JP4765573B2 - Magnetic levitation controller - Google Patents

Description

  The present invention relates to a two-quadrant drive circuit that supplies a drive current to an electromagnet, and a magnetic levitation control device including the two-quadrant drive circuit.

  In a device having a high-speed rotation shaft such as a turbo molecular pump, a magnetic bearing is employed to support the rotation shaft in a non-contact manner. A two-quadrant drive circuit is known as a drive circuit for an electromagnet provided in such a magnetic bearing (see, for example, Patent Document 1).

  In the two-quadrant driving circuit, the driving operation is performed by simultaneously turning on and off the two switching transistors. Turning on both transistors increases the electromagnet current, and turning off both transistors decreases the electromagnet current. That is, by changing the on / off duty ratio, the current of the electromagnet is held, increased, or decreased.

JP 2001-140881 A

  By the way, when a current driving command having a high frequency and a large amplitude that cannot follow the electromagnet current is input to the two-quadrant driving circuit, the two-quadrant driving circuit repeats 100% duty and 0% duty. However, in the two-quadrant driving circuit, the action of decreasing the electromagnet current is larger than the action of increasing the electromagnet current, and therefore the average value of the electromagnet current tends to decrease from the intended average current value. Therefore, when the two-quadrant drive circuit is used in a magnetic levitation device, there is a problem that the average value of the electromagnet current is reduced, the overall gain of the magnetic levitation system is reduced, and it becomes weak against a large disturbance.

According to the first aspect of the present invention, an electromagnet that supports a supported body in a non-contact manner by a magnetic force , a displacement sensor that detects a gap change between the supported body, and a current command for an electromagnet current is output based on a detection signal of the displacement sensor. A current command unit, a first switching element connected to the power supply positive electrode side, a first diode connected in series to the first switching element and an anode connected to the power supply negative electrode side, and connected to the power supply negative electrode side A second switching element, and a second diode connected in series to the second switching element and having a cathode connected to the power supply positive electrode side, and a connection point between the first switching element and the first diode And a two-quadrant drive circuit in which an electromagnet coil is connected between a connection point between the second switching element and the second diode, and an on / off signal for the first and second signals. On-duty of the on / off signal is generated by alternately outputting the first state in which the first and second switching elements are closed and the second state in which the first and second switching elements are opened to be output to the switching element. And a PWM signal generation circuit that controls the electromagnet current by changing the ratio, and the electromagnet current is constant when the on-duty ratio of the on / off signal output from the PWM signal generation circuit is 50%. As described above, the third state in which only one of the first and second switching elements is closed by shifting the on timing or the off timing of the on / off signal input to the first and second switching elements from each other. A generating unit that generates before and after the two states, or generates the third state by temporarily interrupting the second state. , Characterized by comprising.
According to a second aspect of the present invention , in the magnetic levitation control device according to the first aspect, the generator is configured to provide a predetermined time interval during an off period of the on / off signal input to one of the first and second switching elements. An ON signal is inserted.
According to a third aspect of the present invention, in the magnetic levitation control device according to the second aspect, the generator switches the on / off signal input to one of the first and second switching elements from the off state to the on state. An ON signal is inserted immediately before.

  According to the present invention, since a state where one of the two switching elements is on and the other is off is inserted between the state where both of the two switching elements are turned on and the state where both of the two switching elements are turned off. Thus, it is possible to prevent the average value of the electromagnet current from decreasing than the intended average current value.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a magnetic levitation control device according to the present invention. The magnetic levitation control device shown in FIG. 1 shows a control device for a magnetic bearing type turbo molecular pump, and 45 is a rotating shaft of the turbo molecular pump.

  FIG. 2 is a cross-sectional view showing details of the turbo molecular pump main body 1. A rotating body 4 having a plurality of stages of rotating blades 41 and a screw rotor portion 42 is fixed to the rotating shaft 45. Fixed wings 43 are arranged alternately. Further, a screw stator portion 44 is disposed on the base 3 so as to face the rotating screw rotor portion 42.

  The rotary shaft 45 is supported in a non-contact manner by electromagnets 51 and 52 constituting a 5-axis control type magnetic bearing and is driven to rotate by the motor 6. The electromagnets 51 and 52 are composed of a pair of electromagnets. Corresponding to these electromagnets 51 to 53, displacement sensors 55 to 57 for detecting the position of the rotating shaft 45 are provided. Each electromagnet 51 to 53 is provided with a current control circuit for supplying a drive current individually.

  The current control circuit 5 shown in FIG. 1 is shown for one of the pair of electromagnets 51 and includes a current command unit 2 and a drive current supply unit 3. The displacement sensor 55 is a sensor that detects a change in the gap Lg between the rotation shaft 45 and, for example, an inductance type displacement sensor is used.

  The current control circuit 5 adjusts the value of the drive current supplied to the electromagnet 51 so that the gap Lg calculated from the output signal of the displacement sensor 55 becomes a preset set distance. The output signal of the displacement sensor 55 is input to the sensor circuit 21 of the current command unit 2. The sensor circuit 21 changes the inductance change based on the output signal from the displacement sensor 55 into a voltage signal and outputs the voltage signal to the PID control circuit 22 as a sensor signal.

  The PID control circuit 22 controls the sensor signal by P (proportional), I (integral), and D (differential), and gives a current command to the drive current supply unit 3 so that the gap Lg becomes a preset set distance. Is output. The drive current supply unit 3 generates a drive current having a current value corresponding to the current command, and supplies the drive current to the electromagnet 51.

  FIG. 3 is a block diagram showing details of the drive current supply unit 3. The drive current supply unit 3 includes a clock generation circuit 31, a PWM signal generation circuit 32, and a two-quadrant drive circuit 35. The two-quadrant driving circuit 35 is provided with two transistors 351 and 352 and two diodes 353 and 354 as switching elements, and further includes a delay circuit 33 and a reset circuit 34. The reference clock signal P generated by the clock generation circuit 31 is input to the PWM signal generation circuit 32 and the delay circuit 33.

  Based on the reference clock signal P and the current command from the PID control circuit 22 in FIG. 1, the PWM signal generating circuit 32 generates pulse signals G1 and G2 having a duty ratio corresponding to the current command. The signal G1 and the signal G2 are exactly the same signal. The signal G2 is input to the transistor 352 and controls the on / off operation of the transistor 352.

  On the other hand, the reference clock signal P input to the delay circuit 33 is delayed by the delay circuit 33 and then input to the reset circuit 34. The reset circuit 34 is a circuit having a function of resetting the delayed reference clock signal P in synchronization with the rising timing of the next reference clock signal P.

FIG. 4 is a diagram illustrating an example of the signals G1, G2, G3, and G11. Signals G1, G2 are turned off at time t1~t2 and time t4~t5 on, at time t2~t 4. The signal G3 output from the reset circuit 34 rises with a delay of time T1 with respect to the rising edge of the signal G1 (that is, the rising edge of the reference clock signal P), and is turned off in synchronization with the next rising edge of the signal G1. Reset to. The signal G11 input to the transistor 351 of the two-quadrant driving circuit 35 is the sum of the signal G1 and the signal G3, and is turned on at time t6 to t1 and time t3 to t5.

The states of the transistors 351 and 352 to which the signal G11 and the signal G2 are input as drive signals are both in an on state (referred to as state A) from time t1 to t2 and from time t4 to t5, and both are off from time t2 to t3. State (referred to as state B). At time t6 to t1 and time t3 to t4, the transistor 351 is turned on and the transistor 352 is turned off (referred to as state C).

FIG. 5 is a diagram illustrating drive currents in states A to C. In FIG. 5, the transistors 351 and 352 are represented by switch symbols, and R _M and L _M are the resistance and inductance of the electromagnet 51. I _M is an electromagnet current, V _Q1 and V _Q2 are voltage drops when the transistors 351 and 352 are on, and V _D1 and V _D2 are forward voltage drops of the diodes 353 and 354. Supply voltage of the drive circuit is set to V _P.

In the state A, since the transistors 352 and 352 are both on, the current i _M flows from the transistor 351 to the electromagnet 51 to the transistor 352. On the other hand, when the state A changes to the state B and both the transistors 351 and 352 are turned off, electromagnetic energy is accumulated in the electromagnet coil. Therefore, as the energy is released, the diode 353 → the electromagnet 51 → the diode 354. The current i _M flows through the current. Also, in state C, the the transistor 35 1 is turned on, current _{i M} as the transistor 351 → the electromagnet 51 → diode 354 flows.

When the signals G11 and G2 in FIG. 4 are input to the transistors 351 and 352, the state A (t1 to t2) → the state B (t2 to t3) → the state C (t3 to t4) → the state A (t4 to t5) ) And the current i _M having a waveform as shown in FIG. 6A flows through the electromagnet 51. When the slope of the straight line in state A is α _A , the slope in state B is α _B , and the slope in state C is α _C , the following equations (1) to (3) are given.
α _A = (V _P −V _Q1 −V _Q2 −R _M · i _M ) / L _M (1)
α _B = − (V _P + V _D1 + V _D2 + R _M · i _M ) / L _M (2)
α _C = − (V _Q1 + V _D2 + R _M · i _M ) / L _M (3)

_{Here, V P, V Q1, V} Q2, V D1, V D2, R M · i M are all positive values, generally, _{V P} is 12V or _more, V _{Q1, V Q2} is 0 to 1 V, V _{D1, V D2} is 0.5～1V, is _{R M} is less than or equal to the number Omega. As a result, the slope of the portion B is always larger than the slope of the portion A. Therefore, when the signals G1 and G2 having a duty ratio of 50% as shown in FIG. 4 are input to the two-quadrant driving circuit 35, the state A and the state B are repeated, and the average current as shown in FIG. The value will decrease.

However, the magnitude of inclination alpha _C current lines in state C, the gradient alpha _A, a much smaller value than the size of the alpha _B. This is the same when only the transistor 352 is turned on. Therefore, in this embodiment in which the signals G11 and G2 of FIG. 4 are input to the two-quadrant driving circuit 35, the delay time T1 of the signal G3 that causes the state C even if the signals G1 and G2 have a duty ratio of 50%. Is appropriately set to generate the signal G11, the average current value can be kept constant as shown in FIG. Therefore, even if a current command having a high frequency and a large amplitude that cannot be followed by the electromagnet current is input to the drive current supply unit 3, the inconvenience that the average value of the electromagnet current is reduced from the intended average current value is prevented. Can do.

  In addition, noise is generated when the transistors 351 and 352 are turned on and off to switch the current. Conventionally, the state has changed from state B (both off) to state A (both on). Since the switch is turned on with a time difference in the order of B → state C (one side ON) → state A (further one side ON), the noise peak per switching can be reduced and noise can be reduced.

  In the above-described embodiment, the signal G3 is formed immediately before the rise of the signal G1 as shown in FIG. 4, but it may be generated at any position in the off period of the signal G1. Further, as long as the state C is generated between the state A and the state B, the generation method of the signal G11 is not limited to the above. In the embodiment described above, the signal G1 is processed and G2 is left as it is, but this may be reversed. The two-quadrant drive circuit of the present embodiment can be applied not only to a magnetic bearing device of a turbo molecular pump but also to various magnetic levitation control devices including a magnetic bearing.

In the correspondence between the embodiment described above and the elements of the claims, the state A is the first state , the state B is the second state , the state C is the third state , and the delay circuit 33 and the reset circuit 34 are Each of the generation units is configured. The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims.

It is a block diagram which shows one Embodiment of the magnetic levitation control apparatus by this invention. 2 is a cross-sectional view showing details of a turbo molecular pump main body 1. FIG. 4 is a block diagram showing details of a drive current supply unit 3. FIG. It is a figure which shows an example of signal G1, G2, G3, G11. It is a figure explaining the drive current in state AC. Is a diagram showing the waveform of the current i _M flowing through the electromagnet 51, (a) shows a case of this embodiment, an (b) in the case of the prior art.

Explanation of symbols

  2: current command unit, 3: drive current supply unit, 5: current control circuit, 21: sensor circuit, 22: PID control circuit, 31: clock generation circuit, 32: PWM signal generation circuit, 33: delay circuit, 34: Reset circuit, 35: Two-quadrant drive circuit, 51-53: Electromagnet, 351, 352: Transistor, 353, 354: Diode

Claims (3)

  An electromagnet for supporting the supported body in a non-contact manner by a magnetic force;
  A displacement sensor for detecting a gap change with the support;
  A current command unit that outputs a current command of an electromagnet current based on a detection signal of the displacement sensor;
  A first switching element connected to the power supply positive electrode side, a first diode connected in series to the first switching element and having an anode connected to the power supply negative electrode side, and a second switching connected to the power supply negative electrode side And a second diode connected in series to the second switching element and having a cathode connected to the power supply positive electrode side, and a connection point between the first switching element and the first diode; A two-quadrant drive circuit in which a coil of the electromagnet is connected between a connection point of the second switching element and the second diode;
  An on / off signal is output to the first and second switching elements, and a first state in which the first and second switching elements are closed, and a second state in which the first and second switching elements are open In a magnetic levitation control device comprising: a PWM signal generation circuit that controls the electromagnet current by alternately and repeatedly generating and changing the on-duty ratio of the on-off signal.
  ON timing of the ON / OFF signal input to the first and second switching elements so that the electromagnet current is constant when the ON duty ratio of the ON / OFF signal output from the PWM signal generation circuit is 50%. Alternatively, the off timing is shifted from each other, and the third state in which only one of the first and second switching elements is closed is generated before and after the second state, or the second state is temporarily interrupted. A magnetic levitation control device comprising: a generation unit configured to generate the third state.   In the magnetic levitation control device according to claim 1,
  The magnetic levitation control apparatus, wherein the generation unit inserts an ON signal at a predetermined time interval in an OFF period of an ON / OFF signal input to one of the first and second switching elements.   In the magnetic levitation control device according to claim 2,
  The magnetic levitation control, wherein the generator inserts the ON signal immediately before the ON / OFF signal input to one of the first and second switching elements is switched from the OFF state to the ON state. apparatus.

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