Driving device and control method

Abstract

The drive unit includes a transformer, a power converter, and a control device. The transformer has a primary winding and a secondary winding, with a motor winding connected to the secondary winding. The power converter allows current to flow into the primary winding of the transformer. During a first phase after the motor is instructed to start, the control device reduces the fluctuation of the current flowing into the primary winding of the transformer by performing constant current control on the power converter. In a second phase following the first phase, the power converter is controlled by variable voltage and variable frequency control of the motor.

Description

Technical Field

[0001] The embodiments of the present invention relate to a driving device and a control method. Background Technology

[0002] A drive device includes a transformer positioned between the output of a power converter that drives an electric motor and the motor itself. The transformer steps up or steps down the output voltage of the power converter. However, in practice, besides performing the ideal voltage transformation, the transformer can also generate magnetic saturation effects due to DC bias or residual magnetic flux. Sometimes, due to magnetic saturation and residual magnetic flux, the power converter's protection circuit activates, causing the drive device to stop, resulting in unstable drive control.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. Hei 09-223628 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] The problem to be solved by the present invention is to provide a drive device and control method that can further improve the stability of the drive control of a power converter that drives a motor via a transformer.

[0008] Methods for solving problems

[0009] The drive device of this embodiment includes a transformer, a power converter, and a control device. The transformer is a transformer having a primary winding and a secondary winding, with a motor connected to the secondary winding. The power converter allows current to flow into the primary winding of the transformer. During a first phase after the motor is instructed to start, the control device performs constant current control on the power converter to reduce fluctuations in the current flowing into the primary winding of the transformer by allowing current to flow from the power converter into the primary winding of the transformer at a predetermined desired frequency. In a second phase following the first phase, the power converter is controlled by variable voltage and variable frequency control of the motor. Attached Figure Description

[0010] Figure 1 This is a structural diagram of the driving device in the implementation method.

[0011] Figure 2 This is a structural diagram of the power converter according to the implementation method.

[0012] Figure 3AThis is a diagram illustrating the BH characteristics of the transformer used to explain the implementation method.

[0013] Figure 3B This diagram is used as a comparative example to illustrate the excitation state of a transformer when it is energized by a voltage source.

[0014] Figure 3C This is a diagram illustrating the excitation state of a transformer when the current source of the implementation method excites the transformer.

[0015] Figure 4 This is a diagram used to explain the control of the start-up phase of the drive device in the embodiment.

[0016] Figure 5A This is a timing diagram illustrating the operation of the drive device during the start-up phase of the implementation method.

[0017] Figure 5B This is a timing diagram used to illustrate the operation of the drive device in the comparative example during the start-up phase.

[0018] Figure 6A This is a structural diagram of the drive device according to the second embodiment.

[0019] Figure 6B This is a structural diagram of the power converter according to the second embodiment.

[0020] Figure 7 This is a structural diagram of the drive device according to the third embodiment. Detailed Implementation

[0021] Hereinafter, the driving device and control method of the embodiments will be described with reference to the accompanying drawings. Furthermore, in the following description, structures having the same or similar functions will be labeled with the same reference numerals. Also, repeated descriptions of these structures will sometimes be omitted. Furthermore, electrical connections will sometimes be simply referred to as "connections". The term "orthogonal" as used in the following description includes the case of approximately orthogonal connections. Furthermore, the case of "equal in size" also includes the case of approximately equal sizes.

[0022] Figure 1 This is a structural diagram of the driving device 1 in the embodiment. Figure 2 This is a structural diagram of the power converter 4 according to the implementation method.

[0023] The drive unit 1 includes, for example, a power converter 4, a transformer 5, and a control unit 10.

[0024] The power converter 4 includes, for example, a converter 4A, a reactor 4B, and an inverter 4C. The inverter 4C is an example of a power converter that functions as a current-source inverter circuit. Details related to it will be described later.

[0025] Power source 3 supplies AC power to power converter 4. Power converter 4 converts the AC power supplied from power source 3 and uses it to drive motor 2. A mechanical load is connected to the output shaft of motor 2, and the mechanical load rotates according to the rotation of the output shaft of motor 2. Motor 2 is, for example, an induction motor.

[0026] Transformer 5 has a primary winding and a secondary winding. The winding of motor 2 is connected to the secondary winding of transformer 5. Power converter 4 allows the desired current to flow into the primary winding of transformer 5 by switching a power semiconductor element.

[0027] The current detector 6 includes a current sensor. The current detector 6 is, for example, installed in the wiring between the output of the power converter 4 and the primary winding of the transformer 5. The current detector 6 detects the output current of the inverter 4C of the power converter 4, that is, the current flowing into the primary winding of the transformer 5. A current index value representing the detection result of this current is supplied to the control device 10. For example, the output current of the power converter 4 corresponds to the current (line current) flowing into each phase of the primary winding of the transformer 5. Alternatively, the current detector 6 may also be installed in the DC link connecting the converter 4A and the inverter 4C. In this case, the current detector 6 detects the current flowing into the DC link. In the following description, an example of the former will be used as shown in the accompanying drawings.

[0028] The control device 10 is configured to include a feedback control system based on current control, which controls the detection result of the output current of the power converter 4. For example, during the first stage of starting the motor 2, the control device 10 performs constant current control on the power converter 4 based on the detection result of the output current of the power converter 4, thereby reducing the fluctuation of the current flowing into the primary winding of the transformer 5. Then, in the second stage after the first stage, the control device 10 controls the power converter 4 in a manner that performs variable frequency variable voltage control (hereinafter referred to as VVVF control) on the motor 2. As the first stage, a preparation period for controlling the motor 2 by VVVF control is provided to the second stage throughout a predetermined period. For example, current control can also be implemented using the converter 4A, and VVVF control can be implemented using the inverter 4C.

[0029] A more specific example of the control device 10 is shown. For example, the control device 10 includes a first voltage reference generator 11, a second voltage reference generator 12, a first frequency reference generator 13, a frequency reference generator 14, a switching unit 15, an integrator 16, a control signal generation unit 17, a converter 19, and a controller 20.

[0030] Integrator 16 calculates the secondary flux angle φREF by integrating the frequency reference f* based on the frequency reference f* described later. The secondary flux angle φREF is used as the reference phase for the control of motor 2.

[0031] The control signal generation unit 17 generates a control signal GP for switching the power semiconductor elements of each phase contained in the power converter 4 described later, based on the voltage reference V* and the secondary flux angle φREF.

[0032] For example, the control signal generation unit 17 includes a coordinate transformation unit 17A and a PWM control unit 17B.

[0033] The coordinate transformation unit 17A converts the voltage reference V* into a three-phase coordinate system, generating the voltage reference for each phase. For example, based on the scalar voltage reference V* and the secondary flux angle φREF of the motor 2, the coordinate transformation unit 17A converts the voltage reference V* into a three-phase coordinate system using the secondary flux angle φREF, generating the voltage reference for each phase of the converter 4C. The voltage references VU_REF, VV_REF, and VW_REF are the voltage references that define the voltages of phases U, V, and W, respectively. An example of this conversion process is shown in equation (1). The control of the converter 4A is also the same.

[0034] (VU_REF, VV_REF, VW_REF)

[0035] =V*×(sinφREF, sin(φREF-2π / 3), sin(φREF-4π / 3)) (1)

[0036] The PWM control unit 17B generates control signals GP for switching the power semiconductor elements of each phase based on a voltage reference using PWM (Pulse Width Modulation) control with a specified carrier signal. For example, the PWM control unit 17B obtains voltage references VU_REF, VV_REF, and VW_REF, and generates control signals GP for switching the power semiconductor elements of each phase of converter 4C based on these voltage references using PWM control with a specified carrier signal. The PWM control unit 17B supplies control signals GP to the power semiconductor elements of each phase, causing the power semiconductor elements of each phase of converter 4C to switch individually. Furthermore, the control of converter 4A is performed separately for each of the three phases, similar to the control of inverter 4A.

[0037] Converter 19 generates current feedback Ifbk based on the current index value detected by current detector 6. For example, converter 19 generates current feedback Ifbk corresponding to the magnitude of the two-phase or three-phase current detected by current detector 6.

[0038] The first voltage reference generator 11 generates a first voltage reference V1*, which is used as the voltage reference for the first stage of starting the motor 2. The first voltage reference generator 11 determines the value of the first voltage reference V1*, for example, based on a frequency reference f2* described later. There is a correlation between the value of the first voltage reference V1* and the value of the frequency reference f2*.

[0039] For example, the first voltage reference generator 11 includes a starting current diagram generation unit 11A, a subtractor 11B, and a current controller 11C.

[0040] The starting current diagram generation unit 11A generates a starting current diagram that specifies the magnitude of the current value during the starting phase (first phase). The current value shown in the starting current diagram can be specified as a preset fixed value, or it can be specified in a way that the value changes according to the elapsed time after the start of starting. The starting current diagram generation unit 11A supplies a current reference Iref based on the starting current diagram to the subtractor 11B.

[0041] Subtractor 11B subtracts current feedback Ifbk based on the current value detected by current detector 6 from current reference Iref supplied from starting current diagram generation unit 11A, generates current deviation ΔI between current reference Iref and current feedback Ifbk, and supplies current deviation ΔI to current controller 11C.

[0042] The current controller 11C obtains the current deviation ΔI, calculates the voltage reference V1* in a manner that reduces or eliminates the current deviation ΔI, and outputs it as the voltage reference. For example, the current controller 11C calculates the voltage reference V1* by using a proportional-integral operation on the proportional gain KP and integral gain KI of the current deviation ΔI.

[0043] The first frequency reference generator 13 generates a first frequency reference f1* defined in such a way that a current flows into the windings of the motor 2 to demagnetize the motor 2. For example, the first frequency reference generator 13 is used in the starting phase (first stage). The first frequency reference generator 13 generates a signal (frequency reference f1*) containing frequency components that conform to a starting frequency diagram used to define the frequency of the current flowing into the windings of the motor 2. The frequency shown in the starting frequency diagram can be defined as a preset fixed frequency, or it can be defined in such a way that it changes according to the elapsed time after the start of starting. More specifically, the frequency shown in the starting frequency diagram can also be defined in such a way that the frequency gradually decreases according to the elapsed time after the start of starting. The first frequency reference generator 13 supplies the first frequency reference f1* based on the starting frequency diagram to the switching unit 15.

[0044] The second voltage reference generator 12 generates a second voltage reference V2* for variable speed control of the motor 2 as a voltage reference. For example, the second voltage reference generator 12 obtains the frequency reference f2* generated by the frequency reference generator 14 (described later), and generates a second voltage reference V2* for variable speed control of the motor 2 based on the frequency reference f2*. The second voltage reference generator 12 has, for example, a conversion rule for constant V / f control as a conversion rule representing the relationship between its frequency reference f2* and the second voltage reference V2*. This is simply referred to as a V / f diagram.

[0045] Frequency reference generator 14 generates a frequency reference f2* for variable speed control of motor 2. For example, frequency reference generator 14 obtains a frequency F* specified by controller 20 (described later) and generates frequency reference f2* based on frequency F*. Frequency reference generator 14 has a table for quantizing the frequency F* specified by controller 20 to generate frequency reference f2*. This table is set such that as frequency F* increases, the output frequency reference f2* represents a quantized value of a larger value. This conversion characteristic can be appropriately determined based on the design results. Quantization refers to converting the granularity of possible values ​​into jump values ​​with coarser granularity than the values ​​of the input variables, or converting continuously changing input values ​​into values ​​defined with a specified granularity.

[0046] The switching unit 15 includes, for example, switches 151 to 154. Switch 151 (first switch) activates a first voltage reference V1* as a voltage reference V* under the control of controller 20. Switch 152 (second switch) activates a second voltage reference V2* as a voltage reference V* under the control of controller 20. Switch 153 (third switch) activates a first frequency reference f1* as a frequency reference f* under the control of controller 20. Switch 154 (fourth switch) activates a frequency reference f2* as a frequency reference f* under the control of controller 20.

[0047] The controller 20 generates control commands SEL1* and SEL2* for starting the motor 2 in the first stage using the first voltage reference V1* and the first frequency reference f1*, and for starting the second stage using the second voltage reference V2* after the start of the first stage, based on the start request.

[0048] For example, controller 20 controls each switch in the following manner: during the first phase, control command SEL1* is used to switch switches 151 and 153 to be enabled and disabled; during the second phase, control command SEL2* is used to switch switches 152 and 154 to be enabled and disabled. Enabling each switch means, for example, setting each switch to the ON state.

[0049] Next, refer to Figure 2 The power converter 4 is described below.

[0050] The power converter 4 includes a converter 4A, a reactor 4B, and an inverter 4C.

[0051] Converter 4A is, for example, a converter containing multiple thyristors or diodes. Converter 4A rectifies the received AC power into DC power, generating a DC voltage. Converter 4A uses this DC voltage for current control. A reactor 4B is provided in the DC link connecting converter 4A and inverter 4C. Inverter 4C converts the DC power supplied via the DC link into AC power of the voltage and frequency required for speed control of motor 2. Inverter 4C is, for example, constructed by bridging multiple switching elements. These multiple switching elements are controlled by control device 10 for on / off switching.

[0052] For example, Figure 2 The inverter 4C shown is an example of a series-diode inverter using thyristors as switching elements. Each corresponding branch of inverter 4C contains two thyristors and two diodes, connected in series with the two diodes sandwiched between the two thyristors. The connection points of the thyristors and diodes in each branch are interconnected via commutation capacitors. Commutation occurs when a reverse bias voltage is applied to the thyristors through the voltage of the charge stored in the commutation capacitor. Furthermore, this… Figure 2 The circuit structure of the inverter 4C shown is not limited to this; other circuit structures can also be appropriately applied. For example, the inverter 4C can be a two-level inverter or a three-level inverter. This embodiment can be applied regardless of the inverter type or circuit structure.

[0053] Next, refer to Figures 3A-3C The constant current drive of the implementation method will be described.

[0054] Figure 3A This is a diagram illustrating the BH characteristics of transformer 5 in the embodiment. Figure 3B This diagram is used as a comparative example to illustrate the excitation state of transformer 5 when it is energized by a voltage source. Figure 3C This is a diagram illustrating the excitation state of transformer 5 when a current source is used to excite transformer 5 in the embodiment.

[0055] BH characteristics are typically represented by closed curves exhibiting hysteresis. Figure 3A In the example shown, the hysteresis of the BH characteristic is omitted for the relationship between the magnetic flux density B on the vertical axis and the magnetic field H on the horizontal axis. The result of using a piecewise linear approximation of the entire region using three line segments is shown. Residual flux is not shown in the BH characteristic based on this approximation, but because the actual transformer 5 has hysteresis characteristics, residual flux may sometimes be generated.

[0056] Figure 3A The approximate result shown is that the slope (permeability) of line segments in the unsaturated region, relative to the value of the magnetic field H, becomes gentler due to magnetic saturation in the saturated region, where the value of the magnetic field H is larger. The phenomena that may occur when excitation is applied near the boundary between the unsaturated and saturated regions are explained.

[0057] exist Figure 3B In the comparative example shown, transformer 5 is energized using a sinusoidal voltage waveform from a voltage source, causing a current corresponding to the BH characteristic (BH characteristic curve) to flow into the windings of transformer 5. The range of this current variation is indicated by arrows. In this voltage waveform, the current variation amplitude ΔIN during periods of positive voltage is larger than that during periods of negative voltage. Thus, the amplitudes ΔIP and ΔIN become unbalanced, and the current amplitude becomes asymmetrical relative to its polarity.

[0058] In this comparative example, the starting frequency (angular velocity) of the motor 2, controlled by VVVF, is maintained at a low value. When the drive method of the comparative example is applied for over-acceleration control, an unbalanced voltage occurs during startup, which can easily lead to magnetic flux saturation due to the voltage x time area. Furthermore, the magnitude of the residual magnetic flux in the transformer core and its position within the BH characteristic are unclear during startup. Therefore, there is also a risk of overcurrent due to magnetic saturation, which is related to the magnitude of the residual magnetic flux. Sometimes, a gapped transformer is used to avoid this phenomenon. Gapped transformers tend to be larger than gapless transformers.

[0059] In particular, when applied to mechanical loads with high starting torque, increased current is required during startup, sometimes necessitating voltage boosting under VVVF control. This is a major cause of further magnetic saturation in the transformer. When driving such mechanical loads with high starting torque using the comparative example method, overcurrent is easily generated, requiring countermeasures such as installing larger transformers.

[0060] Furthermore, the residual magnetic flux gradually disappears due to the voltage drop caused by the circuit's resistance. In the comparative example's starting method, since excitation is performed at a lower frequency corresponding to the motor's starting speed, applying alternating magnetic flux to the transformer more than a predetermined number of times is time-consuming. Therefore, in the comparative example's starting method, it is difficult to efficiently reduce the residual magnetic flux within the short time required for starting the motor, etc.

[0061] exist Figure 3C In the example of this embodiment shown, a current with a sinusoidal current waveform from a current source excites the transformer 5, thereby applying a voltage corresponding to the BH characteristic (BH characteristic curve) to the windings of the transformer 5. The range of voltage variation is indicated by arrows. The voltage variation amplitude ΔVP during the period when a positive current flows in the positive direction in the current waveform is smaller than the voltage variation amplitude ΔVN during the period when a negative voltage is present. Thus, since the variation amplitudes ΔVP and ΔVN are unbalanced, the voltage amplitude becomes asymmetrical with respect to its polarity. In this case, the center of the variation amplitude, which combines the variation amplitudes ΔIP and ΔIN, is located on the saturation region side compared to the point representing the reference voltage of the voltage waveform. That is, the position of this center moves more towards the side that reduces magnetic saturation and does not move towards the side that increases magnetic saturation. As a result, it acts in the direction where the asymmetry of the residual magnetic flux disappears.

[0062] Reference Figure 4 The control of the start-up phase of the drive device 1 in the embodiment will be described.

[0063] Figure 4This diagram illustrates the control during the start-up phase of the drive unit 1 in the embodiment. Figure 4 In (a) of the diagram, an example of a starting current diagram is shown. Figure 4 In (b) of the diagram, an example of a starting frequency diagram is shown. Figure 4 In (c), an example of a frequency reference f2* generated by quantizing frequency F* using a table is shown.

[0064] Figure 4 The starting current diagram shown in (a) specifies, for example, a current reference Iref applied to the period from the start of startup to the elapsed time T (hereinafter referred to as the first stage). For example, the current reference Iref is determined to be a constant value or a value close to a constant value. Current references Iref with values ​​close to a constant value are also collectively referred to as constant current references Iref.

[0065] Figure 4 The starting frequency diagram shown in (b) specifies the first frequency reference f1* in the first stage described above. For example, based on the first frequency reference f1* specified by the starting frequency diagram, the current flowing into the primary winding of transformer 5 can be given the following characteristics in the first stage to demagnetize transformer 5.

[0066] As a first feature of the first frequency reference f1*, it is defined that the frequency components represented by the first frequency reference f1* include, for example, frequency components higher than a preset frequency. The aforementioned "preset frequency" can be set to a frequency higher than the idling speed of the motor 2 when it starts.

[0067] As a second feature of the first frequency reference f1*, it is defined, for example, that the maximum value of the frequency specified by the first frequency reference f1* is generated just after the start of the first phase period (just after the start-up begins).

[0068] As a third feature of the first frequency reference f1*, it is specified, for example, that during the first phase, after the maximum value of the frequency specified by the first frequency reference f1* is generated, the frequency specified by the first frequency reference f1* decreases monotonically over time.

[0069] As a fourth feature of the first frequency reference f1*, it is specified, for example, that the minimum value of the frequency specified by the first frequency reference f1* reaches a predetermined value during the first stage period.

[0070] One or more of the first to fourth features mentioned above can be assigned as features of the first frequency reference f1*.

[0071] For example, during the first stage, the control device 10 controls the inverter 4C by allowing current to flow into the primary winding of the transformer 5 to demagnetize the transformer 5. During the second stage, the control device 10 controls the inverter 4C by allowing current to flow into the primary winding of the transformer 5 to perform VVVF control on the motor 2.

[0072] At this time, by using a first frequency reference f1* with a first characteristic, the control device 10 can control the inverter 4C in such a way that the current flowing into the primary winding of the transformer 5 to demagnetize the transformer 5 contains a frequency component higher than a preset frequency.

[0073] The control device 10 is able to control the inverter 4C in such a way as, by using a first frequency reference f1* having a second characteristic, the maximum value of the frequency at which the current flowing into the primary winding of the transformer 5 is generated just after the start of the first phase.

[0074] The control device 10 can control the inverter 4C in such a way that, during the first stage, after the maximum value of the frequency of the current flowing into the primary winding of the transformer 5 to demagnetize the transformer 5 is reached, the frequency decreases monotonically over time.

[0075] By using a first frequency reference f1* having a fourth characteristic, the control device 10 can control the inverter 4C in such a way that, in the latter half of the first stage, a minimum frequency of the current flowing into the primary winding of the transformer 5 to demagnetize the transformer 5 is generated. Furthermore, the control device 10 can begin the second stage after the minimum frequency of the current flowing into the primary winding of the transformer 5 to demagnetize the transformer 5 is generated during the first stage.

[0076] The following describes examples of assigning features to the first frequency reference f1* in a manner that satisfies all of the features described above, from the first to the fourth features.

[0077] Reference Figure 5A and Figure 5B The operation of the drive device 1 in the embodiment during the start-up phase will be described. Figure 5A This is a timing diagram illustrating the operation of the drive device 1 during the start-up phase of the embodiment. Figure 5B This is a timing diagram used to illustrate the operation of the drive device in the comparative example during the start-up phase.

[0078] from Figure 5A Starting from the upper side, the following are shown in sequence: (a) the output current and frequency f of inverter 4C, (b) the operating status of inverter 4C, (c) the status of switches 151 and 153, and (d) the status of switches 152 and 154.

[0079] In the initial stage up to time t1, no current (output current) flows through inverter 4C, and motor 2 is in a stopped state. Switches 151 to 154 are all in the off state.

[0080] When the time changes to t1, the controller 20 sends control signals to the frequency reference generator 14 and the switching unit 15 to control them respectively, such as Figure 5A As shown in (b) above, the drive unit 1, which was in a stopped state, starts to operate and enters the operating state. The controller 20, as shown... Figure 5A Set switches 151 and 153 (collectively referred to as SWA) to the ON state as shown in (c) in the diagram. Figure 5A The switching states of switches 152 and 154 (collectively referred to as SWB) are maintained as shown in (d) in the diagram.

[0081] For example, controller 20 sends a frequency F* to frequency reference generator 14 to specify the desired rotational speed of motor 2. Controller 20 sends a selection signal to switch unit 15 to select the desired signal (first signal), switching the state of switch unit 15 to the start-up phase. For example, controller 20 maintains the state thus determined until time t2.

[0082] The frequency reference generator 14 receives the frequency F* supplied, generates the corresponding frequency reference f2* by referring to the table, and supplies the frequency reference f2* to the first voltage reference generator 11, the first frequency reference generator 13, the second voltage reference generator 12 and the switching unit 15.

[0083] Upon receiving the frequency reference f2*, the first voltage reference generator 11 generates a current reference Iref through the starting current diagram generation unit 11A. This current reference Iref is based on a starting current diagram that specifies the magnitude of the current value during the starting phase (first phase). Additionally, the current controller 11C obtains the deviation between the current reference Iref and the current feedback Ifbk, i.e., the current deviation ΔI, and calculates the voltage reference V1* based on the current deviation ΔI. The first voltage reference generator 11 outputs this voltage reference V1*. The voltage reference V1* is used as the voltage reference V*.

[0084] Upon receiving a frequency reference f2*, the first frequency reference generator 13 generates a frequency index f1* based on a startup frequency diagram and supplies it to the switching unit 15. For example, the startup frequency diagram can be preset and tabulated. The startup frequency diagram specifies the magnitude of the frequency f during the startup phase (first phase). For example, as a startup frequency diagram, a frequency index f1* is specified that monotonically decreases from frequency fmax to frequency fmin over time after operation begins. This startup frequency diagram can also be specified as a function of time. The correlation between this frequency and the frequency reference f2* can be predetermined by showing how the value of the frequency index f1* changes accordingly.

[0085] The switching unit 15 is configured to activate the signal used during the startup phase through the aforementioned control. Consequently, a frequency index f1* is supplied to the integrator 16. The integrator 16 integrates the frequency index f1* to generate a secondary flux angle φREF. Furthermore, through this control, a voltage reference V* based on a voltage reference V1* and a secondary flux angle φREF based on the frequency index f1* are supplied to the control signal generation unit 17.

[0086] The control signal generation unit 17 generates a control signal GP based on a voltage reference V1* and a secondary flux angle φREF based on a frequency index f1* to control the inverter 4C of the power converter 4. Alternatively, the control signal generation unit 17 may also generate a control signal GP based on a predetermined voltage reference or voltage reference V1*, the detection voltage of the DC link, and a reference phase related to the AC current on the power supply side 3 to control the converter 4A of the power converter 4.

[0087] The above state continues until time t2.

[0088] For example, such as Figure 5A As shown in (a), the frequency represented by the frequency index f1* gradually decreases from frequency fmax to frequency fmin from time t1 to t2, according to the time elapsed after startup, in a manner specified by the startup frequency diagram. Based on this frequency change, the current period gradually lengthens. The current amplitude during this period is adjusted to be constant through current control.

[0089] When the time changes to t2, the controller 20 sends control signals to the frequency reference generator 14 and the switching unit 15 to control them respectively, such as Figure 5A As shown in (a), the frequency is gradually increased to speed up the motor 2.

[0090] At this time, controller 20 as Figure 5A Set switches 151 and 153 to the switching state as shown in (c) in the diagram, as follows: Figure 5AAs shown in (d), switches 152 and 154 are turned on. Consequently, the outputs of the first voltage reference generator 11 and the first frequency reference generator 13 are disconnected from the subsequent stage, and their output values ​​are invalidated. Instead, the outputs of the second voltage reference generator 12 and the frequency reference generator 14 are connected to the subsequent stage, and their output values ​​are validated.

[0091] As described above, the frequency index f2* output by the frequency reference generator 14 gradually increases from the frequency fmin after time t2.

[0092] The magnitude of the second voltage reference V2* output by the second voltage reference generator 12 increases as the frequency represented by the frequency index f2* increases, according to the V / f graph of the second voltage reference generator 12.

[0093] like Figure 5A As shown, until time t5, the frequency represented by the frequency index f2* increases, and the shaft output torque of motor 2 also increases. During the period from the start of operation at time t1 until time t5, no overcurrent exceeding the threshold OC1 is generated.

[0094] Next, refer to Figure 5B The comparative examples are explained.

[0095] In this comparative example, as described above, no structure for suppressing overcurrent is provided. Therefore, at the start of operation at time t11, even with a low frequency setting, an asymmetrical current will be generated due to the relationship between the starting torque and the magnetic saturation of transformer 5. Consequently, its amplitude may exceed the overcurrent protection threshold OC1. For example, when the threshold OC1 is exceeded at time t11a, operation needs to be stopped to perform overcurrent protection.

[0096] Even if the overcurrent protection threshold OC1 can be raised to threshold OC2 by reconsidering the overall structure, if the transformer is saturated and the residual flux remains high even at time t12, excessive current may still flow due to the torque generated by the acceleration of motor 2. In this case, operation needs to be stopped to perform overcurrent protection when the threshold CO2 is exceeded. Even if this reduces the certainty of stopping operation, it is difficult to prevent it from occurring.

[0097] As can be seen from the comparison with the above comparative example, according to the embodiment, the transformer 5 has a primary winding and a secondary winding, and the motor winding is connected to the secondary winding. The power converter 4 allows current to flow into the primary winding of the transformer 5 by switching the power semiconductor element. During the first stage of starting the motor 2, the control device 10 reduces the fluctuation of the current flowing into the primary winding of the transformer 5 by performing constant current control on the power converter 4. In the second stage after the first stage, the power converter 4 is controlled by VVVF control of the motor 2. As a result, the stability of the drive control of the power converter 4 driving the motor 2 via the transformer 5 can be further improved. The power converter 4 may include an inverter 4C.

[0098] The control device 10 can reduce the current reference Iref of the current flowing into the primary winding of the transformer 5 during the first stage, and reduce the frequency of the current flowing into the primary winding of the transformer 5 as time passes during the first stage. Therefore, the alternating current used to reduce the residual flux of the transformer 5 can circulate more frequently in a shorter time during the first stage, and the residual flux can be reduced in a shorter time.

[0099] During the first stage described above, the control device 10, based on the current detection result, i.e., the current feedback Ifbk, and the current value index, i.e., the current reference Iref, enables the power converter 4 to function through constant current control, thereby limiting the current during the first stage.

[0100] During the first stage described above, the control device 10 controls the power converter 4 by allowing a current to flow into the primary winding of the transformer 5 to demagnetize the transformer 5. Furthermore, during the second stage described above, the control device 10 controls the power converter 4 by allowing a current to flow into the primary winding of the transformer 5 for VVVF control of the motor 2. Therefore, after reducing the residual flux of the transformer 5 in the first stage, the motor 2 can be driven by VVVF control. The less residual flux of the transformer 5, the better; however, as long as the residual flux of the transformer 5 is reduced to a level sufficient to drive the transformer 5 without applying residual flux to its saturation region by the end of the first stage, overcurrent is unlikely to occur.

[0101] The control device 10 can start the second stage during the first stage described above, after the minimum value of the frequency of the current flowing into the primary winding of the transformer 5 to demagnetize the transformer 5 has reached a predetermined value.

[0102] By allowing a high-frequency current to flow through the control device 10 and gradually decreasing the frequency while the current is flowing, the risk of overcurrent caused by magnetic saturation of the transformer 5 can be mitigated, and the residual magnetic flux of the transformer 5 can be reduced during the initial stage of motor 2 startup. Therefore, it is unnecessary to use a transformer with an excessively large rated capacity to address the aforementioned risks.

[0103] In this way, by setting a period for current control during the initial stage of motor 2 starting, even with a large starting torque, the risk of overcurrent can be reduced, and a larger current can be flowed to start the motor.

[0104] <Second Implementation Method>

[0105] The second embodiment will now be described. The example of the first embodiment shown previously was an example using a current-source inverter circuit. In this embodiment, instead, an example using a voltage-source inverter circuit will be described.

[0106] Figure 6A This is a structural diagram of the drive device 1A according to the second embodiment. Figure 6B This is a structural diagram of the power converter 40 according to the second embodiment.

[0107] The drive unit 1A includes, for example, a power converter 40, a transformer 5, and a control unit 50. The power converter 40 and the control unit 50 replace the power converter 4 and the control unit 10 of the drive unit 1.

[0108] The power converter 40 includes, for example, a converter 40A, a capacitor 40B, and an inverter 40C.

[0109] Converter 40A can, for example, have the same structure as converter 40A. Capacitor 40B smooths the power converted by converter 40A. Inverter 40C is constructed by bridging multiple switching elements. Inverter 40C is an example of a power converter that includes a voltage-type inverter circuit. The multiple switching elements are controlled by control device 50.

[0110] The control device 50 includes, for example, a speed controller 50a, a frequency reference generator 50b (referred to as a speed calculation unit in the figure), a flux calculation unit 50c, a magnetizing current calculation unit 50d, a slip frequency calculation unit 50e, an integrator 50f, a three-phase / two-phase coordinate converter 50g, a current controller 50h, a two-phase / three-phase converter 50i, a PWM controller 50j, a first frequency reference generator 50k, a subtractor 50l, a divider 50m, an adder 50n, subtractors 50r and 50s, a switching unit 60, and a controller 70.

[0111] The speed controller 50a calculates the speed deviation by the subtractor 50l, and outputs a torque reference signal Tm* (hereinafter, * denotes the target value) in such a way that the deviation becomes zero. For example, the subtractor 50l calculates the speed deviation as described above using the deviation between the speed reference signal ωr* from the frequency reference generator 50b and the speed feedback signal ωr from the speed sensor (rotor speed detector) 2SS. The flux calculation unit 50c calculates the secondary flux reference signal φ2* of the AC motor 4a based on the speed feedback signal ωr. The divider 50m divides the torque reference signal Tm* by the secondary flux reference signal φ2* to obtain the torque current reference signal iq*. The magnetizing current calculation unit 50d calculates the excitation current reference signal id* based on the secondary flux reference signal φ2*. The slip frequency calculation unit 50e calculates the slip frequency signal ωs based on the torque component current reference signal iq* and the secondary flux reference signal φ2*. Adder 50n calculates the speed reference signal ω2* by adding the slip frequency signal ωs and the speed reference signal ωr*.

[0112] The frequency reference generator 50b receives the frequency F* supplied from the controller 70, generates a corresponding speed reference signal ωr*, and supplies the speed reference signal ωr* to the subtractor 50l. In the generation of the speed reference signal ωr* in the frequency reference generator 50b, the frequency reference generator 50b can use a table to generate the quantized speed reference signal ωr*, as in the aforementioned frequency reference generator 14.

[0113] The first frequency reference generator 50k receives the frequency F* supplied from the controller 70 and generates a corresponding speed reference signal ω1*. The first frequency reference generator 50k can generate the speed reference signal ω1*, for example, based on the aforementioned start-up frequency diagram.

[0114] The torque current reference signal iq*, excitation current reference signal id*, speed reference signal ω1*, and speed reference signal ω2* obtained in this way are given to the switching unit 60.

[0115] For example, the switching unit 60 includes a control signal switching switch 60b, a current setting unit 60c, and a current adjustment unit 60d.

[0116] The current setting unit 60c outputs the starting torque current io*0. The current regulating unit 60d outputs the starting excitation current ip*. The starting torque current io*0 and the starting excitation current ip* can be set to preset current values.

[0117] Control signal switching switch 60b, controlled by controller 70, switches the torque current reference signal iq* and starting torque current io*0, the excitation current reference signal id* and starting excitation current ip*, and the speed reference signal ω1* and speed reference signal ω2*. In the first stage of startup, control signal switching switch 60b outputs the torque current reference signal iq*, the excitation current reference signal id*, and the speed reference signal ω1*. In the subsequent second stage, control signal switching switch 60b outputs the starting torque current io*0, the starting excitation current ip*, and the speed reference signal ω2*. This second stage corresponds to the normal operating state.

[0118] The controller 70 is configured to include a timing device (not shown). The controller 70 receives a start-of-operation command from a host device and begins operation of the drive unit 1A, causing the motor 2 to start in two stages. Based on the elapsed time since receiving the start-of-operation command, the controller 70 controls the control signal switching switch 60b and the first frequency reference generator 50k according to each stage of startup. This control can be implemented according to the control described in the first embodiment.

[0119] The integrator 50f integrates the velocity reference signal ω3*, which is based on one of the velocity reference signals ω1* and ω2*, to obtain the secondary magnetic flux position θ0.

[0120] The three-phase / two-phase coordinate converter 50g uses the secondary flux position θ0 as the quasi-phase to decompose the current signal from the current detector 31 into a torque current feedback signal iq and an excitation current feedback signal id that is orthogonal to it, and outputs them.

[0121] The current controller 50h calculates and outputs the torque voltage reference signal Eq* by multiplying the deviation Δiq between the torque current reference signal iq* calculated by the subtractor 50r and the torque current feedback signal iq by a predetermined gain, in a manner that either decreases or becomes zero. Similarly, the current controller 50h calculates and outputs the excitation voltage reference signal Ed* by multiplying the deviation Δid between the excitation current reference signal id* calculated by the subtractor 50s and the excitation current feedback signal id by a predetermined gain, in a manner that either decreases or becomes zero.

[0122] The two-phase / three-phase converter 50i calculates and outputs the three-phase voltage reference signals Vu*, Vv*, and Vw* based on the torque voltage reference signal Eq*, the excitation voltage reference signal Ed*, and the secondary flux position θ0. Here, the PWM controller 50j outputs a pulse-width modulated gate pulse signal (control signal GP) based on the obtained three-phase voltage reference signals Vu*, Vv*, and Vw*. The control signal GP is applied to the inverter 40C, causing its multiple switching elements to turn on or off, thereby achieving the desired power conversion.

[0123] According to the above embodiment, the control signal generation unit in the drive device 1A generates a control signal GP for switching the power semiconductor elements of the inverter 40C based on a voltage reference and a reference phase. The current controller 50h, the two-phase / three-phase converter 50i, and the PWM controller 50j described above are examples of the control signal generation unit.

[0124] The first current reference generator generates a first current reference that is used as the current reference for the first stage of starting the motor 2. The current setting unit 60c and the current regulating unit 60d are examples of the first current reference generator. The first frequency reference generator 50k generates a first frequency reference that is used as the frequency reference for the first stage.

[0125] The second current reference generator generates a second current reference used as a current reference for variable speed control of the motor 2 in the second stage after the first stage. The magnetizing current calculation unit 50d and the divider 50m are examples of the second current reference generator. The frequency reference generator 50b generates a second frequency reference used as a frequency reference for variable speed control of the motor 2 in the second stage.

[0126] The controller 70 generates control commands for switching signals in the following manner: during the first stage of starting the motor 2, a reference phase based on a first frequency reference and a first current reference are supplied to the control signal generation unit; in the second stage following the first stage, a reference phase based on the frequency reference and a second current reference are supplied to the control signal generation unit. This allows adjustment of the frequency and magnitude of the current flowing into the primary winding of the transformer 5 during the aforementioned first stage. Consequently, similar to the first embodiment, it is possible to suppress operation stoppage due to overcurrent.

[0127] <Third Implementation Method>

[0128] The third embodiment will now be described. The example of the second embodiment shown previously illustrated an example of using a speed sensor 2SS to detect the speed of the motor 2. In this embodiment, instead, an example of so-called sensorless control will be described.

[0129] Figure 7This is a structural diagram of the drive device 1B according to the third embodiment.

[0130] The drive unit 1B replaces the control unit 50, switch unit 60, and controller 70 of the drive unit 1A with a control unit 50A, switch unit 60A, and controller 70A, and removes the speed sensor 2SS.

[0131] Compared to control device 50, control device 50A also includes a speed phase estimation unit 50t. Control device 50A replaces the speed controller 50a, flux calculation unit 50c, and integrator 50f of control device 50 with a speed controller 50Aa, a flux calculation unit 50Ac, and an integrator 50Af. Control device 50A is configured to lack the magnetizing current calculation unit 50d, slip frequency calculation unit 50e, divider 50m, and adder 50n.

[0132] The speed phase estimation unit 50t calculates the speed feedback signal ωr, which represents the estimated value of the speed of the motor 2, and the secondary flux position θ2*, which is used as the secondary flux position θ0 during the operation of the motor 2, based on the torque voltage reference signal Eq*, the excitation voltage reference signal Ed*, the torque current feedback signal iq, and the excitation current feedback signal id.

[0133] The speed feedback signal ωr and the secondary flux position θ2* of the motor 2, generated by the speed phase estimation unit 50t, can be achieved using known methods such as sensorless field-oriented control (FOC). Furthermore, methods using variables other than those described above are known as methods for generating the speed feedback signal ωr and the secondary flux position θ0 (secondary flux position θ2*) of the motor 2. Their application is not limited, and appropriate methods may be used as appropriate.

[0134] Each part in the control device 50A uses the speed feedback signal ωr generated by the speed phase estimation unit 50t to replace the aforementioned speed feedback signal ωr based on the detection value of the speed sensor 2SS.

[0135] For example, the speed controller 50Aa calculates the torque current reference signal iq* in such a way that the deviation of the speed calculated by the subtractor 50l using the speed feedback signal ωr becomes zero. The flux calculation unit 50Ac calculates the excitation current reference signal id* based on the speed feedback signal ωr. The integrator 50Af integrates the speed reference signal ω1* calculated by the first frequency reference generator 50k based on the speed feedback signal ωr to generate the secondary flux position θ1* used when the motor 2 starts.

[0136] The control signal switching switch 60b of the switching unit 60A, controlled by the controller 70A, switches the torque current reference signal iq* and the starting torque current io*0, switches the excitation current reference signal id* and the starting excitation current ip*, and switches the secondary flux position θ1* and the secondary flux position θ2*. In the first stage of startup, the control signal switching switch 60b outputs the torque current reference signal iq*, the excitation current reference signal id*, and the secondary flux position θ1*. In the subsequent second stage, the control signal switching switch 60b outputs the starting torque current io*0, the starting excitation current ip*, and the secondary flux position θ2*. This second stage corresponds to the normal operating state.

[0137] The controller 70A is configured to include a timer (not shown). The controller 70A receives a start-of-operation command from a host device and begins operation of the drive unit 1B, causing the motor 2 to start in two stages. Based on the elapsed time since receiving the start-of-operation command, the controller 70A controls the control signal switching switch 60b and the first frequency reference generator 50k according to each stage of startup. This control can be implemented according to the control described in the first embodiment.

[0138] According to the above-described embodiments, the control signal generation unit, the first current reference generator, the first frequency reference generator 50k, and the frequency reference generator 50b are equivalent to the corresponding parts in the second embodiment.

[0139] The second current reference generator in the third embodiment differs from that in the second embodiment in its correspondence. For example, the speed controller 50Aa and the flux calculation unit 50Ac are examples of the second current reference generator in the third embodiment.

[0140] Furthermore, the controller 70A generates control commands to switch signals in the following manner: in the first stage of motor starting, a reference phase generated based on a first frequency reference is supplied to the control signal generation unit; in the second stage, the estimated result of the second magnetic flux of the motor 2 is supplied to the control signal generation unit.

[0141] The sensorless control-based drive device 1B configured in this way can adjust the frequency and magnitude of the current flowing into the primary winding of the transformer 5 in the first stage using the same control method as in the first embodiment. Therefore, as in the first embodiment, it is possible to suppress operation stoppage due to overcurrent.

[0142] According to at least one embodiment described above, the drive device includes a transformer, a power converter, and a control device. The transformer is a transformer having a primary winding and a secondary winding, with the motor winding connected to its secondary winding. The power converter allows current to flow into the primary winding of the transformer. During the first stage of motor startup, the control device reduces the fluctuation of the current flowing into the primary winding of the transformer by performing constant current control on the power converter. In the second stage after the first stage, the power converter is controlled by variable voltage and variable frequency control of the motor. Therefore, the drive device can further improve the stability of the drive control of the power converter that drives the motor via the transformer.

[0143] Several embodiments of the present invention have been described, but these embodiments are provided by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are also included in the scope of the invention as set forth in the claims and its equivalents.

[0144] Explanation of reference numerals in the attached figures

[0145] 1. Drive unit

[0146] 2 Electric motor

[0147] 3 Power Supply

[0148] 4 Power converter

[0149] 4C Inverter

[0150] 5 Transformers

[0151] 6. Current detector

[0152] 10, 50, 50A control devices

[0153] 11 First Voltage Reference Generator

[0154] 12 Second Voltage Reference Generator

[0155] 13. 50k First Frequency Reference Generator

[0156] 14.50b Frequency Reference Generator

[0157] 15, 60, 60A switch section

[0158] 16 Integrators

[0159] 17 Control Signal Generation Unit

[0160] 20, 70, 70A controllers

Claims

1. A driving device, characterized in that, have: A transformer has a primary winding and a secondary winding, and a motor is connected to the secondary winding. A power converter that allows current to flow into the primary winding of the transformer; and The control device, during a first stage after the motor is instructed to start, reduces the variation in the current flowing into the primary winding of the transformer by constantly controlling the power converter with a current flowing from the power converter into the primary winding of the transformer at a predetermined desired frequency. In a second stage after the first stage, the power converter is controlled by variable voltage and variable frequency control of the motor. The control device controls the frequency of the current flowing through the power converter in such a way that the current flowing into the primary winding of the transformer to demagnetize the transformer contains a frequency component higher than the frequency preset to the desired frequency.

2. The driving device according to claim 1, characterized in that, During the first phase, the control device reduces the current flowing into the primary winding of the transformer as time passes, and, as the desired frequency during the first phase, reduces the frequency of the current flowing into the primary winding of the transformer as time passes.

3. The driving device according to claim 1, characterized in that, The drive device includes a current detector that detects the current flowing into the primary winding of the transformer. During the first phase, the control device performs constant current control through the power converter based on the current detection results and the current value index, i.e., the current reference.

4. The driving device according to claim 1, characterized in that, The control device controls the frequency of the current flowing through the power converter in such a way that, during the first phase, after the maximum frequency of the current flowing into the primary winding of the transformer to demagnetize the transformer is reached, the frequency decreases monotonically over time.

5. The driving device according to claim 1, characterized in that, During the first stage, the control device begins the second stage after the minimum frequency of the current flowing into the primary winding of the transformer to demagnetize the transformer reaches a predetermined value.

6. The driving device according to claim 1, characterized in that, The control device includes: The control signal generation unit generates control signals for switching the power semiconductor elements of the power converter based on a voltage reference and a reference phase. A first voltage reference generator generates a first voltage reference that is used as the voltage reference for the first stage of starting the motor. A first frequency reference generator generates a first frequency reference that is used as the frequency reference for the first stage. A second voltage reference generator generates a second voltage reference used as the voltage reference for variable speed control of the motor in a second stage following the first stage. A frequency reference generator that generates a second frequency reference used as a frequency reference for variable speed control of the motor in the second stage; An integrator that generates a reference phase based on one of the first frequency reference and the second frequency reference; as well as The controller generates a control command to switch signals by supplying the control signal generation unit with the reference phase and the first voltage reference based on the first frequency reference during a first phase of motor startup, and with the reference phase and the second voltage reference based on the frequency reference during a second phase after the first phase.

7. The driving device according to claim 6, characterized in that, have: A first switch that activates the first voltage reference; A second switch that activates the second voltage reference; A third switch that enables the first frequency reference; as well as A fourth switch that activates the second frequency reference; During the first phase, the controller controls the first switch and the third switch respectively in a manner that activates the first voltage reference and the first frequency reference. The controller controls the second switch and the fourth switch respectively during the second phase in a manner that enables the second voltage reference and the second frequency reference.

8. The driving device according to claim 1, characterized in that, The control device includes: The control signal generation unit generates control signals for switching the power semiconductor elements of the power converter based on a voltage reference and a reference phase. A first current reference generator generates a first current reference that is used as the current reference for the first stage of starting the motor. A first frequency reference generator generates a first frequency reference that is used as the frequency reference for the first stage. A second current reference generator generates a second current reference used as the current reference for variable speed control of the motor in a second stage after the first stage. A frequency reference generator that generates a second frequency reference used as a frequency reference for variable speed control of the motor in the second stage; as well as The controller generates a control command to switch signals by supplying a reference phase based on the first frequency reference and the first current reference to the control signal generation unit during a first phase of motor startup, and supplying a reference phase based on the frequency reference and the second current reference to the control signal generation unit during a second phase after the first phase.

9. A control method for a drive device, the drive device comprising: A transformer having a primary winding and a secondary winding, wherein a motor winding is connected to the secondary winding; and A power converter that allows current to flow into the primary winding of the transformer; The control method for the drive device is characterized by comprising: During the first stage of the motor startup, a step is taken to reduce the variation of the current flowing into the primary winding of the transformer by performing constant current control on the power converter in such a way that a current of a predetermined desired frequency flows from the power converter into the primary winding of the transformer. as well as In the second stage following the first stage, the power converter is controlled by variable voltage and variable frequency control of the motor. The step of controlling the frequency of the current flowing through the power converter in such a way that the current flowing into the primary winding of the transformer to demagnetize the transformer contains a frequency component higher than the frequency preset to the desired frequency.

10. A driving device, characterized in that, have: A transformer has a primary winding and a secondary winding, and a motor is connected to the secondary winding. A power converter that allows current to flow into the primary winding of the transformer; and The control device, during a first stage after the motor is instructed to start, reduces the variation in the current flowing into the primary winding of the transformer by constantly controlling the power converter with a current flowing from the power converter into the primary winding of the transformer at a predetermined desired frequency. In a second stage after the first stage, the power converter is controlled by variable voltage and variable frequency control of the motor. During the first phase, the control device reduces the current flowing into the primary winding of the transformer as time passes, and, as the desired frequency during the first phase, reduces the frequency of the current flowing into the primary winding of the transformer as time passes.

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