Power converter

Abstract

A power converter (1) is provided with: transistors (Q11, Q12); an inverter control unit (10) that outputs gate pulses for controlling the transistors (Q11, Q12); a function safety control unit (20) for turning on and outputting a gate drive permission signal when the soundness of the gate cutoff function is not determined; a shut-off circuit (31) that outputs, as a drive signal, the result of the logical AND operation of the gate pulse and the gate drive permission signal; a gate drive circuit (41) that outputs a gate signal on the basis of the drive signal; and a current detection unit (61) that detects a current flowing through a phase including the transistors (Q11, Q12) and outputs a current value, and the function safety control unit (20), on the basis of the current value and the gate signal, determines that the gate signal has changed to ON during a period in which the current does not flow through the transistors (Q11, Q12), and, after determining that the gate signal has changed to ON, outputs the current value to the transistor (Q11, Q12). The gate drive permission signal is temporarily turned off during a period in which the gate pulse is turned on, and whether or not the gate signal has changed to be turned off is determined.

Description

Technical Field

[0001] The present invention relates to a power converter having a power conversion transistor. Background Art

[0002] In recent years, power converters such as inverters and servo amplifiers that drive motors at variable speeds have become popular due to the need for energy conservation. On the other hand, abnormal operation of electrical equipment can sometimes lead to serious accidents, so manufacturers are seeking to improve safety functions. In addition, strict safety specifications are set in each stage of product development, design, production, maintenance, and disposal to suppress the impact on the human body within the allowable range.

[0003] In particular, regarding electrical equipment, there are functional safety standards such as IEC (International Electrotechnical Commission) 61508 and standards such as IEC 61800-5-2 that take into account motor drive systems such as inverters and servo amplifiers.

[0004] In order to comply with these safety standards, electrical equipment needs to be equipped with a functional safety system that has a safety function that does not provide driving force to the electrical equipment and a monitoring function that monitors abnormalities in the safety function. In order to show that the safety standards specified in the safety standards are met, the circuits that constitute the functional safety system need to perform quantitative evaluations such as Failure Modes Effects and Diagnostics Analysis (FMEDA). In addition, when the circuit is changed, impact analysis needs to be implemented for continuous management. Therefore, for functional safety systems, the larger the circuit scale, the higher the management cost.

[0005] In the case of stopping the motor, it has a safe torque off function, i.e., STO (Safe Torque Off) function, which cuts off the energy supplied to the motor. The safe torque off function is implemented by a safety device, etc., which sets a gate drive circuit with a cut-off function between the main circuit and the control device, and cuts off the control signal by shutting down the gate drive circuit according to a cut-off instruction from an independently set safety function circuit, thereby stopping the power supply from the main circuit to the motor, wherein the main circuit supplies power for driving the motor, and the control device generates a control signal for controlling the switching device of the main circuit. As one of the cut-off conditions of the gate drive circuit, the safety function circuit outputs a cut-off instruction when a safe torque off instruction, i.e., a cut-off signal, is input from the outside.

[0006] However, in the case where the cutoff signal is not always input, it is unknown whether the gate drive circuit operates normally when the cutoff signal is actually input. If an attempt is made to input a cutoff signal in a simulated manner to confirm whether the safe torque cutoff function operates normally, the operation of the power converter must be stopped, and the operation rate will decrease. As another method, there is a method of checking the soundness by applying a short-time cutoff confirmation pulse to the gate signal of the gate drive circuit, to which the transistor of the main circuit cannot respond, to investigate the response of the gate drive circuit.

[0007] However, the time width of the confirmation pulse is strictly limited in the following aspects. First, the thickness of the wafer of the switching device, i.e., the transistor, used in the main circuit becomes thinner, and high-speed cut-off is required in the event of an abnormality. Therefore, it is necessary to speed up the response of the gate drive circuit, and the transistor will respond to a short confirmation pulse. As a result, when the integrity of the safe torque disconnection function is confirmed, the error of the output voltage from the main circuit increases. Next, the switching speed of the transistor of the new generation of switching devices such as SiC (Silicon Carbide) becomes faster, and high-frequency switching is performed to utilize this feature. Therefore, it is necessary to speed up the response of the entire gate drive circuit including the cut-off circuit, and the transistor will respond even to a short confirmation pulse. As a result, the error of the output voltage from the main circuit increases because the cut-off confirmation becomes a gate state different from the instruction of the control device.

[0008] To address such a problem, the following technology is disclosed in Patent Document 1, namely, in one on-off cycle of PWM (Pulse Width Modulation) control, the power supply of the gate driving element, i.e., the photocoupler, is cut off when the converter control gate pulse becomes off, the power cut-off state is monitored, and the operation of the gate cut-off function is confirmed, thereby confirming the integrity of the gate cut-off function without affecting the converter control.

[0009] Patent Document 1: Japanese Patent Application Publication No. 2016-127702 Summary of the invention

[0010] However, according to the above-mentioned prior art, there is a problem that it is impossible to confirm the abnormality of the output side of the gate driving element and the state of the gate signal actually input to the transistor. In addition, according to the above-mentioned prior art, in order to perform the operation confirmation of the aforementioned gate cut-off function in a short time such as the timing of the converter control gate pulse turning off in one cycle of the on-off of the PWM control, it is necessary to transmit the information of the on-off timing of the PWM control to the functional safety system, and the independence of the functional safety system and the converter control system cannot be maintained.

[0011] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to obtain a power converter capable of confirming the soundness of a gate cutoff function for a power conversion transistor without affecting normal operation.

[0012] In order to solve the above-mentioned problems and achieve the purpose, the power converter of the present invention is characterized in that it has: two transistors connected in series for use in power conversion; a converter control unit, which outputs a gate pulse for controlling the on and off of the transistor for each transistor; a functional safety control unit, which sets the gate drive enable signal to be turned on and outputs it for each transistor when the soundness of the gate cut-off function of the transistor is not determined; two cut-off circuits, which correspond to each of the two transistors and output the result of the logical AND operation using the gate pulse and the gate drive enable signal as a drive signal; two gate drive circuits, which correspond to each of the two transistors and output the gate signal for driving the transistor to the transistor and the functional safety control unit based on the drive signal; and a current detection unit, which detects the current flowing through the phase including the two transistors and outputs the detection result as a current value to the functional safety control unit. For each transistor, based on the current value and the gate signal, after confirming that the gate signal has changed to on during a period when current is not flowing through the transistor, the functional safety control unit temporarily sets the gate drive enable signal to off during the period when the gate pulse is on, and determines whether the gate signal has changed to off.

[0013] Effects of the Invention

[0014] The power converter of the present invention has an effect of being able to check the soundness of the gate cutoff function of the power conversion transistor without affecting normal operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram showing a configuration example of a power converter according to the first embodiment.

[0016] Figure 2 This is a diagram showing an example of an operation waveform of the power converter according to the first embodiment.

[0017] Figure 3 This is a flowchart showing the operation of the power converter according to the first embodiment.

[0018] Figure 4 This is a diagram showing a configuration example of hardware that realizes a processing circuit of the power converter according to the first embodiment.

[0019] Figure 5 This is a diagram showing a configuration example of a power converter according to the second embodiment.

[0020] Figure 6 FIG. 1 is a first diagram showing an example of an operation waveform of the power converter according to the second embodiment.

[0021] Figure 7 FIG. 2 is a second diagram showing an example of an operation waveform of the power converter according to the second embodiment.

[0022] Figure 8 This is a flowchart showing the operation of the power converter according to the second embodiment. DETAILED DESCRIPTION

[0023] Hereinafter, a power converter according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0024] Implementation Method 1

[0025] Figure 1 1 is a diagram showing a configuration example of a power converter 1 according to Embodiment 1. The power converter 1 includes a converter control unit 10, a functional safety control unit 20, cutoff circuits 31, 32, gate drive circuits 41, 42, gate signal branching units 51, 52, transistors Q11, Q12, freewheeling diodes D11, D12, and a current detection unit 61.

[0026] The converter control unit 10 is a control unit for performing normal power conversion control in the power converter 1. The converter control unit 10 outputs a gate pulse GP11 used for power conversion control, that is, for controlling the gate connection and gate disconnection of the transistor Q11 of the main circuit, to the disconnection circuit 31. Similarly, the converter control unit 10 outputs a gate pulse GP12 used for power conversion control, that is, for controlling the gate connection and gate disconnection of the transistor Q12 of the main circuit, to the disconnection circuit 32. That is, the converter control unit 10 outputs gate pulses GP11 and GP12 for controlling the on and off of the transistors Q11 and Q12 for each transistor Q11 and Q12. In the following description, gate connection is simply referred to as connection, and gate disconnection is simply referred to as disconnection. The main circuit is, for example, an inverter that supplies power to an electric motor not shown in the figure in the power converter 1, but is not limited to this.

[0027] The functional safety control unit 20 is a control unit for performing functional safety control in the power converter 1. Functional safety control refers to the control of a functional safety system having a safety function of not giving a driving force to an electrical device and a monitoring function of monitoring an abnormality of the safety function as described in the background art. In the present embodiment, the functional safety control is the control of the function of safely stopping the power converter 1, specifically, the control of the execution of the gate cutoff and the soundness confirmation action of the gate cutoff function. The functional safety control unit 20 outputs the gate drive enable signal SAF11 for functional safety control to the cutoff circuit 31, and outputs the gate drive enable signal SAF12 for functional safety control to the cutoff circuit 32. The functional safety control unit 20 sets the gate drive enable signals SAF11 and SAF12 to be turned on and output in normal times. Here, normal times refer to the state in which the gate cutoff and the soundness confirmation action of the gate cutoff function are not executed in the power converter 1. The time other than normal times refers to the state in which the gate cutoff and the soundness confirmation action of the gate cutoff function are being executed in the power converter 1. As described above, the functional safety control unit 20 turns on and outputs the gate drive permission signal SAF11 for transistor Q11 when the soundness of the gate cutoff function for transistor Q11 is not determined. The functional safety control unit 20 turns on and outputs the gate drive permission signal SAF12 for transistor Q12 when the soundness of the gate cutoff function for transistor Q12 is not determined.

[0028] When the gate pulse GP11 output from the converter control unit 10 and the gate drive permission signal SAF11 output from the functional safety control unit 20 are both turned on, the cut-off circuit 31 turns on and outputs the drive signal for driving the gate drive circuit 41. Specifically, the cut-off circuit 31 is an AND circuit that performs a logical AND operation using the gate pulse GP11 and the gate drive permission signal SAF11, and outputs the result of the logical AND operation as the drive signal. Similarly, when the gate pulse GP12 output from the converter control unit 10 and the gate drive permission signal SAF12 output from the functional safety control unit 20 are both turned on, the cut-off circuit 32 turns on and outputs the drive signal for driving the gate drive circuit 42. Specifically, the cut-off circuit 32 is an AND circuit that performs a logical AND operation using the gate pulse GP12 and the gate drive permission signal SAF12, and outputs the result of the logical AND operation as the drive signal.

[0029] Since the cut-off circuit 31 performs the above-mentioned operation, the functional safety control unit 20 can set the output of the cut-off circuit 31 to be off by setting the gate drive permission signal SAF11 for the cut-off circuit 31 to be off. That is, the functional safety control unit 20 can cut off the gate pulse GP11 for normal power conversion control output from the converter control unit 10 in the power converter 1, and set the transistor Q11 to the gate-off state. Similarly, since the cut-off circuit 32 performs the above-mentioned operation, the functional safety control unit 20 can set the output of the cut-off circuit 32 to be off by setting the gate drive permission signal SAF12 for the cut-off circuit 32 to be off. That is, the functional safety control unit 20 can cut off the gate pulse GP12 for normal power conversion control output from the converter control unit 10 in the power converter 1, and set the transistor Q12 to the gate-off state.

[0030] The gate drive circuit 41 corresponds to the transistor Q11, and outputs a gate signal for driving the transistor Q11 based on the drive signal output from the cut-off circuit 31. That is, the gate drive circuit 41 drives the transistor Q11 according to the drive signal output from the cut-off circuit 31. Specifically, the gate drive circuit 41 sets the gate signal to be turned on and outputs it when the drive signal is turned on, and sets the gate signal to be turned off and outputs it when the drive signal is turned off. Similarly, the gate drive circuit 42 corresponds to the transistor Q12, and outputs a gate signal for driving the transistor Q12 based on the drive signal output from the cut-off circuit 32. That is, the gate drive circuit 42 drives the transistor Q12 according to the drive signal output from the cut-off circuit 32. Specifically, the gate drive circuit 42 sets the gate signal to be turned on and outputs it when the drive signal is turned on, and sets the gate signal to be turned off and outputs it when the drive signal is turned off.

[0031] The gate signal branching section 51 branches the gate signal output from the gate drive circuit 41 to the transistor Q11. The gate signal branching section 51 outputs one of the branched gate signals to the transistor Q11, and sets the other of the branched gate signals as the feedback signal to the functional safety control section 20, that is, the gate signal FBQ11, and feeds it back to the functional safety control section 20. Similarly, the gate signal branching section 52 branches the gate signal output from the gate drive circuit 42 to the transistor Q12. The gate signal branching section 51 outputs one of the branched gate signals to the transistor Q12, and sets the other of the branched gate signals as the feedback signal to the functional safety control section 20, that is, the gate signal FBQ12, and feeds it back to the functional safety control section 20.

[0032] Here, from the necessity of controlling the operation of the transistor Q11, the current value of the gate signal output from the gate drive circuit 41 to the transistor Q11 is larger than the current value of the drive signal output from the cut-off circuit 31 to the gate drive circuit 41. Therefore, if the gate signal branching section 51 simply branches the gate signal, a large current will flow through the functional safety control section 20 as the gate signal FBQ11. Therefore, the gate signal branching section 51 branches the gate signal output from the gate drive circuit 41 to the transistor Q11 in such a way that the current value of the gate signal FBQ11 fed back to the functional safety control section 20 is less than or equal to the specified current value. As for the cut-off circuit 31, in order to ensure the amount of current required for the operation control of the transistor Q11, the current value of the gate signal may be slightly increased in advance and output in consideration of the amount of current branched to the functional safety control section 20 by the gate signal branching section 51. Similarly, from the necessity of controlling the operation of the transistor Q12, the current value of the gate signal output from the gate drive circuit 42 to the transistor Q12 is larger than the current value of the drive signal output from the cutoff circuit 32 to the gate drive circuit 42. Therefore, if the gate signal branching section 52 simply branches the gate signal, a large current will flow through the functional safety control section 20 as the gate signal FBQ12. Therefore, the gate signal branching section 52 branches the gate signal output from the gate drive circuit 42 to the transistor Q12 in such a manner that the current value of the gate signal FBQ12 fed back to the functional safety control section 20 is less than or equal to the specified current value. As for the cutoff circuit 32, in order to ensure the amount of current required for the operation control of the transistor Q12, the current value of the gate signal may be slightly increased in advance in consideration of the amount of current branched to the functional safety control section 20 by the gate signal branching section 52. Furthermore, the power converter 1 may prevent a large current from flowing into the functional safety control unit 20 by adjusting the input impedance of the transistors Q11 and Q12 and the functional safety control unit 20 , thereby preventing the gate signal branching units 51 and 52 from having the above-mentioned function.

[0033] It can also be said that in the power converter 1, the gate drive circuit 41 outputs the gate signal to the transistor Q11 and the functional safety control unit 20 via the gate signal branch unit 51. Similarly, it can also be said that the gate drive circuit 42 outputs the gate signal to the transistor Q12 and the functional safety control unit 20 via the gate signal branch unit 52.

[0034] The transistor Q11 is a switching device included in the main circuit and performs power conversion in the power converter 1. The power conversion transistor Q11 used for power conversion is turned on and off according to the gate signal output from the gate drive circuit 41. Specifically, the transistor Q11 is gate-on when the gate signal is on, and is gate-off when the gate signal is off. Similarly, the transistor Q12 is a switching device included in the main circuit and performs power conversion in the power converter 1. The power conversion transistor Q12 used for power conversion is turned on and off according to the gate signal output from the gate drive circuit 42. Specifically, the transistor Q12 is gate-on when the gate signal is on, and is gate-off when the gate signal is off. In the present embodiment, the transistors Q11 and Q12 will not be gate-on at the same time.

[0035] The flywheel diode D11 is a diode connected in parallel with the transistor Q11. Similarly, the flywheel diode D12 is a diode connected in parallel with the transistor Q12.

[0036] The current detection unit 61 detects the current I1 flowing through the phase including the transistors Q11 and Q12. The current I1 flowing through the phase is the current flowing through the connection line between the power converter 1 and the motor (not shown) supplied with power by the power converter 1. Specifically, the current detection unit 61 detects the current I1 flowing through the transistor Q11, or the flyback diode D11, or the transistor Q12, or the flyback diode D12. The current detection unit 61 outputs the detection result, i.e., the detected current I1, to the functional safety control unit 20 as a feedback signal, i.e., the current value FBI1. The current I1 is given to the functional safety control unit 20. Figure 1 The arrow shown in the figure is assumed to be in the positive direction. Figure 1 The arrows shown are in the opposite direction of the flow, which is negative. Figure 1 In the example of FIG. 1 , when the current I1 flows through the transistor Q11 or the flyback diode D12 , the current I1 is positive, and when the current I1 flows through the flyback diode D11 or the transistor Q12 , the current I1 is negative.

[0037] The functional safety control unit 20 monitors the gate signal FBQ11 fed back from the gate signal branch unit 51, the gate signal FBQ12 fed back from the gate signal branch unit 52, and the current value FBI1 output from the current detection unit 61. That is, the functional safety control unit 20 monitors the gate signal output from the gate drive circuit 41 to the transistor Q11, the gate signal output from the gate drive circuit 42 to the transistor Q12, and the current I1 flowing through the transistor Q11 or the flyback diode D11 or the transistor Q12 or the flyback diode D12.

[0038] Next, a description will be given of a mechanism for checking the soundness of the gate cutoff function in the power converter 1. In the first embodiment, the gate cutoff function is a function for setting the transistors Q11 and Q12 to a gate-off state when some abnormality is detected in the power converter 1.

[0039] In the power converter 1, the current I1 flows through the transistor Q11 or the flyback diode D12 when the current I1 is in a positive direction, and flows through the flyback diode D11 or the transistor Q12 when the current I1 is in a negative direction. When the current I1 flows through the flyback diode D11, even if the transistor Q11 is turned on at the gate, the current I1 does not flow through the transistor Q11, and continues to flow through the flyback diode D11. Therefore, even if the gate of the transistor Q11 is turned on during the period when the current I1 flows in a negative direction, the current I1 does not flow through the transistor Q11, so the power converter 1 is not affected by the output voltage to be generated by the original converter control. Similarly, when the current I1 flows through the flyback diode D12, even if the transistor Q12 is turned on at the gate, the current I1 does not flow through the transistor Q12, and continues to flow through the flyback diode D12. Therefore, even if the gate of the transistor Q12 is turned on while the current I1 is flowing in the positive direction, the current I1 does not flow through the transistor Q12 , and thus the power converter 1 is not affected by the output voltage to be generated by the original converter control.

[0040] Since the current value FBI1 is fed back from the current detection unit 61, the functional safety control unit 20 can detect in which direction the current I1 flows, positive or negative, based on the current value FBI1. In addition, since the gate signal FBQ11 is fed back from the gate signal branch unit 51, the functional safety control unit 20 can detect the state of the gate signal given to the transistor Q11. Therefore, the functional safety control unit 20 first detects the period during which the current I1 flows in the negative direction based on the current value FBI1 fed back from the current detection unit 61. Even during the period during which the current I1 flows in the negative direction, the converter control unit 10 appropriately turns on or off and outputs the gate pulse GP11 in order to control the operation of the equipment connected to the power converter 1, regardless of the operation of the functional safety control unit 20, etc.

[0041] As described above, since the functional safety control unit 20 turns on the gate drive permission signal SAF11 and outputs it, the converter control unit 10 turns on the gate pulse GP11, so that the cutoff circuit 31 turns on the drive signal and outputs it to the gate drive circuit 41. As a result, the gate drive circuit 41 turns on the gate signal and outputs it to the transistor Q11 based on the turned-on drive signal from the cutoff circuit 31. The gate signal branching unit 51 branches the turned-on gate signal output from the gate drive circuit 41 to the transistor Q11, and feeds back the gate signal FBQ11 to the functional safety control unit 20. The functional safety control unit 20 can detect that the gate signal output from the gate drive circuit 41 is turned on by the feedback of the gate signal FBQ11 from the gate signal branching unit 51.

[0042] The functional safety control unit 20 sets the gate drive enable signal SAF11 to be off during the period when the current I1 flows in a negative direction and the gate signal output from the gate drive circuit 41 is on. Since the gate drive enable signal SAF11 output from the functional safety control unit 20 becomes off, the cutoff circuit 31 sets the drive signal for the gate drive circuit 41 to be off and outputs it. Based on the off drive signal from the cutoff circuit 31, the gate drive circuit 41 sets the gate signal to be off and outputs it to the transistor Q11. The gate signal branching unit 51 branches the off gate signal output from the gate drive circuit 41 to the transistor Q11, and feeds back the gate signal FBQ11 to the functional safety control unit 20.

[0043] The functional safety control unit 20 can detect that the gate signal output from the gate drive circuit 41 is disconnected through the feedback of the gate signal FBQ11 from the gate signal branch unit 51. Therefore, since the gate signal for the transistor Q11 becomes disconnected by setting the gate drive enable signal SAF11 to be disconnected, the functional safety control unit 20 can determine that the gate cutoff function is normal. The functional safety control unit 20 sets the gate drive enable signal SAF11 to be disconnected during the period when the current I1 flows in a negative direction and the gate signal output from the gate drive circuit 41 is turned on. Thereafter, when it is not possible to detect that the gate signal output from the gate drive circuit 41 is disconnected through the feedback of the gate signal FBQ11 from the gate signal branch unit 51, it is determined that the gate cutoff function is abnormal.

[0044] Figure 2 1 is a diagram showing an example of an operation waveform of the power converter 1 according to the first embodiment. Figure 2, the I1 current value is the current I1 detected by the current detection unit 61, and is the current value FBI1 fed back from the current detection unit 61 to the functional safety control unit 20. The Q11 gate pulse is the gate pulse GP11 output from the converter control unit 10. The Q11 gate drive enable signal is the gate drive enable signal SAF11 output from the functional safety control unit 20. The Q11 gate drive circuit output is the gate signal output from the gate drive circuit 41 to the transistor Q11, and is the gate signal FBQ11 fed back from the gate signal branch unit 51 to the functional safety control unit 20. In addition, the description of the signals associated with the transistor Q12, namely the gate pulse GP12, the gate drive enable signal SAF12 and the gate signal FBQ12, is omitted.

[0045] The functional safety control unit 20 determines that the gate cutoff function is normal if the gate signal output from the gate drive circuit 41, i.e., the gate signal FBQ11, is turned off by temporarily turning off the gate drive permission signal SAF11 during the period when the gate pulse GP11 is turned on after confirming that the gate signal output from the gate drive circuit 41, i.e., the gate signal FBQ11, is turned off during the period when the current I1 flows in the negative direction. The functional safety control unit 20 determines that the gate cutoff function is abnormal if it cannot detect that the gate signal output from the gate drive circuit 41, i.e., the gate signal FBQ11, is turned off under the same conditions as above.

[0046] Here, the functional safety control unit 20 does not know the period for which the converter control unit 10 turns on the gate pulse GP11 and outputs it. However, if the information of the shortest period for which the gate pulse GP11 is continuously turned on when the converter control unit 10 turns on the gate pulse GP11 is pre-set, the functional safety control unit 20 can perform the above-mentioned operation by temporarily turning off the gate drive permission signal SAF11 during the shortest period for the gate pulse GP11 to be turned on, that is, turning it on again after being turned off. In addition, the functional safety control unit 20 can also select the shortest on period as the shortest period for the gate pulse GP11 to be continuously turned on from the period for which the gate signal FBQ11 fed back by the gate signal branch unit 51 is turned on when the power converter 1 performs the prescribed period operation. Alternatively, when the power converter 1 supplies power to an electric motor not shown in the figure, usually, in order to make the operation of the electric motor smooth, the power converter 1 will not change the control content extremely in the middle. For the functional safety control unit 20, when the on-period of the previous gate pulse GP11 is greater than or equal to the prescribed period, it can be expected that a certain degree of on-period can be ensured during the on-period of the next gate pulse GP11, for example, even if the on-period is shorter than the previous one. Therefore, the functional safety control unit 20 may temporarily turn off the gate drive enable signal SAF11 during the on-period of the next gate pulse GP11, which can be expected to ensure a certain degree of on-period, based on the on-period of the previous gate pulse GP11.

[0047] As described above, in the power converter 1, the functional safety control unit 20, based on the current value FBI1 and the gate signal FBQ11, temporarily sets the gate drive enable signal SAF11 to be off during a period when the current I1 flows in a negative direction, that is, during a period when the current I1 does not flow through the transistor Q11, and when the gate signal is on, and determines the integrity of the gate cutoff function for the transistor Q11 by whether the gate signal to the transistor Q11 changes to off.

[0048] The operation of the power converter 1 will be described using a flowchart. Figure 3Flowchart showing the operation of the power converter 1 according to Embodiment 1. In the power converter 1, the functional safety control unit 20 determines whether the flow direction of the current I1 is negative, that is, whether the current value FBI1 fed back from the current detection unit 61 is negative (step S11). When the current value FBI1 is positive (step S11: No), the functional safety control unit 20 performs the operation of step S11 again. When the current value FBI1 is negative (step S11: Yes), the functional safety control unit 20 confirms whether the gate signal output from the gate drive circuit 41 to the transistor Q11 is turned on, that is, whether the gate signal FBQ11 fed back from the gate signal branch unit 51 is turned on (step S12). When the gate signal FBQ11 is turned off (step S12: No), the functional safety control unit 20 performs the operation of step S11 again.

[0049] When the gate signal FBQ11 is on (step S12: Yes), the functional safety control unit 20 temporarily turns off the gate drive enable signal SAF11 during the period when the gate signal FBQ11 is on (step S13). The functional safety control unit 20 temporarily turns off the gate drive enable signal SAF11 to confirm whether the gate signal output from the gate drive circuit 41 to the transistor Q11 has changed to be off, that is, whether the gate signal FBQ11 fed back from the gate signal branch unit 51 has changed to be off (step S14). When the gate signal FBQ11 changes to be off (step S14: Yes), the functional safety control unit 20 determines that the gate cutoff function is normal (step S15). In detail, when the functional safety control unit 20 turns the gate drive enable signal SAF11 from being turned on temporarily to being turned off and then turned on again, in accordance with the change of the gate drive enable signal SAF11, when the gate signal FBQ11 fed back from the gate signal branch unit 51 successfully confirms the change of being turned on→off→on, the gate cutoff function is determined to be normal. When the gate signal FBQ11 does not change to being turned off (step S14: No), the functional safety control unit 20 determines that the gate cutoff function is abnormal (step S16). The functional safety control unit 20 may also determine that the gate cutoff function is abnormal when the gate signal FBQ11 changes to being turned off when the gate drive enable signal SAF11 is turned off, but when the gate signal FBQ11 does not change to being turned on when the gate drive enable signal SAF11 is turned on again. When the functional safety control unit 20 determines that the gate cutoff function is abnormal, the gate drive enable signals SAF11 and SAF12 are turned off (step S17).

[0050] Here, if Figure 2As shown, when an abnormality is detected in the determination of the soundness of the gate cut-off function of the transistor Q11, the functional safety control unit 20 may not be able to turn off the gate signal FBQ11 as the feedback signal, that is, the gate signal output from the gate drive circuit 41 to the transistor Q11, even if the gate drive permission signal SAF11 is turned off. However, the functional safety control unit 20 can turn off the gate signal output from the gate drive circuit 42 to the transistor Q12 by turning off the gate drive permission signal SAF12 for the transistor Q12. In this case, the functional safety control unit 20 can issue an alarm to the user of the power converter 1, etc. to indicate that an abnormality has been detected in the soundness of the gate cut-off function, and can also perform control such as cutting off the power supply to the converter control unit 10 and stopping the output of the gate pulses GP11 and GP12 from the converter control unit 10 when the operation of the power converter 1 is to be stopped. As a result, the functional safety control unit 20 can set both the transistors Q11 and Q12 to the gate-off state.

[0051] The operation of the functional safety control unit 20 determining the soundness of the gate cutoff function for the transistor Q11 has been described, but the operation of the functional safety control unit 20 determining the soundness of the gate cutoff function for the transistor Q12 is also the same. When determining the soundness of the gate cutoff function for the transistor Q12, the functional safety control unit 20 temporarily turns off the gate drive permission signal SAF12 during the period when the current I1 flows in the positive direction and the gate of the transistor Q12 is turned on, and checks whether the gate signal FBQ12 is turned off.

[0052] As described above, the functional safety control unit 20 temporarily turns off the gate drive permission signal SAF11 during the period when the gate pulse GP11 is on after confirming that the gate signal FBQ11 has turned on, and determines whether the gate signal FBQ11 has turned off. Similarly, the functional safety control unit 20 temporarily turns off the gate drive permission signal SAF12 during the period when the gate pulse GP12 is on, and determines whether the gate signal FBQ12 has turned off, based on the current value of the current I1 and the gate signal FBQ12 during the period when the current does not flow through the transistor Q12. In addition, when the functional safety control unit 20 determines that the gate cutoff function of one transistor is abnormal, it turns off the gate drive permission signals SAF11 and SAF12 for the two transistors Q11 and Q12.

[0053] Next, the hardware structure of the power converter 1 realizing the first embodiment is described. In the power converter 1, the cut-off circuits 31 and 32 are electrical circuits constituting an AND circuit. The gate drive circuits 41 and 42 are electrical circuits that amplify the current value of the drive signal output from the cut-off circuits 31 and 32. The gate signal branching parts 51 and 52 are electrical circuits that branch the gate signal. The current detection part 61 is a sensor. The transistors Q11 and Q12 and the freewheeling diodes D11 and D12 are semiconductor elements. The converter control part 10 and the functional safety control part 20 are realized by a processing circuit. Figure 4 1 is a diagram showing a configuration example of hardware that realizes a processing circuit of the power converter 1 according to the first embodiment. Figure 4 A configuration example is shown in which the converter control unit 10 and the functional safety control unit 20 are realized by a processing circuit 90 including a processor 91 and a memory 92 .

[0054] The processor 91 is a CPU (Central Processing Unit). The processor 91 may also be a computing device, a microprocessor, a microcomputer, or a DSP (Digital Signal Processor). The memory 92 is a volatile or non-volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), or an EEPROM (registered trademark) (Electrically Erasable Programmable Read Only Memory).

[0055] The memory 92 stores programs for operating as the converter control unit 10 and the functional safety control unit 20. The processor 91 reads and executes the program, so that the converter control unit 10 and the functional safety control unit 20 can be realized. In addition, the program for operating as the converter control unit 10 and the functional safety control unit 20 stored in the memory 92 can be provided to the user in a state of being written on a recording medium such as a CD (Compact Disc)-ROM, a DVD (Digital Versatile Disc)-ROM, etc., or can be provided via a network. In addition, the processor 91 outputs data such as calculation results to the volatile memory of the memory 92. Alternatively, the processor 91 saves the data by outputting data such as calculation results to an auxiliary storage device via the volatile memory of the memory 92.

[0056] Figure 4This is an example of hardware in which the converter control unit 10 and the functional safety control unit 20 are implemented by a general-purpose processor 91 and a memory 92, but the converter control unit 10 and the functional safety control unit 20 may be implemented by a dedicated processing circuit instead of the processor 91 and the memory 92. Here, the dedicated processing circuit is a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a circuit composed of these. In addition, a part of the converter control unit 10 and the functional safety control unit 20 may be implemented by the processor 91 and the memory 92, and the rest may be implemented by a dedicated processing circuit.

[0057] As described above, according to the present embodiment, in the power converter 1, the functional safety control unit 20 determines the period during which the current I1 does not flow through the transistor Q11 based on the current value FBI1 from the current detection unit 61, and determines the period during which the gate signal to the transistor Q11 is turned on based on the gate signal FBQ11 from the gate signal branch unit 51. During the period during which the current I1 does not flow through the transistor Q11, when the gate signal to the transistor Q11 is turned on, the functional safety control unit 20 temporarily turns off the gate drive permission signal SAF11, and determines the soundness of the gate cutoff function for the transistor Q11 by whether the gate signal to the transistor Q11 changes to off. Similarly, the functional safety control unit 20 determines the period during which the current I1 does not flow through the transistor Q12 based on the current value FBI1 from the current detection unit 61, and determines the period during which the gate signal to the transistor Q12 is turned on based on the gate signal FBQ12 from the gate signal branch unit 52. The functional safety control unit 20 temporarily turns off the gate drive permission signal SAF12 when the gate signal to the transistor Q12 is on during the period when the current I1 does not flow through the transistor Q12, and determines the soundness of the gate cutoff function for the transistor Q12 by whether the gate signal to the transistor Q12 changes to off. Thus, the functional safety control unit 20 can confirm the soundness of the gate cutoff function for the power conversion transistors Q11 and Q12 without affecting the normal operation of the power converter 1.

[0058] In addition, the functional safety control unit 20 can confirm the soundness of the gate cutoff function of the transistors Q11 and Q12 of the main circuit without using a short confirmation pulse that the main circuit cannot respond to. In addition, the functional safety control unit 20 can monitor the output status of the gate drive circuits 41 and 42, so it is possible to confirm the soundness including the state of the gate signal actually input to the transistors Q11 and Q12. In addition, the functional safety control unit 20 operates independently without obtaining information such as the timing of the control from the converter control unit 10, so the independence of the converter control unit 10 and the functional safety control unit 20 can be maintained. In addition, the functional safety control unit 20 can confirm the soundness of the gate cutoff function in a state that will not affect the output voltage that is expected to be generated by the original converter control without stopping the operation of the power converter 1, so the reliability of the power converter 1 can be improved.

[0059] Implementation Method 2

[0060] In the first embodiment, the power converter 1 determines whether the gate cutoff function is normal or not by taking two transistors Q11 and Q12, i.e., one branch of a pair of transistors as an object. In the second embodiment, the power converter determines whether the gate cutoff function is normal or not by taking multiple branches of multiple transistor pairs as an object.

[0061] Figure 5 : is a diagram showing a structural example of a power converter 1a involved in Embodiment 2. The power converter 1a has a converter control unit 10a, a functional safety control unit 20a, cut-off circuits 31 to 34, gate drive circuits 41 to 44, gate signal branch units 51 to 54, transistors Q11, Q12, Q21, Q22, freewheeling diodes D11, D12, D21, D22, and current detection units 61, 62. In Embodiment 2, the power converter 1a has a plurality of transistors Q11, Q12, Q21, Q22, that is, a plurality of branches. In addition, the power converter 1a has a plurality of cut-off circuits 31 to 34, a plurality of gate drive circuits 41 to 44, and a plurality of gate signal branch units 51 to 54 corresponding to each of the plurality of transistors Q11, Q12, Q21, Q22. In addition, the power converter 1a has a plurality of current detection units 61, 62 corresponding to each of the plurality of branches. In addition, in Embodiment 2, as Figure 5 The power converter 1a is shown as an example in which the power converter 1a has four transistors Q11, Q12, Q21, and Q22, that is, two branches of two pairs of transistor pairs. However, the power converter may also have three or more branches.

[0062] The converter control unit 10a is a control unit for performing normal power conversion control in the power converter 1a. The converter control unit 10a outputs a gate pulse GP11 for power conversion control, i.e., for controlling the on / off of the transistor Q11 of the main circuit, to the cut-off circuit 31. In addition, the converter control unit 10a outputs a gate pulse GP12 for power conversion control, i.e., for controlling the on / off of the transistor Q12 of the main circuit, to the cut-off circuit 32. In addition, the converter control unit 10a outputs a gate pulse GP21 for power conversion control, i.e., for controlling the on / off of the transistor Q21 of the main circuit, to the cut-off circuit 33. In addition, the converter control unit 10a outputs a gate pulse GP22 for power conversion control, i.e., for controlling the on / off of the transistor Q22 of the main circuit, to the cut-off circuit 34. The main circuit is, for example, an inverter that supplies power to a motor (not shown) in the power converter 1a, but is not limited thereto.

[0063] The functional safety control unit 20a is a control unit for performing functional safety control in the power converter 1a. The functional safety control unit 20a outputs a gate drive enable signal SAF11 for functional safety control to the cut-off circuit 31, outputs a gate drive enable signal SAF12 for functional safety control to the cut-off circuit 32, outputs a gate drive enable signal SAF21 for functional safety control to the cut-off circuit 33, and outputs a gate drive enable signal SAF22 for functional safety control to the cut-off circuit 34. The functional safety control unit 20a turns on the gate drive enable signal SAF11 for the transistor Q11 when the soundness of the gate cut-off function for the transistor Q11 is not determined. The functional safety control unit 20a turns on the gate drive enable signal SAF12 for the transistor Q12 when the soundness of the gate cut-off function for the transistor Q12 is not determined. The functional safety control unit 20a turns on the gate drive enable signal SAF21 for the transistor Q21 when the soundness of the gate cut-off function for the transistor Q21 is not determined. The functional safety control unit 20 a turns on and outputs the gate drive permission signal SAF22 for the transistor Q22 when the soundness of the gate cutoff function for the transistor Q22 is not determined.

[0064] When the gate pulse GP21 output from the converter control unit 10a and the gate drive permission signal SAF21 output from the functional safety control unit 20a are both turned on, the cut-off circuit 33 sets the drive signal for driving the gate drive circuit 43 to be turned on and output. Specifically, the cut-off circuit 33 is an AND circuit that performs a logical AND operation using the gate pulse GP21 and the gate drive permission signal SAF21, and outputs the result of the logical AND operation as the drive signal. Similarly, when the gate pulse GP22 output from the converter control unit 10a and the gate drive permission signal SAF22 output from the functional safety control unit 20a are both turned on, the cut-off circuit 34 sets the drive signal for driving the gate drive circuit 44 to be turned on and output. Specifically, the cut-off circuit 34 is an AND circuit that performs a logical AND operation using the gate pulse GP22 and the gate drive permission signal SAF22, and outputs the result of the logical AND operation as the drive signal. Note that the operations of the cutoff circuits 31 and 32 are the same as those of the cutoff circuits 31 and 32 in the first embodiment.

[0065] Since the cut-off circuit 33 performs the above-mentioned operation, the functional safety control unit 20a can turn off the output of the cut-off circuit 33 by turning off the gate drive permission signal SAF21 for the cut-off circuit 33. That is, the functional safety control unit 20a can cut off the gate pulse GP21 for normal power conversion control output from the converter control unit 10a in the power converter 1a, and put the transistor Q21 in the gate-off state. Similarly, since the cut-off circuit 34 performs the above-mentioned operation, the functional safety control unit 20a can turn off the output of the cut-off circuit 34 by turning off the gate drive permission signal SAF22 for the cut-off circuit 34. That is, the functional safety control unit 20a can cut off the gate pulse GP22 for normal power conversion control output from the converter control unit 10a in the power converter 1a, and put the transistor Q22 in the gate-off state. In addition, the operation of the functional safety control unit 20a for the cut-off circuits 31 and 32 is the same as the operation of the functional safety control unit 20 for the cut-off circuits 31 and 32 in the first embodiment.

[0066] The gate drive circuit 43 corresponds to the transistor Q21, and outputs a gate signal for driving the transistor Q21 based on the drive signal output from the cut-off circuit 33. That is, the gate drive circuit 43 drives the transistor Q21 according to the drive signal output from the cut-off circuit 33. Specifically, the gate drive circuit 43 sets the gate signal to be turned on and outputs it when the drive signal is turned on, and sets the gate signal to be turned off and outputs it when the drive signal is turned off. Similarly, the gate drive circuit 44 corresponds to the transistor Q22, and outputs a gate signal for driving the transistor Q22 based on the drive signal output from the cut-off circuit 34. That is, the gate drive circuit 44 drives the transistor Q22 according to the drive signal output from the cut-off circuit 34. Specifically, the gate drive circuit 44 sets the gate signal to be turned on and outputs it when the drive signal is turned on, and sets the gate signal to be turned off and outputs it when the drive signal is turned off. In addition, the operations of the gate drive circuits 41 and 42 are the same as those of the gate drive circuits 41 and 42 in the first embodiment.

[0067] The gate signal branching section 53 branches the gate signal output from the gate drive circuit 43 to the transistor Q21. The gate signal branching section 53 outputs one of the branched gate signals to the transistor Q21, and sets the other of the branched gate signals as the feedback signal to the functional safety control unit 20a, namely, the gate signal FBQ21, and feeds it back to the functional safety control unit 20a. Similarly, the gate signal branching section 54 branches the gate signal output from the gate drive circuit 44 to the transistor Q22. The gate signal branching section 54 outputs one of the branched gate signals to the transistor Q22, and sets the other of the branched gate signals as the feedback signal to the functional safety control unit 20a, namely, the gate signal FBQ22, and feeds it back to the functional safety control unit 20a. In addition, the operation of the gate signal branching sections 51 and 52 is the same as the operation of the gate signal branching sections 51 and 52 in the first embodiment.

[0068] Similar to the gate signal branching parts 51 and 52, the gate signal branching part 53 outputs the gate signal branch from the gate drive circuit 43 to the transistor Q21 in such a manner that the current value of the gate signal FBQ21 fed back to the functional safety control part 20a is less than or equal to the specified current value. As for the cut-off circuit 33, in order to ensure the amount of current required for the operation control of the transistor Q21, the current value of the gate signal may be slightly increased in advance in consideration of the amount of current branched to the functional safety control part 20a by the gate signal branching part 53, and then the gate signal is output. In addition, the gate signal branching part 54 outputs the gate signal branch from the gate drive circuit 44 to the transistor Q22 in such a manner that the current value of the gate signal FBQ22 fed back to the functional safety control part 20a is less than or equal to the specified current value. As for the cut-off circuit 34, in order to ensure the amount of current required for the operation control of the transistor Q22, the current value of the gate signal may be slightly increased in advance in consideration of the amount of current branched to the functional safety control part 20a by the gate signal branching part 54, and then the gate signal is output. Furthermore, the power converter 1 a may prevent a large current from flowing into the functional safety control unit 20 a by adjusting the input impedance of the transistors Q21 , Q22 and the functional safety control unit 20 a , thereby preventing the gate signal branching units 53 , 54 from having the above-mentioned function.

[0069] The transistor Q21 is a switching device included in the main circuit and performs power conversion in the power converter 1a. The power conversion transistor Q21 used for power conversion is turned on and off according to the gate signal output from the gate drive circuit 43. Specifically, the transistor Q21 is gate-on when the gate signal is on, and gate-off when the gate signal is off. Similarly, the transistor Q22 is a switching device included in the main circuit and performs power conversion in the power converter 1a. The power conversion transistor Q22 used for power conversion is turned on and off according to the gate signal output from the gate drive circuit 44. Specifically, the transistor Q22 is gate-on when the gate signal is on, and gate-off when the gate signal is off. In this embodiment, the transistors Q21 and Q22 will not be gate-on at the same time. In addition, the operation of the transistors Q11 and Q12 is the same as the operation of the transistors Q11 and Q12 in the first embodiment.

[0070] The flywheel diode D21 is a diode connected in parallel with the transistor Q21. Similarly, the flywheel diode D22 is a diode connected in parallel with the transistor Q22. The functions of the flywheel diodes D11 and D12 are the same as those of the flywheel diodes D11 and D12 in the first embodiment.

[0071] The current detection unit 62 detects the current I2 flowing through the phase including the transistors Q21 and Q22. The current I2 flowing through the phase is the current flowing through the connection line between the power converter 1a and the motor (not shown) supplied with power by the power converter 1a. Specifically, the current detection unit 62 detects the current I2 flowing through the transistor Q21 or the flyback diode D21 or the transistor Q22 or the flyback diode D22. The current detection unit 62 outputs the detection result, i.e., the detected current I2, to the functional safety control unit 20a as a feedback signal, i.e., the current value FBI2. The current I2 is expressed as Figure 5 The arrow shown in the figure is assumed to be in the positive direction. Figure 5 The arrows shown are in the opposite direction of the flow, which is negative. Figure 5 In the example, when current I2 flows through transistor Q21 or flyback diode D22, current I2 is positive, and when current I2 flows through flyback diode D21 or transistor Q22, current I2 is negative. In addition, the operation of current detection unit 61 is the same as that of current detection unit 61 in embodiment 1.

[0072] The functional safety control unit 20a monitors the gate signal FBQ11 fed back from the gate signal branch unit 51, the gate signal FBQ12 fed back from the gate signal branch unit 52, the gate signal FBQ21 fed back from the gate signal branch unit 53, the gate signal FBQ22 fed back from the gate signal branch unit 54, the current value FBI1 output from the current detection unit 61, and the current value FBI2 output from the current detection unit 62. That is, the functional safety control unit 20a monitors the gate signal output from the gate drive circuit 41 to the transistor Q11, the gate signal output from the gate drive circuit 42 to the transistor Q12, the gate signal output from the gate drive circuit 43 to the transistor Q21, the gate signal output from the gate drive circuit 44 to the transistor Q22, the current I1 flowing through the transistor Q11 or the flyback diode D11 or the transistor Q12 or the flyback diode D12, and the current I2 flowing through the transistor Q21 or the flyback diode D21 or the transistor Q22 or the flyback diode D22.

[0073] Next, a mechanism for checking the soundness of the gate cutoff function in the power converter 1a will be described. In the second embodiment, the gate cutoff function is a function for setting the transistors Q11, Q12, Q21, and Q22 to a gate-off state when some abnormality is detected in the power converter 1a.

[0074] In the power converter 1a, the current I1 flows through the transistor Q11 or the flyback diode D12 when the current I1 is in a positive direction, and flows through the flyback diode D11 or the transistor Q12 when the current I1 is in a negative direction. When the current I1 flows through the flyback diode D11, even if the transistor Q11 is gate-on, the current I1 does not flow through the transistor Q11, and continues to flow through the flyback diode D11. Therefore, even if the gate of the transistor Q11 is turned on during the period when the current I1 flows in a negative direction, the current I1 does not flow through the transistor Q11, so the power converter 1a is not affected by the output voltage to be generated by the original converter control. Similarly, when the current I1 flows through the flyback diode D12, even if the transistor Q12 is gate-on, the current I1 does not flow through the transistor Q12, and continues to flow through the flyback diode D12. Therefore, even if the gate of transistor Q12 is turned on while current I1 is flowing in the positive direction, current I1 does not flow through transistor Q12, so the power converter 1a is not affected by the output voltage to be generated by the original converter control.

[0075] Since the current value FBI1 is fed back from the current detection unit 61, the functional safety control unit 20a can detect in which direction the current I1 flows, positive or negative, based on the current value FBI1. In addition, since the gate signal FBQ11 is fed back from the gate signal branch unit 51, the functional safety control unit 20a can detect the state of the gate signal given to the transistor Q11. Therefore, the functional safety control unit 20a first detects the period during which the current I1 flows in a negative direction based on the current value FBI1 fed back from the current detection unit 61. Even during the period during which the current I1 flows in a negative direction, the converter control unit 10a, regardless of the operation of the functional safety control unit 20a, etc., appropriately sets the gate pulse GP11 to be turned on or off and outputs it in order to control the operation of the equipment connected to the power converter 1a.

[0076] As described above, since the functional safety control unit 20a turns on the gate drive permission signal SAF11 and outputs it normally, the converter control unit 10a turns on the gate pulse GP11, so that the cutoff circuit 31 turns on the drive signal and outputs it to the gate drive circuit 41. As a result, the gate drive circuit 41 turns on the gate signal and outputs it to the transistor Q11 based on the turned-on drive signal from the cutoff circuit 31. The gate signal branching unit 51 branches the turned-on gate signal output from the gate drive circuit 41 to the transistor Q11, and feeds back the gate signal FBQ11 to the functional safety control unit 20a. The functional safety control unit 20a can detect that the gate signal output from the gate drive circuit 41 is turned on by the feedback of the gate signal FBQ11 from the gate signal branching unit 51.

[0077] The functional safety control unit 20a sets the gate drive enable signal SAF11 to be off during the period when the current I1 flows in a negative direction and the gate signal output from the gate drive circuit 41 is on. Since the gate drive enable signal SAF11 output from the functional safety control unit 20a becomes off, the cut-off circuit 31 sets the drive signal for the gate drive circuit 41 to be off and outputs it. The gate drive circuit 41 sets the gate signal to be off and outputs it to the transistor Q11 based on the off drive signal from the cut-off circuit 31. The gate signal branching unit 51 branches the off gate signal output from the gate drive circuit 41 to the transistor Q11, and feeds back the gate signal FBQ11 to the functional safety control unit 20a.

[0078] The functional safety control unit 20a can detect that the gate signal output from the gate drive circuit 41 is disconnected through the feedback of the gate signal FBQ11 from the gate signal branch unit 51. Therefore, since the gate signal for the transistor Q11 becomes disconnected by setting the gate drive enable signal SAF11 to be disconnected, the functional safety control unit 20a can determine that the gate cutoff function is normal. The functional safety control unit 20a sets the gate drive enable signal SAF11 to be disconnected during the period when the current I1 flows in a negative direction and the gate signal output from the gate drive circuit 41 is turned on. Thereafter, when it is not possible to detect that the gate signal output from the gate drive circuit 41 is disconnected through the feedback of the gate signal FBQ11 from the gate signal branch unit 51, it is determined that the gate cutoff function is abnormal.

[0079] In addition, the functional safety control unit 20a turns off the gate drive enable signal SAF12 while the current I1 flows in the positive direction and the gate of the transistor Q12 is turned on, and checks whether the gate signal FBQ12 is turned off, thereby determining the soundness of the gate cutoff function for the transistor Q12.

[0080] Similarly, in the power converter 1a, the current I2 flows through the transistor Q21 or the flyback diode D22 when the current I2 is in the positive direction, and flows through the flyback diode D21 or the transistor Q22 when the current I2 is in the negative direction. When the current I2 flows through the flyback diode D21, even if the transistor Q21 is turned on at the gate, the current I2 does not flow through the transistor Q21, and continues to flow through the flyback diode D21. Therefore, even if the gate of the transistor Q21 is turned on during the period when the current I2 flows in the negative direction, the current I2 does not flow through the transistor Q21, so the power converter 1a is not affected by the output voltage to be generated by the original converter control. Similarly, when the current I2 flows through the flyback diode D22, even if the transistor Q22 is turned on at the gate, the current I2 does not flow through the transistor Q22, and continues to flow through the flyback diode D22. Therefore, even if the gate of transistor Q22 is turned on while current I2 is flowing in the positive direction, current I2 does not flow through transistor Q22, and thus the power converter 1a is not affected by the output voltage to be generated by the original converter control.

[0081] Since the current value FBI2 is fed back from the current detection unit 62, the functional safety control unit 20a can detect in which direction the current I2 flows, positive or negative, based on the current value FBI2. In addition, since the gate signal FBQ21 is fed back from the gate signal branch unit 53, the functional safety control unit 20a can detect the state of the gate signal given to the transistor Q21. Therefore, the functional safety control unit 20a first detects the period during which the current I2 flows in a negative direction based on the current value FBI2 fed back from the current detection unit 62. Even during the period during which the current I2 flows in a negative direction, the converter control unit 10a, regardless of the operation of the functional safety control unit 20a, etc., appropriately sets the gate pulse GP21 to be turned on or off and outputs it in order to control the operation of the equipment connected to the power converter 1a.

[0082] As described above, since the functional safety control unit 20a turns on the gate drive permission signal SAF21 and outputs it normally, the converter control unit 10a turns on the gate pulse GP21, so that the cutoff circuit 33 turns on the drive signal and outputs it to the gate drive circuit 43. As a result, the gate drive circuit 43 turns on the gate signal and outputs it to the transistor Q21 based on the turned-on drive signal from the cutoff circuit 33. The gate signal branching unit 53 branches the turned-on gate signal output from the gate drive circuit 43 to the transistor Q21, and feeds back the gate signal FBQ21 to the functional safety control unit 20a. The functional safety control unit 20a can detect that the gate signal output from the gate drive circuit 43 is turned on by the feedback of the gate signal FBQ21 from the gate signal branching unit 53.

[0083] The functional safety control unit 20a sets the gate drive enable signal SAF21 to be off during the period when the current I2 flows in a negative direction and the gate signal output from the gate drive circuit 43 is on. Since the gate drive enable signal SAF21 output from the functional safety control unit 20a becomes off, the cut-off circuit 33 sets the drive signal for the gate drive circuit 43 to be off and outputs it. The gate drive circuit 43 sets the gate signal to be off and outputs it to the transistor Q21 based on the off drive signal from the cut-off circuit 33. The gate signal branching unit 53 branches the off gate signal output from the gate drive circuit 43 to the transistor Q21, and feeds back the gate signal FBQ21 to the functional safety control unit 20a.

[0084] The functional safety control unit 20a can detect that the gate signal output from the gate drive circuit 43 is disconnected through the feedback of the gate signal FBQ21 from the gate signal branch unit 53. Therefore, since the gate signal for the transistor Q21 becomes disconnected by setting the gate drive enable signal SAF21 to be disconnected, the functional safety control unit 20a can determine that the gate cutoff function is normal. The functional safety control unit 20a sets the gate drive enable signal SAF21 to be disconnected during the period when the current I2 flows in a negative direction and the gate signal output from the gate drive circuit 43 is turned on. Thereafter, when it is not possible to detect that the gate signal output from the gate drive circuit 43 is disconnected through the feedback of the gate signal FBQ21 from the gate signal branch unit 53, it is determined that the gate cutoff function is abnormal.

[0085] In addition, the functional safety control unit 20a sets the gate drive enable signal SAF22 to off during the period when the current I2 flows in the positive direction and the gate of the transistor Q22 is turned on, and checks whether the gate signal FBQ22 becomes off, thereby determining the soundness of the gate cutoff function for the transistor Q22.

[0086] Figure 6 FIG. 1 is a first diagram showing an example of an operation waveform of the power converter 1 a according to the second embodiment. Figure 7 FIG. 2 is a second diagram showing an example of an operation waveform of the power converter 1 a according to the second embodiment. Figure 6 An example is shown in which a gate cutoff function of the transistor Q21 is abnormal. Figure 7 An example is shown in which the gate cutoff function of the transistor Q11 is abnormal. Figure 6 and Figure 7 In the figure, the I1 current value is the current I1 detected by the current detection unit 61, and is the current value FBI1 fed back from the current detection unit 61 to the functional safety control unit 20a. The I2 current value is the current I2 detected by the current detection unit 62, and is the current value FBI2 fed back from the current detection unit 62 to the functional safety control unit 20a. The Q11 gate pulse is the gate pulse GP11 output from the converter control unit 10a. The Q11 gate drive enable signal is the gate drive enable signal SAF11 output from the functional safety control unit 20a. The Q11 gate drive circuit output is the gate signal output from the gate drive circuit 41 to the transistor Q11, and is the gate signal FBQ11 fed back from the gate signal branch unit 51 to the functional safety control unit 20a. The Q21 gate pulse is the gate pulse GP21 output from the converter control unit 10a. The Q21 gate drive enable signal is the gate drive enable signal SAF21 output from the functional safety control unit 20a. The Q21 gate drive circuit output is a gate signal output from the gate drive circuit 43 to the transistor Q21, and is a gate signal FBQ21 fed back to the functional safety control unit 20a from the gate signal branch unit 53. In addition, the gate pulse GP12, the gate drive enable signal SAF12, and the gate signal FBQ12 associated with the transistor Q12 are omitted. In addition, the gate pulse GP22, the gate drive enable signal SAF22, and the gate signal FBQ22 associated with the transistor Q22 are omitted.

[0087] The functional safety control unit 20a determines that the gate cutoff function is normal if the gate signal output from the gate drive circuit 41, i.e., the gate signal FBQ11, is turned off by temporarily turning off the gate drive permission signal SAF11 during the period when the gate pulse GP11 is turned on after confirming that the gate signal output from the gate drive circuit 41, i.e., the gate signal FBQ11, is turned off during the period when the current I1 flows in the negative direction. The functional safety control unit 20a determines that the gate cutoff function is abnormal if it cannot detect that the gate signal output from the gate drive circuit 41, i.e., the gate signal FBQ11, is turned off under the same conditions as above. Similarly, the functional safety control unit 20a determines that the gate cutoff function is normal if the gate signal output from the gate drive circuit 43, i.e., the gate signal FBQ21, is turned off by temporarily turning off the gate drive permission signal SAF21 during the period when the gate pulse GP21 is turned on after confirming that the gate signal output from the gate drive circuit 43, i.e., the gate signal FBQ21, is turned off during the period when the current I2 flows in the negative direction. The functional safety control unit 20a determines that the gate cutoff function is abnormal if it cannot detect that the gate signal output from the gate drive circuit 43, i.e., the gate signal FBQ21, is turned off under the same conditions as above.

[0088] Here, the functional safety control unit 20a does not know the period for which the converter control unit 10a turns on the gate pulses GP11 and GP21 and outputs them. However, if the information of the shortest period for which the gate pulses GP11 and GP21 are continuously turned on when the converter control unit 10a turns on the gate pulses GP11 and GP21 is pre-set, the functional safety control unit 20a can perform the above-mentioned operation by temporarily turning off the gate drive enable signals SAF11 and SAF21 during the shortest period for which the gate pulses GP21 and GP21 are turned on, that is, turning them on again after turning them off. In addition, the functional safety control unit 20a can also select the shortest on period as the shortest period for which the gate pulses GP11 and GP21 are continuously turned on from the period for which the gate signals FBQ11 and FBQ21 fed back by the gate signal branch units 51 and 53 are turned on when the power converter 1a operates for a specified period. Alternatively, the functional safety control unit 20a may temporarily turn off the gate drive enable signals SAF11 and SAF21 during the on-period of the next gate pulse GP11 and GP21 when a certain on-period is expected to be ensured, based on the on-period of the previous gate pulse GP11 and GP21.

[0089] As described above, in the power converter 1a, the functional safety control unit 20a temporarily turns off the gate drive permission signal SAF11 based on the current value FBI1 and the gate signal FBQ11 during the period when the current I1 flows in a negative direction, that is, during the period when the current I1 does not flow through the transistor Q11 and the gate signal is on, and determines the soundness of the gate cutoff function for the transistor Q11 by whether the gate signal to the transistor Q11 changes to OFF. Similarly, the functional safety control unit 20a temporarily turns off the gate drive permission signal SAF21 based on the current value FBI2 and the gate signal FBQ21 during the period when the current I2 flows in a negative direction, that is, during the period when the current I2 does not flow through the transistor Q21 and the gate signal is on, and determines the soundness of the gate cutoff function for the transistor Q21 by whether the gate signal to the transistor Q21 changes to OFF.

[0090] Here, if Figure 6 As shown, when an abnormality is detected in the determination of the soundness of the gate cutoff function of the transistor Q21, the functional safety control unit 20a may not be able to set the gate signal FBQ21 as the feedback signal, that is, the gate signal output from the gate drive circuit 43 to the transistor Q21 to be turned off even if the gate drive enable signal SAF21 is turned off. However, the functional safety control unit 20a can set the gate signal output from the gate drive circuit 41 to the transistor Q11, the gate signal output from the gate drive circuit 42 to the transistor Q12, and the gate signal output from the gate drive circuit 44 to the transistor Q22 to be turned off by setting the gate drive enable signals SAF11, SAF12, and SAF22 for the transistors Q11, Q12, and Q22 to be turned off. Similarly, as Figure 7As shown, when an abnormality is detected in the determination of the soundness of the gate cutoff function of the transistor Q11, the functional safety control unit 20a may not be able to turn off the gate signal FBQ11 as a feedback signal, that is, the gate signal output from the gate drive circuit 41 to the transistor Q11, even if the gate drive permission signal SAF11 is turned off. However, the functional safety control unit 20a can turn off the gate signal output from the gate drive circuit 42 to the transistor Q12, the gate signal output from the gate drive circuit 43 to the transistor Q21, and the gate signal output from the gate drive circuit 44 to the transistor Q22 by turning off the gate drive permission signals SAF12, SAF21, and SAF22 for the transistors Q12, Q21, and Q22. In such a case, the functional safety control unit 20a can issue an alarm to the user of the power converter 1a, etc. to the effect that an abnormality has been detected in the soundness of the gate cut-off function, or can, when it is desired to stop the operation of the power converter 1a, execute control such as cutting off the power supply to the converter control unit 10a and stopping the output of gate pulses GP11, GP12, GP21, and GP22 from the converter control unit 10a.

[0091] The operation of the functional safety control unit 20a determining the soundness of the gate cutoff function for the transistor Q11 has been described, but the operation of the functional safety control unit 20a determining the soundness of the gate cutoff function for the transistor Q12 is also the same. When determining the soundness of the gate cutoff function for the transistor Q12, the functional safety control unit 20a temporarily turns off the gate drive permission signal SAF12 during the period when the current I1 flows in the positive direction and the transistor Q12 is gate-on, and confirms whether the gate signal FBQ12 has become OFF. In addition, the operation of the functional safety control unit 20a determining the soundness of the gate cutoff function for the transistor Q21 has been described, but the operation of the functional safety control unit 20a determining the soundness of the gate cutoff function for the transistor Q22 is also the same. When determining the soundness of the gate cutoff function for the transistor Q22, the functional safety control unit 20a temporarily turns off the gate drive permission signal SAF22 during the period when the current I2 flows in the positive direction and the transistor Q22 is gate-on, and confirms whether the gate signal FBQ22 has become OFF.

[0092] As described above, the functional safety control unit 20a turns on and outputs a plurality of gate drive enable signals when the soundness of the gate cutoff function for each of the plurality of transistors is not determined. The functional safety control unit 20a temporarily turns off the gate drive enable signal during the period when the gate pulse is on, after confirming that the gate signal has changed to on, during a period when the current does not flow through the transistor, based on the current value and the gate signal for each transistor, and determines whether the gate signal has changed to off.

[0093] In the second embodiment, the power converter 1a determines the gate cutoff function of the transistors Q11, Q12, Q21, and Q22 in a manner similar to the method of determining the gate cutoff function of the transistors Q11, Q12, Q21, and Q22. Figure 3 The method of determining the gate cutoff function of the transistor Q11 is the same in the power converter 1 according to the first embodiment shown. Figure 8 This is a flowchart showing the operation of the power converter 1 a according to the second embodiment. Figure 8 The operation shown in the flowchart is performed after the method for determining the gate cutoff function of the transistors Q11, Q12, Q21, and Q22 in the power converter 1a is implemented. Figure 3 The action of step S17 of the flowchart shown in the figure is repeated, but in the power converter 1a, the functional safety control unit 20a continues to monitor the gate cutoff function when the gate cutoff function of all transistors is normal (step S21: Yes). The functional safety control unit 20a sets all gate drive enable signals SAF11, SAF12, SAF21, and SAF22 to off (step S22) when the gate cutoff function of more than one transistor is abnormal (step S21: No). As described above, the functional safety control unit 20a sets the gate drive enable signals SAF11, SAF12, SAF21, and SAF22 corresponding to each of the plurality of transistors Q11, Q12, Q21, and Q22 to off when more than one transistor in the gate cutoff function of each of the plurality of transistors Q11, Q12, Q21, and Q22 is determined to have an abnormal gate cutoff function.

[0094] In the second embodiment, the hardware configuration of the power converter 1 a is the same as the hardware configuration of the power converter 1 in the first embodiment.

[0095] As described above, according to the present embodiment, in the power converter 1a, the functional safety control unit 20a determines the period during which the current I1 does not flow through the transistors Q11 and Q12 based on the current value FBI1 from the current detection unit 61, determines the period during which the current I2 does not flow through the transistors Q21 and Q22 based on the current value FBI2 from the current detection unit 62, and determines the period during which the gate signal is turned on based on the gate signals FBQ11, FBQ12, FBQ21, and FBQ22 from the gate signal branching units 51 to 54. The functional safety control unit 20a temporarily turns off the gate drive permission signal SAF11 during the period during which the current I1 does not flow through the transistor Q11 and the gate signal to the transistor Q11 is turned on, and determines the soundness of the gate cutoff function for the transistor Q11 by whether the gate signal to the transistor Q11 changes to be turned off. Similarly, the functional safety control unit 20a temporarily turns off the gate drive permission signal SAF12 when the current I1 does not flow through the transistor Q12 and the gate signal to the transistor Q12 is on, and determines the soundness of the gate cutoff function for the transistor Q12 by whether the gate signal to the transistor Q12 changes to off. Similarly, the functional safety control unit 20a temporarily turns off the gate drive permission signal SAF21 when the current I2 does not flow through the transistor Q21 and the gate signal to the transistor Q21 is on, and determines the soundness of the gate cutoff function for the transistor Q21 by whether the gate signal to the transistor Q21 changes to off. Similarly, the functional safety control unit 20a temporarily turns off the gate drive permission signal SAF22 when the current I2 does not flow through the transistor Q22 and the gate signal to the transistor Q22 is on, and determines the soundness of the gate cutoff function for the transistor Q22 by whether the gate signal to the transistor Q22 changes to off. Thus, the functional safety control unit 20a can check the soundness of the gate cutoff function for the power conversion transistors Q11, Q12, Q21, and Q22 without affecting the normal operation of the power converter 1a.

[0096] The structure shown in the above embodiment is only an example, and may be combined with other known technologies, or the embodiments may be combined with each other. Part of the structure may be omitted or changed without departing from the scope of the invention.

[0097] Description of the label

[0098] 1, 1a power converter, 10, 10a converter control unit, 20, 20a functional safety control unit, 31-34 cut-off circuit, 41-44 gate drive circuit, 51-54 gate signal branch unit, 61, 62 current detection unit, D11, D12, D21, D22 freewheeling diodes, Q11, Q12, Q21, Q22 transistors.

Claims

1. A power converter, characterized in that: have: Two transistors connected in series used in power conversion; A converter control unit that outputs a gate pulse for controlling the on and off of each of the transistors; a functional safety control unit configured to turn on and output a gate drive permission signal for each of the transistors when the integrity of the gate cutoff function of the transistor is not determined; two cutoff circuits that correspond to each of the two transistors and output a result of a logical AND operation using the gate pulse and the gate drive enable signal as a drive signal; two gate drive circuits, which correspond to each of the two transistors and output gate signals for driving the transistors to the transistors and the functional safety control unit based on the drive signals; as well as a current detection unit that detects a current flowing through a phase including the two transistors and outputs the detection result as a current value to the functional safety control unit, For each of the transistors, based on the current value and the gate signal, during a period when current is not flowing through the transistor, after confirming that the gate signal has changed to on, the functional safety control unit temporarily sets the gate drive enable signal to off during the period when the gate pulse is on, and determines whether the gate signal has changed to off.

2. The power converter according to claim 1, characterized in that: When the functional safety control unit determines that the gate cutoff function of one of the transistors is abnormal, the functional safety control unit turns off the gate drive permission signals for the two transistors.

3. The power converter according to claim 1, characterized in that: having a plurality of branches consisting of two of the transistors connected in series, A plurality of the cutoff circuits and a plurality of the gate drive circuits are provided corresponding to each of the plurality of transistors. The current detection unit is provided corresponding to each of the plurality of branches. The converter control unit outputs the plurality of gate pulses for controlling on and off of each of the plurality of transistors. The functional safety control unit sets the multiple gate drive enable signals to be turned on and outputted corresponding to each of the multiple transistors without determining the soundness of the gate cutoff function of the transistor. For each of the transistors, based on the current value and the gate signal, after confirming that the gate signal has changed to be turned on during a period when no current flows through the transistor, the gate drive enable signal is temporarily set to be turned off during a period when the gate pulse is on, and it is determined whether the gate signal has changed to be turned off.

4. The power converter according to claim 3, characterized in that: The functional safety control unit turns off the gate drive permission signal for each of the plurality of transistors when it is determined that the gate cutoff function is abnormal with respect to one or more transistors.

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