Power Conversion Device

Abstract

A power conversion device is provided that can suppress delays in control signals input from a control circuit to a drive circuit, while suppressing malfunctions of the drive circuit due to the influence of noise. [Solution] A power conversion device is provided which comprises a main circuit section which converts power by switching a switching element, a drive circuit which drives the switching element, and a control circuit which controls the power conversion operation by the main circuit section by inputting an electrical control signal to the drive circuit via a pair of cables, wherein the drive circuit has a light-emitting section which converts the control signal into an optical signal and a light-receiving section which converts the optical signal back into an electrical signal, the light-emitting section has an output state in which it outputs an optical signal and a stop state in which it stops outputting the optical signal, and the control circuit causes a current to flow through the pair of cables and drive circuit, putting the light-emitting section into the output state, and causes a current to flow in the opposite direction through the pair of cables and drive circuit, putting the light-emitting section into the stop state.

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a power conversion device. [Background technology]

[0002] There is a power conversion device that includes a main circuit unit that has switching elements and converts power by switching the switching elements, a drive circuit for driving the switching elements, and a control circuit that controls the power conversion operation by the main circuit unit by inputting a control signal for controlling the switching of the switching elements to the drive circuit.

[0003] In power conversion devices, an optical isolator such as a photocoupler is provided in the drive circuit to electrically insulate the high-voltage side main circuit from the low-voltage side control circuit. The drive circuit converts an electrical control signal input from the control circuit into an optical signal using the optical isolator, and then converts the optical signal back into an electrical signal using the optical isolator. This electrical signal is then input as a drive signal to the switching element, thereby driving the switching element. This allows signals to be input from the low-voltage side control circuit to the high-voltage side main circuit, while electrically isolating the low-voltage side circuit from the high-voltage side circuit.

[0004] Furthermore, in a power conversion device, an appropriate distance is maintained between the high-voltage side circuit and the control circuit to prevent the control circuit from being affected by noise generated by the switching elements, and therefore the control circuit and the drive circuit are connected via a cable of an appropriate length.

[0005] However, if the length of the cable between the control circuit and the drive circuit is increased, the cable between the control circuit and the drive circuit may be affected by noise generated in the switching element, which may cause the drive circuit to malfunction. For example, noise superimposed on the cable may cause the optical isolator to unintentionally output an optical signal, which may cause the switching element to switch at an unintended timing.

[0006] It has also been proposed to provide a filter circuit at the input of the optical isolator to prevent malfunction of the driver circuit. However, providing a filter circuit at the input of the optical isolator causes a delay in the control signal input from the control circuit to the driver circuit. The delay in the control signal not only causes a delay in the switching of the switching element, but can also hinder the switching speed of the switching element.

[0007] Therefore, it is desirable for the power conversion device to be able to suppress delays in control signals input from the control circuit to the drive circuit, while also being able to suppress malfunctions of the drive circuit due to the influence of noise. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-166506 Summary of the Invention [Problem to be solved by the invention]

[0009] An embodiment of the present invention provides a power conversion device that can suppress delays in control signals input from a control circuit to a drive circuit, while suppressing malfunctions of the drive circuit due to the influence of noise. [Means for solving the problem]

[0010] According to an embodiment of the present invention, there is provided a power conversion device comprising: a main circuit section having a switching element and converting electric power by switching the switching element; a drive circuit that drives the switching element; and a control circuit connected to the drive circuit via a pair of cables and controlling the operation of power conversion by the main circuit section by inputting a control signal, which is an electric signal for controlling the switching of the switching element, to the drive circuit via the pair of cables, wherein the switching element has a pair of main terminals and a control terminal, and has an ON state in which a current flows between the pair of main terminals and an OFF state in which the flow of current between the pair of main terminals is blocked. The drive circuit has a light-emitting section that converts the control signal input from the control circuit into an optical signal, and a light-receiving section that converts the optical signal back into an electrical signal. The light-emitting section has an output state in which it outputs the optical signal and a stop state in which it stops outputting the optical signal. The drive circuit switches between the output state and the stop state of the light-emitting section in response to the control signal from the control circuit, and outputs the optical signal from the light-emitting section in response to the control signal. a control circuit for controlling the switching of the switching element by controlling the switching of the control signal between the first state and the second state; and a power conversion device for controlling the switching of the switching element by controlling the switching of the control signal between the first state and the second state, the power conversion device applying a voltage between the pair of cables in the first state and causing a current to flow through the pair of cables and the drive circuit, thereby causing the light-emitting unit to be in an output state; and applying a voltage between the pair of cables in a direction opposite to that in the first state and causing a current to flow through the pair of cables and the drive circuit in a direction opposite to that in the first state and causing the light-emitting unit to be in a stopped state in the second state. [Effects of the Invention]

[0011] A power conversion device is provided that can suppress delays in control signals input from a control circuit to a drive circuit, while suppressing malfunctions of the drive circuit due to the influence of noise. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram schematically illustrating a power conversion device according to an embodiment. [Figure 2] 2(a) and 2(b) are explanatory diagrams schematically illustrating an example of the operation of the drive circuit and the control circuit according to the embodiment. [Figure 3] FIG. 10 is a block diagram schematically illustrating a reference control circuit. DETAILED DESCRIPTION OF THE INVENTION

[0013] Each embodiment will be described below with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0014] FIG. 1 is a block diagram schematically illustrating a power conversion device according to an embodiment. 1, the power conversion device 10 includes a main circuit unit 12, a drive circuit 14, and a control circuit 16. The power conversion device 10 is applied to a power system that handles a relatively large amount of power, such as a system that supplies power to a power grid or a system that supplies power to a large motor (load).

[0015] The main circuit unit 12 has a switching element 20, and performs power conversion by switching the switching element 20. The main circuit unit 12 is connected to, for example, a power source and a load, converts power supplied from the power source into another power according to the load, and supplies the converted power to the load. The power source is, for example, a generator such as a solar panel or a power system. The load may be a load such as a motor, or may be a power system separate from the power source.

[0016] The switching element 20 has a pair of main terminals and a control terminal. The switching element 20 has an on state and an off state. The on state is a state in which current flows between the pair of main terminals. The off state is a state in which current flow between the pair of main terminals is blocked. The switching element 20 switches between the on state and the off state depending on the voltage between the pair of main terminals and the voltage at the control terminal.

[0017] The off state is not limited to a state in which no current flows between the pair of main terminals, but may also be a state in which a weak current flows between the pair of main terminals within a range that does not affect the operation of the main circuit unit 12. The definitions of the on state and the off state are the same for other switching elements in this specification.

[0018] For example, a self-extinguishing element such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used as the switching element 20. The control terminal is, for example, a gate terminal.

[0019] The main circuit unit 12 has, for example, a plurality of switching elements 20. The main circuit unit 12 is, for example, a full-bridge circuit having four switching elements 20. However, the configuration of the main circuit unit 12 is not limited to the above, and may be any configuration that has at least one switching element 20 and converts input power into another power by switching the switching element 20. The configuration of the main circuit unit 12 may be set appropriately depending on, for example, the power input from a power source or the power supplied to a load.

[0020] The drive circuit 14 drives the switching element 20. The drive circuit 14 is connected to a control terminal of the switching element 20. The drive circuit 14 drives the switching element 20 by inputting a drive signal to the control terminal of the switching element 20.

[0021] The control circuit 16 is connected to the drive circuit 14 via a pair of cables 18a, 18b. The pair of cables 18a, 18b are cables that enable input of electrical signals from the control circuit 16 to the drive circuit 14.

[0022] The control circuit 16 controls the power conversion operation of the main circuit unit 12 by inputting an electrical control signal for controlling the switching of the switching element 20 to the drive circuit 14 via a pair of cables 18a, 18b.

[0023] When the main circuit unit 12 handles a relatively large amount of power, the control circuit 16 may be affected by noise generated during switching of the switching element 20. For this reason, the pair of cables 18a, 18b are set to an appropriate length necessary to ensure an appropriate distance between the high-voltage side circuit and the control circuit 16.

[0024] The length of the pair of cables 18a, 18b is, for example, 50 cm or more. In other words, the control circuit 16 is disposed 50 cm or more away from the drive circuit 14. This makes it possible to prevent the control circuit 16 from malfunctioning due to the influence of noise from the switching element 20.

[0025] The length of the pair of cables 18a, 18b (the distance between the drive circuit 14 and the control circuit 16) is not limited to the above, and may be set appropriately depending on factors such as the amount of power handled by the main circuit unit 12. The length of the pair of cables 18a, 18b (the distance between the drive circuit 14 and the control circuit 16) may be any length that can prevent the control circuit 16 from being affected by noise.

[0026] The control signal input from the control circuit 16 to the drive circuit 14 has a first state for setting the switching element 20 to one of the on state and the off state, and a second state for setting the switching element 20 to the other of the on state and the off state. The control circuit 16 controls the switching of the control signal between the first state and the second state, thereby controlling the switching of the switching element 20.

[0027] The drive circuit 14 generates an electric drive signal based on the control signal input from the control circuit 16, and inputs the generated drive signal to a control terminal of the switching element 20, thereby driving the switching element 20 based on the control signal from the control circuit 16. As a result, the on and off states of the switching element 20 are switched based on the control signal from the control circuit 16, and the power conversion operation by the main circuit unit 12 is controlled based on the control signal.

[0028] When the main circuit unit 12 has a plurality of switching elements 20, the power conversion device 10 includes a plurality of drive circuits 14 corresponding to the respective switching elements 20. The control circuit 16 is connected to each of the drive circuits 14 via a plurality of pairs of cables 18a, 18b provided for each of the drive circuits 14. The control circuit 16 generates a plurality of control signals corresponding to the respective switching elements 20 and inputs the generated control signals to the corresponding drive circuits 14, thereby controlling the switching of each of the switching elements 20. In this way, the control circuit 16 controls the power conversion operation by the main circuit unit 12 having the plurality of switching elements 20.

[0029] However, the number of drive circuits 14 does not necessarily have to be the same as the number of switching elements 20. For example, if the main circuit unit 12 is configured as a full-bridge circuit having four switching elements 20, it may be possible to use a common drive signal for the upper switching element 20 and the lower switching element 20 by inverting the logic. In this case, two drive signals with inverted logic may be generated in one drive circuit 14, thereby driving two switching elements 20, i.e., the upper switching element 20 and the lower switching element 20, with one drive circuit 14. Similarly, the number of control signals generated by the control circuit 16 does not necessarily have to be the same as the number of switching elements 20.

[0030] When the main circuit section 12 has a plurality of switching elements 20, the configuration of the drive circuit 14 and the configuration of the control circuit 16 are not limited to those described above, and may be any configuration that can appropriately control the switching of each of the plurality of switching elements 20 and appropriately control the power conversion operation by the main circuit section 12.

[0031] The drive circuit 14 has a pair of input ports 14a, 14b and a pair of output ports 14c, 14d. The pair of input ports 14a, 14b are connected to a pair of cables 18a, 18b, and are also connected to the control circuit 16 via the pair of cables 18a, 18b. The drive circuit 14 receives control signals from the control circuit 16 via the pair of cables 18a, 18b and the pair of input ports 14a, 14b.

[0032] The output section 14c is connected to a control terminal of the switching element 20. The output section 14d is connected to a main terminal on the low potential side of the switching element 20. The drive circuit 14 inputs a drive signal to the control terminal of the switching element 20 via the pair of output sections 14c, 14d. In other words, the drive circuit 14 switches the switching element 20 between an ON state and an OFF state by changing the voltage between the pair of output sections 14c, 14d.

[0033] The drive signal has a state in which the switching element 20 is set to an ON state and a state in which the switching element 20 is set to an OFF state. The state in which the switching element 20 is set to an ON state is, for example, a state in which the potential of the output section 14c is higher than the potential of the output section 14d. The state in which the switching element 20 is set to an OFF state is, for example, a state in which the potential of the output section 14c is lower than the potential of the output section 14d. In other words, the state in which the switching element 20 is set to an ON state is a state in which a positive voltage is applied to the control terminal of the switching element 20 (a state in which the potential of the control terminal is higher than the potential of the main terminal on the low potential side). In other words, the state in which the switching element 20 is set to an OFF state is a state in which a negative voltage is applied to the control terminal of the switching element 20 (a state in which the potential of the control terminal is lower than the potential of the main terminal on the low potential side). The drive signal is, for example, a pulse-like electric signal that alternates between a high voltage state and a low voltage state.

[0034] However, the drive signal is not limited to the above and may be set appropriately depending on the characteristics of the switching element 20. For example, the drive signal may be the opposite of the above, in which a state in which a positive voltage is applied to the control terminal of the switching element 20 sets the switching element 20 to the off state, and a state in which a negative voltage is applied to the control terminal of the switching element 20 sets the switching element 20 to the on state.

[0035] The drive circuit 14 includes an optical insulating section 30, switching elements 31 and 32, a resistive element 33, and a rectifying element .

[0036] The drive circuit 14 also has a negative potential terminal 14n and a positive potential terminal 14p. The negative potential terminal 14n is connected to the output section 14d. The negative potential terminal 14n is connected to the low potential side main terminal of the switching element 20 via the output section 14d.

[0037] The potential of the positive potential terminal 14p is higher than the potential of the negative potential terminal 14n. The positive potential terminal 14p is a potential setting unit for applying a positive voltage to the control terminal of the switching element 20. The negative potential terminal 14n is a potential setting unit for applying a negative voltage to the control terminal of the switching element 20. The potentials of the positive potential terminal 14p and the negative potential terminal 14n may be generated and set within the drive circuit 14, or may be set based on the supply of power from an external power supply circuit or the like.

[0038] The optical isolator 30 converts the electrical control signal input from the control circuit 16 into an optical signal, and converts the optical signal back into an electrical signal. As a result, the optical isolator 30 allows a drive signal corresponding to the control signal to be input to the main circuit unit 12, and electrically isolates the main circuit unit 12 from the control circuit 16.

[0039] The main circuit unit 12 handles a relatively high voltage. On the other hand, the control circuit 16 operates on a relatively low voltage supplied from a power supply circuit (not shown) or the like. The optical isolation unit 30 electrically isolates the main circuit unit 12 from the control circuit 16, thereby preventing, for example, a high voltage from the main circuit unit 12 from flowing into the control circuit 16 and causing a malfunction of the control circuit 16.

[0040] The optical insulating unit 30 has a light emitting unit 30a and light receiving units 30b and 30c. The light emitting unit 30a has an output state in which it outputs an optical signal, and a stop state in which it stops outputting an optical signal.

[0041] The light-emitting unit 30a is a light-emitting element such as a light-emitting diode. The light-emitting unit 30a has a high-potential terminal (e.g., an anode) and a low-potential terminal (e.g., a cathode). The light-emitting unit 30a radiates light by applying a forward voltage between the high-potential terminal and the low-potential terminal and increasing the magnitude of the current flowing from the high-potential terminal to the low-potential terminal to a predetermined value or greater. In other words, the light-emitting unit 30a enters an output state in which it outputs an optical signal by increasing the magnitude of the current flowing from the high-potential terminal to the low-potential terminal to a predetermined value or greater. Then, the light-emitting unit 30a stops emitting light by reducing the magnitude of the current flowing from the high-potential terminal to a value less than a predetermined value, thereby entering a stopped state in which it stops outputting an optical signal.

[0042] The high potential terminal of the light-emitting unit 30a is connected to one input unit 14a. The low potential terminal of the light-emitting unit 30a is connected to the other input unit 14b. As a result, the light-emitting unit 30a (optical isolation unit 30) receives a control signal from the control circuit 16 via the pair of input units 14a, 14b. The light-emitting unit 30a converts the control signal into an optical signal by outputting an optical signal in response to the input control signal. In other words, the drive circuit 14 switches the light-emitting unit 30a between an output state and a stopped state in response to the control signal from the control circuit 16 switching between a first state and a second state.

[0043] The light-receiving units 30b and 30c receive the optical signal output from the light-emitting unit 30a and convert the optical signal back into an electrical signal. In this example, the optical isolation unit 30 has two light-receiving units 30b and 30c connected in series between the positive potential terminal 14p and the negative potential terminal 14n. The light-receiving unit 30b is, for example, a phototransistor that is turned on when not receiving an optical signal and turned off when receiving an optical signal. The light-receiving unit 30c is, for example, a phototransistor that is turned off when not receiving an optical signal and turned on when receiving an optical signal.

[0044] The optical insulating unit 30 is, for example, a photocoupler. The number of light receiving units provided in the optical insulating unit 30 is not limited to two and may be any number. The optical insulating unit 30 may be configured in any manner that includes at least one light emitting unit and at least one light receiving unit. The optical insulating unit 30 may be configured with, for example, multiple members (elements) that constitute the light emitting unit and multiple members (elements) that constitute the light receiving unit.

[0045] The resistive element 33 is connected in parallel with the light-emitting unit 30a. The resistive element 33 adjusts the magnitude of the voltage applied between the high potential terminal and the low potential terminal of the light-emitting unit 30a. In other words, the resistive element 33 adjusts the magnitude of the current flowing through the light-emitting unit 30a.

[0046] The rectifying element 34 is connected in anti-parallel to the light-emitting unit 30a. The direction of current flow in the rectifying element 34 is opposite to the direction of current flow in the light-emitting unit 30a. This allows the rectifying element 34 to prevent a voltage equal to or greater than a predetermined value from being applied in the reverse direction to the light-emitting unit 30a. In other words, the rectifying element 34 protects the light-emitting unit 30a from reverse voltage.

[0047] For example, when a reverse current flows through the resistive element 33 and a reverse voltage is applied to the light-emitting unit 30a, if the light-emitting unit 30a can withstand the reverse voltage, the drive circuit 14 does not necessarily have to include the rectifying element 34.

[0048] The switching elements 31 and 32 are connected in series between the positive potential terminal 14p and the negative potential terminal 14n. The switching element 31 is turned on when the potential of the control terminal is lowered, and is turned off when the potential of the control terminal is increased. The switching element 32 is turned on when the potential of the control terminal is increased, and is turned off when the potential of the control terminal is lowered.

[0049] The control terminals of the switching elements 31 and 32 are connected to the connection point of the light receiving units 30b and 30c. The connection point of the switching elements 31 and 32 is connected to the output unit 14c. In other words, the connection point of the switching elements 31 and 32 is connected to the control terminal of the switching element 20 via the output unit 14c.

[0050] In the drive circuit 14, when the light-emitting unit 30a is in a stopped state, the light-receiving unit 30b is in an ON state and the light-receiving unit 30c is in an OFF state. As a result, the potential of the control terminals of the switching elements 31 and 32 is set to the potential of the positive potential terminal 14p via the light-receiving unit 30b. Therefore, the switching element 31 is in an OFF state and the switching element 32 is in an ON state, and the potential of the control terminal of the switching element 20 is set to the potential of the negative potential terminal 14n via the switching element 32. Therefore, when the light-emitting unit 30a is in a stopped state, the switching element 20 is in an OFF state.

[0051] On the other hand, when the light-emitting unit 30a is in the output state, the light-receiving unit 30b is in the off state and the light-receiving unit 30c is in the on state. As a result, the potential of the control terminals of the switching elements 31 and 32 is set to the potential of the negative potential terminal 14n via the light-receiving unit 30c. Therefore, the switching element 31 is in the on state and the switching element 32 is in the off state, and the potential of the control terminal of the switching element 20 is set to the potential of the positive potential terminal 14p via the switching element 31. Therefore, when the light-emitting unit 30a is in the output state, the switching element 20 is in the on state.

[0052] In this way, the drive circuit 14 generates the outputs of the switching elements 31 and 32 as drive signals. The drive circuit 14 switches the light-emitting unit 30a between an output state and a stopped state in response to a control signal from the control circuit 16, outputs an optical signal from the light-emitting unit 30a in response to the control signal, and converts the optical signal back into an electrical signal using the light-receiving units 30b and 30c. Based on the converted electrical signal, the drive circuit 14 generates an electrical drive signal. The drive circuit 14 then inputs the generated drive signal to a control terminal of the switching element 20, thereby switching the switching element 20 between an on state and an off state. As a result, the drive circuit 14 generates an electrical drive signal based on the control signal input from the control circuit 16, and by inputting the generated drive signal to the control terminal of the switching element 20, the switching element 20 can be driven based on the control signal from the control circuit 16.

[0053] However, the configuration of the drive circuit 14 is not limited to the above, and may be any configuration that can generate an electric drive signal based on a control signal input from the control circuit 16, and input the generated drive signal to a control terminal of the switching element 20 to drive the switching element 20 based on the control signal from the control circuit 16. For example, the opposite to the above, the switching element 20 may be set to an ON state when the light-emitting unit 30a is in a stopped state, and to an OFF state when the light-emitting unit 30a is in an output state.

[0054] The control circuit 16 has switching elements 41 to 44 and a NOT gate 45. The control circuit 16 also has a positive potential terminal 16p and a common potential terminal 16g. The potential of the common potential terminal 16g is set to a common potential (for example, ground potential). The potential of the positive potential terminal 16p is higher than the potential of the common potential terminal 16g. The potential of the positive potential terminal 16p may be generated and set inside the control circuit 16, or may be set by an external supply.

[0055] The switching elements 41 and 42 are connected in series between the positive potential terminal 16p and the common potential terminal 16g. The switching element 41 is turned on when the potential of the control terminal is lowered, and is turned off when the potential of the control terminal is increased. The switching element 42 is turned on when the potential of the control terminal is increased, and is turned off when the potential of the control terminal is lowered.

[0056] The connection point between the switching elements 41 and 42 is connected to the cable 18b, and the connection point between the switching elements 41 and 42 is connected to the input section 14b of the drive circuit 14 via the cable 18b.

[0057] The switching elements 43 and 44 are connected in series between the positive potential terminal 16p and the common potential terminal 16g. The switching element 43 is turned on when the potential of the control terminal is lowered, and is turned off when the potential of the control terminal is increased. The switching element 44 is turned on when the potential of the control terminal is increased, and is turned off when the potential of the control terminal is lowered.

[0058] The connection point of the switching elements 43 and 44 is connected to the cable 18a, and the connection point of the switching elements 43 and 44 is connected to the input part 14a of the drive circuit 14 via the cable 18a.

[0059] A control command is input to the control terminals of the switching elements 41 and 42. The control command input to the control terminals of the switching elements 41 and 42 has a state for setting the switching element 20 to an ON state and a state for setting the switching element 20 to an OFF state. The state for setting the switching element 20 to an ON state is, for example, a high voltage state (high state). The state for setting the switching element 20 to an OFF state is, for example, a low voltage state (low state). In other words, the high voltage state is a state corresponding to a logic "1" of the digital signal. In other words, the low voltage state is a state corresponding to a logic "0" of the digital signal. The control command is, for example, a pulsed electric signal (digital signal).

[0060] The control terminals of the switching elements 43 and 44 are connected to a NOT gate 45. A control command whose logic is inverted from the control command input to the control terminals of the switching elements 41 and 42 via the NOT gate 45 is input to the control terminals of the switching elements 43 and 44.

[0061] The control commands input to the control terminals of the switching elements 41 and 42 may be control commands generated within the control circuit 16 to control the switching of the switching element 20 (the power conversion operation of the main circuit section 12), or may be control commands input from a higher-level controller or the like to control the switching of the switching element 20.

[0062] 2(a) and 2(b) are explanatory diagrams schematically illustrating an example of the operation of the drive circuit and the control circuit according to the embodiment. Fig. 2(a) schematically shows an example of the operation of the drive circuit 14 and the control circuit 16 when the switching element 20 is turned on. Fig. 2(b) schematically shows an example of the operation of the drive circuit 14 and the control circuit 16 when the switching element 20 is turned off. Note that for convenience, part of the drive circuit 14 is not shown in Figs. 2(a) and 2(b).

[0063] The control command input to the control terminals of the switching elements 41 and 42 is in a high voltage state when the switching element 20 is set to the on state. In this case, the switching element 41 is in the off state, and the switching element 42 is in the on state.

[0064] The control command input to the control terminals of the switching elements 43 and 44 is in a low voltage state when the switching element 20 is set to the ON state by having its logic inverted by the NOT gate 45. In this case, the switching element 43 is in the ON state, and the switching element 44 is in the OFF state.

[0065] Therefore, when a control command to set the switching element 20 to the ON state is input, a current flows through the path of the positive potential terminal 16p, the switching element 43, the cable 18a, the light-emitting unit 30a, the cable 18b, the switching element 42, and the common potential terminal 16g, as shown in Fig. 2(a), and an optical signal is output from the light-emitting unit 30a. In other words, when a control command to set the switching element 20 to the ON state is input, the light-emitting unit 30a is in an output state. This causes the switching element 20 to be in the ON state.

[0066] The control command input to the control terminals of the switching elements 41 and 42 is in a low voltage state when the switching element 20 is set to the off state. In this case, the switching element 41 is in the on state, and the switching element 42 is in the off state.

[0067] The control command input to the control terminals of the switching elements 43 and 44 is inverted in logic by the NOT gate 45, and thus assumes a high voltage state when setting the switching element 20 to the OFF state. In this case, the switching element 43 is in the OFF state, and the switching element 44 is in the ON state.

[0068] Therefore, when a control command to set the switching element 20 to the OFF state is input, as shown in Fig. 2(b), a current flows through the path of the positive potential terminal 16p, the switching element 41, the cable 18b, the rectifying element 34, the cable 18a, the switching element 44, and the common potential terminal 16g, and the output of the optical signal from the light-emitting unit 30a is stopped. In other words, when a control command to set the switching element 20 to the OFF state is input, the light-emitting unit 30a is stopped. As a result, the switching element 20 is turned OFF.

[0069] In this way, the control circuit 16 inputs the outputs of the switching elements 41 to 44 as electrical control signals to the drive circuit 14. The control circuit 16 switches the control signals between the first state and the second state in response to a control command.

[0070] 2(a), in the first state, the control circuit 16 switches the on and off states of the switching elements 41 to 44 as described above, applies a voltage (DC voltage) between the pair of cables 18a and 18b, and causes a current (DC current) to flow through the pair of cables 18a and 18b and the drive circuit 14, thereby putting the light-emitting unit 30a into an output state.

[0071] 2(b), in the second state, the control circuit 16 switches the on and off states of the switching elements 41 to 44 as described above, and applies a voltage (DC voltage) opposite to that in the first state between the pair of cables 18a and 18b, thereby causing a current (DC current) opposite to that in the first state to flow through the pair of cables 18a and 18b and the drive circuit 14, and bringing the light-emitting unit 30a to a stopped state.

[0072] Therefore, in this example, the control circuit 16 sets the control signal to the first state when the switching element 20 is turned on, and sets the control signal to the second state when the switching element 20 is turned off. In other words, the first state is a state for setting the light-emitting unit 30a to an output state. In other words, the second state is a state for setting the light-emitting unit 30a to a stopped state.

[0073] For example, if the drive circuit 14 is in a stopped state when the switching element 20 is turned on and in an output state when the switching element 20 is turned off, then, contrary to the above, the control circuit 16 may set the control signal to the first state when the switching element 20 is turned off and set the control signal to the second state when the switching element 20 is turned on.

[0074] In the first state, the control circuit 16 causes a current to flow through the pair of cables 18a, 18b and the drive circuit 14 in a direction in which an optical signal is output from the light-emitting unit 30a. In other words, in the first state, the control circuit 16 causes a current to flow in a direction from the high potential terminal of the light-emitting unit 30a toward the low potential terminal (the forward direction of the light-emitting unit 30a).

[0075] When the control circuit 16 sets the control signal to the first state, the drive circuit 14 causes the light-emitting unit 30a to output an optical signal by passing a current supplied from the control circuit 16 through the pair of cables 18a, 18b to the light-emitting unit 30a. This allows the drive circuit 14 to have a relatively simple configuration and to set the light-emitting unit 30a to the output state based on the control signal from the control circuit 16.

[0076] Furthermore, when the control circuit 16 sets the control signal to the second state, the drive circuit 14 causes a current to flow through the rectifier element 34 connected in anti-parallel to the light-emitting unit 30a. This allows the light-emitting unit 30a to be in a stopped state while causing a current to flow in the opposite direction to that in the first state. Furthermore, even when a current is caused to flow in the opposite direction to that in the first state, it is possible to prevent a voltage equal to or greater than a predetermined value from being applied in the opposite direction to the light-emitting unit 30a.

[0077] The configuration of the control circuit 16 is not limited to the above, and may be any configuration that can appropriately switch the control signal between the first state and the second state in response to a control command, etc. The configuration of the drive circuit 14 is not limited to the above, and may be any configuration that can appropriately switch the light-emitting unit 30a between the output state and the stopped state in response to a control signal from the control circuit 16.

[0078] FIG. 3 is a block diagram schematically illustrating a reference control circuit. 3, the control circuit 16ref includes a switching element 50. In the control circuit 16ref, the positive potential terminal 16p is connected to the cable 18a. The switching element 50 is provided between the cable 18b and the common potential terminal 16g.

[0079] The control circuit 16ref turns on the switching element 50 and supplies current to the light-emitting unit 30a via the pair of cables 18a and 18b, thereby putting the light-emitting unit 30a into an output state.The control circuit 16ref then turns off the switching element 50 and stops the supply of current to the light-emitting unit 30a, thereby putting the light-emitting unit 30a into a stopped state.

[0080] In the control circuit 16ref configured as described above, when the switching element 50 is turned off, the cable 18b is put into an open state. This puts the cable 18b into a high impedance state, making the cable 18b susceptible to the effects of noise generated in the switching element 20. The effects of the noise superimposed on the cable 18b make the drive circuit 14 more susceptible to malfunction.

[0081] It has also been proposed to suppress malfunction of the drive circuit 14 (optical isolator 30) by providing a filter circuit at the input of the optical isolator 30 (light-emitting unit 30a), for example by providing a capacitor in parallel with the resistive element 33. However, in this case, there is a concern that a delay will occur in the control signal input from the control circuit 16ref to the drive circuit 14, which will cause a delay in the switching of the switching element 20 or hinder the switching of the switching element 20 from being accelerated.

[0082] In contrast, in the power conversion device 10 according to the present embodiment, in the first state, the control circuit 16 applies a voltage between the pair of cables 18a, 18b and causes a current to flow through the pair of cables 18a, 18b and the drive circuit 14, thereby putting the light-emitting unit 30a into an output state. In the second state, the control circuit 16 applies a voltage between the pair of cables 18a, 18b in the opposite direction to that in the first state, thereby causing a current to flow through the pair of cables 18a, 18b and the drive circuit 14 in the opposite direction to that in the first state, thereby putting the light-emitting unit 30a into a stopped state.

[0083] Thus, in the power conversion device 10 of this embodiment, the control circuit 16 passes current through the pair of cables 18a, 18b and the drive circuit 14 in each of a first state for setting the switching element 20 to one of the on state and the off state, and a second state for setting the switching element 20 to the other of the on state and the off state.

[0084] This prevents the pair of cables 18a, 18b from being susceptible to the effects of noise generated in the switching element 20, regardless of whether the switching element 20 is in the on or off state, and prevents the drive circuit 14 (optical isolation section 30) from malfunctioning due to the effects of noise superimposed on the pair of cables 18a, 18b.

[0085] Furthermore, compared to when a filter circuit is provided at the input portion of the optical insulating section 30 (light emitting section 30a), delays occurring in the control signal input from the control circuit 16 to the drive circuit 14 can be suppressed.

[0086] Therefore, in the power conversion device 10 according to this embodiment, it is possible to suppress delays in the control signals input from the control circuit 16 to the drive circuit 14, while suppressing malfunctions of the drive circuit 14 due to the influence of noise.

[0087] The present embodiment includes the following aspects. (Appendix 1) a main circuit section having a switching element and converting power by switching the switching element; a drive circuit for driving the switching element; a control circuit connected to the drive circuit via a pair of cables, and configured to control the power conversion operation of the main circuit by inputting an electrical control signal for controlling the switching of the switching element to the drive circuit via the pair of cables; Equipped with the switching element has a pair of main terminals and a control terminal, and has an ON state in which a current flows between the pair of main terminals and an OFF state in which the current flow between the pair of main terminals is interrupted; the drive circuit includes a light-emitting unit that converts the control signal input from the control circuit into an optical signal, and a light-receiving unit that converts the optical signal back into an electrical signal; the light-emitting unit has an output state in which the light signal is output and a stop state in which output of the light signal is stopped, the drive circuit switches between the output state and the stop state of the light-emitting unit in response to the control signal from the control circuit, outputs the optical signal in response to the control signal from the light-emitting unit, converts the optical signal back into an electrical signal using the light-receiving unit, generates an electrical drive signal based on the converted electrical signal, and inputs the drive signal to the control terminal of the switching element, thereby switching between the on state and the off state of the switching element; The control signal has a first state for setting the switching element to one of the on state and the off state, and a second state for setting the switching element to the other of the on state and the off state, and the control circuit controls the switching of the switching element by controlling the switching of the control signal between the first state and the second state, and in the first state, applies a voltage between the pair of cables and causes a current to flow through the pair of cables and the drive circuit, thereby putting the light-emitting unit into an output state, and in the second state, applies a voltage between the pair of cables in a direction opposite to that in the first state, thereby causing a current to flow through the pair of cables and the drive circuit in a direction opposite to that in the first state, and putting the light-emitting unit into a stopped state. This is a power conversion device.

[0088] (Appendix 2) the light-emitting unit has a high potential terminal and a low potential terminal, and is in the output state of outputting the optical signal by increasing the magnitude of a current flowing from the high potential terminal to the low potential terminal to a predetermined value or greater; In the first state, the control circuit causes a current to flow in a direction from the high potential terminal to the low potential terminal of the light emitting unit, 2. The power conversion device according to claim 1, wherein when the control circuit sets the control signal to the first state, the drive circuit causes a current supplied from the control circuit via the pair of cables to flow to the light-emitting unit, thereby causing the light-emitting unit to output the optical signal.

[0089] (Appendix 3) The power conversion device according to claim 2, wherein the drive circuit has a rectifier element connected inversely in parallel with the light-emitting unit, and when the control circuit sets the control signal to the second state, a current flows through the rectifier element.

[0090] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied 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 modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0091] REFERENCE SIGNS LIST 10...power conversion device, 12...main circuit section, 14...drive circuit, 16, 16ref...control circuit, 18a, 18b...cable, 20...switching element, 30...optical insulation section, 31, 32...switching element, 33...resistance element, 34...rectifier element, 41 to 44...switching element, 45...NOT gate, 50...switching element

Claims

1. a main circuit section having a switching element and converting power by switching the switching element; a drive circuit for driving the switching element; a control circuit connected to the drive circuit via a pair of cables, and configured to control the power conversion operation of the main circuit by inputting an electrical control signal for controlling the switching of the switching element to the drive circuit via the pair of cables; Equipped with the switching element has a pair of main terminals and a control terminal, and has an ON state in which a current flows between the pair of main terminals, and an OFF state in which the current flow between the pair of main terminals is interrupted; the drive circuit includes a light-emitting unit that converts the control signal input from the control circuit into an optical signal, and a light-receiving unit that converts the optical signal back into an electrical signal; the light-emitting unit has an output state in which the light signal is output and a stop state in which output of the light signal is stopped, the drive circuit switches between the output state and the stop state of the light-emitting unit in response to the control signal from the control circuit, outputs the optical signal in response to the control signal from the light-emitting unit, converts the optical signal back into an electrical signal using the light-receiving unit, generates an electrical drive signal based on the converted electrical signal, and inputs the drive signal to the control terminal of the switching element, thereby switching between the on state and the off state of the switching element; The control signal has a first state for setting the switching element to one of the on state and the off state, and a second state for setting the switching element to the other of the on state and the off state, and the control circuit controls the switching of the switching element by controlling the switching of the control signal between the first state and the second state, and in the first state, applies a voltage between the pair of cables and causes a current to flow through the pair of cables and the drive circuit, thereby putting the light-emitting unit into an output state, and in the second state, applies a voltage between the pair of cables in a direction opposite to that in the first state, thereby causing a current to flow through the pair of cables and the drive circuit in a direction opposite to that in the first state, and puts the light-emitting unit into a stopped state. This is a power conversion device.

2. the light-emitting unit has a high potential terminal and a low potential terminal, and is in the output state of outputting the optical signal by increasing the magnitude of a current flowing from the high potential terminal to the low potential terminal to a predetermined value or greater; In the first state, the control circuit causes a current to flow in a direction from the high potential terminal to the low potential terminal of the light emitting unit, 2. The power conversion device according to claim 1, wherein when the control circuit sets the control signal to the first state, the drive circuit causes the light-emitting unit to output the optical signal by flowing current supplied from the control circuit via the pair of cables to the light-emitting unit.

3. 3. The power conversion device according to claim 2, wherein the drive circuit has a rectifying element connected inversely in parallel with the light emitting unit, and when the control circuit sets the control signal to the second state, a current flows through the rectifying element.

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