JPH077967A - Polarity deciding method for load current and inverter - Google Patents

Abstract

PURPOSE:To provide small-sized current polarity deciding means in which a detecting accuracy is not lowered due to a temperature change, etc., with low loss and an inverter having dead time compensating means using the same. CONSTITUTION:The inverter comprises a current detector 6 using a switching element with a current detecting terminal for outputting a microcurrent responsive to a current flowing to switching elements Q1-Q6 of upper and lower arms of an inverter to any of the elements Q1-Q6 to compare the microcurrent from the terminal with a predetermined reference value, and a current direction detector 7 for deciding an instantaneous polarity of the current to be supplied to a load 15 from an output of the detector 6 and a drive signal U- to be supplied to the element with the terminal. Further, a method for deciding a polarity of a load current comprises the steps of forming a correction signal by a voltage corrector 20 based on a direction (polarity) of the current, correcting a signal of a PWM generator 17 through a voltage instruction unit 19, and compensating a dead time at the time of turning ON, OFF the element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load current polarity determining method and an inverter device, and more particularly to a load current polarity determining method and dead time compensating means suitable for dead time compensation of a switching element in the inverter device. .

[0002]

2. Description of the Related Art Generally, a PWM inverter device operates such that when one of a switching element in an upper arm and a switching element in a lower arm is on, the other is off. When switching on and off of both elements, considering the operation delay time of the switching element, a period for temporarily turning off both elements, that is, a dead time is provided,
After that, one of the elements is turned on to prevent the occurrence of a short circuit.

However, when the dead time is provided, an error occurs between the inverter voltage to be originally output and the actual inverter output voltage. As a result, the motor current is distorted,
This causes problems such as generation of vibration and reduction in efficiency.

Therefore, dead time compensation for correcting the PWM signal is performed in consideration of the error voltage due to the dead time. An example thereof is disclosed in Japanese Patent Laid-Open No. 1-186172. The dead time compensation is a method of detecting the polarity of the motor current output from the inverter to the motor and increasing or decreasing the duty of the PWM signal based on the detected value, and is generally widely used.

[0005]

In the above dead time compensation, in order to determine the polarity of the motor current, it is necessary to separately provide means for determining the current polarity. A current transformer or the like is generally used as this means. On the other hand, recently, in order to miniaturize the inverter device, as described in, for example, "Annual Meeting of the Institute of Electrical Engineers of Japan, Industrial Application Division, 1992, ppS27-S32, Akira Kawakami et al.," Application to IPM and its AC drive ". , A hybrid integrated circuit device in which a switching element of an inverter, a drive circuit, and a protection circuit are mounted is reported. Thus, with the background of miniaturization of the inverter device, miniaturization of peripheral parts is desired,
Also for the dead time compensation, miniaturization of the current polarity determination means is required.

However, since the current transformer has magnetic saturation in the magnetic material, there is a limit to miniaturization thereof. Further, the current transformer has a drawback that the sensitivity of current detection is easily affected by temperature changes. On the other hand, when the motor current is detected by using another means for determining the electric current polarity, there is a problem that an extra electric circuit is inserted in the path of the motor current, resulting in a large loss.

It is an object of the present invention to provide a current polarity determining method which is small in size, has low loss, and does not deteriorate in detection accuracy due to temperature changes and the like. Another object of the present invention is to provide a dead time compensation method for an inverter device based on the current polarity determination method.

Another object of the present invention is to provide an inverter device having a current polarity discriminating means and a dead time compensating means.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention uses a switching element for the upper and lower arms in PWM.
In the method of determining the polarity of the load current of the inverter device that alternately turns on and off with a signal and converts direct current into alternating current and supplies it to the load, the presence or absence of current flowing in any of the switching elements of the upper and lower arms is detected, and the switching element is turned on. The present invention proposes a load current polarity determination method that determines the instantaneous polarity of the load current based on the relationship between the current flow direction specific to the switching element and the presence / absence of current during the state.

In order to achieve the above object, the present invention also determines the polarity of the load current of an inverter device which alternately turns on and off the switching elements of the upper and lower arms by a PWM signal to convert direct current into alternating current and supplies it to the load. In the method
The current sense terminal of the switching element detects the presence / absence of a current flowing in one of the switching elements in the upper and lower arms, and the load is determined by the relationship between the current flowing direction and the presence / absence of current unique to the switching element while the switching element is on. The present invention proposes a load current polarity determination method for determining the instantaneous polarity of a current.

In order to achieve the above object, the present invention further determines the polarity of the load current of the inverter device which alternately turns on and off the switching elements of the upper and lower arms by a PWM signal to convert direct current into alternating current and supplies it to the load. In the method, the presence / absence of current flowing in one of the switching elements of the upper and lower arms is detected based on the output voltage of the switching element, and the current flowing direction and the presence / absence of current unique to the switching element are detected while the switching element is in the ON state. The present invention proposes a method for determining the polarity of a load current, which determines the instantaneous polarity of the load current based on the relationship.

In order to achieve the above-mentioned other object, the present invention alternately turns on and off by a PWM signal while sandwiching a dead time for simultaneously turning off the switching elements of the upper and lower arms to convert direct current into alternating current and supply it to a load. In the dead time compensation method for an inverter device, the presence or absence of current flowing in one of the switching elements of the upper and lower arms is detected, and the relationship between the current flowing direction and the presence or absence of current unique to the switching element during the ON state of the switching element. Is used to determine the instantaneous polarity of the load current. Depending on the instantaneous polarity of the load current, one of the PWM signals output to the upper arm and the lower arm can be turned on for a predetermined amount of the ON period of the PWM signal. The dead of the inverter device that increases the increase and decreases the ON period of the PWM signal by the correction amount for the other arm. It proposes a-time compensation method.

In order to achieve the above-mentioned another object, the present invention is connected to a DC power source in the form of upper and lower arms and alternately turned on,
A switching element which is turned off, a PWM signal generating means,
In an inverter device including a drive circuit for driving a switching element according to a PWM signal and converting a direct current into an alternating current and supplying it to a load, means for detecting the presence / absence of a current flowing in one of the switching elements of the upper and lower arms, and a PWM A current direction detecting means connected to the signal generating means and the current detecting means for determining the instantaneous polarity of the load current based on the relationship between the current flowing direction peculiar to the switching element and the presence / absence of current while the switching element is in the ON state. The present invention proposes an inverter device including a voltage command to the PWM signal generating means or a means for outputting a signal for correcting the PWM waveform according to the polarity of the load current.

In order to achieve the above-mentioned another object, the present invention provides a switching element connected to a DC power source in the form of upper and lower arms to alternately turn on and off, a PWM signal generating means, and a PWM signal. In an inverter device including a drive circuit for driving a switching element and converting direct current into alternating current and supplying it to a load, means for detecting the presence or absence of overcurrent flowing in one of the switching elements of the upper and lower arms, and switching of the other of the upper and lower arms. A current flowing direction specific to the switching element is connected to the means for detecting the presence / absence of overcurrent flowing in the element and the presence / absence of the element current, and the PWM signal generating means and the other current detecting means while the switching element is in the ON state. Current direction detection means for determining the instantaneous polarity of the load current based on the relationship with the presence or absence of the element current, and the PWM signal depending on the polarity of the load current. Voltage command or PWM for generating means
An inverter device provided with a means for outputting a signal for correcting a waveform is proposed.

In any of the inverter devices, it is desirable that the switching element has a current sense terminal that outputs a minute current according to the current flowing through the switching element.

In order to achieve the above-mentioned another object, the present invention further provides a switching element which is connected to a DC power source in the form of upper and lower arms and alternately turns on and off, a PWM signal generating means, and a PWM signal. In an inverter device including a drive circuit for driving a switching element and converting a direct current into an alternating current and supplying it to a load, a means for detecting the presence or absence of a current flowing in one of the switching elements of the upper and lower arms based on the output voltage of the switching element. And a current direction which is connected to the PWM signal generating means and the current detecting means and which determines the instantaneous polarity of the load current based on the relationship between the current flowing direction specific to the switching element and the presence / absence of current while the switching element is in the ON state. PW depending on the detection means and the polarity of the load current
The present invention proposes an inverter device provided with a voltage command to the M signal generating means or a means for outputting a signal for correcting a PWM waveform.

The current detecting means in this case is composed of means for detecting the voltage at the connecting portion of the switching elements of the upper and lower arms and means for comparing the voltage at the connecting portion with a predetermined reference voltage.

In any inverter device, the PW
The correction signal output means to the M signal generation means outputs PWM to the upper arm and the lower arm according to the instantaneous polarity of the load current.
For one arm of the signal, P
A means for increasing the ON period of the WM signal and decreasing the ON period of the PWM signal for the other arm by a correction amount can be used.

[0019]

The present invention detects the presence or absence of a current flowing through the switching element of the upper arm or the switching element of the lower arm instead of the load current, and the relationship between the detection result and the current flowing direction specific to the switching element. Therefore, the feature is that the polarity of the load current is determined. Since the upper arm and the lower arm alternately turn on the current flowing through the switching element, the time during which the current flows is shorter than the load current,
The loss in the detection part can be reduced. Further, since the means for detecting the current flowing through the element has the same drive voltage level as the circuit means such as the drive circuit provided in each element, the detection means can be downsized by integrating these circuits together. it can.

As a means for detecting the presence / absence of current flowing through the switching element, a switching element with a current detection terminal is used. Switching element with current detection terminal,
A minute current that changes according to the current flowing between the input terminal and the output terminal of this element can be taken out from the current detection terminal, and the presence or absence of the element current can be grasped by detecting the presence or absence of the minute current. Further, since it is the detection of a minute current, the loss is small. Further, the micro-current detection circuit means can be integrated into an integrated circuit and downsized.

On the other hand, the means for discriminating from the polarity of the voltage applied to the switching element is a means which does not use an element having a special structure such as a switching element with a current detection terminal and is inexpensive. Moreover, since the polarity of the voltage is detected only during the ON period of the switching element, the loss can be reduced, and the detection circuit means can be integrated into an integrated circuit and downsized.

[0022]

Embodiments of the load current polarity determining method and the inverter device according to the present invention will now be described with reference to FIGS. FIG. 1 is a block diagram showing the configuration of an embodiment of an inverter device having a dead time compensating means according to the present invention. In the inverter device of this embodiment, the output stage is configured as a general three-phase inverter bridge. Switching elements Q1, Q3, Q5 are upper arm switching elements of U, V, W phases, respectively, and switching elements Q2, Q4, Q6 are lower arm switching elements of U, V, W phases, respectively. Taking the U phase as an example, switching elements Q1 and Q2 are connected in series, the collector terminal of Q1 is connected to the positive electrode of the main power supply 16, and the emitter terminal of Q2 is connected to the negative electrode of the main power supply 16. The emitter terminal of Q1 and the collector terminal of Q2 are connected to each other, and the connection point is connected to the terminal of the motor 15. Other V,
The same applies to the W phase.

In this embodiment, the switching element Q
Insulated gate bipolar transistors I to Q6
Uses GBT. Further, each element has a current detection terminal, that is, a current sense terminal. The present embodiment is characterized in that an element having a current sense terminal is used as the output stage switching element of the inverter device. However, as the switching element, in addition to the IGBT of the present embodiment, a power MOSFET or A power transistor or the like may be adopted. Switching elements Q1 to Q
Freewheeling diodes D1 to D6 are connected in parallel to 6, respectively.

Next, the structure for one phase will be described by taking the U phase as an example. First, a drive circuit 1 that outputs a gate voltage to the control terminal of the switching element Q1 is provided as a circuit on the upper arm side. The PWM signal U + for turning on / off the switching element Q1 is supplied from the PWM generator 17 to the drive circuit 1. A resistor R1 is connected between the current sense terminal and the emitter terminal of the switching element Q1.
A voltage drop is generated across the resistor R1 according to the current I1 flowing between the collector and the emitter of the switching element Q1, and the voltage across the resistor R1 is input to the current detection circuit 3. The current detection circuit 3 compares the voltage drop across the resistor R1 with a preset reference voltage value, and outputs the comparison result to the overcurrent protection circuit 2. The overcurrent protection circuit 2 determines that the current I1 is equal to or higher than the overcurrent detection level according to the output signal from the current detection circuit 3, and outputs a signal for turning off the switching element Q1 to the drive circuit 1.

Next, the circuit on the lower arm side drives the drive circuit 4 for applying a gate voltage to the control terminal of the switching element Q2 in accordance with the PWM signal U- supplied from the PWM generator 17.
Equipped with. A resistor R2 is connected between the current sense terminal and the emitter terminal of the switching element Q2. Current I flowing between the collector and emitter of switching element Q2
According to 2, the voltage drop is generated across the resistor R2, and the voltage drop across the resistor R2 is input to the current detection circuit 6.
The current detection circuit 6 includes a resistor R2 as shown in FIG.
The voltage drop at both ends is compared with two preset reference voltages, and the result of the comparison is output to the overcurrent protection circuit 5 and the current direction detection circuit 7.

The overcurrent protection circuit 5 determines in response to the output signal of the current detection circuit 6 that the current I2 is equal to or higher than the overcurrent detection level, and outputs a signal for turning off the switching element Q2 to the drive circuit 4. . As shown in FIG. 3 described later, the current direction detection circuit 7 includes a PWM signal U− supplied from the PWM generator 17 to the drive circuit on the lower arm side and the current detection circuit 6.
The direction of the U-phase output current corresponding to the motor current is determined on the basis of the blocking current detection signal from, and as a result, Su is output from the output terminal 8 to the voltage corrector 20.

The U-phase circuit means 11 includes an upper arm side drive circuit 1, an overcurrent protection circuit 2, a current detection circuit 3 and a lower arm side drive circuit 4, an overcurrent detection circuit 5, a current detection circuit 6, and a current direction. The detection circuit 7 is included. The V-phase circuit means 12 and the W-phase circuit means 13 also include circuits of the same configuration. Output Su of the current direction detection circuit in the U-phase circuit means 11
Similarly, the output of the current direction detection circuit in the V-phase circuit means 12 is Sv, and the output of the current direction detection circuit in the W-phase circuit means 13 is Sw. U-phase circuit means 11, V-phase circuit means 12, W-phase circuit means 13 and switching elements Q1 to Q
6, the free wheeling diodes D1 to D6, and the resistors R1 to R6,
It is formed as a hybrid integrated circuit 14.

Next, the configuration of the PWM control circuit 21 of this embodiment will be described. The PWM control circuit 21 includes the PWM generator 1
7, a carrier generator 18, a voltage commander 19, and a voltage corrector 20. The PWM generator 17 compares the voltage command signal input from the voltage command device 19 with the carrier signal input from the carrier generator 18, and creates a PWM signal based on the result. The voltage corrector 20 creates a voltage correction signal based on the output signals Su, Sv, Sw of the current direction detection circuit of each phase, and outputs this signal to the voltage commander 19
To correct the voltage command signal. Although there are various methods for correcting the voltage command signal based on the detection result of the current direction, the present invention mainly relates to the provision of a small current direction detecting means. Detailed description is omitted.

FIG. 2 is a circuit diagram showing an example of the configuration of the current detection circuits 3 and 6. The current sense terminal of the switching element Q1 is connected to one input terminal of the comparator 22, and the reference voltage source 25 is connected to the other input terminal of the comparator 22. The comparator 22 compares the voltage at the current sense terminal with the reference voltage and outputs the result of the comparison to the overcurrent protection circuit 2. Similarly, the current sense terminal of the switching element Q2 is connected to one input terminal of the comparator 24, and the reference voltage source 27 is connected to the other input terminal of the comparator 24. The comparator 24 compares the voltage of the current sense terminal with the reference voltage and outputs the result of the comparison to the overcurrent protection circuit 5. The current sense terminal of Q2 is connected to the input terminal of the comparator 23, and the reference voltage 26 is connected to the other input terminal of the comparator 23. The comparator 23 compares the voltage of the current sense terminal with the reference voltage,
The result of the comparison is output to the current direction detection circuit 7. A feature of this embodiment is that the current sense terminal for detecting overcurrent is also used for detecting the element current.

FIG. 3 is a diagram showing an example of the configuration of the current direction detection circuit 7. The output of the comparator 23 shown in FIG. 2 is connected to one input terminal of the AND circuit 28, and the PWM signal U− supplied from the PWM generator 17 shown in FIG. 1 is connected to the other input terminal of the AND circuit 28. To do. The AND circuit 28 calculates the logical product of the output of the comparator 23 and the PWM signal U− and outputs the result to the D terminal of the D flip-flop circuit 33. On the other hand, the PWM signal U- is set to NO
It is input to the T circuit 29, and the output of the NOT circuit 29 is input to the resistor 30.
Via one end of the capacitor 31 and the input of the Schmitt trigger circuit 32. The other end of the capacitor 31 is grounded. The output of the Schmitt trigger circuit 32 is
It is input to the C terminal of the D flip-flop circuit 33. D
The flip-flop circuit 33 outputs a current direction signal from the Q terminal to the output terminal 8.

The operation of the load current polarity discriminating means of the present embodiment thus constructed will be described by taking the U phase as an example. When a current flows through the switching elements Q1 and Q2, the currents of the switching elements Q1 and Q2 are shunted to the current sense terminal at a constant rate. When the shunted current flows through the sense resistors R1 and R2 connected to the current sense terminal, the voltage at the current sense terminal rises. This voltage is the current detection circuit 3,
Taken in 6. The comparator 22 compares the voltage at the current sense terminal with the reference voltage 25 and outputs an overcurrent signal indicating that the current flowing through the switching element Q1 is equal to or higher than the maximum rated value. The comparator 23 compares the voltage at the current sense terminal with the reference voltage 26 and outputs an element current detection signal indicating that a current is flowing through the switching elements Q1 to Q6. The comparator 24 compares the voltage at the current sense terminal with the reference voltage 27 and outputs an overcurrent signal indicating that the current flowing through the switching element Q2 is equal to or higher than the maximum rated value.

Generally, the current sense terminal is used only for detecting an overcurrent, but the present embodiment is characterized in that this current sense terminal is also used for detecting the element current. The element current signal output from the current detection circuit 3 and the PWM signal U− output from the PWM control circuit 21 to the hybrid integrated circuit 14
Are input to the current direction detection circuit 7, and the polarity of the current of the motor 15 connected to the inverter is determined.

Next, the method of determining the polarity of the motor current, that is, the load current, will be described in more detail. 4 is shown in FIG.
3 is a time chart showing the relationship between the PWM signals U + and U− input to the inverter bridge circuit, the direction of the motor current, and the current flowing through the switching element that forms the inverter bridge circuit in the inverter device of FIG.

For example, the direction of the motor current Iu is positive in the direction from the output terminal of the inverter circuit to the motor terminal. Taking the U phase as an example, when the motor current Iu is positive, the current flows through the return diode D2 of the lower arm regardless of whether the PWM signal U− input to the switching element Q2 is on or off. Does not flow current. On the other hand, when the motor current Iu is negative, the PWM signal U + input to the switching element Q1 of the upper arm
Regardless of whether it is ON or OFF, the current flows through the freewheeling diode D1 of the upper arm, so that no current flows through the switching element Q1.

Therefore, for example, when the PWM signal U- input to the switching element Q2 is in the ON state and no current flows through the switching element Q2, the motor current is positive, so the element current detection signal and the PWM signal U − And AN
When the result is 0, the direction of the motor current is positive, and when the result is 1, it is determined that the direction of the motor current is negative. The operation result is input to the D terminal of the D flip-flop circuit 33 to latch the operation result, and the C terminal for clock input is PWM
The signal U- is input and the calculation result is updated every carrier period.

As described above, the device current detection signal is P
Since it is necessary to sample when the WM signal U- is on, the calculation result is sampled at the rising timing of the PWM signal U-. D flip-flop circuit 3
When the falling edge is input to the C terminal, the output of 3 is updated, but since the calculation result is sampled at the rising edge of the PWM signal U-, the PWM signal U- is NOT
The circuit 29 inverts. Further, after the PWM signal U- is turned on, the time delay until the comparator output becomes high level due to the current flowing through the switching element is taken into consideration, and the resistor 30
Create a delayed signal with the filter of
Input to C terminal. The current direction signal is output from the Q terminal of the D flip-flop circuit 33 to the current direction signal output terminal 8.

Next, in order to compensate the error of the output voltage of the inverter due to the dead time, the PWM control circuit 21
Then, the PWM signal is corrected. FIG. 5 is a diagram showing an error between the voltage command signal to be output by the inverter and the PWM signal input to the inverter bridge circuit. Motor current Iu
Is positive, the output voltage of the inverter is reduced by the shaded portion with respect to the voltage command signal indicating the voltage to be originally output due to the dead time period. When the motor current Iu is negative, the output voltage of the inverter increases with respect to the voltage command signal only in the shaded area due to the influence of the dead time period.

FIG. 6 is a diagram for explaining the operation of dead time compensation control for enlarging or reducing the PWM signal according to the present invention. In order to correct the error voltage shown in FIG. 5, when the motor current Iu is positive, the PWM signal is expanded for the same period as the dead time, and when the motor current Iu is negative, the PWM signal is PWM for the same period as the dead time. The signal is processed by the PWM control circuit 21 so as to be reduced, and the same inverter output voltage as the voltage command signal is obtained.

In this way, when the PWM signal of either the upper arm or the lower arm and the current of the switching element of the arm are detected, the direction of the motor current can be determined.
Here, if the current of the switching element of the lower arm is detected, the level shift circuit considering the potential difference between the upper and lower arms for outputting the detection signal to the outside becomes unnecessary, and the current of the switching element of the upper arm is detected. It is advantageous over the case.

The above is the method of detecting the element current by using the current sense terminal and discriminating the direction of the motor current.
It is also possible to detect the common voltage of the inverter bridge circuit, that is, the output voltage of the inverter to determine the direction of the motor current.

FIG. 7 is a block diagram showing the configuration of another embodiment of the inverter device according to the present invention. The parts other than the phase circuit means 35, 36, 37 of the inverter device are shown in FIG.
The configuration is the same as that of the above embodiment. The U-phase circuit means 35 includes a drive circuit 1, a voltage detection circuit 34, a drive circuit 4, and a current direction detection circuit 7. The V-phase circuit means 36 and the W-phase circuit means 37 have the same configuration. The output of the current direction detection circuit in the U-phase circuit means 35 is Su, and the V-phase circuit means 36
The output of the current direction detection circuit in the inside is Sv, and the output of the current direction detection circuit in the W-phase circuit means 37 is Sw. Also,
U-phase circuit means 35, V-phase circuit means 36, W-phase circuit means 3
7, switching elements Q1 to Q6, free wheeling diode D1
D6 are formed as a hybrid integrated circuit 38.

Here, only the configuration of the U-phase circuit means 35 different from the U-phase circuit means 11 of FIG. 1 will be described. The circuit on the upper arm side includes a drive circuit 1 that supplies a gate voltage to the control terminal of the switching element Q1. PWM signal U + for turning on / off the switching element Q1
Is supplied from the PWM control circuit 21 to the drive circuit 1. The circuit on the lower arm side is P supplied from the PWM control circuit 21.
The drive circuit 4 is provided for applying a gate voltage to the control terminal of the switching element Q2 according to the WM signal U-. Also,
The output terminal voltage Vu of the inverter circuit is detected by the voltage detection circuit 34.
To enter. The voltage detection circuit 34 compares the output terminal voltage Vu of the inverter circuit with a preset reference voltage value, and outputs the result of the comparison to the current direction detection circuit 7.

FIG. 8 is a diagram showing an example of the configuration of the voltage detection circuit 34 for detecting the output terminal voltage Vu of the inverter bridge circuit. In the voltage detection circuit 34, the resistor R7
And the resistor R8 are connected in series, and the connection point is connected to the minus side input terminal of the comparator 39. The other terminal of the resistor R7 is connected to the control power supply Vcc of the voltage detection circuit, and the other terminal of the resistor R8 is connected to the ground line of the voltage detection circuit. Connect the resistor R9 and the resistor R10 in series,
The connection point is connected to the + input terminal of the comparator 39. The other terminal of the resistor R9 is connected to the control power supply Vcc of the voltage detection circuit, and the other terminal of the resistor R10 is connected to the anode side of the diode D7. The cathode side of the diode D7 is connected to the output terminal Vu of the inverter circuit. The comparator 39 outputs the comparison result to the current direction detection circuit 7.

Next, the operation of the inverter device shown in FIG. 7 will be described. PWM input to the inverter bridge circuit
The relationship between the signals U + and U-, the direction of the current flowing through the output terminal of the inverter bridge circuit, that is, the direction of the motor current, and the output terminal voltage Vu of the inverter bridge circuit is as described above with reference to FIG. Also in this case, the direction of the motor current Iu is positive in the direction from the output terminal of the inverter circuit to the motor terminal. When the PWM signal U- is on, the output terminal voltage V of the inverter bridge circuit
If u is a negative potential, the motor current Iu is positive because current is flowing into the motor through the return diode of the lower arm. Further, if the output terminal voltage Vu is the number V of the ON voltage of the switching element, the motor current Iu can be determined to be negative because a current is flowing from the motor to the switching element of the lower arm. On the other hand, when the PWM signal U + is on and the collector voltage Vu of the lower arm switching element is the value obtained by subtracting the number V of the on-voltage of the upper arm switching element from the inverter DC power supply voltage VE, The motor current Iu is positive because the current flows from the switching element to the motor. If the value is higher than the DC power supply voltage VE of the inverter by the amount of the forward voltage drop of the diode, the motor current Iu is determined to be negative because the current flows from the motor to the return diode of the upper arm. You may.

Output terminal voltage V of the inverter bridge circuit
The voltage detection circuit that detects u determines whether or not there is a current flowing through the switching element Q2 based on the output terminal voltage Vu.
The output terminal voltage Vu becomes a high voltage when the switching element Q2 is turned off and exceeds the input level of the comparator 39. Therefore, the detection value Vs of which the voltage is lowered is created by using the resistors R9, R10 and the diode D7. Is input to the negative input terminal of the comparator 39. A reference voltage is input to the + input terminal of the comparator 39. As for the reference voltage, the control power supply Vcc is connected to the resistors R7 and R8.
It is obtained by partial pressure with. The comparator 39 compares the detected value Vs with the reference voltage Vr. If the detected value Vs is larger than the reference voltage Vr, the comparator output is at a high level, that is, an element current detection signal is output. The result of comparison by the comparator 39 is output to the current direction detection circuit 7.

Subsequent current direction detection circuit 7 and PWM
The operation of the control circuit 21 is the same as that of the embodiment shown in FIG. In this way, the inverter output voltage having the same waveform as the voltage command signal is obtained.

[0047]

According to the present invention, the presence or absence of a current flowing through the switching element of the upper arm or the switching element of the lower arm is detected, and the load is determined from the relationship between the detection result and the current flowing direction peculiar to the switching element. It is possible to determine the polarity of the current and use this result to perform optimum dead time compensation.

Further, the means for detecting the presence or absence of the element current using the switching element with the current detection terminal and the means for detecting the presence or absence of the element current from the polarity of the voltage applied to the switching element are both low loss. Further, it is possible to reduce the size by integrating the circuit without being affected by the temperature fluctuation.

Further, by downsizing the current polarity discriminating means, this means can be made into a hybrid integrated circuit and built in the inverter device, so that the number of parts of the entire system can be reduced and the system can be made compact and low in cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an inverter device provided with a dead time compensating means according to the present invention.

FIG. 2 is a circuit diagram showing an example of a configuration of a current detection circuit and a configuration in the embodiment of FIG.

FIG. 3 is a diagram showing an example of a configuration of a current direction detection circuit in the embodiment of FIG.

FIG. 4 is a time chart showing the relationship between the PWM signals U +, U− input to the inverter bridge circuit, the direction of the motor current, and the current flowing through the switching element forming the inverter bridge circuit in the embodiment of FIG. is there.

FIG. 5 is a diagram showing an error between a voltage command signal to be output by an inverter and a PWM signal input to an inverter bridge circuit.

FIG. 6 is a diagram illustrating an operation of dead time compensation control for enlarging or reducing a PWM signal according to the present invention.

FIG. 7 is a block diagram showing the configuration of another embodiment of the inverter device having the dead time compensating means according to the present invention.

FIG. 8 is a diagram showing an example of the configuration of a voltage detection circuit for detecting the output terminal voltage Vu of the inverter bridge circuit in the embodiment of FIG.

[Explanation of symbols]

 Q1 to Q6 switching elements D1 to D6 freewheeling diodes D7 diodes R1 to R6 sense resistors R7 to R10 resistors 1 drive circuit 2 overcurrent protection circuit 3 current detection circuit 4 drive circuit 5 overcurrent protection circuit 6 current detection circuit 7 current direction detection circuit 8 Current Direction Signal Output Terminal 9 Current Direction Signal Output Terminal 10 Current Direction Signal Output Terminal 11 U-Phase Circuit Means 12 V-Phase Circuit Means 13 W-Phase Circuit Means 14 Hybrid Integrated Circuit 15 Induction Motor 16 Main Power Supply (DC Power Supply) 17 PWM generator 18 Carrier generator 19 Voltage commander 20 Voltage corrector 21 PWM control circuit 22 Overcurrent detection comparator 23 Element current detection comparator 24 Overcurrent detection comparator 25 Reference voltage 26 Reference voltage 27 Reference voltage 28 AND circuit 29 NOT circuit 30 Delay resistor 31 Delay capacitor Sensor 32 Schmitt trigger circuit 33 D flip-flop circuit 34 voltage detection circuit 35 U-phase circuit means 36 V-phase circuit means 37 W-phase circuit means 38 hybrid integrated circuit 39 element current detection comparator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsunori Suzuki 7-1, 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Kozo Watanabe 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 in Hitachi, Ltd. Hitachi Research Laboratory

Claims (10)

[Claims] 1. The upper and lower arm switching elements are PWM
In a method of determining the polarity of a load current of an inverter device which alternately turns on and off by a signal to convert direct current into alternating current and supplies it to a load, the presence or absence of a current flowing in one of the switching elements of the upper and lower arms is detected, and the switching element concerned is detected. The method for determining the polarity of the load current is characterized in that the instantaneous polarity of the load current is determined based on the relationship between the current flowing direction specific to the switching element and the presence / absence of the current during the ON state. 2. The upper and lower arm switching elements are PWM
In a method of determining the polarity of a load current of an inverter device which alternately turns on and off by a signal to convert direct current into alternating current and supplies it to a load, the presence or absence of a current flowing in one of the switching elements of the upper and lower arms is detected by a current sense of the switching element. A load current characterized by detecting from a terminal and determining the instantaneous polarity of the load current based on the relationship between the current flowing direction specific to the switching element and the presence or absence of the current while the switching element is in the ON state. Polarity determination method. 3. The upper and lower arm switching elements are PWM
In a method for determining the polarity of a load current of an inverter device which alternately turns on and off by a signal and converts direct current into alternating current and supplies it to a load, the presence or absence of a current flowing in any one of the switching elements of the upper and lower arms is determined by the output voltage of the switching element. Load based on the relationship between the current flowing direction peculiar to the switching element and the presence / absence of the current during the ON state of the switching element. Current polarity determination method. 4. A dead time compensation method for an inverter device for alternately turning on and off by a PWM signal and converting direct current into alternating current to supply to a load while sandwiching a dead time for simultaneously turning off switching elements of the upper and lower arms, wherein the upper and lower arms are provided. The presence or absence of a current flowing through any one of the switching elements is detected, and the instantaneous polarity of the load current is determined by the relationship between the current flowing direction and the presence or absence of the current, which is peculiar to the switching element during the ON state of the switching element. The one of the PWM signals output to the upper arm and the lower arm in accordance with the instantaneous polarity of the load current, the ON period of the PWM signal is increased by a predetermined correction amount. For the other arm, the ON period of the PWM signal is reduced by the correction amount. Dead time compensation method for burner device. 5. A direct current (DC) comprising a switching element connected to a DC power supply in the form of upper and lower arms and alternately turning on and off, a PWM signal generating means, and a drive circuit for driving the switching element according to the PWM signal. In an inverter device for converting a current into an alternating current and supplying it to a load, means for detecting the presence / absence of current flowing in one of the switching elements of the upper and lower arms; the switching element connected to the PWM signal generating means and the current detecting means. A current direction detecting means for determining the instantaneous polarity of the load current according to the relationship between the current flowing direction peculiar to the switching element and the presence / absence of the current during the ON state, and according to the polarity of the load current, PWM
An inverter device comprising: a voltage command to the signal generating means or a means for outputting a signal for correcting the PWM waveform. 6. A direct current circuit comprising: a switching element connected to a DC power supply in the form of upper and lower arms to alternately turn on and off; a PWM signal generating means; and a drive circuit for driving the switching element according to the PWM signal. In an inverter device for converting into AC and supplying it to a load, means for detecting the presence or absence of an overcurrent flowing in one of the switching elements of the upper and lower arms, and the presence or absence of an overcurrent flowing in the other switching element of the upper and lower arms and the element current Means for detecting the presence / absence of the switching element, a current flowing direction specific to the switching element and the presence / absence of the element current connected to the PWM signal generating means and the other current detecting means while the switching element is in an ON state. The current direction detecting means for discriminating the instantaneous polarity of the load current based on the relationship of P and the P direction according to the polarity of the load current. Inverter device is characterized in that a means for outputting a signal for correcting the voltage command or PWM waveform to the M signal generating means. 7. The inverter device according to claim 5, wherein the switching element includes a current sense terminal that outputs a minute current according to a current flowing through the switching element. . 8. A direct current (DC) comprising a switching element connected to a DC power source in the form of upper and lower arms and alternately turned on and off, a PWM signal generating means, and a drive circuit for driving the switching element according to the PWM signal. In an inverter device for converting into AC and supplying it to a load, means for detecting the presence or absence of a current flowing in any of the switching elements of the upper and lower arms based on the output voltage of the switching element, the PWM signal generating means and the current Current direction detection means connected to the detection means and determining the instantaneous polarity of the load current according to the relationship between the current flowing direction and the presence or absence of the current that is specific to the switching element during the period when the switching element is in the on state, It outputs a voltage command to the PWM signal generating means or a signal for correcting the PWM waveform according to the polarity of the load current. An inverter device comprising: 9. The inverter device according to claim 8, wherein the current detecting means compares the voltage of the connecting portion of the switching elements of the upper and lower arms with a predetermined reference voltage. An inverter device comprising: 10. The inverter device according to claim 5, wherein the correction signal output means to the PWM signal generation means includes the upper arm and the lower arm according to an instantaneous polarity of the load current. Among the PWM signals output to the arms, one arm increases the ON period of the PWM signal by a predetermined correction amount, and the other arm decreases the ON period of the PWM signal by the correction amount. An inverter device, characterized in that it is a means for causing it.