control device

Abstract

To favorably restrict secondary rush current in a DC bus through which DC power is outputted from a converter.SOLUTION: A control device for controlling current on DC bus through which DC power is outputted from a converter, which is a preventative circuit for restricting rush current when output of DC power from the converter to the DC bus is initiated, includes: a resistor connected to a positive electrode side or a negative electrode side of the DC bus; a preventative circuit including a relay arranged to the resistor in parallel; a first detection part for detecting a PN voltage between the positive electrode side and the negative electrode side of the DC bus after initiation of DC power output from the converter with the state where the relay is turned off; a second detection part for detecting an AC voltage inputted to the converter; and a control part for switching the relay from off-state to on-state based on the PN voltage detected by the first detection part and the AC voltage detected by the second detection part.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a control device that controls the current of a DC bus from which DC power is output by a converter.

Background Art

[0002] As a power supply system for driving an electric motor such as a motor, systems having a DC bus are widely used. Since various devices that use DC power are connected to this DC bus to realize stable power supply, a capacitor may be provided for the DC bus in some cases. The DC power supplied to such a DC bus may be generated by a converter that converts input AC power into DC power in some cases. Immediately after the converter starts supplying DC power, a DC voltage is suddenly applied to the DC bus, so a steep pulsed inrush current may flow through the DC bus in some cases. Inrush current causes local temperature rise and the like, and is not desirable. Therefore, in the prior art, a prevention circuit for suppressing the peak value of inrush current may be provided on the DC bus in some cases.

[0003] For example, Patent Document 1 discloses a configuration that performs on / off control of a relay based on the bus voltage of an inrush current prevention circuit, in order to prevent welding of the contacts of a power supply relay caused by inrush current provided in a DC bus. Patent Document 2 and Patent Document 3 also disclose configurations that perform on / off control of a relay based on the voltage between the terminals of a capacitor connected to a DC bus.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0005] Generally, a prevention circuit combining a resistor and a relay is often used to suppress the peak value of inrush current in a DC bus. In this prevention circuit, the resistor in the prevention circuit is connected to the DC bus during the period when inrush current occurs, thereby suppressing the peak of the inrush current. On the other hand, if the resistor remains connected to the DC bus, the power of the DC bus will be wasted. Therefore, when the peak value of the inrush current has decreased to a certain extent, the relay is switched off to effectively disconnect the resistor from the DC bus.

[0006] As described above, it is possible to suppress the peak value of inrush current to some extent by using a prevention circuit. However, at the timing when the relay can be switched, the current flow in the DC bus switches abruptly, which may cause a secondary inrush current. In particular, since the DC bus is also affected by the operation of the converter that outputs DC power to it, considering only the electrical state of the DC bus may be insufficient to effectively suppress the secondary inrush current.

[0007] This invention has been made in view of these problems, and aims to provide a technique for suitably suppressing secondary inrush current in a DC bus from which DC power is output from a converter. [Means for solving the problem]

[0008] A control device relating to one aspect of the present disclosure is a control device for controlling the current of a DC bus from which DC power is output from a converter, and includes a prevention circuit for suppressing an inrush current when the output of DC power from the converter to the DC bus is started, the prevention circuit including a resistor connected to the positive or negative side of the DC bus and a relay arranged in parallel with the resistor; a first detection unit for detecting the PN voltage between the positive and negative sides of the DC bus after the output of DC power from the converter is started with the relay turned off; a second detection unit for detecting the AC voltage input to the converter; and a control unit for switching the relay from an off state to an on state based on the PN voltage detected by the first detection unit and the AC voltage detected by the second detection unit.

[0009] The control device disclosed herein is a control device that controls the current in a DC bus from which DC power is output from a converter. Generally, in a DC bus, an inrush current may flow immediately after the start of DC power supply from the converter. Inrush current is a pulsed current, and because its peak value is relatively large, it may have an undesirable effect on electrical equipment connected to the DC bus. Therefore, the control device disclosed herein includes a prevention circuit including a resistor and a relay. When the output of DC power from the converter starts, the relay is turned off, so that the inrush current caused by the start of the output flows into the resistor of the prevention circuit, and the peak value of the inrush current can be suppressed to a lower level. Therefore, by providing the prevention circuit near the part where the output section of the converter is connected to the DC bus (before the capacitor), the effect of the inrush current can be reduced as much as possible on the downstream side of the DC bus (distant from the converter).

[0010] The resistance of the prevention circuit reduces the peak value of the inrush current, but to avoid further energy consumption by the resistance, the prevention circuit needs to switch the relay from the off state to the on state. This allows the current flowing through the DC bus to bypass the resistance, thereby avoiding energy loss in the DC bus. However, the switching of the relay from the off state to the on state in the prevention circuit (hereinafter simply referred to as "relay switching") may cause a secondary inrush current to occur. Since the peak value of this secondary inrush current is also relatively high, it can affect the relay contact life and surrounding equipment, so it is preferable to suppress its peak value to a lower level.

[0011] Therefore, the control device disclosed in this application comprises a first detection unit and a second detection unit, which detect the PN voltage and the AC voltage input to the converter, respectively. The PN voltage is an element directly related to the DC bus. The AC voltage is an element strongly related to the operation of the converter that outputs DC power to the DC bus. Therefore, regarding the secondary inrush current caused by the ON operation of the relay in the prevention circuit, it is important to minimize the potential difference between the relay terminals at the start of the ON operation, that is, at a timing when the energy consumption in the resistor is not unnecessarily long and the peak of the secondary inrush current is low. The applicant has found that the two elements, the PN voltage and the AC voltage, are strongly related to this potential difference. Therefore, the control unit performs relay switching in the prevention circuit based on the PN voltage and the AC voltage detected by the first detection unit and the second detection unit.

[0012] This configuration makes it possible to effectively suppress secondary inrush current caused by relay switching in the prevention circuit. As an example of a control device, it may be a driver unit equipped with an inverter that receives DC power from the DC bus and generates a drive current for driving the motor. The control device, which is a driver unit, may be equipped with an inverter capable of driving one or more motors. The control device, which is a driver unit, may also be configured to include the converter and the DC bus. Furthermore, as an alternative, the control device As an example, a capacitor unit for adjusting voltage fluctuations in a DC bus using capacitors can also be provided. The control device may have configurations other than those described above.

[0013] Furthermore, in the control device described above, the control unit may switch the relay from the off state to the on state when the difference between the AC voltage detected by the second detection unit and the PN voltage detected by the first detection unit falls below a predetermined threshold. The applicant has found that this difference is strongly related to the peak value of the secondary inrush current. Therefore, by setting the timing at which this difference falls below a predetermined threshold as the relay switching timing, not only the inrush current caused by the start of DC power output by the converter, but also the peak value of the secondary inrush current can be suitably suppressed. Note that the AC voltage input to the converter fluctuates over time, but when calculating the difference with the PN voltage, the AC voltage value of a predetermined phase (for example, the peak voltage value) can be used as a representative value.

[0014] Furthermore, the predetermined threshold can be determined by considering the electrical characteristics of the converter and prevention circuit connected to the DC bus. Alternatively, the predetermined threshold may be variably adjusted. For example, if there is a parameter related to the peak value of the secondary inrush current in the DC bus, the predetermined threshold can be variably adjusted according to that parameter. Examples of such parameters include the temperature of the DC bus.

[0015] In the control device described above, the control unit may switch the relay from the off state to the on state if the time derivative of the PN voltage becomes smaller than a predetermined value before the difference falls below a predetermined threshold. As the time derivative of the PN voltage, i.e., the rate of change, decreases, the time required to reach a state where the difference falls below a predetermined threshold increases, and as a result, the amount of energy consumed by the resistor in the prevention circuit may increase. Therefore, in order to avoid such wasted energy consumption, it is preferable to switch the relay from the off state to the on state when the time derivative of the PN voltage becomes smaller than a predetermined value, even if the difference has not yet fallen below a predetermined threshold. It is preferable to determine the predetermined value by considering the balance between energy consumption by the resistor and the adverse effects of secondary inrush current. [Effects of the Invention]

[0016] This technology can provide a suitable method for suppressing secondary inrush current in a DC bus where DC power is output from a converter. [Brief explanation of the drawing]

[0017] [Figure 1] This is a diagram illustrating the schematic configuration of the power supply system. [Figure 2] Figure 1 is a schematic diagram showing the circuit configuration of the driver unit and capacitor unit included in the power supply system. [Figure 3] Figure 2 is a flowchart showing the processing flow for suppressing inrush current in the power supply system. [Figure 4] This figure illustrates the behavior of the inrush current when the process shown in Figure 3 is performed. [Modes for carrying out the invention]

[0018] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and repeated description thereof will be omitted. In the present disclosure, a driver unit and a capacitor unit for supplying driving power to drive a motor are shown as one exemplary embodiment of a control device, but the technical idea related to the control device of the present disclosure can also be applied to devices other than these.

[0019] Figure 1 is a diagram showing a schematic configuration of a power supply system that supplies driving power to a motor. The power supply system includes a converter 10, a capacitor unit 15, and a driver unit 20. The converter 10 receives supply of AC power from an AC power source 7 via a cable 7a and outputs DC power. The output DC power is supplied to the capacitor unit 15 and the driver unit 20, which are arranged adjacent to the converter 10, through a DC bus 11 (see FIG. 2 described later). This DC bus 11 is a conduction path for DC power, and is formed between the converter 10, the capacitor unit 15, and the driver unit 20. Each of the capacitor unit 15 and the driver unit 20 corresponds to the control device of the present disclosure.

[0020] The driver unit 20 is connected to a PLC (Programmable Logic Controller, etc.) not shown in the figure governs servo control of the motor 2 based on instructions from. The control unit 210 of the driver unit 20 (see FIG. 2 described later) is a computer having a CPU and a memory that perform arithmetic processing, and can exhibit various functions by executing a predetermined control program or the like therein. For example, the control unit 210 receives a motion command signal relating to the motion of the motor 2 from a host device via a network and a detection signal from an encoder mounted on the motor 2, and calculates a command value relating to servo control for driving the motor 2. Then, the driver unit 20 supplies driving power for driving the corresponding motor to the motor 2 via the power line 2a in accordance with the calculated command value. The control unit 210 is also configured to execute control related to processing for suppressing inrush current flowing through the DC buses 11 and 21, and the details thereof will be described later. Furthermore, the control unit 210 may be configured to also govern control other than these controls for the motor 2.

[0021] Further, the capacitor unit 15 is a unit having therein a capacitor 155 capable of storing regenerative power from the motor 2. By storing regenerative power in the capacitor 155, it is possible to suppress an excessive increase in the voltage of the DC buses 11 and 151 during regeneration of the motor 2, and the stored power can be used for driving the motor 2. In constructing the power supply system, the capacitor unit 15 is not an essential component, and it is sufficient to determine whether to use the capacitor unit 15, the capacitance of the capacitor 155 incorporated in the capacitor unit 15, and the like in consideration of the operating conditions, load conditions, and the like of the motor 2.

[0022] Motor 2 is driven and controlled by a driver unit 20 to drive a predetermined piece of equipment. The driver unit 20 has a built-in inverter 26, which generates the drive current for motor 2. As an example, the piece of equipment can be various types of machinery (e.g., the arm of an industrial robot or a conveying device), and motor 2 is incorporated into the equipment as an actuator to drive it. Motor 2 is an AC servo motor. Alternatively, motor 2 may be an induction motor or a DC motor. Motor 2 has a detection disc that rotates in conjunction with the rotation of each rotor and is equipped with an encoder capable of detecting the rotation state of the rotor. Furthermore, motor 2 may be a linear motor, in which case a linear encoder is used to detect the position of the movable element.

[0023] Here, the configuration of the driver unit 20 and capacitor unit 15, which correspond to the power supply device in the power supply system shown in Figure 1, will be explained based on Figure 2. In this power supply system, AC power supplied from the AC power source 7 is converted to DC power by the converter 10 and output to the DC bus 11. The driver unit 20 and capacitor unit 15 are configured to be detachable from the DC bus 11. Therefore, the user can remove or attach the devices connected to the DC bus 11 as needed for maintenance or other purposes.

[0024] The internal circuitry of the driver unit 20, in particular, the DC power supplied from the DC bus 11, is input The configuration of the input section 200 will now be described. The input section 200 is the part in the driver unit 20 where DC power from an external source is input, and the DC power input to the input section 200 is supplied to the inverter 26 located downstream. The inverter 26 itself is based on known technology, so its details will not be explained.

[0025] In the input section 200, a resistor 22 and a relay 23 are provided in the positive path of the DC bus 21 to form a prevention circuit that prevents inrush current from flowing from the DC bus 11 to the input section 200 when DC power is supplied from the converter 10 to the DC bus 11 to which the driver unit 20 is connected. In this prevention circuit, the resistor 22 and the relay 23 are connected in parallel. When the relay 23 is off, the current flowing in the positive path passes through the resistor 22, and when the relay 23 is on, the current flows to bypass the resistor 22. More specifically, when DC power is supplied from the converter 10, the relay 23 is in the off state, and the peak value of the inrush current is suppressed by the current flowing through the resistor 22 in the positive path. Then, when the inrush current is detected, the relay 23 is turned on, so that the power supplied from the DC bus 11 is not consumed by the resistor 22. Details of the inrush current suppression process by this prevention circuit will be described later. Alternatively, a PTC (Positive Temperature Coefficient) can be used instead of resistor 22, and a semiconductor switch element can be used instead of relay 23. The same applies to resistor 152 and relay 153, which will be discussed later.

[0026] In addition, a capacitor 25 is placed between the positive and negative paths in the input section 200. The capacitor 25 is positioned to keep voltage fluctuations of the DC bus 21 within an acceptable range and can also store regenerative power from the motor 2 driven by the driver unit 20. Furthermore, a discharge circuit 24 for discharging the power stored in the capacitor 25 is connected between the positive and negative paths. The discharge circuit 24 has a resistor for power consumption and a switch circuit for controlling the voltage applied to the resistor, and the drive of the switch circuit is appropriately controlled by the control unit 210. Moreover, a detection unit 27 is provided in the input section 200 to detect the PN voltage between the positive and negative paths. The PN voltage detected by the detection unit 27 is passed to the control unit 210.

[0027] Furthermore, the power supply system is equipped with a detection unit 8 that detects the AC voltage input to the converter 10 (the AC voltage in cable 7a). The AC voltage detected by the detection unit 8 is then transmitted to the control unit 210 of the driver unit 20.

[0028] Next, the capacitor unit 15 will be described. Since the capacitor unit 15 is not a unit for driving a motor, it does not have a built-in inverter 26 like the driver unit 20. However, its input section 150 has an electrical configuration that is generally the same as the input section 200 of the driver unit 20. That is, the input section 150 has a resistor 152 and a relay 153 that constitute an inrush current prevention circuit provided on the positive side path of the DC bus 151, a capacitor 155 and a discharge circuit 154 provided between the positive and negative paths of the DC bus 151.

[0029] Thus, the power supply system, composed of the driver unit 20 and the capacitor unit 15, provides drive power for controlling the motor 2 and recovers regenerative power from the motor 2. Here, we consider the timing when the power supply system starts operating, that is, when the converter 10 starts supplying DC power to the DC bus 11. At this point, the capacitors 25 and 155 in the driver unit 20 and capacitor unit 15 have no charge stored. Therefore, when the output of DC power from the converter 10 starts, a pulsed inrush current is generated in the DC buses 21 and 151 within the driver unit 20 and capacitor unit 15. At this time, The relay 23 in the stop circuit is in the off state, and therefore the inrush current flows through the resistor 22 to the downstream side of the DC bus 21 where the capacitor 25 is located.

[0030] If the peak value of the inrush current becomes excessively high, it can have undesirable effects on electrical equipment connected to the DC bus 21. Therefore, as described above, the relay 23 of the prevention circuit is controlled to allow the current to pass through the resistor 22 in order to suppress the peak value. However, if the state of passing through the resistor 22 is maintained when the peak value of the inrush current is low, the power consumption effect of the resistor 22 becomes significant and undesirable. Therefore, when the peak value of the inrush current has decreased to a certain extent, the relay 23 of the prevention circuit is switched from the off state to the on state so that the current flowing through the DC bus 21 can bypass the resistor 22. However, switching the relay 23 in the prevention circuit to the on state causes a momentary change in the path through which the current flows, and there is a risk that a pulse-like current with a relatively high peak value, i.e., a secondary inrush current, may occur at the switching timing. This secondary inrush current may also have undesirable effects on electrical equipment connected to the DC bus 21 due to its high peak value. Therefore, the driver unit 20 has a configuration to suppress the secondary inrush current.

[0031] In detail, the control unit 210 is configured to perform the inrush current suppression process shown in Figure 3. Figure 3 is a flowchart showing the flow of the inrush current suppression process in the DC bus 21 of the driver unit 20. This suppression process is repeatedly performed by the control unit 210 at predetermined intervals. Figure 4 is a diagram showing the changes in each parameter related to the inrush current when the suppression process shown in Figure 3 is performed. The parameters shown in Figure 4 are (a) and (A), where (a) and (A) are the AC voltage peak value detected by the detection unit 8 (lines L1 and L10 are examples of voltage values ​​after 3-phase rectification) and the PN voltage detected by the detection unit 27 (lines L2 and L4 are shown). (b) and (B) represent the inrush current flowing through the DC bus 21, and (c) and (C) represent the transition between the ON and OFF states of the relay 23 in the prevention circuit. In relation to (b) and (B), P1 to P4 indicate the peak of the inrush current. Also in Figure 4, (a) to (c) on the left side of the drawing show the transition of each parameter in the case where the peak value of the DC voltage L1 applied to the converter 10 is relatively low, and (A) to (C) on the right side of the drawing show the transition of each parameter in the case where the peak value of the DC voltage L10 applied to the converter 10 is relatively high. The difference in DC voltage between the two cases is expressed as ΔV_AC_peak, and for example, this voltage difference is thought to be due to voltage fluctuations of the AC power supply 7, etc.

[0032] Here, the inrush current suppression process shown in Figure 3 will be explained with reference to Figure 4. Note that when the converter 10 starts operating in the power supply system, the relay 23 of the prevention circuit is in the off state. First, in S101, it is determined whether the converter 10 has started operating and whether power has been supplied to the DC bus 21 of the driver unit 20 via the DC bus 11. In the power supply system, for example, the converter 10, capacitor unit 15, and driver unit 20 are connected to a higher-level device (PLC, etc.) not shown by the diagram via control signal lines, so the driver unit 20 can understand the operating status of the converter 10 via these control signal lines. If the determination in S101 is positive, the process proceeds to S102, and if the determination is negative, the suppression process shown in Figure 3 is terminated.

[0033] Next, in S102, the detection unit 27 detects the PN voltage in the driver unit 20, and in S103, the detection unit 8 detects the AC voltage applied to the converter 10. Then, in S104, based on the PN voltage detected in S102 and the AC voltage detected in S103, it is determined whether or not the switching timing has arrived to switch the relay 23 in the prevention circuit from the off state to the on state. Specifically, when the difference between the AC voltage and the PN voltage falls below a predetermined threshold, it can be determined that the switching timing has arrived. Note that the AC voltage fluctuates over time, so the voltage value (e.g., amplitude value (peak) at a predetermined phase point) is important. Alternatively, the maximum value of the AC voltage (or PN voltage) can be used as the representative value, and the difference between the AC voltage and the PN voltage can be calculated.

[0034] The criteria for determining the outcome in S104 can be expressed by the following equation 1. V_AC_peak-V_PN < VF_D+V_R+Va (Formula 1) V_AC_peak: Peak value of AC voltage V_PN: PN voltage VF_D: Voltage element based on the electrical characteristics of converter 10 V_R: Voltage element based on the electrical characteristics of resistor 22 VA: Other adjustment elements The expression "VF_D+V_R+Va" on the right-hand side of Equation 1 corresponds to the predetermined threshold mentioned above. That is, in S104, when the difference between the AC voltage and the PN voltage falls below a threshold based on the electrical characteristics of the electrical equipment related to the DC buses 11 and 21, switching the relay 23 of the prevention circuit to the ON state is permitted (affirmed). If the result in S104 is affirmed, the process proceeds to S105; if it is denied, the process from S102 onwards is repeated.

[0035] Then, in S105, based on the positive determination made in S104, relay 23 is switched from the off state to the on state. By performing the relay 23 switching process based on the correlation between the AC voltage and the PN voltage in this way, the effects of fluctuations in the AC voltage applied to the converter 10 are canceled, and the relay 23 switching process is performed under a steadily stable voltage environment. As a result, the peak value of the secondary inrush current caused by the relay 23 switching process can be steadily suppressed to a low value, and electrical equipment connected to the DC buses 11 and 21 can be suitably protected from inrush current.

[0036] Here, the effects of the suppression process in Figure 3 will be explained based on Figure 4. As mentioned above, the left side of Figure 4 (a) to (c) corresponds to the case where the AC voltage is relatively low, and the right side (A) to (C) corresponds to the case where the AC voltage is relatively high. The difference in AC voltage between the two is the peak voltage ΔV_AC_peak. Here, timing t1 in Figure 4 is the timing when the converter 10 starts operating. Therefore, after timing t1, the PN voltage rises over time as shown by lines L2 and L4. Also, immediately after the rise in the PN voltage, a current suddenly starts to flow in the DC bus, so as shown in (b) and (B), inrush current peaks P1 and P1' appear. These peaks P1 and P1' are mitigated by the resistor 22 of the prevention circuit, but in the case on the right side of Figure 4, the AC voltage is higher, so peak P1' is higher than peak P1.

[0037] Here, in the case where the AC voltage is relatively low, the timing at which the inrush current begins to flow and the judgment process in S104 according to Equation 1 is determined to be positive is timing t2. Also, as shown by line L11 in (c), the relay 23 of the prevention circuit is switched from the off state to the on state at timing t2. At this time, the difference between the AC voltage and the PN voltage is represented as V_AC_peak-V_PN(t2) in Figure 4. This difference satisfies the conditions of Equation 1 above. The peak of the secondary inrush current at timing t2 is represented by P2. By adjusting the predetermined threshold shown in Equation 1, the switching timing t2 of the relay 23 of the prevention circuit and the peak P2 of the secondary inrush current at that time can be adjusted to the desired settings, thereby suitably avoiding the adverse effects of the secondary inrush current.

[0038] Furthermore, in Figure 4, for reference, if the relay 23 of the prevention circuit is switched at a timing t3 earlier than timing t2, as shown by line L12 in (c), a secondary inrush current will occur at that timing t3. A current peak P3 will appear. At this time, the difference between the AC voltage and the PN voltage is represented as V_AC_peak-V_PN(t3) in Figure 4, and this difference does not satisfy the condition of Equation 1 above. Therefore, peak P3 will be larger than peak P2 above, and there is concern about adverse effects due to secondary inrush current.

[0039] Next, we will explain the case where the AC voltage is relatively high (see the right side of Figure 4 (A) to (C)). In this case, since the AC voltage is higher than in the case where it is relatively low, the timing at which the judgment process of S104 according to Equation 1 is determined to be positive is later than the timing t2, which is timing t4. Then, as shown by line L14 in (C), the relay 23 of the prevention circuit is switched from the off state to the on state at timing t4. As a result, the peak P4 of the secondary inrush current appears at timing t4. At this time, the difference between the AC voltage and the PN voltage is represented as V_AC_peak-V_PN(t4) in Figure 4. Since this difference satisfies the conditions of Equation 1 above, it is approximately the same as the difference V_AC_peak-V_PN(t2) in the case where the AC voltage is relatively low. As a result, even when the AC voltage is relatively high, the peak value of the secondary inrush current peak P4 can be made approximately the same as the peak value of the secondary inrush current peak P2 in the case where the AC voltage is relatively low.

[0040] Furthermore, let's assume that at timing t5, when the PN voltage is the same as at timing t2 in the case where the AC voltage is relatively low, the relay 23 of the prevention circuit is switched from the off state to the on state as shown by line L15 in (C). Timing t5 is earlier than timing t4. In this case, at timing t5, a secondary inrush current peak P5 will appear. At timing t5, the AC voltage is relatively high, so the terminal voltage of capacitor 25 becomes high, and the peak value of peak P5 exceeds the peak values ​​of peaks P2 and P4 mentioned above.

[0041] As shown in Figure 3, the suppression process allows for stable control of the secondary inrush current peak P2 to the desired state without being affected by fluctuations in the AC voltage applied to the converter 10, thereby effectively avoiding the adverse effects of secondary inrush current.

[0042] <Example 1> In the suppression process shown in Figure 3, a positive determination is made in S104, and the switching process of the relay 23 of the prevention circuit is executed. However, if the time derivative (rate of change) of the PN voltage in the DC bus 21 becomes excessively small due to some factor, it may take an excessively long time for the inrush current to start flowing and for the positive determination to be made in the S104 process. In this case, the current in the DC bus will continue to flow through the resistor 22, resulting in wasted energy consumption, which is undesirable. Therefore, in the suppression process, if the time derivative of the PN voltage becomes smaller than a predetermined value before the switching timing of the relay 23 arrives (i.e., before the positive determination is made in S104), the relay 23 may be switched from the off state to the on state. This predetermined value should be set appropriately, taking into account the balance between the energy consumption by the resistor 22 and the peak value of the secondary inrush current.

[0043] Furthermore, in S104 of the suppression process shown in Figure 3, the predetermined threshold value on the right-hand side of Equation 1 may be variably adjusted based on parameters such as the temperature of the DC bus 21. This takes into account that the peak value of the secondary inrush current that appears may vary depending on the temperature of the DC bus. The predetermined threshold value may also be variably adjusted based on other factors.

[0044] <Modification 2> In the embodiments described above, the suppression process in the driver unit 20 was mentioned, but this suppression process can also be applied to the capacitor unit 15. In that case, A detection unit is provided in the capacitor unit 15 to detect the PN voltage of the DC bus 151, and the PN voltage and the AC voltage detected by the detection unit 8 are passed to the control unit of the capacitor unit 15, where the above-mentioned suppression process is executed.

[0045] <Variation 3> Furthermore, the driver unit 20 in the embodiments described above may be configured as a unit including a converter 10 and a DC bus 11. In this case, AC power is input to the driver unit 20, converted to DC power by the internal converter 10, and output to the DC bus 11. The DC power on the DC bus 11 is then supplied to the inverter 26.

[0046] <Note 1> A control device (20) that controls the current of a DC bus (11, 21) from which DC power is output from a converter (10), A prevention circuit for suppressing inrush current when the output of DC power from the converter (10) to the DC bus (11, 21) begins, the prevention circuit includes a resistor (22) connected to the positive or negative side of the DC bus (21) and a relay (23) arranged in parallel with the resistor (22), A first detection unit (27) detects the PN voltage between the positive and negative terminals of the DC bus (21) after the output of DC power from the converter (10) has started while the relay (23) is turned off, A second detection unit (8) detects the AC voltage input to the converter (10), A control unit (210) switches the relay (23) from the off state to the on state based on the PN voltage detected by the first detection unit (27) and the AC voltage detected by the second detection unit (8), A control device equipped with the following features. [Explanation of Symbols]

[0047] 2 motors 7 AC power supply 8 Detection unit 10 Converters 11, 21 DC bus 15 Capacitor Unit 20 Driver Units 24 Discharge circuit 25 Capacitors 26 Inverter 27 Detection unit 210 Control Unit

Claims

1. A control device that controls the current of a DC bus from which DC power is output from a converter, A prevention circuit for suppressing inrush current when the output of DC power from the converter to the DC bus begins, the prevention circuit including a resistor connected to the positive or negative side of the DC bus and a relay connected in parallel with the resistor, A first detection unit detects the PN voltage between the positive and negative terminals of the DC bus after the DC power output from the converter starts while the relay is turned off, A second detection unit for detecting the AC voltage input to the converter, A control unit that switches the relay from the off state to the on state based on the PN voltage detected by the first detection unit and the AC voltage detected by the second detection unit, Equipped with, The control unit switches the relay from the off state to the on state when the difference between the AC voltage detected by the second detection unit and the PN voltage detected by the first detection unit falls below a predetermined threshold. The control unit switches the relay from the off state to the on state if the time derivative of the PN voltage becomes smaller than a predetermined value before the difference falls below a predetermined threshold. Control device.

2. The control device is a driver unit equipped with an inverter that receives DC power from the DC bus and generates a drive current for driving the motor. The control device according to claim 1.

3. The control device includes the converter and the DC bus, The control device according to claim 2.

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