Power conversion device

Abstract

To provide a power conversion device that can effectively cool an inverter circuit with a fan while a motor is running by using regenerative power.SOLUTION: In a motor regeneration state where a regenerative braking circuit 103 is turned on, a control unit 109 of a power conversion device 100 connects a DC unit 102 to a storage battery 107 and stores the regenerative power in the storage battery 107, and in the motor powering state where the regenerative braking circuit 103 is turned off, the control unit 109 connects a fan 108 to the storage battery 107 or the DC unit 102 and drives the fan 108.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] A power conversion device is a device that can control an electric motor at a variable speed independent of the commercial frequency by converting AC voltage to DC voltage and then converting it back to AC voltage. During deceleration, when the rotation speed estimated from the frequency output from the power conversion device becomes lower than the rotation speed of the electric motor, the electric motor operates as a generator. As a result, the power conversion device receives regenerative energy from the electric motor, causing the voltage in the DC section of the power conversion device to rise. In a typical power conversion device, if the DC section voltage exceeds the device's allowable range, it determines that a DC section overvoltage abnormality has occurred and stops its output.

[0003] The regenerative energy increases as the difference in rotational speed during deceleration increases. In other words, overvoltage abnormalities are more likely to occur when the difference in rotational speed is large or when the moment of inertia of the load connected to the induction motor is large. As the regenerative energy increases, the power conversion device itself becomes unable to absorb it. For this reason, a function is known in which, when the DC section voltage exceeds a certain value, the regenerative energy is consumed as heat by a resistor (braking resistor) connected to the power conversion device. For example, Patent Document 1 discloses an inverter overvoltage protection device that synchronizes the operating period of the inverter overvoltage protection device with the operating period of a cooling fan that cools the regenerative resistor and inverter circuit, thereby extending the life of the cooling fan. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-215362 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the operating period of the inverter overvoltage protection device is short, the operating time of the cooling fan will also be short. Also, the inverter circuit of the power conversion device generates more heat when power is supplied from the power source to the inverter circuit or when the inverter circuit is operating than when the inverter overvoltage protection device is operating. Therefore, there is a problem that the cooling effect for the inverter circuit cannot be sufficiently obtained. [Means for solving the problem]

[0006] A power conversion device according to one aspect of the present invention comprises a rectifier circuit that converts AC power into DC power, a DC unit provided downstream of the rectifier circuit, a regenerative braking circuit connected in parallel to the DC unit, an inverter circuit provided in the DC unit that converts the DC power to AC power and supplies it to a motor, a storage battery, a fan that cools the inverter circuit, and a control unit that controls the electrical connections between the DC unit, the storage battery, and the fan, wherein in a motor regeneration state in which the regenerative braking circuit is turned on, the control unit connects the DC unit to the storage battery to store regenerative power in the storage battery, and in a motor powering state in which the regenerative braking circuit is turned off, the control unit connects the fan to the storage battery or the DC unit to drive the fan. [Effects of the Invention]

[0007] According to the present invention, the inverter circuit can be effectively cooled by a fan when the motor is powered using regenerative power. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing the basic configuration of a power conversion device according to this embodiment. [Figure 2] FIG. 2 is a flowchart showing an example of control of the opening and closing circuit by the control unit. [Figure 3] FIG. 3 is a diagram showing a comparative example. [Figure 4] FIG. 4 is a diagram showing an example of a specific configuration of the connection switching circuit. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and appropriate omissions and simplifications have been made for clarity of explanation. Furthermore, in the following description, identical or similar elements and processes are given the same reference numerals, and duplicate explanations may be omitted. Note that the content described below merely shows an example of an embodiment of the present invention, and the present invention is not limited to the following embodiment, and can be implemented in various other forms.

[0010] 1 is a diagram showing the basic configuration of a power conversion device 100 according to this embodiment. The power conversion device 100 receives AC power from an AC power source AC, converts the received AC power to DC power using a rectifier circuit, and then reconverts the DC power back into AC power to control the rotation of a motor. The power conversion device 100 includes a rectifier circuit 101, a DC unit 102, a regenerative braking circuit 103, an inverter circuit 104, a connection switching circuit 106, a storage battery 107, a fan 108, a control unit 109, and a DC voltage detection unit 110.

[0011] Rectifier circuit 101 is composed of multiple diodes. Rectifier circuit 101 receives three-phase AC power from an AC power source AC via input terminals R, S, and T, and performs full-wave rectification on the received three-phase AC power to convert it into DC power. The DC power converted by rectifier circuit 101 is smoothed by DC unit 102 and supplied to inverter circuit 104. DC unit 102, which is composed of a smoothing capacitor, adjusts the converted DC power to a stable DC by repeatedly charging and discharging. DC voltage detection unit 110 detects the voltage of DC unit 102.

[0012] The inverter circuit 104 receives the DC power and reconverts it into AC power. The reconverted AC power is supplied to the motor M connected to the output terminals U, V, and W, driving the motor M. The rotation speed of the motor M can be controlled by changing the frequency of this AC power to an arbitrary value.

[0013] A regenerative braking circuit 103 is provided on the DC lines (wire P, wire N) of the DC unit 102 so as to be connected in parallel with the DC unit 102. The regenerative braking circuit 103 is composed of a switching element and a diode connected in series. The diode is connected so that its cathode is on the wire P side. In this embodiment, a storage battery 107 and a fan 108 are connected to the DC unit 102 via a connection switching circuit 106. The fan 108 cools the inverter circuit 104. The storage battery 107 is provided to store regenerative power during regenerative control. The regenerative power stored in the storage battery 107 is used to drive the fan 108.

[0014] The connection switching circuit 106 includes three open / close circuits SW1 to SW3 that can be connected and disconnected. The positive electrode side of the storage battery 107 is connected to the positive electrode side (wire P) of the DC unit 102 via the open / close circuits SW1 and SW2. The negative electrode side of the storage battery 107 is connected to the negative electrode side (wire N) of the DC unit 102. The positive electrode side of the fan 108 is connected to the positive electrode side (wire P) of the DC unit 102 via the open / close circuits SW2 and SW3. The negative electrode side of the fan 108 is connected to the negative electrode side (wire N) of the DC unit 102. The open / close circuit SW3 connects the open / close circuits SW1 and SW2 with the positive electrode side of the fan 108.

[0015] The switching control of the switching circuits SW1 to SW3 provided in the connection switching circuit 106 is performed by a control unit 109. The control unit 109 includes a CPU (Central Processing Unit) such as a microcomputer, and performs on / off control of the regenerative braking circuit 103 and the switching control of the switching circuits SW1 to SW3. Note that a control device that controls the power conversion device 100 may also have the function of the control unit 109.

[0016] Fig. 2 is a flowchart showing an example of the control of the switching circuits SW1 to SW3 by the control unit 109. When the power conversion device 100 is started, the control unit 109 starts the processing shown in Fig. 2. At the start of the processing, the regenerative braking circuit 103 is in the OFF state, and the switching circuits SW1 to SW3 of the connection switching circuit 106 are all in the open state.

[0017] In step S1, the control unit 109 acquires the DC voltage of the DC unit 102 detected by the DC voltage detection unit 110. In step S2, the control unit 109 determines whether the detected DC voltage V exceeds a predetermined determination value Vth. If it is determined in step S2 that V>Vth (YES), the control unit 109 recognizes that the motor is in a regenerative state and proceeds to step S3. On the other hand, if it is determined in step S2 that V≦Vth (NO), the control unit 109 recognizes that the motor is in a powering state and proceeds to step S6.

[0018] <Processing when the motor is in regenerative mode> If it is determined in step S2 that V>Vth (YES) and the process proceeds to step S3, the control unit 109 turns on the operation state of the regenerative braking circuit 103 in step S3. In step S4, the control unit 109 opens the switching circuits SW2 and SW3 to disconnect the DC unit 102 from the fan 108. Because the switching circuit SW3 is open, the fan 108 is disconnected from both the storage battery 107 and the storage battery 107, and the fan 108 is stopped. In step S5, the control unit 109 closes the switching circuits SW1 and SW2 to connect the DC unit 102 to the storage battery 107. As a result, the generated regenerative power is supplied to and stored in the storage battery 107. After the process of step S5 is executed, the process returns to step S2.

[0019] As described above, the power conversion device 100 supplies power having an arbitrary frequency to the motor M to drive the motor M. If there is a sudden change in the frequency of the AC power being supplied, or if the moment of inertia of a device or object connected to the motor M is large, a state (motor regeneration state) may occur in which the actual motor rotation speed is faster than the rotation speed of the motor M caused by the frequency output by the power conversion device 100.

[0020] In the motor regeneration state, the motor M acts as a generator, and the power conversion device 100 receives regenerative energy as regenerative power. When the power conversion device 100 receives regenerative power, the voltage of the DC section 102 (DC voltage between the wirings P and N) rises. Depending on the amount of regenerative energy, an overvoltage abnormality may occur. In the present embodiment, in order to prevent the power conversion device 100 from having an overvoltage abnormality, when the DC voltage V detected by the DC voltage detection unit 110 exceeds the determination value Vth, the control unit 109 operates the regenerative braking circuit 103 and controls so as to store the regenerative power in the storage battery 107.

[0021] <Processing in the case of the motor power running state> When it is determined in step S2 that V≤Vth and the process proceeds to step S6, in step S6, the control unit 109 turns off the regenerative braking circuit 103. In step S7, the control unit 109 opens the switching circuits SW1 and SW2 to disconnect the DC section 102 and the storage battery 107. As a result, the power supply of the regenerative power to the storage battery 107 stops. In step S8, the control unit 109 determines whether or not the remaining charge amount of the storage battery 107 is less than a predetermined charge amount Wth. The charge amount Wth is a determination reference value for determining whether or not the storage battery 107 is undercharged. For example, the control unit 109 estimates the charge amount from the voltage value of the storage battery 107, and compares the estimated charge amount with the preset charge amount Wth to determine whether or not the remaining charge amount is insufficient. Note that the charge amount Wth, which is the determination reference value, is set to, for example, about 30% of the charge amount at full charge. In step S8, when it is determined that the remaining charge amount <Wth (insufficient), the process proceeds to step S9, and when it is determined that the remaining charge amount ≥Wth (not insufficient), the process proceeds to step S11.

[0022] (Processing in the case of insufficient remaining charge amount) If it is determined in step S8 that the remaining charge is insufficient and the process proceeds to step S9, in step S9 the control unit 109 opens the opening and closing circuits SW1 and SW3 to disconnect the storage battery 107 from the fan 108. In step S10, the control unit 109 closes the opening and closing circuits SW2 and SW3 to connect the DC unit 102 to the fan 108. As a result, power is supplied from the DC unit 102 to the fan 108, and the fan 108 is driven. Once the process of step S10 has been executed, the process returns to step S1.

[0023] (Processing when remaining charge is sufficient) If it is determined in step S8 that the remaining charge is not insufficient (NO) and the process proceeds to step S11, in step S11 the control unit 109 opens the opening / closing circuits SW2 and SW3 to disconnect the DC unit 102 from the fan 108. In step S12, the control unit 109 closes the opening / closing circuits SW1 and SW3 to connect the storage battery 107 to the fan 108. As a result, the regenerative power stored in the storage battery 107 is supplied to the fan 108, and the fan 108 is driven by the regenerative power stored in the motor regeneration state. Once the process of step S12 has been executed, the process returns to step S8.

[0024] FIG. 3 is a diagram illustrating a comparative example. In the power conversion device 200 illustrated in FIG. 3, a braking resistor 201 is provided in a regenerative braking circuit 103. The on / off control of the regenerative braking circuit 103 is performed by a control unit (not shown) of the power conversion device 200. In the motor regenerative state, the switch element of the regenerative braking circuit 103 is turned on, and a current flows from the wiring P to the wiring N via the braking resistor 201 and the switch element of the regenerative braking circuit 103. As a result, the regenerative power (regenerative energy) is consumed as heat by the braking resistor 201, suppressing an increase in DC voltage. In this way, the braking resistor 201 serves to protect the circuit by consuming excess energy as heat. The braking resistor 201 operates mainly when the regenerative state is entered due to the deceleration operation of the motor. In the device described in the above-mentioned Patent Document 1, a fan is provided to cool the braking resistor and the inverter circuit, and the operating period of the overvoltage protection is synchronized with the operating period of the fan.

[0025] However, the inverter circuit 104 generates more heat while power is being supplied to the inverter circuit 104 from the AC power supply AC or while the inverter circuit 104 is operating than during overvoltage protection operation. Therefore, in this embodiment, the fan 108 is always operated when the motor is in the power running state as described above, thereby more effectively cooling the inverter circuit 104.

[0026] Furthermore, in the comparative example, regenerative energy in the motor regenerative state is consumed as heat by braking resistor 201, but in this embodiment, the regenerative energy is stored in storage battery 107 as regenerative power, and the stored regenerative power is used to drive fan 108 in the motor powering state. In other words, the regenerative energy is not wasted as heat, but is used to cool inverter circuit 104. As a result, energy conservation in power conversion device 100 can be achieved.

[0027] Furthermore, in this embodiment, when the remaining charge of the storage battery 107 is insufficient in the motor powering state, the fan 108 is connected to the DC unit 102 and driven. That is, the storage battery 107 is charged only by regenerative power, and when the stored regenerative power is insufficient and the remaining charge is insufficient, power (power supply power) is supplied from the DC unit 102 to the fan 108. In this way, the storage battery 107 is used only when storing regenerative power and when the stored regenerative power is used to drive the fan 108. This makes it possible to suppress deterioration of the storage battery 107 and to extend the life of the storage battery 107.

[0028] If the storage battery 107 is fully charged in the motor regeneration state, the regenerated energy may be consumed by driving the fan 108 with the regenerated power, without storing the regenerated power in the storage battery 107. Also, a braking resistor may be provided in advance, and the regenerated energy may be consumed by the fan 108 and / or the braking resistor.

[0029] Fig. 4 is a diagram showing an example of a specific configuration of the connection switching circuit 106. Although not shown in Fig. 1, the fan 108 is connected to the connection switching circuit 106 via a DC-DC converter 120. Each of the switch circuits SW1 to SW3 in Fig. 1 is composed of a FET (Field Effect Transistor), which is a semiconductor switching element. The switch circuit SW2 is composed of a pair of FETs 2A and 2B.

[0030] The drain side of FET1, which constitutes the switching circuit SW1, is connected to the positive electrode of the storage battery 107. The sources of FET2A and FET2B, which constitute the switching circuit SW2, are connected to each other. The drain side of FET2A is connected to the source side of FET1, which constitutes the switching circuit SW1. The drain side of FET2B is connected to the positive electrode side (wiring P) of the DC unit 102. The drain side of FET3, which constitutes the switching circuit SW3, is connected to the connection point between the switching circuits SW1 and SW2, i.e., the connection point between FET1 and FET2A. In this way, by configuring the connection switching circuit 106 with semiconductor switching elements (FETs), it is possible to reduce the size of the system.

[0031] In the switching circuit SW2, the source sides of FET2A and FET2B are connected together, so that the body diodes of both are connected in reverse. This prevents backflow from the storage battery 107 to the DC unit 102 via the body diodes when FET2A and FET2B are off. Even when FET1 is off and the switching circuit SW1 is open, auxiliary charging of the storage battery 107 is possible through the body diode of FET1 when the switching circuit SW2 is closed.

[0032] According to the above-described embodiment, the following advantageous effects are achieved.

[0033] 1, 2, etc., power conversion device 100 includes rectifier circuit 101 that converts AC power into DC power, DC unit 102 provided downstream of rectifier circuit 101, regenerative braking circuit 103 connected in parallel to DC unit 102, inverter circuit 104 provided in DC unit 102 that converts the DC power converted by rectifier circuit 101 into AC power and supplies the AC power to motor M, storage battery 107, fan 108 that cools inverter circuit 104, and control unit 109 that controls electrical connections between DC unit 102, storage battery 107, and fan 108. In a motor regenerative state in which regenerative braking circuit 103 is turned on, control unit 109 connects DC unit 102 and storage battery 107 to store regenerative power in storage battery 107 (steps S2 to S5). In addition, in the motor powering state where the regenerative braking circuit 103 is turned off, the fan 108 is connected to the storage battery 107 or the DC unit 102 to drive the fan 108 (steps S2 to S12).

[0034] In this way, in the motor powering state, the fan 108 is driven by connecting it to the storage battery 107 or the DC unit 102, so that the inverter circuit 104 is always cooled by the fan during powering, effectively suppressing a rise in temperature of the inverter circuit 104. Furthermore, the regenerative power stored in the storage battery 107 during motor regeneration is effectively used to drive the fan 108, so energy can be saved without wasting the regenerative power as in the comparative example.

[0035] (2) In the above (1), as shown in FIG. 2, when the remaining charge of the storage battery 107 is equal to or greater than a predetermined amount (charge amount Wth) in the motor powering state, the control unit 109 connects the storage battery 107 to the fan 108 and drives the fan 108 (steps S8, S11, S12), and when the remaining charge of the storage battery 107 is less than the predetermined amount (charge amount Wth) in the motor powering state, the control unit 109 connects the DC unit 102 to the fan 108 and drives the fan 108 (steps S8 to S10).

[0036] Thus, when the remaining charge of the storage battery 107 is insufficient (remaining charge < Wth), the fan 108 is driven by the power of the DC unit 102 without passing through the storage battery 107. Therefore, the usage time of the storage battery 107 is reduced as much as possible, and deterioration of the storage battery 107 can be suppressed.

[0037] (3) In (1) above, as shown in FIG. 1, a DC voltage detection unit 110 for detecting the voltage of the DC unit 102 is provided. The control unit 109 can appropriately determine the motor state by determining the motor power running state and the motor regeneration state based on the detected voltage of the DC voltage detection unit 110.

[0038] ((x)) In (1) above, as shown in FIGS. 1, 4, etc., the control unit 109 includes a connection switching circuit 106 that switches the connection state between the storage battery 107, the fan 108, and the DC unit 102. The connection switching circuit 106 includes an open / close circuit SW1 (first circuit) including a FET1 whose drain is connected to the positive electrode of the storage battery 107, a pair of FETs 2A and 2B whose sources are connected to each other, and the drain of one FET 2B is connected to the positive electrode of the DC unit 102 while the drain of the other FET 2A is connected to the source of the FET1 of the open / close circuit SW1. An open / close circuit SW2 (second circuit), and an open / close circuit SW3 (third circuit) capable of connecting and disconnecting the connection point between the open / close circuit SW1 and the open / close circuit SW2 and the positive electrode of the fan 108.

[0039] Thus, by configuring the connection switching circuit 106 with semiconductor switching elements (FETs), the system can be miniaturized. Further, by connecting the sources of the FETs 2A and 2B to each other, the body diodes of both are connected in reverse, so that reverse flow from the storage battery 107 to the DC unit 102 through the body diodes when the FETs 2A and 2B are off can be prevented. Also, even when the FET1 is off and the open / close circuit SW1 is in an open state, when the open / close circuit SW2 is in a closed state, the storage battery 107 can be replenished through the body diode of the FET1.

[0040] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments. [Explanation of symbols]

[0041] 100, 200... power conversion device, 101... rectifier circuit, 102... DC section, 103... regenerative braking circuit, 104... inverter circuit, 106... connection switching circuit, 107... storage battery, 108... fan, 109... control section, 110... DC voltage detection section, 120... DC-DC converter, 201... braking resistor, M... motor, SW1 to SW3... opening and closing circuit

Claims

1. a rectifier circuit that converts AC power into DC power; a DC unit provided in a subsequent stage of the rectifier circuit; a regenerative braking circuit connected in parallel to the DC portion; an inverter circuit provided in the DC unit for converting the DC power into AC power and supplying the AC power to a motor; A storage battery and a fan for cooling the inverter circuit; a control unit that controls electrical connections between the DC unit, the storage battery, and the fan, The control unit In a motor regeneration state in which the regenerative braking circuit is turned on, the DC unit and the storage battery are connected to store regenerative power in the storage battery, In a motor powering state in which the regenerative braking circuit is turned off, the power conversion device connects the fan to the storage battery or the DC unit to drive the fan.

2. The power conversion device according to claim 1, The control unit When the remaining charge of the storage battery is equal to or greater than a predetermined amount in the motor powering state, the storage battery and the fan are connected to each other; When the remaining charge of the storage battery is less than a predetermined amount in the motor powering state, the power conversion device connects the DC unit to the fan.

3. The power conversion device according to claim 1, a DC voltage detection unit that detects the voltage of the DC unit; The control unit determines whether the motor is in a power running state or a regenerative state based on the detected voltage of the DC voltage detection unit.

4. The power conversion device according to claim 1, the control unit includes a connection switching circuit that switches a connection state between the storage battery, the fan, and the DC unit; The connection switching circuit a first circuit including a field effect transistor (FET) having a drain connected to a positive electrode of the storage battery; a second circuit including a pair of FETs whose sources are connected to each other, the drain of one FET being connected to the positive electrode of the DC section and the drain of the other FET being connected to the source of the FET of the first circuit; a third circuit that can connect and disconnect a connection point between the first circuit and the second circuit and a positive electrode of the fan.

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