JP4211743B2 - Charger - Google Patents

Description

  The present invention relates to a charging device.

  Charging devices using resonant inverters are efficient and low in noise, but when the output is controlled and the output is throttled, the resonance conditions are not met and the efficiency becomes worse, resulting in increased noise. In some cases, control could be impossible.

Therefore, in a resonance type power supply including a push-pull resonance circuit that includes two switching elements, a resonance capacitor, and a resonance inductor and converts a DC input into a high-frequency output by alternately turning on and off the switching elements. By switching the period during which both switching elements are turned off (dead time) and the lowest switching frequency, it has become possible to reduce the charging current in constant voltage charging. (For example, see Patent Document 1)
JP 2003-134817 A

  The conventional charging device performs zero voltage switching, and the possible conditions for zero voltage switching are determined in proportion to the charging current.

For example, when the current that flows to the primary side of the transformer with forward coupling is taken out as the charging current from the secondary side, the primary winding number of the transformer, the secondary winding number, the primary winding maximum current, the secondary winding maximum current Are N1, N2, Ip and Is, respectively.
N1 ・ Ip = N2 ・ Is
There is a relationship.

Furthermore, if the inductance of the resonance inductor is Lr, the capacitance of the resonance capacitor is Cr, and the primary voltage of the transformer is Vp,
^{LrIp 2/2> CrVp 2/} 2
It becomes. From the above two equations, the resonance condition is satisfied if the current flowing on the secondary side of the transformer, that is, the charging current is larger than a certain value.

  This possible condition for zero voltage switching is not affected by the battery voltage. If the limit charging current value at which the zero voltage switching is possible when the battery voltage is 20 V is 5 A, the limit charging when the battery voltage is 0 V is assumed. The current value is also 5A.

  In other words, when performing constant current charging, the resonance condition is satisfied even if the charging voltage is increased, or if the resonance condition is satisfied at the initial stage of charging, even if the completion of charging is approaching.

  However, when performing constant voltage charging, as the charging current value decreases, the switching frequency increases and the current flowing through the resonance inductor decreases. And since the charging current gradually decreases, resonance conditions are not satisfied midway, zero voltage switching becomes impossible and loss increases, and in some cases, the switching element breaks due to temperature rise, or the output decreases. Could not be.

  This invention is made | formed in view of the said reason, The objective is to provide the charging device comprised by the resonance type inverter which can perform constant current charge and constant voltage charge.

  The invention of claim 1 includes a first switching element, a second switching element, a resonance capacitor, and a resonance inductor, and alternately turns on and off the first and second switching elements to convert a DC input into a high frequency output. A push-pull resonance type inverter unit and a control unit that controls the operation of the switching element of the inverter unit, and the battery charges the battery with a constant current or a constant voltage according to the output of the inverter unit. There is a switching means between the resonant mode for voltage switching and the non-resonant mode that does not switch the switching element to zero voltage, and the charging current is gradually reduced during constant voltage charging so that resonance occurs when the charging current falls below a predetermined value. It is characterized by shifting from the mode to the non-resonant mode.

  According to the present invention, not only constant current charging but also constant voltage charging can be performed by switching between a resonance mode and a non-resonance mode while using a resonance type inverter that can reduce switching loss and noise.

  According to a second aspect of the present invention, in the first aspect, the control unit extends a period in which both the first and second switching elements are off in the non-resonant mode.

  According to the present invention, the resonance mode and the non-resonance mode can be switched with a simple circuit configuration.

  According to a third aspect of the present invention, in the second aspect of the present invention, the control unit determines a period during which the first and second switching elements are both off in the non-resonant mode between the resonance capacitor and the resonance inductor. It is characterized by being an integral multiple of the resonance period.

  According to the present invention, switching loss and noise in the non-resonant mode can be minimized. Therefore, a switching element with a low rating can be used, and furthermore, noise countermeasure components can be downsized or omitted.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the control unit sets a plurality of non-resonant modes having different periods during which both the first and second switching elements are off, and the constant voltage Switching to any one of the non-resonant modes is performed according to the charging current at the time of charging.

  According to the present invention, the control region can be expanded, constant voltage charging can be performed on batteries with various charging voltages, and in switching frequency control of the switching element, from the minimum value to the maximum value of the switching frequency. The range can be narrowed, and the size of the noise filter can be reduced.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the control unit sets a charging voltage for performing constant voltage charging to a predetermined voltage value.

  According to the present invention, when a constant voltage charging function is added to a constant current charger using a resonant inverter, the addition of components can be minimized.

  According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the control unit includes a comparator that compares a detected value of the charging current with a reference value, and controls the charging current according to the comparison result. In the constant voltage charging, the charging current is reduced stepwise by changing the reference voltage stepwise.

  According to the present invention, charge current control during constant voltage charging can be performed using the constant current charge control function.

  As described above, according to the present invention, it is possible to perform not only constant current charging but also constant voltage charging by switching between a resonance mode and a non-resonance mode while using a resonance type inverter that can reduce switching loss and noise. effective.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
As shown in FIG. 1, the charging device of the present invention includes a rectifying / smoothing circuit 1 that rectifies and smoothes an AC power supply AC, and a switching circuit that includes FETs each having a source terminal connected to the negative voltage side output of the rectifying / smoothing circuit 1. A series circuit of resonance inductors Le1, L1, L2, Le2 connected between the drain terminals of the elements FET1, FET2 and switching elements FET1, FET2 and having a connection point connected to the positive voltage side output of the rectifying / smoothing circuit 1 and resonance This is a two-stone push-pull partial resonance circuit comprising a series circuit of capacitors C1 and C2 and a series circuit of inductors L3 and L4 magnetically coupled to inductors L1 and L2. Resonance type inverter unit 2 to be converted and inductors L3 and L4 connected in series to each end of an anode and cathodes connected to each other. Smoothing connected between the rectifying unit 3 comprising the diodes D1 and D2, the choke coil L5 having one end connected to the connection point of the diodes D1 and D2, and the connection point between the other end of the choke coil L5 and the inductors L3 and L4 Between the output of the smoothing unit 4 and the smoothing unit 4, the battery pack 5 including a series circuit of a plurality of batteries to which the output of the inverter unit 2 is supplied by applying a DC voltage across the capacitor C 3. A resistor R3 inserted between the negative voltage side terminal of the battery pack 5 and the negative voltage side terminal of the capacitor C3 and connected to the series circuit of the resistors R1 and R2 connected to divide and detect the charging voltage. And a control unit 6 that controls the operation of the switching elements FET1 and FET2.

  Then, the switching elements FET1 and FET2 alternately turn on and off the DC voltage obtained by rectifying and smoothing the output of the AC power supply AC by the rectifying / smoothing circuit 1, so that when the switching element FET1 is on, a current is supplied to the inductor L1. To induce a voltage in the inductor L3, and when the switching element FET2 is on, a current is passed through the inductor L2 to induce a voltage in the inductor L4. The induced voltages of the inductors L3 and L4 are rectified by the diodes D1 and D2, and a DC voltage smoothed by the choke coil L5 and the capacitor C3 is applied to the battery pack 5.

  The charging device shown in FIG. 1 is used in a quick charger for an electric tool, and the type of the battery pack 5 of the load includes a NiCd battery, a NiMH battery, a lithium ion battery, and the like. The battery voltage is a nominal voltage of 7.2 V, There are 9.6V, 12V, 15.6V and 24V, and there are also 2Ah and 3Ah capacities. Thus, each battery pack 5 of various battery types, voltages, and capacities can be charged with a single charger. In the lithium ion battery, first, constant current charging is performed, and when the charging voltage (battery voltage) reaches a specified value, constant voltage charging is performed.

  Hereinafter, switching control of the switching elements FET1 and FET2 by the control unit 6 of the present embodiment will be described.

  The control unit 6 includes a microcomputer 6a, a comparator 6b, a control circuit unit 6c, and an amplifier 6g as main components. The microcomputer 6a receives the voltage at the connection point between the resistors R1 and R2 as the detected value Sv of the charging voltage and generates the PWM signal Spwm based on the detected charging voltage value Sv. The PWM signal Spwm is the signal output of the microcomputer 6a. The signal is smoothed by a series circuit of a resistor 6d and a capacitor 6e connected between the ends, and is input as a current reference value Sref to the comparator 6b via the resistor 6f. Further, the microcomputer 6a generates a control signal Sa for switching the dead time and the switching frequency, and outputs it to the control circuit unit 6c.

  Further, the charging current detection value Si ′ obtained by amplifying the charging current detection value Si, which is the voltage across the resistor R3, by the amplifier 6g is input to the comparator 6b. The comparator 6b compares the detected charging current value Si 'with the current reference value Sref, and outputs the difference as a feedback signal Sfb to the control circuit unit 6c.

  In the control circuit unit 6c, by supplying a current proportional to the feedback signal Sfb to the secondary side of the photocoupler, charging current correction information is transmitted to the primary side control IC. Then, the switching operation of the switching elements FET1 and FET2 is controlled so that the charging current detection value Si ′ and the current reference value Sref match, that is, the feedback signal Sfb becomes zero.

  FIG. 2 shows waveforms of drive signals S1 and S2 output to the switching elements FET1 and FET2 by the control circuit unit 6c during output control. FIG. 2 (a) shows when the output is large, and FIG. 2 (b) shows when the output is small. The drive signals S1 and S2 and the dead time Td during which both the switching elements FET1 and FET2 are off are kept constant, and the frequency control is performed. When the output is reduced (squeezed), the switching frequency is increased, and when the output is increased, the switching frequency is decreased.

  Further, the control circuit unit 6c operates the switching elements FET1 and FET2 in two modes of a resonance mode (soft switching) in which zero voltage switching is performed and a non-resonance mode (hard switching) in which zero voltage switching is not performed. The resonance mode is used when the output is large, and the non-resonance mode is used when the charging current is very small as in trickle charging. As shown in FIGS. 3A and 3B, the waveforms of the drive signals S1 and S2 in the non-resonant mode and in the non-resonant mode, the dead time Td is short, and the dead time in the non-resonant mode. Td becomes longer. In the non-resonant mode, since the current flowing through the switching elements FET1, FET2 and the inductors L1 to L4 is small, the switching loss and noise are sufficiently smaller than in the resonant mode where the output is large.

  Here, FIG. 4 is a control table showing the relationship between the charging voltage and the charging current when switching between the resonance mode and the non-resonance mode in constant current charging in the conventional NiCd battery and NiMH battery charging apparatus. The resonance mode region A0 that operates in the resonance mode when the charging current is large I2 to I3, and the non-resonance mode region B0 that operates in the nonresonance mode when the charging current is 0 to I1 is set within the range of the charging voltage 0 to V1. Has been. Here, I2 = 5A, I3 = 10A, and V1 = 40V.

  FIG. 5 is a control table showing the relationship between the charging voltage and the charging current when switching between the resonance mode and the non-resonance mode in this embodiment, and sets the resonance mode region A1 and the non-resonance mode region B1. is doing. A resonance mode region A1 that operates in the resonance mode is set for I2 to I3 where the charging current is large, and a non-resonance mode region B1 that operates in the nonresonance mode is set in the range of the charging voltage 0 to V1 when the charging current is 0 to I1. Further, in the charging currents I1 and I2, the resonance mode region A1 and the non-resonance mode B1 are set in the vicinity of the constant voltage charging start voltage V0, and the control region is increased as compared with the conventional control table of FIG. I1 <I2 <I3).

FIG. 6 shows the change of the charging current with respect to the charging time. First, the microcomputer 6a determines the charging voltage based on the charging voltage detection value Sv, and if the charging voltage is equal to or lower than the constant voltage charging start voltage V0, Constant current charging, in which the reference current Sref is kept constant and the charging current is kept constant, is performed in the resonance mode. (Time t0 to t1 in FIG. 6)
When the charging voltage gradually rises while performing constant current charging in the resonance mode and the charging voltage reaches the constant voltage charging start voltage V0, constant voltage charging is started in the resonance mode. At this time, the microcomputer 6a reduces the PWM signal Spwm to reduce the current reference value Sref to the comparator 6b. Then, the control circuit unit 6c drives the switching elements FET1 and FET2 so that the charging current decreases. When the charging current decreases, the battery pack 5 has an internal resistance, so that the charging voltage is changed from the constant voltage charging start voltage V0. A little lower. When charging is continued for a while at this reduced charging voltage, the charging voltage rises again. When the constant voltage charging start voltage V0 is reached, the above process is performed again to lower the charging current. Thereafter, the above process is repeated, and the charging current gradually decreases stepwise.

Since the microcomputer 6a generates the PWM signal Spwm, the target value of the current charging current is known, the charging current decreases stepwise, and the average voltage of one cycle of the PWM signal Spwm is less than or equal to the predetermined voltage. Then, it is determined that the charging current has decreased to the specified current value I2 ′, and a control signal Sa for shifting from the resonance mode to the non-resonance mode is output to the control circuit unit 6c. The control circuit unit 6c The switching elements FET1 and FET2 are driven in a non-resonant mode in which the dead times of the FET1 and FET2 are increased. Then, after the transition to the non-resonant mode, the charging current is gradually reduced step by step while the constant voltage charging is continued, and the charging is completed when the charging current becomes a specified value or less. (Times t1 to t2 in FIG. 6)
The constant voltage charging start voltage V0 is determined according to the specifications of the battery pack 5, and in this embodiment, constant voltage charging with other voltages is not performed. Therefore, in the control table of FIG. The control region exists only in the vicinity of the constant voltage charging start voltage V0. For example, when a charging voltage is very low as in a lithium ion battery, protective charging is performed, constant current charging is performed in a normal state, and constant voltage charging is performed when the charging voltage is high, as in this embodiment. The control region that exists over the entire range of the charging current only needs to be secured in the vicinity of the charging voltage at the time of constant voltage charging, and the constant voltage charging function of this embodiment is applied to the constant current charger using the resonance type inverter. When adding, the addition of parts can be minimized.

  As described above, this embodiment has a constant voltage charging function as well as a constant current charging function while using a resonance type inverter that can reduce switching loss and noise. A voltage charging function can be added to quickly charge a lithium ion battery.

  Next, switching of the dead time Td performed when switching between the resonance mode and the non-resonance mode will be described. FIG. 7 shows waveforms of the drain voltage Vds1, the drain current Id1, the drain voltage Vds2 and the drain current Id2 of the switching element FET1 in the resonance mode, and FIG. 8 shows the drain voltage of the switching element FET1 in the non-resonance mode. The waveforms of Vds1, drain current Id1, drain voltage Vds2 of the switching element FET2, and drain current Id2 are shown.

  First, in the resonance mode, as shown in FIG. 7, the switching operation of the switching element FET1 and the switching operation of the switching element FET2 are performed in the same period, and the dead time Td is short.

  Next, the dead time Td is made longer than the resonance mode to shift from the resonance mode to the non-resonance mode. After the switching elements FET1 and FET2 are both turned off at the dead time Td, the energy stored in the series circuit of the resonance inductors L1 and Le1, the series circuit of the resonance inductors L2 and Le2, and the resonance capacitors C1 and C2 The switching element to be turned on next is turned on when the resonance voltage (voltage at the connection point between the switching element and the resonance capacitor) becomes low. That is, the dead time Td is set to be an integral multiple of the resonance period, and switching loss and noise can be minimized. Therefore, low-rated switching elements FET1 and FET2 can be used, and noise countermeasure components can be reduced in size or omitted.

  In the present embodiment, as shown in FIG. 8, the dead time Td is set to three times the resonance period so that the next switching element is turned on when the resonance voltage Vr is lowered for the third time in the dead time Td. Yes. Since the resonance period is determined by the magnitude of the leakage inductance and the capacitance of the resonance capacitor, the next switching element can be turned on when the resonance voltage Vr becomes low regardless of the output.

  9 and 10 are examples of poor dead time Td setting in the non-resonant mode. FIG. 9 shows that the next switching element is turned on before the drain voltage Vd becomes low (falling). After the voltage Vd becomes low (rising), the next switching element is turned on, and the pulse current Ip is generated in the drain current Id, and the switching loss and noise increase.

(Embodiment 2)
FIG. 11 is a control table showing the relationship between the charging voltage and the charging current when switching between the resonance mode and the non-resonance mode of the present embodiment, and shows a resonance mode region A1 and two non-resonance mode regions B1, B2 is set.

  In the same manner as in the first embodiment, the resonance mode region A1 that operates in the resonance mode when the charging current is large I2 to I3, and the non-resonance mode region B1 that operates in the first nonresonance mode when the charging current is 0 to I1 is considerably small. The voltage is set in the range of 0 to V1. In the present embodiment, in the charging currents I1 and I2, the non-resonant mode region B2 that operates in the second non-resonant mode is set in the range of the charging voltages 0 to V1.

  First, in the resonance mode, as in the first embodiment, as shown in FIG. 7, the switching operation of the switching element FET1 and the switching operation of the switching element FET2 are performed in the same period, and the dead time Td is short.

  In the first resonance mode, as in the first embodiment, as shown in FIG. 8, the dead time Td is set so that the next switching element is turned on when the resonance voltage Vr is lowered for the third time at the dead time Td. Is set to three times the resonance period.

  In the second resonance mode, as shown in FIG. 12, the dead time Td is set to twice the resonance period so that the next switching element is turned on when the resonance voltage Vr is lowered for the second time at the dead time Td. Is set.

  As described above, in this embodiment, by switching the non-resonant mode to two stages, the control region can be expanded, and constant voltage charging can be performed on the battery pack 5 of various charging voltages. In the switching frequency control of the FET 2, the range from the minimum value to the maximum value of the switching frequency can be narrowed, and the noise filter can be reduced in size.

  In addition, the structure of the charging device of this embodiment is shown by FIG. 1 similarly to Embodiment 1, and description is abbreviate | omitted.

It is a figure which shows the structure of Embodiment 1 of this invention. The waveform of the drive signal of the switching element is shown. (A) is a waveform when the output is large (b) is a waveform when the output is small. The waveform of the drive signal of the switching element is shown. (A) is the waveform of the resonance mode (b) is the waveform of the non-resonance mode. It is a figure which shows the control table of the conventional constant current charge. It is a figure which shows the control table of Embodiment 1. FIG. It is a figure which shows the change of the charging current with respect to charging time same as the above. It is a figure which shows the dead time of the resonance mode same as the above. It is a figure which shows the dead time of a nonresonant mode same as the above. It is a figure which shows the 1st bad example of the dead time setting of a nonresonant mode same as the above. It is a figure which shows the 2nd bad example of the dead time setting of a nonresonant mode same as the above. It is a figure which shows the control table of Embodiment 2 of this invention. It is a figure which shows the dead time of a nonresonant mode same as the above.

Explanation of symbols

AC AC power supply 1 Rectification / smoothing circuit 2 Inverter unit 3 Rectification unit 4 Smoothing unit 5 Battery pack 6 Control unit FET1, FET2 Switching element L1, L2, Le1, Le2 Resonance inductor C1, C2 Resonance capacitor L3, L4 Inductor

Claims (6)

Push-pull resonance type inverter unit that includes first and second switching elements, a resonance capacitor, and a resonance inductor, and converts a DC input into a high-frequency output by alternately turning on and off the first and second switching elements. And a control unit that controls the operation of the switching element of the inverter unit, and the battery is constant current charged or constant voltage charged by the output of the inverter unit,
The control unit has a switching means between a resonance mode in which the switching element is zero-voltage switched and a non-resonance mode in which the switching element is not zero-voltage switched. The charging current is gradually reduced during constant voltage charging so that the charging current is predetermined. A charging device that shifts from a resonance mode to a non-resonance mode when the value falls below a value. The charging device according to claim 1, wherein the control unit lengthens a period in which both the first and second switching elements are off in the non-resonant mode. In the non-resonant mode, the control unit sets a period during which both the first and second switching elements are off to an integral multiple of a resonance period of the resonance capacitor and the resonance inductor. The charging device according to claim 2. The control unit sets a plurality of non-resonant modes in which the first and second switching elements are both off, and changes to any non-resonant mode according to a charging current during constant voltage charging. The charging device according to claim 1, wherein the charging device is switched. The charging device according to claim 1, wherein the control unit sets a charging voltage for performing constant voltage charging to a predetermined voltage value. The control unit includes a comparator that compares a detected value of the charging current with a reference value, controls the charging current according to the comparison result, and changes the reference voltage stepwise during constant voltage charging. The charging device according to claim 1, wherein the charging current is reduced stepwise.

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