becomes long.

  As a result, the amount of power that is the integral value of the current flowing through the MOSFET that is the lower arm is greater than the amount of power that is the integral value of the current flowing through the IGBT that is the upper arm. As a result, in this case, since the current value is lower than I1, the lower arm MOSFET is more efficient than the IGBT, so the loss of the inverter device, which is the sum of the losses of the switching elements of the upper arm and the lower arm. Can be reduced as compared with the driving method shown in FIG. 8 in which the average output voltage is Vdc / 2.

That is, the efficiency of the upper arm IGBT is η (IGBT), the efficiency of the lower arm MOSFET is η (MOSFET), the amount of power flowing through the upper arm IGBT is P (IGBT), and the amount of power flowing through the lower arm MOSFET is P When it is (MOSFET), the total loss L (TOTAL) is given by (Equation 1) shown below.
(Formula 1)
L (TOTAL) = P (IGBT) × (1−η (IGBT)) + P (MOSFET) × (1−η (MOSFET))
In this case, since η (MOSFET) is larger than η (IGBT) and P (MOSFET) is larger than P (IGBT), the total loss L (TOTAL) is P (MOSFET) and P (IGBT). ) Is reduced compared to the case where they are equal.

  FIG. 5 is a timing chart showing another example of the switching timing characteristics of the PWM modulation method of the inverter device according to the first embodiment of the present invention.

When the current value output from the inverter device 2 to the motor 3 is larger than the current I1 shown in FIG. 2, the average output voltage of the inverter device 2 is higher than Vdc / 2 (in this case, as shown in FIG. 5). Is set to 7 × Vdc / 8). The average voltage of the voltage output to the motor 3 increases, but the line voltage applied between the terminals of the three-phase winding of the motor is the same as in FIG. By applying a voltage obtained by increasing the average voltage by this method to the motor 3, the efficiency of the inverter device 2 can be improved.

The principle will be described with reference to FIG.
FIG. 6 is another example of a characteristic diagram showing the characteristics of the amount of electric power passing through the switching elements on the upper arm side and the lower arm side of the inverter device according to Embodiment 1 of the present invention.

  When the current value output to the motor is higher than I1, as shown in FIG. 5, the average value of the output voltage of the inverter device 2 is set to a value higher than Vdc / 2. When the inverter device 2 is operated as described above, as can be seen from the driving waveform of the switching element in FIG. 5, the on-time of the switching elements 22 to 24 of the upper arm is the on-time of the switching elements 25 to 27 of the lower arm. Longer than time. That is, since the average output voltage is high, the on-time of the switching elements 25 to 27 on the upper arm side becomes long.

  As a result, the amount of power that is the integral value of the current flowing through the IGBT that is the upper arm is greater than the amount of power that is the integral value of the current flowing through the MOSFET that is the lower arm. As a result, in this case, since the current value is higher than I1, the upper arm IGBT is more efficient than the MOSFET. Therefore, the inverter device 2 is the sum of the losses of the switching elements of the upper arm and the lower arm. The loss can be reduced as compared with the driving method shown in FIG. 8 where the average output voltage is Vdc / 2.

  That is, since η (IGBT) is larger than η (MOSFET) and P (IGBT) is larger than P (MOSFET), the total loss L (TOTAL) is equal to P (MOSFET) and P (IGBT). It is reduced compared to the case.

  FIG. 7 is a characteristic diagram showing switching characteristics of the output voltage with respect to the output current in the control means of the inverter device according to the first embodiment of the present invention. The control means 21 changes the average value of the three-phase AC output voltages output from the inverter device 2 based on the current values detected by the current detection means 28a and 28b. In particular, in the case of the current I1, the average value of the output voltage, which is a setting for flowing current evenly through the switching elements of the upper arm and the lower arm, is set to Vdc / 2.

  Furthermore, if the current value is larger than I1, the amount of power on the upper arm side, which becomes the load of the upper arm, is increased by increasing the average value of the output voltage accordingly, and the load of the switching element of the upper arm with high efficiency is increased. To reduce the total loss.

  Conversely, if the current value is smaller than I1, the average value of the output voltage is decreased accordingly, thereby increasing the lower arm electric energy serving as the load on the lower arm side, and the high-efficiency lower arm switching element. The load can be increased and the total loss can be reduced.

Further, in this case, P (IGBT) × (1−η (IGBT)) which is a loss generated in the IGBT of the switching element of the upper arm and P (MOSFET) which is a loss generated in the MOSFET of the switching element of the lower arm X (1-η (MOSFET)) is a substantially equal value, and the loss balance of the switching elements of the upper arm and the lower arm is maintained, so that the heat generation balance of the switching elements is maintained, and the inverter device has high reliability. Is realized.

In the first embodiment, MOSFET elements are used as lower arm switching elements 25 to 27 as low load and high efficiency switching elements, and IGBTs are used as upper arm switching elements 22 to 24 as high load and high efficiency switching elements. However, the reverse configuration, that is, the MOSFET element is used as the switching element 25-27 of the upper arm as a low-load and high-efficiency switching element, and the high-load high-efficiency switching element is I
Similar control can be performed when the GBT is used as the switching elements 22 to 24 of the lower arm.

  In this case, if the current value is larger than I1, the average value of the output voltage is decreased accordingly, thereby increasing the amount of power on the lower arm side serving as the load of the lower arm, and the lower arm with high efficiency. The load on the switching element is increased to reduce the total loss.

  On the other hand, if the current value is smaller than I1, the average value of the output voltage is increased accordingly to increase the amount of upper arm power that becomes the load on the upper arm side, and the high-efficiency switching element of the upper arm is increased. The load can be increased and the total loss can be reduced.

  In the first embodiment, a MOSFET element is used as a low-load and high-efficiency switching element, and an IGBT is used as a high-load and high-efficiency switching element. Needless to say, a semiconductor element such as a gallium nitride (GaN) transistor element may be used instead of the MOSFET, and a bipolar transistor element may be used instead of the IGBT.

  As described above, the present invention relates to an inverter device. In an inverter device using different types of switching elements such as IGBTs and MOSFETs for upper and lower arms, the inverter circuit loss is achieved by optimally controlling the switching elements. This is useful for an inverter device that is highly efficient and highly reliable.

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Inverter apparatus 3 Motor 4 Rectifier circuit 5 Smoothing capacitor 21 Control means 22-24 Upper arm side switching element 25-27 Lower arm side switching element 28a, 28b Current detection means

Claims (6)

A switching circuit composed of a plurality of upper and lower arms;
In an inverter device comprising a control means for driving the switching circuit by a PWM modulation method, and outputting a sine wave voltage ,
The switching element constituting the upper arm side switching circuit and the switching element constituting the lower arm side switching circuit are composed of different types of switching elements,
Said control means, based on the conditions that determine the ON resistance of the switching elements constituting the lower arm side switching circuit, the magnitude relation between the on-resistance of the switching elements constituting the upper arm side switching circuit, the sine wave An inverter device , wherein an average output voltage of the voltage is shifted to a low voltage side or a high voltage side from an intermediate voltage of a power supply voltage supplied to the switching circuit . The control means has an average output of the sine wave voltage under the condition that the on-resistance of the switching element constituting the lower arm side switching circuit is smaller than the on resistance of the switching element constituting the upper arm side switching circuit. The voltage is shifted to a lower voltage side than the intermediate voltage of the power supply voltage, and the on-resistance of the switching element constituting the upper arm side switching circuit is smaller than the on resistance of the switching element constituting the lower arm side switching circuit. 2. The inverter device according to claim 1, wherein an average output voltage of the sine wave voltage is shifted to a higher voltage side than an intermediate voltage of the power supply voltage under conditions . It further comprises current detection means for detecting the output current value,
The control means has a magnitude relationship between the output current value detected by the current detection means and a predetermined current value defined by switching elements constituting the upper arm side switching circuit and the lower arm side switching circuit. Having a comparing means for judging,
The control means determines a magnitude relationship between the on-resistance of the switching element constituting the upper arm side switching circuit and the on-resistance of the switching element constituting the lower arm side switching circuit based on the determination result of the comparison means. The inverter device according to claim 2 . The control means is configured to adjust the output current value detected by the current detection means according to the magnitude of the output current value.
The inverter device according to claim 3 , wherein an average output voltage value of the sinusoidal voltage is shifted . 5. The inverter device according to claim 1, wherein different types of switching elements constituting the upper arm side switching circuit and the lower arm side switching circuit are a MOSFET and an IGBT. 6. 5. The inverter device according to claim 1, wherein the different types of switching elements constituting the upper arm side switching circuit and the lower arm side switching circuit are a GaN transistor and an IGBT.