JP7351196B2 - Power converter and control method for power converter - Google Patents

Description

The present invention relates to a power conversion device that drives a magnetic levitation coil for a magnetic bearing included in a motor, and a method of controlling the power conversion device.

With the increasing demand for energy saving in the market, it has become common to use a power converter that has the function of adjusting the optimal rotational speed, motor output, etc. according to the operating state of the motor, which is often used as a power source. Power conversion devices include, for example, not only those installed in machine tools and robots, but also servos, inverters, and the like controlled by controllers. Power converters can flexibly adjust rotational speed, rotational torque, etc., and in recent years, applications have emerged for power converters that allow fans and pumps to rotate at higher speeds and are used for new applications. Specifically, power converters are used to drive high-speed rotation motors, gas turbine motors, and the like.

By using a high-speed rotation motor, the size of the motor can be reduced. By using a gas turbine motor instead of an engine as the drive source for gas turbines that require high-speed rotation, it is possible to electrify the gas turbine, improving the responsiveness of the gas turbine and enabling high-speed rotation. . However, when the motor is rotated at high speed, when the rotation speed exceeds a certain speed, the influence of friction of the bearing cannot be ignored and it becomes difficult to rotate the rotor. Non-Patent Document 1 discloses a technique for highly accurately controlling the current flowing through a magnetic bearing that levitates the shaft of a rotor by magnetic force.

"MUTEC Magnetic Bearing Controller" [Retrieved on July 30, 2021] Internet <URL: http://www.mutecs.co.jp/products/mbc.html>

However, in this type of conventional technology, it is necessary to excite the coil used in the magnetic bearing, and it is also necessary to control the current flowing through the coils for a total of two axes, the X axis and the Y axis. It is necessary to use two single-phase inverters. Further, in the conventional technology, it is necessary to control the position of the shaft by feeding back a detection signal detected by a distance sensor or the like that detects the magnetically levitated position of the shaft. For this reason, the power conversion device that precisely controls the two inverters is not mass-produced and is a specially designed product, which poses a problem of high manufacturing costs.

The present invention has been made in view of the above, and an object of the present invention is to obtain a power conversion device that can suppress increases in manufacturing costs.

In order to solve the above-mentioned problems and achieve the objects, a power conversion device according to the present invention provides a power conversion device that controls current flowing through a first coil and a second coil included in a magnetic bearing that supports a motor shaft in a non-contact manner. The device includes a first switching element and a second switching element connected in series, and one end of the first coil is connected to a connection point between the first switching element and the second switching element. an arm, and a third switching element and a fourth switching element connected in series, and the other end of the first coil and one end of the second coil are connected to a connection point between the third switching element and the fourth switching element. and a fifth switching element and a sixth switching element connected in series, the other end of the second coil being connected to a connection point between the fifth switching element and the sixth switching element. a main circuit having a third upper and lower arm connected to the main circuit; a pulse width modulation signal that fixes the duty ratio of the second upper and lower arms to any value from 0% to 100%; and a control circuit that controls on/off operations of each of the first to sixth switching elements by generating a pulse width modulation signal that changes the duty ratio of each of the third upper and lower arms.

According to the present invention, it is possible to suppress an increase in manufacturing costs.

Configuration diagram of a power conversion device according to an embodiment of the present invention Figure 1 shows the arrangement of the magnetic bearing and shaft. Figure 2 shows the arrangement relationship between the magnetic bearing and the shaft. Functional block diagram of control circuit Flowchart to explain the operation of the control circuit Diagram showing an example of a pulse pattern of a PWM signal A diagram showing an example of carrier waveforms compared in the triangular wave comparison section of FIG. 4. A diagram showing the operating state of the switching element when a current in the + direction flows through the coil 11a. A diagram showing the operating state of the switching element when a current in the − direction flows through the coil 11a. A diagram showing the operating state of the switching element when a current in the + direction flows through the coil 12a. A diagram showing the operating state of the switching element when a current in the − direction flows through the coil 12a. A diagram showing the waveform of the PWM signal when the command current is controlled at U phase = 2A and W phase = -1A. Configuration diagram of a comparative example of a power conversion device according to an embodiment of the present invention Diagram to explain the relationship between current direction and duty ratio

EMBODIMENT OF THE INVENTION Below, the power converter device and the control method of a power converter device which concern on embodiment of this invention are demonstrated in detail based on drawing. Note that the present invention is not limited to this embodiment.

(Embodiment)
FIG. 1 is a configuration diagram of a power conversion device according to an embodiment of the present invention. The power conversion device 100 is a device that controls current supplied to the magnetic bearing coils 11a and 12a of the motor 300 that rotates at high speed. A 3-phase AC power supply 200 is connected to the power conversion device 100, and the power conversion device 100 converts the 3-phase AC current supplied from the 3-phase AC power supply 200 into an AC current of a desired value, and converts the 3-phase AC current supplied from the 3-phase AC power supply 200 into an AC current of a desired value, and then converts the 3-phase AC current supplied from the 3-phase AC power supply 200 into an AC current of a desired value. supply to. Note that rotation control of a rotor (not shown) included in the motor 300 is performed by an inverter device (not shown) or the like.

The rectifier circuit 1 rectifies a three-phase AC voltage from a three-phase AC power supply 200, and inputs the rectified voltage to the main circuit 2 via a DC bus (a positive DC bus P and a negative DC bus N). Although the power conversion device 100 includes the rectifier circuit 1, the main circuit 2 may be configured to receive a DC voltage supplied from a DC power source (not shown) instead of the rectifier circuit 1. In this case, the positive pole of the DC power supply is connected to the positive DC bus P, and the negative pole of the DC power supply is connected to the negative DC bus N.

The main circuit 2 is a general three-phase inverter main circuit that converts the voltage supplied from the rectifier circuit 1 into a three-phase AC voltage via a positive DC bus P and a negative DC bus N.

The main circuit 2 includes a first upper and lower arm 8a, a second upper and lower arm 8b, and a third upper and lower arm 8c. The six switching elements S ₁ to S ₆ that constitute the first upper and lower arms 8a, the second upper and lower arms 8b, and the third upper and lower arms 8c are a group of switching elements connected in a three-phase bridge.

3 switching elements S₁, S₃, S_FiveEach of these is a high-side switching element (upper arm) connected to the positive DC bus P. 3 switching elements S₂, S₄, S₆Each of these is a low-side switching element (lower arm) connected to the negative DC bus N. In the following, a plurality of switching elements S₁～S₆If not distinguished from each other, they may be simply referred to as "switching elements." The switching element is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), or the like. The switching elements are respectively turned on or off according to gate drive signals input from the gate drive circuit 6.

The first upper and lower arms 8a include a switching element S ₁ (first switching element) and a switching element S ₂ (second switching element) connected in series. One end of the U-phase wiring of the three-phase wiring 7 is connected to the connection point 7a between the switching element _S1 and the switching element _S2 . The connection point 7a is electrically connected to one end of the coil 11a (first coil) via the U-phase wiring.

The second upper and lower arms 8b include a switching element S ₃ (third switching element) and a switching element S ₄ (fourth switching element) that are connected in series. One end of the V-phase wiring of the _three- phase wiring 7 is connected to the connection point 7b between the switching element S3 and the switching element _S4 . Connection point 7b is electrically connected to the other end of coil 11a and one end of coil 12a (second coil) via V-phase wiring.

The third upper and lower arms 8c include a switching element _S5 (fifth switching element) and a switching element _S6 (sixth switching element) connected in series. One end of the W-phase wiring of the three-phase wiring 7 is connected to the connection point 7c between the switching element _S5 and the switching element _S6 . Connection point 7c is electrically connected to the other end of coil 12a via W-phase wiring.

As shown in FIG. 1, of the three-phase wiring 7, the V-phase wiring is connected to each end of the coil 11a and the coil 12a, so it is used as a common wiring for the coil 11a and the coil 12a. ing. With such a connection configuration, one power converter 100 equipped with a general-purpose inverter main circuit (main circuit 2) can perform magnetic bearings without using two single-phase power converters (described later). It becomes possible to control the energization of the coils 11a and 12a, which are magnetic levitation coils.

The gate drive circuit 6 converts a pulse width modulation (PWM) signal input from the control circuit 5 into a gate drive signal that is a voltage signal with a value that can drive the switching element, and inputs the gate drive signal to the switching element. This is a circuit that does this.

The control circuit 5 is a circuit that generates and outputs a plurality of PWM signals for controlling the on/off operations of the plurality of switching elements S ₁ to S ₆ forming the main circuit 2. The control circuit 5 is composed of, for example, an FPGA (Field-Programmable Gate Array). In addition to FPGA, the control circuit 5 may be composed of a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), or a combination of these. It can be anything.

The control circuit 5 is equipped with an analog conversion IC (Integrated Circuit) such as an ADC (Analog to Digital Converter), and converts current values (detected values Iu and Iw of the current sensor 4) and voltage values (detected values of the voltage sensor 3). ), the value of the distance from the shaft of the magnetically levitated rotor to the coil 11a or the coil 12a (detected values Du, Dw of a distance sensor (not shown)), etc. are acquired, and predetermined calculations are performed using control software. Through predetermined calculations, PWM signals corresponding to each of the plurality of switching elements are generated using a PWM generation method such as the triangular wave comparison method or the space vector modulation method, and the plurality of generated PWM signals are sent to the gate drive circuit. 6 is input.

The plurality of PWM signals include three upper arm PWM signals and three lower arm PWM signals. The three upper arm PWM signals are sent to the three switching elements S constituting the upper arm.₁, S₃, S_FiveThis is a signal for on/off control of each of the following. The three lower arm PWM signals are sent to the three switching elements S constituting the lower arm.₂, S₄, S₆This is a signal for on/off control of each of the following. These PWM signals cause the two switching elements forming each of the upper and lower arms to operate in a complementary manner.

The voltage sensor 3 detects the voltage applied to the DC bus, and inputs the detected voltage value to the control circuit 5 as the detection value of the voltage sensor 3.

The current sensor 4 is a current detection element such as a shunt resistor provided in each of the three-phase wiring 7 connecting the main circuit 2 and the motor 300, for example, in order to detect the current flowing through each of the coils 11a and 12a. The shunt resistor inputs information indicating the value of the detected current to the control circuit 5 as a current detection value. Note that the current sensor 4 may be any sensor such as a CT (Current Transformer) as long as it can detect the current of each phase. Note that the current may be detected by detecting only the currents of two of the three phases, and calculating the current of the remaining one phase by utilizing the fact that the motor current is in three-phase balance.

In this way, the power conversion device 100 is configured to include a general-purpose rectifier circuit 1, a main circuit 2, and a gate drive circuit 6.

Next, the configuration of the motor 300 including the coil 11a and the coil 12a will be described with reference to FIGS. 2 and 3.

FIG. 2 is a first diagram showing the arrangement relationship between the magnetic bearing and the shaft. FIG. 3 is a second diagram showing the arrangement relationship between the magnetic bearing and the shaft. In FIGS. 2 and 3, the X-axis direction, the Y-axis direction, and the Z-axis direction represent a direction parallel to the X-axis, a direction parallel to the Y-axis, and a direction parallel to the Z-axis, respectively. The X-axis direction, the Y-axis direction, and the Z-axis direction are orthogonal to each other. The XY plane, YZ plane, and ZX plane are, respectively, a virtual plane parallel to the X-axis direction and the Y-axis direction, a virtual plane parallel to the Y-axis direction and the Z-axis direction, and a virtual plane parallel to the Z-axis direction and the X-axis direction. represents. Among the X-axis directions, the direction indicated by the arrow is the plus X-axis direction, and the opposite direction is the minus X-axis direction. Among the Y-axis directions, the direction indicated by the arrow is the positive Y-axis direction, and the direction opposite to this direction is the negative Y-axis direction. Among the Z-axis directions, the direction indicated by the arrow is the plus Z-axis direction, and the opposite direction is the minus Z-axis direction. Note that in FIGS. 2 and 3, illustrations of a stator (a stator core provided on the inner surface of the frame 13) and a rotor (a rotor provided on the outer peripheral surface of the shaft 10) that constitute the motor 300 are omitted.

Each of the two magnetic bearings 11 includes an iron core 11b and a coil 11a wound around the iron core 11b. The two magnetic bearings 11 are arranged opposite to each other and separated in the X-axis direction so as to sandwich the shaft 10 therebetween. Among the two coils 11a shown in FIG. 2, one coil 11a is supplied with a first alternating current, and the other coil 11a is supplied with a second alternating current that has been inverted by a first current inverting circuit (not shown). Ru. As a result, a magnetic force that attracts the shaft 10 is generated in one coil 11a, and a magnetic force that repels the shaft 10 is generated in the other coil 11a. As a result, the shaft 10 can be supported in the X-axis direction without contact.

Each of the two magnetic bearings 12 includes an iron core 12b and a coil 12a wound around the iron core 12b. The two magnetic bearings 12 are arranged opposite to each other and separated in the Y-axis direction so as to sandwich the shaft 10 therebetween. Among the two coils 12a shown in FIG. 2, one coil 12a is supplied with a third alternating current, and the other coil 12a is supplied with a third alternating current that has been inverted by a second current inverting circuit (not shown). Ru. As a result, a magnetic force that attracts the shaft 10 is generated in one coil 12a, and a magnetic force that repels the shaft 10 is generated in the other coil 12a. As a result, the shaft 10 can be supported in the Y-axis direction without contact.

The control circuit 5 adjusts the magnetic force acting on the shaft 10 in the radial direction (the direction perpendicular to the direction in which the shaft extends, that is, the direction parallel to the XY plane) by adjusting the current flowing through the coils 11a and 12a. , the shaft 10 can be supported in a non-contact manner.

In addition, in order to rotatably support at least two locations in the axial direction (Z-axis direction) of the shaft 10, two or more magnetic bearings 11 and two or more magnetic bearings 12 are arranged apart from each other in the Z-axis direction of the shaft 10. be done. In FIG. 3, two sets of magnetic bearings 12 are shown spaced apart from each other in the Z-axis direction. Although not shown in FIG. 3, two sets of magnetic bearings 11 are similarly arranged apart from each other in the Z-axis direction. In order to support the shaft 10 in a non-contact manner by these two sets of magnetic bearings 12 and magnetic bearings 11, two power conversion devices 100 shown in FIG. 1 are used.

As shown in FIG. 2, in addition to the magnetic bearing 11 and the magnetic bearing 12, the motor 300 includes a distance sensor that detects the distance (gap) in the radial direction between the magnetic bearing 11 and the shaft 10 using, for example, magnetic force. 14, a distance sensor 15 for detecting the distance between the magnetic bearing 12 and the shaft 10 using magnetic force is provided. The distance sensor 14 and the distance sensor 15 are fixed to the frame 13 shown in FIG. 3, for example. The distance sensor 14 and the distance sensor 15 are also called gap sensors, and are a type of displacement sensor that non-contactly measures a minute distance between the object to be measured (shaft 10) and the magnetic bearing. Note that the distance sensor 14 and the distance sensor 15 may be of a capacitive type, an ultrasonic type, an optical type, etc. in addition to a method of detecting distance using magnetic force, and any of these methods may be adopted.

It is also assumed that the motor 300 is provided with a touchdown bearing (not shown) that supports the shaft in place of the magnetic bearings 11 and 12 when power supply is stopped.

Next, a configuration example of the control circuit 5 will be described with reference to FIG. 4. FIG. 4 is a functional block diagram of the control circuit. Note that here, by fixing the on-duty ratio of the upper and lower arms of the V phase to 50% and changing the duty ratio of the upper and lower arms of the U phase and W phase, the U phase and V phase A configuration example will be described in which the current flowing through the coil 11a connected between the W phase and the V phase is controlled, and the current flowing through the coil 12a connected between the W phase and the V phase is controlled. The duty ratio is the ratio of the pulse width (on time) of the PWM signal to the period (pulse period) of the PWM signal generated by the control circuit 5.

In a general-purpose inverter, for example, in order to drive a three-phase motor, the coordinates of each phase current detection signal from a current sensor are transformed into two-phase (dq-axes) actual current values, and the current command value after the coordinate transformation is A control signal to the gate drive circuit is generated by feedback control based on the current value and the actual current value. On the other hand, the control circuit 5 of the power conversion device 100 according to the present embodiment controls the current of the coil 11a and the coil 12a individually, so that the control system of the coil 11a and the coil 12a includes a subtraction unit 51, It has a position adjustment section 52 (Automatic Position Controller), a subtraction section 53, and a current adjustment section 54 (Automatic Current Regulator). Further, the control circuit 5 includes a triangular wave comparator 55.

Next, the operation of the control circuit 5 will be explained with reference to FIG. FIG. 5 is a flowchart for explaining the operation of the control circuit.

The timing at which the process of step S1 shown in FIG. 5 is executed is, for example, when power supply to the motor 300 from the power conversion device 100 shown in FIG. 1 is started. In step S1, the subtraction unit 51 inputs the command distance and the detected value Du or Dw from the distance sensors 14 and 15.

In step S2, the subtraction unit 51 calculates a distance deviation between the input command distance and the detected value Du or Dw. The distance deviation can be determined by distance deviation=command distance−detection value Du, or distance deviation=command distance−detection value Dw. The detected value Du is information indicating the distance of the gap in the X-axis direction detected by the distance sensor 14 shown in FIG. 2, for example. The detected value Dw is information indicating the distance of the gap in the Y-axis direction detected by the distance sensor 15 shown in FIG. 2, for example. The distance deviation calculated by the subtraction section 51 is input to the position adjustment section 52.

In step S3, the position adjustment unit 52 calculates a current set value (command current) using, for example, PI (Proportional Integral) control, PID (Proportional Integral Derivative) control, etc. so that the input distance deviation becomes zero. and input it to the subtraction section 53.

In step S4, the subtraction unit 53 calculates a current deviation between the input command current calculated by the position adjustment unit 52 and the detected value Iu or Iw from the current sensor. The current deviation can be determined by current deviation = commanded current - detected value Iu, or current deviation = commanded current - detected value Iw. The current deviation calculated by the subtraction unit 53 is input to the current adjustment unit 54.

In step S5, the current regulator 54 calculates the U-phase voltage command value and the W-phase voltage command value using, for example, PI control or PID control so that the input current deviation becomes zero. Furthermore, the current regulator 54 calculates the duty ratio by dividing each of the calculated U-phase voltage command value and W-phase voltage command value by the detected value Vdc (DC voltage) of the voltage sensor 3. These are input to the triangular wave comparator 55 as the U-phase command voltage and the W-phase command voltage, respectively.

In step S6, the triangular wave comparator 55 sets the duty ratio of the triangular wave having a predetermined period, the command voltages of the U phase and W phase from the current regulator 54, and the upper and lower arms of the V phase to 50%. Input the command voltage. Then, the triangular wave comparator 55 generates a PWM signal for controlling the on/off operations of the switching elements forming the upper and lower arms of each of the U-phase, V-phase, and W-phase, using the triangular wave comparison method.

For example, if the standard value (ideal value for levitation) of the gap from the shaft 10 to the coil 11a is 10 μm, if the gap distance calculated based on the detected value from the distance sensor 14 changes from 10 μm to 9 μm or 11 μm. , position adjustment and current adjustment are performed to correct the gap distance of 1 μm. Then, with the duty ratio of the upper and lower arms of the V phase set to 50%, the duty ratio of the upper and lower arms of the U phase is adjusted to increase or decrease according to the voltage command from the current adjustment section 54.

For example, if the reference value (ideal value for levitation) of the gap from the shaft 10 to the coil 12a is 10 μm, the gap distance calculated based on the detected value from the distance sensor 15 changes from 10 μm to 9 μm or 11 μm. Then, position adjustment and current adjustment are performed so as to correct the gap distance of 1 μm. Then, with the duty ratio of the upper and lower arms of the V phase set to 50%, the duty ratio of the upper and lower arms of the W phase is adjusted to increase or decrease according to the voltage command from the current adjustment section 54.

Note that the duty ratio of the upper and lower arms of the V phase may be fixed to, for example, 50%, but it may also be fixed to any value other than 50%, for example, from 51 to 60% or from 49% to 40%. good.

Further, the duty ratio of the upper and lower arms of the V phase may be fixed at 50%, but may be successively changed to an optimal value within a range of, for example, 60% to 40%. For example, when the rotation speed of the motor 300 changes, the gap from the shaft 10 to the coil 11a or the coil 12a may change due to dimensional tolerances of the shaft 10 or the rotor. Therefore, the optimum duty ratio may be selected according to the amount of variation in the gap. Specifically, for example, table information in which current values and duty ratio correction amounts are associated is set in the control circuit 5, and the control circuit 5 refers to the table to determine whether the current detected by the speed change is When the current changes, the duty ratio correction amount corresponding to the current is read out from the table, and the read duty ratio correction amount is input to the triangular wave comparison section 55. The triangular wave comparison section 55 takes into account the input duty ratio correction amount. , the PWM signal is generated by sequentially correcting the duty ratio of the upper and lower arms of the V phase and comparing the corrected duty ratio with the command voltage.

The subtraction unit 51, position adjustment unit 52, subtraction unit 53, current adjustment unit 54, and triangular wave comparison unit 55 included in the control circuit 5 store programs for realizing these functions in memory, and control the operation of the control circuit 5. This is realized by a controlling CPU (Central Processing Unit) reading and executing the program.

Next, a specific example of the current flowing through the coil 11a and the coil 12a with the V-phase duty ratio set to 50% will be described with reference to FIGS. 6 to 9.

FIG. 6 is a diagram showing an example of a pulse pattern of a PWM signal. FIG. 7 is a diagram showing an example of carrier waveforms compared by the triangular wave comparison section of FIG. 4. FIG. 8A is a diagram showing the operating state of the switching element when a current in the + direction is passed through the coil 11a. FIG. 8B is a diagram showing the operating state of the switching element when a current in the negative direction is passed through the coil 11a. FIG. 8C is a diagram showing the operating state of the switching element when a positive current is passed through the coil 12a. FIG. 8D is a diagram showing the operating state of the switching element when a current in the negative direction is passed through the coil 12a.

Normally, when the main circuit 2 is driven with the degree of modulation set to 50%, no current is output from the main circuit 2 because it is in a zero vector state. However, even in this case, since the switching itself of the switching element is being performed, the upper and lower arms of the U, V, and W phases are controlled so that they are in the same switch state, and the output lines (3-phase No potential difference occurs between the upper and lower arms of each phase when viewed from the wiring 7).

Here, as shown in FIGS. 8A and 8B, the current is controlled to flow in the + or - direction through the coil 11a, and the current is controlled to flow in the + or - direction through the coil 12a as shown in FIGS. 8C and 8D. An example of operation will be described in which the upper and lower arms of the V phase are switched at a duty ratio of 50% while controlling. Note that, as described above, it is assumed that the V-phase wiring is used as a common wiring (common) for the two coils 11a and 12a.

FIG. 6 shows an example of a pulse pattern of a PWM signal when a current is caused to flow in this manner. Further, FIG. 7 shows the carrier waveform used in the triangular wave comparator 55 and the command voltage with a duty ratio of 50%.

The duty ratio of the V phase is fixed at 50%, so if the duty ratio of the U phase is less than 50%, the potential of the U phase wiring will be higher than the potential of the V phase wiring, so in the section where the carrier peaks. , as shown in FIGS. 8A and 8B, a current corresponding to the difference in duty ratio flows into the coil 11a.

On the other hand, when the duty ratio of the W phase is more than 50%, the potential of the W phase wiring is higher than the potential of the V phase wiring, so in the carrier valley section, the duty ratio is A current corresponding to the difference flows into the coil 12a.

In this way, by adjusting the duty ratio of each of the U phase and W phase based on 50%, it is possible to flow current in any direction in the U phase and W phase, and furthermore, it is possible to flow current in any direction to any value. Can conduct current. That is, by fixing the duty ratio of one specific phase among the three phases to, for example, 50%, and increasing or decreasing the duty ratios of the remaining two phases, it is possible to individually control the current of the two coils.

FIG. 9 is a diagram showing the waveform of the PWM signal when the command current is controlled at U phase = 2A and W phase = -1A. In FIG. 9(1), the current flowing in the U phase, the current flowing in the V phase, and the current flowing in the W phase are each shown by a solid line, a dashed line, and a broken line. The vertical axis is the command current, and the horizontal axis is time. In FIG. 9(2), the duty ratios for controlling the operations of the upper and lower arms of each of the U-phase, V-phase, and W-phase are shown by solid lines, broken lines, and dashed-dotted lines. The vertical axis is the duty ratio, and the horizontal axis is time. FIG. 9(3) shows the waveforms of the U-phase, V-phase, and W-phase PWM signals. The vertical axis is the value of the PWM signal, and the horizontal axis is time.

When the duty ratio of the V phase is fixed at 50% and PI control is performed with U phase = 2A and W phase = -1A as target currents, -1A flows through the V phase, so Iu (U phase current) + Iv (V phase current) + Iw (W phase current) = 2A + (-1A) + (-1A) = 0.

Note that the functions of the control circuit 5 can be realized only by changing the software without changing the hardware configuration of the control circuit included in the general-purpose inverter. As for input interfaces such as the voltage sensor 3 and current sensor 4, analog input functions normally provided in general-purpose inverters can be used, so there is no need to change the hardware configuration.

In this embodiment, a configuration example of the control circuit 5 will be described in which the duty ratio of the upper and lower arms of the V phase is fixed at 50% and the duty ratio of the upper and lower arms of each of the remaining two phases is changed. However, the configuration example of the control circuit 5 is not limited to this. That is, the control circuit 5 fixes the duty ratio of the upper and lower arms of one specific phase to, for example, 50% among the upper and lower arms of the three phases, and sets the duty ratio of the upper and lower arms of each of the remaining two phases. It may be configured to change. That is, it may be configured such that one phase other than the V phase is fixed at a duty ratio of 50%, and the duty ratios of the remaining two phases are changed.

Furthermore, in this embodiment, a configuration example has been described in which the upper and lower arms of each of the U, V, and W phases are the first upper and lower arms, the second upper and lower arms, and the third upper and lower arms. The correspondence relationship with the upper and lower arms is not limited to this.

For example, if the upper and lower arms of the U, V, and W phases are set as the third upper and lower arms, the second upper and lower arms, and the first upper and lower arms, and the duty ratio of the V-phase upper and lower arms is fixed to a specific value, the U The duty ratio of each of the upper and lower arms of the phase and the upper and lower arms of the W phase may be changed.

Further, for example, the upper and lower arms of the U, V, and W phases are respectively set as the second upper and lower arms, the first upper and lower arms, and the third upper and lower arms, and the duty ratio of the upper and lower arms of the U phase is fixed to a specific value. , the duty ratio of each of the V-phase upper and lower arms and the W-phase upper and lower arms may be changed. In this case, the common wiring is connected to the connection point of the two switching elements that make up the upper and lower arms of the U phase, and the coils 11a and 12a are connected to the connection points of the two switching elements that make up the other two upper and lower arms. Ru.

Further, for example, the upper and lower arms of the U, V, and W phases are respectively set as the third upper and lower arms, the first upper and lower arms, and the second upper and lower arms, and the duty ratio of the upper and lower arms of the W phase is fixed to a specific value. , the duty ratio of each of the V-phase upper and lower arms and the U-phase upper and lower arms may be changed. In this case, the common wiring is connected to the connection point of two switching elements forming the upper and lower arms of the W phase, and the coil 11a and the coil 12a are connected to the connection point of the two switching elements forming the other two upper and lower arms. Ru.

Further, for example, the upper and lower arms of the U, V, and W phases are respectively set as the second upper and lower arms, the third upper and lower arms, and the first upper and lower arms, and the duty ratio of the upper and lower arms of the U phase is fixed to a specific value. , the duty ratio of each of the V-phase upper and lower arms and the W-phase upper and lower arms may be changed. In this case, the common wiring is connected to the connection point of the two switching elements that make up the upper and lower arms of the U phase, and the coils 11a and 12a are connected to the connection points of the two switching elements that make up the other two upper and lower arms. Ru.

Further, for example, the upper and lower arms of the U, V, and W phases are set as the third upper and lower arms, the second upper and lower arms, and the first upper and lower arms, and the duty ratio of the V-phase upper and lower arms is fixed to a specific value. , the duty ratio of each of the U-phase upper and lower arms and the W-phase upper and lower arms may be changed. In this case, the common wiring is connected to the connection point of two switching elements forming the upper and lower arms of the V phase, and the coil 11a and the coil 12a are connected to the connection point of the two switching elements forming the other two upper and lower arms. Ru.

Next, the configuration of a comparative example of the power conversion device 100 will be described. FIG. 10 is a configuration diagram of a comparative example of a power conversion device according to an embodiment of the present invention. In the following, parts that are the same as those in the embodiment described above will be given the same reference numerals, explanations thereof will be omitted, and different parts will be described.

A single-phase power conversion device 100A according to a comparative example includes a main circuit 2A, a control circuit 5A, and a gate drive circuit 6A instead of the main circuit 2, control circuit 5, and gate drive circuit 6.

The main circuit 2A is a so-called single-phase inverter that converts the voltage supplied from the rectifier circuit 1 into a single-phase AC voltage via a positive DC bus P and a negative DC bus N. The main circuit 2A includes two upper and lower arms (for example, a first upper and lower arm 8a and a second upper and lower arm 8b).

The connection point 7a of the first upper and lower arms 8a is electrically connected to one end of the coil 11a via the single-phase wiring 7A. The connection point 7b of the second upper and lower arms 8b is electrically connected to the other end of the coil 11a via the single-phase wiring 7A.

Note that a device similar to the single-phase power conversion device 100A connected to the coil 11a is connected to the coil 12a.

The control circuit 5A is a circuit that generates and outputs a plurality of PWM signals for controlling the on/off operations of the plurality of switching elements S ₁ to S ₄ forming the main circuit 2A.

The gate drive circuit 6A is a circuit that converts the PWM signal input from the control circuit 5A into a gate drive signal that is a voltage signal with a value that can drive the plurality of switching elements S ₁ to S ₄ and inputs the gate drive signal to the switching elements. It is.

In the comparative example shown in FIG. 10, the common wiring between the coil 11a and the coil 12a shown in FIG. 1 is not used, and one single-phase power converter 100A is connected to each of the coil 11a and the coil 12a. There is. That is, two single-phase power converters 100A are required to control the energization of the coils 11a and 12a, which are magnetic levitation coils for magnetic bearings.

Therefore, in the comparative example of FIG. 10, a general-purpose inverter for driving a three-phase motor cannot be used, and the structure becomes complicated. Furthermore, since the control circuits 5A of the two single-phase power converters 100A must cooperate to control the energization of the coils 11a and 12a, the control becomes complicated. Therefore, there are concerns about a decrease in reliability and a decrease in yield during manufacturing.

On the other hand, the main circuit 2 of the power conversion device 100 of the present embodiment includes a first upper and lower arm to which one end of the first coil is connected to a connection point between the first switching element and the second switching element, and a first upper and lower arm. a second upper and lower arm to which the other end of the first coil and one end of the second coil are connected to the connection point between the third switching element and the fourth switching element; and the second upper and lower arms to which the fifth and sixth switching elements connect. and a third upper and lower arm to which the other end of the second coil is connected. Therefore, by changing the connection method to the existing motor 300, it is possible to control the energization of the coils 11a and 12a, which are magnetic levitation coils for magnetic bearings, while using one general-purpose three-phase inverter. Become.

Therefore, it is possible to suppress an increase in design man-hours associated with the development of the power conversion device 100, and it is also possible to suppress an increase in manufacturing cost of a system that implements energization of a magnetic levitation coil for a magnetic bearing. Furthermore, since the number of inverters is halved, an increase in the installation space for inverters can be suppressed. Further, since the structure of the inverter is simplified and the control is also simplified, it is possible to suppress a decrease in reliability and a decrease in manufacturing yield.

Furthermore, the control circuit 5 of the power converter 100 of the present embodiment changes the respective Duty ratios of the first and third upper and lower arms while fixing the Duty ratio of the second and lower arms to a specific value. . The duty ratio of each of the first upper and lower arms and the third upper and lower arms may be configured to be set to a value that controls the current flowing through the first coil and the second coil so as to obtain an arbitrary flying distance.

With this configuration, the duty ratio of the second upper and lower arms is fixed, so the burden of arithmetic processing on the control circuit 5 is reduced, and the control circuit 5 can be configured using an inexpensive CPU with low processing capacity, resulting in high-speed rotation. It is possible to suppress an increase in the manufacturing cost of the power converter 100 while ensuring the magnetic levitation distance of the shaft 10.

Further, the control circuit 5 of the power conversion device 100 of the present embodiment may be configured to fix the duty ratio of the second upper and lower arms to 50%. With this configuration, the duty ratio of each of the first and third vertical arms can be adjusted while the duty ratio of the second vertical arm is fixed at 50%, so the burden of calculation processing on the control circuit 5 is reduced. It is possible to use a cheaper CPU and the like, and furthermore, there is no need to set the duty ratio, which saves the adjustment effort, so that it is possible to further suppress an increase in the manufacturing cost of the power conversion device 100.

Furthermore, the method for controlling the power conversion device 100 according to the present embodiment includes a first switching element and a second switching element connected in series, and a motor shaft is connected to a connection point between the first switching element and the second switching element. A first upper and lower arm to which one end of a first coil of a magnetic bearing supported in a non-contact manner is connected, a third switching element and a fourth switching element connected in series, and a third switching element and a fourth switching element. a second upper and lower arm to which the other end of the first coil and one end of the second coil for magnetic bearing are connected to the connection point; and a fifth switching element having a fifth switching element and a sixth switching element connected in series. and a third upper and lower arm to which the other end of the second coil is connected to the connection point with the sixth switching element. calculating a command current such that the deviation between the distance between the gap between at least one of the first coil and the shaft and the command distance becomes zero, and the deviation between the command current and the current flowing through at least one of the first coil and the second coil becomes zero. A step of calculating the command voltage of two phases out of the three phases, and setting the command voltage of each of the two phases and the duty ratio of the upper and lower arms of the remaining one phase to any value from 0% to 100%. A pulse width modulation signal with the duty ratio of the second upper and lower arms fixed at any value from 0% to 100% based on the command voltage fixed to and generating a pulse width modulated signal that changes the ratio.

FIG. 11 is a diagram for explaining the relationship between the current direction and the duty ratio. For example, when the direction of the current flowing through the coil is the same in the U phase and the W phase, the control circuit 5 does not fix the duty ratio of the upper and lower arms of the V phase to 50%, but sets it to any value from 0% to 49%. It may be configured to be fixed at this value or at any value from 51% to 100%.

For example, if the duty ratio of the upper and lower arms of the V phase is set to 0% or 100%, the inverter can generate alternating current, but it can also be operated as an inverter that outputs direct current with limited + or - directions. . By moving in this manner, the voltage utilization rate can be increased, so the DC intermediate voltage, which had to be raised to about twice the voltage actually used, can be lowered, and current ripple can also be reduced.

However, depending on the control situation, it may not be possible to handle cases where current must flow in either phase in the negative (plus) direction. "Depending on the control situation, it is necessary to flow current in either phase in the negative (plus) direction" is a case where it is determined that the current cannot flow with the fixed duty ratio of the second upper and lower arms. The reason why the current flows in this way is that if the current flows in a direction that is not originally expected, the duty ratio of the upper and lower arms of the V phase cannot be fixed at 0% or 100%. In this case, it can be handled by returning the duty ratio of the V-phase upper and lower arms to 50%. However, when the duty ratio is 50%, the maximum current value that can be output is up to half of the maximum current value that can be output when the duty ratio of the upper and lower arms of the V phase is fixed at 0% or 100%. .

For example, in actual operation, if the magnitude of the current flowing in the positive direction is large at a ratio of 8:2, the duty ratio of the upper and lower arms of the V phase may be fixed at 20% or the like. When the duty ratio is set to 20%, the current becomes 0, so positive current control from 20% to 100% and negative current control from 0% to 20% are performed.

If the duty ratio is fixed at 50%, an inverter circuit with a correspondingly large capacity is required, so there is a great advantage of making the value of the fixed duty ratio of the V phase variable.

The control circuit 5 may change the duty ratio of the V phase during operation. However, when switching (changing) the duty ratio, the control circuit 5 uses the value of the duty ratio of the U phase and W phase to be converted inside the control circuit (inside the control circuit 5) based on the command voltage. Change the gain coefficient and output limiter values. This is because the range and magnitude of the current that can be output changes.

The configurations shown in the embodiments above are examples of the contents of the present invention, and can be combined with other known techniques, and the configurations can be modified without departing from the gist of the present invention. It is also possible to omit or change parts.

1: Rectifier circuit 2, 2A: Main circuit 3: Voltage sensor 4: Current sensor 5, 5A: Control circuit 6, 6A: Gate drive circuit 7: 3-phase wiring 7A: Single-phase wiring 7a, 7b, 7c: Connection point 8a : First vertical arm 8b : Second vertical arm 8c : Third vertical arm 10 : Shafts 11, 12 : Magnetic bearings 11a, 12a : Coils 11b, 12b : Iron core 13 : Frames 14, 15 : Distance sensors 51, 53 : Subtraction Section 52: Position adjustment section 54: Current adjustment section 55: Triangular wave comparison section 100: Power conversion device 100A: Single-phase power conversion device 300: Motor Du, Dw: Detection values Iu, Iw: Detection value N: Negative electrode side DC bus P: Positive side DC bus bar

Claims (2)

A power conversion device that controls current flowing through a first coil and a second coil included in a magnetic bearing that supports a motor shaft in a non-contact manner,
a first upper and lower arm having a first switching element and a second switching element connected in series, and one end of the first coil being connected to a connection point between the first switching element and the second switching element; a third switching element and a fourth switching element, the other end of the first coil and one end of the second coil being connected to a connection point between the third switching element and the fourth switching element; 2 upper and lower arms, and a third coil having a fifth switching element and a sixth switching element connected in series, and the other end of the second coil is connected to a connection point between the fifth switching element and the sixth switching element. a main circuit having an upper and lower arm;
a pulse width modulation signal that fixes the duty ratio of the second upper and lower arms to any value from 0% to 100%; and a pulse width that changes the duty ratio of each of the first and third upper and lower arms. a control circuit that controls on/off operations of each of the first switching element to the sixth switching element by generating a modulation signal;
Equipped with
When the control circuit determines that current cannot flow with the fixed duty ratio of the second upper and lower arms, it performs processing to return the duty ratio of the second upper and lower arms, which was fixed to a value other than 50%, to 50%. , power converter. One end of a first coil included in a magnetic bearing that includes a first switching element and a second switching element connected in series and supports a shaft of a motor in a non-contact manner at a connection point between the first switching element and the second switching element. and a third switching element and a fourth switching element connected in series, the other end of the first coil being connected to the connection point of the third switching element and the fourth switching element. a second upper and lower arm connected to one end of a second coil of the magnetic bearing; a fifth switching element and a sixth switching element connected in series; A method for controlling a power conversion device comprising a main circuit having a third upper and lower arm to which the other end of the second coil is connected to a connection point,
calculating a command current such that a deviation between a command distance and a gap distance between at least one of the first coil and the second coil and the shaft is zero;
calculating command voltages for two of the three phases such that the deviation between the current flowing through at least one of the first coil and the second coil and the command current is zero;
The duty of the second upper and lower arms is determined based on the command voltage of each of the two phases and the command voltage that fixes the duty ratio of the upper and lower arms of the remaining one phase to any value from 0% to 100%. a step of generating a pulse width modulation signal whose ratio is fixed at any value from 0% to 100%, and a pulse width modulation signal which changes the duty ratio of each of the first upper and lower arms and the third upper and lower arms; and,
including;
If it is determined that current cannot flow with the fixed duty ratio of the second upper and lower arms, the power converter performs processing to return the duty ratio of the second upper and lower arms, which has been fixed to a value other than 50%, to 50%. Control method.

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