JPH06259151A - Current control circuit - Google Patents

Abstract

PURPOSE:To increase the load capacity by supplying the detection currents of plural coils magnetically connected together to a differential amplifier and applying a pulse to the gate terminal of a switching element in response to the deviation between the output of the differential amplifier and a current command. CONSTITUTION:Two coils of an electromagnet 72 are magnetically connected to each other so that their magnetic fluxes are generated in the same direction. Then a comparator 11 compares the signal of a rectangular wave transmitter 12 with the current of the electromagnet 72 to generate the pulse string signal in response to the result of comparison performed between the current of the electromagnet 72 detected by a differential amplifier 8 and the current command input of a comparator 9. A command is sent to a gate driver 13 and the switching elements 1 and 2 are repetitively turned on and off. When both elements 1 and 2 are turned on, the currents flowing to the electromagnet 72 are increased and then reduced vice versa. Therefore the elements 1 and 2 can work in a normal state and with no breakage even if no synchronization is secured between both elements. Thus the load capacity is increased without increasing the capacity of a switching element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a current control circuit including a switching element having an electromagnet including an inductance, an electric motor or the like as a load.

[0002]

2. Description of the Related Art Current control circuits are used in industrial servomotors, magnetic bearings and magnetic levitation devices that are supported in a non-contact manner. To improve these performances, the performance of the current control circuits must be improved. I won't. Therefore, recently, a current control circuit using a switching element has been used to reduce the loss. A conventional current control circuit using a switching element, which supplies current in only one direction, will be described with reference to FIG. In the figure, 1 is a first switching element, 2 is a second switching element, 3 is a first diode, 4 is a second diode, 5 is a first shunt resistor for current detection, and 6 is a current detection. Second shunt resistor, 7 is a load electromagnet with inductance,
8 is a differential amplifier for current detection, 9 is a comparator, 10 is a phase controller, 11 is a second comparator, 12 is a triangular wave oscillator, 1
Reference numeral 3 is a gate driver. First switching element 1
Has one terminal connected to the (+) side of the main circuit power source and the other terminal connected to the cathode of the first diode 3. The second switching element 2 has one terminal of the three terminals connected to the anode of the second diode 4 and the other terminal connected to the ground of the main circuit power supply through the second shunt resistor 6. The anode of the first diode 3 is connected to the ground of the main circuit power supply via the first shunt resistor 5,
The cathode of the second diode 4 is connected to the (+) side of the main circuit power supply. One terminal of the electromagnet 7 is connected to the contact points of the cathodes of the first switching element 1 and the first diode 3, and the other terminal is connected to the contact points of the second diode 4 and the second switching element 2. There is. Of the two input terminals of the differential amplifier 8, one is connected to the contact point of the first diode 3 and the first shunt resistor 5, and the other is connected to the second switching element 2 and the second shunt resistor 6.
Connected to the contact. One of the two inputs of the comparator 9 is the current command input, the other is the output of the differential amplifier 8, and the output of the comparator 9 is connected to the input of the phase controller 10. One input of the second comparator 11 is connected to the output of the phase controller 10, and the other input is connected to the output of the triangular wave oscillator 12. The input of the gate driver 13 is connected to the output of the second comparator 11,
One of the two outputs is connected to the gate of the first switching element 1 and the other is the second switching element 2
Is connected to the gate. In such a configuration,
When the main circuit current detected by the differential amplifier 8, that is, the current flowing through the load electromagnet 7 is smaller than the current command input of the comparator 9, the phase controller 10 operates to increase the output signal.
The second comparator 11 receiving this signal is the triangular wave oscillator 12
The pulse train signal is generated in comparison with the above signal and the command is sent to the gate driver 13. In response to this, the switching elements 1 and 2 are repeatedly turned on and off. When it is on, the current flowing through the load electromagnet 7 increases, and when it is off, the load electromagnet 7
The current flowing through it decreases. As the output of the phase controller 10 increases, the probability of turning on increases, so the current flowing through the electromagnet 7 of the load increases on average. On the other hand, when the main circuit current detected by the differential amplifier 8 is larger than the current command input to the comparator 9, the phase controller 10 works to reduce the output signal. The second comparator 11 receiving this signal compares it with the signal of the triangular wave oscillator 12 to generate a pulse train signal and sends a command to the gate driver 13. In response to this, the switching elements 1 and 2 are repeatedly turned on and off. When it is on, the current flowing through the load electromagnet 7 increases, and when it is off, the current flowing through the load electromagnet 7 decreases. When the output of the phase controller 10 becomes small, the probability of being turned on becomes low, so that the current flowing through the electromagnet 7 of the load decreases on average. In this way, since the switching elements 1 and 2 are repeatedly turned on and off, the electric current of the electromagnet 7 of the load has a triangular ripple, but on average, the electric current is controlled by following the electric current command input to the comparator 9. It One way to improve the responsiveness of the current control is to reduce the inductance of the electromagnet 7 of the load, but if the inductance is reduced, the current ripple increases, so the oscillation frequency of the triangular wave oscillator 12 is increased to increase the ripple. Is suppressing the increase.

[0003]

As described above, when the current response is improved, the oscillating frequency of the triangular wave oscillator 12 is increased, so that the delay of the switching element cannot be ignored. The switching elements 1 and 2 need to be turned on at the same time, but in reality, since the delays are slightly different from each other, it is necessary to configure the gate driver 13 according to the element. This gate driver 13 has a triangular wave oscillator 1
The higher the oscillation frequency of 2 is, the more difficult it is and the more troublesome it is. Also, when increasing the current capacity according to the load, it is sufficient to increase the capacity of the switching element, but there are limits to the actual elements, so two identical current control systems are configured and two coils are wound around the electromagnet of the load. A method of driving in parallel (Japanese Patent Laid-Open Nos. 61-113216 and 62-43713) is also considered. However, preparing two sets of the same configuration is not only uneconomical, but also has the drawback that two control systems interfere with each other and cause various troubles. SUMMARY OF THE INVENTION It is an object of the present invention to provide a current control circuit that does not require complete synchronization of switching elements and can increase load capacity without increasing the capacity of switching elements.

[0004]

To achieve the above object, the present invention comprises a pair of first and second coils magnetically coupled so that generated magnetic fluxes have the same direction. One end of the first coil is connected to a connection point between one end of the first switching element and the cathode of the first diode, and the other end of the first coil is grounded via the first current detector. The other end of the first switching element is connected to a positive DC power supply, the anode of the first diode is connected to a negative DC power supply, and one end of the second coil is connected to the second switching power supply. The one end of the element and the anode of the second diode are connected to each other, and the other end of the second coil is grounded via a second current detector.
The other end of the switching element is connected to the negative DC power supply, the cathode of the second diode is connected to the positive DC power supply, and a differential amplifier for inputting the detection currents of the first and second coils And a gate driver for applying an output pulse whose duty varies depending on the deviation between the output of the differential amplifier and the current command to the gate terminals of the first and second switching elements.

[0005]

With this configuration, when the two switching elements are turned on, the current of one coil flows from the (+) side of the main circuit power supply to the ground via the switching element, the coil and the shunt resistor for current detection. The current increases, and the current of the other coil flows from the ground side of the main circuit power supply to the (-) side via the current detection shunt resistor, coil and switching element, and the current increases,
When the two switching elements are turned off, the current in one coil flows from the (-) side of the main circuit power supply to the ground via the diode, the coil, and the shunt resistor for current detection, so that the current decreases and the other coil's current decreases. Since the current flows from the ground side of the main circuit power supply to the (+) side via the shunt resistor for current detection, coil and diode, the current decreases and the switching elements are damaged even if the two switching elements cannot be synchronized. Without the need for a well-tuned gate driver to perform any of the above without a normal operation, and when increasing the overall capacitance, add two coils to the electromagnet of the load and wind it above each. Since the same operation as above is performed by configuring the same main circuit as above, and it is not necessary to add another control circuit, it is easy to increase the capacity. Than it is.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining an embodiment of the present invention. In the figure, 1 is a first switching element and 2 is a second switching element.
Switching element, 3 is a first diode, 4 is a second diode
, 5 is the first shunt resistor for current detection,
6 is a second shunt resistor for current detection, 72 is an electromagnet of a load having an inductance, 8 is a differential amplifier for current detection, 9 is a comparator, 10 is a phase controller, 11 is a second comparator, Reference numeral 12 is a triangular wave oscillator, and 13 is a gate driver. In the first switching element 1, one of the three terminals is connected to the (+) side of the main circuit power supply and the other terminal is connected to the cathode of the first diode 3 whose anode is connected to the (-) side of the main circuit power supply. It is connected. In the second switching element 2, one of the three terminals is connected to the anode of the second diode 4 whose cathode is connected to the (+) side of the main circuit power supply, and the other terminal is connected to the (-) of the main circuit power supply. Has been done. Electromagnet 72
Is wound with two coils, one of the two coils has one end connected to the ground through the first shunt resistor 5, and the other end has the first switching element 1
And the first diode 3 are connected to each other, one end of the other coil is connected to the ground through the second shunt resistor 6, and the other end is connected to the second diode 4
And the contact of the second switching element 2 are connected.
The two coils of the electromagnet 72 are wound so that the direction in which current flows from one coil to the first shunt resistor 5 is the same as the direction in which current flows from the second shunt resistor 6 to the other coil. Has been done. One coil of the electromagnet 72 and the contact point of the first shunt resistor 5 and the other coil of the electromagnet 72 and the contact point of the second shunt resistor 6 are respectively connected to two inputs of the differential amplifier 8. . One of the two inputs of the comparator 9 is a current command input,
The other is the output of the operational amplifier 8, and the output of the comparator 9 is input to the phase controller 10. One input of the second comparator 11 is the output of the phase controller 10, and the other input is the output of the triangular wave oscillator 12. The input of the gate driver 13 is connected to the output of the comparator 11, one of the two outputs is connected to the gate of the first switching element 1 and the other is connected to the gate of the second switching element 2. ing. In such a configuration, when the main circuit current detected by the differential amplifier 8, that is, the current of the electromagnet 72 is smaller than the current command input of the comparator 9, the phase controller 1
0 works to increase the output signal. The second comparator 11 receiving this signal compares it with the signal of the triangular wave oscillator 12 to generate a pulse train signal and sends a command to the gate driver 13. In response to this, the switching elements 1 and 2 are repeatedly turned on and off. Here, the direction in which the current flows from the marked terminals of the two coils of the electromagnet 72 to the coils is defined as the positive direction. When the switching elements 1 and 2 are turned on, the current flowing through the electromagnet 72 increases, and when the switching elements 1 and 2 are turned off, the current flowing through the electromagnet 72 decreases. As the output of the phase controller 10 increases, the probability of turning on increases, so that the current flowing through the electromagnet 72 increases on average. On the other hand, when the main circuit current detected by the differential amplifier 8 is larger than the current command input to the comparator 9, the phase controller 10 works to reduce the output signal. The second comparator 11 receiving this signal compares it with the signal of the triangular wave oscillator 12 to generate a pulse train signal and sends a command to the gate driver 13. In response to this, the switching elements 1 and 2 are repeatedly turned on and off. When it is on, all the currents flowing through the electromagnet 72 increase, and when it is off, all the currents flowing through the electromagnet 72 decrease. When the output of the phase controller 10 becomes small, the probability of being on becomes low, so that the currents flowing through the electromagnets 72 all decrease on average. In this way, the switching elements 1, 2
Is repeatedly turned on and off, the current of the electromagnet 72 has a ripple of a triangular wave, but on average, the current is controlled by following the current command input to the comparator 9. One way to improve the responsiveness of this current control is to reduce the inductance of the electromagnet 7, but if the inductance is reduced, the current ripple increases, so the triangular wave oscillator 12
Increase the oscillation frequency of to reduce the ripple. At this time, even if the operations of the two switching elements 1 and 2 are slightly deviated from each other, since the main circuit including each coil is separate, the same operation as above does not occur and no problem occurs. For example, when the two switching elements 1 and 2 are turned on and the currents of the two coils of the electromagnet 72 are increasing, the current of the switching element 1 stops flowing when only the switching element 1 is turned off. From the (-) side to the ground through the first diode 3 and the coil and the first shunt resistor 5, and the current decreases. Further, when the two switching elements 1 and 2 are off and the currents of the two coils of the electromagnet 72 are decreasing, if only the first switching element 1 is on, from the (−) side of the main circuit power supply until then. First
The current that has flowed to the ground through the diode 3 and the coil and the first shunt resistor 5 is reduced instead of flowing from the first switching element 1 through the coil and the first shunt resistor 5. Begins to increase. When the two switching elements 1 and 2 are on and the currents of the two coils of the electromagnet 72 are increasing, only when the second switching element 2 is off, and when the two switching elements 1 and 2 are off, the electromagnet is off. When only the second switching element 2 is turned on when the currents of the two coils of 72 are decreasing, the same operation as above is performed in any of the cases.
Therefore, it is not necessary to strictly adjust the gate driver 13 and increase the synchronization between the two switching elements 1 and 2 as the oscillation frequency of the triangular wave oscillator 12 is increased.
Further, when increasing the capacity of the electromagnet 72, a plurality of electromagnet coil groups are provided, each of which constitutes a main circuit similar to that of FIG. 1, and the signal of the gate driver 13 is shared as the gate signal of the added switching element. The total current can be detected by adding a current detection differential amplifier and adding signals from the same number of differential amplifiers as the coil set. FIG. 2 is a block diagram showing a second embodiment of the present invention. Each coil has the same number of turns, and when the switching element 1a is on, a positive DC power source (+) → 1a → coil → shunt 5 →
It flows to GND (ground), and when switched off, negative DC power supply (-) → diode 3 → coil → shunt 5 → GND
It flows with (ground). Therefore, since (+) and (-) only supply current, the average current of each becomes 1/2 of the coil average current. When the number of coils having the same structure is increased, the (+) and (−) capacities also increase accordingly. Half the switching period (ie half the total time) is because the flywheel current is pumping up the power supply,
Conventionally, it is regenerated to the same (+), but in the present invention,
The switching element 2a connected to (-) has the same function. GND when 2a turns on
→ shunt 6 → coil → 2a → (-) flow, and when turned off, GND → shunt 6 → coil → diode 4 →
Since the current flows to (+) and (+) and (-) only flow in current, the currents that were only supplied when 1a is turned on and off are summed up. Therefore, even if a current flows through the two coils, the (+) and (-) currents become zero on average, and the power supply can have a small capacity. When the capacity is increased, the same rise (that is, the same frequency characteristic) can be maintained by increasing the number of coil turns and simultaneously increasing the voltage according to the number of turns, but a large capacity switching element is required. With large capacity, the frequency characteristics are generally poor, and there are restrictions. Therefore, as in the present invention, a switching element connected to (+) and a switching element connected to (-) are paired. When the capacity is increased, the capacity of the power supply can be minimized by increasing the capacity in pairs so that the supply and inflow of the (+) and (-) currents are balanced. Thus, the comparator 9, which is a main part of the current control circuit, the phase controller 10, the second comparator 11, and the triangular wave oscillator 12 are combined to form one current control system, which is a concern in the conventional method. The problem of control system interference does not occur. The above is an example of controlling the current of the electromagnet.
The present invention can be applied to the case of controlling the current supplied to the stator of the servo motor instead of the electromagnet.
FIG. 3 is a diagram showing a coil wound around the stator 16 of the motor. In this figure, the terminal a _{1 of} each coil,
a ₂ , a ₃ and a ₄ respectively represent the same terminals as in FIG. The other coil terminals b _{1 to} b ₄ and c _{1 to} c ₄ are also connected to the same circuit as in FIG. For example, if the currents flowing in the respective coils are controlled by current commands with a 120 ° phase shift, the rotor 17 of the motor can be rotated.

[0007]

According to the present invention, the performance can be improved by raising the carrier frequency of the switching type current control circuit without strictly adjusting the gate signal of the switching element according to the dynamic characteristics of the switching element. The load capacity and the current control circuit capacity can be increased simply by increasing the number of coil turns and adding a corresponding main circuit and differential amplifier without increasing the element capacity. Has the effect of improving the performance of the servo motor.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a coil wound around a stator of a motor.

FIG. 4 is a diagram showing an embodiment of a conventional current control circuit.

[Explanation of symbols]

 1 1st switching element 2 2nd switching element 1a, 2a, 1b, 2b Switching element 3 1st diode 4 2nd diode 5 1st current detection shunt resistance 6 2nd current detection shunt resistance 7 , 72 Electromagnet 8 Current detection differential amplifier 9 Comparator 10 Phase controller 11 Second comparator 12 Triangular wave oscillator 13 Gate driver 14 Positive DC power supply 15 Negative DC power supply 16 Stator 17 Rotor

Claims (3)

[Claims] 1. A pair of first and second coils that are magnetically coupled so that generated magnetic fluxes are in the same direction, and one end of the first coil is connected to one end of the first switching element. 1
Connected to the cathode of the diode, the other end of the first coil is grounded via the first current detector, and the other end of the first switching element is connected to a positive DC power supply. , The anode of the first diode is connected to a negative DC power source, and one end of the second coil is connected to a connection point between one end of the second switching element and the anode of the second diode, The other end of the second coil is grounded via a second current detector, the other end of the second switching element is connected to the negative DC power supply, and the cathode of the second diode is the positive electrode. Differential amplifier connected to the DC power supply of the first and second coils and inputting the detection currents of the first and second coils, and the output pulse whose duty changes according to the deviation between the output of the differential amplifier and the current command. , The second switchon Current control circuit, characterized in that a gate driver for applying to the gate terminal of the device. 2. The positive and second coils, the first and second switching elements, the first and second current detectors, and the first and second diodes are provided in the same number, respectively, A common DC power supply to the plurality of first switching elements and a plurality of second diodes, and a negative DC power supply to the plurality of second switching elements and a plurality of first diodes, respectively. A current comprising: a gate driver connected to the gate terminals of the plurality of first and second switching elements; and a differential amplifier for inputting the detection current of the plurality of first and second coils. Control circuit. 3. The first and second coils wound around a stator of an electric motor for each phase, and a gate driver which is provided for each phase and drives the first and second switching elements. , A differential amplifier provided for each phase for inputting the detected currents of the first and second coils, and the gate according to the deviation between the current command and the output of the differential amplifier for each phase. A current control circuit characterized by driving a driver.