Power converter
A universal overvoltage suppression circuit with controlled resistance value management addresses the inefficiencies of custom design, enhancing overvoltage suppression and fault clearance in power conversion devices.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TMEIC CORP (100 00)
- Filing Date
- 2024-12-20
- Publication Date
- 2026-07-02
AI Technical Summary
The design of overvoltage suppression circuits for power conversion devices is time-consuming and costly due to varying system configurations, requiring individual customization for each device.
A power conversion device with a universal overvoltage suppression circuit that includes a resistor element, switching element, and control device, which sets thresholds and controls the equivalent resistance value through pulse width modulation or frequency modulation to manage overvoltage, reducing the need for individual design and customization.
This approach reduces the effort and cost associated with designing overvoltage suppression circuits by allowing a common design to be adapted to different system requirements, effectively suppressing overvoltage while minimizing manufacturing costs and ensuring rapid fault clearance.
Smart Images
Figure 2026110252000001_ABST
Abstract
Description
Technical Field
[0001] Embodiments of the present invention relate to a power conversion device.
Background Art
[0002] There is a power conversion device including a converter that performs at least one of conversion from DC power to another power and conversion from another power to DC power. In such a power conversion device, the DC voltage of the converter may rise and become an overvoltage. For example, when the converter is connected to a power system and performs at least one of conversion from DC power to AC power and conversion from AC power to DC power, during an accident of the power system, current may flow from the power system side into the converter, causing an overvoltage of the DC voltage of the converter.
[0003] Therefore, an overvoltage suppression circuit for suppressing the overvoltage of the DC voltage is provided on the DC side of the converter. The overvoltage suppression circuit includes a resistive element and a switching element. When the DC voltage of the converter becomes an overvoltage, the overvoltage suppression circuit turns on the switching element and consumes the energy on the DC side of the converter with the resistive element, thereby suppressing the rise of the DC voltage.
[0004] The manner in which the DC voltage of the converter rises during an accident of the power system or the like varies depending on the system configuration of the power conversion device and the like for each power conversion device. Therefore, the required resistance value and the like in the resistive element of the overvoltage suppression circuit also vary for each power conversion device. Therefore, in a power conversion device, the design of the overvoltage suppression circuit is performed each time for each power conversion device according to requirements such as the system configuration.
[0005] However, if the design of the overvoltage suppression circuit is performed each time for each power conversion device, it takes time to design the overvoltage suppression circuit, and there are concerns about an increase in design cost and manufacturing cost.
[0006] Therefore, in a power conversion device, it is desired to be able to suppress the labor of designing the overvoltage suppression circuit. [Prior art documents] [Patent Documents]
[0007] [Patent Document 1] Patent No. 3162710 [Overview of the project] [Problems that the invention aims to solve]
[0008] Embodiments of the present invention provide a power conversion device that can reduce the effort required to design an overvoltage suppression circuit. [Means for solving the problem]
[0009] According to an embodiment of the present invention, the present invention includes a converter having a pair of DC terminals and performing at least one of the following operations: converting DC power supplied through the pair of DC terminals into another power, and converting another power into DC power and outputting the converted DC power to the pair of DC terminals; an overvoltage suppression circuit connected to the pair of DC terminals and performing an overvoltage suppression operation to suppress an overvoltage of the DC voltage between the pair of DC terminals; a control device that controls the operation of the converter and the overvoltage suppression circuit; and a voltage detector that detects the magnitude of the DC voltage between the pair of DC terminals and inputs a voltage detection value representing the detection result of the magnitude of the DC voltage between the pair of DC terminals to the control device, wherein the overvoltage suppression circuit includes a resistor element, a first state in which the resistor element is connected between the pair of DC terminals, and a connection between the resistor element and the pair of DC terminals A power conversion device is provided which includes a switching element that switches between a second state and a second state that resolves a continuous state, wherein the control device sets two thresholds with respect to the voltage detection value: an operating level and a stop level set to a value lower than the operating level, and when the voltage detection value becomes equal to or greater than the operating level, it causes the overvoltage suppression circuit to perform the overvoltage suppression operation, and after the overvoltage suppression circuit has performed the overvoltage suppression operation, when the voltage detection value becomes equal to or less than the stop level, it causes the overvoltage suppression circuit to stop performing the overvoltage suppression operation, and controls the switching of the switching element so that the equivalent resistance value of the overvoltage suppression circuit with respect to the DC voltage between the pair of DC terminals becomes a desired resistance value during the period in which the overvoltage suppression circuit performs the overvoltage suppression operation. [Effects of the Invention]
[0010] A power conversion device is provided that reduces the effort required to design overvoltage suppression circuits. [Brief explanation of the drawing]
[0011] [Figure 1] This is a schematic block diagram showing a power conversion device according to an embodiment. [Figure 2] This graph schematically illustrates an example of the operation of a control device. [Figure 3] This is an explanatory diagram illustrating an example of the operation of a control device. [Figure 4] Figures 4(a) and 4(b) are schematic graphs illustrating an example of alternating current. [Figure 5] This is an explanatory diagram illustrating a schematic variation of the operation of a control device. [Figure 6] Figures 6(a) to 6(c) are block diagrams schematically representing modified examples of the first and second transducers. [Modes for carrying out the invention]
[0012] Each embodiment will be described below with reference to the drawings. Please note that the drawings are schematic or conceptual, and the relationships between the thickness and width of each part, as well as the ratios of the sizes of the parts, are not necessarily identical to those of reality. Furthermore, even when representing the same part, the dimensions and ratios may differ between drawings. In this specification and in each figure, elements similar to those described above are denoted by the same reference numerals, and detailed explanations are omitted as appropriate.
[0013] Figure 1 is a schematic block diagram showing a power conversion device according to an embodiment. As shown in Figure 1, the power converter 10 comprises a first converter 11, a second converter 12, an overvoltage suppression circuit 14, a voltage detector 16, and a control device 18.
[0014] The first converter 11 is connected to the AC circuit 2a. The first converter 11 performs at least one of the following: conversion of AC power supplied from the AC circuit 2a to DC power, and conversion of DC power to AC power corresponding to the AC circuit 2a. In this example, the AC power of the AC circuit 2a is three-phase AC power. The first converter 11 performs at least one of the following: conversion of three-phase AC power to DC power, and conversion of DC power to three-phase AC power. The AC circuit 2a is, for example, a power system. The first converter 11 is connected to the AC circuit 2a (power system) via, for example, a transformer or circuit breaker (not shown).
[0015] The first converter 11 has a pair of DC terminals 21a and 21b, and a plurality of AC terminals 22a to 22c. The pair of DC terminals 21a and 21b are terminals for performing at least one of input and output of DC power.
[0016] In this example, the first converter 11 has three AC terminals 22a to 22c corresponding to each phase of the three-phase AC power of the AC circuit 2a. The first converter 11 is connected to the AC circuit 2a via the plurality of AC terminals 22a to 22c.
[0017] The first converter 11 has, for example, six switching elements 24 connected in a three-phase full-bridge between a pair of DC terminals 21a and 21b, and performs power conversion by switching each switching element 24. In other words, the first converter 11 performs at least one of the operations of converting the DC power supplied via the pair of DC terminals 21a and 21b into three-phase AC power, and converting the three-phase AC power into DC power and outputting the converted DC power to the pair of DC terminals 21a and 21b.
[0018] Further, the first converter 11 further has, for example, a charge storage element 26 provided between the pair of DC terminals 21a and 21b. In other words, the charge storage element 26 is connected in parallel to each switching element 24. The charge storage element 26 suppresses fluctuations in the DC voltage between the pair of DC terminals 21a and 21b. The charge storage element 26 is, for example, a DC capacitor. In this example, the first converter 11 is a three-phase two-level inverter.
[0019] The second converter 12 is connected to the AC circuit 2b. The second converter 12 performs at least one of the conversion of AC power supplied from the AC circuit 2b into DC power and the conversion of DC power into AC power corresponding to the AC circuit 2b. In this example, the AC power of the AC circuit 2b is three-phase AC power. The second converter 12 performs at least one of the conversion of three-phase AC power into DC power and the conversion of DC power into three-phase AC power. The AC circuit 2b is, for example, a power system different from the AC circuit 2a. The second converter 12 is connected to the AC circuit 2b via, for example, a transformer or a line breaker (not shown).
[0020] The second converter 12 has a pair of DC terminals 31a and 31b and a plurality of AC terminals 32a to 32c. In this example, the second converter 12 has three AC terminals 32a to 32c corresponding to each phase of the three-phase AC power of the AC circuit 2b. The second converter 12 is connected to the AC circuit 2b via the plurality of AC terminals 32a to 32c and is connected to the first converter 11 via the pair of DC terminals 31a and 31b. The pair of DC terminals 31a and 31b of the second converter 12 are connected to the pair of DC terminals 21a and 21b of the first converter 11.
[0021] The power conversion device 10, for example, converts the AC power supplied from the AC circuit 2a into DC power by the first converter 11, converts the converted DC power into another AC power corresponding to the AC circuit 2b by the second converter 12, and supplies the converted AC power to the AC circuit 2b. Also, conversely, the power conversion device 10, for example, converts the AC power supplied from the AC circuit 2b into DC power by the second converter 12, converts the converted DC power into another AC power corresponding to the AC circuit 2a by the first converter 11, and supplies the converted AC power to the AC circuit 2a.
[0022] Thus, the power converter 10 converts AC power to another AC power by, for example, the power conversion operations of the first converter 11 and the second converter 12. The first converter 11 and the second converter 12 are, for example, BTB (Back To Back) converters. The first converter 11 and the second converter 12 perform, for example, voltage conversion and frequency conversion of the AC power.
[0023] Note that AC circuits 2a and 2b are not limited to power systems, but may also be AC loads such as AC generators or motors. For example, AC circuit 2a may be a power system and AC circuit 2b may be an AC load. AC circuits 2a and 2b may be any circuits that perform at least one of the following: supplying AC power to the power converter 10 and receiving AC power from the power converter 10.
[0024] The second converter 12 has, for example, six switching elements 34 connected in a three-phase full bridge between a pair of DC terminals 31a and 31b and three AC terminals 32a to 32c, and performs power conversion by switching each switching element 34. In this example, the second converter 12 is a three-phase two-level inverter, similar to the first converter 11.
[0025] The overvoltage suppression circuit 14 is connected to a pair of DC terminals 21a and 21b of the first converter 11. In this example, the overvoltage suppression circuit 14 is also connected to a pair of DC terminals 31a and 31b of the second converter 12. In other words, the overvoltage suppression circuit 14 is located between the pair of DC terminals 21a and 21b of the first converter 11 and the pair of DC terminals 31a and 31b of the second converter 12.
[0026] The overvoltage suppression circuit 14 performs an overvoltage suppression operation to suppress the overvoltage of the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11. In other words, the overvoltage suppression circuit 14 suppresses the overvoltage of the DC voltage between the pair of DC terminals 31a and 31b of the second converter 12.
[0027] The overvoltage suppression circuit 14 includes a resistive element 40, a switching element 42, and rectifier elements 44 and 46.
[0028] The resistive element 40 is provided between a pair of DC terminals 21a and 21b of the first transducer 11. The resistance value of the resistive element 40 is set, for example, according to the maximum capacity of the overvoltage suppression function of the overvoltage suppression circuit 14. The resistance value of the resistive element 40 is, for example, 1Ω. The resistance value of the resistive element 40 is set to a sufficiently small value so that, for example, the DC energy of the first transducer 11 (energy stored in the charge storage element 26) is appropriately consumed and the overvoltage of the DC voltage of the first transducer 11 is appropriately suppressed. The resistive element 40 consumes the DC energy of the first transducer 11 by converting it into heat. For this reason, the resistive element 40 is designed to withstand the temperature rise associated with the consumption of energy on the DC side of the first transducer 11. The resistive element 40 is designed to have a heat capacity corresponding to the DC energy of the first transducer 11. Therefore, the resistive element 40 is designed to have a relatively large capacity (large volume). The resistive element 40 is, for example, a low-resistance, high-capacity resistive element.
[0029] The switching element 42 is provided between the resistive element 40 and one of the pair of DC terminals 21a and 21b of the first converter 11. In this example, the switching element 42 is provided between the resistive element 40 and the high-potential DC terminal 21a. The switching element 42 may also be provided between the resistive element 40 and the low-potential DC terminal 21b.
[0030] The switching element 42 switches between a first state in which the resistive element 40 is connected between the pair of DC terminals 21a and 21b of the first converter 11, and a second state in which the connection between the resistive element 40 and the pair of DC terminals 21a and 21b of the first converter 11 is removed. In other words, the overvoltage suppression circuit 14 has the above-mentioned first state and second state, and switches between the first state and the second state by switching the switching element 42.
[0031] In other words, the first state is a state in which the pair of DC terminals 21a and 21b of the first converter 11 are connected via the resistor element 40. Therefore, by setting the overvoltage suppression circuit 14 to the first state, the DC energy of the first converter 11 (energy stored in the charge storage element 26) flows to the resistor element 40, and the DC energy of the first converter 11 is consumed by the resistor element 40. As a result, by setting the overvoltage suppression circuit 14 to the first state, the overvoltage of the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 can be suppressed.
[0032] In other words, the first state is a state in which the DC energy of the first converter 11 flows into the resistive element 40, and the second state is a state in which the inflow of the DC energy of the first converter 11 into the resistive element 40 is suppressed.
[0033] The switching element 42 has, for example, a pair of main terminals and a control terminal. The switching element 42 also has an ON state in which current flows between the pair of main terminals and an OFF state in which the current flowing between the pair of main terminals is interrupted. Note that the OFF state is not limited to a state in which the current flowing between the pair of main terminals is completely interrupted, but may also be a state in which a weak current that does not affect the operation of the overvoltage suppression circuit 14 flows between the pair of main terminals. In other words, the OFF state is a state in which the magnitude of the current flowing between the pair of main terminals is smaller than that of the ON state.
[0034] One main terminal of the switching element 42 is connected to one DC terminal 21a. The other main terminal of the switching element 42 is connected to one end of the resistor element 40. The other end of the resistor element 40 is connected to the other DC terminal 21b. As a result, when the switching element 42 is turned off, the overvoltage suppression circuit 14 enters the second state, and when the switching element 42 is turned on, the overvoltage suppression circuit 14 enters the first state. In other words, the overvoltage suppression circuit 14 is a chopper circuit. However, the configuration of the overvoltage suppression circuit 14 is not limited to this, and any configuration that allows for appropriate switching between the first state and the second state by switching the switching element 42 is acceptable.
[0035] The switching element 42 is, for example, a self-excited semiconductor switching element such as an IGBT. However, the switching element 42 is not limited to this, and may be any element capable of appropriately switching between the first state and the second state.
[0036] The rectifier element 44 is provided in parallel with the resistor element 40. The direction of the current flowing through the rectifier element 44 is opposite to the direction of the current flowing through the resistor element 40 when the overvoltage suppression circuit 14 is in the first state (when the switching element 42 is in the ON state). The rectifier element 44 allows the current based on the energy stored in the inductance component of the resistor element 40 to circulate within a loop-shaped path formed by the resistor element 40 and the rectifier element 44 when, for example, the switching element 42 is switched from the ON state to the OFF state. In this way, the rectifier element 44 prevents the first converter 11, the second converter 12, the overvoltage suppression circuit 14, etc. from failing due to the energy stored in the inductance component of the resistor element 40. The rectifier element 44 is, for example, a freewheeling diode.
[0037] The rectifier element 46 is provided in antiparallel to the switching element 42. The direction of the current flowing through the rectifier element 46 is opposite to the direction of the current flowing through the switching element 42 when the overvoltage suppression circuit 14 is in the first state (when the switching element 42 is in the ON state). The rectifier element 46 suppresses the application of a reverse voltage between the pair of main terminals of the switching element 42 when the switching element 42 is switched from the ON state to the OFF state. The rectifier element 46 is, for example, a freewheeling diode.
[0038] The voltage detector 16 detects the magnitude of the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11. The voltage detector 16 is connected to the control device 18. The voltage detector 16 inputs a voltage detection value, which represents the result of detecting the magnitude of the DC voltage between the pair of DC terminals 21a and 21b, to the control device 18.
[0039] The control device 18 controls the operation of the first converter 11, the second converter 12, and the overvoltage suppression circuit 14, respectively. The control device 18 controls the power conversion operation of the first converter 11 by, for example, controlling the switching of each switching element 24. Similarly, the control device 18 controls the power conversion operation of the second converter 12 by, for example, controlling the switching of each switching element 34.
[0040] The control device 18 controls the overvoltage suppression operation of the overvoltage suppression circuit 14 based on the voltage detection value input from the voltage detector 16. The control device 18 is connected, for example, to the control terminal of the switching element 42 and controls the switching of the switching element 42 between the on state and the off state based on the voltage detection value, thereby controlling the overvoltage suppression operation of the overvoltage suppression circuit 14. In other words, the control device 18 controls the switching between the first state and the second state of the overvoltage suppression circuit 14 based on the voltage detection value.
[0041] Figure 2 is a graph that schematically represents an example of the operation of the control device. As shown in Figure 2, the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 may rise, for example, if the AC circuit 2a is a power system and an accident occurs in the power system.
[0042] As shown in Figure 2, the control device 18 sets two thresholds for the detected voltage: an operating level and a stop level that is set to a value lower than the operating level. When the detected voltage exceeds the operating level, the control device 18 causes the overvoltage suppression circuit 14 to perform an overvoltage suppression operation. After the overvoltage suppression operation has been performed by the overvoltage suppression circuit 14, the control device 18 causes the overvoltage suppression circuit 14 to stop performing the overvoltage suppression operation when the detected voltage falls below the stop level.
[0043] Furthermore, the control device 18 stops the operation of the first converter 11 and the second converter 12 if, for example, the voltage detection value becomes equal to or above the operating level while the first converter 11 and the second converter 12 are operating. For example, if the operating level is set within a range in which the first converter 11 and the second converter 12 can operate, the operation of the first converter 11 and the second converter 12 may continue even when the voltage detection value becomes equal to or above the operating level.
[0044] If the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 rises due to a power system fault, as shown in Figure 2, after the overvoltage suppression circuit 14 stops performing the overvoltage suppression operation, if the power system fault continues, the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 may rise again.
[0045] In this case, as shown in Figure 2, the control device 18 repeatedly performs the overvoltage suppression operation of the overvoltage suppression circuit 14 and stops the execution of the overvoltage suppression operation of the overvoltage suppression circuit 14 according to the voltage detection value until the fault in the power system is eliminated. Eliminating the fault in the power system means, for example, opening the circuit breaker installed between the AC circuit 2a and the first converter 11, thereby interrupting the connection between the AC circuit 2a and the first converter 11 with the circuit breaker.
[0046] Figure 3 is an explanatory diagram illustrating an example of the operation of the control device. As shown in Figure 3, the control device 18 controls the switching of the switching element 42 so that the equivalent resistance value of the overvoltage suppression circuit 14 with respect to the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 becomes a desired resistance value during the period in which the overvoltage suppression circuit 14 performs overvoltage suppression operation. In other words, the control device 18 controls the switching between the first and second states of the overvoltage suppression circuit 14 so that the equivalent resistance value of the overvoltage suppression circuit 14 with respect to the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 becomes a desired resistance value during the period in which the overvoltage suppression circuit 14 performs overvoltage suppression operation.
[0047] The control device 18 controls the equivalent resistance value of the overvoltage suppression circuit 14 to a desired resistance value by controlling the switching of the switching element 42, for example, by pulse width modulation control (PWM control). More specifically, the control device 18 controls the switching between the first state and the second state (switching between the on state and the off state of the switching element 42) at a constant period, and also controls the equivalent resistance value of the overvoltage suppression circuit 14 to a desired resistance value by changing the time ratio (duty cycle) between the period of the first state and the period of the second state.
[0048] For example, as shown in Figure 3, if the resistance of the resistor element 40 is 1Ω, the equivalent resistance of the overvoltage suppression circuit 14 can be made 2Ω by setting the ratio of the first state period to 50%, and the equivalent resistance of the overvoltage suppression circuit 14 can be made 4Ω by setting the ratio of the first state period to 25%. In this way, the magnitude of the equivalent resistance of the overvoltage suppression circuit 14 can be controlled by controlling the ratio of the first state period.
[0049] The control device 18 controls the switching of the switching element 42, for example, by a predetermined ratio of the duration of the first state. The ratio of the duration of the first state is set, for example, according to the system requirements of the power converter 10. The system requirements of the power converter 10 include, for example, the magnitude of the DC voltage between a pair of DC terminals 21a and 21b, the magnitude of the AC voltage in the AC circuit 2a (magnitude of the voltage of another power), and the degree of suppression of DC voltage overvoltage (discharge rate). This makes it possible to suppress DC voltage overvoltage between a pair of DC terminals 21a and 21b with an appropriate resistance value according to the system requirements of the power converter 10.
[0050] The control device 18 is not limited to pulse width modulation control; for example, it may control the switching of the switching element 42 by frequency modulation control (PFM control) to control the equivalent resistance value of the overvoltage suppression circuit 14 to a desired resistance value. More specifically, the control device 18 may control the equivalent resistance value of the overvoltage suppression circuit 14 to a desired resistance value by, for example, keeping the length of the first state period constant and changing the length of the second state period.
[0051] In pulse width modulation control, the period is kept constant, and the time ratio between the first state and the second state is changed by varying the length of the first state and the length of the second state. On the other hand, in frequency modulation control, the length of the first state is kept constant, and the time ratio between the first state and the second state is changed by varying the length and period of the second state. As a result, in the case of frequency modulation control, as in the case of pulse width modulation control, the equivalent resistance value of the overvoltage suppression circuit 14 can be controlled to a desired resistance value.
[0052] The control device 18 may, for example, perform control by combining pulse width modulation control and frequency modulation control. The manner in which the control device 18 controls the switching of the switching element 42 is not limited to the above, and any manner in which the switching of the switching element 42 is controlled to appropriately control the equivalent resistance value of the overvoltage suppression circuit 14 to a desired resistance value by alternately switching between a first state and a second state and changing the time ratio between the period of the first state and the period of the second state.
[0053] Furthermore, the switching period Tc (the switching period of the switching element 42) between the first and second states must take into account the time constant τ, which is calculated as the product of the charge storage element 26 and the resistive element 40. The control device 18 makes the switching period Tc between the first and second states shorter than the time constant τ. For example, the control device 18 makes the period Tc shorter than 0.1 times the time constant τ (Tc < 0.1 × τ). As a result, for example, as shown in Figure 3, the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 can be gradually reduced by switching between the first and second states.
[0054] The control device 18 receives, for example, a setting signal. The control device 18 may receive a setting signal from an external device, for example, by communicating with an external device, such as a higher-level controller. The control device 18 may also receive a setting signal from an operation unit (not shown) provided on the power converter 10, for example. In other words, the setting signal may be input to the control device 18 based on manual operation by the user.
[0055] The control device 18 changes the time ratio between the period of the first state and the period of the second state in response to an input setting signal. This allows the equivalent resistance value of the overvoltage suppression circuit 14 to be changed in response to the input setting signal. For example, when the system requirements of the power converter 10 change, a setting signal can be input to the control device 18 to set an appropriate resistance value according to the changed system requirements.
[0056] Figures 4(a) and 4(b) are schematic graphs illustrating an example of alternating current. Figures 4(a) and 4(b) schematically represent an example of the alternating current (system current) flowing between the AC circuit 2a and the first converter 11.
[0057] When the overvoltage suppression circuit 14 is in the first state, the effect of reducing the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 is largely related to the resistance value of the overvoltage suppression circuit 14 (the resistance value of the resistive element 40). The smaller the resistance value of the overvoltage suppression circuit 14, the faster the discharge of the charge storage element 26 occurs, and the greater the effect of reducing the DC voltage.
[0058] On the other hand, the resistance value of the overvoltage suppression circuit 14 also affects the AC current between the AC circuit 2a and the first converter 11 when a fault occurs in the power system (AC circuit 2a). When a fault occurs in the power system, as shown in Figures 4(a) and 4(b), a DC component may be superimposed on the AC current between the AC circuit 2a and the first converter 11, potentially increasing the magnitude of the AC current.
[0059] In this case, if the resistance value of the overvoltage suppression circuit 14 is too small (the overvoltage suppression effect is too strong), as shown in Figure 4(a), the attenuation of the AC component of the current flowing between the AC circuit 2a and the first converter 11 will increase, and the time until the magnitude of the current flowing between the AC circuit 2a and the first converter 11 becomes zero may increase. In order to open the circuit breaker installed between the AC circuit 2a and the first converter 11 and eliminate the fault in the power system, the magnitude of the current flowing between the AC circuit 2a and the first converter 11 must be zero. Therefore, if the resistance value of the overvoltage suppression circuit 14 is too small, the time until the fault in the power system is eliminated may increase.
[0060] In contrast, when the resistance value of the overvoltage suppression circuit 14 is set to an appropriate value, as shown in Figure 4(b), the attenuation of the AC component of the current flowing between the AC circuit 2a and the first converter 11 is reduced, and the time until the magnitude of the current flowing between the AC circuit 2a and the first converter 11 becomes zero can be shortened compared to the case where the resistance value of the overvoltage suppression circuit 14 shown in Figure 4(a) is too small. The time until a fault in the power system is cleared can be shortened.
[0061] Thus, the resistance value of the overvoltage suppression circuit 14 is not simply a matter of being small; it needs to be set to an appropriate value according to the system requirements of the power converter 10. For this reason, the resistance value of the overvoltage suppression circuit 14 needs to be set for each power converter 10. However, designing the overvoltage suppression circuit 14 and setting the resistance value for each power converter 10 each time would be time-consuming, and there are concerns about increased design and manufacturing costs.
[0062] In contrast, in the power converter 10 according to this embodiment, the control device 18 controls the switching of the switching element 42 so that the equivalent resistance value of the overvoltage suppression circuit 14 with respect to the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 becomes a desired resistance value during the period in which the overvoltage suppression circuit 14 performs an overvoltage suppression operation.
[0063] As a result, in the power converter 10 according to this embodiment, the effort required to design the overvoltage suppression circuit 14 each time for each power converter 10 can be reduced. For example, by setting the resistance value of the resistor element 40 to a sufficiently low value in advance, the overvoltage suppression circuit 14 can be used in common for multiple power converters 10 with different system requirements. This can also suppress increases in design costs and manufacturing costs. Furthermore, by setting the equivalent resistance value of the overvoltage suppression circuit 14 to an appropriate value, it is possible to achieve both the suppression of failure of the first converter 11 due to DC voltage overvoltage and the rapid removal of power system faults.
[0064] Furthermore, in the power converter 10 according to this embodiment, the control device 18 changes the time ratio between the period of the first state and the period of the second state in accordance with the input setting signal. This makes it possible to easily set an appropriate resistance value according to the changed system requirements without requiring changes to the circuit configuration of the overvoltage suppression circuit 14, for example, when the system requirements of the power converter 10 change.
[0065] Figure 5 is an explanatory diagram illustrating a schematic variation of the operation of the control device. As shown in Figure 5, in this example, the control device 18 sets two operating levels with respect to the detected voltage value: a first operating level and a second operating level set to a value higher than the first operating level. When the detected voltage value becomes equal to or greater than the first operating level, the control device 18 sets the ratio of the duration of the first state to the first ratio and causes the overvoltage suppression circuit 14 to perform an overvoltage suppression operation.
[0066] Then, after the control device 18 has caused the overvoltage suppression circuit 14 to perform overvoltage suppression operation at the first ratio, if the DC voltage rises and the voltage detection value becomes higher than the first operating level (a second operating level), the control device 18 sets the ratio of the first state period to a second ratio, which is higher than the first ratio, and causes the overvoltage suppression circuit 14 to perform overvoltage suppression operation. In this example, the first ratio is 50% and the second ratio is 100%. However, the first and second ratios are not limited to the above and may be any ratios.
[0067] In this way, two operating levels, a first operating level and a second operating level, are set, and the second ratio is set to a higher ratio than the first ratio when the voltage detection value becomes equal to or higher than the second operating level. As a result, when the overvoltage suppression operation is performed at the first ratio, for example, the attenuation of the AC component of the current flowing between the AC circuit 2a and the first converter 11 can be reduced, and the time required to clear a power system fault can be shortened. When the overvoltage suppression operation is performed at the second ratio, for example, the effect of suppressing DC voltage overvoltage can be further enhanced, and failure of the first converter 11 due to DC voltage overvoltage can be suppressed more appropriately. Therefore, for example, it is possible to more appropriately achieve both the suppression of failure of the first converter 11 due to DC voltage overvoltage and the rapid clearing of power system faults.
[0068] Furthermore, the number of operating levels is not limited to two; there may be three or more. In other words, the control device 18 may set multiple operating levels with different magnitudes of DC voltage for the detected voltage. In addition, the control device 18 may set the ratio of the duration of the first state according to the detected voltage using a predetermined calculation formula, for example, rather than being limited to setting thresholds. For example, the control device 18 increases the ratio of the duration of the first state as the detected voltage increases, based on multiple operating levels or a calculation formula. This makes it possible to more appropriately achieve both the suppression of failure of the first converter 11 due to DC voltage overvoltage and the rapid removal of power system faults.
[0069] For example, if the voltage detection value exceeds the operating level and the ratio of the first state period is set to the first ratio, causing the overvoltage suppression circuit 14 to perform an overvoltage suppression operation, and if the voltage detection value does not fall below the stop level even after a predetermined time has elapsed, the control device 18 may set the ratio of the first state period to a second ratio, which is higher than the first ratio, and cause the overvoltage suppression circuit 14 to perform an overvoltage suppression operation. For example, the control device 18 may increase the ratio of the first state period as the elapsed time since the start of the overvoltage suppression operation increases. This allows, for example, the DC voltage between the pair of DC terminals 21a and 21b of the first converter 11 to be reduced more appropriately by performing an overvoltage suppression operation.
[0070] Figures 6(a) to 6(c) are block diagrams schematically representing modified examples of the first and second transducers. As shown in Figure 6(a), the first converter 11a and the second converter 12a may be three-phase three-level inverters. The first converter 11a has three DC terminals 21a to 21c: a high-potential terminal 21a, a low-potential terminal 21b, and a neutral point terminal 21c. In this case, the power converter 10 includes two overvoltage suppression circuits 14 and two voltage detectors 16, provided between a pair of DC terminals 21a and 21c and between a pair of DC terminals 21b and 21c, respectively.
[0071] As shown in Figure 6(b), the first converter 11b and the second converter 12b may be single-phase three-level inverters. In this case, the first converter 11b has two AC terminals 22a and 22b corresponding to the single-phase AC power of the AC circuit 2a. Similarly, the second converter 12b has two AC terminals 32a and 32b corresponding to the single-phase AC power of the AC circuit 2b. The first converter 11b and the second converter 12b perform at least one of the following: conversion from single-phase AC power to DC power, and conversion from DC power to single-phase AC power. Thus, the power converted by the first converter 11b and the second converter 12b is not limited to three-phase AC power, but may also be single-phase AC power.
[0072] As shown in Figure 6(c), the first converter 11c and the second converter 12c may also be single-phase two-level inverters.
[0073] The power converted by the first and second converters is not limited to AC power, but may also be DC power or other types of power. The power converted by the first and second converters may be any power different from the DC power between the pair of DC terminals. The configuration of the first and second converters is not limited to the above, and may be any configuration having a pair of DC terminals and performing at least one of the following operations: converting DC power supplied through the pair of DC terminals into another type of power, and converting another type of power into DC power and outputting the converted DC power to the pair of DC terminals.
[0074] Furthermore, the configuration of the power converter is not limited to a configuration with two converters, a first converter and a second converter, but may be any configuration with at least one converter. The converter may also be connected to a DC circuit such as a DC load or DC power supply via a pair of DC terminals.
[0075] This embodiment includes the following aspects. (Note 1) A converter having a pair of DC terminals, which performs at least one of the following operations: converting DC power supplied through the pair of DC terminals into another power, and converting another power into DC power and outputting the converted DC power to the pair of DC terminals. An overvoltage suppression circuit connected to the pair of DC terminals and performing an overvoltage suppression operation to suppress overvoltage of the DC voltage between the pair of DC terminals, A control device that controls the operation of the converter and the overvoltage suppression circuit, A voltage detector that detects the magnitude of the DC voltage between the pair of DC terminals and inputs a voltage detection value representing the detection result of the magnitude of the DC voltage between the pair of DC terminals to the control device, Equipped with, The overvoltage suppression circuit described above is Resistor element and, A switching element that switches between a first state in which the resistive element is connected between the pair of DC terminals and a second state in which the connection between the resistive element and the pair of DC terminals is removed, It has, The control device sets two thresholds for the voltage detection value: an operating level and a stop level set to a value lower than the operating level. When the voltage detection value becomes equal to or greater than the operating level, it causes the overvoltage suppression circuit to perform the overvoltage suppression operation. After the overvoltage suppression circuit has performed the overvoltage suppression operation, when the voltage detection value falls below the stop level, it causes the overvoltage suppression circuit to stop performing the overvoltage suppression operation. During the period in which the overvoltage suppression circuit performs the overvoltage suppression operation, the power conversion device controls the switching of the switching element so that the equivalent resistance value of the overvoltage suppression circuit with respect to the DC voltage between the pair of DC terminals becomes a desired resistance value.
[0076] (Note 2) The power conversion device according to Appendix 1, wherein the control device alternately switches between the first state and the second state during the period in which the overvoltage suppression circuit performs the overvoltage suppression operation, and controls the switching of the switching element to change the time ratio between the period of the first state and the period of the second state, thereby controlling the equivalent resistance value of the overvoltage suppression circuit to a desired resistance value.
[0077] (Note 3) The converter further includes a charge storage element provided between the pair of DC terminals, The power conversion device described in Appendix 2, wherein the control device makes the switching period between the first state and the second state shorter than the time constant calculated by the product of the charge storage element and the resistive element.
[0078] (Note 4) The control device is a power conversion device as described in Appendix 3, wherein the period is shorter than 0.1 times the time constant.
[0079] (Note 5) The power conversion device according to any one of the appendices 2 to 4, wherein the control device increases the proportion of the period of the first state as the voltage detection value increases during the period in which the overvoltage suppression circuit performs the overvoltage suppression operation.
[0080] (Note 6) The resistive element is provided between the pair of DC terminals, The switching element is provided between the resistive element and one of the pair of DC terminals in the power conversion device according to any one of the appendices 1 to 5.
[0081] (Note 7) The overvoltage suppression circuit further comprises a rectifier element provided in parallel with the resistive element, The power conversion device as described in Appendix 6, wherein the direction of the current flowing through the rectifier element is opposite to the direction of the current flowing through the resistive element when the overvoltage suppression circuit is in the first state.
[0082] (Note 8) The power conversion device according to Appendix 6 or 7, wherein the overvoltage suppression circuit further comprises a rectifier element provided in antiparallel to the switching element.
[0083] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]
[0084] 2a, 2b…AC circuits, 10…Power converter, 11, 11a~11c…First converter, 12, 12a~12c…Second converter, 14…Overvoltage suppression circuit, 16…Voltage detector, 18…Control device, 21a~21c…DC terminals, 22a~22c…AC terminals, 24…Switching element, 26…Charge storage element, 31a, 31b…DC terminals, 32a~32c…AC terminals, 34…Switching element, 40…Resistor element, 42…Switching element, 44, 46…Rectifier element
Claims
1. A converter having a pair of DC terminals, which performs at least one of the following operations: converting DC power supplied through the pair of DC terminals into another power, and converting another power into DC power and outputting the converted DC power to the pair of DC terminals. An overvoltage suppression circuit connected to the pair of DC terminals and performing an overvoltage suppression operation to suppress overvoltage of the DC voltage between the pair of DC terminals, A control device that controls the operation of the converter and the overvoltage suppression circuit, A voltage detector that detects the magnitude of the DC voltage between the pair of DC terminals and inputs a voltage detection value representing the detection result of the magnitude of the DC voltage between the pair of DC terminals to the control device, Equipped with, The overvoltage suppression circuit described above is Resistor element and, A switching element that switches between a first state in which the resistive element is connected between the pair of DC terminals and a second state in which the connection between the resistive element and the pair of DC terminals is removed, It has, The control device sets two thresholds for the voltage detection value: an operating level and a stop level set to a value lower than the operating level. When the voltage detection value becomes equal to or greater than the operating level, it causes the overvoltage suppression circuit to perform the overvoltage suppression operation. After the overvoltage suppression circuit has performed the overvoltage suppression operation, when the voltage detection value falls below the stop level, it causes the overvoltage suppression circuit to stop performing the overvoltage suppression operation. During the period in which the overvoltage suppression circuit performs the overvoltage suppression operation, the power conversion device controls the switching of the switching element so that the equivalent resistance value of the overvoltage suppression circuit with respect to the DC voltage between the pair of DC terminals becomes a desired resistance value.
2. The power conversion device according to claim 1, wherein the control device alternately switches between the first state and the second state during the period in which the overvoltage suppression circuit performs the overvoltage suppression operation, and controls the switching of the switching element to change the time ratio between the period of the first state and the period of the second state, thereby controlling the equivalent resistance value of the overvoltage suppression circuit to a desired resistance value.
3. The converter further includes a charge storage element provided between the pair of DC terminals, The power conversion device according to claim 2, wherein the control device makes the switching period between the first state and the second state shorter than the time constant calculated by the product of the charge storage element and the resistive element.
4. The power conversion device according to claim 3, wherein the control device makes the period shorter than 0.1 times the time constant.
5. The power conversion device according to claim 2, wherein the control device increases the ratio of the period of the first state as the voltage detection value increases during the period in which the overvoltage suppression circuit performs the overvoltage suppression operation.
6. The resistive element is provided between the pair of DC terminals, The power conversion device according to claim 1, wherein the switching element is provided between the resistive element and one of the pair of DC terminals.
7. The overvoltage suppression circuit further comprises a rectifier element provided in parallel with the resistive element, The power conversion device according to claim 6, wherein the direction of the current flowing through the rectifier element is opposite to the direction of the current flowing through the resistive element when the overvoltage suppression circuit is in the first state.
8. The power conversion device according to claim 6, wherein the overvoltage suppression circuit further comprises a rectifier element provided in antiparallel to the switching element.