JP4467752B2 - Current control method and current control circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a current control method and a current control circuit, which allows a large current to flow through a coil as a load and improves the response.
[0002]
[Prior art]
Magnetic bearings are used as bearings for turbo molecular pumps, work spindles, centrifuges, and the like. In this magnetic bearing, a plurality of electromagnets are arranged around a rotating shaft, and the rotating shaft is supported in a non-contact manner by the magnetic attractive force of the electromagnet. In addition, the magnetic attraction force of each electromagnet is controlled by controlling the current flowing through each electromagnet so that the rotation center of the rotation shaft occupies the rotation center position of the magnetic bearing.
[0003]
Next, a conventional current control circuit for controlling the current flowing through the electromagnet of the magnetic bearing will be described with reference to FIGS.
[0004]
FIG. 2 shows a transistor-controlled current control circuit 10 which is currently mainstream. In the transistor variable current control circuit 10, an electromagnet coil 1, a variable resistance transistor 11, and a resistance element 12 are connected in series. A diode 13 and a resistance element 14 are connected in parallel to the electromagnet coil 1, and a diode 15 is connected in reverse parallel to the variable resistance transistor 11. The transistor control circuit 16 sends a transistor control signal a to the base of the variable resistance transistor 11.
[0005]
The emitter-collector resistance of the transistor 11 changes according to the value of the transistor control signal a. That is, when the value of the transistor control signal a increases, the resistance between the emitter and the collector of the transistor 11 decreases, and the current flowing through the transistor 11 and thus the current flowing through the electromagnet coil 1 increases. Conversely, when the value of the transistor control signal a decreases, the resistance between the emitter and the collector of the transistor 11 increases, and the current flowing through the transistor 11 and thus the current flowing through the electromagnet coil 1 decreases. Thus, by adjusting the value of the transistor control signal a, the current flowing through the electromagnet coil 1 is controlled to control the electromagnetic attractive force of the electromagnet.
[0006]
FIG. 3 shows a PWM current control circuit 20. The current control circuit 20 is constituted by an H-type mixed bridge circuit. That is, a switching element 21 made of an FET (field effect transistor) is connected to the upper arm of the first phase (left phase) of the H-type mixed bridge circuit, and the regeneration is performed to the lower arm of the first phase (left phase). A diode 22 is connected, a regenerative diode 23 is connected to the upper arm of the second phase (right phase), and a switching element 24 made of FET is connected to the lower arm of the second phase (right phase). . A diode 25 is connected to the switching element 21 and a diode 26 is connected to the switching element 24 in antiparallel. A resistance element 27 and the electromagnet coil 1 are connected in series to the load branch.
[0007]
The difference circuit 28 detects a voltage drop at the resistance element 27 and outputs a current detection signal b indicating the value of the load current flowing through the electromagnet coil 1 to the PWM control circuit 29. The PWM control circuit 29 sends a PWM signal c such that the value of the current detection signal b becomes a set value to the switching elements 21 and 24. The switching elements 21 and 24 are turned ON / OFF according to the high / low of the PWM signal c. When the switching elements 21 and 24 are in the ON state (conducting state), a current flows along a path of power source → switching element 21 → resistance element 27 → electromagnetic coil 1 → switching element 24 → ground. When the switching elements 21 and 24 are in the OFF state (cut-off state), a current flows along the path of ground → regenerative diode 22 → resistive element 27 → electromagnetic coil 1 → regenerative diode 23 → power source.
[0008]
When the load current value becomes smaller than the set value and the current detection signal b becomes small, the pulse width of the PWM signal c is widened (the high level period is lengthened), and the ON period of the switching elements 21 and 24 is set. Lengthen. On the contrary, when the load current value becomes larger than the set value and the current detection signal b becomes large, the pulse width of the PWM signal c is shortened (high level period is shortened) and the ON period in the switching elements 21 and 24 is set. To shorten. In this way, the load current that flows through the electromagnet coil 1 can be controlled.
[0009]
In this PWM method,
(1) Even when the switching elements 21 and 24 are in the OFF state (cut-off state), the electrical energy storage effect of the electromagnet coil 1 is used to make ground → regenerative diode 22 → resistive element 27 → electromagnetic coil 1 → regenerative diode. Current can flow along the path of 23 → power supply,
(2) Since the switching loss in the switching elements 21 and 24 is small, there is an advantage that the power consumption is small and the size can be reduced.
[0010]
[Problems to be solved by the invention]
By the way, the transistor variable system shown in FIG. 2 has the greatest drawback that loss (heat generation) in the drive circuit (variable resistance transistor 11) is large. For this reason, a large power source and a large heat radiating plate are required, so that there is a disadvantage that the size cannot be reduced.
[0011]
On the other hand, in the PWM method shown in FIG. 3, since the current control is performed by turning on and off the switching elements 21 and 24, electrical noise must be reduced. For this purpose, the carrier (switching) frequency is set to an audible frequency. Need to be higher. However, in the PWM method, when the carrier frequency is increased, the time constant for the rise and fall of the current uniquely determined by the voltage applied to the electromagnet coil 1 and the inductance and resistance of the electromagnet coil 1 is large. There is a problem that the current cannot flow and the electromagnetic attractive force by the electromagnet coil 1 is limited.
[0012]
An object of the present invention is to provide a current control method and a current control circuit capable of flowing a large current with low power consumption and excellent responsiveness in view of the above prior art.
[0013]
[Means for Solving the Problems]
The configuration of the current control method of the present invention that solves the above problems includes two switching elements, a coil that is a load connected between the two switching elements, and a regeneration that discharges electrical energy accumulated in the coils. In a current control method having a diode and switching the two switching elements,
When the value of the load current flowing through the coil is smaller than the current target value, the switching element on the downstream side of the coil is forcibly turned on, and the current due to the electric energy accumulated in the coil is switched downstream. It is characterized by circulating in a closed circuit composed of an element, the regenerative diode and the coil.
[0014]
The current control circuit of the present invention includes two switching elements, a coil that is a load connected between the two switching elements, a regenerative diode that discharges electrical energy accumulated in the coil, In a current control circuit having a switching signal control circuit for sending a switching signal to two switching elements,
When the value of the load current flowing through the coil is smaller than the current target value, a commutation path control circuit for forcibly bringing the switching element downstream of the coil into a conductive state is provided.
[0015]
The current control circuit according to the present invention has a configuration in which the first switching element is connected to the upper arm of the first phase, the first regenerative diode is connected to the lower arm of the first phase, and the upper arm of the second phase is connected. An H-shaped bridge circuit formed by connecting a second regenerative diode, connecting a second switching element to the lower arm of the second phase, and connecting a coil to the load branch;
A switching signal control circuit for sending a switching signal to the first switching element and the second switching element;
Load current detecting means for detecting the value of the load current;
Commutation path control means for forcibly bringing the second switching element into a conductive state when the detected load current value is smaller than a preset load current target value.
[0016]
The switching element is a field effect transistor.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
[0018]
FIG. 1 shows a PWM current control circuit 100 according to an embodiment of the present invention. The main circuit of the current control circuit 100 is composed of an H-type mixed bridge circuit. That is, the switching element 101 made of FET is connected to the upper arm of the first phase (left phase) of the H-type mixed bridge circuit, and the regenerative diode 102 is connected to the lower arm of the first phase (left phase). The regenerative diode 103 is connected to the upper arm of the second phase (right phase), and the switching element 104 made of FET is connected to the lower arm of the second phase (right phase). A diode 105 is connected to the switching element 101, and a diode 106 is connected to the switching element 104 in antiparallel. Further, the resistance element 107 and the electromagnet coil 1 are connected in series to the load branch. That is, the electromagnetic coil 1 that is a load is connected between the upstream side switching element 101 and the downstream side switching element 104.
[0019]
A direct current is supplied to the current control circuit 100 from the power supply 30. Then, as will be described later, the value of the load current flowing through the electromagnetic coil 1 is adjusted by controlling the switching operation of the switching elements 101 and 104.
[0020]
The difference circuit 108 detects a voltage drop in the resistance element 107 and outputs a current detection signal b indicating the value of the load current flowing in the electromagnet coil 1 to the PWM control circuit 109. The PWM control circuit (switching signal control circuit) 109 sends a PWM signal (switching signal) c such that the value of the current detection signal b becomes a set value to the switching elements 101 and 104. Note that the PWM signal c is sent directly to the switching element 101, but the PWM signal c is sent to the switching element 104 via the OR circuit 110. The carrier frequency in the PWM control circuit 109 is set high to reduce electrical noise.
[0021]
The commutation path control circuit 111 compares the value of the current detection signal b with the current target value, and when the value of the current detection signal b exceeds the current target value (that is, the value of the load current exceeds the current target value). The commutation path control signal d that is at a low level is output, and the value of the current detection signal b is lower than the current target value (that is, the load current value is lower than the current target value). The commutation path control signal d which is at a high level is output. This commutation path control signal d is input to the switching element 104 on the downstream side via the OR circuit 110.
[0022]
The control operation of the current control circuit 100 configured as described above includes (1) when the value of the current detection signal b exceeds the current target value, and (2) when the value of the current detection signal b falls below the current target value. This will be explained separately.
[0023]
(1) Control operation in the case where the value of the current detection signal b exceeds the current target value (that is, the load current value exceeds the target value).
In this case, the commutation path control signal d is at a low level. On the other hand, the PWM signal c is input to the switching elements 101 and 104, and the switching elements 101 and 104 are switched on and off in accordance with the high and low of the PWM signal c.
[0024]
When the switching elements 101 and 104 are turned on (conductive state), a current flows along the path of the power source 30 → the switching element 101 → the resistance element 107 → the electromagnetic coil 1 → the switching element 104 → the ground.
[0025]
When the switching elements 101 and 104 are in the OFF state (cut-off state), the electric energy accumulated in the electromagnet coil 1 causes the discharge of ground → regenerative diode 102 → resistive element 107 → electromagnetic coil 1 → regenerative diode 103 → power source 30. Current flows along the path. The current flowing along such a discharge path is rapidly attenuated and forcibly discharged, and the discharge proceeds rapidly. The reason why the current flowing in the discharge path rapidly attenuates is as follows. When the carrier frequency is increased, the rise of the current uniquely determined by the voltage applied to the electromagnetic coil 1 and the inductance and resistance of the electromagnetic coil 1 This is because the current is suppressed due to the time constant for falling. However, in this case, the value of the current detection signal b (load current value) exceeds the current target value, which is rather convenient.
[0026]
(2) Control operation when the value of the current detection signal b is lower than the current target value (that is, when the load current value is lower than the current target value).
In this case, the commutation path control signal d is at a high level. On the other hand, the switching element 101 is turned ON / OFF according to the high / low of the PWM signal c. Further, since the high-level commutation path control signal d is input to the switching element 104 via the OR circuit 110, the switching element 104 is forcibly turned on regardless of whether the PWM signal c is high or low.
[0027]
For this reason, when the PWM signal c is at a high level, the switching elements 101 and 104 are both turned on (conductive state). At this time, a current flows along a path of the power source 30 → the switching element 101 → the resistance element 107 → the electromagnetic coil 1 → the switching element 104 → the ground.
[0028]
In a state in which the PWM signal c is at a low level, the switching element 101 is in an OFF state (blocking state), but the switching element 104 is maintained in an ON state (conduction state). For this reason, the electric energy accumulated in the electromagnet coil 1 circulates (commutates) the current along the closed circuit of the electromagnet coil 1 → the switching element 104 → the regenerative diode 102 → the resistance element 107 → the electromagnet coil 1. Since the electric current is circulated (commutated) along such a closed circuit, the discharge of electric energy is delayed and the attenuation of the circulating current flowing in the closed circuit becomes slow.
[0029]
For this reason, when the PWM signal c changes from the low level to the high level, the load current value increases from the value of the circulating current (load current) that has not been attenuated so much, so that the load current may be increased. it can. As a result, a large current can flow while increasing the carrier frequency. In addition, since the switching element 104 is selectively turned on according to the value of the current detection signal b, low power consumption and high responsiveness can be realized simultaneously. Also, the advantages of the low power consumption and the high tracking capability of current control that are inherent to the PWM method are maintained.
[0030]
【The invention's effect】
As described above in detail with the embodiment, in the current control method of the present invention, two switching elements, a coil that is a load connected between the two switching elements, and the coil stored in the coil are stored. In a current control method having a regenerative diode for discharging electric energy and switching the two switching elements, when the value of the load current flowing through the coil is smaller than a current target value, switching downstream of the coil is performed. The element was forced to be in a conductive state, and a current due to the electric energy accumulated in the coil was circulated and circulated in a closed circuit including the downstream switching element, the regenerative diode, and the coil.
In the current control circuit of the present invention, two switching elements, a coil that is a load connected between the two switching elements, a regenerative diode that discharges electrical energy accumulated in the coils, and the two In a current control circuit having a switching signal control circuit for sending a switching signal to the switching element, when the value of the load current flowing through the coil is smaller than the current target value, the switching element on the downstream side of the coil is forcibly turned on. The configuration includes a commutation path control circuit.
[0031]
Due to such a configuration, in the present invention, it is possible to select a current fall time uniquely determined by a voltage applied to a coil such as an electromagnetic coil, a coil inductance, and a resistance. It is possible to flow a large current while suppressing the release of electrical energy from the coil at the time. In addition, the characteristic of low power consumption, which is a merit of the conventional switching method, can be realized at the same time.
[0032]
In the current control circuit of the present invention, the first switching element is connected to the upper arm of the first phase, the first regeneration diode is connected to the lower arm of the first phase, and the second arm is connected to the second arm of the second phase. A regenerative diode, a second switching element connected to the lower arm of the second phase, and a coil connected to the load branch, and a first switching element and a second switching element A switching signal control circuit for sending a switching signal to the load, load current detection means for detecting the value of the load current, and when the detected load current value is smaller than the current target value, the second switching element is forcibly turned on And a commutation path control means.
In this case, the switching element is a field effect transistor.
[0033]
Due to such a configuration, in the present invention, it is possible to select a current fall time uniquely determined by a voltage applied to a coil such as an electromagnetic coil, a coil inductance, and a resistance. It is possible to flow a large current while suppressing the release of electrical energy from the coil at the time. In addition, the characteristic of low power consumption, which is a merit of the conventional switching method, can be realized at the same time.
Moreover, the present invention can be easily realized by adding commutation path control means to a conventional current control circuit using an H-type bridge circuit.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a current control circuit according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a conventional transistor variable current control circuit;
FIG. 3 is a circuit diagram showing a conventional PWM current control circuit;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electromagnetic coil 30 Power supply 100 Current control circuit 101,104 Switching element (FET)
102, 103 Regenerative diodes 105, 106 Diode 107 Resistance element 108 Difference circuit 109 PWM control circuit 110 OR circuit 111 Commutation path control circuit b Current detection signal c PWM signal d Commutation path control signal

Claims (4)

A current that has two switching elements, a coil that is a load connected between the two switching elements, and a regenerative diode that discharges the electrical energy stored in the coil, and performs switching operation of the two switching elements In the control method,
When the value of the load current flowing through the coil is smaller than the current target value, the switching element on the downstream side of the coil is forcibly turned on, and the current due to the electric energy accumulated in the coil is switched downstream. A current control method characterized by circulating in a closed circuit comprising an element, the regenerative diode and the coil. Two switching elements, a coil that is a load connected between the two switching elements, a regenerative diode that discharges electrical energy stored in the coils, and a switching signal that sends a switching signal to the two switching elements In a current control circuit having a control circuit,
A current control comprising a commutation path control circuit that forcibly turns on a switching element downstream of the coil when a value of a load current flowing through the coil is smaller than a target current value. circuit. The first switching element is connected to the upper arm of the first phase, the first regenerative diode is connected to the lower arm of the first phase, the second regenerative diode is connected to the upper arm of the second phase, and the second An H-shaped bridge circuit in which a second switching element is connected to the lower arm of the phase and a coil is connected to the load branch;
A switching signal control circuit for sending a switching signal to the first switching element and the second switching element;
Load current detecting means for detecting the value of the load current;
A commutation path control means for forcibly bringing the second switching element into a conductive state when the detected load current value is smaller than the current target value. 4. The current control circuit according to claim 2, wherein the switching element is a field effect transistor.

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