JP6915566B2 - Power converter and power conversion system - Google Patents

Description

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

As automobiles in recent years, electric vehicles such as hybrid vehicles and electric vehicles have been attracting attention. Such an electric vehicle includes a power storage device including a secondary battery and the like, and a motor generator for receiving electric power from the power storage device to generate driving force. The motor generator generates a driving force at the time of starting or accelerating, and converts the kinetic energy of the vehicle into electric energy at the time of braking or the like and collects it in the power storage device. In this way, in order to control the motor generator according to the traveling condition 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 is provided with a smoothing capacitor to stabilize the supplied DC power, and the voltage applied to the smoothing capacitor during the operation of the power conversion device, that is, during the period when the DC power is supplied from the power storage device or the like. Charges are accumulated according to.

For example, Patent Document 1 provides a highly efficient power conversion device and a method of consuming residual charge in the power conversion device by avoiding the occurrence of steady power loss caused by discharge resistance. The power conversion device is a power conversion device 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 generators, each of which is connected in parallel to the capacitor and generates 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 according to a control signal input to the control power. By changing the resistance value between the electrodes, it is possible to form a conductive state and a non-conducting state. Further, the power conversion device consumes the residual charge of the capacitor between the capacitor and at least one phase voltage generating unit when the supply of DC power from the power supply unit is stopped. The current circulation path forming means for forming the current circulation path and at least one switching element arranged in the current circulation path are intermediate between the resistance value corresponding to the conduction state and the resistance value corresponding to the non-conduction state. A control signal adjusting means for adjusting the corresponding control signal is further provided so that the resistance value appears.

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

Japanese Unexamined Patent Publication No. 2008-61300

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

An object of the present invention is to solve the above problems, a 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 power using the power conversion device. It is to provide a conversion system.

The power conversion device according to the first invention is
An input smoothing section containing a first capacitor that smoothes the input voltage,
A switching unit that includes an inductor and an insulating transformer to switch the smoothed voltage and convert it to a predetermined output voltage.
An output smoothing unit including a second capacitor that smoothes the power-converted output voltage,
A power conversion device including a control unit that controls the switching unit during operation and after the operation is stopped.
After the operation of the power conversion device is stopped, the control unit controls the switching unit so that the electric charge of the first capacitor is circulated through the inductor and the insulating transformer of the switching unit to flow a circulating current. It is characterized by that.

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

Further, in the power conversion device, the control unit sets the switching frequency of the control signal of the switching unit after the operation of the power conversion device is stopped.
(1) Cosine waveform,
It is characterized in that (2) the waveform of the down chirp or (3) the waveform of the down chirp gradually decreases from a predetermined intermediate time.

Furthermore, in the power conversion device, the switching unit is
A plurality of switching elements on the primary side, the inductor, and a primary side portion including the primary winding of the insulating transformer.
Includes a plurality of switching elements on the secondary side and a secondary side portion including the 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 conversion device is stopped, or a dead time during which the plurality of switching elements on the primary side do not operate. It is characterized in that the switching unit is controlled so as to increase the size.

Further, the power conversion device is characterized in that the control unit reduces the circulating current with a predetermined waveform when the circulating current reaches a predetermined maximum value after the operation of the power conversion device is stopped. And.

Further, in the power conversion device, the control unit reduces the circulation current with a linear down-charp waveform when the circulation current reaches a predetermined maximum value after the operation of the power conversion device is stopped. It is characterized by.

The power conversion system according to the second invention is
With the power converter
It is characterized by including 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 a current between the electrolytic capacitor and the inductor, electric charges are consumed by utilizing the circuit pattern, switching loss, and copper loss of the insulating transformer. I made it. As a result, the electric charge of the electrolytic capacitor can be discharged only by changing the switching pattern without the need for an additional circuit.

It is a block diagram which shows the structural example of the power conversion system which concerns on Embodiment 1. FIG. It is a circuit diagram which shows the structural example of the power conversion apparatus 100 of FIG. FIG. 5 is a timing chart showing control signals of the switching elements Q1 to Q8 when the power conversion device 100 of FIG. 2 is boost-switched. FIG. 5 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. It is a timing chart which shows the control signal of each switching element Q1 to Q8 and the inductor current IL at the time of the capacitor discharge control processing executed by the power conversion apparatus 100 of FIG. It is a circuit diagram which shows the circulation current Icir in the period T1 to T4 of FIG. It is a figure which shows the problem in the capacitor discharge control processing of the power conversion apparatus 100 which concerns on embodiment, and is the timing chart which shows the simulation result of the capacitor current IC1, the input voltage Vin, and the circulation current Icir. A method of changing the switching pattern so as to maintain the current effective value with the passage of time according to the first modification, and showing a method of changing the on ratio of the primary side arm, the carrier voltage Vcarrier and the reference voltage Vref. It is a timing chart of. It is a timing chart which shows the control signal of each switching element Q1 to Q4 by the method of FIG. 7A. FIG. 5 is a timing chart showing a method of changing a switching pattern so as to maintain an effective current value with the passage of time according to the second modification, and gradually lowering the switching frequency fs. It is a timing chart which shows the control signal of each switching element Q1 to Q4 by the method of FIG. 8A. It is a graph which shows 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 circulation current Icil in the power conversion apparatus of the conventional example when the switching frequency fs is fixed to 100kHz. The simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed by a linear downcharp from the time 0.5s in the power conversion device 100 according to the first embodiment and its modified example are shown. It is a timing chart. A timing chart showing the simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed from the time 0s by the cosine down chirp in the power conversion device 100 according to the first embodiment and its modification. Is. In the timing chart showing the simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed from the time 0s by the linear down chirp in the power conversion device 100 according to the first embodiment and the modified example. be. It is a graph which shows the simulation result of the discharge time when the input voltage Vin discharges to 10V in the power conversion apparatus 100 which concerns on Embodiment 1 and the modification. It is a graph which shows the simulation result of the discharge time when the input voltage Vin is discharged to 1V in the power conversion apparatus 100 which concerns on Embodiment 1 and the modification. It is a graph which shows the simulation result of the maximum current value IC1max flowing through the electrolytic capacitor C1 in the power conversion apparatus 100 which concerns on Embodiment 1 and the modification. It is a timing chart which shows the control signal of each switching element Q1 to Q8 and the inductor current IL at the time of the capacitor discharge control processing executed by the power conversion apparatus 100 which concerns on Embodiment 2. FIG. It is a circuit diagram which shows the circulation current Icir in the period T1 to T6 of the capacitor discharge control processing of FIG. It is a timing chart which shows the simulation result of the capacitor current IC1, the input voltage Vin, and the circulation current Icir at the time of the capacitor discharge control processing at the time of the capacitor discharge control processing of FIG. It is an enlarged view around time 0s of FIG. In the power conversion device 100 according to the second embodiment, the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the circulating current Icil is clipped to the maximum value and the switching frequency fs is changed by a linear downcharp from time 0.5s. It is a timing chart which shows the simulation result. It is an enlarged view around time 0s of FIG.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. The same or similar components are designated by the same reference numerals, and detailed description thereof will be omitted.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration example of the 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 DCAC-converts the DC voltage output from the storage battery 1 into an AC voltage, then ACDC-converts the AC voltage into a DC voltage and outputs the DC voltage to form a so-called buck-boost converter device. The DCAC inverter device 101 converts a DC voltage into an AC voltage and outputs the DC voltage to the load 2.

FIG. 2 is a circuit diagram showing a configuration example of the power conversion device 100 of FIG. In FIG. 2, the power conversion device 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. 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, converts the input DC voltage into an AC voltage, then converts the changed AC voltage into a DC voltage, and outputs a smoothing unit 5 composed of an electrolytic capacitor C2 and voltage detection. The voltage is output to the DCAC inverter device 101 via the device 16 and the switches SW3 and SW4. Here, the switches SW1 to SW4 are turned on when the power converter 100 is operating, while they are turned off when the power converter 100 is not operating. The input smoothing section 3 and the output smoothing section 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 power conversion device 100 has stopped operating, while the electrolytic capacitor C2 has a capacity larger than that of the electrolytic capacitor C1 and is rapidly discharged after the power conversion device 100 has stopped operating. No discharge is required.

The voltage detector 15 detects the input voltage Vin at both ends of the input smoothing unit 3 and outputs it to the control unit 10. Further, the voltage detector 16 detects the output voltage Vout at both ends of the output smoothing unit 5 and outputs the output 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, so that the power conversion device 100 operates as a bidirectional converter device during normal operation and is operated as a bidirectional converter device. After the operation is completed, the capacitor discharge control process shown in FIG. 4 or the like is executed to rapidly discharge the electric charge accumulated in the electrolytic capacitor C1 of the input smoothing unit 3.

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 connected in parallel to the switching elements Q1 to Q4, respectively. .. The switching elements Q1 to Q4 are on / off controlled by each control signal from the control unit 10, converts the input DC voltage into an AC voltage, and is the primary winding of the insulating transformer 13 via the current detector 17 and the inductor 14. Output to L1. Further, 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 connected in parallel to each of 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, converts the input DC voltage into an AC voltage, and is a DCAC inverter via the output smoothing unit 5, the voltage detector 16, and the switches SW3 and SW4. Output to device 101.

The current detector 17 detects the flowing current value 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 power supply voltage required by the control unit 10 based on the output voltage Vout of the output smoothing unit 5. Is output to the control unit 10.

In the power conversion device 100 configured as described above, during its operation operation, the switches SW1 to SW4 are turned on, the DC voltage from the storage battery 1 is DCAC-converted, and then the ACDC is converted and output to the DCAC inverter device 101. do. On the other hand, during the capacitor discharge process, the switches SW1 to SW4 are turned off, the switching unit 4 is controlled until the electric charge of the electrolytic capacitor C1 of the input smoothing unit 3 is discharged, and circulation is performed between the electrolytic capacitor C1 and the inductor Ls. By switching so as to circulate the current Icir, the electric charge is consumed by utilizing the circuit pattern and switching loss of the power converter 100 and the copper loss of the insulating transformer 13.

FIG. 3A is a timing chart showing control signals of the switching elements Q1 to Q8 when the power conversion device 100 of FIG. 2 is boost-switched. As shown in FIG. 3A, in boost switching, the control signals of the switching elements Q1 and Q4 and the control signals of the switching elements Q2 and Q3 are controlled so as to be inverted with each other, and the control signals of the switching elements Q1 and Q4. The control signal of the switching element Q7 falls at a time delayed by a predetermined phase difference (hereinafter, referred to as “boost switching phase difference”) D1 from the rising edge of the switching element Q7, while the control signal of the switching element Q8 rises.

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 of the switching element Q1 and the control signal of the switching element Q3 are controlled so as to be inverted from each other, and the control signal of the switching element Q2 and the control signal of the switching element Q4 Are controlled so as to be inverted with each other, and here, a predetermined phase difference (hereinafter, "phase difference of step-down switching") 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 of the switching element Q2 rises (or the control signal of the switching element Q4 rises) at a time delayed by D2.

FIG. 4 is a timing chart showing the control signals of the switching elements Q1 to Q8 and the inductor current IL during the capacitor discharge control process executed after the normal operation of the power conversion device 100 of FIG. 2 is stopped, and FIG. 5 is a timing chart of FIG. It is a circuit diagram which shows the circulation current Icir in the period T1 to T4.

As is clear from FIG. 4, each control signal of the switching elements Q1 and Q4 is used as an inverted signal of each control signal of the switching elements Q2 and Q3, the switching elements Q5 and Q6 are always turned off, and the switching elements Q7 and Q8 are always turned off. When turned on, a short-circuit current flows through the insulating transformer 13. Here, the positive / negative of the short-circuit current is controlled by switching the switching elements Q1 and Q4 and the switching elements Q2 and Q3 in an inverting relationship with each other. The switching frequency fs at this time is preferably selected in consideration of the turn-off loss of the switching elements Q1 to Q8 (201 in FIG. 4). For example, when the switching elements Q1 to Q8 are formed by using a SiC or GaN semiconductor, a high frequency of about 100 kHz is set to the switching frequency fs.

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

For example, in the period T1, the switching elements Q1, Q4, Q7, and Q8 are turned on, so that the circulating current Icil 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 the switching element Q4. On the other hand, in the secondary winding L2 of the insulating transformer 13, the secondary winding L2 flows from the secondary winding L2 to the switching elements Q8 and Q7.

Further, in the period T2, the switching elements Q2, Q3, Q7, and Q8 are turned on, so that the circulating current Icil 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, in the secondary winding L2 of the insulating transformer 13, the secondary winding L2 flows from the secondary winding L2 to the switching elements Q8 and Q7.

Further, in the period T3, the switching elements Q2, Q3, Q7, and Q8 are turned on, so that the circulating current Icil 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 the line L1 and the switching element Q3. On the other hand, in the secondary winding L2 of the insulating transformer 13, the secondary winding L2 flows from the secondary winding L2 to the switching elements Q8 and Q7.

Furthermore, since the switching elements Q1, Q4, Q7, and Q8 are turned on during the period T4, the circulating current Icil 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 the winding L1 and the switching element Q4. On the other hand, in the secondary winding L2 of the insulating transformer 13, the secondary winding L2 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, but the switching elements Q5 and Q6 that can obtain the same short-circuit state may be the 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 for a desired time. The problem arises that the battery cannot be completely discharged.

FIG. 6 is a diagram showing a problem in the capacitor discharge control process of the power conversion device 100 according to the embodiment, and is a timing chart showing simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir. As is clear from FIG. 6, it can be understood that the circulating current Icir gradually decreases with the discharge of the electric charge of the electrolytic capacitor C1, and the discharge capacity of the power conversion device 100 decreases. The following modified examples are proposed to solve this problem.

FIG. 7A shows a method of changing the switching pattern so as to maintain the current effective value with the passage of time according to the first modification, and shows a method of changing the on ratio of the primary side arm with the carrier voltage Vcarrier. It is a timing chart of the reference voltage Vref, and FIG. 7B is a timing chart showing the control signals of the switching elements Q1 to Q4 by the method of FIG. 7A. Further, FIG. 8A is a timing chart according to the second modification, which is a method of changing the switching pattern so as to maintain the current effective value with the passage of time, and shows a method of gradually lowering the switching frequency fs. FIG. 8B is a timing chart showing control signals of the switching elements Q1 to Q4 by the method of FIG. 8A.

Therefore, in order to solve the above-mentioned problems, the gate switching pattern of the control signal of each switching element Q1 to Q4 is changed as follows so as to maintain the current effective value with the passage of time.
(Modification 1) As shown in FIGS. 7A and 7B, the duty ratio of each control signal of the switching elements Q1 to Q4 of the primary side arm is changed with the passage of time while holding the switching frequency fs. , Q4 are changed so as to be larger than the control signals of the switching elements Q2 and Q3. That is, the circulating current Icil is maintained by biasing the circulating current Icil to either positive or negative, that is, by biasing the circulating current Icil to one side of the switching elements Q1 and Q4, the current effective value Can be increased, and iron loss can also be used to discharge. The duty ratio of each control signal of the switching elements Q1 and Q4 may be exchanged with the duty ratio of each control signal of the switching elements Q2 and Q3.
(Modification 2) As shown in FIGS. 8A and 8B, the switching frequency fs is changed to be lowered with the passage of time. 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 by the method of FIG. 8A. As a method of gradually lowering the switching frequency fs, as shown in FIG. 9, a cosine chirp 301, a linear down chirp 302, a linear chirp 303 or the like is preferable as the down chirp wave used for the carrier waveform. Here, from the viewpoint of element stress of the switching elements Q1 to Q4, switching may be performed at a constant frequency at the initial stage of discharge, and down chirp may be performed from the middle. 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 the simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icil in the conventional power conversion device when the switching frequency fs is fixed at 100 kHz. Further, FIG. 10B shows the capacitor current IC1, the input voltage Vin, and the circulating current Icil when the switching frequency fs is changed from the time 0.5s by the linear downcharp in the power conversion device 100 according to the first embodiment and its modified example. It is a timing chart which shows the simulation result of. From the comparison of FIGS. 10A and 10B, by changing the switching frequency fs from the time 0.5s with a linear down chirp, the circulating current Icir can be maintained and the electric charge of the electrolytic capacitor C1 can be discharged within a desired time. You can see that.

FIG. 10C shows the simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Irir when the switching frequency fs is changed from the time 0s by the cosine down chirp in the power conversion device 100 according to the first embodiment and its modified example. It is a timing chart shown. Further, FIG. 10D shows the simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icir when the switching frequency fs is changed from the time 0s by the linear downcharp in the power conversion device 100 according to the first embodiment and the modified example. It is a timing chart which shows. From the comparison with FIGS. 10C and 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 the simulation result of the 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 modified example. Further, FIG. 11B is a graph showing the 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 modified example. Further, FIG. 12 is a graph showing the 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 modified example.

As is clear from the simulation results of FIGS. 11A, 11B and 12, the "linear down chirp from the middle" method satisfies the discharge time and enables discharge with the least 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. A circulating current Icil 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 a circulating current on the secondary side induced by the circulation current is generated. As a result, the electric charge is
(1) Copper loss of the primary winding L1 of the insulating transformer 13, turn-off loss of each switching element Q1 to Q4, conduction loss,
(2) Equivalent series resistance (ESR) of electrolytic capacitor C1 of input smoothing section 3, circuit pattern loss,
(3) Copper loss of the secondary winding L2 of the insulating transformer 13 and a switching element that is always on,
Can be configured to be consumed by.
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. As a result, 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 (discharging the residual charge of a capacitor within a specified time).

In the above-described first embodiment, 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 device 100 is stopped. The present invention is not limited to this, and the circulating current may be reduced by a predetermined waveform.

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

If the switching elements Q1 to Q8 are operated at a frequency that matches the turn-off characteristics as in the first embodiment, for example, an IGBT or MOSFET will operate at a relatively low frequency (up to about 50 kHz). On the other hand, when the frequency is operated at a low frequency, the short-circuit current flowing through the switching elements Q1 to Q8 and the insulating transformer 13 increases due to the long on-time, and the semiconductor devices and the insulating transformer 13 constituting the switching elements Q1 to Q8 increase. There is a problem of damage.

Therefore, by increasing the dead time in FIG. 13 as compared with the first embodiment, the switching elements Q1 and Q4 and the switching elements Q2 and Q3 are subjected to measures such as monitoring the maximum value of the inductor current IL flowing through the inductor 14. The on-time may be reduced as compared with the first embodiment so that the control unit 10 controls the maximum value of the inductor current IL. 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 in low frequency operation. In addition, it may be used in combination with the method using the chirp wave shown in FIG.

FIG. 15 is a timing chart showing the simulation results of the capacitor current IC1, the input voltage Vin, and the circulating current Icil during the capacitor discharge control process of FIG. 13. Further, FIG. 16 is an enlarged view of FIG. 15 near time 0s.

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, a large current is generated at the initial stage of discharge as shown in FIGS. 15 and 16, and the switching elements Q1 to Q8 in the circuit are generated. Etc. may be destroyed.

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

Therefore, as shown in FIGS. 17 and 18, when the maximum value of the inductor current IL is monitored and the maximum value is reached, the linear down chapter of FIG. 8 is used in combination to reduce the circulating current Icir, or the switching element. By adjusting the dead time so that the off period (dead time) of Q1 to Q4 is longer than that of the conventional example, it is possible to achieve both discharge within the time and protection of the switching elements Q1 to Q8 in the circuit.

As described above, according to the second embodiment, the operation and effect of the first embodiment can be obtained, and the discharge within the time and the protection of the switching elements Q1 to Q8 in the circuit can be compatible with each other.

As described in detail above, according to the power conversion device 100 according to the present invention, during the capacitor discharge process, the switches SW1 to SW4 are turned off, and the switching unit is used until the electric charge of the electrolytic capacitor C1 of the input smoothing unit 3 is discharged. By controlling 4 and switching so that the circulating current Icil circulates between the electrolytic capacitor C1 and the inductor Ls, the circuit pattern and switching loss of the power conversion device 100 and the copper loss of the insulating transformer 13 are utilized. To consume the electric charge. As a result, 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 electric vehicles such as hybrid vehicles and electric vehicles, and can be applied to, for example, a power supply system when the storage battery 1 is a solar cell.

1 Storage battery 2 Load 3 Input smoothing unit 4 Switching unit 5 Output smoothing unit 10 Control unit 11, 12 Switching circuit 13 Insulation transformer 14 Inductor 15, 16 Voltage detector 17 Current detector 20 Power supply unit 100 Power conversion device 101 DCAC inverter device D1 to D8 Reverse blocking diode L1 Primary winding L2 Secondary winding Ls Inductor Q1 to Q8 Switching element SW1 to SW4 Switch

Claims (3)

An input smoothing section containing a first capacitor that smoothes the input voltage,
A switching unit that includes an inductor and an insulating transformer to switch the smoothed voltage and convert it to a predetermined output voltage.
An output smoothing unit including a second capacitor that smoothes the power-converted output voltage,
A power conversion device including a control unit that controls the switching unit during operation and after the operation is stopped.
After the operation of the power conversion device is stopped, the control unit controls the switching unit so that the electric charge of the first capacitor is circulated through the inductor and the insulating transformer of the switching unit to flow a circulating current. ,
The circulating current flows on the primary side of the insulating transformer in a path including the first capacitor, the inductor, and the primary winding of the insulating transformer, and on the secondary side of the insulating transformer. Flowing in a path that includes the secondary winding of the insulating transformer and does not include the second capacitor,
After the operation of the power conversion device is stopped, the control unit circulates the electric charge of the first capacitor while gradually lowering the switching frequency of the control signal of the switching unit.
The power conversion device is characterized in that, after the operation of the power conversion device is stopped, the switching frequency of the control signal of the switching unit is gradually lowered from a predetermined intermediate time with a down chirp waveform. The switching unit is
A plurality of switching elements on the primary side, the inductor, and a primary side portion including the primary winding of the insulating transformer.
Includes a plurality of switching elements on the secondary side and a secondary side portion including the 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 conversion device is stopped, or all of the plurality of switch elements on the primary side are turned off. The power conversion device according to claim 1, wherein the switching unit is controlled so as to increase the dead time. The power conversion device according to claim 1 or 2,
A power conversion system including an inverter device that converts an output voltage output from the power conversion device into an AC voltage.

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