JP2019149867A - Power converter and power conversion system - Google Patents

Abstract

To provide a power converter that can prevent an increase in size of the power converter compared with a prior art and discharge electrical charge accumulated in a capacitor, and a power conversion system using the power converter.SOLUTION: A power converter 100 comprises: an input smoothing unit 3 including a first capacitor C1 that smooths an input voltage; a switching unit 4 that includes an inductor Ls and an insulating transformer 13 and switches the smoothed voltage to be power-converted into a predetermined output voltage; an output smoothing unit 5 including a second capacitor C2 that smooths the power-converted output voltage; and a control unit 10 that controls the switching unit 4 during operation and after a stop of the operation. After the stop of operation of the power converter 100, the control unit 10 controls the switching unit 4 to cause the electrical charge of the first capacitor C1 to circulate through the inductor Ls and insulating transformer 13 of the switching unit 4 to flow in a circulation current to flow.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power conversion device such as an insulated DCDC converter, and a power conversion system using the same.

  As an automobile in recent years, an electric vehicle such as a hybrid car or an electric car has attracted attention. Such an electric vehicle includes a power storage device including a secondary battery and a motor generator for receiving electric power from the power storage device and generating a driving force. The motor generator generates driving force when starting or accelerating, and converts kinetic energy of the vehicle into electric energy and recovers it to the power storage device during braking or the like. Thus, in order to control the motor generator according to the traveling state of the vehicle, the electric vehicle is equipped with a power conversion device that generates AC power from DC power, such as an inverter device. The power conversion device includes a smoothing capacitor to stabilize the supplied DC power, and an applied voltage is applied to the smoothing capacitor during operation of the power conversion device, that is, during a period in which DC power is supplied from a power storage device or the like. The electric charge according to is accumulated.

  For example, Patent Document 1 provides a highly efficient power conversion device and a method for consuming residual charges in the power conversion device by avoiding the occurrence of steady power loss caused by a discharge resistor. The power converter is a power converter capable of supplying AC power to an external load, and includes a power supply unit configured to be able to supply DC power, and first and second power lines connected to the power supply unit. , A capacitor connected between the first and second power lines, and a plurality of phase voltage generation units each connected in parallel to the capacitor and generating a corresponding phase voltage. Here, in the power conversion device, each of the plurality of phase voltage generation units includes a plurality of switching elements connected in series, and each of the switching elements outputs in accordance with a control signal input to control power. By changing the resistance value between the electrodes, the conductive state and the non-conductive state can be formed. Further, the power conversion device is configured to consume residual charge of the capacitor between the capacitor and at least one of the phase voltage generation units when the supply of DC power from the power supply unit is stopped. Current circulation path forming means for forming a current circulation path; and at least one switching element arranged in the current circulation path between the resistance value corresponding to the conduction state and the resistance value corresponding to the non-conduction state. Control signal adjusting means for adjusting the corresponding control signal so that a resistance value appears is further provided.

  That is, in Patent Document 1, after the normal operation of the power conversion device, in order to discharge the charge of the capacitor on the input side, the resistance value between the on-resistance and the off-resistance is set by setting the gate of the switching element to an intermediate voltage. And the discharge current is consumed by the switching element.

JP 2008-61300 A

  However, the method of Patent Document 1 requires an intermediate voltage generation mechanism as shown in the gate voltage adjustment circuit 20 in FIG. 4A, which increases the size of the power converter and increases its cost. There was a problem.

  SUMMARY OF THE INVENTION The object of the present invention is to solve the above problems, and to increase the power conversion device capable of discharging the electric charge accumulated in the capacitor without increasing the size of the power conversion device as compared with the prior art, and using the same. To provide a conversion system.

The power conversion device according to the first invention is:
An input smoothing unit including a first capacitor for smoothing the input voltage;
A switching unit including an inductor and an insulation transformer, and switching the smoothed voltage to convert the power to a predetermined output voltage;
An output smoothing unit including a second capacitor for smoothing the power-converted output voltage;
A power conversion device including a control unit that controls the switching unit during operation and after operation stop,
The controller controls the switching unit to circulate the electric charge of the first capacitor through the inductor and the insulating transformer of the switching unit to flow a circulating current after the operation of the power converter is stopped. It is characterized by that.

  In the power conversion device, the control unit circulates the charge of the first capacitor while changing a duty ratio of a control signal of the switching unit after the operation of the power conversion device is stopped.

  Further, in the power conversion device, the control unit circulates the charge of the first capacitor while gradually decreasing the switching frequency of the control signal of the switching unit after the operation of the power conversion device is stopped. Features.

Furthermore, in the power conversion device, the control unit, after stopping the operation of the power conversion device, the switching frequency of the control signal of the switching unit,
(1) Cosine waveform,
(2) It is characterized by being gradually reduced in a down chirp waveform or (3) a down chirp waveform from a predetermined halfway time.

Still further, in the power conversion device, the switching unit includes:
A primary side portion including a plurality of primary side switching elements, the inductor, and a primary winding of the insulating transformer;
A secondary side portion including a plurality of secondary side switching elements and a secondary winding of the insulating transformer;
The control unit reduces the circulating current when the circulating current reaches a predetermined maximum value after the operation of the power converter is stopped, or the dead time during which the plurality of switching elements on the primary side do not operate The switching unit is controlled to increase the value.

  Still further, in the power converter, the control unit reduces the circulating current with a predetermined waveform when the circulating current becomes a predetermined maximum value after the operation of the power converter is stopped. And

  Still further, in the power converter, the control unit reduces the circulating current with a linear down-chirp waveform when the circulating current reaches a predetermined maximum value after the operation of the power converter is stopped. It is characterized by.

The power conversion system according to the second invention is:
The power converter;
And an inverter device that converts an output voltage output from the power conversion device into an AC voltage.

  According to the power conversion device or the like according to the present invention, by switching so as to circulate the current between the electrolytic capacitor and the inductor, the electric charge is consumed using the circuit pattern, the switching loss, and the copper loss of the insulating transformer. I made it. Thereby, the electric charge of the electrolytic capacitor can be discharged only by changing the switching pattern without the need for additional circuits.

1 is a block diagram illustrating a configuration example of a power conversion system according to a first embodiment. It is a circuit diagram which shows the structural example of the power converter device 100 of FIG. It is a timing chart which shows the control signal of each switching element Q1-Q8 when carrying out pressure | voltage rise switching of the power converter device 100 of FIG. It is a timing chart which shows the control signal of each switching element Q1-Q8 when carrying out step-down switching of the power converter device 100 of FIG. It is a timing chart which shows the control signal and inductor current IL of each switching element Q1-Q8 at the time of the capacitor | condenser discharge control process performed by the power converter device 100 of FIG. FIG. 5 is a circuit diagram showing a circulating current Icir during a period T1 to T4 in FIG. It is a figure which shows the subject in the capacitor | condenser discharge control process of the power converter device 100 which concerns on embodiment, Comprising: It is a timing chart which shows the simulation result of the capacitor | condenser current IC1, the input voltage Vin, and the circulating current Icir. A carrier voltage Vcarrier and a reference voltage Vref showing a method of changing a switching pattern so as to maintain an effective current value as time elapses, according to the first modification, and showing a method of changing the ON ratio of the primary arm. It is a timing chart. It is a timing chart which shows the control signal of each switching element Q1-Q4 by the method of FIG. 7A. 10 is a timing chart showing a method of changing a switching pattern so as to maintain an effective current value as time elapses, according to Modification 2, and gradually decreasing the switching frequency fs. It is a timing chart which shows the control signal of each switching element Q1-Q4 by the method of FIG. 8A. It is a graph which shows the various change methods of the switching frequency fs by the method of FIG. 8A. It is a timing chart which shows the simulation result of the capacitor current IC1, the input voltage Vin, and the circulating current Icir in the conventional power converter when the switching frequency fs is fixed to 100 kHz. The simulation result of capacitor current IC1, input voltage Vin, and circulating current Icir when switching frequency fs is changed by linear down chirp from time 0 and 5s in power converter 100 concerning Embodiment 1 and its modification is shown. It is a timing chart. Timing chart showing simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed by cosine down chirp from time 0s in the power conversion device 100 according to the first embodiment and its modification. It is. In the power converter device 100 which concerns on Embodiment 1 and a modification, it is a timing chart which shows the simulation result of the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed by linear down chirp from time 0s. is there. It is a graph which shows the simulation result of the discharge time when the input voltage Vin discharges to 10V in the power converter device 100 which concerns on Embodiment 1 and a modification. It is a graph which shows the simulation result of the discharge time when the input voltage Vin discharges to 1V in the power converter device 100 which concerns on Embodiment 1 and a modification. It is a graph which shows the simulation result of the maximum electric current value IC1max which flows into the electrolytic capacitor C1 in the power converter device 100 which concerns on Embodiment 1 and a modification. 6 is a timing chart showing control signals and inductor currents IL of switching elements Q1 to Q8 during a capacitor discharge control process executed by the power conversion device 100 according to the second embodiment. It is a circuit diagram which shows the circulating current Icir in the period T1-T6 of the capacitor | condenser discharge control process of FIG. It is a timing chart which shows the simulation result of the capacitor current IC1, the input voltage Vin, and the circulating current Icir at the time of the capacitor discharge control process at the time of the capacitor discharge control process of FIG. FIG. 16 is an enlarged view around time 0s in FIG. 15. In the power conversion device 100 according to the second embodiment, the maximum value of the circulating current Icir is clipped, and the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed by linear down chirp from time 0.5s. It is a timing chart which shows a simulation result. FIG. 18 is an enlarged view around time 0s in FIG. 17.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the same or similar component, and detailed description is abbreviate | omitted.

(Embodiment 1)
FIG. 1 is a block diagram illustrating a configuration example of a power conversion system according to the first embodiment. In FIG. 1, the power conversion system according to the first embodiment includes a power conversion device 100 and a DCAC inverter device 101.

  In FIG. 1, the power conversion device 100 DC-AC converts the DC voltage output from the storage battery 1 into an AC voltage, and then AC-DC converts the AC voltage into a DC voltage and outputs it to constitute a so-called buck-boost converter device. The DCAC inverter device 101 converts a DC voltage into an AC voltage and outputs it to the load 2.

  FIG. 2 is a circuit diagram showing a configuration example of the power conversion apparatus 100 of FIG. In FIG. 2, the power converter 100 includes an input smoothing unit 3, a switching unit 4, an output smoothing unit 5, a control unit 10, voltage detectors 15 and 16, a power supply unit 20, and switches SW1 to SW4. It is configured with.

  The DC voltage output from the storage battery 1 is input to the switching unit 4 via the input smoothing unit 3 including the switches SW1 and SW2, the voltage detector 15, and the electrolytic capacitor C1. The switching unit 4 is controlled by the control unit 10 and converts an input DC voltage into an AC voltage, then converts the changed AC voltage into a DC voltage, and outputs an output smoothing unit 5 composed of an electrolytic capacitor C2, voltage detection Is output to the DCAC inverter device 101 via the switch 16 and the switches SW3 and SW4. Here, the switches SW <b> 1 to SW <b> 4 are turned on when the power conversion device 100 is operating, and are turned off when the power converter 100 is not operating. The input smoothing unit 3 and the output smoothing unit 5 each smooth and output so as to minimize the ripple of the input DC voltage. The electrolytic capacitor C1 needs to be rapidly discharged after the operation of the power conversion device 100 is stopped, while the electrolytic capacitor C2 has a capacity larger than that of the electrolytic capacitor C1, and the rapid operation after the operation of the power conversion device 100 is stopped. No discharge is required.

  The voltage detector 15 detects the input voltage Vin across the input smoothing unit 3 and outputs it to the control unit 10. The voltage detector 16 detects the output voltage Vout across the output smoothing unit 5 and outputs it to the control unit 10. The control unit 10 controls the switches SW1 to SW4 to generate and output control signals for the switching elements Q1 to Q8, thereby causing the power conversion device 100 to operate as a bidirectional converter device during normal operation. After the operation is completed, the electric charge accumulated in the electrolytic capacitor C1 of the input smoothing unit 3 is rapidly discharged by executing the capacitor discharge control process of FIG.

  The switching unit 4 includes switching circuits 11 and 12, an insulating transformer 13, and an inductor 14 having an inductance Ls. Here, the switching circuit 11 includes switching elements Q1 to Q4 which are four MOSTFETs connected in a bridge shape, and reverse blocking diodes D1 to D4 respectively connected in parallel to the switching elements Q1 to Q4. . The switching elements Q1 to Q4 are ON / OFF controlled by each control signal from the control unit 10, convert the input DC voltage into an AC voltage, and pass through the current detector 17 and the inductor 14, the primary winding of the insulating transformer 13 Output to L1. The switching circuit 12 includes switching elements Q5 to Q8, which are four MOSTFETs connected in a bridge shape, and reverse blocking diodes D5 to D8 respectively connected in parallel to the switching elements Q5 to Q8. The switching elements Q5 to Q8 are ON / OFF controlled by each control signal from the control unit 10, convert the input DC voltage into an AC voltage, and output the DCAC inverter through the output smoothing unit 5, the voltage detector 16 and the switches SW3 and SW4. Output to the device 101.

  The current detector 17 detects the value of the flowing current and outputs it to the control unit 10. The power supply unit 20 discharges the electric charge accumulated in the output smoothing unit 5 when the power conversion device 100 is not operating, and generates a necessary power supply voltage in the control unit 10 based on the output voltage Vout of the output smoothing unit 5. To the control unit 10.

  In the power conversion device 100 configured as described above, during the operation operation, the switches SW1 to SW4 are turned on, the DC voltage from the storage battery 1 is DCAC converted, and then ACDC converted and output to the DCAC inverter device 101. To do. On the other hand, during the capacitor discharging process, the switches SW1 to SW4 are turned off, and the switching unit 4 is controlled until the electric charge of the electrolytic capacitor C1 of the input smoothing unit 3 is discharged, and circulated between the electrolytic capacitor C1 and the inductor Ls. By switching so that the current Icir circulates, the circuit pattern and switching loss of the power conversion device 100 and the copper loss of the insulating transformer 13 are used to consume charges.

  FIG. 3A is a timing chart showing control signals of the switching elements Q1 to Q8 when the power conversion device 100 of FIG. As shown in FIG. 3A, in step-up switching, control signals for switching elements Q1 and Q4 and control signals for switching elements Q2 and Q3 are controlled so as to be inverted from each other, and control signals for switching elements Q1 and Q4 are controlled. The control signal for the switching element Q7 falls while the control signal for the switching element Q8 rises at a time delayed by a predetermined phase difference (hereinafter referred to as “step-up switching phase difference”) D1 from the rising edge of the switching element Q8.

  FIG. 3B is a timing chart showing control signals of the switching elements Q1 to Q8 when the power conversion device 100 of FIG. 2 is step-down switched. As shown in FIG. 3B, in step-down switching, the control signal for switching element Q1 and the control signal for switching element Q3 are controlled to be inverted from each other, and the control signal for switching element Q2, the control signal for switching element Q4, Are controlled so as to be inverted from each other. Here, a predetermined phase difference (hereinafter referred to as “step-down switching phase difference”) from the rising edge of the control signal of the switching element Q1 (or the falling edge of the control signal of the switching element Q3). The control signal for switching element Q2 falls (or the control signal for switching element Q4 rises) at a time delayed by D2.

  4 is a timing chart showing control signals and inductor currents IL of the switching elements Q1 to Q8 during the capacitor discharge control process executed after the normal operation of the power conversion device 100 of FIG. 2 is stopped. FIG. It is a circuit diagram which shows circulating current Icir in the period T1-T4.

  As is apparent from FIG. 4, the control signals of the switching elements Q1 and Q4 are inverted signals of the control signals of the switching elements Q2 and Q3, the switching elements Q5 and Q6 are always off, and the switching elements Q7 and Q8 are always on. By turning on, a short-circuit current flows through the insulating transformer 13. Here, the switching elements Q1 and Q4 and the switching elements Q2 and Q3 are switched in an inversion relationship with each other, thereby controlling the polarity of the short-circuit current. The switching frequency fs at this time is preferably selected in consideration of the turn-off loss (201 in FIG. 4) of the switching elements Q1 to Q8. For example, when the switching elements Q1 to Q8 are formed using a SiC or GaN semiconductor, a high frequency of about 100 kHz is set as the switching frequency fs.

  In the present embodiment, the electric charge of the electrolytic capacitor C1 is consumed by the turn-off loss of the switching elements Q1, Q2, Q3, and Q4 using the circulating current Icir generated in FIG. 5 at this time.

  For example, in the period T1, the switching elements Q1, Q4, Q7, and Q8 are turned on. Therefore, the circulating current Icir on the primary side of the insulating transformer 13 is the primary winding of the switching element Q1, the inductor 14, and the insulating transformer 13. It flows through L1 and switching element Q4. On the other hand, the secondary winding L2 of the insulating transformer 13 flows from the secondary winding L2 to the switching elements Q8 and Q7.

  Further, since the switching elements Q2, Q3, Q7, and Q8 are turned on in the period T2, the circulating current Icir on the primary side of the insulating transformer 13 is the switching element Q2, the primary winding L1 of the insulating transformer 13, It flows through the inductor 14 and the switching element Q3. On the other hand, the secondary winding L2 of the insulating transformer 13 flows from the secondary winding L2 to the switching elements Q8 and Q7.

  Further, since the switching elements Q2, Q3, Q7, and Q8 are turned on during the period T3, the circulating current Icir on the primary side of the insulating transformer 13 is the primary winding of the switching element Q2, the inductor 14, and the insulating transformer 13. It flows through line L1 and switching element Q3. On the other hand, the secondary winding L2 of the insulating transformer 13 flows from the secondary winding L2 to the switching elements Q8 and Q7.

  Further, in the period T4, the switching elements Q1, Q4, Q7, and Q8 are turned on, so that the circulating current Icir on the primary side of the insulating transformer 13 is the primary of the switching element Q1, the inductor 14, and the insulating transformer 13. It flows through winding L1 and switching element Q4. On the other hand, the secondary winding L2 of the insulating transformer 13 flows from the secondary winding L2 to the switching elements Q8 and Q7.

  In the present embodiment, the always-on switching elements are Q7 and Q8. However, the switching elements Q5 and Q6 capable of obtaining a similar short-circuit state may be always-on switching elements.

  However, for example, when the switching loss or the circuit pattern loss is relatively small, or when the capacity of the smoothing electrolytic capacitor C1 is relatively large, the circulating current Icir decreases with the discharge of the smoothing electrolytic capacitor C1, and the desired time is reached. There arises a problem that it cannot be fully discharged.

  FIG. 6 is a diagram illustrating a problem in the capacitor discharge control process of the power conversion device 100 according to the embodiment, and is a timing chart illustrating simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir. As can be seen from FIG. 6, it can be understood that the circulating current Icir gradually decreases as the electric charge of the electrolytic capacitor C1 is discharged, and the discharge capability of the power converter 100 decreases. In order to solve this problem, the following modification is proposed.

  FIG. 7A is a method of changing a switching pattern so as to maintain a current effective value as time elapses, according to the first modification, and shows a method of changing the ON ratio of the primary side arm. 7B is a timing chart showing the reference voltage Vref. FIG. 7B is a timing chart showing control signals for the switching elements Q1 to Q4 in the method shown in FIG. 7A. FIG. 8A is a timing chart showing a method of changing the switching pattern so as to maintain the current effective value as time elapses, and a method of gradually decreasing the switching frequency fs, according to the modification 2. FIG. 8B is a timing chart showing control signals of the switching elements Q1 to Q4 in the method of FIG. 8A.

Therefore, in order to solve the above-described problem, the gate switching pattern of the control signal of each of the switching elements Q1 to Q4 is changed as follows so that the current effective value is maintained with time.
(Modification 1) As shown in FIGS. 7A and 7B, the switching frequency fs is maintained, and the duty ratio of each control signal of the switching elements Q1 to Q4 of the primary side arm is changed over time with the switching element Q1. , Q4 are changed so as to be larger than the control signals of the switching elements Q2, Q3. That is, the circulating current Icir is biased to flow either positively or negatively, thereby holding the circulating current Icir, that is, by flowing the circulating current Icir biased to one side of the switching elements Q1, Q4, Can be increased, and the iron loss can also be used for discharging. It should be noted that the duty ratio of each control signal of switching elements Q1 and Q4 may be exchanged with the duty ratio of each control signal of switching elements Q2 and Q3.
(Modification 2) As shown in FIGS. 8A and 8B, the switching frequency fs is changed to be lowered as time elapses. That is, the switching frequency fs is down-chirped and gradually lowered.

  FIG. 9 is a graph showing various methods of changing the switching frequency fs in the method of FIG. 8A. As a method of gradually decreasing the switching frequency fs, as shown in FIG. 9, a cosine chirp 301, a linear down chirp 302, a linear chirp 303 from the middle, etc. are suitable as the down chirp wave used for the carrier waveform. Here, from the viewpoint of the element stress of the switching elements Q1 to Q4, switching may be performed at a constant frequency in the initial stage of discharge and down-chirped halfway. The timing for switching to the down chirp wave may be set by monitoring the voltage of the electrolytic capacitor C1 of the input smoothing unit 3.

  FIG. 10A is a timing chart showing simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir in the conventional power converter when the switching frequency fs is fixed to 100 kHz. FIG. 10B shows the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed by linear down chirp from time 0.5s in the power conversion device 100 according to the first embodiment and its modification. It is a timing chart which shows the simulation result of. From the comparison between FIG. 10A and FIG. 10B, the switching frequency fs is changed by linear down chirp from time 0.5s, so that the circulating current Icir can be maintained and the charge of the electrolytic capacitor C1 can be discharged within a desired time. I understand that.

  FIG. 10C shows simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed by cosine down chirp from time 0s in the power conversion device 100 according to the first embodiment and its modification. It is a timing chart which shows. FIG. 10D shows the simulation result of the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed by linear down chirp from time 0s in the power conversion device 100 according to the first embodiment and the modification. It is a timing chart which shows. From the comparison between FIG. 10C and FIG. 10D, it can be seen that by gradually reducing the switching frequency fs, the circulating current Icir can be maintained and the electric charge of the electrolytic capacitor C1 can be discharged within a desired time.

  FIG. 11A is a graph showing a simulation result of discharge time when the input voltage Vin is discharged to 10 V in the power conversion device 100 according to the first embodiment and the modification. FIG. 11B is a graph showing a simulation result of the discharge time when the input voltage Vin is discharged to 1 V in the power conversion device 100 according to the first embodiment and the modification. Further, FIG. 12 is a graph showing a simulation result of the maximum current value IC1max flowing through the electrolytic capacitor C1 in the power conversion device 100 according to the first embodiment and the modification.

  As is apparent from the simulation results of FIGS. 11A, 11B, and 12, the “linear down chirp from the middle” method satisfies the discharge time and can discharge without applying the most element stress (best mode). I understood.

As described above, according to the present embodiment, during the capacitor discharge process, the switches SW1 to SW4 are turned off, and the switching unit 4 is controlled until the electric charge of the electrolytic capacitor C1 of the input smoothing unit 3 is discharged. The circulating current Icir is circulated between the electrolytic capacitor C1 and the primary side of the insulating transformer 13, and the switching unit 4 is controlled so that the secondary circulating current induced thereby is generated. As a result, the charge is
(1) Copper loss of the primary winding L1 of the insulation transformer 13 and turn-off loss, conduction loss of the switching elements Q1 to Q4,
(2) Equivalent series resistance (ESR) of electrolytic capacitor C1 of input smoothing unit 3, circuit pattern loss,
(3) Copper loss of the secondary winding L2 of the insulating transformer 13 and a normally-on switching element,
Can be configured to consume.
That is, the electric charge is consumed by utilizing the circuit pattern and switching loss of the power conversion device 100 and the copper loss of the insulating transformer 13. Thereby, the electric charge of the electrolytic capacitor C1 can be discharged only by changing the switching pattern without the need for an additional circuit. It can be applied as a technical means for complying with the CHAdeMO standard (discharge the residual charge of the capacitor within a specified time).

  In Embodiment 1 described above, the control unit 10 reduces the circulating current with a linear down-chirp waveform when the circulating current reaches a predetermined maximum value after the operation of the power conversion apparatus 100 is stopped. The present invention is not limited to this, and the circulating current may be reduced with a predetermined waveform.

(Embodiment 2)
FIG. 13 is a timing chart showing control signals and inductor currents IL of the switching elements Q1 to Q8 during the capacitor discharge control process executed by the power conversion device 100 according to the second embodiment. FIG. 14 is a circuit diagram showing the circulating current Icir during the period T1 to T6 of the capacitor discharge control process of FIG.

  When operating at a frequency that matches the turn-off characteristics of the switching elements Q1 to Q8 as in the first embodiment, for example, IGBTs or MOSFETs operate at a relatively low frequency (up to about 50 kHz). On the other hand, when the low frequency operation is performed, the on-time is increased, so that the short circuit current flowing through the switching elements Q1 to Q8 and the insulating transformer 13 increases, and the semiconductor device and the insulating transformer 13 constituting the switching elements Q1 to Q8 There is a problem of damage.

  Therefore, by increasing the dead time of FIG. 13 as compared with the first embodiment, the switching elements Q1 and Q4 and the switching elements Q2 and Q3 are monitored by measures such as monitoring the maximum value of the inductor current IL flowing through the inductor 14. The control unit 10 may control the maximum value of the inductor current IL by reducing the on-time compared to the first embodiment. By this method, the electric charge of the electrolytic capacitor C1 can be softly discharged while protecting the semiconductor devices of the switching elements Q1 to Q8 and the insulating transformer 13 even at low frequency operation. In addition, you may use together with the method using the chirp wave shown in FIG.

  FIG. 15 is a timing chart showing simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir during the capacitor discharge control process in the capacitor discharge control process of FIG. FIG. 16 is an enlarged view around the time 0s in FIG.

  When the switching frequency fs is lowered from 100 kHz to 50 kHz, which is lower than that, in the case of low frequency operation, as shown in FIGS. 15 and 16, a large current is generated in the initial stage of discharge, and switching elements Q1 to Q8 in the circuit are generated. There is a risk of destroying etc.

  FIG. 17 illustrates the power converter 100 according to the second embodiment, in which the circulating current Icir is clipped to the maximum value, and the capacitor current IC1, the input voltage Vin, and the circulation when the switching frequency fs is changed by linear down chirp from time 0.5s. It is a timing chart which shows electric current Icir. FIG. 18 is an enlarged view of the vicinity of time 0s in FIG.

  Therefore, as shown in FIGS. 17 and 18, the maximum value of the inductor current IL is monitored, and when the maximum value is reached, the circulating current Icir is lowered by using the linear down chirp of FIG. By adjusting the dead time so that the off period (dead time) of Q1 to Q4 is longer than that of the conventional example, both discharge in time and protection of the in-circuit switching elements Q1 to Q8 can be achieved.

  As described above, according to the second embodiment, the effects of the first embodiment can be obtained, and both the discharge in time and the protection of the in-circuit switching elements Q1 to Q8 can be achieved.

  As described above in detail, according to the power conversion device 100 of the present invention, during the capacitor discharge process, the switches SW1 to SW4 are turned off, and the switching unit until the electric charge of the electrolytic capacitor C1 of the input smoothing unit 3 is discharged. 4 is controlled so as to circulate the circulating current Icir between the electrolytic capacitor C1 and the inductor Ls, thereby utilizing the circuit pattern and switching loss of the power converter 100 and the copper loss of the insulating transformer 13. The electric charge was consumed. Thereby, the electric charge of the electrolytic capacitor C1 can be discharged only by changing the switching pattern without the need for an additional circuit. The present invention is not limited to an electric vehicle such as a hybrid vehicle or an electric vehicle, and can be applied to, for example, a power supply system when the storage battery 1 is a solar cell.

DESCRIPTION OF SYMBOLS 1 Storage battery 2 Load 3 Input smoothing part 4 Switching part 5 Output smoothing part 10 Control parts 11 and 12 Switching circuit 13 Insulation transformer 14 Inductor 15 and 16 Voltage detector 17 Current detector 20 Power supply part 100 Power converter 101 DCAC inverter apparatus D1 to D8 Reverse blocking diode L1 Primary winding L2 Secondary winding Ls Inductors Q1 to Q8 Switching elements SW1 to SW4 Switch

Claims (8)

An input smoothing unit including a first capacitor for smoothing the input voltage;
A switching unit including an inductor and an insulation transformer, and switching the smoothed voltage to convert the power to a predetermined output voltage;
An output smoothing unit including a second capacitor for smoothing the power-converted output voltage;
A power conversion device including a control unit that controls the switching unit during operation and after operation stop,
The controller controls the switching unit to circulate the electric charge of the first capacitor through the inductor and the insulating transformer of the switching unit to flow a circulating current after the operation of the power converter is stopped. The power converter characterized by the above-mentioned.   2. The power conversion according to claim 1, wherein the control unit circulates the charge of the first capacitor while changing a duty ratio of a control signal of the switching unit after the operation of the power conversion device is stopped. apparatus.   The said control part circulates the electric charge of a said 1st capacitor | condenser, reducing the switching frequency of the control signal of the said switching part gradually after the operation stop of the said power converter device. Power conversion device. The control unit, after stopping the operation of the power converter, the switching frequency of the control signal of the switching unit,
(1) Cosine waveform,
4. The power converter according to claim 3, wherein the power converter is gradually lowered with a waveform of down chirp or (3) a waveform of down chirp from a predetermined halfway time. The switching unit is
A primary side portion including a plurality of primary side switching elements, the inductor, and a primary winding of the insulating transformer;
A secondary side portion including a plurality of secondary side switching elements and a secondary winding of the insulating transformer;
The control unit reduces the circulating current when the circulating current reaches a predetermined maximum value after the operation of the power converter is stopped, or the dead time during which the plurality of switching elements on the primary side do not operate The power converter according to claim 1, wherein the switching unit is controlled to increase the value.   6. The power conversion according to claim 5, wherein the controller reduces the circulating current with a predetermined waveform when the circulating current reaches a predetermined maximum value after the operation of the power converter is stopped. apparatus.   The said control part reduces the said circulating current with the waveform of a linear down chirp, when the said circulating current becomes a predetermined maximum value after the operation stop of the said power converter device. Power conversion device. The power conversion device according to any one of claims 1 to 7,
A power conversion system comprising: an inverter device that converts an output voltage output from the power conversion device into an AC voltage.

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