JP6731864B2 - Constant current digital power supply current control method and constant current digital power supply device - Google Patents

Description

The present invention relates to a current control method for a constant current digital power supply and a constant current digital power supply device including the method.

2. Description of the Related Art In recent years, power supplies used for lighting devices such as LEDs (Light Emitting Diodes) and LDs (Laser Diodes) are becoming smaller, more accurate, and less expensive. A switching power supply is widely used as a DC power supply for the power supply for driving these devices.

The control method used for the switching power supply includes an analog control method and a digital control method. In the analog control method, control is performed using an analog circuit including a transistor, a coil, a capacitor, a resistor, and the like.

On the other hand, the digital control method is provided with an AD (Analog Digital) converter and a microcomputer, and is controlled by a digital signal processing circuit that realizes operations such as PID control. That is, in order to obtain a constant current, the signal acquired from the current detection circuit is sampled by the AD converter and digitized. The deviation between the digitized output current value and the set current value is calculated, the command value is obtained by the digital controller (P, PI, PID control), and the chopper circuit is further controlled by the PWM (Pulse Width Modulation) control. This is a method of feeding the target current to the load by feeding back to.

Compared with the analog control method, this digital control method can be realized with a simple circuit configuration and can be flexibly controlled according to the load, external conditions, etc., so performance improvement such as downsizing and cost reduction can be achieved. It is possible.

In addition, in order to reduce the size, increase the accuracy, and reduce the cost of the switching power supply, the circuit configuration of the shunt resistor, operational amplifier, and single power supply is used to continuously control from the low current range to the rated current. When driven by a power supply, linearity is lost in the vicinity of GND (ground), so it is difficult to accurately control the target current.

To solve this problem, for example, in Patent Document 1, the current can be detected with high accuracy without being affected by the offset of the current detection operational amplifier, and the current detection operational amplifier also has a single power supply configuration. A switching power supply device is disclosed which enables the current control with high accuracy and high speed. FIG. 17 is a circuit configuration diagram showing a configuration example of the current detection operational amplifier described in Patent Document 1.

JP, 2007-189775, A

However, the current detection circuit disclosed in Patent Document 1, which uses the current detection operational amplifier as a single power supply and enables high-precision current control, has a large number of parts because parts such as transistors and capacitors are used in addition to resistors. However, there is a problem that it is difficult to reduce the cost because the cost is increased accordingly.

The present invention has been made in view of the above conventional problems, and an object thereof is to enable a control circuit of a power supply device to be driven by a single power supply, and to provide feedback control in a region where an operational amplifier is used with the single power supply. An object of the present invention is to provide a current control method that enables current control.

The present invention relates to a current control method for a constant current digital power supply device, which controls on/off of a switching element by a digitally controlled pulse width modulation signal and outputs a predetermined output current to a load based on an input voltage. When the current value is equal to or higher than the predetermined current value, a constant current is output by feedback control, and when the set current value is less than the predetermined current value, a constant current is output by feedforward control, and the load characteristics are sampled and measured beforehand. , The relation between the command value of the feedforward control and the set current value is approximated by a polynomial, and the set current value is substituted into the polynomial to make the command value of the feedforward control, and the command value is multiplied by the compensation coefficient to perform pulse width modulation. A current control method for a constant current digital power supply, which is characterized in that it is a control amount of a signal, and a constant current digital power supply device provided with the current control method.

According to the present invention, in a power supply circuit used with a single power supply, a constant current can be taken out from a low current region where feedback cannot be performed only by controlling a program.

1 is a schematic configuration diagram of a step-down chopper type constant current digital power supply device. It is a block diagram of a control circuit of a digital control system. It is a figure explaining that a control method changes with a set current value of the present invention. It is a figure explaining the change of the command value of feedforward control before and behind pilot current measurement. It is a figure explaining acquisition of a command value by pilot current measurement, and calculation of a compensation coefficient. It is a signal processing flowchart of the control circuit of a digital control system. It is the figure which showed the signal processing flow of the pilot current measurement in the signal processing flow figure of the control circuit of a digital control system. It is the figure which showed the signal processing flow of feedforward control + load characteristic compensation in the signal processing flow diagram of the control circuit of a digital control system. It is the figure which showed the signal processing flow of feedback control in the signal processing flow figure of the control circuit of a digital control system. It is a flowchart of the main program of the digital control system of the present invention. 7 is a flowchart of an AD conversion completion interrupt program of a digital control method. It is a flowchart of a pilot current measurement program. It is a flow chart of a pilot current sending control program. It is a flow chart of a program of feedforward control + load characteristic compensation. It is a flow chart of a program of feedback control. 4 is a flowchart of a program of another method of measuring pilot current. This is a circuit configuration of the related art in which a current detection operational amplifier capable of detecting a current with high accuracy can be configured with a single power supply.

A constant current digital power supply device that is an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a step-down chopper type constant current digital power supply device according to an embodiment of the present invention.
The constant current digital power supply device 10 shown in FIG. 1 includes an input power supply 11, a capacitor 12, a switching element 13, a wheel diode 14, an inductor 15, a capacitor 16, a current detection circuit (shunt resistor) 17, a differential amplifier 19, and a control circuit 20. Composed of. A load 18 is connected to the output of the constant current digital power supply device 10.
The current detection circuit 17 uses a shunt resistor, a hall element, a current transformer, and the like.

The constant-current digital power supply device 10 supplies a load 18 with an output current whose constant current is controlled by using the input power supply 11 as a DC power supply. The input power supply 11 may be a constant voltage power supply obtained by rectifying and smoothing a commercial AC power supply. The capacitor 12 is a smoothing capacitor and reduces the noise of the input power supply 11 and the noise of the switching element 13 in the subsequent stage.

The switching element 13 is PWM-controlled by a digital PWM generator in the control circuit 20. While the switching element 13 is on, an output current flows from the switching element 13 to the inductor 15, the shunt resistor 17, and the load 18, and electric power is stored in the inductor 15. While the switching element 13 is off, the output current flows to the wheel diode 14, the inductor 15, the shunt resistor 17, and the load 18 by the electric power stored in the inductor 15.

The inductor 15 and the capacitor 16 form a filter circuit, which reduces ripple noise and smoothes the output current. The voltage generated across the shunt resistor 17 is amplified by the differential amplifier 19 and input to the control device 20 as a current value feedback signal.
With these configurations, the constant current controlled by the constant current digital power supply device 10 is supplied to the load 18.

FIG. 2 is a block diagram of the control circuit 20 of the digital control system shown in FIG. The control circuit 20 includes a set current input unit 25, an AD converter 21, an AD converter 22, a digital signal processing circuit 23, and a digital PWM generator 24.
The set current value is input to the set current input unit 25 from outside the constant current digital power supply device 10 by, for example, SPI (Serial Peripheral Interface) communication or the like. The AD converter 21 converts the output current value amplified by the differential amplifier 19 shown in FIG. 1 into a digital value. The AD converter 22 converts the voltage value of the input power supply 11 into a digital value. Both are input to the digital signal processing circuit 23.

The digital PWM generator 24 outputs a pulse signal for turning on/off the switching element 13 according to a command value corresponding to the output current calculated by the digital signal processing circuit 23.
Although not shown, the digital signal processing circuit 23 is composed of a CPU, a ROM, a RAM, etc., and realizes constant current control by executing a program stored in the ROM.

FIG. 3 is a diagram for explaining that the control method differs according to the set current value of the present invention. The horizontal axis is the set current and the vertical axis is the output current, and is a diagram showing a method of controlling the output current range that is a dead zone of AD conversion.
The present invention outputs a constant current by feedback (FB) control when the set current value is equal to or more than a predetermined current value, and performs feed forward (FF) control and load characteristic compensation when the set current value is less than the predetermined current value. Outputs constant current in combination.

In the constant current digital power supply device 10 of the present embodiment, the differential amplifier 19 that detects the output current is composed of a single power supply, and loses its linearity near GND. Therefore, when the current value is less than the predetermined current value, constant current control is performed by a combination method of feedforward control and load characteristic compensation.
In the present embodiment, the predetermined current value is 0.5 A, but a current value other than 0.5 A may be used depending on the difference in performance of the differential amplifier 19 and the control range of the power supply device.

In the constant current control of the combined method of the feed forward control and the load characteristic compensation of the present invention, the output current is sampled and measured in advance in a state where a specific load is connected to the power supply device 10 in advance, and a corresponding command value is obtained, The relationship between the set current value and the command value is approximated by a polynomial (a pseudo circuit is emulated from the polynomial). Then, a specific set current value for feedforward control is substituted into the polynomial to calculate a command value, and this command value is set in the digital PWM generator 24. According to this method, even a non-linear load can be dealt with.

However, the feedforward control approximates the load characteristics when a specific load is connected in advance by a polynomial, but the output current according to the command value calculated by the polynomial differs between the prespecified load and the actual load, Further, when the load characteristic changes due to the change of the environmental temperature, it deviates from the actual current value.

In the present invention, in response to the difference between the load specified in advance and the actual load and the difference in the output current due to environmental changes such as temperature, during the period of the feedforward control, a short-term test current (hereinafter, "Pilot current") is applied to the load and the relationship between the pilot current and the output current is measured. The PI control command value at the time when the output current of the pilot current reaches the target value (hereinafter, the target value of the output current of the pilot current is referred to as a “measurement threshold”) is acquired and the compensation coefficient is calculated. The compensation coefficient is multiplied by the command value of the feedforward control to obtain a designated value for compensating for a difference in load, temperature change, and the like.
Here, the pilot current is a polynomial that approximates the relationship between the set current value and the command value by sampling the output current when a specific load is connected to the power supply device in advance. It is the current that is output to the load for a short time.

In the pilot current measurement, the immediately preceding feedforward control is switched to the feedback control, and the PI control command value of the feedback control is sampled and acquired.
In the present embodiment, when the pilot current target value is set to 1.0 A and the slew rate value is set to 0.18 A, a sampling period (in the present embodiment, the period is about 15 μs at 66 kHz. Since the target current for each) is suppressed to 0.18A, the target value is 0.18A, 0.36A, 0.54A, 0.72A, 0.90A, 1.0A and 6 sampling cycles. Reach On the other hand, if the output current measurement threshold is 0.5 A, the pilot current measurement ends when the output current reaches the measurement threshold 0.5 A.

The slew rate value may be set in consideration of the follow-up of the load characteristics with respect to the current increase in the pilot current measurement. For example, if the slew rate value is reduced, it takes time to measure the pilot current, but the sampling error can be reduced, and the command value for PI control when the output current reaches the target value is a more accurate value. Becomes

Next, a method of sending the pilot current will be described with reference to FIG.
FIG. 4 is a diagram for explaining the pilot current measurement and the change in the command value of the feedforward control before and after the measurement. The horizontal axis represents time, and the vertical axis represents the Iff command value for feedforward control (hereinafter, the command value for feedforward control is referred to as "If command value").

As shown in FIG. 4, the current stop period is provided before the pilot current is sent from the sampling period next to the feedforward control immediately before the measurement of the pilot current. As a result, it is possible to prevent the setting current value of the immediately preceding feedforward control from affecting the measurement result by the pilot current.

After the current stop period, the set current value of the pilot current is set from "0A" in the current stop period to the pilot current target value (1.0A in this embodiment), and the measurement is started. The pilot current increases stepwise for each sampling period due to the function of the slew rate controller.
The pilot current measurement is performed by the feedback control, and the command value of the PI control calculator of the feedback control when the output current reaches the measurement threshold value (0.5 A in this embodiment) (hereinafter, the command value of the feedback control is “Ipi”). (Referred to as “command value”) and used as an input value for calculating the compensation coefficient. The pilot current measurement is carried out periodically, and the moving average value of the Ipi command values obtained continuously is used as the input value for the compensation coefficient calculation.

When the compensation coefficient is calculated, the Iff command value for the next feedforward control after the pilot current measurement is completed is the Iff command after compensation obtained by multiplying the Iff command value calculated by the polynomial by the compensation coefficient as shown in FIG. The value is set in the digital PWM generator 24.

Next, a method of calculating the compensation coefficient will be described with reference to FIG.
FIG. 5 is a diagram illustrating acquisition of a command value and calculation of a compensation coefficient by measuring a pilot current. The horizontal axis represents the set current, and the vertical axis represents the Iff command value for feedforward control. The solid curve is a load characteristic specified in advance and is approximated by a polynomial. The two dotted curves show the change in the polynomial with the compensation factor applied.

The difference between the average value of the Ipi command values obtained by the pilot current measurement and the Iff command value of the measurement threshold value calculated by the polynomial (hereinafter referred to as “reference value”) is the change in the command value with respect to the load current. Therefore, a new command value for the feedforward control with respect to the load variation is set by compensating the change amount with the Iff command value calculated by the polynomial.

For the set current in the feedforward control, usually, the set current value (A in FIG. 5) is substituted into the polynomial (solid curve shown in FIG. 5) to calculate the Iff command value (a in FIG. 5) for the feedforward control. Then, this Iff command value is multiplied by the voltage variation coefficient of the input power supply 11 and the PWM gain, which will be described later, and set in the digital PWM generator 24.

Since the pilot current measurement is executed by feedback control, the Ipi command value (b1 in FIG. 5) when the pilot current is sent and the output current becomes the measurement threshold value (B in FIG. 5) is acquired. This Ipi designated value is a moving average value of a plurality of consecutive Ipi command values in order to eliminate a sampling error. At this time, the Iff command value (b0 in FIG. 5) by the polynomial of the measurement threshold value (B in FIG. 5) is a reference value, so the compensation coefficient is obtained by the following formula.
Compensation coefficient=(Ipi average value−reference value)*AGC gain+1.0 (1)
Here, the AGC (Auto Gain Control) gain is determined by actually measuring the maximum value of the load variation, but is adjusted by each power supply device.

In the next feedforward control in which the pilot current measurement is completed and the compensation coefficient is updated, when the set current value is set, the set current value (for example, C in FIG. 5) is input to the polynomial to perform the feedforward control. The Iff command value (c0 in FIG. 5) is calculated, and this Iff command value is multiplied by the compensation coefficient obtained by the pilot current measurement. That is,
Command value after compensation of feedforward control=specified value (c0) obtained from polynomial*compensation coefficient (2)
Thus, an If command value corresponding to a change in load characteristics, a temperature change, or the like is output.

The above description is for the case where the Ipi average value is larger than the reference value (b0 in FIG. 5), and can be similarly obtained when the Ipi average value is smaller than the reference value (b2 in FIG. 5). , C2). In this case, the “Ipi average value−reference value” in the equation (1) is a negative value.
The dotted line curve including b1 shown in FIG. 5 is the case where the actual command value is larger than the command value calculated by the polynomial. That is, after calculation of the compensation coefficient, the If value of the set current becomes as if the command value was calculated by the polynomial shown by the dotted line, and it is possible to deal with actual load fluctuations and the like.
The dotted curve including b2 is a polynomial to which a compensation coefficient is applied when the actual Ipi command value is smaller than the Iff command value calculated by the polynomial.

Next, the functions and signal flows of the control circuit 20 shown in FIG. 2 will be described.
FIG. 6 is a signal processing flow chart of the control circuit 20 of the digital control system which realizes the current control method of the present invention.

The functions related to pilot current measurement include a pilot current measurement timing controller 31, a pilot current measurement controller 40, a switch 46, a switch 47, a moving average calculator 43, a deviation calculator 44, an AGC gain multiplier 45, a switch 48, and a slew rate controller 39. , Deviation calculator 38, PI control calculator 36, digital PWM generator 24, driver 37, current detection circuit 17, differential amplifier 19, and AD converter 21.

Next, the function related to the control in which the feedforward control is combined with the load characteristic compensation is realized by the set current detector 33, the switch 48, the slew rate controller 39, the switch 49, the converter 42, the digital PWM generator 24, and the driver 37. It

Further, the functions related to the feedback control include a set current detector 33, a switch 48, a slew rate controller 39, a deviation calculator 38, a switch 46, a PI control calculator 36, a digital PWM generator 24, a driver 37, a current detection circuit 17, It is realized by the differential amplifier 19 and the AD converter 21.

The function related to the fluctuation of the input voltage is realized by the AD converter 22, the converter 34, and the PWM gain multiplier 35. These are functions used for both pilot current measurement, feedforward control combined with load characteristic compensation, and feedback control.
Further, a symbol in which “+” is superimposed on “◯” shown in FIG. 6 is an adder, and a symbol in which “x” is superimposed on “◯” is a multiplier.
Further, the switch 49 and the converter 41 have a function of adding a command value by the feedforward control to the feedback control if necessary.

Here, compensation for fluctuations in the input voltage will be described.
Since the load of the constant current digital power supply device 10 of the present embodiment has a wide current control range due to a specific load characteristic such as LD (Laser Diode), it is necessary to reduce the load of the program for feedback control as much as possible. is there. Therefore, with respect to the fluctuation of the input voltage of the input power supply 11, the ratio of the input voltage to a constant reference voltage value (hereinafter, referred to as “reference DC voltage”) is calculated as a voltage fluctuation coefficient. The command value is multiplied by the voltage fluctuation coefficient to reduce the load of the program for feedback control as the command value for PWM control.

That is, when the input voltage rises, the current increases by the amount corresponding to the voltage rise. In order to suppress the increase, the command value input to the digital PWM generator 24 is multiplied by this voltage fluctuation coefficient (a value smaller than 1 if the voltage increases because the reference DC voltage is divided by the input voltage) By reducing the value, the output current can be suppressed without relying on the feedback control.
In the present embodiment, the reference DC voltage value is 55V, but the reference DC voltage value is changed according to the input voltage of the input power supply 11.

Here, the signal input to the digital PWM generator 24 of the present embodiment is not the command value itself calculated by the PI control calculator 36, but the PWM count value corresponding to the command value is set. The digital PWM generator 24 controls the switching element of the chopper circuit by the output pulse corresponding to the PWM count value and outputs a constant current.
The count value input to the digital PWM generator 24 is referred to as the control amount of the pulse width modulation (PWM) signal.

Next, each function of the pilot current measurement shown in FIG. 7 will be described.
FIG. 7 is a diagram showing a signal processing flow of pilot current measurement in the digital signal processing flow chart shown in FIG.
The pilot current measurement timing controller 31 outputs a signal for starting pilot current measurement at constant intervals. The pilot current measurement controller 40 receives this signal and connects the switch 48 to the pilot current measurement side. The switch 46 is connected because the pilot current measurement is performed by feedback control. Further, the switch 47 is connected so that the Ipi command value when the output current reaches the target value (measurement threshold value) can be acquired.

Here, the slew rate controller 39 will be described. When the set current value rises or falls, the slew rate controller 39 adds (or subtracts) the slew rate value for each sampling cycle if there is a difference between the set current value and the previous (one previous sampling cycle) set value. ) Do.

The pilot current measurement controller 40 determines the current stop period, the pilot current sending period, and the end of the pilot current measurement, and controls the pilot current according to the periods. The pilot current output from the pilot current measurement controller 40 is suppressed by the function of the slew rate controller 39 from changing the set current exceeding the slew rate value, and is input to the deviation calculator 38. The other output current is detected by the current detection circuit 17, then AD-converted by the AD converter 21 via the differential amplifier 19, and input to the deviation calculator 38. The deviation calculator 38 calculates the deviation between the two inputs, and outputs it to the PI control calculator 36.

The Ipi command value calculated by the PI control calculator 36 is multiplied by the voltage variation coefficient calculated by the converter 34 and the PWM gain of the PWM gain multiplier 35, and is input to the digital PWM generator 24. The driver 37 is driven by the output pulse of the digital PWM generator 24 to output a current.

Further, since the pilot current measurement is performed at regular intervals, a plurality of Ipi specified values when the output current reaches the measurement threshold value are acquired by continuous pilot current measurement, and the moving averages thereof are calculated as a moving average calculator. 43.

As shown in Expression (1), the deviation between the calculated moving average value and the reference value calculated by substituting the measurement threshold value of the output current into the polynomial is calculated, and the deviation is multiplied by the AGC gain. The calculated compensation coefficient is used in the control in which the feedforward control is combined with the load characteristic compensation.
The compensation for the fluctuation of the input voltage is performed by multiplying the voltage fluctuation coefficient calculated by the converter 34 by the Ipi command value and inputting it to the digital PWM generator 24.

Next, each function relating to a combination method of low-current (setting current is less than 0.5 A) feedforward control and load characteristic compensation will be described.
FIG. 8 is a diagram showing a signal processing flow of feedforward control+load characteristic compensation in the signal processing flow chart shown in FIG.

When the set current detector 33 compares the set current with a predetermined current value (0.5 A) and determines that the current is low, the switch 48 is connected to the set current side. The set current is output by the function of the slew rate controller 39 while suppressing a change in the set current that exceeds the slew rate value.
The switch 49 is connected to the load characteristic compensation side by a polynomial, and the converter 42 calculates the Iff command value by a polynomial from the set current value. The calculated Iff command value is multiplied by the compensation coefficient calculated by the pilot current measurement, further multiplied by the voltage variation coefficient of the converter 34 and the PWM gain of the PWM gain multiplier 35, and then input to the digital PWM generator 24. .. As a result, current control is performed in accordance with the difference between the load specified in advance and the actual load and the temperature change.

Next, the signal flow of the normal feedback control (set current is 0.5 A or more) and each function will be described.
FIG. 9 is a diagram showing a signal processing flow of feedback control in the signal processing flow chart shown in FIG.
When the set current detector 33 compares the set current with a predetermined current value (0.5 A) and determines that the set current is not less than the predetermined current value, the switch 46 is turned on to form a control loop, and feedback control becomes possible.

When the switch 48 is connected to the set current side, the set current is input to the slew rate controller 39, and a change in the set current value exceeding the slew rate value is suppressed from rising or falling. The output of the slew rate controller 39 is connected to one of the deviation calculators 38. The output current signal detected by the current detection circuit 17 and AD-converted by the AD converter 21 via the differential amplifier 19 is input to the other input terminal. The deviation calculator 38 calculates the deviation between the two inputs and outputs it to the PI control calculator 36.

The Ipi command value calculated by the PI control calculator 36 is multiplied by the voltage variation coefficient calculated by the converter 34 and the PWM gain of the PWM gain multiplier 35, and is input to the digital PWM generator 24. The output pulse of the digital PWM generator 24 drives the driver 37 to control the output current.

Here, the switch 49 is connected to the converter 41 side as shown in FIG. 9, and the output of the slew rate controller 39 is converted to an Ipi command value by feedback control via the converter 41 (function of outputting the input as it is). It is a signal processing flow to be added.
That is, a signal processing flow of a combined output of feedback control and feedforward control is shown. It should be noted that the switch 49 is not connected in the case of control using only the Ipi command value of the feedback control. Further, the switch 47 is off in the feedback control.

Further, in the digital signal processing flow of FIG. 6, the limiter for setting the upper limit value and the lower limit value of the signal is omitted. For example, limiters provided before and after the PI control calculator 36 have a function of preventing the control system from becoming unstable.

Above, the description of each function of the digital signal processing flow of the present invention shown in FIG. 6 is completed, and hereinafter, a program for realizing the current control method of the present invention will be described with reference to a flowchart.
These programs are stored in the memory (ROM) of the digital signal processing circuit 23 shown in FIG. 2 and are executed by the CPU of the digital signal processing circuit 23.

FIG. 10 is a flowchart of the main program of the digital control method of the present invention.
This program starts when the power is turned on and is initialized in step S10. By the initialization, for example, the memory is cleared to “0”, and the initial values are set to various parameters necessary for controlling the constant current digital power supply device 10.

Next, the process of starting the pilot current measurement is carried out at regular intervals (S11). The initialization flag is set and the sequence counter is cleared to "0" every time the specified time has elapsed (S11). The main program repeats this process, and when an interrupt occurs, shifts to the interrupt program.
Here, the numerical value of the sequence counter is used in the following meaning.
0 to 13 ... Current stop period 14 to 255 ... Pilot current sending period 256 ... · Pilot current measurement end value

FIG. 11 is a flowchart of a digital control type AD conversion completion interrupt program. This program is executed by generating an AD conversion completion interrupt when the output current is AD converted in each sampling cycle. The current control method of the present invention is realized by this interrupt processing program.
When an AD conversion completion interrupt occurs, the AD conversion value of the input voltage is read, the reference DC voltage value is divided by the input voltage value to calculate the voltage variation coefficient, and the voltage variation coefficient is stored in the memory (S101).

In step S102, the set current value is read. Next, it is determined whether the set current value is 0.5 A or more (S103). When the set current value is 0.5 A or more (S103, YES), the feedback control subroutine program of step S104 is executed. When the program ends, the interrupt processing program ends and returns to the main program.

On the other hand, when the set current value is less than 0.5 A (S103, NO), it is determined whether the sequence count value is 0 to 255 (S105). If the sequence count value is 256 (S105, NO), the feedforward control+load characteristic compensation subroutine program of step S106 is executed. When the program ends, the interrupt processing program ends and returns to the main program.

If the sequence count is 0 to 255 (S105, YES), the pilot current measurement subroutine program is executed (S107). When the program ends, the interrupt processing program ends and returns to the main program.

Next, of the three subroutine programs shown in FIG. 11, the pilot current measurement program will be described first, and then the feedforward control+load characteristic compensation program and the feedback control program will be described in this order.
FIG. 12 is a flowchart of the pilot current measurement program. This program executes the sending of the pilot current, the measurement of the output current, and the acquisition of the Ipi command value described with reference to FIGS. 4 and 5.
In step S201, it is determined whether the initialization flag has been set. The initialization flag is set by the main program at regular intervals. If the initial flag is set (S201, YES), the process proceeds to step S204, and the pilot current measurement is initialized.

In step S204, the set current value is set to 0A, the sequence count value is set to "1", and the initialization flag is cleared. Since the pilot current measurement is executed by the feedback control, the feedback control subroutine program is executed in the next step S205. When the feedback control subroutine program ends, the pilot current measurement process in this sampling period ends.

On the other hand, if the initialization flag is not set (S201, NO), the sequence count value is incremented by 1 (S202), and it is determined in step S203 whether the current is in the current stop period. The pilot current measurement is a current stop period until the sequence count value reaches 13, and the set current value in that period is 0A.

If it is the current stop period (S203, YES), the feedback control subroutine program of step S205 is executed, and the process of measuring the pilot current in this sampling period ends.
If it is not the current stop period (S203, NO), it is determined in step S206 whether it is the pilot current sending period.
If the pilot current sending period has ended (S206, NO), the pilot current measurement process of this sampling period ends after the pilot measurement end process of step S209.
On the other hand, in the pilot current sending period (S206, YES), it is determined whether the output current has reached the target value (measurement threshold value, here 0.5 A) (S207).
If the output current has not reached the target value (S207, NO), the subroutine program for pilot current transmission control in step S208 is executed, and the pilot current measurement process of this sampling cycle ends.

On the other hand, if the output current has reached the target value (S207, YES), the Ipi command value of the pilot current is acquired in step S210, and the Ipi specified value of the pilot current measurement of this sampling cycle and the Ipi of the previous sampling cycle are acquired. A moving average value with respect to the command value (moving average value of the two Ipi command values) is obtained, and the compensation coefficient is calculated by the equation (1).
The compensation coefficient is stored in the memory of the digital signal processing circuit 23.
Although the Ipi command value is two moving average values in this program, it may be three or more moving average values, or may be a weighted average value of Ipi command values obtained continuously.

In the next step S211, if the output current has reached the target value (measurement threshold value) before the end of the pilot current transmission period, the sequence count value is smaller than 255, so the sequence count value is set to the measurement end value 256. ..

FIG. 13 is a flowchart of the pilot current transmission control program. 13 is a detailed flowchart of the subroutine program of step S208 shown in FIG. This program realizes the function of the slew rate controller 39 by a program.
In step S301, it is determined whether or not the pilot current target value is smaller than the set value of the set current of the feedforward control of the previous time (the sampling period one before).

In the case of the pilot current measuring method shown in FIG. 4, since there is a current stop period, the previously set value is 0 A, so if the pilot current target value is 1.0 A, the determination is “not small” (S301, NO) and step S302. Move to. In the measurement method in which the pilot current target value shown in FIG. 4 is once set to 0 A, the determination in step S301 does not result in “YES”, but in another method of pilot current measurement described below, it may result in “YES”. The determination of S301 is provided.
The previous set value is the set current value of the immediately previous sampling cycle, and the current set value is the set current value of the sampling cycle currently being executed.

When "YES" in step S301, the pilot current target value is substituted for the current set value (S303). Then, the feedback control subroutine program of step S305 is executed, and this program ends.
In step S302, it is determined whether the previously set value has reached the pilot target current value. If the previously set value has reached the pilot current target value (S302, YES), there is no need to change the set value, so the feedback control subroutine program of step S305 is executed, and this program ends.

On the other hand, if the previous set value has not reached the pilot current target value (S302, NO), the slew rate value is added to the previous set value (S304) to increase the pilot current set value.
Then, the feedback control subroutine program of step S305 is executed, and this program ends.

FIG. 14 is a flowchart of a program for feedforward control+load characteristic compensation. It is a detail of the subroutine program of step S106 shown in FIG.
In step S401, the set current value is substituted into the polynomial to obtain the Iff command value. Here, the polynomial for calculating the Iff command value from the set current value is, for example,
Iff command value=A(1-X) ³ +BX+C... (3)
Can be expressed as Here, X is a set current value, and A, B and C are coefficients. The polynomial equation (3) is an example, and there are various polynomial equations depending on the characteristics of the load specified in advance.
In step S402, the Iff command value is multiplied by the compensation coefficient calculated by the pilot current measurement. In step S403, the command value obtained by multiplying the compensation coefficient is further multiplied by the PWM gain and the voltage variation coefficient to obtain the final command value, which is input to the digital PWM generator 24 (S404).

FIG. 15 is a flowchart of a feedback control program.
The details of the subroutine program executed in step S205 of FIG. 12 and step S305 of FIG. 13 in addition to step S104 of FIG.
In step S501, the deviation between the set current value and the output current value is obtained. Next, the PI control calculator 36 substitutes the deviation into the PI control equation to calculate the Ipi command value (S502).
Here, the PI control equation is, for example,
Ipi command value (current time)=Ipi command value (previous time)+k0*deviation (current time)
+k1* deviation (previous time)... (4)
Can be expressed as Here, the deviation is "set current value-output current value", and k0 and k1 are coefficients. In addition, as described above, the previous time and the current time are the previous sampling period and the sampling period of the program currently being executed.

Next, in step S503, the calculated command value is multiplied by the PWM gain and the voltage variation coefficient to obtain a final command value, which is input to the digital PWM generator 24 (S504).
In the feedback control program, the processing of the slew rate controller is omitted.

As described above, according to the current control method of the present invention, the constant current can be taken out from the low current region where the feedback control cannot be performed by only the program control in the power supply circuit used with the single power supply.

(Second pilot current measuring method)
FIG. 16 is a flowchart of a program of a method different from the pilot current measuring method described with reference to FIG.
In this method, a pilot current (target current is 0.5 A) is periodically output to the load in a short period of time, and the Ipi command value of the PI control calculator 36 of the feedback control of the sampling cycle in which the output current converges within a certain range. To get The compensation coefficient is calculated by the equation (1) from the reference value calculated by substituting the average value of the plurality of Ipi command values continuously acquired and the target current value into the polynomial.

The difference from the method shown in FIG. 12 is that there is no current stop period, the set current value of the previous sampling cycle is inherited as it is, and the current value rises to the target value for pilot current measurement (decrease in some cases). By doing so, instead of acquiring the Ipi command value when the output current reaches the target value (crosses the target value), the Ipi command value when the output current converges within a certain range of the target value is acquired. is there.

In the pilot current measurement shown in FIG. 16, it is determined whether the initialization flag is set in step S601. If the initialization flag is set (S601, YES), the sequence count in step S602 is set to "0" and the initialization flag is cleared. Further, the Iff command value of the feedforward control is taken over as the Ipi command value of the feedback control.

Next, the feedback control subroutine program of step S603 is executed, and the pilot current measurement program of this sampling period ends.
On the other hand, if the initialization flag is not set (S601, NO), the sequence count value is incremented by 1 (S604), and it is determined whether it is the pilot current sending period of step S605.

If it is not the pilot current sending period (S605, NO), the pilot current measurement end process of step S610 is executed, and the pilot current measurement program of this sampling period is ended.
On the other hand, if it is the pilot current transmission period (S605, YES), it is determined in step S606 whether the current difference between the previous value and the current value of the output current is within a certain value. If the difference is not within a fixed value (for example, 0.01 A) (S606, NO), it is determined that the output current is not stable yet, and the subroutine program for pilot current transmission control in step S607 is executed. When the program ends, the pilot current measurement program for this sampling period ends.
On the other hand, if the difference between the previous value and the current value of the output current is within a certain value (S606, YES), the process of step S608 is performed.

In the process of step S608, the Ipi command value of the pilot current is acquired, the command value (current value), the Ipi command value (previous value) in the previous sampling cycle, and the moving average value are calculated, and the formula (1 ) Calculate the compensation coefficient indicated by.
The compensation coefficient is stored in the memory because it is used in the program of feedforward control+load characteristic compensation.

Next, in step S609, if the current difference between the previous value and the current value of the output current is within a certain value before the end of the pilot current sending period, even if the sequence count value is still smaller than 255, the sequence count value Is set to the measurement end value of 256 (S609). When the process ends, the pilot current measurement program for this sampling period ends.

In step S606 of the pilot current measurement program shown in FIG. 16, it is determined whether the current difference between the previous value and the current value of the output current is within a certain value. There is also a method of determining (for example, 25 as the sequence count value) and acquiring the Ipi command value of the pilot current. In this case, the elapsed period is determined by evaluating the actual load characteristics.

10... Constant current digital power supply device, 19... Differential amplifier, 20... Control circuit, 21, 22... AD converter, 23... Digital signal processing circuit, 24... Digital PWM Generator, 31... Pilot current measurement timing controller, 33... Set current detector, 34... Converter, 36... PI control calculator, 38... Deviation calculator, 39... Slew rate controller, 40... Pilot current measurement controller, 41, 42... Converter, 43... Moving average calculator, 44... Deviation calculator, 45... AGC gain multiplier.

Claims (8)

A current control method for a constant current digital power supply device, wherein a switching element is on/off controlled by a digitally controlled pulse width modulation signal, and a predetermined output current is output to a load based on an input voltage.
When the set current value is equal to or higher than the predetermined current value, a constant current is output to the load by feedback control,
When the set current value is less than the predetermined current value, a constant current is output to the load by feedforward control,
By sampling and measuring the characteristics of the load in advance, the relationship between the command value of the feedforward control and the set current value is approximated by a polynomial, and the set current value is substituted into the polynomial to command the feedforward control. And a control value of the pulse width modulation signal by multiplying the command value by a compensation coefficient. A current control method for a constant current digital power supply device according to claim 1, comprising:
A current control method for a constant current digital power supply device, wherein the compensation coefficient is obtained from the behavior of the output current when the test current is changed and output to the load. A current control method for a constant current digital power supply device according to claim 2, wherein
The test current is stepwise changed in a predetermined sampling cycle and output to the load, and the compensation coefficient is calculated based on a feedback control command value at a time point when the output current reaches a predetermined measurement threshold. A characteristic current control method for a constant current digital power supply device. A current control method for a constant current digital power supply device according to claim 3,
When the reference value is a command value of the feedforward control calculated by substituting the measurement threshold value into the polynomial as the set current value,
Obtaining an average value by continuously acquiring a command value for feedback control of a sampling cycle in which the output current has reached the measurement threshold value, and calculating the compensation coefficient from the difference between the reference value and the average value. A method for controlling a current of a constant current digital power supply device characterized by: A current control method for a constant current digital power supply device according to any one of claims 2 to 4, comprising:
A current control method for a constant current digital power supply device, comprising: providing a current stop period for stopping the output current before outputting the test current. A current control method for a constant current digital power supply device according to claim 2, wherein
The test current is output to the load, and the command value of the feedback control of the sampling cycle in which the output current converges within a certain range of the target current value is continuously acquired a plurality of times to obtain the average value, and the target current value is set. A constant current digital power supply device characterized in that a command value of the feedback control calculated by substituting it into the polynomial as a current value is used as a reference value, and the compensation coefficient is calculated from a difference between the reference value and the average value. Current control method. A current control method for a constant current digital power supply device according to any one of claims 1 to 6, comprising:
With respect to the fluctuation of the input voltage of the constant current digital power supply device, the ratio of the input voltage value to a constant reference voltage value is taken as a voltage fluctuation coefficient, and the command value is multiplied by the voltage fluctuation coefficient to obtain a pulse width modulated signal. A current control method for a constant current digital power supply device, which is characterized in that a controlled variable is used. A constant current digital power supply device comprising the current control method of the constant current digital power supply device according to claim 1.

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