Electric-power conversion apparatus

Abstract

By providing: a main circuit portion (11) that performs electric power conversion between a DC circuit portion (100) and a load (120); a voltage detection portion (13) that detects a voltage generated in an inductance component between two points set in wiring that connects the DC circuit portion (100) and the main circuit portion (11); and a short-circuit detection portion (200) having a first comparator (201) that outputs a detection signal, when the voltage detected by the voltage detection portion (13) exceeds a first threshold-value voltage, and a second comparator (203) that detects occurrence of a short-circuit, when the detection signal of the first comparator (201) continues for a period of time determined in advance or longer, short-circuit detection which can be designed easily and performed with sufficient margin against erroneous detection can be realized.

Description

Power Conversion Device

[0001] The present disclosure relates to a power conversion device.

[0002] Power semiconductors, which act as switches, are essential in power conversion devices. To ensure the quality of power conversion devices, it is known to provide a function for detecting overcurrents caused by power semiconductor failures or noise malfunctions, stopping power conversion, and preventing damage to or fire from occurring in the device. For example, Patent Document 1 describes a method for detecting short circuits by providing a current-limiting reactor that limits the current between an inverter and a capacitor and acquiring the voltage across the current-limiting reactor.

[0003] In Patent Document 1, the use of a current-limiting reactor limits the short-circuit current, lengthening the time from the onset of a short circuit to device breakdown compared to when a current-limiting reactor is not used. This allows for a longer time window between short-circuit detection and tripping. Furthermore, because the current-limiting reactor maintains a constant current gradient, the only factors contributing to the variation in the voltage across the current-limiting reactor are the inductance of the current-limiting reactor itself and the applied voltage. This simplifies design and eliminates false detections even when the gate resistance and the input capacitance or gate threshold voltage, which are related to the switching characteristics of the power semiconductor, change. Additionally, to enable fast short-circuit detection, a bias circuit, such as a Zener diode, is used to cut off voltage across the current-limiting reactor below a certain value. The circuit distinguishes between overcurrent during a short circuit and current during normal operation by determining whether the voltage remains constant for a predetermined time.

[0004] Japanese Utility Model Application Publication No. 58-11993

[0005] However, the use of a current-limiting reactor increases the size of the device and increases costs. Therefore, if short-circuit detection is performed using the voltage generated across the parasitic inductance in the wiring without using a current-limiting reactor, the voltage generated across the parasitic inductance will vary depending on the applied voltage of the power semiconductor, variations in element characteristics, and the operating mode of the power conversion device. This variation makes it difficult to design a detection circuit, and there is a risk of false detection due to the lack of tolerance.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a power conversion device having a short-circuit detection circuit that is easy to design and has a tolerance for erroneous detection, even when short-circuit detection is performed using the voltage generated in parasitic inductance.

[0007] The power conversion device disclosed herein includes a main circuit section that performs power conversion between a DC circuit section and a load, a voltage detection section that detects the voltage generated in an inductance component between two points on a wiring that connects the DC circuit section and the main circuit section, and a short circuit detection section that has a first comparator that outputs a detection signal when the voltage detected by the voltage detection section exceeds a first threshold voltage, and a second comparator that detects the occurrence of a short circuit when the detection signal of the first comparator continues for a predetermined time or longer.

[0008] According to the power conversion device of the present disclosure, even when short circuit detection is performed using the voltage generated in the inductance component in the wiring, short circuit detection can be performed with ease of design and with a tolerance for erroneous detection.

[0009] 1 is a block diagram showing a configuration of a power conversion device according to a first embodiment; FIG. 2 is a circuit diagram showing an example of a specific configuration of the power conversion device according to the first embodiment; FIG. 3 is a block diagram showing configurations of a voltage detection unit and a short circuit detection unit of the power conversion device according to the first embodiment; FIG. 4 is a diagram showing an example of a circuit configuration of the voltage detection unit and the short circuit detection unit of the power conversion device according to the first embodiment; FIG. 5 is a current and voltage waveform diagram at turn-on, illustrating noise components during switching of a power semiconductor element; FIG. 6 is a schematic waveform diagram of current and voltage waveforms illustrating surge voltages during turn-off of a power semiconductor element; FIG. 7 is a schematic waveform diagram illustrating the operating principle of the short circuit detection unit in the power conversion device according to the first embodiment; FIG. 8 is a schematic waveform diagram of a detection L voltage and a second comparator input voltage when (a) one phase is switching and (b) two phases are switching, illustrating a method of determining a threshold voltage of the power conversion device according to the first embodiment; FIG. 9 is a schematic diagram illustrating the tolerance in the short circuit detection circuit of the power conversion device according to the first embodiment, where (a) the power supply Vcc is not shared and (b) the power supply Vcc is shared; and FIG. 10 is a diagram showing an example of a circuit configuration of the voltage detection unit and the short circuit detection unit of the power conversion device according to a second embodiment. FIG. 10 is a schematic waveform diagram illustrating the operating principle of a short circuit detection unit in a power conversion device according to embodiment 2. FIG. 11 is a schematic diagram illustrating a tolerance in a short circuit detection circuit of a power conversion device according to embodiment 2. FIG. 12 is a diagram illustrating an example of a circuit configuration of a voltage detection unit and a short circuit detection unit of a power conversion device according to embodiment 3. FIG. 13 is a schematic diagram illustrating a tolerance in a short circuit detection circuit unit of a power conversion device according to embodiment 3. FIG. 14 is a diagram illustrating an example of a circuit configuration of a voltage detection unit and a short circuit detection unit of a power conversion device according to embodiment 3. FIG. 15 is a block diagram illustrating a configuration of a power conversion device according to embodiment 4. FIG. 16 is a circuit configuration diagram illustrating an example of a specific configuration of a power conversion device according to embodiment 4. FIG. 17 is a diagram illustrating an example of a hardware configuration when a control unit of a power conversion device according to an embodiment is a microcomputer.

[0010] Hereinafter, preferred embodiments of a power conversion device according to the present disclosure will be described with reference to the drawings. The same components and corresponding parts are designated by the same reference numerals, and detailed descriptions thereof will be omitted. Similarly, in the following embodiments, redundant descriptions of components designated by the same reference numerals will be omitted.

[0011] Embodiment 1. Fig. 1 is a block diagram showing the configuration of a power conversion device according to embodiment 1. In Fig. 1, a power conversion device 10 performs power conversion between a DC circuit section 100 and a load 120, and is made up of a main circuit section 11 and a control section 12 that controls this main circuit section 11.

[0012] The control unit 12 includes a voltage detection unit 13 and a short-circuit detection unit 200. The voltage detection unit 13 detects a voltage generated in a parasitic inductance (inductance component) 111 between two points N1 and N2 set in a connection wiring unit 110 between the DC circuit unit 100 and the power conversion device 10. The short-circuit detection unit 200 determines whether a short circuit has occurred in the power conversion device based on the output of the voltage detection unit 13.

[0013] 1 shows an example in which two points N1 and N2 on the negative wiring are set as points for detecting the differential voltage of the connection wiring unit 110, but detection may also be performed using two points on the positive wiring. Using two points on the positive side has the advantage of not being affected by common-mode noise, but requires insulation when transmitting the short-circuit detection signal to the short-circuit detection unit 200.

[0014] The wiring of the connection wiring unit 110 may be not only wiring on the board, but also cables and wiring inside the power semiconductor elements. Also, if a current detection chip resistor for controlling the main circuit unit 11 is present between the main circuit unit 11 and the DC circuit unit 100, the voltage may be detected using the inductance component of the chip resistor. Note that when detecting using a chip resistor, there is also a voltage increase due to the resistance component, so the detection tolerance can be improved by providing a differentiation circuit in the voltage detection unit 13 to remove the voltage increase due to the resistance component.

[0015] Fig. 2 is a circuit diagram showing an example of a specific configuration of the power conversion device according to embodiment 1. In Fig. 2, a DC circuit unit 100 has an AC power supply 100b and a three-phase PWM converter 100a that converts AC voltage to DC voltage, and a main circuit unit 11 has a three-phase inverter 11p that drives a three-phase electric motor 120a that is a three-phase AC load.

[0016] The three-phase inverter 11p that drives the three-phase motor 120a is widely used in home appliances such as air conditioners and refrigerators, electric vehicles, industrial equipment, and the like.

[0017] The three-phase PWM converter 100a is composed of an AC reactor 101a, power semiconductor elements Ma to Mf, and a capacitor 14. The three-phase inverter 11p is composed of power semiconductor elements M1 to M6. While this embodiment uses MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) as an example of the power semiconductor module, the present invention is not limited to this and any element that functions as a switching element may be used. It is clear that the number of power semiconductor elements, the number of phases of the power conversion device 10, the number of DC circuit units 100 or loads 120, and the detailed circuit configuration are not limited to those described below.

[0018] 2, the capacitor 14 is mounted on the DC circuit section 100, but the capacitor 14 may be provided in the main circuit section 11, or may be provided in both the DC circuit section 100 and the main circuit section 11. Therefore, there is no limit to the number and locations of the capacitors 14. The capacitor 14 does not necessarily have to smooth the frequency components originating from the AC power supply 100b, and a film capacitor or a ceramic capacitor may be used instead of an electrolytic capacitor.

[0019] 3 is a block diagram of the voltage detection unit 13 and short-circuit detection unit 200 of the power conversion device according to the first embodiment. The voltage detection unit 13 is configured to monitor a voltage VL generated in an inductance component 111 between two points N1 and N2 set at an interval on the connection wiring unit 110. The short-circuit detection unit 200 is configured to detect whether a current IL flowing through the inductance component 111 is in an overcurrent state. Hereinafter, the voltage VL will be referred to as a detection L voltage VL, and the current IL will be referred to as a detection L current IL.

[0020] Specifically, the voltage detection unit 13 is equipped with a filter circuit 13a that removes noise components superimposed on the detection L voltage VL due to switching, etc. The short-circuit detection unit 200 is made up of a first comparator 201 that outputs a signal when the voltage reaches or exceeds a certain voltage, an integrator 202 that integrates the signal from the first comparator 201 and converts the time width of the signal into a voltage, and a second comparator 203 that outputs an overcurrent detection signal Ssc when the output voltage of the integrator 202 falls below or exceeds a predetermined value.

[0021] If the noise component superimposed on the detection L voltage VL is small compared to the voltage rise due to the slope of the overcurrent, the filter circuit 13a may not be provided. Also, if the detection L voltage VL is small, an amplifier such as an operational amplifier may be added to amplify the voltage.

[0022] 4 is a diagram showing an example of the circuit configuration of the voltage detection unit 13 and the short-circuit detection unit 200 of the power conversion device according to the first embodiment. The filter circuit 13a is a low-pass filter composed of a resistor R1 and a capacitor C1, and a set point N1 on the wiring, a ground point GND (a hollow triangle in FIG. 4) of the filter circuit 13a, and one end of the capacitor C1 are connected, and a set point N2 on the wiring and one end of the resistor R1 of the filter circuit 13a are connected. The other end of the capacitor C1 and the other end of the resistor R1 are connected to a first comparator 201.

[0023] Here, when power semiconductor elements that perform high-speed switching operations, such as SiC-MOSFETs, GaN-HEMTs (High Electron Mobility Transistors), or Si-IGBTs (Insulated Gate Bipolar Transistors), are used as switching elements of the three-phase inverter 11p, taking a MOSFET as an example, the drain current Id, which is a switching current, may pulsate at a frequency fsn immediately after turning on, as shown in Fig. 5. This pulsating current is superimposed as a voltage on the wiring of the voltage detection unit 13, resulting in erroneous detection. Therefore, when a low-pass filter is provided in the filter circuit 13a, the cutoff frequency should be set to fsn or less.

[0024] Furthermore, when the above-described power semiconductor elements (e.g., MOSFETs) that perform high-speed switching are applied to the three-phase inverter 11p, the drain-source voltage (surge voltage) Vds at turn-off becomes larger (Vdsmax in FIG. 6) at high speeds shown by the solid lines compared to at low speeds shown by the dashed lines in FIG. 6, exceeding the element breakdown voltage Vdsp and destroying the element, so the inductance for short-circuit detection must be set so as to satisfy the condition of the following formula (1). Note that, in this example, the power semiconductor elements have been described as MOSFETs, but this is not limited to this.

[0025]

[0026] In equation (1), the inductance component 111 for short circuit detection is L [H], the inductance between the capacitor including the inductance component 111 and the power semiconductor element (MOSFET) is Lloop [H], the inductance between the capacitor not including the inductance component 111 and the MOSFET element is La [H], the element withstand voltage of the MOSFET element is Vdsp [V], the maximum voltage of the DC circuit unit 100 is Vdcmax [V], and the maximum current gradient of the MOSFET element is di / dt, where Lloop = La + L.

[0027] 4, the other end of the resistor R1 and capacitor C1, which is the output of the filter circuit 13a, is connected to the non-inverting input terminal (+) of a first comparator 201, and a first threshold voltage Vref1 generated by a threshold voltage generator 204 is input to the inverting input terminal (-) of the first comparator 201. The output of the first comparator 201 is connected to an integrator 202 composed of a resistor R2 and a capacitor C2. The output of the first comparator 201 is connected to one end of the resistor R2, and one end of the capacitor C2 is connected to the ground GND. Although the integrator 202 is composed of the resistor R2 and the capacitor C2, an integrating circuit using an operational amplifier may also be used.

[0028] The output of the integrator 202 is connected to the non-inverting input terminal (+) of a second comparator 203, and the second threshold voltage Vref2 generated by the threshold voltage generator 204 is input to the inverting input terminal (-) of the second comparator 203. The output of the second comparator 203 becomes the overcurrent detection signal Ssc.

[0029] In the threshold voltage generation unit 204, both the first threshold voltage Vref1 and the second threshold voltage Vref2 are generated from a common power supply Vcc by resistor voltage dividers R3 to R5. As will be described in detail later, using a common power supply Vcc has the advantage of improving the tolerance of the detection circuit. Although not shown, the power supply for the first comparator 201 and the second comparator 203 may be the power supply Vcc of the threshold voltage generation unit 204, or another power supply may be used.

[0030] 7 is a schematic waveform diagram illustrating the operating principle of the short-circuit detection unit 200 in the power conversion device according to the first embodiment. From the top, the diagram shows the detection L current IL, the detection L voltage VL, the output voltage of the first comparator 201, the input voltage of the second comparator 203, and the overcurrent detection signal Ssc. The solid waveform in FIG. 7 shows an example of a waveform during a short circuit, and the dotted waveform shows an example of a waveform during a turn-on operation, which is a normal switching operation. For simplicity, the explanation of the operating principle in FIG. 7 assumes that no noise components are generated during switching, and ignores the presence of the filter circuit 13a.

[0031] During normal switching operation, a load current ILoad flows through a certain phase due to a power semiconductor element that is turned on. Also, just before the element is turned on, the load current ILoad flows through a diode connected to a power semiconductor element of that phase that is not turned on. During a short circuit, the arm is short-circuited, with no load current ILoad flowing, and the element on the opposite side of the phase where the power semiconductor element that is turned on is destroyed or receives an erroneous signal and is already turned on.

[0032] At time t0, a positive-side or negative-side power semiconductor device in one phase of the three-phase inverter is turned on, causing the detection L current IL to start flowing, and the detection L voltage VL to rise accordingly. Next, at time t1, the detection L voltage VL becomes greater than the first threshold voltage Vref1, causing the output voltage of the first comparator 201 to rise and become a high detection signal.

[0033] When the output voltage of the first comparator 201 becomes a high detection signal, the input voltage of the second comparator 203 begins to gradually rise by the integrator 202. As can be seen from Figure 7, the high duration of the output voltage of the first comparator 201 is converted by the integrator 202 into the height of the input voltage of the second comparator 203. This conversion simplifies the design and provides a margin for error detection. Up to this point, the operation is the same during normal switching operation and when a short circuit occurs.

[0034] During normal switching operation at time t2, the detection L current IL flows only up to the load current ILoad, so the slope of the detection L current IL becomes gentler and the detection L voltage VL becomes lower than the first threshold voltage Vref1. As a result, the output voltage of the detection signal of the first comparator 201 switches from high to low, and the input voltage of the second comparator 203 also begins to gradually decrease. Thereafter, when the detection L current IL reaches the load current ILoad, the switching operation is completed.

[0035] At time t2, when a short circuit occurs, the detection L current IL is not limited by the load, unlike in normal switching operation, so the detection L current IL continues to rise even at time t2. As a result, the detection L voltage VL also continues to maintain a value greater than the first threshold voltage Vref1, and the input voltage of the second comparator 203 also continues to rise.

[0036] When a short circuit occurs at time t3, the input voltage of the second comparator 203 continues to rise, and after a predetermined time has elapsed, i.e., when the input voltage of the second comparator 203 exceeds the second threshold voltage Vref2, the overcurrent detection signal Ssc goes high, and a short circuit is detected. From the above, it can be seen that the detection circuit of embodiment 1 can be used to distinguish between normal switching operation and a short circuit. When a short circuit is detected in a power conversion device such as that of embodiment 1, the device can be prevented from being destroyed by an arm short circuit by controlling the power semiconductor elements of the three-phase PWM converter 100a and the three-phase inverter 11p to the off state.

[0037] In the explanation of the operating principle of the short circuit detection unit 200, the values ​​of the first threshold voltage Vref1 and the second threshold voltage Vref2 are set so as to be able to distinguish between normal switching in which one power semiconductor element is turned on and an arm short circuit. However, in order to create a detection circuit that does not make erroneous detections in the power conversion device of the three-phase inverter 11p, the first threshold voltage Vref1 and the second threshold voltage Vref2 need to be determined based on the operating conditions of the three-phase inverter 11p.

[0038] 7, the detection method of embodiment 1 distinguishes between normal switching and a short circuit based on the difference in the duration of the detection signal during which the input voltage to first comparator 201 exceeds first threshold voltage Vref1. Note that the above explanation is based on the detection L voltage VL, ignoring filter circuit 13a. Therefore, in order to prevent erroneous detection, first, the maximum duration condition during which the input voltage to first comparator 201 exceeds first threshold voltage Vref1 during normal switching operation is determined, and the minimum duration condition during which the input voltage to first comparator 201 exceeds first threshold voltage Vref1 is determined during a short circuit.

[0039] Then, the input voltage of the second comparator 203 under the maximum and minimum time width conditions is calculated, and the second threshold voltage Vref2 is set between the peak values ​​of these two values. As can be seen from Fig. 7, the second threshold voltage Vref2 is set between the input voltage peaks of the second comparator 203 during normal switching operation and during short circuit.

[0040] During normal switching operation, the current condition that results in the maximum time width is when the main circuit unit 11 and the load 120 are operating at the maximum current. This is because the larger the current value, the longer the current rise time, and therefore the longer the time width of the detection L voltage VL. In the explanation of the operating principle of the short circuit detection unit 200 above, a certain power semiconductor element is turned on in the operating mode. However, for example, in a three-phase inverter 11p, when a three-phase AC voltage is output to the electric motor 120a by PWM control, the power semiconductor elements of two phases may turn on at approximately the same timing.

[0041] FIG. 8 shows the detection L voltage VL when one phase of the three-phase inverter 11p switches at the maximum load current and when two phases switch at approximately the same time. The maximum load current is the sum of the currents during two-phase switching. As can be seen from FIG. 8, depending on the first threshold voltage Vref1 set, the time width t2sw when two phases switch at approximately the same time, resulting in overlapping of the current gradients di / dt, is greater than the time width t1sw when one phase switches at the maximum current. Therefore, determining the second threshold voltage Vref2 based solely on one-phase switching may result in erroneous detection. Therefore, the second threshold voltage Vref2 must be determined based on the maximum time width condition when the current gradients of two or more phases overlap.

[0042] In the above explanation of the operating principle of the short circuit detection unit 200, a short circuit is considered to occur when no load current is flowing. However, there is a mode in which a power semiconductor element breaks down and a short circuit occurs when a load current is flowing. This is called an ON-state short circuit. An arm short circuit when no load current is flowing ranges from 0 [A] to the saturated current, but an ON-state short circuit ranges from the load current I Load to the saturated current, shortening the time during which the detection L voltage VL is generated. Therefore, if ON-state short circuits are also to be detected, the second threshold voltage Vref2 can be set based on the minimum time width condition for ON-state short circuits.

[0043] In the circuit configuration of the short circuit detection unit 200 described above, the first and second threshold voltages are both generated using the same power supply Vcc of the threshold voltage generation unit 204. This is to improve the tolerance against erroneous detection even when a high-speed switching power semiconductor element is used in the power conversion device without using a current-limiting reactor.

[0044] That is, FIG. 9 shows the tolerance of the detection circuit of the threshold voltage generation unit 204 when the power supply is not shared (FIG. 9(a)) and when the power supply is shared (FIG. 9(b)). The solid line in the figure indicates the minimum voltage line during a short circuit, and the dashed line indicates the maximum voltage line during normal switching operation. The vertical axis represents the input voltage to the first comparator 201, which becomes the detection L voltage VL when there is no filter circuit. The horizontal axis represents the input voltage to the second comparator 203, which is synonymous with the time width at each height of the input voltage to the first comparator 201.

[0045] It is possible to distinguish between a short circuit and a normal switching operation by setting the first and second threshold voltages Vref1 and Vref2 midway between the solid line indicating a short circuit and the dashed line indicating a normal switching operation in Fig. 9. For example, the value on the vertical axis at point A in Fig. 9 represents the first threshold voltage Vref1, and the value on the horizontal axis at point A represents the second threshold voltage Vref2.

[0046] If the power supply Vcc of the threshold voltage generator 204 is not shared, the power supply that determines the first threshold voltage Vref1 and the power supply that determines the second threshold voltage Vref2 may vary within the same positive range or the same negative range, or may vary within different positive and negative ranges, so the variation in threshold voltage will be within the range of the dotted rectangle as shown in Figure 9(a). Note that if this dotted rectangle touches the solid line that indicates a short circuit or the dashed line that indicates normal switching, a false detection will occur.

[0047] In contrast, when the threshold voltage generation unit 204 shares a common power supply, the first threshold voltage Vref1 and the second threshold voltage Vref2 only vary by the same positive value or the same negative value, and therefore, as shown in FIG. 9( b), the variation in threshold voltage only varies along the dotted arrow from the upper right to the lower right of the graph. Therefore, it can be seen that the tolerance represented by the solid arrow is improved in FIG. 9( b) compared to FIG. 9( a). Therefore, even if the characteristics during short-circuiting or normal switching change depending on the gate resistance, gate threshold voltage, input capacitance, gate voltage, temperature, etc., a detection circuit that is less likely to detect errors can be achieved.

[0048] While it is possible to use a Zener diode or the like to cut off the detection L voltage VL below a certain voltage value and detect a short circuit when that voltage remains above a predetermined value for a certain period of time, in the first embodiment, as shown in FIG. 4 , a short circuit detection unit 200 is used in which a threshold voltage is generated from a common power supply for two comparators 201 and 203. A short circuit is detected when the input voltage of the first comparator 201 exceeds a first threshold voltage Vref1 for a certain period of time. The reason for this is that if a Zener diode is used in the bias circuit, variations in the Zener voltage may result in variations similar to those shown in FIG. 9( a). Furthermore, Zener diodes have a large voltage dependency in the parasitic capacitance present in parallel with them, and the Zener voltage, which is the voltage at which they are cut, also depends on the current. Therefore, if a low-pass filter is included in the filter circuit, the voltage dependency of the Zener diode's parasitic capacitance significantly changes the cutoff frequency depending on the voltage, complicating the design of the filter circuit 13a.

[0049] Even when the filter circuit 13a is not used, the voltage waveform after the Zener diode is not the same as the waveform obtained by cutting the detection L voltage VL below the Zener voltage due to the voltage characteristics of the parasitic capacitance. Therefore, the voltage after the Zener diode must be obtained by actual measurement or simulation analysis, and the first and second threshold voltages Vref1 and Vref2 must be set based on that. In contrast, if the short-circuit detection unit 200 is configured with two comparators 201 and 203, the threshold voltage can be determined from the detection L current IL and the detection L voltage VL, making the design easier. Furthermore, because the Zener voltage of a Zener diode is current-dependent, the threshold fluctuation range on the vertical axis of Figure 9(a) further expands, further reducing the tolerance of the detection circuit.

[0050] As described above, the power conversion device 10 according to the first embodiment can perform short circuit detection with a simple design and sufficient tolerance against erroneous detection by using the voltage detection unit 13 that detects the detection L-voltage VL generated in the inductance component 111 between the two points N1 and N2 set in the connection wiring unit 110 between the DC circuit unit 100 and the three-phase inverter 11p, and the short circuit detection unit 200 that is composed of the two comparators 201 and 203. As a result, it becomes possible to prevent the short circuit from spreading to an accident such as a converter failure or fire.

[0051] Embodiment 2 In the first embodiment, the output voltage of the filter circuit 13a is connected to the non-inverting input terminal (+) of the first comparator 201, and the first threshold voltage Vref1 is connected to the inverting input terminal (-) of the first comparator 201. In the second embodiment, the output of the filter circuit 13a is connected to the inverting input terminal (-) of the first comparator 201, and the first threshold voltage Vref1 is connected to the non-inverting input terminal (+) of the first comparator 201. With this configuration, it is possible to improve the areas with low tolerances shown in FIG. 9(b) in the first embodiment.

[0052] 10 is a diagram showing an example of the circuit configuration of the voltage detection unit 13 and the short circuit detection unit 200 of the power conversion device according to embodiment 2. Note that the overall configuration of the power conversion device is the same as that of embodiment 1, so illustration and description thereof will be omitted.

[0053] The filter circuit 13a is a low-pass filter composed of a resistor R1 and a capacitor C1. A set point N1 on the wiring is connected to the ground point GND of the filter circuit 13a and one end of the capacitor C1, and a set point N2 on the wiring is connected to one end of the resistor R1 of the filter circuit 13a. The other end of the capacitor C1, which is the output of the filter circuit 13a, is connected to the other end of the resistor R1 and is then connected to the inverting input terminal (-) of a first comparator 201. A first threshold voltage Vref1 generated by a threshold voltage generator 204 is input to the non-inverting input terminal (+) of the first comparator 201. The output of the first comparator 201 is connected to one end of the resistor R2, and one end of the capacitor C2 is connected to the ground point GND.

[0054] The output of the integrator 202 is connected to the non-inverting input terminal (+) of a second comparator 203, and a second threshold voltage Vref2 generated by a threshold voltage generator 204 is input to the inverting input terminal (-) of the second comparator 203. The output of the second comparator 203 becomes the overcurrent detection signal Ssc. The threshold voltage generator 204 generates both the first threshold voltage Vref1 and the second threshold voltage Vref2 by dividing a common power supply Vcc using resistor dividers R3 to R6.

[0055] 11 is a schematic waveform diagram illustrating the operating principle of the short-circuit detection unit 200 in the power conversion device according to the second embodiment. From the top, the diagram shows the detection L current IL, the detection L voltage VL, the output voltage of the first comparator 201, the input voltage of the second comparator 203, and the overcurrent detection signal Ssc. The solid waveform in FIG. 11 shows an example of a waveform during a short circuit, and the dotted waveform shows an example of a waveform during a turn-on operation, which is a normal switching operation. The prerequisites for the load current and the like are the same as those in the first embodiment.

[0056] At time t0, a positive-side or negative-side power semiconductor device in one phase of the three-phase inverter is turned on, causing the detection L current IL to begin flowing, and the detection L voltage VL also rises accordingly. Next, at time t1, the detection L voltage VL becomes greater than the first threshold voltage Vref1, causing the output voltage of the first comparator 201 to change from high to low. The high state is defined as 5 V, and the low state is defined as 0 V.

[0057] When the output voltage of the first comparator 201 goes low, the input voltage of the second comparator 203 starts to gradually decrease by the integrator 202. As can be seen from Fig. 11, the duration of the low state of the output voltage of the first comparator 201 is converted into the height of the input voltage of the second comparator 203 by the integrator 202. Up to this point, the operation is the same during normal switching operation and during a short circuit.

[0058] During normal switching operation at time t2, the detection L current IL flows only up to the load current ILoad, so the slope of the detection L current IL becomes gentler and the detection L voltage VL becomes lower than the first threshold voltage Vref1. As a result, the output voltage of the first comparator 201 switches from low to high, and the input voltage of the second comparator 203 also begins to gradually increase. Thereafter, when the detection L current IL reaches the load current ILoad, the switching operation is completed.

[0059] At time t2, when a short circuit occurs, the detection L current IL during a short circuit is not limited by the load, unlike during normal switching operation, so the detection L current IL continues to rise even at time t2. As a result, the detection L voltage VL also continues to maintain a value greater than the first threshold voltage Vref1, and the input voltage of the second comparator 203 also continues to fall.

[0060] When a short circuit occurs at time t3, the input voltage of the second comparator 203 continues to decrease, becomes smaller than the second threshold voltage Vref2, the overcurrent detection signal Ssc goes low, and a short circuit is detected. From the above, it can be seen that the detection circuit of the second embodiment can be used to distinguish between normal switching operation and a short circuit.

[0061] FIG. 12 shows the tolerance of the detection circuit in embodiment 2. The solid line in the figure indicates the minimum voltage line during a short circuit, and the dotted line indicates the maximum voltage line during normal switching operation. The vertical axis represents the input voltage to the first comparator 201, which would be the detection L voltage VL if the filter circuit 13a were not present. The horizontal axis represents the input voltage to the second comparator 203, which is equivalent to the time width at each magnitude of the input voltage to the first comparator 201.

[0062] 12, it is possible to distinguish between short circuit and normal switching by setting the first and second threshold voltages at, for example, point B. The value on the vertical axis at point B in FIG. 12 represents the first threshold voltage Vref1, and the value on the horizontal axis at point B represents the second threshold voltage Vref2.

[0063] Compared to the first embodiment, the inversion and non-inversion of the input to the first comparator 201 are reversed, and therefore the order of magnitude of the numerical values ​​along the horizontal axis is reversed as shown in Fig. 12, and therefore the directions of fluctuation of the first and second threshold voltages Vref1 and Vref2 and the maximum and minimum voltage lines during normal switching operation and short circuit are nearly parallel to each other. Therefore, the low tolerance at the upper right and lower left of the arrows representing threshold fluctuations in Fig. 9(b) in the first embodiment can be improved by adopting the configuration of the second embodiment.

[0064] As described above, the power conversion device according to the second embodiment can improve the areas where the tolerance for short circuit detection of the short circuit detection unit 200 of the first embodiment is low by connecting the output of the filter circuit 13a to the inverting input terminal (-) of the first comparator 201 and connecting the first threshold voltage Vref1 to the non-inverting input terminal (+) of the first comparator.

[0065] Third Embodiment In the first and second embodiments, the type of the first comparator 201 is not specified, and the circuit outputs either low or high. In the third embodiment, the type of the first comparator 201 is set to be an open collector or open drain, and further, a common power supply is used for the power supply Vcc of the threshold voltage generation unit 204 and the power supply that pulls up the output unit of the first comparator 201. The third embodiment improves the tolerance of the short-circuit detection unit 200 in the first and second embodiments.

[0066] 13 is a diagram showing an example of the circuit configuration of the voltage detection unit 13 and the short circuit detection unit 200 of the power conversion device according to embodiment 3. Note that the overall configuration of the power conversion device is the same as that of embodiment 1, and therefore illustration and description thereof will be omitted.

[0067] The filter circuit 13a is a low-pass filter composed of a resistor R1 and a capacitor C1, and a set point N1 on the wiring, a ground point GND of the filter circuit 13a, and one end of the capacitor C1 are connected, and a set point N2 on the wiring is connected to one end of the resistor R1 of the filter circuit 13a. The other end of the capacitor C1, which is the output of the filter circuit 13a, is connected to the other end of the resistor R, and is connected to the non-inverting input terminal (+) of a first comparator 201. A first threshold voltage Vref1 generated by a threshold voltage generator 204 is input to the inverting input terminal (-) of the first comparator 201.

[0068] Here, the first comparator 201 is of an open collector or open drain type, and one end of a resistor R2 and a capacitor C2 of an integrator 202, which is composed of a resistor R2 and a capacitor C2, and one end of a pull-up resistor R7 connected to a power supply Vcc of a threshold voltage generating unit 204 are connected to the output of the first comparator 201. One end of the capacitor C2 of the integrator 202 is connected to the ground point GND, and the non-inverting input terminal (+) of a second comparator 203 is connected to the output of the integrator 202.

[0069] The inverting input terminal (-) of the second comparator 203 receives the second threshold voltage Vref2 generated by the threshold voltage generator 204. The output of the second comparator 203 serves as the overcurrent detection signal Ssc. The threshold voltage generator 204 generates both the first threshold voltage Vref1 and the second threshold voltage Vref2 by dividing a common power supply Vcc using resistor dividers R3 to R6.

[0070] In the same manner as in the first embodiment, the third embodiment has the first threshold voltage Vref1 connected to the inverting input terminal (−) of the first comparator 201 and the output of the filter circuit 13a connected to the non-inverting input terminal (+), but they may be connected in the opposite manner as in the second embodiment. In the third embodiment, it is sufficient that the power supply for the second threshold voltage Vref2 and the power supply that pulls up the output of the first comparator 201 are common, and they do not need to use a common power supply for generating the first threshold voltage Vref1.

[0071] The operating principle of short-circuit detection in the power conversion device according to embodiment 3 is the same as that of embodiment 1, so illustrations and explanations will be omitted. FIG. 14 shows a diagram illustrating the tolerance of the short-circuit detection unit 200 according to embodiment 3. The solid line in the diagram indicates the minimum voltage line during a short circuit, and the dotted line indicates the maximum voltage line during normal switching operation. The vertical axis represents the input voltage to the first comparator 201, which would be the detection L voltage VL if the filter circuit 13a were not present. The horizontal axis represents the input voltage to the second comparator 203, which is synonymous with the time width at each magnitude of the input voltage to the first comparator 201.

[0072] 14, it is possible to distinguish between short circuit and normal switching by setting the first and second thresholds at, for example, point C. The value on the vertical axis at point C in FIG. 14 represents the first threshold voltage Vref1, and the value on the horizontal axis at point C represents the second threshold voltage Vref2.

[0073] By adopting the configuration of embodiment 3, even if the power supply of the threshold voltage generating unit 204 varies and the second threshold voltage Vref2 changes at a certain rate, the input voltage of the second comparator 203 also changes at a similar rate, so the second threshold voltage Vref2 on the horizontal axis does not fluctuate.

[0074] Here, in the third embodiment, the type of first comparator 201 is an open collector or open drain, but the same effect as in the third embodiment can be obtained even if first comparator 201 has a push-pull configuration and the power supply Vcc of threshold voltage generation unit 204 and the power supply voltage of the first comparator are shared as shown in Fig. 15. This is because, even if the power supply of threshold voltage generation unit 204 varies and second threshold voltage Vref2 changes at a certain rate, the input voltage of second comparator 203 also changes at a similar rate.

[0075] The configuration of FIG. 14 eliminates fluctuations in the second threshold voltage Vref2 on the horizontal axis, but fluctuations remain in the first threshold voltage Vref1 on the vertical axis. To further improve this, the first threshold voltage Vref1 can be varied depending on the magnitude of the change in the voltage difference between the positive and negative sides of the connection wiring unit 110. This is because, as the voltage difference in the DC circuit unit 100 increases, the short-circuit minimum voltage width line shown by the solid line in FIG. 14 increases along both the vertical and horizontal axes. When the voltage difference is large, the first threshold voltage increases, but the short-circuit minimum voltage width line also increases along both the vertical and horizontal axes, thereby improving the tolerance for false short-circuit detection. A specific circuit example is a configuration in which the first threshold voltage Vref1 is generated by resistor voltage division from the positive side of the DC circuit unit 100.

[0076] Up until now, only power supply variations that have a significant effect on the detection tolerance have been considered with regard to threshold voltage variations, but since there are other variations as well, such as variations in voltage dividing resistors, these can also be taken into consideration when designing. As described above, in the third embodiment, by using an open collector or open drain type for the first comparator 201 and further using a common power supply for the power supply Vcc of the threshold voltage generation unit 204 and the power supply that pulls up the output of the first comparator 201, the tolerance of the short-circuit detection unit 200 can be further improved compared to the first and second embodiments.

[0077] Fourth Embodiment This fourth embodiment relates to short-circuit detection in a case where the main circuit unit configuration of the power conversion device exemplified in the first embodiment is different and the main circuit units are connected in multiple parallel configurations. Fig. 16 shows a block diagram of an example of the configuration of a power conversion device according to the fourth embodiment. In Fig. 16, a power conversion device 10 performs power conversion between a DC circuit unit 100 and electric motors 120a, 120b as loads, and has a configuration in which main circuit units 11a, 11b and electric motors 120a, 120b are connected in parallel.

[0078] The power converter 10 includes main circuit units 11a and 11b and a control unit 12 for controlling the main circuit units 11a and 11b. The control unit 12 includes a voltage detection unit 13 for detecting a voltage generated in an inductance component 111 between set points N1 and N2 on wiring set in a connection wiring unit 110 between the DC circuit unit 100 and the power converter 10, and a short-circuit detection unit 200 for determining whether or not a short circuit has occurred in the power converter based on the output of the voltage detection unit 13. Note that, although Fig. 16 shows a configuration in which there is only one inductance component 111 for voltage detection, each of the main circuit units 11a and 11b may be provided with an inductance component for voltage detection.

[0079] 17 is a block diagram showing a specific configuration of a power conversion device according to embodiment 4. Here, as an example, the DC circuit unit 100 includes an AC power supply 100b and a three-phase PWM converter 100a that converts AC voltage into DC voltage, and the main circuit units 11a and 11b include three-phase inverters that drive three-phase electric motors 120a and 120b that are three-phase AC loads.

[0080] The three-phase PWM converter 100a is composed of an AC reactor 101a, power semiconductor elements Ma to Mf, and a capacitor 14a, and the main circuit units 11a and 11b are composed of power semiconductor elements M1 to M12 and a capacitor 14b. As in the first embodiment, the configuration of the DC circuit unit 100 and the main circuit unit 11, the type and number of power semiconductor elements, the number of phases of the power conversion device 10, the number and locations of capacitors, etc. are not limited.

[0081] The fourth embodiment is a power conversion device with a two-parallel configuration that drives two three-phase motors 120a, 120b, and is employed, for example, in the outdoor unit circuit of an air conditioner. One three-phase motor is a compressor motor, and the other is a fan motor. The configurations of the voltage detection unit 13 and the short-circuit detection unit 200 may be any of those of the first to third embodiments, and the operating principle of the short-circuit detection unit 200 is also the same. However, in a configuration with only one three-phase inverter, the second threshold voltage Vref2 is determined taking into account the overlap of the maximum current gradients di / dt of the two phases. However, in the case of multiple parallel main circuit units 11a, 11b, the number of phases where the maximum current gradients di / dt overlap increases, and therefore the second threshold voltage Vref2 must be determined based on the duration when the number of phases where the di / dt overlap is at its maximum.

[0082] In the configuration of embodiment 4, too, the voltage detection unit 13 and the short-circuit detection unit 200 provided in the common control unit 12 can detect a short circuit that occurs in the inductance component 111 between the set points N1 and N2 on the wiring set in the connection wiring unit 110 that forms the common path of the parallel-connected main circuit units 11a and 11b, and can stop the operation of the power converter for protection. Note that when a short circuit is detected in the power conversion device as in embodiment 4, the device can be prevented from being destroyed by an arm short circuit by turning off the power semiconductor elements of the three-phase PWM converter 100a and the parallel-connected main circuit units 11a and 11b.

[0083] So far, the method of implementing short circuit detection according to the present disclosure in the main circuit section has been described, but it is clear that this method can also be applied to the DC circuit section 100. Furthermore, although short circuit detection has been performed using an analog circuit in the short circuit detection circuit, short circuit detection may also be performed using a digital circuit such as an FPGA (Field-programmable gate array) or a microcontroller.

[0084] FIG. 18 shows an example of hardware using a microcomputer. The converter includes a processor 1000 and a storage device 2000. Although not shown, the storage device includes a volatile storage device such as a random access memory (RAM) and a nonvolatile auxiliary storage device such as a flash memory. Alternatively, a hard disk auxiliary storage device may be used instead of the flash memory. The processor 1000 executes a program input from the storage device 2000 to perform the above-described short-circuit detection. In this case, the program is input from the auxiliary storage device to the processor 1000 via the volatile storage device. The processor 1000 may output data such as voltage data detected by the voltage detection unit and calculation results to the volatile storage device of the storage device 2000, or may store the data in the auxiliary storage device via the volatile storage device. Furthermore, when a microcomputer is used, it is easy to output signals to turn off the power semiconductor elements of the three-phase PWM converter 100a and the paralleled main circuits 11, 11a, and 11b.

[0085] Although various exemplary embodiments and examples are described in this disclosure, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are contemplated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is extracted and combined with components of other embodiments.

[0086] 10: power conversion device, 11, 11a, 11b: main circuit section, 12: control section, 13: voltage detection section, 13a: filter circuit, 100: DC circuit section, 110: connection wiring section, 111: inductance component, 120: load, 200: short circuit detection section, 201: first comparator, 202: integrator, 203: second comparator, 204: threshold voltage generation section.

Claims

1. A power conversion device comprising: a main circuit section that performs power conversion between a DC circuit section and a load; a voltage detection section that detects a voltage generated in an inductance component between two points on a wiring that connects the DC circuit section and the main circuit section; and a short circuit detection section that has a first comparator that outputs a detection signal when the voltage detected by the voltage detection section exceeds a first threshold voltage, and a second comparator that detects the occurrence of a short circuit when the detection signal of the first comparator continues for a predetermined time or longer.

2. The power conversion device according to claim 1, further comprising an integrator between the first comparator and the second comparator, the integrator converting the duration of the detection signal of the first comparator into a voltage, and when the detection signal continues for a predetermined time or longer, the converted voltage exceeds a second threshold voltage, causing the second comparator to determine that a short circuit has occurred.

3. A power conversion device as described in claim 2, further comprising a threshold voltage generating unit that generates the first threshold voltage and the second threshold voltage, wherein a power supply for generating the first threshold voltage and a power supply for generating the second threshold voltage are common.

4. A power conversion device as described in claim 2 or 3, characterized in that the first comparator has an inverting input terminal and a non-inverting input terminal, a first threshold voltage is input to the inverting input terminal, and a voltage output from the voltage detection unit is input to the non-inverting input terminal.

5. A power conversion device as described in claim 2 or 3, characterized in that the first comparator has an inverting input terminal and a non-inverting input terminal, a first threshold voltage is input to the non-inverting input terminal, and a voltage output from the voltage detection unit is input to the inverting input terminal.

6. A power conversion device according to any one of claims 2 to 4, characterized in that the first comparator is an open collector or open drain, and a power supply for generating the second threshold voltage and a power supply for pulling up the output of the first comparator are shared.

7. The power conversion device according to any one of claims 2 to 4, wherein the first comparator has a push-pull configuration, and a power supply for generating the second threshold voltage and a power supply for the first comparator are shared.

8. The power conversion device according to claim 6, characterized in that the first threshold voltage is changed in response to a change in the voltage difference between a positive wiring and a negative wiring connecting the DC circuit unit and the main circuit unit.

9. A power conversion device as claimed in any one of claims 2 to 7, characterized in that the voltage detection section is provided with a low-pass filter for removing current pulsation occurring in the main circuit section.

10. A power conversion device as described in any one of claims 2 to 9, characterized in that the main circuit unit is composed of a three-phase inverter, and when voltages detected by the voltage detection unit overlap in time due to switching of multiple phases of the three-phase inverter, the second threshold voltage is determined based on the duration of a period during which the voltage values ​​of the multiple phases detected in an overlapping manner are equal to or greater than the first threshold voltage.

11. A power conversion device as described in any one of claims 1 to 10, characterized in that when configured with a plurality of the loads and a plurality of the main circuit sections, the voltage detection section detects the voltage on the wiring connecting the plurality of the main circuit sections and the DC circuit section.

12. A power conversion device as claimed in any one of claims 1 to 11, characterized in that when the short circuit detection unit detects a short circuit, all of the power semiconductor elements in the DC circuit unit and the main circuit unit are turned off.

13. If a capacitor is connected between the positive and negative wiring connecting the DC circuit unit and the main circuit unit, the inductance between the capacitor including the inductance component L and the power semiconductor element in the main circuit unit is Lloop, the inductance between the capacitor not including the inductance component L and the power semiconductor element is La, the element withstand voltage of the power semiconductor element is Vdsp, the maximum voltage of the DC circuit unit is Vdcmax, the maximum current gradient of the power semiconductor element is di / dt, and Lloop=La+L, 13. The power conversion device according to claim 1, wherein the following relationship holds:

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