JP2011130577A - Dc power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC power supply unit capable of reducing the loss, when a switching element is on, even if voltage attenuation conditions change due to a change in the output current. <P>SOLUTION: The DC power supply unit includes a full-bridge inverter 20, a transformer 30, a rectifier circuit 40, a smoothing circuit 50 and a control circuit 70 for controlling the full-bridge inverter 20. In the unit, the full-bridge inverter 20 has first-fourth switching elements QA-QD, the control circuit 70 alternately turns on and off the first and second switching elements QA, QB and the third and fourth switching elements QC, QD at a predetermined cycle, and the output of the full-bridge inverter is subjected to pulse-width modulation, by changing the timing for turning on the third and fourth switching elements QC, QD using an ON-time point of the first and second switching elements QA, QB as a reference. The DC power supply unit includes an output voltage current detecting circuit 60 for detecting the current which flows through a load, and the control circuit 70 controls at least either first or second dead time, on the basis of the detected current. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a DC power supply device including a full bridge inverter.

  Conventionally, a full-bridge inverter, a transformer that converts an AC voltage output from the full-bridge inverter, a rectifier circuit that rectifies an AC voltage output from the secondary side of the transformer, and a rectifier that has been rectified by the rectifier circuit There is known a DC power supply device including a smoothing circuit that smoothes a rectified current and supplies the rectified current to a load (see Patent Document 1).

  Such a DC power supply includes an input voltage detection unit that detects an input voltage input to the full bridge inverter, an input current detection unit that detects an input current input to the full bridge inverter, and an output voltage that detects a voltage applied to the load. The control circuit has a detection unit, and the control circuit controls on / off of each switching element of the full-bridge inverter based on the input voltage detected by the input voltage detection unit and the output voltage detected by the output voltage detection unit. To do.

  The full bridge inverter has first to fourth arms provided with switching elements, the first arm and the second arm are connected in series, and the third arm and the fourth arm are connected in series. Then, the first and second switching elements of the first and second arms are alternately turned on and off so that a predetermined dead time (first dead time) occurs at a predetermined frequency, and the third and fourth at the same predetermined frequency. The third and fourth switching elements of the arm are turned on and off alternately so that a dead time (second dead time) occurs.

  The first and second arms are used as fixed arms and the phase shift is used as a reference, and the third and fourth arms (shift arms) are shifted in phase (timing at which the switching element is turned on) from the fixed arms.

  That is, in the DC power supply device, the control circuit 1 adjusts the switching frequency and the phase shift amount so that the output voltage detected by the output voltage detection unit is constant, and the peak value of the current flowing through the switching element is excessively increased. Is suppressed, and high-efficiency, low-noise power control is performed.

  Further, in such a DC power supply device, when each switching element is turned off, the voltage rise is delayed due to the charging of the resonance capacitor connected in parallel to each switching element. Therefore, each switching element becomes a zero voltage switching operation and the switching loss is reduced. can do.

JP 2006-33923 A

  However, in such a DC power supply device, when it is turned on, a loss is caused by turning on each switching element after a certain period of time by using partial resonance to attenuate the switch voltage of the fixed arm and the shift arm. It is small. However, since the voltage attenuation condition changes depending on the output state of the power supply, the switch voltage is not sufficiently attenuated in the dead time that is set to a certain time, and therefore the loss when the switching element is on cannot be reduced. was there.

  That is, as shown in FIG. 3, when the second dead time is set so that the conversion efficiency becomes the highest when the output current is 100%, the conversion efficiency decreases in a region where the output current is small. Conversely, if the second dead time is set so that the conversion efficiency becomes the highest when the output current is 20%, the conversion efficiency is lowered in a region where the output current is large.

  Further, as shown in FIG. 4, when the first dead time is set so that the conversion efficiency becomes the highest when the output current is 100%, the conversion efficiency is lowered in a region where the output current is small. Conversely, if the first dead time is set so that the conversion efficiency becomes the highest when the output current is 20%, the conversion efficiency is lowered in the region where the output current is large.

  An object of the present invention is to provide a DC power supply device that can reduce a loss when a switching element is on even if a voltage attenuation condition changes due to a change in output current.

According to the first aspect of the present invention, there is provided a phase shift control type full bridge inverter that converts a voltage of a DC power source into an AC voltage, a transformer that converts an AC voltage output from the full bridge inverter into a predetermined AC voltage, and the transformer A rectifying circuit for rectifying the AC voltage output from the secondary side of the rectifier, a smoothing circuit for smoothing the rectified current rectified by the rectifying circuit and supplying the rectified current to the load, and a control means for controlling the full-bridge inverter. The full bridge inverter has first to fourth arms to which switching elements are respectively connected, the first arm and the second arm are connected in series, the third arm and the fourth arm are connected in series, and the control The means alternately turns the first and second switching elements of the first and second arms, and alternately turns the third and fourth switching elements of the third and fourth arms alternately. DC power supply device that performs pulse width modulation on the output of the full bridge inverter by changing the timing at which the third and fourth switching elements are turned on with reference to the on time of the first and second switching elements Because
A current detection circuit for detecting a current flowing through the load;
The control means has a dead time during which the third switching element and the fourth switching element are turned off, and the first switching element and the second switching element are turned off based on the current detected by the current detection circuit. At least one of the dead times is controlled.

  According to the present invention, even when the voltage attenuation condition changes depending on the output state of the power supply, it is possible to reduce the loss when the switching element is on, thereby improving the conversion efficiency in a wide output range of the output current. it can.

It is the circuit diagram which showed the structure of the direct-current power supply device which concerns on this invention. It is a time chart of the principal part of the direct-current power supply device shown in FIG. It is the graph which showed the relationship of the conversion efficiency with respect to an output current when changing a 2nd dead time. It is the graph which showed the relationship of the conversion efficiency with respect to an output current when changing a 1st dead time.

  Hereinafter, an embodiment which is an embodiment of a DC power supply according to the present invention will be described with reference to the drawings.

[First embodiment]
A DC power supply device 10 shown in FIG. 1 includes a phase shift control type full-bridge inverter 20 that converts a DC power supply voltage into an AC voltage, a transformer 30 that converts an AC voltage output from the full-bridge inverter 20, A rectifier circuit 40 that rectifies an AC voltage output from the secondary side of the transformer 30; a smoothing circuit 50 that smoothes the rectified current rectified by the rectifier circuit 40 and supplies the rectified current to the load; Based on the output voltage / current detection circuit 60 that detects the output voltage and output current, and the voltage and current detected by the output voltage / current detection circuit (current detection circuit) 60, each switching element (first to first) of the full-bridge inverter 20 is detected. 4 switching elements) and a control circuit (control means) 70 for controlling on / off of QA to QD.

  The full-bridge inverter 20 has first to fourth arms S1 to S4 to which switching elements QA to QD are connected, respectively. The first arm S1 and the second arm S2 are connected in series, and the third arm S3 and the fourth arm The arm S4 is connected in series. Resonant capacitors CA to CD are connected to the switching elements QA to QD.

  The transformer 30 converts the voltage Vp applied to the primary coil 31 into a predetermined voltage Vs corresponding to the turn ratio of the primary and secondary coils 31 and 32. One terminal of the primary coil 31 is connected to the connection point of the first and second arms S1 and S2 of the full bridge inverter 20, and the other terminal of the primary coil 31 is connected to the connection point of the third and fourth arms S3 and S4. It is connected. One terminal of the secondary coil 32 of the transformer 30 is connected to an anode of a diode DA described later, and the other terminal of the secondary coil 32 is connected to an anode of a diode DC described later.

  The rectifier circuit 40 includes four diodes DA to DD, and full-wave rectifies the AC voltage output from the secondary coil 32 of the transformer 30.

The smoothing circuit 50 includes an output inductor Lout and an output capacitor Cout, and smoothes the rectified voltage output from the rectifier circuit 40 to output it as a DC voltage.
[Operation]
Next, the operation of the DC power generation apparatus 10 configured as described above will be described.

  When a main switch (not shown) is turned on, a switching signal is output from the control circuit 70, and the switching elements QA to QD are turned on / off at the timing shown in FIG. That is, the switching elements QA and QB of the first and second arms S1 and S2 are alternately switched so that a predetermined dead time (time points t3 to t4, t7 to t8...: First dead time: dead time) occurs at a predetermined frequency. The switching elements QC and QD of the third and fourth arms S3 and S4 are turned on and off at the same predetermined frequency so that a dead time (time t1 to t2, t5 to t6...: Second dead time: dead time) occurs. Turn on and off alternately.

  The voltage Vp shown in FIG. 2 is applied to the primary coil 31 of the transformer 30 by turning on / off the switching elements QA to QD, and the voltage Vs shown in FIG. 2 is output from the secondary coil 32 of the transformer 30.

  The voltage Vs is rectified by the rectifier circuit 40, smoothed by the smoothing circuit 50, and supplied to a load (not shown) as a DC voltage.

  The output voltage / current detection circuit 60 detects the voltage and current output from the smoothing circuit 50, that is, the voltage and current supplied to the load, and the control circuit 70 is based on the voltage and current detected by the output voltage / current detection circuit 60. Thus, the pulses applied to the primary coil 31 of the transformer 30 by controlling on / off of the switching elements QA to QD so that the voltage, current, and power supplied to the load become constant voltage, constant current, and constant power. The pulse width (time t0 to t1, t4 to t5) of the voltage (Vp) is changed. That is, the output current Io, the output voltage, and the output power are made constant by pulse width modulation.

  Here, the dead time will be described. The dead time TD2 is between the time points t1 and t2 and between the time points t5 and t6 in FIG. 2, but the dead time TD2 between the time points t1 and t2 will be described because only the polarities are different.

The time from when the switching element QD is turned off to when the switching element QC is turned on is the time until the voltage of the resonance capacitor CD is charged to the input DC voltage Ein (inverter drive voltage) or the voltage of the resonance capacitor CC is discharged to 0V. If the capacitor CC and the capacitor CD are equivalently combined at the location of CD to be Ccd (not shown), the voltage of Ccd is the output current Io because the output inductor Lout continues the state immediately before the switching element QD is turned off. Is a voltage charged with a current converted by the turns ratio of the transformer 30. Therefore, the voltage Vcd of Ccd is
Vcd (t) = (Io × Ns × t) / (Ccd × Np)
It becomes. Here, Np is the number of turns of the primary winding (primary coil 31) of the transformer 30, and Ns is the number of turns of the secondary winding (secondary coil 32) of the transformer 30. When Vcd = Ein, the on-voltage of the switching element QC is 0V, so the dead time TD2 is
TD2 = (Ein × Ccd × Np) / (Io × Ns)
It becomes. In principle, since the dead time TD2 is proportional to the reciprocal of the output current Io, it can be approximated as follows.

TD2≈A / Io (1)
However, A is a constant unique to the circuit. Further, since the dead time TD2 becomes long in the region where the output current Io is small, an upper limit is set.

  Next, when the switching signal is output from the control circuit 70 and the switching elements QA to QD are turned on / off, there is a difference between the on time and the off time due to the characteristics of the switching elements QA to QD. An approximate expression obtained by adding the time of the difference to the expression (1) is as follows.

TD2≈ (A / Io) + B (2)
However, B is a circuit specific constant. Also in this case, in the region where the output current Io is small, the dead time TD2 becomes long, so an upper limit is set. When the OFF delay time is long, the constant B is positive, and when the ON delay time is long, the constant B is negative.

  Although there are many fluctuation elements of the dead time TD2, the optimum dead time TD2 is calculated by calculating or actually measuring another fluctuation element x having a large influence and the correction formula f (x) of the dead time TD2, and adding it to the expression (2). Can be requested.

TD2 = (A / Io) + B + f (x) (3)
Or, TD2 = (A / Io) + B × f (x)
f (x) is a function of x, and f (x) may be not only one term but also a plurality of terms. For example, f (x1), f (x2) ...
However, also in this case, the dead time TD2 becomes long in the region where the output current Io is small, so an upper limit is set.

  Examples of other variable elements x include an inverter input voltage Ein and a power supply ambient temperature.

  In the first embodiment, the control circuit 70 obtains the dead time TD2 from the equation (1), (2), or (3) based on the output current Io detected by the output voltage / current detection circuit 60, and obtains the obtained time. The on-time timing of the switching elements QC and QD is shifted back and forth so that the dead time TD2 is reached.

  For example, as shown in FIG. 2, when the switching elements QA to QD are turned on / off, the output current is Io, and the output voltage or output current or output power is kept at a predetermined power, When the dead time obtained by the equation (2) or (3) is, for example, twice TD2 shown in FIG. 2, switching is performed by delaying Δt time from the time point t2, t6... So that the dead time becomes TD2 × 2. The elements QC and QD are turned on at time points t2 'and t6'.

  By doing this, the time during which the switching elements QA, QD are simultaneously turned on and the time during which the switching elements QB, QC are simultaneously turned on, and the ON / OFF repetition period of the switching elements QA to QD are changed. In other words, the dead time TD2 can be adjusted (controlled) without changing the pulse width of the pulse voltage (Vp) and the period (frequency) of the pulse.

  For this reason, even if the dead time TD2 is controlled, the output voltage, the output current, and the output power can be kept constant.

By controlling the dead time TD2, the switch voltage (the voltages of the resonant capacitors CC and CD when the switching elements QC and QD are turned on) can be sufficiently attenuated regardless of the output current Io. Loss when the elements QC and QD are on can be reduced. For this reason, the conversion efficiency of the DC power supply device 10 can be improved in a wide output range of the output current Io.
[Second Embodiment]
Next, a case where the dead time TD1 is controlled will be described.

  In the state from switching element QA off to switching element QB on, voltage Vab when switching element QB is on is in series resonance of resonance capacitors CA and CB on the sides of arms S1 and S2 and leakage inductance Lr of transformer 30. Therefore, the following equation is obtained. Here, the resonant capacitors CA and CB are equivalently synthesized at the location of the resonant capacitor CB to form a Cab (not shown).

Vab (t) = Ein - ( (Io × Ns) / (Cab × Np × ω)) × ε - α t × sinωt
It becomes. However, α = R / 2Lr ω = √ (1 / (Cab × Lr) −α ² ).

Since the voltage of Vab is damped, the switching element QB is turned on in the first valley. Therefore, the dead time TD1 is
TD1 = π / 2ω
It becomes. Therefore,
Vab (TD1) = Ein - ( (Io × Ns) / (Cab × Np × ω)) × ε - β
It becomes. However, β = πα / 2ω.

Since the dead time TD1 is a fixed time,
TD1 = C (4)
It becomes. However, C is a circuit specific constant. Incidentally, since the voltage Vab to be switched decreases as the output current Io increases, the on-loss of the switching elements QA and QB is small when the output current Io is large, and is large when the output current Io is small.

Next, a difference occurs in the delay time between on and off due to the characteristics of the switching elements QA and QB. When the time component of the difference is added to equation (4),
TD1 = C + D (5)
It becomes. However, D is a constant unique to the circuit.

  In addition, although there are many fluctuation elements of TD1, it is possible to obtain an optimum TD1 by calculating or actually measuring another fluctuation element x having a large influence and a correction equation g (y) of TD1, and adding it to the equation (5). it can.

TD1 = C + D + g (y) or TD1 = C + D × g (y) (6)
However, y is another variable factor. g (y) is a function of y, and g (y) may be not only one term but also a plurality of terms. For example, g (y1), g (y2).

  Here, since the variable element having a large influence is the output current Io, TD1 is determined using the equation (6).

  Then, TD1 is calculated from the equation (6) based on the output current Io detected by the output voltage / current detection circuit 60, and the control circuit 70 turns on / off the switching elements QA to QD so that the calculated dead time TD1 is reached. To control.

  Here, the time when the switching elements QA and QB are turned off is shifted back and forth between the time points t3 and t7 shown in FIG. 2 so that the calculated dead time TD1 is reached.

  By doing in this way, the same effect as Example 1 can be acquired. Note that there are input DC voltage Ein, power supply ambient temperature, and the like as variable factors having a large influence, and TD1 may be calculated from these input DC voltage Ein and power supply ambient temperature.

  The present invention is not limited to the first and second embodiments. For example, the dead time TD1 and the dead time TD2 are controlled based on the output current Io detected by the output voltage / current detection circuit 60. Of course, design changes and additions are allowed without departing from the scope of the claimed invention.

10 DC power supply device 20 Full bridge inverter 30 Transformer 40 Rectifier circuit 50 Smoothing circuit 60 Output voltage current detection circuit (current detection circuit)
70 Control circuit (control means)
QA-QD switching element S1-S4 arm

Claims (1)

A phase shift control type full-bridge inverter that converts the voltage of the DC power supply to an AC voltage, a transformer that converts the AC voltage output from the full-bridge inverter into a predetermined AC voltage, and a secondary side of the transformer. A rectifier circuit that rectifies the alternating voltage, a smoothing circuit that smoothes the rectified current rectified by the rectifier circuit and supplies the rectified current to a load, and a control unit that controls the full-bridge inverter. The switching device includes first to fourth arms connected to each other, the first arm and the second arm are connected in series, the third arm and the fourth arm are connected in series, and the control means includes the first and second arms. The first and second switching elements of the two arms are alternately turned on and off, and the third and fourth switching elements of the third and fourth arms are alternately turned on and off at regular intervals. A DC power supply device that performs pulse width modulation on the output of the full bridge inverter by changing the timing of turning on the third and fourth switching elements with reference to the on time of the first and second switching elements,
A current detection circuit for detecting a current flowing through the load;
The control means has a dead time during which the third switching element and the fourth switching element are turned off, and the first switching element and the second switching element are turned off based on the current detected by the current detection circuit. A DC power supply apparatus that controls at least one of dead times.

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