JP2021111993A - Control program for dc/dc converter - Google Patents

Abstract

To provide a control program for a DC/DC converter capable of preventing subharmonic oscillation without performing slope compensation.SOLUTION: A control device 9 executes: a first step of acquiring sampling results of an input voltage Vi, an output voltage Vo and an inductor current IL flowing to an inductor 6 during a past switching term Ts; and a second step of calculating a time ratio M during time ratio change unit term N×switching term Ts in such a manner that a peak calculation value of the inductor current IL achieves a current command value ILcom within a current target setting term M. In the second step, the current target setting term M is set to an integral value satisfying the condition of M≥N/2+1 after 1/2 of the time ratio change unit term N.SELECTED DRAWING: Figure 3

Description

The present invention relates to a control program for a DC / DC converter.

In recent years, as a DC / DC converter, a method of performing switching control by a so-called peak current control type has attracted attention (see, for example, Patent Document 1). According to the technique described in Patent Document 1, the output current flowing through the switching element is converted into IV by the IV conversion means, the inductor current is converted into a voltage and detected, and the peak current of the inductor is a current command. Feedback control is performed so that the value is reached. It is known that the peak current mode control type is superior in transient response characteristics as compared with the control method using the so-called voltage mode and average current mode.

On the other hand, digital control methods that can handle a wide range of input / output conditions have become widespread. If the control method of the DC / DC converter can be fully digitized, the hardware can be greatly simplified, and the size and cost can be reduced. However, in the digital control method, the voltage and current are sampled discretely, so even if the conventional digital control method is directly increased in frequency, the number of samplings per control cycle is reduced. In the above-mentioned peak current control type, it is necessary to continuously detect the current in real time, so that it becomes difficult to continuously detect the current at a high sampling frequency by applying the digital control method.

In the technique described in Patent Document 1, the peak current control type current command value is generated by using a digital compensator, but the command value is converted into an analog signal by the D / A converter and then compared with the current detection value. By doing so, insufficient sampling is avoided. However, since an extra analog circuit is required, the size of the circuit board becomes large and the cost increases.

Further, if the peak current control type is adopted, there is a risk of subharmonic oscillation. Normally, the oscillation is prevented by performing slope compensation, but if the slope compensation value is set too large, high-speed response cannot be achieved. Therefore, it is necessary to set the optimum slope compensation value, which requires man-hours.

JP-A-2015-33200

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control program of a DC / DC converter capable of preventing subharmonic oscillation without slope compensation.

According to the first aspect of the present invention, the output voltage (Vo) is set to the target voltage by switching and controlling the energizing current flowing through the inductor (6) while changing the time ratio every time the time ratio change unit cycle N is an integral multiple of the switching cycle. The target is the control program of the DC / DC converter (1) that controls the voltage.

According to the invention of claim 1, the control device (9) acquires the sampling results of the input voltage (Vi), the output voltage (Vo), and the inductor current ( _{IL) flowing through the inductor in the past switching cycle.} The first step and the second step of calculating the time ratio during the time ratio change cycle so that the peak calculated value of the inductor current reaches the current command value in the current target setting cycle M are executed. At this time, in the second procedure, the current target setting cycle M is set to an integer value satisfying the condition of M ≧ N / 2 + 1 after half of the time ratio change unit cycle N. As a result, subharmonic oscillation can be prevented without slope compensation.

Electrical configuration diagram of DC / DC converter according to one embodiment A flowchart for explaining the contents of the digital arithmetic processing according to the embodiment. Part 1 of a timing chart showing the flow of processing according to one embodiment Explanatory drawing of the error between the ideal steady-state current flowing through the inductor according to one embodiment and the actual current. Part 2 of the timing chart showing the flow of processing according to one embodiment Part 3 of the timing chart showing the flow of processing according to one embodiment

Hereinafter, an embodiment applied to the DC / DC converter 1 will be described. The DC / DC converter 1 illustrated in FIG. 1 is composed of a Buck converter that converts an input voltage Vi input from a DC voltage source 2 into a voltage and supplies a DC output voltage Vo to a load 3.

-Structure of DC / DC Converter 1 The DC / DC converter 1 is configured by using a switching element 4, a diode 5, an inductor 6, and capacitors 7 and 8. In this embodiment, the switching element 4 is composed of an N-channel MOSFET, but the type of the switching element 4 is not limited.

The DC voltage source 2 is applied to the drain of the switching element 4 via the capacitor 8. The cathode and anode of the diode 5 are connected between the source and the ground of the switching element 4. The common connection point between the source of the switching element 4 and the cathode of the diode 5 is connected to one end of the inductor 6, and a capacitor 7 is connected between the other end of the inductor 6 and the ground. A load 3 is connected to the subsequent stage of the capacitor 7.

The control device 9 controls the energizing current of the inductor 6 by the peak current mode control method, and controls the output voltage Vo to a predetermined target voltage. The control device 9 has the same switching period Ts, and executes PWM (Pulse Wide Modulation) control for controlling the time ratio D, that is, the so-called duty ratio. The control device 9 includes a digital arithmetic circuit 10 capable of executing a predetermined digital arithmetic processing such as a DSP. The control device 9 also includes a driver 11 and A / D converters 13 to 15.

The current path of the inductor 6 and the current sensor 12 is provided, the current sensor 12 current conducted to the inductor 6, i.e. detects the inductor current I _L. A / D converter 13 outputs the inductor current _{I L} to the digital arithmetic circuit 10 converts A / D.

Further, the A / D converter 14 A / D-converts the output voltage Vo and outputs it to the digital arithmetic circuit 10. The A / D converter 15 A / D-converts the input voltage Vi and outputs it to the digital arithmetic circuit 10.

The digital arithmetic circuit 10 inputs the output data of the A / D converters 13 to 15, digitally performs digital arithmetic processing using this data by the peak current mode control method, and outputs a digital command value indicating the time ratio D in which the arithmetic processing is performed. Output to driver 11. At this time, the digital arithmetic circuit 10 calculates the time ratio D based on the inductance value L of the inductor 6, the inductor current _IL , and the output voltage Vo, and outputs a digital command value indicating the time ratio D to the driver 11.

The driver 11 inputs a digital command value from the digital arithmetic circuit 10 and applies a pulse having a predetermined switching cycle Ts and an input time ratio D to the gate of the switching element 4. The driver 11 outputs an on drive signal to the gate of the switching element 4 during the on period according to a given time ratio D, and outputs an off drive signal to the gate of the switching element 4 during the off period.

-Basic flow of digital arithmetic processing The contents of digital arithmetic processing executed by the digital arithmetic circuit 10 will be described below. FIG. 2 exemplifies the flow of the processing procedure in a simplified manner. Digital arithmetic circuit 10 in step S1, S2, the output voltage Vo in the past the switching period Ts, acquires the inductor current _{I L} (first procedure equivalent), the slope _m OFF of the inductor current _{I L,} and calculates _{m ON} , The time ratio D is calculated based on the _{inclination m OFF} and m _{ON in step S3 (corresponding to the second step).} Then, the control device 9 switches and controls the switching element 4 using the time ratio D calculated by the digital arithmetic circuit 10.

The inclination m _OFF indicates an inclination while the switching element 4 is switching off. The inclination m _ON indicates the inclination while the switching element 4 is switching on. Number of A / D converter 13 samples the inductor current I _L is once per cycle of the switching period Ts. The number of times the A / D converter 15 samples the output voltage Vo is also once per cycle of the switching cycle Ts.

Slope m _OFF during operation method OFF period of tilt m _OFF at step S1 is when the voltage across the inductor 6 and the v _L, using the general formula (1) can be obtained as equation.

Here, the output voltage Vo [] sampled by the A / D converter 14 for each switching cycle Ts is defined as shown in FIG. Assume also during switching of period relating to the calculation, the slope _m OFF of the inductor current _{I L,} a constant _{m ON. When the slope m OFF} [n] (= m _OFF [n-1]) during the off period shown in FIG. 3 is obtained from the output voltage Vo [n-1], the equation (2) is obtained.

Digital arithmetic circuit 10 calculates the slope _{m OFF} of the inductor current _{I L} by using in step S1 of FIG. 2 (2). The n-1 period inductor current _IL [n-1] is expressed by the recurrence formula in relation to the n-2 period inductor current _IL [n-2] as shown in equation (3). be able to.

As shown in FIG. 3, the sampling time T _sample indicates the time from the timing when the switch drive signal is turned on to the timing when the A / D converter 14 samples the output voltage Vo. Further, D [n-2] indicates the time ratio D in the n-2th cycle, that is, the so-called duty ratio. In order to establish equation (3), it is necessary to sample the inductor current _{I L} during the ON period of the switching element 4, the sampling time _{T sample} is below (4-1) below, (4- 2) It is set to satisfy the equation.

_-Method of calculating the slope m ON in step S2 Further, when the equation (3) is _{solved for the inclination m ON} [n] during the ON period, it can be expressed as the equation (5).

By substituting Eq. (2) into Eq. (5) and solving it, the inductor currents _IL [n-2], _IL [n-1] in the n-2nd cycle and the n-1th cycle, and n− _{The inclination m ON} [n] during the ON period of the nth cycle can be obtained by using the time ratio D [n-2] of the second cycle. Accordingly, the digital arithmetic circuit 10, the past recent batchwise inductor current _I L _[n-2], with I L [n-1], the formula (2) and formula from relationship during the on-time of (5) The inclination m _ON [n] can be calculated.

_-Basic calculation method of the time ratio D [] in step S3 After that, the digital calculation circuit 10 calculates the current command value ILcom [n] based on the predetermined calculation logic of the peak current mode control method, and steps. In S3, the time ratio D [n] for reaching the current command value I _{Lcom [n] is calculated.}

After the digital arithmetic circuit 10 calculates the time ratio D [n], the control device 9 drives the switching element 4 based on the calculated time ratio D [n]. After that, the digital arithmetic circuit 10 sequentially repeats the processing in the switching cycle Ts from the next time onward from step S1. As a result, the control device 9 can control the output voltage Vo to the target voltage by continuing the switching control of the switching element 4.

Since the present embodiment is characterized by a method for calculating the time ratio D [], the technical significance of the method will be described below, and then a specific example will be given to explain the method for calculating the time ratio D [] in detail.
-Explanation of comparative technology Generally, the digital control technology of the peak current mode control method uses sampling data of the past output voltage Vo [] and the past input voltage Vi [], and is a P control method, a PI control method, and a PID control method. _{The current command value ILcom} [] is calculated based on a predetermined control method such as. After that, when the time ratio D [] reaching the current command value I _Lcom [] is obtained, the slope compensation value ms indicating a positive slope is used as shown in the equation (6). Then, by increasing the slope m _ON during the on-time of the inductor current I _{L [n]} Temporarily peak calculated value of the inductor current I _L is controlled to reach the next current command value I _{Lcom [n]} There is.

In this equation (6), the second term on the right side shows the increase in inductor current I _L during n-1-th cycle of the ON period. Third term on the right side shows the decrease of the inductor current I _L during n-1 cycle of off-period. The fourth term on the right side shows the increase of the inductor current I _L during the n-th cycle of the ON period. By performing slope compensation using the slope compensation value ms that satisfies the following equation (7) in the fourth term on the right side of equation (6), an error is generated every unit time even if switching control is repeated periodically for a long period of time. It becomes possible to compensate and prevent subharmonic oscillation.

However, if the slope compensation value ms is made too large as explained in the background technology column, high-speed response will not be possible if the deviation from _{the slope m ON [n] during the actual on period becomes large, which is optimal.} It takes a lot of man-hours to derive a slope compensation value ms.

-Technical significance of the present embodiment Therefore, the inventors searched for a condition capable of converging the error without using the slope compensation value ms even when the switching control is repeated. The inventors are considering a peak current mode control method in which the time ratio D [] is changed every time the time ratio change unit cycle N × switching cycle Ts. The time ratio change unit period N is an integer value of 1 or more. Hereinafter, the current target setting cycle will be described as M.

The Figure 4 shows a target current flowing through the inductor 6 in the steady state by broken lines shows an example of an actual inductor current I _L flowing through the inductor 6 with a solid line. The ideal steady-state current will repeatedly fluctuate up and down between _{a predetermined high current value I HI} and a predetermined low current value I _LO. When the actual inductor current I _L and ΔI ideal initial value of the error in the steady current of the inductor 6 L _(0), the error after the completion subsequent N cycle of the switching cycle (= N · Ts) ΔI _L (N · Ts) can be expressed as the following equation (8).

As shown in equation (8), a current error generated a dose of the switching period Ts is the final error [Delta] I L _(N · Ts) by being integrated N times. It is assumed that the error ΔD of the time ratio D at this time is constant during the N period. The inductor current I _L of the error of the reference value [Delta] I L ₍₀₎ corresponds to the error accumulated current value to reach the target current value to the M-th can be expressed as equation (9).

（１０）式を（８）式に代入すると（１１）式のようになる。

Solving Eq. (9) for ΔD · Ts gives Eq. (10).

Substituting Eq. (10) into Eq. (8) gives Eq. (11).

When an ideal steady current is flowing through the inductor 6, the time ratio D is uniquely determined between _{the slope m ON during the on period and the slope m OFF} during the off period. Therefore, when equation (11) is expanded based on the steady-state relationship between the time ratio D and the inclinations m _ON and m _{OFF, the following equation (12) is obtained.}

When the absolute value of the error current [Delta] I L when the elapsed N cycles _(N · Ts) is less than 1, as shown in (13), by continuing the same peak current mode control scheme thereafter, the ideal It will eventually converge to a normal steady current, and harmonic oscillation will not occur.

Solving this equation (13) for the time ratio D gives equation (14).

Since the time ratio D is 1 or less, it can be expressed as in Eq. (15).

If the relationship between the current target setting cycle M and the time ratio change unit cycle N shown in the equation (15) is satisfied, the slope compensation can be eliminated. That is, if the time ratio change unit cycle N = 1, the current target setting cycle M = 2 or more may be an integer value, and if the time ratio change unit cycle N = 2, the current target setting cycle M = 2 or more. It should be done.

Further, if the time ratio change unit cycle N = 3, the current target setting cycle M = 3 or more may be set, and if the time ratio change unit cycle N = 4, the current target setting cycle M = 3 or more may be set. .. If the time ratio change unit cycle N is increased, the number of operations of the time ratio D per unit time can be reduced, and the amount of calculation can be reduced. If the amount of calculation can be reduced, even if a low-spec digital calculation circuit 10 is used, a higher switching frequency can be supported. For example, by making the time ratio change unit cycle N larger than 1, a bottleneck in calculation time can be avoided.

On the contrary, if the response performance at which the output voltage Vo reaches the target is emphasized, it is desirable to make the time ratio change unit cycle N and the current target setting cycle M as small as possible, and set the time ratio change unit cycle N = 1. good. At this time, it is desirable that the current target setting cycle M = 2 satisfying the condition of the equation (15).

Specific Example of Calculation Method of Time Ratio D [] in Step S3 A specific example will be described when the time ratio change unit cycle N = 1 and the current target setting cycle M = 2 as described above. In particular, a specific example of the calculation method of the time ratio D [] in step S3 of FIG. 2 will be described. _{The digital calculation circuit 10 calculates the current command value ILcom} [] based on a predetermined control method such as a P control method, a PI control method, or a PID control method using the sampling data of the past output voltage Vo []. .. _{The digital arithmetic circuit 10 may calculate the current command value ILcom} [] by using the sampling data of the past input voltage Vi [] together with the sampling data of the past output voltage Vo [].

_{For example, the digital arithmetic circuit 10 calculates the current command value ILcom} [n-1] by using the sampling data of, for example, the latest output voltage Vo [n-2] before the timing t0 in FIG. For example, if the output voltage Vo [n-2] is high, the current command value I _Lcom [n-1] is set low, and if the output voltage Vo [n-2] is low, the current command value I _Lcom [n-1] is set. It is good to set it high.

As illustrated in FIG. 3, the output voltage Vo is gradually changed while generating a phase delay in accordance with a change in inductor current I _L. As described above, when the ratio change unit period N = 1, by the target current setting period M = 2, the digital arithmetic circuit 10, M = 2-th cycle to the inductor current peak operation value is the current command value I _L The time ratio D [n-1] is calculated so as to reach _{I Lcom [n-1].} The control device 9 drives the switching element 4 based on the time ratio D [n-1] calculated by the digital arithmetic circuit 10.

Similarly, in the switching cycle Ts of the subsequent timings t0 to t1, the digital arithmetic circuit 10 calculates the current command value _ILcom [n] using the sampling data of the output voltage Vo [n-1] most recently in the past.

As illustrated in FIG. 5, similarly in the switching period Ts of the timing t0 to t1, the digital arithmetic circuit 10, M = peak calculated value of the second cycle to the inductor current _{I L} current command value _{I Lcom} to [n] The time ratio D [n] is calculated so as to reach it. The control device 9 drives the switching element 4 at timings t1 to t2 based on the time ratio D [n-1] calculated by the digital arithmetic circuit 10.

Similarly, after the timing t2 after that, the control device 9 repeats the switching control according to the peak current mode control method. Then, as illustrated in FIG. 6, the inductor current _{I L} reaches the current command value _I Lcom [n + 1]. Thus the control unit 9, while preventing subharmonic oscillation of the DC / DC converter 1 can be switching controlled to the inductor current _{I L} reaches the current command value _{I Lcom} [].

As described above, according to the control apparatus 9 of this embodiment, obtains the input voltage Vi, output voltage Vo, sampling results of the inductor current I _L flowing through the inductor 6 in the past switching period Ts, the inductor current I The time ratio D [] between the time ratio change unit cycle N × the switching cycle Ts is calculated so that the peak calculation value of _{L reaches the current command value I Lcom in the current target setting cycle M.} At this time, when the current target setting cycle M is set to an integer value satisfying the condition of M ≧ N / 2 + 1 after half of the time ratio change unit cycle N, subharmonic oscillation is performed without slope compensation. Can be prevented.

Further, according to the present embodiment, the sampling period of the A / D converters 13 to 15 is once in one cycle of the switching cycle Ts. Therefore, it is not necessary to shorten the sampling period of the A / D converters 13 to 15, and it is possible to cope with the case of operating at a higher switching frequency. Digital arithmetic circuit 10 of the control unit 9, that based on the sampling results of the past two times of the inductor current I _L, the inductor current I _L to calculate the ratio D [] when it reaches the peak calculated value, the switching period Switching control by the peak current mode control method can be realized while sampling every Ts.
According to this embodiment, it can be fully digitalized and configured.

(Other embodiments)
The present invention is not limited to the configuration example of the above-described embodiment, and various modifications or extensions are possible. Further, for example, it is also possible to apply the configurations of the above-described embodiments in combination.

The form in which the Buck converter is exemplified as the DC / DC converter 1 has been described, but the present invention is not limited to this. For example, a forward converter may be applied, another type of DC / DC converter may be applied, and the types are not limited. Further, the DC / DC converter 1 can be applied to either a step-down type or a step-up type. Further, by using the sampling data of the input voltage Vi, the slope m _off calculated based on the relationship (output voltage Vo- input voltage Vi) / inductance L, may be performed calculation of the slope m _on ..

The switching element 4 may be configured by using any kind of transistor. The switching element 4 may be configured by using, for example, a bipolar NPN transistor, a PNP transistor, or the like.

The digital arithmetic circuit 10 of the control device 9 and its method according to the present disclosure are provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. It may be realized by a dedicated computer. Alternatively, the digital arithmetic circuit 10 of the control device 9 and its method described in the present disclosure may be realized by a dedicated computer provided by configuring the processor with one or more dedicated hardware logic circuits.

Alternatively, the digital arithmetic circuit 10 of the control device 9 and its method according to the present disclosure are composed of a processor and a memory programmed to execute one or a plurality of functions and one or more hardware logic circuits. It may be realized by one or more dedicated computers configured in combination with a processor. Further, the computer program may be stored in a computer-readable non-transitional tangible recording medium as an instruction executed by the computer.

An embodiment in which a part of the above-described embodiment is omitted as long as the problem can be solved can also be regarded as an embodiment. In addition, any conceivable aspect can be regarded as an embodiment as long as it does not deviate from the essence of the invention specified by the wording described in the claims.

Although the present invention has been described in accordance with the above-described embodiment, it is understood that the present invention is not limited to the embodiment or structure. The present invention also includes various modifications and modifications within a uniform range. In addition, various combinations and forms, as well as other combinations and forms including one element, more, or less, are also within the scope and ideology of the present invention.

In the drawing, 1 is a DC / DC converter, 6 is an inductor, 9 is a control device, Vi is an input voltage, Vo is an output voltage, _IL is an inductor current, M is a current target setting cycle, and N is a time ratio change unit cycle. Is shown.

Claims (5)

DC / DC converter (1) that controls the output voltage (Vo) to the target voltage by switching control of the energizing current flowing through the inductor (6) while changing the time ratio every time the time ratio change unit cycle N × switching cycle Ts. Control program of
In the control device (9),
The first procedure for acquiring the sampling results of the input voltage (Vi), the output voltage (Vo), and the inductor current ( _{IL) flowing through the inductor in the past switching cycle, and}
The second step of calculating the time ratio between the time ratio change unit cycle N × switching cycle Ts so that the peak calculated value of the inductor current reaches the current command value in the current target setting cycle M, and
Is to execute
In the second procedure, the control program of the DC / DC converter sets the current target setting cycle M to an integer value satisfying the condition of M ≧ N / 2 + 1 after half of the time ratio change unit cycle N. The DC / DC converter control program according to claim 1, wherein the sampling result acquired by the first procedure is the result of sampling once for each of the switching cycles in the past. In the first procedure, sampling results in the last two switching cycles in the past are acquired, and in the second procedure, the time ratio of the switching cycle is calculated based on the sampling results in the most recent two switching cycles. The control program for a DC / DC converter according to claim 2. The control program for a DC / DC converter according to claim 1, wherein the time ratio change unit cycle N = 1 and the current target setting cycle M = 2. The control program for a DC / DC converter according to claim 1, wherein the DC / DC converter is composed of a Buck converter.

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