JP6805787B2 - EMI noise reduction method for charger - Google Patents

Description

The present invention relates to a method for reducing EMI noise of a charger for charging a secondary battery such as a lead storage battery.

Patent Document 1 and the like include an inverter using an Istucci element that converts a DC voltage into an arbitrary AC voltage, and a device that converts an AC voltage from the inverter into a DC with a rectifier to charge a secondary battery (hereinafter simply referred to as a battery). Is known.
EMC (Electromagnetic compatibility) "electromagnetic compatibility" measures to suppress electrical noise emitted from electrical products such as chargers (EMI) and prevent electrical products from causing trouble due to electrical noise from the surroundings (EMS) Is attracting attention. The charger is one of them.

Patent No. 5589771

There are the following methods as EMC measures for inverters.
(1) The switching speed when the switching element is turned on / off is slowed down to reduce the generation of noise. For example, when an IGBT is used as a switching element, the switching speed becomes slower when the gate resistance is increased. When the switching speed is slowed down, the voltage and current rate of change dV / dt and dI / dt become smaller and noise is reduced.
However, if the switching speed is slowed down, the loss during switching becomes large, and it is necessary to consider the decrease in efficiency and cooling. Since the switching loss is proportional to the frequency, the switching loss becomes remarkable in the inverter at a high frequency.

(2) As shown in FIG. 2, a CRD snubber is connected in parallel with the switching element T, and the current when the switching element T is off is bypassed to the capacitor to reduce dV / dt. In FIG. 2, D is a diode and C is a capacitor. When the switching element T is turned off, the current Id flowing through the switching element T flows from the diode D to the capacitor C. As the voltage rises while charging the current Id to the capacitor C, dV / dt becomes smaller. The resistor R is a resistor for limiting the current flowing from the capacitor C to the switching element T when the switching element T is turned on. In this method, there is no loss due to the snubber resistor R when the switching element T is turned off, but the loss of the resistor R is large because the discharge is discharged through the resistor R when the switching element T is turned on. The loss due to the resistor R is determined by 0.5 × C × Ed ^ 2 × f, and is proportional to the frequency as in item (1), so the switching loss becomes remarkable in a high frequency inverter.

(3) As shown in FIG. 3, dV / dt can be reduced by connecting a CR snubber in parallel with the switching element T and bypassing the current Id when the switching element T is off to the capacitor C. An example in which this snubber circuit is applied is shown in FIG.
In this method, it is necessary to increase the resistance value to some extent (R ≧ 2√L / C) so that vibration conditions cannot be created. When the current is small, dV / dt is effective, but when the current is large, the resistance bears the voltage of Id (off current) × R (resistance value), so the effect of reducing dV / dt is reduced. Further, since the current of the capacitor passes through the resistor both when the switching element T is off and when it is on, the loss of the resistor is doubled as described in the above item (2). On the contrary, if the resistance value is reduced (R <2√L / C), vibration will occur, so it is not generally used. Here, L is the inductance of the wiring of the DC circuit shown in FIG. 4, and is wired so that the value is as small as possible.

(4) In the above item (3), it is stated that the resistance value is (R ≧ 2√L / C) to prevent vibration, but the resistance value is intentionally reduced (R <2√L / C) to vibrate. It is also possible to reduce the loss to dV / dt with the knowledge that The reason for adopting this method is that the frequency of the vibration current is lowered by the capacitor C, so even if the price of the circuit component rises to some extent due to the vibration, it is advantageous if it is cheaper than the countermeasure cost of EMC. According to this method, the circuit configuration is the same as that in FIG. 4, but only the resistance value is different. However, the method of intentionally reducing the resistance value has the following problems in addition to vibration.

The on / off of the switching element in the inverter 1 arm operates in the opposite direction on the plus side and the minus side. That is, when the switching element Tv is on, the switching element Ty is off. However, the switching time of the IGBT, etc. that is actually used is fast on and slow off, so if an on / off signal is given at the same time, Tv and Ty will be turned on at the same time, causing a short circuit between the upper and lower PNs and a large current to the IGBT. It will flow and destroy the IGBT. To prevent this, a signal is given that turns on later than off. This time is called dead time. The dead time should be greater than or equal to the time difference between the switch off and on, but if it is too large, the off period of both the upper and lower switches will increase and the maximum output voltage (transformer TF primary voltage) will decrease. In the case of an IGBT, it is generally about 1 μs.

The operation at the time of off will be described with reference to FIGS. 4 to 6. When the switching elements Tv and Tx are turned on in Fig. 4 and the current Id is flowing from Tv → TF → Tx, when Tv is turned off at point A in Fig. 5, the current Id hardly changes, so the current of Id is the capacitor Cv. It is charged with 1/2 × Id (dashed line in FIG. 5), discharged from the capacitor Cy with 1/2 × Id (dashed line in FIG. 5), and flows. As a result, the voltage of the switching element Tv rises as shown by the dotted line, and the voltage of the switching element Ty falls as shown by the solid line. The time AB at this time is the charge / discharge time t, and the charge / discharge time t = 2CEd / Id. The time between AC is the dead time tdet. If tdet> t, the capacitor completes charging and discharging within the dead time.

Next, the time when the current Id is small is shown in FIG. In FIG. 6, since the current is small, the charging / discharging of the capacitor is not completed even at the time C when the dead time ends. Therefore, when the switching element Ty is turned on at the point C, the voltage between Ty becomes zero, so that the capacitor Cy is As shown in the figure, it is suddenly discharged and Cv is also suddenly charged. As a result, the dV / dt of Tv and Ty becomes large. Also, large currents can damage switches and capacitors. The charging time to the capacitor Cv and the discharging time from Cy are the same, and are represented by t = 2CEd / Id described above. Here, Ed is the DC voltage of the DC link.

As an example, a specific value will be described. When Ed = 300V, Id = 100A, C = 0.1uF, t = 0.6μs, so if the dead time is 1μs, the charging and discharging of the capacitor will be completed within that time, but when Id = 10A, t = 6μs. Then Ty turns on before the capacitor completes charging and discharging. As a result, since the electric charge remains in the capacitor Cy, it is short-circuited by Ty and discharged. On the other hand, since no electric charge is accumulated in the capacitor Cv, it is charged rapidly from the DC link, and as a result, dV / dt and dI / dt become large, which adversely affects EMC.

An object of the present invention is to provide an EMI noise reduction method effective for EMC that can reduce dV / dt and dI / dt when the switching element is turned off.

In the present invention, a DC voltage is converted into an AC voltage by an inverter in which a snubber circuit is connected in parallel with each switching element, the converted AC voltage is converted into a DC voltage by a rectifier, and the DC voltage is adjusted stepwise or gradually. In the charging method with a charger that charges the battery while reducing the charging current
When the charging current to the battery becomes equal to or less than a predetermined value (pushing charging current), the on-time of the switching element is delayed.

In the present invention, the snubber circuit is a CR snubber circuit in which a resistor and a capacitor are directly connected, and the resistance value of the snubber circuit is set to a value as small as possible.

Further, in the present invention, the dead time of the inverter is shortened when the charging current to the battery becomes equal to or less than a predetermined value.

In the present invention, a DC voltage is converted into an AC voltage by an inverter in which a snubber circuit is connected in parallel with each switching element, and the converted AC voltage is output to a rectifier via a transformer to be converted into a DC voltage and converted. In the charging method with a charger, the battery is charged while adjusting the DC voltage and gradually or gradually reducing the charging current.
A series circuit of the contactor and the reactor is connected in parallel with the transformer.
The snubber circuit is a CR snubber circuit in which a resistor and a capacitor are directly connected, and the resistance value of the snubber circuit is set to a value as small as possible.
When the charging current to the battery becomes equal to or less than a predetermined value (pushing charging current), the dead time of the inverter is reduced corresponding to the charging voltage, and the contactor is turned on to pass a dummy current to the reactor. is there.

Further, according to the present invention, when the charging current to the battery is other than a predetermined value (pushing charging current) and the charging current becomes small, the dead time is gradually increased corresponding to the charging current.

Further, the present invention is characterized in that the charging current to the battery is a current equal to or higher than a predetermined value (pushing charging current), and the contactor is turned on to a small charging start current at the start of charging to allow a dummy current to flow through the reactor. Is to be.

As described above, according to the present invention, by reducing the resistance value R in the CR snubber circuit, dV / dt and dI / dt when the IGBT is turned off can be reduced, which is effective for EMC. In addition, the loss due to resistance can be reduced. Furthermore, by lengthening the on-time only when the charging current is small, it is possible to prevent a decrease in charging efficiency other than when charging by pushing in, and there is no need to add new parts, making it possible to support EMC by downsizing. Is.

The schematic block diagram of the charger which shows embodiment of this invention. CRD snubber schematic. CR snubber schematic. Schematic configuration of the charger connected to the CR snubber circuit. Operation explanatory diagram of CR snubber circuit. Operation explanatory diagram of CR snubber circuit. Operation explanatory diagram of CR snubber circuit. Characteristic diagram of IGBT.

In the first embodiment of the present invention, a DC voltage is converted into an AC voltage by an inverter in which a snubber circuit is connected in parallel with each switching element and output to a rectifier via a transformer, while adjusting the converted DC voltage. In the charging method with a charger that charges the battery while gradually or gradually reducing the charging current, a series circuit of a contactor and a reactor is connected in parallel with the transformer. The resistance value of the snubber circuit is set to a value as small as possible, and when the charging current to the battery becomes less than the pushing charging current, the dead time is reduced corresponding to the charging voltage, and the contactor is turned on to allow a dummy current to flow through the reactor. Is.

Further, in the second embodiment, when the charging current to the battery becomes equal to or less than the indentation charging current, the on-time of the switching element is delayed. This will be described below with reference to the figure.

FIG. 1 shows a configuration diagram of a charger applied to the EMI noise reduction method of the present invention, and this charger is mounted on an electric vehicle or the like. IV is an inverter consisting of switching elements Tu, Yv, Tx, Ty such as IGBTs, and CR snubber circuits composed of resistors and capacitors are connected in parallel to each switching element Tu, Yv, Tx, Ty, respectively, and not shown. Converts the voltage from the DC power supply to AC. The primary winding of the transformer TF is connected to the AC output side of the inverter IV, the secondary winding is connected to the AC input side of the rectifier Cov, and the AC output of the inverter IV is converted into a DC voltage by the rectifier Cov. The battery BAT is charged by adjusting the DC voltage by the converted DC voltage via a switching means (not shown) and gradually or gradually reducing the charging current.

In this embodiment, a series circuit of the contactor (switch) MC and the reactor Lx is connected in parallel with the transformer TF. Further, the resistance value R of the snubber circuit may be intentionally reduced to 1/2 or less of (2√L / C) so that the resistance value is zero. The contact MC is turned on when the charging current to the battery BAT becomes small and the capacitor of the snubber circuit does not discharge during the dead time. When the contact MC is turned on, the reactor Lx is connected in parallel with the transformer TF, and by passing a current through this reactor Lx, the current when the IGBT is turned off is increased, and the capacitor of the CR snubber circuit is discharged during the dead time. It is composed.

As a method of charging the battery BAT, it is charged with a large current, for example, 200A, and when the voltage of the battery BAT rises to a predetermined voltage (about 90V for a battery with a rating of 72V), it gradually becomes 100A, 50A, 25A ( Or gradually) reduce the charging current to charge. And finally, it is pushed and charged with a smaller current of about 10A. At this time, the charger needs a maximum voltage (about 110V if the rated voltage of the battery is about 150% and the rated voltage is 72V).

The smaller the dead time, the higher the maximum voltage can be. Therefore, if the dead time is determined by indentation charging 10A, which requires the maximum voltage for the above reason, the charging voltage is low at other currents, so the dead time may be increased. Means. For example, in Fig. 6, if the inverter frequency is 20 kHz (cycle 50 μs), the indentation charge voltage is 110 V, and the dead time is 1 μs, the on-time at this time is 50 / 2-1 = 24 (μs) and the charge voltage is 90 V. Since the on-time of is 24 x 90/110 = 19.6 (μs), the required dead time at 90V is 50 / 2-19.6 = 5.4 (μs), that is, if the dead time is 5μs, the charging voltage of 90V is set. It can be secured.

In addition, control may become unstable if the dead time is too large than the charge / discharge time without switching the dead time to a small value only during push-in charging. In that case, the charging current is the time other than push-in charging. The dead time may be gradually increased as it becomes smaller. Further, even if a large current is not indented charging, when starting from a small current at the start of charging, charging / discharging may not be performed within the dead time. Even in such a case, the contactor MC may be turned on and the reactor Lx may be connected.

Next, as described in the above section (4), the minimum current required when the dead time is 5 μs from t = 2CEd / Id will be described using the values in the above example.
When the dead time is t = 5 μs, the current Id = 2CEd / t = 2 × 0.1 × 300/5 = 12 (A). That is, when the dead time is 5 μs, it is not necessary to pass a current through the reactor Lx if the charging current is 12 A or more. It is only necessary to pass a current through the reactor Lx when the indentation charge is 10A.

Next, when the dead time is 1 μs, the current Id required for the reactor Lx must be discharged for 1 μs, so Id = 2 × 0.1 × 300/1 = 60 (A). In the above calculation, the ratio of the primary and secondary turns of the transformer TF is 1: 1 and the charging current and Id are the same.
From the above, in FIG. 6, the dead time is set to 5 μs during normal charging (25 A or more), the dead time is set to 1 μs during push charging (10 A), and the contactor MC is turned on to apply current to the reactor Lx. If it is made to flow, dV / dt and dI / dt become small at all charging currents, which is effective for EMC.

Therefore, according to this embodiment, the following effects can be obtained.
(A) By reducing the resistance value R in the CR snubber circuit, dV / dt and dI / dt when the IGBT is turned off can be reduced, which is effective for EMC. In addition, the loss due to resistance can be reduced.
(B) By reducing the dead time only when the charging current is small and passing a dummy current through the reactor Lx connected in parallel with the transformer TF, a switching element such as an IGBT can be selected with the maximum charging current. As a result, even if the reactor Lx is connected, it is not necessary to increase the IGBT, and the reactor Lx is not connected during charging other than push charging, so that the efficiency does not deteriorate.

In the embodiment shown in FIG. 1, the effects shown in the above items (a) and (b) are obtained, but a series circuit of the contactor MC and the reactor Lx is required, and a component is also required.
In the second embodiment, the charger shown in FIG. 4 is applied by slowing down the on-speed (hereinafter referred to as on-time) of the switching elements Tu, Tv, Tx, and Ty constituting the inverter when the charging current is small. It improves the EMC effect.

FIG. 7 shows the current flowing through the capacitor of the CR snubber circuit and the voltage waveform of the switching element by delaying the on-time of the switching element when the charging current is small. Taking the switching elements Tv and Ty connected in series of the inverter IV as an example, when the switching element turns on slowly, the resistance value of the switching element gradually decreases from infinity to zero. As a result, the electric charge of the capacitor Cy is discharged while being limited by the resistance value of the switching element Ty, the electric charge of the capacitor Cv is charged, and the voltage of the switching element Tv gradually rises, and the dV / dt is dV / dt as compared with FIG. It becomes smaller. However, if the on-time is slowed down, the voltage and current rate of change dV / dt and dI / dt become smaller and noise is reduced, but if the switching speed is slowed down, the loss during switching becomes larger and efficiency is reduced and cooling is taken into consideration. Is required.

In FIG. 4, the switching loss Pon when turned on per switching element is
Pon ＝ 1/3 × Ed × Id × ton × f
Will be. Here, Ed: DC voltage, Id: DC current, ton: On time, f: Frequency,
Since the switching loss is proportional to the frequency as shown in the above equation, the switching loss becomes remarkable in the inverter of a high frequency.

Since the DC current Id is small when the on-time of the switching element is delayed only when the charging current is small, the switching loss Pon does not become large as compared with the normal charging current even if the on-time ton is increased. In this embodiment, the on-time is not simply lengthened when the charging current is small, but the on-time is lengthened by increasing the gate resistance of the switching element as shown in FIG. FIG. 8 shows the relationship between the gate resistance of the IGBT on the horizontal axis and the switching time on the vertical axis, and the lengthening on time corresponds to tr in FIG.

Therefore, according to this embodiment, by reducing the resistance value R in the CR snubber circuit, dV / dt and dI / dt when the IGBT is turned off can be reduced, which is effective for EMC. In addition, the loss due to resistance can be reduced. Furthermore, by lengthening the on-time only when the charging current is small, it is possible to prevent a decrease in charging efficiency other than during push-in charging, and there is no need to add new parts, making it possible to support EMC by downsizing. Is.

IV ... Inverter
TF ... transformer
Cov ... Rectifier
BAT ... Battery (secondary battery)
MC ... Contactor
Lx ... Reactor
Tu, Tv, Tx, Ty ... Switching element
C ... Capacitor
R ... resistance

Claims (3)

An inverter with a snubber circuit connected in parallel with each switching element converts DC voltage to AC voltage, and a rectifier converts the converted AC voltage to DC voltage, and gradually or gradually charges the charging current while adjusting the DC voltage. In the charging method with a charger that charges the battery while reducing it,
When the charging current to the battery becomes equal to or less than a predetermined value (pushing charging current), the on-time of the switching element is delayed .
A method for reducing EMI noise in a charger, wherein the snubber circuit is a CR snubber circuit in which a resistor and a capacitor are directly connected, and the resistance value of the snubber circuit is set to a value as small as possible. An inverter with a snubber circuit connected in parallel with each switching element converts DC voltage to AC voltage, and a rectifier converts the converted AC voltage to DC voltage, and gradually or gradually charges the charging current while adjusting the DC voltage. In the charging method with a charger that charges the battery while reducing it,
When the charging current to the battery is reduced below a predetermined value (pushing charge current), to slow down the on-time of the switching element, EMI noise reduction charger characterized by shortening the dead time of the inverter Method. Wherein when the charging current to the battery is equal to or less than a predetermined value, EMI noise reduction method charger that claim 1, wherein the wherein to shorten the dead time of the inverter.

Images