JP2016208770A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine more accurately the temperature of a semiconductor switching element that constitutes a power conversion circuit, without providing a temperature sensor.SOLUTION: At a timing when an output current of a voltage type bridge inverter 6 becomes a predetermined value and all of a plurality of semiconductor switching elements 61 constituting the inverter 6 are controlled to an off state, a forward voltage of a freewheeling diode 62 that is connected in antiparallel to a predetermined semiconductor switching element 61 is detected so that the temperature of the diode 62 can be determined on the basis of a correlation relationship between forward voltages and temperatures when a forward current value of the freewheeling diode 62 is a predetermined value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power converter that can be suitably implemented as a power conditioner used in a power generation system such as a solar power generation system or a fuel cell power generation system.

  The following Patent Document 1 is provided integrally with a semiconductor switching element for the purpose of surely detecting an instantaneous temperature rise accompanying energization of a semiconductor switching element used in a power converter such as a three-phase inverter device. A freewheeling diode connected in reverse parallel to both ends of the semiconductor switching element, a current detecting means for detecting a forward current of the freewheeling diode, a voltage detecting means for detecting a forward voltage of the freewheeling diode, a current detecting means, There is disclosed a power converter provided with temperature estimation means for estimating the temperature of the freewheeling diode based on the values of the forward current and the forward voltage detected by the voltage detection means.

  In this conventional power converter, as described in the paragraph numbers 0031 to 0036 of the specification, the forward voltage VF of the freewheeling diode in the mode D when all the switching elements (IGBTs) of the inverter bridge circuit are off is set. The peak voltage is detected, the forward current IF of the freewheeling diode at the peak is sampled and held, and data of current-voltage characteristics according to the temperature of the freewheeling diode is detected from the detected forward current IF and forward voltage VF. Is applied to the corresponding temperature curve to obtain the temperature data at that time, and the value of the obtained temperature data is converted into an analog signal via the D / A converter, and is proportional to the temperature of the freewheeling diode. A DC voltage signal is output as an estimated temperature signal.

Japanese Patent Laid-Open No. 7-234162

  However, since the detected values of the forward current IF and the forward voltage VF include various noise components associated with the switching operation or the like, the temperature estimation based on these two variables has a large error, and an accurate temperature is determined. I can't.

  Therefore, an object of the present invention is to more accurately determine the temperature of a semiconductor switching element.

  In order to achieve the above object, the present invention takes the following technical means.

  That is, the present invention relates to a power conversion circuit including a semiconductor switching element and a diode provided integrally with the semiconductor switching element, and the semiconductor switching element is periodically arranged to cause the power conversion circuit to perform a predetermined power conversion operation. In a power converter comprising power conversion control means for on / off control, voltage detection means for detecting a forward voltage of the diode, and temperature determination means for determining the temperature of the diode, a semiconductor by the power conversion control means Timing generation means for generating a timing at which a forward current flowing through the diode becomes a predetermined value during on / off control of the switching element is further provided, and the voltage detection means is configured to generate a timing signal generated by the timing generation means. The temperature determining means is configured to detect a forward voltage. , And it is characterized in that it is configured to determine the temperature of the diode on the basis of said predetermined value and the detected forward voltage by said voltage detecting means (claim 1).

  According to the power converter of the present invention, by detecting the forward voltage of the diode at a timing when the forward current of the diode becomes a predetermined value, the temperature of the diode can be determined using the forward current as a constant, Thereby, the determination accuracy can be further improved, and the temperature of the diode, that is, the temperature of the semiconductor switching element integrated therewith can be detected more accurately. In addition, it is not necessary to separately provide a temperature sensor such as a thermistor that directly measures the temperature of the diode or the semiconductor switching element, so that the circuit configuration can be simplified and the cost can be reduced. Since the temperature is directly determined, the determination accuracy can be improved and the protection margin can be reduced as compared with the measurement by the temperature sensor installed at a location away from the diode.

  The power converter of the present invention further includes a reactor connected in series with the semiconductor switching element, and the power conversion control means controls the semiconductor switching element on / off so as to control a current flowing through the reactor. When the semiconductor switching element is turned on, a current flowing through the reactor passes through the semiconductor switching element, and a reverse voltage is applied to the diode. When the semiconductor switching element is turned off, the current flows through the reactor during the on control. The current may pass through the diode as a forward current by the current holding action of the reactor, and the timing generation means may generate a timing at which the forward current flows through the diode by turning off the semiconductor switching element ( Claim 2). According to this, due to the current holding action of the reactor, a current substantially equivalent to the current flowing through the semiconductor switching element when the semiconductor switching element is turned on flows through the diode when the semiconductor switching element is turned off. Since the current flowing through the reactor during the on / off state of the element can be regarded as substantially uniform, although some ripples occur, power conversion is performed by detecting the forward voltage at the timing when the forward current flows through the diode. The target value of the reactor current controlled by the control means and the detected value of the current sensor for detecting the reactor current can be used as the forward current value of the diode, and since the reactor current is controlled by the power conversion control means, Detect the forward current itself Less error, thereby determining a temperature of more accurately diode.

  The present invention is preferably applicable to any power conversion circuit having a reactor, and it is possible to determine the temperature of a free-wheeling diode provided in one semiconductor switching element constituting an inverter bridge circuit of a grid-connected inverter, It can be used for determining the temperature of a backflow preventing diode constituting the chopper circuit.

  That is, the present invention provides a voltage-type bridge inverter provided with a plurality of semiconductor switching elements and a free-wheeling diode connected in reverse parallel to both ends of each semiconductor switching element, and the voltage-type bridge inverter. And a plurality of semiconductor switching elements for controlling an output current of the voltage-type bridge inverter so as to convert and output a DC input power of the voltage-type bridge inverter to a predetermined AC power. Power conversion control means for periodically turning on / off the voltage, voltage detection means for detecting a forward voltage of the diode integrated with at least one semiconductor switching element of the plurality of semiconductor switching elements, and temperature of the diode A temperature changer for determining the power The voltage source bridge inverter further includes a timing generating means for generating a timing at which the output current of the voltage source bridge inverter becomes a predetermined value and all of the plurality of semiconductor switching elements are controlled to be off, and the voltage detecting means is generated by the timing generating means. Configured to detect a forward voltage of the diode at a timing, and the temperature determination unit is configured to determine the temperature of the diode based on the forward voltage detected by the voltage detection unit and the predetermined value. (Claim 3).

  According to the power converter of the present invention, DC power supplied to the input side of the voltage-type bridge inverter is converted into AC power and output by so-called current mode control of the voltage-type bridge inverter by the power conversion control means. . In such a power conversion operation, all semiconductor switching elements constituting the inverter bridge are simultaneously turned on to prevent excessive through current from flowing. Therefore, when switching the semiconductor switching elements to be turned on, all semiconductor switching elements are switched. A dead time for turning off the element is provided. Even during this dead time, the current flowing through the reactor is slightly reduced by the current holding action of the interconnected reactor, but is substantially maintained, and the current is connected in reverse parallel to one of the semiconductor switching elements. It passes through the freewheeling diode and is returned to the input side. The present invention pays attention to the fact that the value of the forward current of the freewheeling diode is substantially equivalent to the control target value of the output current by the power conversion control means, and the output current controlled by the power conversion control means is By detecting the forward voltage of the freewheeling diode at the dead time when the predetermined value is reached, the forward current of the freewheeling diode itself is not detected, and the output that is output as a result of the control. It becomes possible to treat the detected current value as a forward current value in a constant manner, which makes it possible to more accurately calculate the current value based on the relationship data or function between the forward voltage and the temperature when the forward current is a predetermined value. The temperature of the semiconductor switching element can be determined.

  In the power converter according to the invention, the voltage detection means detects a forward voltage of a diode integrated with the semiconductor switching element having the highest temperature among the plurality of semiconductor switching elements. ). According to this, all of the plurality of semiconductor switching elements can be protected from destruction due to overheating while simplifying the circuit configuration.

  The bridge inverter may be a full-bridge type or a half-bridge type, and may output a single-phase alternating current or a two-phase or three-phase alternating current. Further, it may be a two-level inverter or a multi-level inverter such as a three-level inverter. In the case of a three-level inverter, eight semiconductor switching elements are required, and one of the semiconductor switching elements that is expected to be the highest temperature is specified in advance by experiments or the like. It can be configured to determine the temperature.

  The present invention also provides a step-up chopper provided with a reactor, a semiconductor switching element, and a backflow prevention diode, a DC link capacitor provided on the output side of the step-up chopper, and boosting the input voltage of the step-up chopper to increase the input voltage of the step-up chopper. Power conversion control means for periodically turning on / off the semiconductor switching element so as to output to the power supply, voltage detection means for detecting the forward voltage of the diode, and temperature determination means for determining the temperature of the diode. The power converter further comprises timing generating means that operates in a steady state where the input current of the boost chopper becomes a predetermined value and generates a timing after a predetermined delay time from the turn-off timing of the semiconductor switching element, The voltage detection means is generated by the timing generation means. It is configured to detect a forward voltage of the diode by imming, and the temperature determination unit is configured to determine a temperature of the diode based on the forward voltage detected by the voltage detection unit and the predetermined value. (Claim 5).

  According to the power converter of the present invention, the reactor current is gradually increased by short-circuiting the reactor to the input-side power source when the semiconductor switching element is on, and the reactor current is maintained when the semiconductor switching element is off-control. As a result, the output side of the reactor is boosted to generate a forward voltage in the diode, and the reactor current passes through the diode as it is and is supplied to the DC link capacitor. The present invention pays attention to the fact that the forward current of the diode is substantially equivalent to the reactor current, that is, the input current of the step-up chopper, and the input current controlled by the power conversion control means becomes a predetermined value. By detecting the forward voltage of the diode at the time of off-control of the semiconductor switching element when operating in the state, it is possible to detect the control target value of the input current or the input current without detecting the forward current of the diode itself. It is possible to treat the detected value as a forward current value in a constant manner, which makes it possible to more accurately detect the diode temperature based on the relationship data or function between the forward voltage and temperature when the forward current is a predetermined value. As a result, the temperature of the semiconductor switching element integrated therewith can be determined.

  As described above, according to the power converter of the first aspect of the present invention, by detecting the forward voltage of the diode at a timing when the forward current of the diode becomes a predetermined value, the forward current is set as a constant. The temperature of the diode can be determined, thereby further improving the determination accuracy and more accurately detecting the temperature of the diode, that is, the temperature of the semiconductor switching element integrated therewith. In addition, it is not necessary to separately provide a temperature sensor such as a thermistor that directly measures the temperature of the diode or the semiconductor switching element, so that the circuit configuration can be simplified and the cost can be reduced. Since the temperature is directly determined, the determination accuracy can be improved and the protection margin can be reduced as compared with the measurement by the temperature sensor installed at a location away from the diode.

  According to the power converter of claim 2 of the present invention, a current substantially equivalent to the current flowing through the semiconductor switching element when the semiconductor switching element is on-controlled by the current holding action of the reactor is The current that flows through the diode when the element is controlled to be off and the current that flows through the reactor during the on / off state of these semiconductor switching elements can be considered to be substantially uniform although some ripples and the like occur. By detecting the forward voltage, the target value of the reactor current controlled by the power conversion control means and the detected value of the current sensor that detects the reactor current can be used as the forward current value of the diode. Because it is controlled by the power conversion control means, Less errors than to detect the forward current itself, thereby determining the temperature of more accurately diode.

  In the power converter according to claim 3 of the present invention, the forward voltage of the freewheeling diode is detected at the dead time when the output current controlled by the power conversion control means reaches a predetermined value. Without detecting the forward current of the freewheeling diode itself, it becomes possible to treat the control target value or the detected value of the output current output as a result of control as a forward current value in a constant manner. The temperature of one semiconductor switching element can be more accurately determined based on the relationship data or function between the forward voltage and the temperature when the forward current is a predetermined value.

  Moreover, according to the power converter which concerns on Claim 4 of this invention, all the several semiconductor switching elements can be protected from destruction by overheating, simplifying a circuit structure.

  In the power converter according to claim 5 of the present invention, the semiconductor switching element is controlled to be off when the input current controlled by the power conversion control means is operating in a steady state at a predetermined value. By detecting the forward voltage of the diode, it is possible to treat the control target value of the input current or the detected value of the input current as a forward current value without detecting the forward current of the diode. Thus, it is possible to more accurately determine the temperature of the diode, and hence the temperature of the semiconductor switching element integrated therewith, based on the relationship data or function between the forward voltage and the temperature when the forward current is a predetermined value.

1 is a schematic circuit block diagram of a power converter (power conditioner) according to an embodiment of the present invention. It is a circuit block diagram which shows the 1st Example of the voltage detection means of the same electric power converter, and a timing generation means. It is a circuit block diagram which shows the 2nd Example of the voltage detection means and timing generation means of the power converter. It is a circuit block diagram which shows the 3rd Example of the voltage detection means and timing generation means of the power converter. It is a circuit block diagram which shows the 4th Example of the voltage detection means and timing generation means of the power converter. It is operation | movement explanatory drawing of the inverter (2nd power converter circuit) of the power converter. 3 is an operation timing chart of the inverter. It is an output current waveform diagram of the inverter. It is an operation | movement timing chart of the converter (1st power converter circuit) of the power converter.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of a power conditioner 1 (power converter) according to an embodiment of the present invention. The power conditioner 1 generates DC generated power output from a power generation unit 2 such as a solar cell array. The AC power is converted to AC power connected to the commercial power system 3 and output to the commercial power system 3, and the converter 4 (first power conversion circuit), the DC link capacitor 5 and the inverter 6 (second power conversion) Circuit), a disconnection protection relay 7 provided between the output unit of the power conversion unit (the output unit of the inverter 6 in the illustrated example) and the commercial power system 3, and the power The control part 8 (power conversion control part) which controls the operation | movement of a conversion part and the protection relay 7 is provided.

  The power generation unit 2 may have a conventionally known appropriate configuration, and generally includes a plurality of solar cell modules connected in series or in parallel, and is installed on a site, a roof of a building, or the like. As the power generation unit 2, a fuel cell or other power generation device can be used.

  The control unit 8 controls each power conversion operation in the converter 4 and the inverter 6 and the opening / closing operation of the protection relay 7, and a display unit (not shown) including a liquid crystal display attached to the casing of the power conditioner 1. ) Display control and various abnormality detection controls in the power conditioner 1. The control unit 8 includes a microprocessor (not shown) as a control center on a control board, and drives each semiconductor switching element constituting the converter 4 and the inverter 6 based on a control signal from the microprocessor. A drive circuit (not shown) for outputting a signal is provided.

  The power conversion unit may also have a conventionally known appropriate configuration, and in the illustrated embodiment, the DC power supplied from the power generation unit 2 corresponds to the maximum value of the AC system voltage (for example, 280 V in the case of 200 V AC power). The DC / DC converter 4 that converts the power to boost the voltage to a predetermined voltage (for example, 350V) and outputs it to the DC link capacitor 5 and the DC power supplied via the DC link capacitor 5 to AC power linked to the system power. A DC / AC inverter 6 that performs power conversion and outputs it to the system 3 can be configured.

  The converter 4 includes a DC reactor 41, a semiconductor switching element 42 such as an IGBT that controls the stored energy of the DC reactor 41, and a backflow prevention diode 43 that prevents a backflow of current from the DC link capacitor 5 to the DC reactor 41. The cathode chopper circuit of the diode 43 is connected to the positive electrode side of the DC link capacitor 5. The semiconductor switching element 42 is connected in reverse parallel to an FWD 44 (free wheeling diode) for commutating a load current. In this embodiment, the semiconductor switching element 42 and the backflow prevention diode 43 are integrally incorporated in one power module such as an IPM (intelligent power module), and preferably the backflow prevention diode 43 is provided in the semiconductor switching element 42. It is possible to use the one mounted in the vicinity.

  The inverter 6 is a full-bridge voltage-type bridge inverter, and is configured by connecting four semiconductor switching elements 61 such as IGBTs in an H-bridge type and connecting a free-wheeling diode 62 to each semiconductor switching element 61 in antiparallel. An interconnection reactor 63 is provided on the output side. This inverter 6 controls the output current so that the output current becomes an AC waveform synchronized with the system power by performing so-called current mode control (current control of the voltage source inverter) by the control unit 8. At the time of power output to DC, DC power from the DC link capacitor 5 is converted into AC power by PWM control or PAM control and output to the system 3. In this embodiment, the four semiconductor switching elements 61 and the freewheeling diode 62 are integrally incorporated in one power module such as an IPM (intelligent power module), and preferably the semiconductor switching elements 61 and A device in which the freewheeling diode 62 is mounted close to each other can be used.

  An input voltage sensor 10 and an input current sensor 11 are provided in the input electric circuit on the input side of the converter 4, and an output voltage sensor 12 and an output current sensor 13 are provided in the output electric circuit on the output side of the inverter 6. The detected values of 10, 11, 12, and 13 are input to the control unit 8 and used as control parameters for the power conversion operation in the converter 4 and the inverter 6.

  Further, the first voltage detection circuit 14 (voltage detection means) for detecting the forward voltage of the backflow prevention diode 43 of the converter 4 and one semiconductor switching element 61 constituting the inverter 6 are connected in reverse parallel. A second voltage detection circuit 15 (voltage detection means) for detecting the forward voltage of the freewheeling diode 62 is provided. These first and second voltage detection circuits 14 and 15 may have equivalent circuit configurations or different circuit configurations. 2 to 5 show circuit configuration examples that can be used as the first and second voltage detection circuits 14 and 15, respectively.

  In the embodiment shown in FIG. 2, the voltage across the diodes 43 and 62 to be measured is divided by the voltage dividing circuit 16, and the divided voltage signal is supplied to the sample and hold circuit 18 via the buffer amplifier 17. It is configured. Note that an isolation amplifier is used as the buffer amplifier 17.

  A sampling timing signal generated by the timing generator 19 is also input to the sample hold circuit 18, and the input voltage from the buffer amplifier 17 is sampled at the sampling timing indicated by the sampling timing signal, and the sampled voltage value is sampled. Is held and output to the control unit 8 as a voltage detection signal (analog value).

  In the embodiment shown in FIG. 3, the voltage divided by the voltage dividing circuit 16 is sampled and held by the sample and hold circuit 18, and the output voltage of the sample and hold circuit 18 is output to the control unit 8 via the buffer amplifier 17. Yes.

  The embodiment shown in FIG. 4 is a configuration example that can be used when insulation is not particularly required, and the buffer amplifier can be omitted as shown in the figure.

  The embodiment shown in FIG. 5 is a configuration example that can be used when the microprocessor of the control unit 8 has a high performance. The sample hold circuit 18 is omitted and the output of the buffer amplifier 17 is used as an analog input terminal of the microprocessor. The input voltage is sampled at the sampling timing generated by the timing generation means 19 by the microprocessor. Thus, the microprocessor functions as the sample hold means 18.

  The timing generation unit 19 can adopt an appropriate configuration, and the microprocessor of the control unit 8 can function as the timing generation unit 19, or the timing generation unit 19 can be provided by a dedicated circuit provided separately from the control unit 8. The timing generation means 19 can also be configured by a combination of the microprocessor of the control unit 8 and a dedicated circuit that operates based on a control signal from the microprocessor. The sampling timing generated by the timing generation means 19 may be generated by calculation in a microprocessor, or generated based on a drive signal generated by a drive circuit that drives the converter 4 or the inverter 6. Also good. The present invention is characterized by the timing when the timing generating means 19 generates the timing, and the circuit configuration itself of the timing generating means 19 may be an appropriate configuration.

  Next, in order to describe the sampling timing generated by the timing generation means 19, the operation of the inverter 6 will be described first.

  FIG. 6 is an operation explanatory diagram for explaining the operation principle of the inverter 6. The output current of the inverter 6 is controlled by periodically repeating the four operation modes 1 to 4 shown in the figure. . In mode 1, the upper right and lower left switches are turned on, and the lower right and upper left switches are turned off. At this time, as shown in the graph on the upper right of the circuit diagram, the interconnection reactor is positively connected to the power supply side. The current flowing through the interconnected reactor increases. In mode 3, the lower right and upper left switches are turned on, and the upper right and lower left switches are turned off. At this time, as shown in the graph on the upper right of the circuit diagram, the interconnection reactor is reversely connected to the power supply side. Current flowing through the system reactor decreases. By alternately switching between these modes 1 and 3 and appropriately controlling the durations of the modes 1 and 3 by PWM control, an alternating current linked to the system power as shown in FIG. 8 is output. Also, when switching from mode 1 to mode 3 and when switching from mode 3 to mode 1 to prevent all switches from being turned on when switching between modes 1 and 3, the mode is switched to modes 2 and 4. As shown in the figure, there is a dead time to turn off all the switches. During this dead time, the current flowing through the interconnected reactor cannot be changed suddenly by the magnetic energy conservation law of the reactor. The reactor current is circulated to the power supply side. In one embodiment, the dead time is about 1 to 2 microseconds.

  FIG. 7 is a timing chart showing the transition of the control signal of the positive side switching element and the negative side switching element of the upper arm of the inverter 6 and the voltage across the negative side switching element to be measured when the output current is around 0 A (near the zero cross point). It is a chart. Since each semiconductor switching element has a slight delay time at the time of turn-on and turn-off, there is a slight difference between the dead time on the control logic and the dead time on the actual output. Therefore, the timing generation means 19 for the inverter 6 preferably detects the dead time on the actual output, or obtains correlation data between the dead time on the logic and the dead time on the output in advance by experiment, An appropriate timing can be generated based on the correlation data and the logic dead time.

  In this embodiment, the timing generating means 19 for the inverter 6 is configured so that the output current, that is, the interconnected reactor current is 1A ± α (allowable error), as shown in FIG. As shown in FIG. 7, the voltage at both ends of the negative side switching element 61 becomes a negative voltage and a forward voltage is applied to the freewheeling diode 62, so that the current flowing through the interconnection reactor 63 is A dead time signal composed of a pulse signal indicating the sampling timing is generated at the timing of circulating through 62.

  The timing at which the interconnected reactor current is 1 A can be determined by an appropriate method. For example, from the zero cross point where the reactor current becomes 1 A with reference to the zero cross point of the output current waveform (control target waveform) shown in FIG. May be a timing after the elapsed time, or may be determined based on a detection value of the output current sensor 13, or may be determined at a timing when the control target value of the control unit 8 is 1 A. Also good.

  Since this dead time signal is not generated when the interconnected reactor current is not 1A ± α, this ensures that the current flowing through the freewheeling diode 62 is 1A ± α when the forward voltage of the freewheeling diode 62 is sampled. it can.

  The storage unit of the control unit 8 stores in advance relationship data or a relational expression between the forward voltage and the temperature of the freewheeling diode 62 when the forward current is 1 A, and the microprocessor of the control unit 8 stores a predetermined value. At the timing or regularly, the forward voltage value of the freewheeling diode 62 sampled and held by the voltage detection circuit 14 is monitored, and based on the forward voltage value and the relational data or relational expression, the freewheeling diode Control is configured so as to determine the temperature of 62 and, in turn, the temperature of the semiconductor switching element 61. Thus, the control unit 8 that performs the determination constitutes a temperature determination unit that determines the temperature of the freewheeling diode 62. As a relational expression, for example, forward voltage Vf = a × temperature T + b (a and b are constants, a is −2 mV / ° C.), for example.

FIG. 9 is a timing chart for explaining the timing generation logic of the sampling timing generation means 19 for the converter 4. First, the operation principle of the converter 4 will be described. When a PWM-controlled step-up chopper drive signal is output to the semiconductor switching element 42, the DC reactor 41 is connected to the power supply unit 2 when the semiconductor switching element 42 is turned on, and the reactor current is Gradually increase from I _L1 to I _L2 . On the other hand, at the time of off control, the output voltage of the DC reactor 41 is boosted to generate a forward voltage in the backflow prevention diode 43, and the reactor current passes through the diode 43 and is supplied to the DC link capacitor 5. At this time, the reactor current That is, the forward current flowing through the diode 43 and the forward voltage of the diode 43 gradually decrease as shown in the figure.

  The sampling timing generation means 19 for the converter 4 operates in a steady state where the input current (reactor current) of the boost chopper becomes a predetermined value, and the predetermined timing while the semiconductor switching element 42 is turned off. At the timing, a pulse signal indicating the sampling timing is generated. The state where the input current of the boost chopper becomes a predetermined value may be a state created by active control. For example, the switching element 42 is set so that the input current becomes a predetermined value in order to determine an overheat state of the switching element. PWM control may be performed. Also, instead of performing active current control, for example, the maximum input current that increases the risk of overheating is set to a predetermined value, and the sampling timing generating means 19 sets the sampling timing when operating at the maximum input current. It can also be configured to generate. In addition, it can be configured to generate a sampling timing when operating at any one of a plurality of input current values.

  The ripple of the DC reactor current of the step-up chopper may be relatively large even in a steady state, and the noise component due to the switching operation increases immediately after the semiconductor switching element 42 is turned off. The pulse signal is output at a timing after a predetermined delay time Δt from the turn-off timing. This delay time Δt can be a time when the reactor current including the ripple is just an average value (that is, the input current value of the boost chopper). For example, when half of the off time has elapsed from the turn-off timing, can do.

Further, the following equation (1) is established when the semiconductor switching element 42 is turned on, and the following equation (2) is established when the semiconductor switching element 42 is turned off.
L × (I _L2 −I _L1 ) / Ton = Vin Expression (1)
L × (I _L2 −I _L1 ) / Toff = Vo−Vin−Vf Equation (2)
Vin: power supply voltage, Ton: on time, Toff: off time, L: DC reactor inductance, Vo: DC link voltage, Vf: diode forward voltage (can be ignored because it is sufficiently small compared to Vo and Vin)

The power supply voltage Vin can be detected by the input voltage sensor 10, the inductance L is a constant, and Ton and Toff are parameters on the control of the control unit 8 and are known by the control unit 8. Vo is also a DC link voltage detection sensor. (Not shown). Accordingly, the amount of ripple of the reactor current (I _L2 −I _L1 ) can be calculated from these equations (1) and (2), and the relationship between this and the off time Toff makes it possible to calculate the reactor current per unit time during the off time. The amount of decrease and the slope of the straight line during the reactor current OFF time Toff in FIG. 9 are known, while the average value of the reactor current is known from the detected value of the input current sensor 11. It is possible to calculate an accurate reactor current value after a delay time Δt. By sampling and holding the forward voltage of the diode 43 when the reactor current value is a predetermined current value for which relational data or a relational expression is prepared in advance, the temperature of the diode 43 and thus the semiconductor switching element can be more accurately determined. The temperature of 42 can be determined.

  The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate. For example, in the above-described embodiment, an example of a power conditioner including a converter and an inverter has been described. However, the present invention can be implemented as a power converter including only a converter or a power converter including only an inverter. The semiconductor switching element and the diode need only be thermally integrated. For example, the semiconductor switching element component and the diode component that are separately supplied may be mounted on the substrate so as to be thermally integrated. Good.

1 Power converter (power conditioner)
4 Power conversion circuit (converter)
41 DC reactor 42 Semiconductor switching element 43 Backflow prevention diode 5 DC link capacitor 6 Power conversion circuit (inverter)
61 Semiconductor switching element 62 Free-flowing diode 63 Interconnected reactor 8 Power conversion control means (control unit)
14 Voltage detection means (voltage detection circuit for converter diode)
15 Voltage detection means (voltage detection circuit for inverter diode)
19 Timing generation means

Claims (5)

A power conversion circuit including a semiconductor switching element and a diode provided integrally with the semiconductor switching element, and power for periodically on / off controlling the semiconductor switching element to cause the power conversion circuit to perform a predetermined power conversion operation In a power converter comprising conversion control means, voltage detection means for detecting a forward voltage of the diode, and temperature determination means for determining the temperature of the diode,
The power generation control means further includes timing generation means for generating a timing at which a forward current flowing through the diode becomes a predetermined value during the on / off control of the semiconductor switching element by the power conversion control means, and the voltage detection means includes the timing generation means The diode is configured to detect a forward voltage of the diode at a generation timing, and the temperature determination unit determines the temperature of the diode based on the forward voltage detected by the voltage detection unit and the predetermined value. A power converter characterized by being configured.   2. The power converter according to claim 1, further comprising a reactor connected in series with the semiconductor switching element, wherein the power conversion control means controls the semiconductor switching element to control current flowing through the reactor. When the semiconductor switching element is on-controlled, a current flowing through the reactor passes through the semiconductor switching element, and a reverse voltage is applied to the diode, and when the semiconductor switching element is off-controlled, the reactor is turned on during the on-control. The flowing current passes through the diode as a forward current due to a current holding action of a reactor, and the timing generating means generates a timing at which the forward current flows through the diode by turning off a semiconductor switching element. To power converter. A voltage-type bridge inverter provided with a plurality of semiconductor switching elements and each semiconductor switching element and having a free-wheeling diode connected in reverse parallel to both ends of each semiconductor switching element, and provided on the output side of the voltage-type bridge inverter The plurality of semiconductor switching elements are periodically turned on / off in order to control the output current of the voltage-type bridge inverter so as to convert and output the DC input power of the voltage-type bridge inverter to a predetermined AC power. Power conversion control means for controlling off, voltage detection means for detecting a forward voltage of the diode integrated with at least one semiconductor switching element of the plurality of semiconductor switching elements, and temperature determination means for determining the temperature of the diode In a power converter comprising:
Timing generating means for generating a timing at which the output current of the voltage source bridge inverter becomes a predetermined value and all of the plurality of semiconductor switching elements are controlled to be turned off, and the voltage detecting means at the timing generated by the timing generating means. The diode is configured to detect a forward voltage of the diode, and the temperature determination unit is configured to determine a temperature of the diode based on the forward voltage detected by the voltage detection unit and the predetermined value. A power converter characterized by that.   4. The power converter according to claim 3, wherein the voltage detecting means detects a forward voltage of a diode integrated with a semiconductor switching element having the highest temperature among the plurality of semiconductor switching elements. vessel. A step-up chopper provided with a reactor, a semiconductor switching element, and a backflow prevention diode, a DC link capacitor provided on the output side of the step-up chopper, and the semiconductor so as to step up the input voltage of the step-up chopper and output it to the DC link capacitor In a power converter comprising: power conversion control means for periodically turning on / off a switching element; voltage detection means for detecting a forward voltage of the diode; and temperature determination means for determining the temperature of the diode.
The voltage detection means further comprises timing generating means that operates in a steady state where the input current of the boost chopper becomes a predetermined value and generates a timing after a predetermined delay time from the turn-off timing of the semiconductor switching element. The diode is configured to detect a forward voltage of the diode at a timing generated by the timing generator, and the temperature determination unit is configured to detect the forward voltage of the diode based on the forward voltage detected by the voltage detector and the predetermined value. A power converter configured to determine a temperature.

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