JP2007053895A - Inverter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small inverter device capable of detecting an actual value of a current or a value having correspondence relation with the actual value. <P>SOLUTION: The device is provided with a current detector (shunt resistance 15) between a lower arm switching element X and a negative side connection point 2b of a DC current source. The device is also provided with a control device 7 for calculating a product between a time when only one lower arm switching element is in an ON state and a value obtained by squaring the time by a current value to be detected by a current detector of this phase, and a product between a time when only two lower arm switching elements are in an ON state and a value obtained by squaring the time by the sum of current values to be detected by this two-phase current detector. Thus, a value having correspondence relation with the actual value current can be calculated only by a control software without adding a current circuit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inverter device that detects an effective value of current or a value correlated with the effective value.

  Conventionally, regarding current detection of an inverter device, it is known to provide a shunt resistor between the lower arm switching element and the ground to detect an instantaneous value of a phase current required for control (for example, refer to Patent Document 1). .

  FIG. 12 is a circuit diagram of a conventional inverter device and its periphery. Regarding the switching element 2 of the inverter circuit 37 of the inverter device 122, the upper arm switching element is defined as U, V, W, and the lower arm switching element is defined as X, Y, Z. The upper arm switching elements U, V, W are connected to the positive connection point 2a of the DC power supply 1, and the lower arm switching elements X, Y, Z are connected to the negative connection point 2b of the DC power supply 1, respectively. Are connected in series at the central connection point 2c. As the switching element 2, a transistor, an IGBT, or the like is used. The diode 3 constituting the inverter circuit 37 serves as a return route for the current flowing through the stator winding 28.

  A shunt resistor 15 is provided between the U-phase lower arm switching element X and the ground, a shunt resistor 16 is provided between the V-phase lower arm switching element Y and the ground, and a shunt resistor 17 is provided between the W-phase lower arm switching element Z and the ground. .

The control circuit 107 of the inverter device 122 calculates an instantaneous value of the phase current of each phase (hereinafter referred to as a lower arm current) based on the voltage from each shunt resistor. The control circuit 107 controls the switching element 2 constituting the inverter circuit 37 based on the calculated phase current value, rotation speed command signal (not shown), etc., and switches the DC voltage from the battery 1 by PWM modulation. As a result, an alternating current is output to the stator winding 28 constituting the motor 30. Then, the rotor 29 is driven.
Japanese Unexamined Patent Publication No. 2003-209976 (page 21, FIG. 14)

  When a shunt resistor is provided as a current sensor between the lower arm switching element and the ground, the instantaneous value of the phase current is calculated, but the effective value current or a current correlated with the effective value is not detected. . Therefore, it is impossible to detect power loss and heat generation of a current detector such as a shunt resistor provided as a current sensor. Furthermore, it is impossible to detect the effective value current of the current of the DC power supply line from the DC power supply (hereinafter referred to as DC current) or a current correlated with the effective value. Therefore, power loss and heat generation due to the internal resistance of the DC power supply cannot be detected.

  Moreover, the addition of an electric circuit that converts the instantaneous value of current into an effective value, the addition of a current sensor to the DC power supply line, and the like increase the size of the inverter device.

  The present invention solves such a conventional problem, and an object of the present invention is to provide an inverter device that is small and can detect the effective values of the lower arm current and the direct current or values correlated with the effective values.

  In order to solve the above problems, an inverter device of the present invention includes a circuit in which an upper arm switching element connected to a positive connection point of a DC power source and a lower arm switching element connected to a negative connection point are connected in series. An inverter circuit comprising two or three phases, connecting a central connection point connecting the upper arm switching element and the lower arm switching element to the load, and switching the DC voltage of the DC power supply to output an AC current to the load; Detected by the current detector at a time when the current arm and the lower arm switching element of the phase including the current detector are ON between the central connection point and the negative connection point of at least one phase. And a control device for calculating a product of the squared current value.

  With the above configuration, it is possible to calculate a value having a correlation with the effective value of the lower arm current of the phase including the current detector with only the control software without adding an electric circuit. Then, the effective value itself can be calculated by performing the square root operation by dividing by the calculation target time.

  In the case of a three-phase inverter circuit, a current detector is provided between the central connection point and the negative connection point of at least two phases, and the lower arm switching element of only one phase is turned on among the phases having the current detector. Product of the current time and the value obtained by squaring the current value detected by the current detector of the phase at the time, and the lower arm switching element of only two phases of the phases equipped with the current detector is ON And a control device that calculates the product of the current time and the value obtained by squaring the sum of the current values detected by the two-phase current detector at that time.

  With the configuration described above, it is possible to calculate a value having a correlation with the effective value of the direct current between the inverter circuit and the direct-current power source with only control software without adding an electric circuit. Then, the effective value itself can be calculated by performing the square root operation by dividing by the calculation target time.

  Therefore, it is possible to realize an inverter device that is small and can detect the effective value of the lower arm current and the direct current or a value correlated with the effective value.

  The inverter device of the present invention is small without adding a special circuit, and is correlated with the effective value or effective value of the lower arm current and the current of the DC power supply line from the instantaneous current value between the lower arm switching element and the ground. The value can be detected, and the power loss and heat generation of the current detector and the DC power source can be detected.

  According to a first aspect of the present invention, there is provided a circuit in which an upper arm switching element connected to a positive connection point of a DC power source and a lower arm switching element connected to a negative connection point are connected in series with two or three phases. An inverter circuit that outputs an alternating current to the load by switching a direct current voltage of a direct current power source by connecting a central connection point connecting the switching element and the lower arm switching element to the load; and at least one phase of the central connection point; A current detector, a time when the lower arm switching element of the phase including the current detector is ON, and a value obtained by squaring the current value detected by the current detector at that time And a control device for calculating the product of

  With the above configuration, it is possible to calculate the value that correlates with the effective value of the lower arm current with only control software without adding an electric circuit, and it is compact without adding a special circuit and effective for the lower arm current. An inverter device capable of detecting a value correlated with the value can be realized.

The second invention further calculates the effective value of the lower arm current based on the calculation result in the inverter device of the first invention. Thereby, it is possible to realize a small-sized inverter device that can detect the effective value of the lower arm current.

  According to a third invention, in the inverter device of the first or second invention, the current detector is a shunt resistor. As a result, it becomes possible to detect power loss and heat generation of the shunt resistor through which a current having a large effective value in a rectangular wave shape with a high peak can be detected, which can contribute to improvement in reliability.

  According to a fourth invention, in the inverter device according to the first to third inventions, the calculation is performed only for one phase. In the case of two phases, a half-wave current having the same waveform flows in each phase. Therefore, since the same calculation result is obtained for both phases, it is sufficient to calculate only for one phase. In the case of three phases, since the three phases are balanced, the phases differ by 120 degrees, but currents of the same waveform flow. Therefore, since the same calculation result is obtained for all three phases, only one phase needs to be calculated. Thereby, the calculation burden can be reduced.

  A fifth invention comprises a three-phase circuit in which an upper arm switching element connected to a positive connection point of a DC power source and a lower arm switching element connected to a negative connection point are connected in series, An inverter circuit that outputs an alternating current to the load by switching the DC voltage of the DC power supply by connecting the central connection point connecting the lower arm switching element to the load, and at least a two-phase central connection point and a negative connection point Between the current detector and the time during which the lower arm switching element of only one of the phases equipped with the current detector is ON, and the current value detected by the current detector of the phase at that time is 2 The product of the squared value and the time when the lower arm switching element of only two phases among the phases equipped with the current detector is ON, and the current detector of the two phases at that time. It is obtained by a control device for calculating the product of the squared value of the sum of the current value.

  With the configuration described above, it is possible to calculate a value having a correlation with the effective value of the direct current that is the current of the direct current power supply line by using only the control software without adding an electric circuit. Therefore, it is possible to realize an inverter device that is small and can detect a value correlated with the effective value of the DC current without adding a special circuit such as a current sensor to the DC power supply line.

  In a sixth aspect of the present invention, an effective value of a direct current flowing between the inverter circuit and the direct current power source is further calculated based on a calculation result in the inverter device of the fifth aspect of the invention. Thereby, it is possible to realize an inverter device that is small and can detect the effective value of the DC current without adding a special circuit such as a current sensor to the DC power supply line.

  According to a seventh aspect, in the inverter device according to the fifth or sixth aspect, the current detection by the current detector is performed at a time when all the lower arm switching elements are ON. As a result, a slight error occurs, but it is easy to secure time for current detection.

  According to an eighth aspect of the invention, in the inverter device of the fifth to seventh aspects of the invention, the calculation is performed over a phase width of 120 degrees. At a phase width of 120 degrees, it is possible to grasp the tendency of a round of the phase width of 360 degrees of the current change that varies depending on the phase due to torque fluctuations, etc., so that the calculation can be performed quickly.

  According to a ninth aspect, in the inverter device according to the fifth to seventh aspects, the calculation is performed over one rotation of the motor. Thereby, an accurate calculation result including current fluctuation due to torque fluctuation over one rotation of the motor can be obtained.

A tenth aspect of the invention is the inverter device of the fifth to seventh aspects of the invention, wherein the current detector is provided only in two phases. When the effective value of the current is obtained, if the phase range is specified, it is possible to provide only two phases without providing each of the three phases. Thereby, a current detector can be reduced.

  According to an eleventh aspect of the invention, in the inverter device of the tenth aspect of the invention, the calculation is performed over a phase width of 120 degrees in a specific phase. The effective value of the current can be obtained within this range. Thereby, the calculation burden can be reduced.

  A twelfth aspect of the invention is the inverter device according to the first to eleventh aspects of the invention, which is mounted on a vehicle. Since it is small and can detect the effective value of the direct current or a value correlated with the effective value, it can contribute to a reduction in size and weight that is important as a vehicle-mounted device.

  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 shows an electric circuit diagram of the inverter device according to Embodiment 1 of the present invention. The difference from FIG. 12, which is an electric circuit diagram of a conventional inverter device, is that the control circuit 107 is the control circuit 7 and the inverter device 122 is the inverter device 22. The same reference numerals are used for the same portions. Also, the diodes connected in parallel with the upper arm switching elements U, V, W and the lower arm switching elements X, Y, Z are defined as 3U, 3V, 3W and 3X, 3Y, 3Z, respectively. The upper arm switching elements U, V, W are connected to the positive connection point 2a of the DC power supply 1, and the lower arm switching elements X, Y, Z are connected to the negative connection point 2b of the DC power supply 1, respectively. Are connected in series at the central connection point 2c.

  The control circuit 7 is connected to the upper arm switching elements U, V, W and the lower arm switching elements X, Y, Z by connection lines 18 and controls each switching element. When the switching element is an IGBT or a power MOSFET, the gate voltage is controlled. When the switching element is a power transistor, the base current is controlled.

  A shunt resistor 15 is provided between the U-phase lower arm switching element X and the ground, a shunt resistor 16 is provided between the V-phase lower arm switching element Y and the ground, and a shunt resistor 17 is provided between the W-phase lower arm switching element Z and the ground. . The control circuit 7 calculates the instantaneous value of the phase current of each phase based on the voltage from each shunt resistor. Based on the calculated phase current, rotation speed command signal (not shown), etc., the switching element 2 constituting the inverter circuit 37 is controlled, and the DC voltage from the battery 1 is switched by PWM modulation, whereby the AC current Is output to the stator winding 28 constituting the motor 30.

  The control circuit 7 calculates the effective value of the lower arm current or a value correlated with the effective value based on the instantaneous values of the switching and phase currents. This will be described below using a case where a sinusoidal alternating current is output as an example.

  FIG. 2 is an example of a duty characteristic diagram of each phase output of the inverter device for sine wave drive, and shows a case of three-phase modulation. In this characteristic diagram, a U-phase terminal voltage 41, a V-phase terminal voltage 42, and a W-phase terminal voltage 43 are shown. These terminal voltages are realized by duty (%) indicated on the vertical axis by PWM modulation.

FIG. 3 is a timing chart of switching within the carrier period of the three-phase modulation, and an example of ON / OFF of the upper arm switching elements U, V, W and the lower arm switching elements X, Y, Z within the carrier period. Is shown. This is generally realized by a triangular wave and a timer function of a microcomputer. However, in order to simplify the display, a dead time for preventing a short circuit between the upper arm switching element and the lower arm switching element is omitted.

  3 is a timing chart in the vicinity of the point α in FIG. As shown in FIG. 3, switching of each switching element has four mode periods (a), (b), (c), and (d), and an electric circuit diagram for explaining a current path in each period is shown in FIG. To FIG.

  In the period (a) shown in FIG. 4, all the upper arm switching elements U, V, W are OFF, and all the lower arm switching elements X, Y, Z are ON. U-phase current iU and V-phase current iV flow from the diodes 3X and 3Y in parallel with the lower arm switching elements X and Y to the stator winding 28, respectively, and the W-phase current iW flows from the stator winding 28 to the lower arm switching element. It flows out to Z. That is, current circulates between the lower arm and the motor 30. Therefore, power is not supplied from the battery 1 to the inverter circuit 37.

  In the period (b) shown in FIG. 5, the upper arm switching element U is ON, and the lower arm switching elements Y and Z are ON. U-phase current iU flows from upper arm switching element U to stator winding 28, V-phase current iV flows from diode 3Y in parallel with lower arm switching element Y to stator winding 28, and W-phase current iW is fixed. It flows from the child winding 28 to the lower arm switching element Z. Therefore, the battery 1 is in an energized state in which power is supplied from the battery 1 to the inverter circuit 37. At this time, a U-phase current flows through the power supply line.

  In the period (c) shown in FIG. 6, the upper arm switching elements U and V are ON, and the lower arm switching element Z is ON. U-phase current iU and V-phase current iV flow from upper arm switching elements U and V to stator winding 28, respectively, and W-phase current iW flows from stator winding 28 to lower arm switching element Z. Therefore, the battery 1 is in an energized state in which power is supplied from the battery 1 to the inverter circuit 37. A W-phase current flows through the power supply line.

  In the period (d) shown in FIG. 7, all the upper arm switching elements U, V, W are ON, and all the lower arm switching elements X, Y, Z are OFF. U-phase current iU and V-phase current iV flow from upper arm switching elements U and V to stator winding 28, respectively, and W-phase current iW flows from stator winding 28 to diode 3W in parallel with upper arm switching element W. Is flowing into. That is, current circulates between the upper arm and the motor 30. Therefore, power is not supplied from the battery 1 to the inverter circuit 37.

  FIG. 8 shows the lower arm current due to the above switching. The positive side indicates the current that flows out of the stator winding 28, and the negative side indicates the current that flows into the stator winding 28.

  The lower arm switching element X is ON only in the period (a). At this time, the U-phase current iU flows to the stator winding 28 in the lower arm switching element X.

  The lower arm switching element Y is ON in the periods (a) and (b). At this time, the V-phase current iV flows to the stator winding 28 in the lower arm switching element Y.

  The lower arm switching element Z is ON in the period (a), the period (b), and the period (c). At this time, the W-phase current iW flows from the stator winding 28 to the lower arm switching element Z.

Here, the product of the time during which the lower arm switching element is ON and the value obtained by squaring the current value detected by the shunt resistor at the time is calculated in the first half and the second half in the carrier period,
By dividing the sum by the time of the carrier cycle, a value correlated with the effective value of the lower arm current in the carrier cycle can be obtained. Alternatively, the calculation may be performed only in the first half or the second half of the carrier period, and the value may be divided by the half of the carrier period.

  Here, the value having a correlation with the effective value is a value obtained by squaring the effective value. Therefore, the power consumption of this shunt resistor can be calculated by multiplying this value by the resistance value of the shunt resistor through which this current flows. Further, heat generation can be estimated from the characteristics of the power consumption and the shunt resistance.

  The U-phase current iU, the V-phase current iV, and the W-phase current iW can be detected by the shunt resistor 15, the shunt resistor 16, and the shunt resistor 17, respectively. If the time during which each lower arm switching element is ON is measured. Usually, a separate electric circuit is required. However, since the control circuit 7 controls the switching element 2 constituting the inverter circuit 37, the ON / OFF status and the ON time of the upper arm switching element and the lower arm switching element are already known. In addition, the carrier cycle has been grasped. For this reason, the control circuit 7 does not need to measure the carrier period during which each lower arm switching element is ON.

  Therefore, the control circuit 7 can easily calculate the product of the time when the lower arm switching element is ON and the value obtained by squaring the current value detected by the shunt resistor at that time without adding an electric circuit. it can. Then, the value correlated with the effective value of the lower arm current is calculated over the period to be calculated, the sum of them is obtained, and the effective value is squared, that is, the effective value by dividing by the time of the period. Can be obtained. Also, the effective value itself can be obtained by calculating the above-mentioned calculated value to the 1/2 power, that is, the square root.

  Therefore, it is possible to obtain an inverter device that is small and can detect the effective value of the lower arm current or a value correlated with the effective value. Then, using the effective value of the lower arm current or a value correlated with the effective value, output adjustment such as output limitation or stop can be performed to suppress heat generation of the shunt resistor and improve reliability. Further, since the current of the inverter circuit is a rectangular wave current having a large peak value, the effective value is large, and the power loss and heat generation of the shunt resistor are large. Therefore, this method can be used effectively. The present invention can be applied not only to the shunt resistor but also to various elements and components provided in the current flow path.

  In the above embodiment, when a three-phase circuit is provided in which an upper arm switching element connected to the positive connection point of the DC power source and a lower arm switching element connected to the negative connection point are connected in series. Explained. In the case where two phases are provided, for example, a circuit in a form in which W of the upper arm switching element W, the diode 3W, the lower arm switching element Z, the diode 3Z, the shunt resistor 17, and the stator winding 28 is eliminated can be considered. In this case, single-phase alternating current flows through the stator winding 28. Moreover, as a load, a transformer, a single phase motor, etc. can be considered. The waveform corresponding to FIG. 2 is only one of the U-phase terminal voltage 41, the V-phase terminal voltage 42, and the W-phase terminal voltage 43.

  In the case of two phases, a half-wave current having the same waveform flows in each phase. Therefore, since the same calculation result is obtained for both phases, it is sufficient to calculate only for one phase. In the case of three phases, since the three phases are balanced, the phases are 120 degrees different from each other, but the same waveform current flows. Therefore, since the same calculation result is obtained for all three phases, only one phase needs to be calculated. Thereby, the calculation burden can be reduced.

In the above embodiment, the motor is not specified, but an induction motor, a sensorless DC brushless motor, or the like may be used. Although PWM modulation has been described for three-phase modulation, two-phase modulation can be similarly applied. Moreover, although the case where a sinusoidal alternating current was output was demonstrated,
The present invention can also be applied to a 120-degree conduction method, PAM modulation, and the like. Although an example in which the instantaneous value of the current from the shunt resistor is directly input to the control circuit 7 is shown, an operational amplifier that performs signal amplification, voltage shift, and the like may be provided between the shunt resistor and the control circuit 7.

  Further, the current detector is not limited to these shunt resistors, and other current sensors such as those using a Hall element or using a forward voltage of a diode may be used. In addition, the current detector may be incorporated in the inverter circuit, or may be provided between the central connection point and the lower arm switching element.

(Embodiment 2)
A method of calculating the effective value of the direct current flowing between the battery 1 and the inverter device 22 or a value correlated with the effective value based on the switching of the lower arm and the lower arm current will be described.

  FIG. 9 shows an example of a direct current in the carrier cycle of the example shown in the first embodiment. In the period (a), current does not flow because the current circulates between the lower arm and the motor 30. In the period (b), the U-phase current iU flows, and in the period (c), the W-phase current iW flows. In the period (d), current does not flow because the current circulates between the upper arm and the motor 30.

  This is the same as the result of obtaining the sum of the plus current and minus current in FIG. In the period (a), the sum of the currents of the three phases is zero. In the period (b), as shown in FIG. 5, the lower arm switching elements Y and Z are ON, and the sum of the W-phase current iW and the V-phase current iV becomes the U-phase current iU. In the period (c), as shown in FIG. 6, only the lower arm switching element Z is ON, and the W-phase current iW flows.

FIG. 10 shows an enlarged view of the time axis of FIG. Here, τ1 * iU ² + τ2 * iW ² is performed in the first half and the second half in the carrier period, and the sum is divided by the time of the carrier period, thereby correlating with the effective value of the direct current in the carrier period. Can be requested. The calculation may be performed only in the first half or the second half of the carrier period, and the value may be divided by the half of the carrier period. Here, the value having a correlation with the effective value is a value obtained by squaring the effective value. Therefore, the power consumption of this resistor can be calculated by multiplying this value by the resistance value of the resistor through which this current flows. For example, power loss and heat generation due to the internal resistance of the battery 1 can be calculated.

  iV and iW can be detected by the shunt resistor 16 and the shunt resistor 17, but if the time τ1 from t1 to t2, the time τ2 from t2 to t3, the time τ2 from t4 to t5, and the time τ1 from t5 to t6 are measured, A separate electric circuit is required.

  However, since the control circuit 7 controls the switching element 2 constituting the inverter circuit 37, the ON / OFF status and the ON time of the upper arm switching element and the lower arm switching element are already known. In addition, the carrier cycle has been grasped. That is, τ1, which is the simultaneous ON time of the lower arm switching elements Y and Z, τ2, which is the ON time of the lower arm switching element Z, and the carrier period τ are already known. Therefore, the control circuit 7 does not need to measure the time τ1 from t1 to t2, the time τ2 from t2 to t3, the time τ2 from t4 to t5, the time τ1 from t5 to t6, and the carrier period τ.

Therefore, the control circuit 7 calculates the product of the time during which only one lower arm switching element is ON and the square of the current value detected by the shunt resistance of the phase at that time, and only two lower arm switching elements. Can be easily calculated without adding an electric circuit, and the product of the time during which the signal is ON and the square of the current value detected by the shunt resistance of the phase at that time. Then, over the period in which the effective value of DC current or a value correlated with the effective value is calculated, the above calculation is performed, the sum of them is obtained, and the effective value is squared by dividing by the time of the period. That is, a value having a correlation with the effective value can be obtained. Further, the effective value itself can be obtained by multiplying the calculated value by the power of 1/2, that is, by obtaining the square root.

  Therefore, it is possible to obtain an inverter device that is small and can detect an effective value of a direct current or a value correlated with the effective value. Then, using the effective value of these DC currents or a value correlated with the effective value, output adjustment such as output limitation and stop can be performed to improve reliability. Targets include suppression and protection of heat generation due to the internal resistance of the battery 1, suppression and protection of resistance generated in series with the DC power supply line, and when a current smoothing capacitor is provided in parallel with the battery 1, the smoothing capacitor There are heat suppression and protection.

  In the above embodiment, the current value is detected by the current detector in the period (b) and the period (c). That is, the current value is detected by the current detector of the two phases during the period (b) during which the lower arm switching elements Y and Z of only the two phases are ON. Further, the current value is detected by the current detector for the phase during the period (c) during which the lower arm switching element Z for only one phase is ON.

However, it may be difficult to detect the current value by the current detector in the periods (b) and (c) where the time is short. Therefore, since the change in each phase current is small within a short carrier period, the current value is set by the current detector during the period (a) shown in FIG. 8, that is, when all the lower arm switching elements are ON. It is conceivable to detect. As a result, a slight error occurs, but it is easy to secure time for current detection. In the above embodiment, the motor is not specified, but any of an induction motor, a sensorless DC brushless motor, and the like may be used. Although PWM modulation has been described for three-phase modulation, two-phase modulation can be similarly applied. Moreover, although the case where a sinusoidal alternating current was output was demonstrated, it is applicable also to a 120 degree | times energization system, PAM modulation, etc. Although an example in which the instantaneous value of the current from the shunt resistor is directly input to the control circuit 7 is shown, an operational amplifier that performs signal amplification, voltage shift, and the like may be provided between the shunt resistor and the control circuit 7. Further, the current sensor is not limited to the shunt resistor.

  As described above, the case where the shunt resistors are provided for the three phases has been described. However, as long as the V-phase current iV and the W-phase current iW can be detected in the above example, it is sufficient that the two-phase current can be detected. In this case, however, the detectable period is limited. As the circuit, a circuit in which the shunt resistor 15 is omitted can be considered.

(Embodiment 3)
FIG. 11 shows the relationship between the phase and the U-phase phase current (iU) 51, the V-phase phase current (iV) 52, and the W-phase phase current (iW) 53. The current change due to the phase makes a round with a phase width of 360 degrees. Further, these phase currents appear in the direct current as shown in FIG. Therefore, by calculating the effective value of DC current or a value correlated with the effective value for every 360 degrees of phase width, the effective value change related to the phase caused by torque fluctuation etc. is made a round, and an accurate value is obtained. It is done. On the other hand, the phase width of 120 degrees is repeated three times at a phase width of 360 degrees as one break of the current change tendency. It is possible to grasp the tendency of the phase width of 360 degrees of the current change that varies depending on the phase due to torque fluctuation or the like. Therefore, the calculation can be quickly performed by calculating the effective value of the direct current or a value correlated with the effective value for each phase width of 120 degrees.

In a motor having a magnet rotor, such as a sensorless DC brushless motor, the phase width of 360 degrees and one rotation of the magnet rotor do not necessarily match due to the number of poles of the magnet rotor. Therefore, by calculating the effective value of the DC current over one rotation of the magnet rotor, that is, the motor, or a value correlated with the effective value, an accurate DC current including current fluctuation due to torque fluctuation over one rotation of the motor is obtained. The effective value of or the value correlated with the effective value can be obtained.

  Consider a detectable period in the circuit in which the shunt resistor 15 is omitted so that only two-phase currents described in the second embodiment, that is, the V-phase current iV and the W-phase current iW can be detected. The range in which this circuit can detect the effective value of the direct current or a value correlated with the effective value is the same as that in the second embodiment, and is around time α in FIG. That is, from the intersection of the W-phase terminal voltage 43 and the V-phase terminal voltage 42 to the intersection of the U-phase terminal voltage 41 and the V-phase terminal voltage 42.

  Unlike the second embodiment, when a U-phase current iU and a V-phase current iV flow as direct currents, from the intersection of the U-phase terminal voltage 41 and the W-phase terminal voltage 43 on the left side of the above, the W-phase terminal Up to the intersection of the voltage 43 and the V-phase terminal voltage 42. Both of these periods are equal, and the phase is 60 degrees. The direct current is a repetition of the current pattern at 120 degrees in this specified phase range. Thereby, the calculation burden can be reduced.

  The phase current of each phase in FIG. 11 is in phase with the terminal voltage of each phase in FIG. 2, but this is for convenience of drawing and does not always match.

(Embodiment 4)
An inverter device mounted on a vehicle is required to be small and light. A battery is used as a drive source. And it may be exposed to high temperature environment. Therefore, it is effective to apply and mount the inverter device of the present invention on a vehicle.

  As described above, since the inverter device according to the present invention is small and can detect the effective value of current or a value correlated with the effective value, it can be applied to various consumer products, various industrial devices, and various mobile devices. it can. The load can be applied to AC devices other than motors.

Electrical circuit diagram of inverter device according to Embodiment 1 of the present invention Duty characteristic diagram of each phase output of inverter device for sine wave drive Switching timing chart within carrier cycle Electrical circuit diagram showing current path in period (a) Electrical circuit diagram showing current path in period (b) Electrical circuit diagram showing current path in period (c) Electrical circuit diagram showing current path in period (d) Explanatory diagram of lower arm current calculation according to Embodiment 1 of the present invention DC current diagram in carrier cycle according to Embodiment 2 of the present invention Explanatory drawing of DC current calculation concerning Embodiment 2 of this invention Characteristics explanatory diagram of phase and each phase current waveform according to Embodiment 3 of the present invention Electric circuit diagram of conventional inverter device with current detector on lower arm

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery 2 Switching element 2a Positive side connection point 2b Negative side connection point 2c Center connection point 3 Diode 7 Controller 15 Current detection shunt resistance of U phase lower arm 16 Current detection shunt resistance of V phase lower arm 17 W phase lower Shunt resistor for arm current detection 22 Inverter device 30 Motor 37 Inverter circuit U, V, W Upper arm switching element X, Y, Z Lower arm switching element

Claims (12)

A circuit in which an upper arm switching element connected to a positive connection point of a DC power source and a lower arm switching element connected to a negative connection point are connected in series is provided in two or three phases, and the upper arm switching element and the lower arm An inverter circuit that outputs an alternating current to the load by switching a direct current voltage of the direct current power source by connecting a central connection point connecting the arm switching elements to the load, at least one phase of the central connection point and the negative connection point A value obtained by squaring the current detector and the time when the lower arm switching element of the phase including the current detector is ON between the side connection point and the current value detected by the current detector at that time An inverter device comprising: a control device that calculates a product of The control device is based on a calculation result of a product of a time when the lower arm switching element of the phase including the current detector is ON and a value obtained by squaring the current value detected by the current detector at the time. Furthermore, the inverter apparatus of Claim 1 which calculates the effective value of the electric current which flows into a current detector. The inverter device according to claim 1, wherein the current detector is a shunt resistor. The inverter device according to any one of claims 1 to 3, wherein the calculation is performed for only one phase. A three-phase circuit comprising a series connection of an upper arm switching element connected to a positive connection point of a DC power source and a lower arm switching element connected to a negative connection point, the upper arm switching element and the lower arm switching element And an inverter circuit that outputs an alternating current to the load by switching a DC voltage of the DC power supply, and at least two phases of the central connection point and the negative connection point. Between the current detector and the time when the lower arm switching element of only one of the phases including the current detector is ON, and the current value detected by the current detector of the phase at that time And the time when the lower arm switching element of only two phases among the phases equipped with the current detector is ON and the time before the two phases Inverter apparatus characterized by comprising a control device for calculating the product of the squared value of the sum of the current value detected by the current detector. The control device includes a time when the lower arm switching element of only one phase is turned on among the phases including the current detector and a value obtained by squaring the current value detected by the current detector of the phase at the time. And the sum of the current value detected by the current detector of the two phases at the time when the lower arm switching element of only two phases of the phases equipped with the current detector is ON The inverter device according to claim 5, wherein an effective value of a direct current flowing between the inverter circuit and the direct current power source is calculated based on a calculation result of a product of the squared value. The inverter device according to claim 5, wherein the time is replaced with a time during which all the lower arm switching elements are ON. The inverter device according to any one of claims 5 to 7, wherein the operation is performed over a phase width of 120 degrees. The inverter device according to any one of claims 5 to 7, wherein the calculation is performed over one rotation of the motor when the load is a motor. The inverter device according to claim 5, wherein the current detector is provided only in two phases. The inverter device according to claim 10, wherein the calculation is performed over a phase width of 120 degrees in a specific phase. The inverter apparatus as described in any one of Claims 1-11 mounted in a vehicle.