JP4427667B2 - Multiphase switching converter and control method thereof - Google Patents

Description

  The present invention relates to a multiphase switching converter and a control method thereof, and more particularly to a technique for realizing improvement in power efficiency, low output voltage ripple characteristics, and elimination of a balance control circuit for inductor current.

A polyphase step-down converter is generally used to reduce output voltage ripple and improve load response characteristics. The polyphase step-down converter is composed of a plurality of step-down converters connected in parallel, and the above characteristics can be obtained by driving the phases of these converters while shifting by a predetermined angle.

However, in the multiphase converter, as the input / output voltage step-down ratio is larger, the low output voltage ripple characteristic cannot be obtained unless the number of converters connected in parallel is increased. In addition, there is a problem that the inductor current of each converter is unbalanced due to variations in characteristics of circuit components, and a control circuit that balances the current becomes indispensable.
Further, in the step-down converter, the drain-source voltage changes from the voltage of the input power supply to 0 V at the time of switching switching, so that the switching loss increases as the input power supply voltage increases. Therefore, in applications where the step-down ratio of the input / output voltage is large, the power efficiency is significantly reduced.

Therefore, the features of the present invention are as follows (1) to (5).
(1) The first switching element, the input smoothing capacitor, and the first inductor are connected in series in this order from the positive terminal of the input power source to the positive terminal of the load, and the negative terminal of the load is connected to the ground of the input power source. An output smoothing capacitor is connected in parallel to both ends of the positive and negative terminals of the load, and a first rectifier is connected between an intermediate point between the input smoothing capacitor and the first inductor and the ground of the input power source, A second switching element and a second inductor are sequentially connected from an intermediate point between the first switching element and the input smoothing capacitor to a positive terminal of the load, and an intermediate point between the second switching element and the second inductor. And a second rectifying element connected between the input power source and the ground of the input power source.
(2) The first switching element, the input smoothing capacitor, and the first inductor are connected in series from the positive electrode of the input power supply to the positive terminal of the load, and the negative terminal of the load is connected to the ground of the input power supply. An output smoothing capacitor is connected in parallel to both ends of the positive and negative terminals of the load, and a first rectifier is connected between an intermediate point between the input smoothing capacitor and the first inductor and the ground of the input power source, A second switching element and a second inductor are sequentially connected from an intermediate point between the first switching element and the input smoothing capacitor to a positive terminal of the load, and an intermediate point between the second switching element and the second inductor. It said between ground of the input power supply by connecting a second rectifier element constitutes the switching converter, the first and second switching elements, the phase difference of a predetermined angle, and, at a given time The first switching element is turned on in the first period, both the first and second switching elements are turned off in the second period, and the second switching element is turned on in the third period. A control method for a multiphase switching converter, wherein a DC voltage is supplied to a load by repeating a series of controls in which only the first switching element is turned on and both the first and second switching elements are turned off in the fourth period. .
(3) The first switching element, the input smoothing capacitor, and the first inductor are connected in series in this order from the positive terminal of the input power source to the positive terminal of the load, and the negative terminal of the load is connected to the ground of the input power source. An output smoothing capacitor is connected in parallel across the positive and negative terminals of the load, and a third switching element is connected between an intermediate point between the input smoothing capacitor and the first inductor and the ground of the input power source, A second switching element and a second inductor are sequentially connected from an intermediate point between the first switching element and the input smoothing capacitor to a positive terminal of the load, and an intermediate point between the second switching element and the second inductor. And a ground of the input power source, a fourth switching element is connected.
(4) The first switching element, the input smoothing capacitor, and the first inductor are connected in series from the positive electrode of the input power source to the positive terminal of the load, and the negative terminal of the load is connected to the ground of the input power source. An output smoothing capacitor is connected in parallel across the positive and negative terminals of the load, and a third switching element is connected between an intermediate point between the input smoothing capacitor and the first inductor and the ground of the input power source, A second switching element and a second inductor are sequentially connected from an intermediate point between the first switching element and the input smoothing capacitor to a positive terminal of the load, and an intermediate point between the second switching element and the second inductor. fourth connecting the switching elements constituting the switching converter, the first and second switching elements, the phase difference of a predetermined angle between the ground of the input power supply In addition, driving at a predetermined time ratio, only the first switching element is turned on in the first period, both the first and second switching elements are turned off in the second period, and in the third period, A series of control is repeated in which only the second switching element is turned on and both the first and second switching elements are turned off in the fourth period, and the third switch element is alternately arranged with the first switch element. A control method for a multi-phase switching converter, wherein switching is performed and the fourth switching element is alternately switched with the second switching element to supply a DC voltage to a load.
(5) The current waveform flowing through the first and second inductors of the switching converter according to (3) is allowed to swing positive and negative, and at the time of switching switching between the first switching element and the third switching element, By creating a dead time period during which both switching elements are turned off, and similarly, by creating a dead time period during which both switching elements are turned off when switching between the second switching element and the fourth switching element. The method for controlling a multi-phase switching converter according to (3), wherein zero voltage soft switching is performed.

The control method of the multiphase switching converter according to the present invention can provide a step-down ratio that is twice that of a conventional multiphase step-down converter, thereby reducing switching loss and output voltage ripple. Furthermore, since the inductor current flowing through each phase is automatically balanced, a control circuit for current balancing is unnecessary. Note that the multi-phase switching converter control method of the present invention can be realized with the number of components required to add one capacitor to the conventional multi-phase step-down converter.

That is, the polyphase step-down converter according to the present invention (1) has a newly added capacitor that divides the input voltage by half, so that it apparently behaves as if the converter is operating at half the input power supply voltage. . This action reduces switching loss and output voltage ripple. Further, since the voltage of the capacitor automatically changes so as to balance the currents flowing through the inductors in the converter, a control circuit for current balance is not necessary.
In the invention (2), as described above, the first and second switching elements are driven at a predetermined angle, preferably a phase difference of 180 degrees, and at a predetermined time ratio, preferably a time ratio D ≦ 0.5. Thus, only the first switching element is turned on in the first period, both the first and second switching elements are turned off in the second period, and only the second switching element is turned on in the third period. Is turned on, and in the fourth period, by repeating the control to turn off both the first and second switching elements, a voltage about half of the power supply voltage is generated in the input smoothing capacitor, and the first period Then, a voltage obtained by subtracting the voltage of the input capacitor and the output smoothing capacitor from the voltage of the input power source is added to the first inductor, and the first inductor is applied during the second to fourth periods. The voltage of the output smoothing capacitor is applied to the inductor in the direction opposite to the first period, while in the third period, the terminal voltage of the output smoothing capacitor is applied to the second inductor from the input capacitor. In the first, second and fourth periods, the voltage of the output smoothing capacitor is applied to the second inductor in the direction opposite to that in the third period. For example, a two-phase triangular wave current waveform is induced in the second inductor, and the two-phase triangular wave current waveform is smoothed by the output smoothing capacitor to supply a DC voltage to the load.
The first rectifying element is a third switching element, the second rectifying element is a fourth switching element, and the third switching element is alternately switched with the first switching element, Even if the fourth switching element is alternately switched with the second switching element, the same effect of control can be obtained.

In addition, the two-phase excitation current waveform of the two-phase switching converter swings positively and negatively so that both switching elements are turned off at the time of switching switching between the first switching element and the third switching element. A time period may be created, and similarly, a dead time period in which both switching elements are turned off at the time of switching between the second switching element and the fourth switching element may be created. Thereby, zero voltage soft switching can be realized.

There are a plurality of specific circuit configuration examples of the polyphase switching converter in the present invention, and the present invention is not limited to the circuit examples described below.

FIG. 1 shows a circuit diagram of a two-phase switching converter as an example of a multi-phase switching converter according to the present invention. The circuit configuration of the converter of this example is different from the conventional two-phase step-down converter in that an input smoothing capacitor Ci is connected in series with the main switch of the first-phase step-down converter. The input positive terminal of the step-down converter of the first phase is connected. The first-phase step-down converter includes a first main switching element Sa that is a MOSFET, a diode Da that is a rectifying element, and an inductor La, and the second-phase step-down converter includes a second main switching element Sb and a diode. It consists of Db and inductor Lb. Co is an output smoothing capacitor, Vi is an input DC power supply, and R is a load. The control unit includes a PWM (Pulse Width Modulator) and a driver Driver.

The positive electrode Ei of the input DC power supply is connected to the drain of the first main switching element Sa, the source of the first main switching element Sa is connected to one end of the input smoothing capacitor Ci, and the other end of the input smoothing capacitor Ci is the inductor The other end of the inductor La is connected to one end of the load R, and the other end of the load R is connected to the negative electrode of the input DC power supply Ei. The anode of the diode Da is connected to the connection point between the input smoothing capacitor Ci and the inductor, and the cathode of the diode Da is connected to the negative electrode of the input DC power supply Ei. The drain of the second main switching element Sb is connected to the connection point between the source of the first main switching element Sa and the input smoothing capacitor Ci, and the source of the second main switching element Sb is connected to one end of the inductor Lb. The other end is connected to a connection point between the inductor La and the load R. The anode of the diode Db is connected to a connection point between one end of the second main switching element Sb and the inductor Lb, and the cathode of the diode Db is connected to the negative electrode of the input DC power supply Ei.

2 to 4 show an equivalent circuit in each switching state of this embodiment, and FIG. 5 shows voltage and current waveforms of each part of the circuit.

First, in the state a, as in the equivalent circuit shown in FIG. 2, the first main switching element Sa is turned on and the second main switching element Sb is turned off, and the inductor La includes the input DC power supply Ei, the input smoothing capacitor Ci, and the output. Connected to smoothing capacitor Co. Thereby, energy is accumulated in the inductor La from the input DC power supply Ei, and the inductor current iLa increases linearly. Note that the change amount ΔiLaON of the inductor current in this state is expressed by the following equation.

状態b〜cでは、図３、図４に示す等価回路のように、第１メインスイッチング素子Saがオフとなり、インダクタLaが、出力平滑コンデンサCoと連結される。これにより、インダクタLaに蓄えられているエネルギーが出力平滑コンデンサCoへ供給されると共に、インダクタ電流iLaが線形的に減少する。なお、この状態におけるインダクタ電流の変化量ΔiLaOFFは、次式で表される。

In states b to c, as in the equivalent circuits shown in FIGS. 3 and 4, the first main switching element Sa is turned off, and the inductor La is connected to the output smoothing capacitor Co. As a result, the energy stored in the inductor La is supplied to the output smoothing capacitor Co and the inductor current iLa decreases linearly. Note that the change amount ΔiLaOFF of the inductor current in this state is expressed by the following equation.

一方、状態cでは、図４に示す等価回路のように、第１メインスイッチング素子Saがオフ、第２メインスイッチング素子Sbがオンとなり、第２メインスイッチング素子SbとダイオードDaを通して、インダクタLbが、入力平滑コンデンサCiと出力平滑コンデンサCoに連結される。これにより、入力平滑コンデンサCiからインダクタLbにエネルギーが蓄積されると共に、インダクタ電流iLaが線形的に増加する。なお、この状態におけるインダクタ電流の変化量ΔiLbONは、次式で表される。

On the other hand, in the state c, as in the equivalent circuit shown in FIG. 4, the first main switching element Sa is turned off, the second main switching element Sb is turned on, and the inductor Lb is passed through the second main switching element Sb and the diode Da. The input smoothing capacitor Ci and the output smoothing capacitor Co are connected. Thereby, energy is accumulated in the inductor Lb from the input smoothing capacitor Ci, and the inductor current iLa increases linearly. Note that the amount of change ΔiLbON of the inductor current in this state is expressed by the following equation.

状態a、b、dでは、図２、図３に示す等価回路のように、第2メインスイッチング素子Sbがオフとなり、インダクタLbが、出力平滑コンデンサCoと連結される。これにより、インダクタLbに蓄えられているエネルギーが出力平滑コンデンサCoへ供給されると共に、インダクタ電流iLbが線形的に減少する。なお、この状態におけるインダクタ電流の変化量ΔiLbOFFは、次式で表される。

In states a, b, and d, as in the equivalent circuits shown in FIGS. 2 and 3, the second main switching element Sb is turned off, and the inductor Lb is connected to the output smoothing capacitor Co. As a result, the energy stored in the inductor Lb is supplied to the output smoothing capacitor Co, and the inductor current iLb decreases linearly. Note that the change amount ΔiLbOFF of the inductor current in this state is expressed by the following equation.

定常状態では、式(1)と(2)の和は零となるため、次式が得られる。

In the steady state, the sum of equations (1) and (2) is zero, so the following equation is obtained.

同様に、式(3)と(4)の和も零となるため、次式が得られる。

Similarly, since the sum of equations (3) and (4) is also zero, the following equation is obtained.

式(5)、(6)より、入力平滑コンデンサの電圧Vciは、次式で求められる。

From the equations (5) and (6), the voltage Vci of the input smoothing capacitor is obtained by the following equation.

式(5)、(7)から、入出力電圧の変換率(Eo/Ei )は、次の式として求められる。

From Expressions (5) and (7), the input / output voltage conversion rate (Eo / Ei) is obtained as the following expression.

式(8)から分かるように、本発明における２相式のスイッチングコンバータは、従来の降圧形コンバータの２倍の降圧比を得ることが可能である。したがって、メインスイッチのング素子オン時間を２倍取れるため、出力電流リップルが低減できる。また、図５に示すように、各状態の転換時において、メインスイッチング素子とダイオードの両端電圧の変化幅は、入力電源電圧の半分であるため、スイッチング損失が低減される。

As can be seen from the equation (8), the two-phase switching converter according to the present invention can obtain a step-down ratio that is twice that of the conventional step-down converter. Therefore, since the on-time of the main switch can be doubled, the output current ripple can be reduced. Also, as shown in FIG. 5, the change width of the voltage across the main switching element and the diode is half of the input power supply voltage at each state change, so that the switching loss is reduced.

また、入出力電圧の変換比は次式に書き換えられる。

In addition, the input / output voltage conversion ratio can be rewritten as:

この入力平滑コンデンサ電圧VCiの変化により、自動的に、インダクタ電流の平均値が負荷電流の半分(Io/2 )にバランスされる。

Due to the change in the input smoothing capacitor voltage VCi, the average value of the inductor current is automatically balanced to half the load current (Io / 2).

In a switching power supply, a diode is normally used as a rectifying element, but this rectifying diode has a forward voltage drop of at least 0.5 V, so that the power efficiency is greatly reduced in a low-voltage power supply. Therefore, in the case of a low voltage output, a synchronous rectification method using a semiconductor switching element instead of a rectifying diode and alternately turning on and off with the main switching element is effective. In this case, since the on-resistance of the FET is as small as several mΩ, the power supply efficiency can be greatly improved.
Therefore, the diode which is the rectifying element of the circuit shown in FIG. 1 can be replaced with a switching element for synchronous rectification as shown in FIG. That is, unlike FIG. 1, a third main switching element (synchronous rectification switch) Sra is provided instead of the diode Da, and the third main switching element (synchronous rectification switching element) SRa is provided at the connection point between the input smoothing capacitor Ci and the inductor La. The drain of the third main switching element SRa is connected to the negative electrode of the input DC power supply Ei. On the other hand, a fourth main switching element (synchronous rectification switching element) SRb is provided instead of the diode Db, and the drain of the fourth main switching element SRb is connected to the connection point of the first main switching element Sa and the inductor La. The source of the main switching element SRb is connected to the negative electrode of the input DC power supply Ei.

As shown in the schematic diagram of FIG. 7, the FET main switching elements Sa, Sb, SRa, SRb have parasitic capacitances CSa, CSb, CSRa, CSRb. Therefore, the energy stored in the parasitic capacitance during the period when the switching element is off is discharged as a short-circuit current at the moment when the switch is turned on, generating a switching surge and power loss. In order to solve this switching problem, a technique called soft switching is applied to the circuit of the second embodiment. In order to realize soft switching, as shown in FIG. 8, a state a ′ between a state a and a state b, a period in which both the first main switching element Sa and the third main switching element SRa are turned off, a second main switching element called state c ′ between the state c and the state d, and a state where both the second main switching element Sb and the fourth main switching element SRb called the state b ′ are turned off between b and the state c A period during which both Sb and the fourth main switching element SRb are off, and a period during which both the first main switching element Sa and the third main switching element SRa are in the state d ′ between the state d and the state a. If the inductance is set so that the triangular wave inductor currents iLa and iLb of the inductor always swing positive and negative as shown in FIG. Shift switching is possible.
As described above, this embodiment can be realized by generating the switching state as described above in the dead time periods a ′, b ′, c ′, and d ′ without adding any special components.

In order to evaluate the present embodiment shown in FIG. 6, an experiment was conducted with the following circuit parameters.
Ei: 12 V, Eo: 1.2 V, Ci: 100mF, Co: 500mF, La, Lb: 0.45mH,
Switching frequency: 250 kHz.
FIG. 12 shows the relationship of the output voltage with respect to the duty ratio. It can be seen that for an input voltage of 12V, the output voltage is stepped down in proportion to half the time ratio. FIG. 13 shows a comparison of efficiency with a conventional two-phase step-down converter. In this experiment, the duty ratio is adjusted and the output voltage is fixed at Eo: 1.2V. Under this condition, the efficiency was improved especially at light loads, and an improvement of around 5% was observed. Further, the efficiency is improved particularly at light loads, and an improvement of about 5% is observed. An efficiency improvement of 2% was confirmed even under heavy load. FIG. 14 shows drain-source voltage waveforms of the first and second main switching elements (synchronous rectification switching elements). It can be seen that the voltage of the switch is about 6V, which is half of the input power supply voltage.
FIG. 15 shows a circuit diagram when the two-phase method of FIG. 1 is expanded to three phases. In this case, the input smoothing capacitor Cib is connected in series with the main switch Sb of the step-down converter of the second phase, and the input terminal of the step-down converter of the third phase is connected to the intermediate point between the input smoothing capacitor Cib and the main switch Sb. Just connect. In the case of three phases, each switch is switched with a phase difference of 90 degrees, and the duty ratio is used in the range of 0 to about 0.33. Further, based on the same principle, the present system can be further multiphased. FIG. 16 shows the case of four phases.

A polyphase converter is used for a power supply for digital IC because it can reduce output voltage ripple and speed up load response characteristics. In the present invention, the control of the two-phase step-down converter as the above means makes it possible to reduce switching loss, output voltage ripple, and inductor current balance circuit. It makes a great contribution to the manufacturing industry.

FIG. 2 is a circuit diagram in Example 1. It is a figure which shows the equivalent circuit in the state a of the circuit in Example 1. FIG. It is a figure which shows the equivalent circuit in the states b and d of the circuit in Example 1. FIG. It is a figure which shows the equivalent circuit in the state c of the circuit in Example 1. FIG. It is a voltage-current waveform diagram of each part of the circuit. 6 is a circuit diagram in Example 2. FIG. It is a schematic diagram of the parasitic component of FET of the circuit in Example 2. FIG. It is a voltage-current waveform figure at the time of performing soft switching in the circuit in Example 2. FIG. It is a figure which shows the equivalent circuit in the state d at the time of performing soft switching of the circuit in Example 2. FIG. It is a figure which shows the equivalent circuit in dead time period d 'at the time of performing the soft switching of the circuit in Example 2. FIG. It is a figure which shows the equivalent circuit in the state a at the time of performing soft switching of the circuit in Example 4. It is a figure which shows the relationship between the duty ratio of the circuit in Example 2, and an output voltage. It is the figure which compared the power efficiency of the circuit in Example 2, and the conventional 2-phase step-down converter. It is a figure in Example 2 and shows the drain-source voltage of the conventional synchronous rectification switch. It is a circuit diagram at the time of extending the 2 phase system of FIG. 1 to 3 phases. It is a circuit diagram at the time of extending the 2 phase system of FIG. 1 to 4 phases.

Explanation of symbols

Ei input DC power supply
Sa, Sb, SRa, SRb 1st to 4th main switching elements
Ci, Co capacitors
La, Lb inductor
Da, Db diode
R load

Claims (5)

A first switching element, an input smoothing capacitor, and a first inductor are connected in series in this order from the positive terminal of the input power source to the positive terminal of the load, and the negative terminal of the load is connected to the ground of the input power source. An output smoothing capacitor is connected in parallel to both ends of the negative terminal, a first rectifier element is connected between an intermediate point between the input smoothing capacitor and the first inductor and the ground of the input power source, and the first A second switching element and a second inductor are connected in order from an intermediate point between the switching element and the input smoothing capacitor to the positive terminal of the load, and an intermediate point between the second switching element and the second inductor and the input power source A multiphase switching converter, characterized in that a second rectifying element is connected to the ground. A first switching element, an input smoothing capacitor, and a first inductor are connected in series in this order from the positive terminal of the input power source to the positive terminal of the load, and the negative terminal of the load is connected to the ground of the input power source. An output smoothing capacitor is connected in parallel to both ends of the negative terminal, a first rectifier element is connected between an intermediate point between the input smoothing capacitor and the first inductor and the ground of the input power source, and the first A second switching element and a second inductor are connected in order from an intermediate point between the switching element and the input smoothing capacitor to the positive terminal of the load, and an intermediate point between the second switching element and the second inductor and the input power source second by connecting a rectifier element constitutes the switching converter, the first and second switching elements, the phase difference of a predetermined angle, and a predetermined duty ratio between the ground Driving, only the first switching element is turned on in the first period, both the first and second switching elements are turned off in the second period, and only the second switching element is turned on in the third period. A control method for a multi-phase switching converter, characterized in that a DC voltage is supplied to a load by repeating a series of controls to turn on and turn off both the first and second switching elements in a fourth period. A first switching element, an input smoothing capacitor, and a first inductor are connected in series in this order from the positive terminal of the input power source to the positive terminal of the load, and the negative terminal of the load is connected to the ground of the input power source. An output smoothing capacitor is connected in parallel across the negative terminal, a third switching element is connected between an intermediate point between the input smoothing capacitor and the first inductor and the ground of the input power source, A second switching element and a second inductor are connected in order from an intermediate point between the switching element and the input smoothing capacitor to the positive terminal of the load, and an intermediate point between the second switching element and the second inductor and the input power source A multi-phase switching converter, wherein a fourth switching element is connected to the ground. A first switching element, an input smoothing capacitor, and a first inductor are connected in series in this order from the positive terminal of the input power source to the positive terminal of the load, and the negative terminal of the load is connected to the ground of the input power source. An output smoothing capacitor is connected in parallel across the negative terminal, a third switching element is connected between an intermediate point between the input smoothing capacitor and the first inductor and the ground of the input power source, A second switching element and a second inductor are connected in order from an intermediate point between the switching element and the input smoothing capacitor to the positive terminal of the load, and an intermediate point between the second switching element and the second inductor and the input power source connect the fourth switching element and a switching converter between the ground, the first and second switching elements, the phase difference of a predetermined angle, or , Driven at a predetermined time ratio, only the first switching element is turned on in the first period, both the first and second switching elements are turned off in the second period, and the first switching element is turned off in the third period. Only the second switching element is turned on, and a series of control for turning off both the first and second switching elements in the fourth period is repeated, and the third switching element is alternately switched with the first switching element. And switching the fourth switch element alternately with the second switching element to supply a DC voltage to the load. A current waveform flowing through the first and second inductors of the switching converter according to claim 3 is allowed to swing positively and negatively, and at the time of switching switching between the first switching element and the third switching element, both switching elements are Similarly, zero voltage soft switching is performed by creating a dead time period in which both the second switching element and the fourth switching element are switched off, thereby creating a dead time period in which both switching elements are off. The method for controlling a multiphase switching converter according to claim 3, wherein:

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