Drive system and control method

Abstract

The present invention provides a drive system and control method that can reduce the ripple effect of motor load fluctuations when driving multiple motors using AC power. [Solution] The drive system controls the speed of multiple motors using AC power. The drive system comprises a transformer, an AC-DC converter, a DC-DC converter, a DC-AC converter, and a control unit. The transformer generates first AC power from AC power according to the turns ratio of the primary and secondary windings. The AC-DC converter generates primary DC power using the first AC power. The DC-DC converter generates secondary DC power using the primary DC power. The DC-AC converter generates second AC power using the secondary DC power. The control unit controls at least the DC-DC converter to generate the secondary DC power.

Description

Technical Field

[0001] Embodiments of the present invention relate to a drive system and a control method.

Background Art

[0002] There is a drive system that controls the speed of a motor driven using alternating current power. Since the fundamental frequency of the alternating current supplied from the power grid is fixed, in the drive system, a power conversion unit is used to convert the fundamental frequency of the alternating current and implement speed control of the motor serving as the load. By the way, in the case of individually driving a plurality of motors in a drive system, the influence due to load fluctuations of the motors may spread to the power supply side, peripheral circuits, etc.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a drive system and a control method capable of reducing the spread of the influence due to load fluctuations of motors when driving a plurality of motors using alternating current power.

[0005] The drive system of the embodiment controls the speed of multiple motors using AC power. The drive system comprises a transformer, an AC-DC converter, a DC-DC converter, a DC-AC converter, and a control unit. The transformer generates first AC power from AC power according to the turns ratio of the primary and secondary windings. The AC-DC converter generates primary DC power using the first AC power. The DC-DC converter generates secondary DC power using the primary DC power. The DC-AC converter generates second AC power using the secondary DC power. The control unit controls at least the DC-DC converter to generate the secondary DC power. [Brief explanation of the drawing]

[0006] [Figure 1] A schematic diagram of the drive system according to the embodiment. [Figure 2] A diagram illustrating the configuration around the DC-DC converter in the embodiment. [Figure 3] A diagram illustrating the operation of the DC-DC converter in this embodiment. [Figure 4A] A schematic diagram of the control unit of the AC / DC converter according to the embodiment. [Figure 4B] A diagram illustrating the operation of the ACDC converter in this embodiment. [Figure 5A] A schematic diagram of the control unit of the DC-DC converter according to the embodiment. [Figure 5B] A diagram illustrating the operation of the DC-DC converter in this embodiment. [Figure 6A] A schematic diagram of the control unit of the DC-AC converter according to the embodiment. [Figure 6B] A diagram illustrating the operation of the DCAC converter in this embodiment. [Figure 7] A schematic diagram of the drive system according to the embodiment. [Figure 8] A schematic diagram of the drive system according to the embodiment. [Figure 9] Schematic diagram of the comparative drive system. [Modes for carrying out the invention]

[0007] The drive system and control method of the embodiment will be described below with reference to the drawings. In the following explanation, components with the same or similar functions will be denoted by the same reference numeral. Furthermore, redundant explanations of these components may be omitted. Note that the term "connected" may be used to simply refer to an electrical connection.

[0008] (First embodiment) The drive system 1 of the embodiment will be described with reference to Figure 1. Figure 1 is a schematic diagram of the drive system 1 of the embodiment.

[0009] The drive system 1 controls the speed of multiple motors 4 that are driven using AC power. This drive system 1 includes, for example, a transformer 5, a main circuit 10, and a control unit 20. In this embodiment, the main circuit 10 includes an AC-DC converter 11, a DC-DC converter 13, and a DC-AC converter 15.

[0010] Motor 4 is an example of multiple AC motors driven by multiphase AC power. For example, each of the motors 4 is a three-phase AC motor. Alternatively, other configurations of multiphase AC motors (multiphase AC motors) may be used. The embodiment illustrated below is an example of controlling multiple motors, and motor 4 includes motors 41 and 42. When these are not specifically distinguished, they may simply be referred to as motor 4.

[0011] Transformer 5 generates a first AC power from the AC power on the primary side according to the turns ratio of the primary and secondary windings. For example, the primary side of transformer 5 is configured to be connectable to a power grid or generator.

[0012] The AC-DC converter 11 is an example of an AC-DC power converter. The AC-DC converter 11 may be configured to be regenerative and enable bidirectional power conversion. For example, the primary side of the AC-DC converter 11 is connected to the secondary winding of the transformer 5. The primary side of the AC-DC converter 11 is connected to the secondary winding of the transformer 5. The secondary side of the AC-DC converter 11 is connected to the first DC link. The AC-DC converter 11 converts AC power into DC power during the power running of the motor 4 and converts DC power into AC power during regeneration. The AC-DC converter 11 during power running generates primary-side DC power using the first AC power generated by the transformer 5. A capacitor 12 is provided in the first DC link.

[0013] The DC-DC converter 13 is an example of a bidirectional DC power converter. The primary side of the DC-DC converter 13 is connected to the first DC link. The secondary side of the DC-DC converter 13 is connected to the second DC link. The DC-DC converter 13 generates secondary-side DC power using the primary-side DC power generated by the AC-DC converter 11. A capacitor 14 is provided in the second DC link. A more specific example of the DC-DC converter 13 and its periphery will be described later.

[0014] The DC-AC converter 15 is an example of an AC-DC power converter. The DC-AC converter 15 may be configured to be regenerative and enable bidirectional power conversion. The primary side of the DC-AC converter 15 is connected to the secondary winding of the transformer 5. The secondary side of the DC-AC converter 15 is connected to the first DC link. The DC-AC converter 15 generates the second AC power using the primary-side DC power generated by the transformer 5.

[0015] The DC-AC converter 15 of the embodiment includes a DC-AC converter 151 (first DC-AC converter) that supplies AC power to the first motor 41 and a DC-AC converter 152 (second DC-AC converter) that supplies AC power to the second motor 42. The DCAC converters 151 and 152 are connected to the second DC link (second DC side) of the DCDC converter 13.

[0016] The control unit 20 controls at least the DCDC converter 13 to generate secondary-side DC power.

[0017] The control unit 20 may further control the ACDC converter 11 to adjust the primary-side DC voltage using the first AC power. Also, the control unit 20 may control the DCAC converter 15 to adjust the second-side AC voltage applied to the motor 4 using the secondary-side DC power.

[0018] Referring to FIG. 2, an example of the DCDC converter 13 will be described. FIG. 2 is a configuration diagram around the DCDC converter 13 of the embodiment. The DCDC converter 13 is provided between the first DC link and the second DC link. The DCDC converter 13 performs power conversion (DC / DC conversion) between the primary-side DC voltage Vdc11 obtained by dividing the first DC link and the secondary-side DC voltage Vdc2 applied to the second DC link.

[0019] The DC-DC converter 13 shown in Figure 2 is a collection of DC / DC converters (referred to as DAB converters) with a DAB (Dual active bridge) configuration. For example, the DC-DC converter 13 includes the first to fifth DC / DC converters with DAB configurations (130A, 130B, ...). The primary side (ACDC converter 11 side) of each DC / DC converter (130A, 130B, ...) is connected in series with each other. The secondary side (DCAC converter 15 side) of each DC / DC converter (130A, 130B, ...) is connected in parallel with each other. The configuration of each DC / DC converter (130A, 130B, ...) is the same. Sometimes, each DC / DC converter (130A, 130B, ...) is collectively referred to as each DC / DC converter 130 without distinction. The DC / DC converters 130 shown in Figure 2 consist of two units, DC / DC converter 130A and DC / DC converter 130B, but there is no limit to the number of units and they can be changed as needed. An example of a specific configuration is shown for DC / DC converter 130A, and the notation of the configuration within DC / DC converter 130B is omitted.

[0020] Each DC / DC converter 130 includes a primary bridge circuit 13PB, a transformer 13PT, and a secondary bridge circuit 13SB. The primary bridge circuit 13PB and the secondary bridge circuit 13SB are examples of a pair of single-phase full-bridge circuits with the same configuration.

[0021] The primary bridge circuit 13PB constitutes a single-phase full bridge, including semiconductor devices S1 to S4. Semiconductor devices S1 and S2 constitute a first leg connected in series. Similarly, semiconductor devices S3 and S4 constitute a second leg connected in series.

[0022] Similarly, the secondary bridge circuit 13SB constitutes a single-phase full bridge, including semiconductor devices S5 to S8. Devices S5 and S6 constitute the third leg. Similarly, devices S7 and S8 constitute the fourth leg. In the following explanation, semiconductor devices S1 to S8 will be collectively referred to as device S.

[0023] Device S comprises a self-extinguishing switching element and a diode. The switching element can be any self-extinguishing element such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), or GCT (Gate Commutated Turn-off) thyristor as shown in the figure. The diode is connected in antiparallel to the switching element to form a free-wheeling diode (FWD). In the case of a MOSFET, the diode may be a body diode.

[0024] Transformer 13PT is an isolated pulse transformer for power applications with a turns ratio of N:1. The relationship between the voltage ratio of its primary side voltage e1 and secondary side voltage e2 and the turns ratio N of transformer 13PT is e1 = N·e2. The value of N can be arbitrarily determined. Furthermore, an inductance element may be provided in series with the winding of the transformer 13PT, or it may be provided in a distributed manner across multiple windings. A filter may also be provided as needed.

[0025] The DC-DC converter 13 formed as described above has insulating properties due to the action of the high-frequency link by the transformer 13PT.

[0026] The DC voltage of the first DC link, which is the input side of the DC-DC converter 13, is controlled by the AC-DC converter 11 to reach a target value of the desired DC voltage, as in the embodiment described above. For example, the control unit 20 controls the output voltage of the DC-DC converter 13 (secondary bridge circuit 13SB) to reach a target value. This adjusts the active power transmitted through the transformer 13PT in the DC-DC converter 13.

[0027] The DC-DC converter 13 described above includes one or more DAB converters associated with the motor 4. As described above, the first DC side of the multiple DAB converters, which is the AC / DC converter 11 side, is connected in series with each other. The second DC side of the multiple DAB converters, which is the DC / AC converter 15 side, is connected in parallel with each other.

[0028] In this way, by connecting the first DC side of the DC-DC converter 13, which is on the AC-DC converter 11 side, in series with each other, the input voltage of each stage is reduced. If the rated input voltage of each stage is equal, the input voltage of the DC-DC converter 13 can be increased. This makes it possible to reduce the current value per unit of power.

[0029] With the above configuration, the rated voltage of the AC / DC converter 11 can be increased, resulting in a lower current value compared to using an AC / DC converter of the same capacity but with a relatively lower rated voltage. This reduces current-related losses and allows for a smaller device by simplifying the components for thermal management. By using an isolated DAB converter as the DC-DC converter 13, secondary failures caused by a failure in the high-voltage circuit spreading to the low-voltage circuit can be suppressed.

[0030] The control unit 20 should control the power conversion by each DAB converter so that the DC input voltage of each DC / DC converter 130 is equal. For example, the following control procedure can be implemented to ensure that the DC input voltage of each DC / DC converter 130 is equal.

[0031] Let's organize the above structure from a different perspective. The rated voltage of the AC / DC converter 11 is higher than the rated voltage of the AC / DC converter 11. It is preferable to set the switching frequency of the DC-AC converter 15 higher than the switching frequency of the AC-DC converter 11. For example, by using a DC-AC converter 15 with a relatively high PWM control switching frequency, the controllability (responsiveness, stability, etc.) of the motor 4 can be improved.

[0032] As shown in Figure 2, the DC / DC converter 13 is comprised of five DC / DC converters 130A, 130B, 130C, 130D, and 130E, in that order from the top. The primary voltages of DC / DC converters 130A, 130B, 130C, 130D, and 130E are defined as Vdc11, Vdc12, Vdc13, Vdc14, and Vdc15, respectively.

[0033] The primary voltage references for DC / DC converters 130A, 130B, 130C, 130D, and 130E are defined as Vdc11 ref, Vdc12 ref, Vdc13 ref, Vdc14 ref, and Vdc15 ref, respectively.

[0034] The sum of the primary voltages of each DC / DC converter 130 equals the voltage Vdc1 of the first DC link. Vdc1=Vdc11+Vdc12+ Vdc13+Vdc14+ Vdc15

[0035] The sum of the primary voltage references of each DC / DC converter 130 is equal to the voltage reference Vdc1ref of the first DC link. Vdc1ref=Vdc11ref+Vdc12ref+ Vdc13ref+Vdc14ref+ Vdc15ref

[0036] If the primary voltage references of each DC / DC converter 130 are to be made equal, then it is appropriate to use a value obtained by dividing the voltage reference Vdc1ref of the first DC link into five equal parts. Vdc11ref=Vdc12ref= Vdc13ref=Vdc14ref= Vdc15ref=(Vdc1ref) / 5

[0037] The drive system 1 of this embodiment controls the speed of multiple motors using AC power. The drive system 1 comprises a transformer 5, an AC / DC converter 11, a DC / DC converter 13, a DC / AC converter 15, and a control unit 20. The transformer 5 generates first AC power from AC power according to the turns ratio of the primary and secondary windings. The AC / DC converter 11 generates primary DC power using the first AC power. The DC / DC converter 13 generates secondary DC power using the primary DC power. The DC / AC converter 15 generates second AC power using the secondary DC power. The control unit 20 controls at least the DC / DC converter 13 to generate secondary DC power.

[0038] Next, the operation of the DC-DC converter constituting this drive system 1 will be described. Figure 5 is a diagram illustrating the operation of the DC-DC converter of this embodiment. Here, the primary voltage of the transformer 13PT is denoted as e1, and the secondary voltage as e2. For simplicity of explanation, the turns ratio is assumed to be 1. Voltages e1 and e2 output AC pulse voltages with respect to time T, as shown in Figures 5(a) and 5(b).

[0039] In this case, as shown in Figure 5(a), the voltage e2 on the secondary side of the transformer 13PT lags the primary side voltage e1 by δ [rad], and power can be supplied from the primary side to the secondary side based on this phase difference. Furthermore, as shown in Figure 5(b), the voltage e2 on the secondary side of the transformer 13PT leads the primary side voltage e1 by δ [rad], allowing power to be supplied from the secondary side to the primary side based on this phase difference. Here, in the DC-DC converter 13, the power P output from the primary side to the secondary side is expressed as "P = (Vdc1 × Vdc2 / ωL) × (δ - δ2 / π)".

[0040] In the above-described formula for the power supply PDC, Vdc1 is, for example, the voltage across the capacitor 12 related to the DC-DC converter 13. Vdc2 is the voltage across capacitor 14. ω is the angular frequency, expressed as ω = 2πf. In this case, f is the frequency of the voltage waveform applied by the control unit 20 to the transformer 13PT. L is the sum of the conductor inductances of the current path. The above formula assumes a turns ratio of 1, but it is advisable to modify the formula according to the turns ratio.

[0041] The control unit 20 controls the phase difference in each DC / DC converter 130 so that the voltage distribution described above is approximately equal.

[0042] (Regarding AC / DC converter control) Next, we will explain the control of the AC / DC converter 11.

[0043] Figure 4A is a diagram illustrating the configuration of the control unit (power conversion control unit 25) of the ACDC converter according to the embodiment. Figure 4B is a diagram illustrating the operation of the ACDC converter 11 according to the embodiment. For example, the power conversion control unit 25 controls the AC / DC converter 11 based on the voltage Vdc1 of the first DC link, its voltage command value (DC voltage reference Vdcref), and AC current detection values ​​(Id, Iq, etc.).

[0044] The power conversion control unit 25 generates a reference wave for controlling the AC / DC converter 11 based on the DC voltage Vdc1 of the DC link of the corresponding AC / DC converter 11. The reference wave is, for example, a voltage waveform.

[0045] The power conversion control unit 25 described above includes, for example, a subtractor 25a, an AVR control 25b, a subtractor 25c, an ACR control 25d, a three-phase dq inverse conversion unit 25e, a PWM control unit 25f, a subtractor 25g, and an ACR control 25h. In addition to the above, the power conversion control unit 25 may also include a single-phase dq conversion unit, a DC voltage reference generation unit, and the like (not shown).

[0046] For example, the three-phase dq conversion unit performs three-phase dq conversion using a reference phase based on the voltage waveform supplied from the transformer 5 to the AC / DC converter 11, and decomposes it into an active current component and a reactive current component.

[0047] The DC voltage reference generation unit generates a DC voltage reference Vdcref. For example, the DC voltage reference generation unit may adjust the magnitude of a predetermined DC voltage reference Vdcref based on a command from the power conversion control unit 26.

[0048] The subtractor 25a, for example, uses the DC voltage reference Vdcref supplied from the DC voltage reference generation unit as the control target value, and subtracts the DC voltage VD1 of the first DC link from the DC voltage reference Vdcref to calculate the DC voltage error ΔVD1. Based on the DC voltage error ΔVD1, the AVR control 25b calculates a q-axis current reference Iqref1 such that the DC voltage VD1 of the first DC link becomes equal to the DC voltage reference Vdcref.

[0049] The subtractor 25c subtracts the q-axis current Iq from the q-axis current reference Iqref1 to calculate the q-axis current error ΔIq1. Based on the q-axis current error ΔIq1, the ACR control 25d calculates the q-axis voltage reference Vq1 such that the q-axis current Iq becomes equal to the q-axis current reference Iqref1.

[0050] The subtractor 25g calculates the d-axis current error ΔId1 by subtracting the d-axis current Id from the d-axis current reference Idref1. The ACR control 25h calculates the d-axis voltage reference Vd1 such that the d-axis current Id becomes equal to the d-axis current reference Iqref1, based on the d-axis current error ΔId1.

[0051] The 3-phase dq inverse transformer 25e performs a single-phase dq inverse transformer with the phase (θ) supplied from the PLL 515 as the reference phase, based on the d-axis voltage reference Vd1 and the q-axis voltage reference Vq1, to calculate the voltage reference signals Vuref, Vvref, and Vwref. The single-phase dq inverse transformer is the reverse transformer of the single-phase dq transformer. The PWM control unit 25f supplies pulses converted by PWM based on voltage reference signals uref, Vvref, and Vwref and a predetermined carrier signal to the gate pulse generation unit 2112. The gate pulse generation unit 2112 supplies gate pulses GP1111 generated based on the supplied pulses to the ACDC converter 11.

[0052] (Regarding DC-DC converter control) Figure 5A is a diagram illustrating the configuration of the DC-DC converter control unit of the embodiment. Figure 5B is a diagram illustrating the operation of the DC-DC converter 13 of the embodiment.

[0053] For example, the power conversion control unit 27 controls the DC-DC converter 13 based on the voltage Vdc2 of the second DC link, its voltage command value Vdc2_ref, and the input voltages Vdc11, 12, 13, 14, 15, etc., on the first DC link side.

[0054] The power conversion control unit 27 generates phase difference information for controlling the active power flowing through each DC / DC converter 130 of the DC-DC converter 13, based on the DC voltage Vdc2 of the second DC link on the output side of the DC-DC converter 13.

[0055] For example, the power conversion control unit 27 includes a subtractor 27a, an AVR control 27b, a balance controller 27c, a phase difference control 27d, and a PWM control unit 27e.

[0056] The subtractor 27a uses the secondary DC voltage reference Vdc2ref supplied from, for example, a higher-level control device as the control target value, and subtracts the DC voltage Vdc2 of the secondary DC link from the secondary DC voltage reference Vdc2ref to calculate the DC voltage error ΔVdc2. Based on the DC voltage error ΔVdc2, the AVR control 27b calculates a power command Pref such that the DC voltage Vdc2 of the secondary DC link becomes equal to the secondary DC voltage reference Vdc2ref. The balance controller 27c generates power commands Pref1, Pref2, Pref3, Pref4, and Pref5, which specify the amount of power to be converted by each DC / DC converter 130. The phase difference control 27d generates phase difference commands (δref1, δref2, δref3, δref4, δref5) for controlling the phase difference of each DC / DC converter 130 based on the power commands Pref1, Pref2, Pref3, Pref4, and Pref5.

[0057] The PWM control unit 27e generates gate signals for controlling the DC-DC converter 13 based on the above phase difference commands (δref1, δref2, δref3, δref4, δref5).

[0058] The DC-DC converter 13 (DAB converter) generates an AC signal with a predetermined phase difference based on the gate signal supplied from the power conversion control unit 27. This controls the magnitude and direction of the active power flowing through the DC-DC converter 13.

[0059] In actual devices, even if the DC voltages Vdc11, Vdc12, Vdc13, Vdc14, and Vdc15 at the input side of each stage are controlled to be the same voltage, they may still be different.

[0060] (Regarding DC-AC converter control) This section explains DC-AC converter control. Figure 6A is a diagram illustrating the configuration of the control unit (power conversion control unit 26) of the DCAC converter according to the embodiment. Figure 6B is a diagram illustrating the operation of the DCAC converter 15 according to the embodiment. The power conversion control unit 26 includes, for example, a subtractor 26a, a q-axis current reference generation unit 26b, a subtractor 26c, a q-axis current adjustment unit 26d, a dq inverse conversion unit 26e, a PWM control unit 26f, a subtractor 26g, and a d-axis current adjustment unit 266h.

[0061] The power conversion control unit 26 may further include a dq conversion unit (not shown).

[0062] The dq conversion unit transforms the detected output currents Iu, Iv, and Iw of the three-phase AC into a rotating coordinate system (dq-axis coordinate system) that is rotated by a phase θ with respect to the u-axis of the uvw-axis stationary coordinate system. The dq conversion unit outputs the feedback values ​​of the q-axis current Iq and the d-axis current Id.

[0063] The subtractor 26a calculates the difference between the speed reference Spref and the speed feedback value Sp. The q-axis current reference generation unit 26b (ASR) generates a q-axis current reference Iqref such that the speed reference ω and the speed feedback value Sp are equal, based on the calculation result (speed error ΔSp) of the subtractor 26a. The speed reference Spref is the target value of the rotational speed of the motor 4, and this value is specified by the higher-level device.

[0064] The subtractor 26c subtracts the q-axis current Iq from the q-axis current reference Iqref to calculate the q-axis current error ΔIq. The q-axis current adjustment unit 26d generates the q-axis voltage reference Vqref through a predetermined calculation based on the q-axis current error ΔIq.

[0065] The subtractor 26g subtracts the d-axis current Id from the d-axis current reference Idref to calculate the d-axis current error ΔId. The d-axis current adjustment unit 26h generates the d-axis voltage reference Vdref through a predetermined calculation based on the d-axis current error ΔId.

[0066] The dq inverse conversion unit 26e performs a dq inverse conversion on the q-axis voltage reference vqref and the d-axis voltage reference vdref, with the phase θ being the reference phase. The dq inverse conversion is the reverse conversion of the dq conversion performed by the dq conversion unit. The dq inverse conversion unit 26e calculates the inverter voltage references Vuref, Vvref, and Vwref through the dq inverse conversion. The inverter voltage references Vuref, Vvref, and Vwref are examples of voltage reference signals in inverter control.

[0067] The PWM control unit 26f performs PWM conversion on inverter voltage references Vuref, Vvref, and Vwref based on predetermined carrier signals, and supplies gate pulses generated by PWM conversion to each inverter.

[0068] The power conversion control unit 26 controls each DCAC converter 15 in the manner described above. The above configuration is common to the aforementioned power conversion control unit 26.

[0069] According to the above embodiment, the drive system 1 comprises the transformer 5, the AC / DC converter 11, the DC / DC converter 13, the DC / AC converter 15, and the control unit 20, thereby reducing the ripple effect of motor load fluctuations when driving multiple motors using AC power. Furthermore, with the above-described drive system 1, it is not necessary to directly connect the AC / DC converter and the DC / AC inverter via a DC link. This makes it possible to set the DC voltages of the AC / DC converter and the DC / AC inverter to different voltages.

[0070] (Second embodiment) Referring to Figure 7, the drive system 1A of the second embodiment will be described. Figure 7 is a schematic diagram of the drive system 1A of the embodiment. This embodiment differs from the first embodiment in that, as shown in Figure 7, a DC-DC converter is provided in association with each of the multiple motors 4, compared to the configuration shown in Figure 1 above. For example, the DC-DC converter 13 of this embodiment includes a DC-DC converter 131 (first DC-DC converter) connected to the DC side of the ADC converter 11, and a DC-DC converter 132 (second DC-DC converter) connected to the DC side of the ADC converter 11. The DCAC converter 15 of this embodiment includes a DCAC converter 151 (first DCAC converter) and a DCAC converter 152 (second DCAC converter). The DCAC converter 151 (first DCAC converter) is connected to the second DC side of the DCDC converter 131 and supplies AC power to the motor 41 (first motor). The DCAC converter 152 (second DCAC converter) is connected to the second DC side of the DCDC converter 132 and supplies AC power to the motor 42 (second motor). As a result, by providing separate DC-DC converter and DC-AC converter sets for motor 41 and motor 42, interference caused by load fluctuations in motor 41 and motor 42 can be reduced compared to the first implementation system described above.

[0071] According to this embodiment, by providing a DC-DC converter in association with each of the multiple motors 4, the propagation of effects due to motor load fluctuations can be reduced when driving multiple motors using AC power.

[0072] (Third embodiment) Referring to Figure 8, the drive system 1B of the third embodiment will be described. Figure 8 is a schematic diagram of the drive system 1B of the embodiment. In this embodiment, compared to the configuration shown in Figure 1, a third motor, motor 43, is further included in motor 4, as shown in Figure 8. In this case, the DCAC converter 15 further includes a third DCAC converter, the DCAC converter 17, which supplies AC power to the motor 43. The DCAC converter 17 is connected to the DC side of the AC / DC converter 11. For example, when the DC voltage of the first DC link is higher than the voltage of the second DC link, the DCAC converter 17 can use a relatively high DC voltage as its power source.

[0073] According to this embodiment, the DC-AC converter 15B, which is connected to the DC side of the AC-DC converter 11, is used to supply AC power to the motor 43. This reduces the ripple effect of motor load fluctuations when driving multiple motors using AC power.

[0074] (Regarding comparative examples common to each embodiment) Refer to Figure 9 to describe the comparative example drive system 1Z. Figure 9 is a schematic diagram of the comparative example drive system 1Z. The drive system 1Z includes transformers 5A, 5B, and 5C. The primary sides of transformers 5A, 5B, and 5C are connected to a common power grid. The secondary side of transformer 5A is connected in order to an AC / DC converter 11A, a DC / AC converter 15, and a motor 41. The secondary side of transformer 5B is connected in order to an AC / DC converter 11A, a DC / AC converter 15, and a motor 42. In this configuration, multiple transformers are required to convert the power of the fundamental frequency component of the AC power supply. As the capacity of each transformer increases, the area it occupies expands, which can make placement difficult. Also, because each system is independent, the effects of load fluctuations in each system can reach the primary side of each transformer. In contrast, the above-described embodiment can address the above-described problems.

[0075] According to at least one embodiment described above, the drive system controls the speed of multiple motors using AC power. The drive system comprises a transformer, an AC-DC converter, a DC-DC converter, a DC-AC converter, and a control unit. The transformer generates first AC power from AC power according to the turns ratio of the primary and secondary windings. The AC-DC converter generates primary DC power using the first AC power. The DC-DC converter generates secondary DC power using the primary DC power. The DC-AC converter generates second AC power using the secondary DC power. The control unit controls at least the DC-DC converter to generate the secondary DC power. This makes it possible to reduce the propagation of effects due to motor load fluctuations when driving multiple motors using AC power.

[0076] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel 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, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

[0077] (Note) The embodiment can be configured as follows. (1) A drive system that controls the speed of multiple motors using alternating current power, A transformer that generates first AC power from AC power according to the turns ratio of the primary and secondary windings, An AC / DC converter that generates primary DC power using the first AC power, A DC-DC converter that generates secondary DC power using the primary DC power, A DC-AC converter that generates a second AC power using the aforementioned secondary DC power, A control unit that controls the DC-DC converter to generate the secondary DC power, and A drive system equipped with the following features. (2) In the drive system relating to (1) above, The control unit further The AC / DC converter is controlled to adjust the primary DC voltage using the first AC power. It is preferable to control the DC-AC converter to adjust the second AC voltage applied to the motor using the secondary DC power. (3) In the drive system relating to (1) or (2) above, The aforementioned DC-DC converter is The system may include one or more DAB converters associated with the motor. (4) In the drive systems relating to (1) to (3) above, The aforementioned multiple DAB converters are The first DC side, which is the AC / DC converter side, is connected in series with each other. The second DC side, which is the DCAC converter side, is connected in parallel with each other. The control unit, It is advisable to control the power conversion by each DAB converter so that the DC input voltage of each DAB converter is equal. (5) In the drive systems relating to (1) to (4) above, The motor includes a first motor and a second motor, The DCAC converter, A first DC-AC converter that supplies AC power to the first motor, The system includes a second DC-AC converter that supplies AC power to the second motor, The first DC-AC converter and the second DC-AC converter are It is preferable that it be connected to the second DC side of the DC-DC converter. (6) In the drive systems relating to (1) to (4) above, The motor includes a first motor and a second motor, The aforementioned DC-DC converter, A first DC-DC converter connected to the DC side of the AC-DC converter, It includes a second DC-DC converter connected to the DC side of the aforementioned AC-DC converter, The DCAC converter, A first DCAC converter connected to the second DC side of the first DC-DC converter and supplying AC power to the first motor, It is preferable that a second DCAC converter is included, which is connected to the second DC side of the second DC-DC converter and supplies AC power to the second motor. (7) In the drive system relating to (1) to (4) above, The motor further includes a third motor, The DCAC converter, It is preferable that a third DC-AC converter, connected to the DC side of the AC-DC converter and supplying AC power to the third motor, is further included. (8) In the drive systems described in (1) to (7) above, It is desirable that each component be configured to be regenerative. It would be good to do so. (9) The control method of the embodiment is: A transformer that generates first AC power from AC power according to the turns ratio of the primary and secondary windings, An AC / DC converter that generates primary DC power using the first AC power, A DC-DC converter that generates secondary DC power using the primary DC power, The system includes a DC-AC converter that generates a second AC power using the aforementioned secondary DC power, A control method for a drive system that controls the speed of multiple motors using alternating current power, The system may include controlling the DC-DC converter to generate the secondary DC power. [Explanation of symbols]

[0078] 1 Drive System 4 motors 41 First Motor 42 Second Motor 43 Third Motor 5 transformers 10 Main circuit 11 ACDC converter 12, 14 Capacitors 13 DC-DC converters 15 DC-AC Converters 20 Control Unit

Claims

1. A drive system that controls the speed of multiple motors using alternating current power, A transformer that generates first AC power from AC power according to the turns ratio of the primary and secondary windings, An AC / DC converter that generates primary DC power using the first AC power, A DC-DC converter that generates secondary DC power using the primary DC power, A DC-AC converter that generates a second AC power using the aforementioned secondary DC power, A control unit that controls the DC-DC converter to generate the secondary DC power, and A drive system equipped with the following features.

2. The control unit further The AC / DC converter is controlled to adjust the primary DC voltage using the first AC power. The DC-AC converter is controlled to adjust the second AC voltage applied to the motor using the secondary DC power. The drive system according to claim 1.

3. The DCDC converter is Includes one or more DAB converters associated with the motor, The drive system according to claim 1.

4. The aforementioned multiple DAB converters are, The first DC side, which is the ADC converter side, is connected in series with each other. The second DC side, which is the DC-AC converter side, is connected in parallel with each other. The control unit, The power conversion by each DAB converter is controlled so that the DC input voltage of each DAB converter is equal. The drive system according to claim 3.

5. The motor includes a first motor and a second motor, The DC-AC converter, A first DC-AC converter that supplies AC power to the first motor, The system includes a second DC-AC converter that supplies AC power to the second motor, The first DC-AC converter and the second DC-AC converter are The second DC side of the DC-DC converter is connected The drive system according to claim 4.

6. The motor includes a first motor and a second motor, The DCDC converter, A first DC-DC converter connected to the DC side of the ADC converter, It includes a second DC-DC converter connected to the DC side of the ADC converter, The DC-AC converter, A first DC-AC converter connected to the second DC side of the first DC-DC converter and supplying AC power to the first motor, This includes a second DC-AC converter connected to the second DC side of the second DC-DC converter, which supplies AC power to the second motor. The drive system according to claim 4.

7. The motor further includes a third motor, The DC-AC converter, The system further includes a third DC-AC converter, which is connected to the DC side of the ADC converter and supplies AC power to the third motor. The drive system according to claim 4.

8. Each component is configured to be regenerative. A drive system according to any one of claims 1 to 7.

9. A transformer that generates first AC power from AC power according to the turns ratio of the primary and secondary windings, An AC / DC converter that generates primary DC power using the first AC power, A DC-DC converter that generates secondary DC power using the primary DC power, The system includes a DC-AC converter that generates a second AC power using the aforementioned secondary DC power, A control method for a drive system that controls the speed of multiple motors using alternating current power, At least the DC-DC converter is controlled to generate the secondary DC power. A control method including

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