JP2007028836A - Inverter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized inverter device that can detect an effective value of a direct current or a value correlated with the effective value. <P>SOLUTION: As shown in Fig.1, the inverter device comprises a current detector (shunt resistor 10) between an inverter circuit and a DC power supply, and also comprises a control circuit 7 that operates a product of a time when only one of upper arm switching elements (U, V, and W) is turned on and a value obtained by multiplying a current value detected by the current detector, and a product of the time when the one switching element is turned on and the value obtained by multiplying the current value detected by the current detector. By this, the value correlated with a current of the effective value can be calculated by using only control software. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  Conventionally, with regard to detection of direct current from a direct current power supply, there is a method in which a current sensor is provided in the power supply line from the direct current power supply to the inverter device to detect the peak value of direct current and the average value by integration of a resistor and a capacitor. It is known (see, for example, Patent Document 1).

  FIG. 11 is a circuit diagram of a conventional inverter device and its periphery. The control circuit 108 of the inverter device 121 controls the switching element 2 constituting the inverter circuit 37 based on a rotation speed command signal (not shown) and the like, and switches the DC voltage from the battery 1 by PWM modulation. An alternating current is output to the stator winding 28 constituting the motor 30. Then, the rotor 29 is driven. A current sensor 6 is provided between the battery 1 and the inverter circuit 37.

  For the switching element 2, the upper arm switching element is defined as U, V, W, and the lower arm switching element is defined as X, Y, Z. 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.

  The instantaneous value of the direct current detected by the current sensor 6 is converted into an average current by an average current detection circuit 11 configured by an operational amplifier, an integration circuit including a resistor and a capacitor, and the like, and is transmitted to the control circuit 108. Then, the power consumption of the inverter device 121 is calculated from the product of the voltage of the battery 1 and the average current. The power consumption calculation is indispensable for limiting the power consumption of the inverter device 121 so as not to exceed the allowable value of the battery 1 that is a DC power supply.

The instantaneous value of the direct current detected by the current sensor 6 is converted to a low level signal when the peak current detection circuit 12 configured by an operational amplifier or the like exceeds an allowable value, and is sent to the control circuit 108. Communicated. When the signal becomes a low level, the operation of the switching element 2 is stopped and the switching element 2 is prevented from being damaged.
Japanese Patent Laid-Open No. 7-67248 (5th page, FIGS. 1 and 2)

  In the conventional method of detecting a direct current from a direct current power source, an average current and a peak current are detected. However, the effective value current or the current correlated with the effective value is not detected. Therefore, power loss and heat generation due to the internal resistance of the DC power source cannot be detected. In addition, when the current sensor is composed of a shunt resistor, the power loss and heat generation of the shunt resistor cannot be detected. Furthermore, if an electric circuit capable of converting an instantaneous value of a direct current into an effective value is added, the inverter device becomes large.

  An object of the present invention is to solve such a conventional problem, and to provide an inverter device that is small in size and can detect an effective value of a direct current or a value correlated with an effective value.

  In order to solve the above-mentioned problem, the inverter device of the present invention includes a current detector between the DC power source and the time when only one upper arm switching element is ON and is detected by the current detector at that time. And the product of the time when only one lower arm switching element is ON and the value obtained by squaring the current value detected by the current detector at that time. It is provided with a control device for calculating.

  With the above configuration, it is possible to calculate a value having a correlation with the effective current only with the control software without adding an electric circuit. Further, the effective value itself can be calculated by performing a square root operation. Therefore, it is possible to realize an inverter device that is small and can detect an effective value of a direct current or a value correlated with the effective value.

  The inverter device of the present invention is small in size without adding a special circuit, and can detect an effective value of a direct current or a value correlated with an effective value.

  The first invention comprises two or more phases of a circuit in which an upper arm switching element connected to the positive side of a DC power source and a lower arm switching element connected to the negative side are connected in series, and the upper arm switching element and the lower arm switching An inverter circuit that outputs an alternating current to the load by switching the DC voltage of the DC power supply by connecting the connection point with the element to the load, a current detector between the DC power supply and the inverter circuit, and a plurality of upper arms The product of the time when only one of the switching elements is ON and the value obtained by squaring the current value detected by the current detector at that time, and only one of the plurality of lower arm switching elements is ON And a control device that calculates the product of the current time and the value obtained by squaring the current value detected by the current detector at that time.

  With the above configuration, it is possible to calculate a value that correlates with the rms current with only control software without adding an electric circuit, and a compact inverter device that can detect a value that correlates with the rms value of the DC current is realized. it can.

  According to a second invention, in the inverter device of the first invention, a time when only one of the upper arm switching elements is ON and a value obtained by squaring the current value detected by the current detector at the time. Based on the product and the calculation result of the product of the time when only one of the lower arm switching elements is ON and the value obtained by squaring the current value detected by the current detector at that time, further DC A control device for calculating an effective value of a direct current flowing between the power source and the power source is provided. As a result, a small-sized inverter device that can detect the effective value of the direct current can be realized.

  According to a third aspect, in the inverter device according to the first or second aspect, 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 fourth invention, in the inverter device according to the first to third inventions, the calculation is executed 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.

  According to a fifth invention, in the inverter device of the first to fourth inventions, the current detector is a shunt resistor. As a result, it becomes possible to detect power loss and heat generation of the shunt resistor in 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.

  A sixth invention is an inverter device according to the first to fifth inventions, which is mounted on a vehicle. Thereby, since it is small and can detect the effective value of DC current or a value correlated with the effective value, it can contribute to the 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. 11, which is an electrical circuit diagram of a conventional inverter device, is that the average current detection circuit 11 and the peak current detection circuit 12 are deleted, the control circuit 108 becomes the control circuit 7, and the inverter device 121 becomes the inverter device 21. It is a point. Further, the current sensor 6 is replaced with a shunt resistor 10 as a current detector, and an instantaneous value of the direct current is directly input to the control circuit 7. The same reference numerals are used for other identical 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 control circuit 7 of the inverter device 21 controls the switching element 2 constituting the inverter circuit 37 based on a rotation speed command signal (not shown) and the like, and switches the DC voltage from the battery 1 by PWM modulation, An alternating current is output to the stator winding 28 constituting the motor 30. That is, 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 the connection line 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.

  The instantaneous value of the direct current detected by the shunt resistor 10 is transmitted to the control circuit 7 and used for determination for protecting the switching element 2 and the like. Further, the control circuit 7 calculates an effective value of the direct current flowing between the battery 1 and the inverter device 21 or a value correlated with the effective value based on the instantaneous values of the switching and the direct current.

  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 and V-phase current 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 W-phase current flows from the stator winding 28 to the lower arm switching element Z. ing. 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. The U-phase current flows from the upper arm switching element U to the stator winding 28, the V-phase current flows from the diode 3Y in parallel with the lower arm switching element Y to the stator winding 28, and the W-phase current flows to the stator winding. 28 flows out 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. The U-phase current and the V-phase current flow from the upper arm switching elements U and V to the stator winding 28, respectively, and the W-phase current flows from the stator 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. 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 and V-phase current flow from upper arm switching elements U and V to stator winding 28, respectively, and W-phase current flows from stator winding 28 to diode 3W in parallel with upper arm switching element W. Yes. 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 an example of a direct current in the carrier cycle according to the above. In the period (a) and the period (d), the U-phase current iU flows in the period (b), and the W-phase current iW flows in the period (c). Since the current is a rectangular wave having a large peak value, the effective value is large, and the power loss and heat generation of the shunt resistor 10 are large.

  As shown in FIGS. 3 to 7, the power line current, that is, the presence or absence of a direct current, and the energization time can be known when the upper arm switching elements U, V, W are turned on and off. When the upper arm switching element does not have an ON phase, it does not flow (not energized). When only one phase is ON, the current of that phase flows (energized). When the two phase is ON, the current of the remaining phase flows (energized). It does not flow when all three phases are ON (not energized).

  Here, when the upper arm switching element 2 phase is ON, since the lower arm switching elements of the remaining phases are ON, it can be rephrased as follows. That is, when only one phase is turned on among the upper arm switching elements provided for a plurality of phases, a current flows (of the relevant phase), and when only one phase is turned on among the lower arm switching elements provided for the plural phases (of the relevant phase). Current flows.

FIG. 9 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 DC current in the carrier period. The value can be determined. 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.

Although iU and iW can be detected by the shunt resistor 10, the time τ1, t2 to t2 from t1 to t2
If a time τ2 of 3, a time τ2 of t4 to t5, and a time τ1 of 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, the ON time τ1 of the upper arm switching element U, the ON time τ2 of the lower arm switching element Z, and the carrier period τ have been grasped. 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 determines the product of the time during which only one of the upper arm switching elements is ON and the square of the current value detected by the shunt resistor 10 at that time, and one of the lower arm switching elements. The product of the time during which only one is ON and the square of the current value detected by the shunt resistor 10 at that time can be easily calculated without adding an electric circuit.

  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. In other words, a value correlated with the effective value can be obtained. In addition, the effective value itself can be obtained by obtaining the square root of the calculated value.

  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. Further, by using the effective value of these direct currents or a value correlated with the effective value, output adjustment such as output limitation and stop can be performed to improve the reliability. Targets include power loss and heat generation due to the internal resistance of the battery 1, and power loss, heat generation suppression, and protection of the shunt resistor 10. In the case where a current smoothing capacitor is provided in parallel with the battery 1, heat generation of the smoothing capacitor is suppressed and protected.

  In the above embodiment, the motor is not specified, but any of 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, it is applicable also to a 120 degree | times energization system, PAM modulation, etc. Although an example in which the instantaneous value of the direct current from the shunt resistor 10 is directly input to the control circuit 7 has been shown, an operational amplifier that performs signal amplification, voltage shift, etc. may be provided between the shunt resistor 10 and the control circuit 7. good. Further, the current sensor is not limited to the shunt resistor.

(Embodiment 2)
FIG. 10 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 a 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 and the like is made a round, and an accurate average value is obtained. can get.

  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, the accurate DC current including the current fluctuation due to torque fluctuation over one rotation of the motor can be calculated. The effective value of or the value correlated with the effective value can be obtained.

  The phase current of each phase in FIG. 10 is in phase with the terminal voltage of each phase in FIG. 2, but this is an example and does not necessarily match.

(Embodiment 3)
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 mount and apply the inverter device of the present invention to a vehicle.

  As described above, since the inverter device according to the present invention is small and can detect the effective value of DC current or a value correlated with the effective value, it can be applied to various consumer products, various industrial devices, and various mobile devices. Applicable. 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) DC current characteristics in the carrier cycle of the inverter device for sine wave drive Explanatory drawing of the current calculation which concerns on Embodiment 1 of this invention Characteristic explanatory diagram of phase and each phase current waveform according to Embodiment 2 of the present invention Electrical circuit diagram of an inverter device equipped with a conventional DC current detector

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery 2 Switching element 3 Diode 7 Control circuit 10 Shunt resistance 21 Inverter apparatus 30 Motor 37 Inverter circuit U, V, W Upper arm switching element X, Y, Z Lower arm switching element

Claims (6)

A circuit in which two or more phases of an upper arm switching element connected to the positive side of a DC power source and a lower arm switching element connected to the negative side are connected in series is provided, and the connection between the upper arm switching element and the lower arm switching element An inverter circuit for connecting a point to a load and switching the DC voltage of the DC power supply to output an AC current to the load; a current detector between the DC power supply and the inverter circuit; and a plurality of upper arms The product of the time when only one of the switching elements is ON and the value obtained by squaring the current value detected by the current detector at that time, and only one of the plurality of lower arm switching elements is And a control device that calculates a product of a time during which the current is ON and a value obtained by squaring the current value detected by the current detector at the time. Inverter device to be. The control device includes a product of a time during which only one of the upper arm switching elements is ON and a value obtained by squaring the current value detected by the current detector at that time, and one of the lower arm switching elements. Based on the calculation result of the product of the time when only one is ON and the value obtained by squaring the current value detected by the current detector at that time, the effective DC current flowing between the DC power supply The inverter apparatus of Claim 1 which calculates a value. The inverter device according to claim 1, wherein the calculation is performed over a phase width of 120 degrees. The inverter apparatus as described in any one of Claims 1-3 which performs a calculation over 1 rotation of a motor, when load is a motor. The inverter device according to any one of claims 1 to 4, wherein the current detector is a shunt resistor. The inverter apparatus as described in any one of Claims 1-5 mounted in a vehicle.