JP2007202329A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power converter for operating a reverse voltage applying circuit by using a simple constitution without providing an external circuit for a microcomputer. <P>SOLUTION: The power converter is provided with a pair of main circuit switching elements 5 connected to a diode 6, a reverse voltage applying means 7 for applying a reverse voltage to the diode 6, a means 13c for generating a PWM fundamental signal for driving the main switching elements 5, and the microcomputer internally having a one-shot pulse generating means 20 connected to the PWM fundamental signal generating means 13c and generating a signal for driving the reverse voltage applying means 7 for a predetermined period based on the PWM fundamental signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power conversion device that uses an FET as at least one of main circuit switching elements and supplies power to a load.

  In recent years, MOSFETs with high efficiency due to their low ON resistance, such as super junction MOSFETs, have been developed. Conventionally, a power conversion device using a MOSFET as a switching element provided in an inverter circuit in a power conversion device that drives an inductive load has been proposed (see Patent Document 1).

In the power conversion device in this proposal, due to the reverse current generated in the parasitic diode (diode that is naturally created on the circuit due to the structure of the MOSFET) connected in reverse parallel to the MOSFET according to ON / OFF of the MOSFET as the switching element. In order to reduce the loss, a reverse voltage application circuit is provided. That is, when one MOSFET is changed from ON to OFF by the reverse voltage application circuit, the reverse voltage is applied to the parasitic diode before the ON timing of the other MOSFET paired with the MOSFET. The reverse voltage applied is a PWM (Pulse Wide Modulation) basic signal generated by comparing a triangular wave signal with a reference signal based on a reference frequency and a reference voltage, and an OFF signal of a MOSFET that applies the reverse voltage. This is based on drive signals generated in combination.
Japanese Patent Laid-Open No. 10-327585

Here, in Patent Document 1, ON / OFF of the operation of the reverse voltage application circuit is controlled by the potential discrimination circuit. FIG. 5 is a time chart showing the ON or OFF state of each signal generated based on the PWM basic signal generated from the reference signal and the triangular wave signal. Symbols from “t1” to “t4” are attached to the pulses of the PWM basic signal. In this time chart, a pair of main circuit switching elements are described as “upper arm” and “lower arm”, respectively, and “upper arm switching signal” and “lower arm switching signal” are each MOSFET that is a switching element. Is a signal output to drive the. The “upper arm reverse voltage application signal” and the “lower arm reverse voltage application signal” are provided for driving the reverse voltage application circuit, and are switching elements in the reverse voltage application circuit for applying the reverse voltage to each parasitic diode. (Hereinafter referred to as “reverse voltage application switching element”) is a signal output to instruct the application of the reverse voltage.

  In the potential determination circuit of Patent Document 1, when a PWM basic signal as shown at the top of the time chart of FIG. 5 is generated, the upper arm switching signal for driving the upper arm MOSFET changes from ON to OFF. Thereafter, it is necessary to apply a reverse voltage to the parasitic diode of the upper arm MOSFET before the lower arm MOSFET is turned on, and to finish applying the reverse voltage after the lower arm MOSFET is turned on.

  In other words, after the upper arm switching signal for driving the upper arm MOSFET changes from ON to OFF, after providing a slight delay, the potential discrimination circuit sets the upper arm reverse voltage application signal to ON as shown by the solid line a. Thereafter, by maintaining the ON state for a predetermined time, the upper arm reverse voltage application signal is turned OFF after the lower arm is turned ON.

  Here, as shown in FIG. 5, the upper and lower arms are simultaneously turned ON between the switching signals of the upper arm and the lower arm, and only the respective ON signals are set for a predetermined time (this time is set to be short). Hereinafter, it is called “dead time” or “delay time”, and its time width is expressed as “td”).

  Therefore, the potential discriminating circuit that generates the reverse voltage application signal is turned on when a predetermined time ta (ta <td) is delayed from the upper arm switching signal OFF, and is then kept on for tb (ta + tb> td). After that, an upper arm reverse voltage application signal that is turned off must be output. Similarly, after the lower arm switching signal for driving the lower arm MOSFET changes from ON to OFF, the lower arm reverse voltage application signal must be output as shown by the solid line b.

  In recent years, in order to cope with such a power converter for driving a three-phase motor, a microcomputer that generates a PWM basic signal therein and outputs a signal for controlling ON / OFF of a main circuit switching element based on the PWM basic signal has been developed. Developed and adopted. When such a microcomputer is used, a potential determination circuit for controlling ON / OFF of the operation of the reverse voltage application circuit is provided outside the microcomputer.

  Further, depending on the type of microcomputer, there is a type in which a one-shot pulse generating means for generating a one-shot pulse signal based on an external input and outputting the same to the outside is provided. Therefore, it is conceivable to use a microcomputer capable of outputting the upper and lower arm switching signals and having the one-shot pulse generating means, and outputting the upper and lower arm reverse voltage application signals from the one-shot pulse generating means.

  However, in the conventional one-shot pulse generating means of a microcomputer, a trigger signal serving as a trigger for generating the output signal is externally input to the microcomputer. Therefore, for example, in an inverter circuit that drives a three-phase DC brushless motor, for example, when all the switching elements are MOSFETs, switching of the six upper and lower arms output to the outside from the microcomputer via the output terminal It was necessary to return the signal from the six external trigger input terminals back into the microcomputer. As described above, there is a problem that the area of the printed circuit board on which the microcomputer is mounted becomes large due to the useless wiring of returning its output to the microcomputer again.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to output upper and lower arm reverse voltage application signals without increasing the external wiring of the microcomputer that drives the switching element of the power converter. It is possible to provide a power conversion device with a simplified circuit configuration.

  A feature of the embodiment of the present invention is that, in the power converter, a pair of main circuit switching elements connected to a DC voltage source and supplying power to the load by ON and OFF driving are composed of a pair of FETs, and a pair of A diode connected in reverse parallel to each of the main circuit switching elements, reverse voltage applying means for applying a reverse voltage lower than the voltage of the DC power source to the diode connected in reverse parallel to the FET, and a pair of main circuit switching elements are turned on , A PWM basic signal generating means for generating a PWM basic signal for driving OFF, and a one-shot for generating a reverse voltage applying signal for driving the reverse voltage applying means for a predetermined period based on the PWM basic signal connected to the PWM basic signal generating means And a microcomputer having pulse generation means therein.

  According to the present invention, a power conversion device that simplifies the circuit configuration by allowing the microcomputer to output an upper / lower arm reverse voltage application signal without increasing the external wiring of the microcomputer that drives the switching element. Can be provided.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

(First embodiment)
As shown in FIG. 1, in the power conversion device 1 according to the first embodiment of the present invention, an inverter circuit 3 is connected in series to the power supply line of the DC voltage source 2, and the inverter circuit 3 is connected to the output side. Is connected to an inductive load 4 such as a motor.

  The inverter circuit 3 is connected to the upper element MOSFETs 5u to 5w and the lower element MOSFETs 5x to 5z which are main circuit switching elements by a three-phase bridge connection. Here, MOSFETs 5u and 5x, MOSFETs 5v and 5y, and MOSFETs 5w and 5z constitute a pair of main circuit switching elements. These MOSFETs 5 are, for example, super junction MOSFETs. Diodes (parasitic diodes) 6u to 6w and 6x to 6z are connected in antiparallel between the sources and drains of the MOSFETs 5u to 5w and 5x to 5z. Although these switching elements are constituted by low ON resistance MOSFETs, one of the pair of main circuit switching elements may be an IGBT, in which case the upper element is an IGBT and the lower element is a MOSFET. It is preferable to make it.

  Drive means 14 u to 14 w and 14 x to 14 z are respectively provided at the gates of the main circuit switching elements 5, and each main circuit switching element 5 is driven by the drive means 14 based on a switching signal output from the microcomputer 13. Is driven ON and OFF by the output of.

  The diodes 6u to 6w and 6x to 6z are connected to reverse voltage application circuits 7u to 7w and 7x to 7z as reverse voltage application means, respectively. Each of these reverse voltage application circuits 7 has a low voltage DC voltage source 8 having a voltage lower than that of the DC voltage source 2, and the reverse voltage application circuits 7x to 7z share the low voltage DC voltage source 8x. A low voltage DC voltage source 8 is connected between the sources and drains of the MOSFETs 5u to 5w and 5x to 5z, respectively.

  Resistors 9u to 9w and 9x to 9z are provided in series with the low-voltage DC voltage source 8 of the reverse voltage application circuit 7, and capacitors 10u to 10w and 10x to 10z are connected in parallel. The resistor 9 is provided in order to prevent an inrush current accompanying charging of the capacitor 10. Further, reverse voltage application switching elements 11u to 11w and 11x to 11z and diodes 12u to 12w and 12x to 12z for preventing reverse current flow are connected on the power supply line of the low voltage DC voltage source 8. Here, a MOSFET with low power consumption is suitably used for the reverse voltage application switching element 11.

  As shown in FIG. 2, the microcomputer 13 includes an output port 13e that outputs upper and lower arm switching signals to be applied to the U-phase to W-phase and X-phase to Z-phase main circuit switching elements 5, and U-phase to W-phase. The output circuit 20 is connected to the inverter circuit 3 through an output port 20 a provided in the one-shot pulse generation means 20 that outputs a signal for driving the X-phase to Z-phase reverse voltage application circuit 7. In FIG. 2, only a single output phase, that is, the U-phase portion is shown for explanation, and such a configuration is required for three phases in the three-phase inverter device.

  Furthermore, the microcomputer 13 generates a reference signal generating means 13a for generating a reference signal, a triangular wave signal generating means 13b for generating a triangular wave signal of a predetermined period, and a reference in order to generate a switching signal applied to the main circuit switching element. The PWM basic signal generating means 13c for inputting the output of the signal generating means 13a and the output of the triangular wave signal generating means 13b and generating a basic PWM signal for generating a switching signal, and this PWM basic signal are inputted. Inverting means 13dc and delay means 13da, 13db. A signal applied to the drive means 14 via the output port 13e of the microcomputer 13 through the delay means 13da and 13db in the final stage is used to drive the upper and lower arm switching signals (hereinafter referred to as “switching signals”). α ”)). In the first embodiment, the reference signal generating unit 13 a and the triangular wave signal generating unit 13 b are provided in the microcomputer 13, but may be provided outside the microcomputer 13.

  The PWM basic signal generation means 13c generates a PWM basic signal that is a basis of the switching signal applied to the main circuit switching element, based on the magnitude comparison between the reference signal and the triangular wave signal. That is, as shown in FIG. 5 described above, the PWM basic signal is generated so as to be turned on or off based on the result of the magnitude comparison between the reference signal and the triangular wave signal.

  The inversion means 13dc is configured by an inverter circuit that inverts each input PWM basic signal. The delay means 13da and 13db are circuits that delay only the ON timing of the input PWM basic signal by td time. From the viewpoint of efficiency, this time is preferably as short as possible (for example, about 2 to 3 μs) within a range in which a short circuit can be prevented.

  Further, the microcomputer 13 generates an upper and lower arm reverse voltage application signal (hereinafter referred to as “switching signal β”) to be applied to the reverse voltage application switching element 11 through the gate driving means 15u to 15w and 15x to 15z. One-shot pulse generating means 20 is provided. A signal input to the trigger input 20b of the one-shot pulse generation means 20 is a switching signal α.

  The switching signal α is generated as the switching signal β by the one-shot pulse generation means 20 and then output from the output port 20a, and is sent to the reverse voltage application circuit 7 (reverse voltage application switching element 11) via the gate drive means 15. Supplied.

  The one-shot pulse generation means 20 delays the ON signal input as a trigger by a predetermined time ta, then outputs the ON signal, and then holds the ON state for tb time, and then sets it as the OFF signal. That is, the switching signal β is applied to the reverse voltage application switching element 11 with a delay of ta time from the time when the switching signal of the main circuit switching element 5 changes from ON to OFF, continues ON for tb time, and then turns OFF. It will be. As a result, the reverse voltage application switching element 11 can apply a reverse voltage to the (parasitic) diode 6 over a period before and after the MOSFET paired with the corresponding MOSFET shifts from OFF to ON. As a result, the reverse current flowing through the (parasitic) diode connected in reverse parallel to the MOSFET can be suppressed. Here, the times ta and tb can be set by the firmware of the microcomputer, and are set in advance based on the characteristics of the switching element, the circuit constant of the reverse voltage application circuit, and the like.

  The trigger signal selection means 21 uses the input six switching signals α (for each switching element, but two are shown only for the U phase in FIG. 2) as trigger signals for the one-shot pulse generation means 20. Whether or not to send is selected for each switching signal α. That is, when all of the six switching elements of the three-phase inverter device are MOSFETs, all six switching signals α are supplied to the one-shot pulse generating means 20 as trigger signals. However, for example, when any one of the upper and lower arms is an element other than a MOSFET, the reverse voltage application operation is not required. In such a case, the switching signal α corresponding to the element other than the MOSFET is set to one. It is possible not to cause useless operation by not sending it as a trigger signal to the shot pulse generating means 20. As a result, the microcomputer can be used even if the type and arrangement of the switching elements are different, so that it has versatility.

  The selection in the trigger signal selection means 21 can be set by microcomputer firmware.

  By using a signal generated inside the microcomputer as described above, it is not necessary to input a trigger signal from the outside of the microcomputer when generating a switching signal to be applied to the reverse voltage application switching element 11. It is possible to provide a power conversion device that simplifies a circuit configuration in which upper and lower arm reverse voltage application signals are output from a microcomputer without increasing external wiring.

  In addition, the trigger signal selection unit selects whether to send the input signal as a trigger to the one-shot pulse generation unit 20 by, for example, firmware register setting. Therefore, by changing the firmware register setting, the FET Even if some are used, it can be easily handled.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. Note that, in the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals, and the description of the same components is omitted because it is duplicated.

  The difference from the first embodiment is that the microcomputer in the second embodiment can also receive an input of a trigger signal from the outside, and the PWM basic signal generated internally in the trigger signal selection means And an external trigger signal are selected.

  As shown in FIG. 3, the trigger signal selection means 21 provided in the microcomputer 13 according to the second embodiment of the present invention includes a PWM signal generated inside the microcomputer, a microcomputer 13 is input with a trigger signal from an external trigger signal generating means 30 provided outside. The trigger signal selection means 21 can select a necessary signal from these input signals.

  A signal to be applied to the reverse voltage application switching element 11 based on a signal generated inside the microcomputer 13 by internal connection without inputting a trigger signal from the outside of the microcomputer 13 as in the first embodiment. This microcomputer 13 can be used only for the inverter circuit 3 provided with the reverse voltage application circuit 7, and the versatility of the microcomputer is reduced.

  Therefore, when the MOSFET is not used as a switching element and the inverter circuit 3 is not provided with the reverse voltage application circuit 7, one or a plurality of input terminals of the microcomputer are used for inputting an externally generated trigger signal. Thus, the versatility of the microcomputer is enhanced by adopting a configuration in which either a signal generated inside the microcomputer or a signal generated outside can be selected and used.

  The trigger signal selection means 21 can select either an externally input signal or the upper and lower arm switching signal α as a signal to be sent as a trigger to the one-shot pulse generation means 20 by setting a firmware register. Therefore, the trigger signal to be easily selected can be changed by changing the firmware register setting.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the third embodiment, the same components as those described in the first or second embodiment are denoted by the same reference numerals, and the description of the same components is duplicated. Omitted.

  The third embodiment is characterized in that the function given to the pins provided in the microcomputer 13 can be appropriately changed.

  That is, the function given to the pins provided in the microcomputer 13 is used only for the output of the switching signal β applied to the reverse voltage application switching element 11 generated by the one-shot pulse generation means 20, for example. If fixed and set as described above, the use as the microcomputer 13 is limited. Therefore, as shown in FIG. 4, for example, in the case of register setting 1, the one shot pulse generating means is used by changing the register setting of the firmware to the function provided to the pins provided in the microcomputer 13. The function as an output port for outputting the switching signal β generated at 20 is given, or in the case of register setting 3, the function as an interrupt signal input pin is given to each pin. To be able to change.

  Thus, the versatility of the microcomputer 13 can be improved by changing the function of the pins provided in the microcomputer 13, for example, by changing the register setting of the firmware so that the function setting can be easily changed. it can.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

It is a whole lineblock diagram showing the power converter in an embodiment of the invention. It is a block diagram which shows the structure of the microcomputer in 1st Embodiment. It is a block diagram which shows the structure of the microcomputer in 2nd Embodiment. It is the table | surface which showed the example of the register setting of the pin of the microcomputer in 3rd Embodiment. It is a time chart which shows the signal applied to a main circuit switching element and a parasitic diode in the conventional embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Power converter device, 2 ... DC voltage source, 3 ... Inverter circuit, 4 ... Inductive load, 5 ... Main circuit switching element, 6 ... Parasitic diode, 7 ... Reverse voltage application circuit, 12 ... Diode, 13 ... Microcomputer 20 ... One shot pulse generating means, 21 ... Trigger signal selecting means, 30 ... External trigger signal generating means

Claims (2)

A pair of main circuit switching elements, each of which is connected to a DC voltage source and supplies power to the load by ON and OFF driving, and which is composed of an FET;
A diode connected in antiparallel to each of the pair of main circuit switching elements;
Reverse voltage application means for applying a reverse voltage lower than the voltage of the DC power supply to the diode connected in reverse parallel to the FET;
The PWM basic signal generating means for generating a PWM basic signal for driving the pair of main circuit switching elements ON and OFF, and the PWM basic signal generating means connected to the reverse voltage applying means based on the PWM basic signal. A microcomputer having a one-shot pulse generating means for generating a reverse voltage application signal to be driven for a period;
A power conversion device comprising: In the microcomputer, a trigger signal selection that selects a PWM basic signal generated in the PWM basic signal generating means and an external trigger signal generated outside the microcomputer and inputs the selected signal to the one-shot pulse generating means The power conversion apparatus according to claim 1, further comprising: means.

Images