JP7043071B2 - Current measuring device and inverter - Google Patents

Description

The present invention relates to a technique for measuring an output current from an inverter.

Large-capacity batteries are installed in electric vehicles and hybrid vehicles. The direct current from the battery is converted to alternating current by the inverter and supplied to the alternating current motor to drive the wheels.
The current measuring device that monitors the output current from this inverter has the output line from the inverter as the primary side, connects a resistor to the secondary side, and measures the voltage of the resistor to flow to the output line from the inverter. It measures the current.
Further, as other current measuring devices, there are those using a magnetic core and a Hall element, and those measuring a voltage drop due to a shunt resistance.
As a current measuring device for measuring such a current, the one described in Patent Document 1 is known.
The current sensor for measuring the current in the semiconductor switch described in Patent Document 1 includes a coil wound around a non-magnetic toroidal core located around the conductor through which the measured current flows, and a conductor passing through the toroid. It is equipped with an integrator that integrates the current according to the voltage between the open terminals of the coil winding, which is proportional to the time differential of the current flowing through the coil, and a control circuit that resets the integrator once every cycle.

U.S. Pat. No. 5015945

However, when a current transformer or a Hall element is used, magnetic saturation of the magnetic core may occur in either case, and accurate measurement may not be possible. Therefore, when measuring a large current of 100 A or more, a large magnetic core that does not magnetically saturate even with a large current is required. Since the large magnetic core becomes larger than the inverter, miniaturization is hindered.

Further, when a shunt resistor is used for the current measuring device, the current flowing through the shunt resistor becomes a loss, so that it cannot be used with a large current. In addition, the accuracy is low because the influence of noise is large.

Since the current sensor described in Patent Document 1 uses a non-magnetic toroidal core, it is possible to avoid the limitation of magnetic saturation. When an attempt is made to measure the output current of the inverter using this current sensor, the circuit configuration shown in FIG. 13 is obtained.

As shown in FIG. 13, the inverter 150 includes an upper arm 154 and a lower arm 155 connected in series between one power supply line 152 from the battery 151 and the other power supply line 153. In the current sensor 160, the output of the coil 161 wound around the non-magnetic toroidal core is connected to the integrator 162 by the operational amplifier.

The combined current from the upper arm 154 and the lower arm 155 of the inverter 150 is differentiated by the coil 161. Then, by integrating by the integrator 162, the integrated value of the integrator 162 is output as a current value.

However, since the inverter in an automobile outputs a current in a frequency band of several hundred Hz from direct current, it is difficult to measure the current due to the droop characteristic of the integrator 162.
This is because the amount of change in the magnetic flux intersecting with the coil 161 is reflected in the voltage, so that the change in voltage is small at low frequencies and the output voltage is small. Therefore, it is difficult to separate voltage and noise in principle. Further, in the integrator 162 composed of the operational amplifier, the change in the capacitor discharge resistance and the time constant equal to or less than the time constant of the capacitor cannot be measured.

Therefore, an object of the present invention is to provide a current measuring device and an inverter capable of measuring an output current even if the output current from the inverter is a large current and a low frequency.

The current measuring device of the present invention is a current measuring device that detects an output current from an inverter provided with an upper arm and a lower arm connected in series between one power supply line from a power supply and the other power supply line. , The air-core coil surrounding either one of the first wiring between the one power supply line and the upper arm, or the second wiring between the other power supply line and the lower arm, or both wirings. A pair of air-core coils surrounding each, an integrating circuit that integrates the output from the air-core coil, and an output from the integrating circuit, that is, the output at turn-on and the output at turn-off of the upper arm or the lower arm. It is characterized by having an approximation value calculation circuit that takes an absolute value of an output and connects peaks in time series, or connects absolute values after a predetermined time has elapsed from the peaks to perform linear approximation.

According to the current measuring device of the present invention, even if the output current from the inverter has a low frequency, the change in the current flowing through each of the upper arm and the lower arm frequently occurs during one cycle of the output current. Therefore, it can be treated as a high frequency. Therefore, the air-core coil outputs the change in the current flowing through each of the upper arm and the lower arm as a derivative, and the integrator circuit integrates the current values at the turn-on and turn-off of the arm.

Further, an approximate value calculation circuit for averaging the absolute values of the turn-on output and the turn-off output of the upper arm or the lower arm, which are the outputs from the integrating circuit, can be provided.
Since the current that becomes the peak waveform at turn-on and turn-off from the air core coil is discrete and has a large fluctuation range, instead, the approximate value calculation circuit calculates the approximate value and makes it a continuous current value. , The current value can be set according to the change in the output current of the inverter.

Calculated based on the difference between the current value assumed at turn-on calculated based on the current value from the integrating circuit and the actual current value at turn-on from the integrating circuit, or the current value from the integrating circuit. A ripple component calculation circuit for calculating either or both of the current value assumed at the turn-off and the actual current value at the turn-off from the integrating circuit can be provided. The ripple component calculation circuit calculates the difference between the current value assumed at turn-on and the actual current value, or the difference between the current value expected at turn-off and the actual current value at turn-off. Can be calculated.

A failure detection circuit that calculates the sum and / or difference of the outputs from the respective integrating circuits connected to the pair of air core coils and compares them with the threshold value can be provided.
When the value of the sum of the currents of the upper arm and the lower arm changes to a certain value or more, it can be determined that a failure has occurred in each component or the inverter of the current measuring device of the present invention. Failure can be detected by calculating the sum of the outputs from the integrator circuit and comparing it with the threshold value. In addition, when the difference in the output of the integrator circuit at turn-on and turn-off between the upper arm or lower arm suddenly increases beyond a certain range, a large current such as a short-circuit current is applied to the upper arm or lower arm. It may be flowing. Therefore, the failure can be detected by calculating the difference in the output value from each integration circuit in the failure detection circuit and comparing it with the threshold value.

Calculates the difference between the output from the integrating circuit immediately before including the turn-on and / or turn-off of either or both of the upper arm and the lower arm, and the output immediately after including the peak value. It can be provided with a correction circuit to be used. The correction circuit calculates the difference between the output immediately before including the turn-on and turn-off times and the output immediately after including the peak value. By doing so, even if the output immediately before is biased, it can be removed from the peak value immediately after, so that an accurate peak value can be calculated.

A correction circuit that calculates the difference between the output from the integrator circuit immediately before the turn-on of either or both of the upper arm and the lower arm and the output at the end of the reverse recovery period. Can be provided. The correction circuit can eliminate the influence of overshoot by setting the measurement immediately after the turn-on after the reverse recovery period.

Calculate the difference between the output from the integrator circuit immediately before, including the turn-off of either or both of the upper arm and the lower arm, and the output after waiting for the tail period after the fall period. It can be provided with a correction circuit to be used. By performing the measurement immediately after the turn-off by the correction circuit after waiting for the tail period after the fall period, it is possible to prevent the circuit in the subsequent stage from referring to an undervalued value.

The output from the integrating circuit, immediately before including the turn-on time and / or the turn-off time of either or both of the upper arm and the lower arm, is the first timing, from the lapse of the switching time to the end of the switching cycle. It is possible to provide a correction circuit for integrating and averaging the outputs from the first timing to the second timing when the timing between them is the second timing. The correction circuit can eliminate the influence of overshoot by setting the measurement immediately after the turn-on after the switching time (reverse recovery period).

The inverter of the present invention has a direction in which the output current flows out or a direction in which the output current flows by the output signal from the integrating circuit of the current measuring device of the present invention and the switching signal of the upper arm or the lower arm. It is characterized by having a control unit for determining any of them.

According to the inverter of the present invention, it is not possible to determine whether the output current is in the flow direction or the output current is in the flow direction only by the output signal from the integrating circuit of the current measuring device of the present invention. Therefore, it is possible to determine whether the output current is flowing in either direction by the control unit determining whether the turn-on time or the turn-off time is based on the switching signal that controls the switching of the upper arm or the lower arm.

Since the present invention can detect the current values at the turn-on and turn-off of the arm, it is possible to measure the output current even if the output current from the inverter is a large current and a low frequency.

It is a figure which shows the current measuring apparatus which concerns on Embodiment 1, an inverter which measures an output current by a current measuring apparatus, and a three-phase AC motor which an inverter supplies power. It is a figure of the waveform for demonstrating the operation of the current measuring apparatus shown in FIG. 1, and is the figure which shows the waveform of the current value output by the 3rd arm, and the waveform of the average value of the output current of an inverter. It is a figure of the waveform for demonstrating the operation of the current measuring apparatus shown in FIG. 1, and is the figure which shows the current waveform flowing through the lower arm. It is a figure of the waveform for demonstrating the operation of the current measuring apparatus shown in FIG. 1, and is the figure which shows the output voltage waveform from an air core coil. It is a figure of the waveform for demonstrating the operation of the current measuring apparatus shown in FIG. 1, and is the figure which shows the output waveform from an integrator circuit (incomplete integrator circuit). It is a figure for demonstrating the calculation method of the approximate current value by an approximate value calculation circuit, and is the figure which shows the absolute value of the waveform from an integrator circuit (incomplete integrator circuit). It is a figure for demonstrating the calculation method of the approximate current value by an approximate value calculation circuit, and is the figure which shows the waveform of the linear approximation which connected the peaks in time series from the waveform shown in FIG. 2E. It is a figure for demonstrating the calculation method of the approximate current value by an approximate value calculation circuit, and is the figure which shows the waveform which took the absolute value of the output from an integrator circuit (incomplete integrator circuit). It is a figure which shows the current waveform for demonstrating the calculation method of the ripple component by the ripple component calculation circuit. It is a figure for demonstrating the correction circuit of the current measuring apparatus which concerns on Embodiment 2 of this invention. It is a figure of the waveform for demonstrating the operation of the correction circuit shown in FIG. 5, and is the figure which shows the current waveform which shows the current flowing through the lower arm. It is a figure of the waveform for demonstrating the operation of the correction circuit shown in FIG. 5, and is the figure which shows the output waveform from the integrating circuit (incomplete integrating circuit). FIG. 5 is a waveform diagram for explaining the operation of the correction circuit shown in FIG. 5, and is an enlarged view of part A of FIG. 6B for explaining immediately before and after the turn-off of the lower arm when the correction circuit corrects. It is a figure for demonstrating the correction circuit of the current measuring apparatus which concerns on Embodiment 3 of this invention. It is a figure of the waveform for demonstrating the operation of the correction circuit shown in FIG. 7, and is the figure which shows the current waveform which shows the current flowing through the lower arm. It is a figure of the waveform for demonstrating the operation of the correction circuit shown in FIG. 7, and is the figure which shows the output waveform from the integrating circuit (incomplete integrating circuit). FIG. 7 is a waveform diagram for explaining the operation of the correction circuit shown in FIG. 7, and is an enlarged view of part B of FIG. 8B for explaining immediately before and after the turn-on of the lower arm when the correction circuit corrects. It is a figure for demonstrating the correction circuit of the current measuring apparatus which concerns on Embodiment 4 of this invention. 9 is a waveform diagram for explaining the operation of the correction circuit shown in FIG. 9, and is a diagram showing a current waveform showing a current flowing through the lower arm. It is a figure of the waveform for demonstrating the operation of the correction circuit shown in FIG. 9, and is the figure which shows the output waveform from the integrating circuit (incomplete integrating circuit). 9 is a waveform diagram for explaining the operation of the correction circuit shown in FIG. 9, and is an enlarged view of part C of FIG. 10B for explaining immediately before and after the turn-off of the lower arm when the correction circuit corrects. It is a figure for demonstrating the correction circuit of the current measuring apparatus which concerns on Embodiment 5 of this invention. FIG. 11 is a waveform diagram for explaining the operation of the correction circuit shown in FIG. 11, and is a diagram showing a current waveform showing a current flowing through the lower arm. It is the figure of the waveform for demonstrating the operation of the correction circuit shown in FIG. 11, and is the figure which cut out and enlarged the switching period from the waveform of the current shown in FIG. 12A. FIG. 11 is a waveform diagram for explaining the operation of the correction circuit shown in FIG. 11, and is an enlarged waveform diagram at the time of turn-on and the time of turn-off. It is a figure of the waveform for demonstrating the operation of the correction circuit shown in FIG. 11, and is the figure which shows the output waveform from the integrating circuit (incomplete integrating circuit). FIG. 11 is a waveform diagram for explaining the operation of the correction circuit shown in FIG. 11, and is a diagram showing an enlarged output waveform of a part of FIG. 12B for explaining the turn-on time of the lower arm when the correction circuit corrects. be. It is a figure for demonstrating the conventional current measuring apparatus.

10 Inverter 11 1st arm 12 2nd arm 13 3rd arm 111, 121, 131 Upper arm 112, 122, 132 Lower arm 14 Control unit 20 Current measuring device 21, 22 Air core coil 23 Measuring circuit 231 Integral circuit 232 Approximate value Calculation circuit 233 Ripple component calculation circuit 234 Failure detection circuit 235,236,237,238 Correction circuit BT Battery MT Three-phase AC motor LH Power supply line LL Ground line L1 1st wiring L2 2nd wiring L3 3rd wiring iu, iv, iv Output current vu1, vu2, vv1, vv2, vw1, vw2 Induced electromotive current i_low, i_high Current Su1, Su2, Sv1, Sv2, Sw1, Sw2 Gate signal Su _out , Sv _out , Sw _out signal Xw1 _avg , Xw2 _avg signal t _n , T _n-2 at turn-off t _n-1 , t _{n + 1} at turn-on Xn, X _n-1 , X _n-2 , X _{n + 1} , X _on , X _off current value L _off , L _on straight line X _rip Ripple component Xw1 _rip , Xw2 _rip signal t ₀ 1st timing t ₁ 2nd timing

(Embodiment 1)
The current measuring device and the inverter according to the first embodiment of the present invention will be described with reference to the drawings.
The inverter 10 shown in FIG. 1 converts a direct current from a battery BT into an alternating current to drive a three-phase alternating current motor MT.
In the inverter 10, the first arm 11 to the third arm 13, which are three arms for outputting the current of each phase, have one power supply line from the battery BT (power supply line LH on the positive electrode side of the battery BT) and the other power supply. It is connected in parallel with the wire (ground wire LL on the negative electrode side of the battery BT).
In the first arm 11 to the third arm 13, the upper arms 111, 121, 131 and the lower arms 112, 122, 132 are connected in series.

The upper arms 111 to 131 are connected to the power line LH by the first wiring L1. The lower arms 112 to 132 are connected to the ground wire LL by the second wiring L2. The upper arms 111 to 131 and the lower arms 112 to 132 are connected by a third wiring L3.

The upper arms 111 to 131 and the lower arms 112 to 132 are composed of a switching element and a freewheeling diode. The switching element is formed of a semiconductor device. For example, as the switching element, a bipolar transistor, a MOSFET (metal-oxide-semiconductor field-effect transistor), an IGBT (Insulated Gate Bipolar Transistor), or the like can be used. In particular, an IGBT capable of passing a large current and having a high switching speed is desirable.

The inverter 10 includes a control unit 14 that controls switching between the upper arms 111 to 131 and the lower arms 112 to 132.
The control unit 14 has gate signals Su1, Su2, Sv1, Sv2, Sw1, which are switching signals from the first arm 11 to the third arm 13 based on the signals Su _out , Sv _out , Sw _out from the current measuring device 20. Sw2 is controlled to adjust the current values and frequencies of the output currents iu, iv, and iw from the third wiring L3 of each arm 11 to 13.

The current measuring device 20 measures the current output by the inverter 10, outputs the measurement results to each phase, and outputs the signals Su _out , Sv _out , and Sw _out to the inverter 10.
The current measuring device 20 has both wirings of the first wiring L1 between the power supply line LH and the upper arms 111 to 131 and the second wiring L2 between the ground wire LL and the lower arms 112 to 132, respectively. Each phase is provided with a pair of air-core coils 21 and 22 that surround it. In the first embodiment, a Rogoski coil is used as the air core coils 21 and 22.

Further, the current measuring device 20 measures the output currents iu, iv, iwa based on the induced voltages vu1, v22, vv1, vv2, vw1, vw2 generated in the air core coils 21 and 22 of each phase. Is prepared for each phase.

The measurement circuit 23 calculates an approximate value connected to an integration circuit 231 that integrates the induced electromotive forces vu1, v22, vv1, vv2, vw1, vw2 generated by the air core coils 21 and 22, and the output of the integration circuit 231. It includes a circuit 232, a ripple component calculation circuit 233, and a failure detection circuit 234.
The integrator circuit 231 can function the operational amplifier as an integrator for analog processing, or can perform AD conversion for digital processing. In the case of digital processing, the arithmetic circuit can be integrated by using an arithmetic circuit for obtaining the area of the waveform from the air core coils 21 and 22.

The approximate value calculation circuit 232 has a function of calculating the average current of the output currents iu, iv, and iw. The ripple component calculation circuit 233 has a function of calculating the ripple component included in the output currents iu, iv, and iwa. The failure detection circuit 234 has a function of comparing the current flowing through the upper arms 111 to 131 with the current flowing through the lower arms 112 to 132.
The fault detection circuit 234 can use an operational amplifier with a differential input.

The operation of the current measuring device 20 according to the first embodiment of the present invention configured as described above will be described with reference to the drawings.
The control unit 14 of the inverter 10 outputs the gate signals Su1, Su2, Sv1, Sv2, Sw1, Sw2 for switching the on state and the off state of the switching element of the first arm 11 to the third arm 13. When the switching elements of the upper arms 111 to 131 are on and the switching elements of the lower arms 112 to 132 are off, the current i_high flows through the upper arms 111 to 131 and the switching elements of the upper arms 111 to 131 are off. When the switching elements of the lower arms 112 to 132 are on, the current i_low flows.
Due to the combined current of the current i_high and the current i_low, the output currents iu, iv, and iw become three-phase alternating current and are output from the inverter 10 to the three-phase alternating current motor MT. As shown in FIG. 2A, since the output currents iu, iv, and iw (i_out) are currents obtained by combining the currents i_high and the current i_low, they have a saw blade-like waveform and become a pseudo sine wave.

The three-phase AC motor MT is rotated by the output currents iu, iv, and iwa from the inverter 10.

Here, the operation of current measurement by the current measuring device 20 will be described. The current measurement will be described by taking as an example an air core coil 22 mounted on the lower arm 132 of the third arm 13 and a measurement circuit 23 for measuring the third arm 13. Since the other air-core coils 21 and 22 mounted on the first arm 11 and the second arm 12 and the other measuring circuit 23 for measuring the current flowing through the first arm 11 and the second arm 12 have the same operation. Omit.

A current i_low as shown in FIG. 2B flows through the second wiring L2 between the lower arm 132 of the third arm 13 and the ground wire LL.
When the switching element changes from the on state to the off state (at the time of turn-off), the current i_low is cut off and does not flow. From the off state to the on state (at the time of turn-on), the current i_low suddenly starts to flow, and then in FIG. It is blocked.

As shown in FIG. 1, since the second wiring L2 is surrounded by the air core coil 22, an induced electromotive force is generated in the air core coil 22 by the current flowing through the second wiring L2. The peak value of this induced electromotive force is a voltage proportional to the derivative of the current i_low flowing through the lower arm 132, as shown in FIG. 2C.
However, since the waveform of this induced electromotive force is delayed in switching of the lower arm 132 and the air core coil 22 is an incomplete differentiating circuit, the waveform has an infinite amplitude and a width of 0, and does not become a waveform at turn-off and turn-on. It becomes a peak waveform with a finite amplitude and a width that changes rapidly.

In the measurement circuit 23, the output from the air core coil 22 is input to the integration circuit 231. The integrator circuit 231 integrates the output from the air core coil 22, so that the integrator circuit 231 outputs an output signal as shown in FIG. 2D. The peak value at the time of turn-on and the time of turn-off of this output signal indicates the current value of the output current iw of the third arm 13. In FIG. 2D, since the integrating circuit 231 is an inverting type, the output direction is shown in the opposite direction.

In the example shown in FIG. 2D, the output from the air core coil 22 is integrated by the integrator circuit 231 and the voltage value rises to a peak. However, the integrator circuit 231 has an incomplete integration in which the operational amplifier functions as an integrator. Since it is a circuit, when the voltage drops sharply, the output waveform gradually decays due to the discharge of the capacitor. However, even if the integrator circuit 231 is an incomplete integrator circuit, if a peak can be detected, there is no problem because this peak value is proportional to the turn-on and turn-off currents of the currents i_low and i_high.

In this way, even if the output current iw is low frequency, the changes in the currents i_low and i_high flowing in the upper arms 111 to 131 and the lower arms 112 to 132, respectively, frequently occur during one cycle of the output current iw. Since it is generated, it can be treated as a high frequency. Therefore, the air-core coils 21 and 22 output the changes in the currents i_low and i_high as derivatives, and the integrator circuit 231 integrates them to obtain the current values at the turn-on and turn-off of the first arm 11 to the third arm 13. It can be detected as a voltage value from the integrator circuit 231. Therefore, the current measuring device 20 can measure the output currents iu, iv, iwa even if the output currents iu, iv, iwa from the inverter 10 are large currents and low frequencies.

The integrator circuit 231 outputs the signal Svw1 on the upper arm 131 side and Svw2 on the lower arm side to the inverter 10.

Next, the output from the integrating circuit 231 is input to the approximate value calculation circuit 232. In the approximate value calculation circuit 232, first, the waveform after incomplete integration by the integration circuit 231 (see FIG. 2D) is taken as the absolute value of the output at the turn-on and the output at the turn-off of the lower arm 132 (see FIG. 2E). Specifically, the negative value of the waveform signal at the time of turn-on is converted into a positive value.

Next, in the approximate value calculation circuit 232, after converting to an absolute value waveform (see FIG. 2E), the current value is connected by connecting the peaks at the time of turn-on and the peak at the time of turn-off with a straight line as shown in FIG. 2F. Convert to.
In power converters such as inverter circuits, the load is often the winding of a motor. Therefore, the current value does not change suddenly. Therefore, it is possible to convert to a current value by taking an absolute value for the waveform from the integrating circuit 231 and performing a linear approximation.
In this case, the peaks are connected by a straight line, but the absolute value after a predetermined time has elapsed from the peak may be approximated by a straight line in order to remove noise.
This predetermined time can be a reverse recovery period (reverse recovery period) of the upper arm and the lower arm at the time of turn-on. Further, at the time of turn-off, the tail period after the fall period in the upper arm and the lower arm can be set. Further, the predetermined time can be arbitrarily set in consideration of the influence on the peak waveform.
In this way, the approximation value calculation circuit 232 changes the output currents iu, iv, and iwa (see FIG. 1) by making the current values continuous by linear approximation instead of the peak values that are discrete and have a large fluctuation range. The current value can be adjusted accordingly.

Further, in the approximate value calculation circuit 232, it is also possible to calculate an approximate current value by averaging the absolute values of the output at the time of turn-on and the output at the time of turn-off of the lower arm 132. Hereinafter, the peak voltage value output from the integrator circuit 231 will be described as a current value.
As shown in FIG. 3, the approximate value calculation circuit 232 first holds the current value X _n-2 of t _n-2 at the time of turn-off that first appears. Since the current value X _{n- 1 of t n-1} at the time of turn-on that appears next is a negative value as shown in FIG. 2D, when the approximate value calculation circuit 232 takes an absolute value, it becomes a positive value. Then, the approximate value calculation circuit 232 calculates the average of the current value X _n-2 held up to t _n-1 at turn-on and the current value X _n -1 at t _n-1 at turn-on. This average value is an approximate current value of the output currents iu, iv, and iwa up to t _n at the next turn-off.

In this way, the approximate value calculation circuit 232 calculates the approximate value and uses it as a continuous current value instead of the discrete peak value having a large fluctuation range, so that the output currents iu, iv, and iw can be changed. It can be a current value. The approximate value calculation circuit 232 outputs the approximate current values of the currents flowing through the upper arm 131 and the lower arm 132 of the third arm 13 to the inverter 10 as signals Xw1 _avg and Xw2 _avg .

The output from the integrator circuit 231 is input to the ripple component calculation circuit 233. The ripple component calculation circuit 233 calculates the difference between the current value assumed at the time of turn-on and the actual current value, and the difference between the current value assumed at the time of turn-off and the actual current value.
As shown in FIG. 4, the current value assumed at the time of turn-on is an equation of a straight line L _off from continuous turn-off time t _n-2 and t _n and the respective current values X _n-2 and X _n at that time. Is obtained, and the current value X _on at turn-on obtained from this equation is t _n-1 .
Similarly, the current value assumed at the time of turn-off is a straight line L _on from t _n-1 and t _{n + 1} at the time of continuous turn-on and the current values X _n-1 and X _{n + 1} at that time, respectively. The equation is obtained, and the current value X _off at _turn -off obtained from this equation is obtained.

Here, the straight line L _off is as shown in equation (2) based on the equation of the straight line connecting these two points (see equation (1)) from the coordinates (x1, y1) and (x2, y2) of the two points. Can be expressed in.

・・・（１）

... (1)

・・・（２）

... (2)

Therefore, the estimated current value X _on at t _n-1 at the time of turn-on can be estimated by the equation (3).

・・・（３）

... (3)

However, since the actual current value at t _n-1 at turn-on was X _n-1 , the difference can be calculated by X _on -X _n-1 to change from t _n-1 at turn-on to t at the next turn-off. The ripple component in the period up to _n-1 can be X _rip .

Further, the current value X _off of t _n at the time of turn-off can be estimated by the equation (4) in the same manner.

・・・（４）

... (4)

Since the actual current value at t _n at turn-off was X _n , the ripple component X _rip can be obtained by calculating the difference by X _off −X _n .
In this way, the ripple component calculation circuit 233 obtains the ripple component X _rip , the ripple component on the upper arm 131 side of the third arm 13 is the signal Xw1 _rip , and the ripple component on the lower arm 132 side is the signal Xw2 _rip . Output to 10.

In the first embodiment, the ripple component calculation circuit 233 calculates both the ripple component at the time of turn-on and the ripple component at the time of turn-off, but even if one of the ripple components is calculated, it is included in the output current. It is a guide for the ripple component. However, in order to measure the ripple component more accurately, it is desirable to calculate both the turn-on time and the turn-off time.

The output from the integrator circuit 231 is input to the failure detection circuit 234. In the failure detection circuit 234, the difference and the sum of the output from the integrator circuit 231 on the upper arm 131 side and the output from the integrator circuit 231 on the lower arm 132 side are calculated.

When the inverter 10 is operating normally, for example, the sum of the outputs of the integrator circuit 231 at the time of turn-on and the time of turn-off in the upper arm 131 or the lower arm 132 becomes almost 0 in principle. This is because the load connected to the output is generally an inductive load and there is no sudden change in current, and the sum of the currents (i_high, i_low) of the upper arm 131 and the lower arm 132 is the output current iw. The sum of the currents of 131 and the lower arm 132 does not have a steep change in current. Therefore, the sum of the outputs of the integrator circuit 231 is also a small value excluding the noise component.

However, when the value of the sum of the currents of the upper arm 131 and the lower arm 132 changes to a certain value or more, each component of the current measuring device 20 such as the air core coils 21 and 22 and the operational amplifier of the integrator circuit 231 and each component It can be determined that a failure has occurred in the inverter 10.
Therefore, in the failure detection circuit 234, the noise component is removed from the sum of the output values from the respective integration circuits 231 connected to the pair of air core coils 21 and 22 with a filter or the like, and the value is monitored in advance. Failure can be detected by comparing with the set threshold value and determining whether or not it is above the threshold value.

Further, for example, when the difference between the outputs of the integrator circuit 231 at the time of turn-on and the time of turn-off in the upper arm 131 or the lower arm 132 suddenly increases beyond a certain range, a large current such as a short-circuit current increases. It may be flowing to the arm 131 or the lower arm 132.
Therefore, the failure detection circuit 234 monitors the difference in the output values from the respective integration circuits 231 connected to the pair of air core coils 21 and 22, and compares them with the preset threshold values to compare the threshold values. Failure can be detected by determining whether or not the above is the case.
With the above configuration, it is not necessary to separately provide a judgment circuit for the upper arm and the lower arm, and a failure can be detected with a simple configuration.

In the failure detection circuit 234, when the sum of the current i_high and the current i_low is larger than the threshold value and the difference is larger than the threshold value, it can be output to the inverter 10 as a signal Xw _fail for detecting an abnormality. .. In the present embodiment, both the sum and the difference between the current i_high and the current i_low are monitored, but either one may be used. Further, although the signal Xw _fail has both an abnormality at the time of sum and an abnormality at the time of difference, the signal line is separated so that the abnormality at the time of sum and the abnormality at the time of difference are notified separately. You may do it.

In the inverter 10, the control unit 14 has gate signals Su1, Su2, Sv1, Sv2, Sw1, from the first arm 11 to the third arm 13 based on the signals Su _out , Sv _out , Sw _out from the current measuring device 20. Control Sw2.

In the output signal from the integrator circuit 231, the current i_high flowing in the upper arms 111 to 131 or the current i_low flowing in the lower arms 112 to 132 is at the turn-off time in the direction of flowing out to the three-phase AC motor MT, and in the three-phase AC motor MT. A peak waveform as shown in FIG. 2C is generated at each turn-off in the direction of flowing from. The same applies at the time of turn-on.

Therefore, the inverter 10 cannot determine whether the switching is when the switch flows out to the three-phase AC motor MT or the switching when the switch flows from the three-phase AC motor MT only by the output signal from the integrating circuit 231.

Therefore, in the control unit 14 of the inverter 10, when the gate signals Su1, Sv1, Sw1 that control the upper arms 111 to 131 are on, the current i_high flows from the upper arms 111 to 131 to the three-phase AC motor MT. It can be determined that there is. Further, when the gate signals Su1, Sv1 and Sw1 are in the off state, it can be determined that the current i_high is in the state of flowing from the three-phase AC motor MT from the upper arms 111 to 131.

Similarly, when the gate signals Su2, Sv2, Sw2 controlling the lower arms 112 to 132 are on, it can be determined that the current i_low is in a state of flowing out from the lower arms 112 to 132 to the three-phase AC motor MT. Further, when the gate signals Su2, Sv2, and Sw2 are in the off state, it can be determined that the current i_low is in a state of flowing from the lower arms 112 to 132 from the three-phase AC motor MT.

In this way, the control unit 14 can determine which current direction the output signal from the integrating circuit 231 has with respect to the upper arms 111 to 131 and the lower arms 112 to 132 by the gate signal.

In the first embodiment, the direction of the current is determined by the gate signal to the arms 11 to 13, but the air core coils 21 and 22 are arranged on the switching element side and the freewheeling diode side of the arms 11 to 13. By arranging the two separately, the direction of the current may be discriminated by the air-core coil on the freewheeling diode side.

In the first embodiment, the current measuring device has been described by taking an inverter that supplies three-phase alternating current to the three-phase alternating current as an example. However, the inverter shall output single-phase alternating current equipped with one arm. Or, it can output multi-phase alternating current other than three-phase alternating current.
Further, in the first embodiment, the air core coils 21 and 22 are mounted for the upper arms 111 to 131 and the lower arms 112 to 132, respectively, but the current measuring device must be provided with the failure detection circuit 234. , The air core coils 21 and 22 may be either one.

(Embodiment 2)
The current measuring device according to the second embodiment of the present invention will be described with reference to the drawings.
In the current measuring device according to the second embodiment, the correction circuit is connected to the subsequent stage of the integrating circuit. FIG. 5 shows a correction circuit 235 connected to the output of the integrating circuit 231 connected to the air core coil 21 for the lower arm 132 of the third arm, but the current measuring device according to the second embodiment shows the correction circuit 235. The correction circuit 235 is connected to the output of the integrating circuit 231 for each upper arm and for each lower arm. Hereinafter, the lower arm 132 will be described as an example on behalf of the first arm 11 to the third arm 13.

A gate signal Sw2, which is a switching signal for instructing turn-on and turn-off of the lower arm 132 of the third arm 13, is connected to the correction circuit 235 from the control unit 14 in the inverter 10 shown in FIG.

Since the lower arm 132 is cut off at the time of turn-off and energized at the time of turn-on, the current i_low flows as shown in FIG. 6A. By differentiating this current i_low with the air core coil 22 and integrating it with the incomplete integration circuit 231 to obtain a sharp waveform that peaks at turn-on and turn-off as shown in FIG. 6B and then attenuates. ..
However, when the peak waveform of FIG. 6B is microscopically viewed, it may be biased. In that case, since the bias is added to the peak value of the peak waveform, the original peak value cannot be measured accurately, and the average current is calculated by the approximate value calculation circuit 232 and the ripple component is calculated by the ripple component calculation circuit 233. May cause problems.

Therefore, as shown in FIG. 6C, in the correction circuit 235, the values immediately before the turn-on and turn-off of the lower arm 132 from the integration circuit 231 are held, and when the peak value immediately after is detected, the value immediately before is detected. Calculate the output difference between the value of and the peak value immediately after.
The correction circuit 235 determines the turn-on time and the turn-off time by the gate signal Sw2.

In this way, the correction circuit 235 calculates the difference between the output immediately before including the turn-on and turn-off times and the output immediately after including the peak value. By doing so, it is possible to calculate an accurate peak value from the integrating circuit 231.

Here, the time constant of the integrator circuit 231 configured by the incomplete integrator circuit is shorter than the reciprocal of the switching time of the semiconductor element by the upper arms 111, 121, 131 and the lower arms 112, 122, 132. By doing so, it is possible to facilitate the integration circuit 231 to follow the switching of the upper arm and the lower arm at the time of turn-on and at the time of turn-off.

In the second embodiment, the correction circuit 235 calculates the difference in output both at the time of turn-on and at the time of turn-off, but either one may be used.

(Embodiment 3)
The current measuring device according to the third embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 7, in the current measuring device according to the third embodiment, the correction circuit 236 is connected to the subsequent stage of the integrating circuit 231 as in the second embodiment.
As shown in FIGS. 8A to 8C, the correction circuit 236 determines the reverse recovery period (reverse recovery period) t of the upper arm and the lower arm when calculating the output difference immediately after the turn-on of the upper arm and the lower arm. After waiting for _rr , the output value from the integrating circuit 231 is measured. For example, if the period from the start of switching to the end of the reverse recovery period _trr is defined as an IGBT for the upper arm and the lower arm, it can be set to 500 ns per 1000 V withstand voltage. For example, in the case of an IGBT having a withstand voltage of 2000 V, the correction circuit 236 can measure the output value from the integrating circuit 231 immediately after 1 μs.
In FIG. 8C, the waveform is shown upside down for convenience.

This is because if the measurement immediately after is within the reverse recovery period _trr , for example, in the case of the lower arm 132, the forward current flowing through the diode of the upper arm 131 is switched in the reverse direction when the lower arm 132 is turned on. At that time, since the current in the opposite direction flows for a moment due to the carrier movement, this momentary current flows to the lower arm 132, which causes an overshoot, and the integrating circuit 231 may output an excessive value.
Therefore, the correction circuit 236 can eliminate the influence of overshoot by setting the measurement immediately after the turn-on to be after the reverse recovery period _trr .

At this time, the value immediately before the turn-on is the turn-on time. Even if the immediately preceding value is set to turn-on, there is no problem because the switching of the upper arm or the lower arm is delayed due to the gate signal.
Further, by setting the output value at the time of turn-on, the interval between the two time points to be measured can be minimized, so that accurate measurement is possible.

(Embodiment 4)
The current measuring device according to the fourth embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 9, in the current measuring device according to the fourth embodiment, the correction circuit 237 is connected to the subsequent stage of the integrating circuit 231 as in the second embodiment.
As shown in FIGS. 10A to 10C, when calculating the output difference immediately after the turn-off of the upper arm and the lower arm, the correction circuit 237 has a fall period t in the upper arm and the lower arm, and a tail period t after the _fall . After waiting for the _tail , the output value from the integrating circuit 231 is measured. For example, if the upper arm and the lower arm are IGBTs, the period from the start of switching to the end of the tail period t _tail can be 500 ns per 1000 V withstand voltage.

For example, when the upper arm and the lower arm are IGBTs, it takes time for the excess carriers remaining on the collector side to disappear by recombination even if the voltage between the collector and the emitter rises at the time of turn-off. Therefore, the current cannot be completely cut off and the current flows for a certain period of time. Therefore, if the measurement of the output value is within the tail period t _tail even after the fall period t _fall , the circuit in the subsequent stage detects an undervalued value. This is because there is a risk that it will end up.

Therefore, the correction circuit 237 can prevent the circuit in the subsequent stage from referring to an undervalued value by performing the measurement immediately after the turn-off while waiting for the tail period t _tail after the fall period t _fall . can.
At this time, the values immediately before the turn-on and the turn-off can be the turn-off time as in the third embodiment.

(Embodiment 5)
The current measuring device according to the fifth embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 11, in the current measuring device according to the fifth embodiment, the correction circuit 238 is connected to the subsequent stage of the integrating circuit 231 as in the second embodiment.
The correction circuit 238 integrates a certain period of the output waveform from the integration circuit 231 and divides the integrated value by the integration period to average the waveform.

For example, in the lower arm 132 shown in FIG. 1, the current is cut off at the time of turn-off and the current is energized at the time of turn-on, so that the current i_low flows as shown in FIG. 12A.
FIG. 12B is an enlargement of the switching cycle (the period from turn-on to the next turn-on or from turn-off to the next turn-off) cut out from the current waveform shown in FIG. 12A. In FIG. 12B, the current i_low flowing through the lower arm 132 is shown by a solid line, and the voltage across the lower arm 132 is shown by a dotted line.
In FIG. 12C, it is an enlarged waveform at the turn-on time and the turn-off time shown in FIG. 12B.
In FIG. 12D, it is a waveform when this current i_low is differentiated by the air core coil 22 and integrated by the integration circuit 231 which is an incomplete integration circuit. It becomes a sharp waveform that peaks at turn-on and turn-off and then decays. FIG. 12E is an enlarged view of a portion D of FIG. 12D.

As can be seen from FIG. 12C, at the time of turn-on, the switching time (reverse recovery period) overshoot occurs and an excessive current flows. This is because, as shown in FIG. 12E, the overshoot also appears at the output obtained by integrating the signal from the air core coil 22 by the integrator circuit 231. If an excessive value that becomes an overshoot is output from the integrating circuit 231, it affects the calculation of the approximate value calculation circuit 232 and the ripple component calculation circuit 233.

Therefore, in the correction circuit 238, as shown in the equation (5), from immediately before the turn-on time (first timing t ₀ ) to after the switching time (second timing t ₁ ) is integrated and averaged.

・・・（５）
ここで、第１タイミングｔ₀は、補正回路２３８が、電圧値をＡＤ変換してメモリにデジタル値を格納して演算するものであれば、出力波形が立ち上がったタイミングとすることができる。また、補正回路２３８がアナログ回路により構成されたものであれば、出力波形の立ち上がりを検出したタイミングとすることができる。

... (5)
Here, the first timing t ₀ can be the timing at which the output waveform rises if the correction circuit 238 AD-converts the voltage value and stores the digital value in the memory for calculation. Further, if the correction circuit 238 is configured by an analog circuit, it can be set as the timing at which the rising edge of the output waveform is detected.

The second timing t ₁ can be from the time when the switching time elapses to the end of the switching cycle. Therefore, the integration time from the first timing t ₀ to the second timing t ₁ can be set so as to have the relationship shown in the equation (6).
Switching time ≤ integration time (t ₁ -t ₀ ) ≤ switching cycle ... (6)

In this embodiment, the integration time (ns) is set to semiconductor withstand voltage (V) / 2. Further, it can be set to 1/40 of the switching cycle. Further, the reverse recovery period can be 10 times or more (measurement error within 5%) of _trr .

In this way, the correction circuit 238 can eliminate the influence of overshoot by setting the measurement immediately after the turn-on after the switching time (reverse recovery period _trr ). By doing so, the influence of the vibration of the waveform and the reverse recovery period can be reduced.
In addition, although the state in which the waveform overshoots is shown in FIG. 12E, it is shown by inverting the top and bottom of the waveform for convenience, as in FIG. 8C.

In the above example, the turn-on time of the lower arm 132 has been described, but even at the turn-off time, the period from immediately before the turn-on time (first timing t ₀ ) to after the switching time (second timing t ₁ ) is integrated and averaged. As a result, the influence of the turn-off on the circuit in the subsequent stage can be reduced as in the case of the turn-on.

In the second to fifth embodiments, the switching (turn-on, turn-off) timing is performed from the gate signal (for example, the gate signal Sw2 to the lower arm 132), but as a simple method, the integrator circuit 231 is used. The rising and falling edges of the output and the rising and falling edges of the output of the air core coils 21 and 22 sensors can be detected by the trigger circuit and replaced with the timing signal of switching by the gate signal. In this case, although the accuracy is lowered, the circuit configuration and the connection wiring are simplified, so that the cost can be reduced.

The present invention is suitable for all devices that use inverters, and is particularly suitable for inverters for electric vehicles.

Claims (8)

A current measuring device that detects the output current from an inverter equipped with an upper arm and a lower arm connected in series between one power line from a power source and the other power line.
An air-core coil that surrounds either one of the first wiring between the one power line and the upper arm, or the second wiring between the other power line and the lower arm, or both wirings, respectively. A pair of air-core coils surrounding the wire and
An integrator circuit that integrates the output from the air core coil,
The output from the integrating circuit, which is the absolute value of the output at turn-on and the output at turn-off of the upper arm or the lower arm, is taken from the peak, if it is at turn-on, at the time when the reverse recovery period elapses, at the time of turn-off. If there is, a current measuring device equipped with an approximate value calculation circuit that performs linear approximation by connecting the absolute values at the time when the tail period elapses after the fall period. It is a current value assumed at turn-on calculated based on the current value from the integrator circuit, and a linear equation is obtained from the coordinates of continuous turn-off and each current value at that time, and is obtained from this equation. It is the difference between the current value at the time of turn-on and the actual current value at the time of turn-on from the integrator circuit, or the current value assumed at the time of turn-off calculated based on the current value from the integrator circuit, and is continuous. A linear equation is obtained from the turn-on and the respective current values at that time, and one of the difference between the turn-off current value obtained from this equation and the actual current value at the turn-off from the integrator circuit. The current measuring device according to claim 1, further comprising a ripple component calculation circuit for calculating, or both. The sum and / or difference of the outputs from the respective integrating circuits connected to the pair of air-core coils is calculated and compared with the threshold value to determine the failure of the air-core coil, the integrating circuit or the inverter. The current measuring device according to claim 1, further comprising a failure detection circuit for detection. The difference between the output from the integrator circuit from the turn-on or turn-off to immediately before the peak and the output immediately after including the peak value in one or both of the upper arm and the lower arm. The current measuring device according to any one of claims 1 to 3 , further comprising a correction circuit for calculating and outputting to the approximate value calculation circuit. Calculate the difference between the output from the integrator circuit from the turn-on time to just before the peak time and the output when the reverse recovery period ends in one or both of the upper arm and the lower arm. The current measuring device according to any one of claims 1 to 3 , further comprising a correction circuit for outputting to the approximate value calculation circuit. The difference between the output from the integrator circuit from the turn-off time to just before the peak time and the output after the tail period after the fall period in one or both of the upper arm and the lower arm. The current measuring device according to any one of claims 1 to 3 , further comprising a correction circuit for calculating and outputting to the approximate value calculation circuit. The output from the integrating circuit, the first timing from the turn-on or turn-off to just before the peak, and the switching cycle from the time when the reverse recovery period elapses in one or both of the upper arm and the lower arm. The output from the first timing to the second timing is integrated when the timing from the turn-on to the next turn-on or from the turn-off to the end of the switching cycle is set as the second timing. The current measuring device according to any one of claims 1 to 3 , further comprising a correction circuit for averaging and outputting to the approximate value calculation circuit. The direction in which the output current flows out or the output due to the output signal from the integrating circuit of the current measuring device according to any one of claims 1 to 7 and the switching signal of the upper arm or the lower arm. An inverter equipped with a control unit that determines which direction the current flows in.

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