JP2018125938A - Method for controlling current of constant current digital power supply and constant current digital power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling a current for making it possible to drive a control circuit of a constant current digital power supply device by a single power supply and to control a current in a low current region in which feedback control is not possible even when an operational amplifier is used with the single power supply.SOLUTION: With a method for controlling a current of a constant current digital power supply device that performs on/off control of a switching element by a pulse width modulation signal subjected to digital control to output prescribed output a current to a load based on an input voltage, a constant current is output to the load through feedback control when a set current value is a prescribed current value or more, the constant current is output to the load through feed forward control when the set current value is less than the prescribed current value, a relationship between a command value of the feed forward control and the set current value is approximated by a polynomial equation by sampling characteristics of the load in advance, the set current value is substituted into the polynomial equation and specified as the command value of the feed forward control, and the command value is multiplied by a compensation coefficient to be an amount of control of the pulse width modulation signal.SELECTED DRAWING: Figure 6

Description

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

  In recent years, power supplies used in lighting devices such as LEDs (Light Emitting Diodes) and LDs (Laser Diodes) have been reduced in size, accuracy, and cost. A switching power supply is widely used as a DC power supply for powering these devices.

  Control methods used for the switching power supply include an analog control method and a digital control method. In the analog control method, control is performed using an analog circuit including transistors, coils, capacitors, resistors, and the like.

  On the other hand, the digital control system includes an AD (Analog Digital) converter and a microcomputer, and performs control 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 PWM (Pulse Width Modulation) control. This is a method of feeding the target current to the load by feeding back to the load.

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

  Furthermore, in order to reduce the size, accuracy, and cost of switching power supplies, continuous control is performed from the low current range to the rated current with a circuit configuration such as a shunt resistor, operational amplifier, and single power supply. When driven by a power source, the linearity is lost in the vicinity of GND (ground), so that it is difficult to accurately control the target current.

  To deal with this problem, for example, Patent Document 1 discloses that 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 has a single power supply configuration. A switching power supply device is disclosed that enables this and thereby enables high-precision and high-speed current control. FIG. 17 is a circuit configuration diagram showing a configuration example of the current detection operational amplifier described in Patent Document 1. In FIG.

JP 2007-189775 A

  However, the current detection circuit disclosed in Patent Document 1 that uses a current detection operational amplifier as a single power source and enables high-precision current control uses components such as a transistor and a capacitor in addition to a resistor, so the number of components increases. Therefore, there is a problem that the cost is increased and it is difficult to reduce the cost.

  The present invention has been made in view of the above-described conventional problems, and its object is to enable a control circuit of a power supply device to be driven by a single power supply, and in a region where feedback control cannot be performed even if an operational amplifier is used with a single power supply. It 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 that performs on / off control of a switching element by a pulse width modulation signal that is digitally controlled, and outputs a predetermined output current to a load based on an input voltage. A constant current is output by feedback control when the current value is equal to or greater than the predetermined current value, and a constant current is output by feedforward control when the set current value is less than the predetermined current value, and the load characteristics are sampled and measured in advance. Approximate the relationship between the feedforward control command value and the set current value with a polynomial, substitute the set current value into the polynomial to obtain the feedforward control command value, and multiply the command value by the compensation coefficient to modulate the pulse width. A current control method for a constant current digital power supply, characterized in that the control amount of a signal is used, and a constant current digital power supply apparatus having the current control method A.

  According to the present invention, it is possible to take out a constant current from a low current region where feedback is not possible with only a program control in a power supply circuit used with a single power supply.

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 the setting electric current values of this invention. It is a figure explaining the change of the command value of pilot current measurement and feedforward control before and behind that. It is a figure explaining acquisition of the 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 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 figure 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 diagram of the control circuit of a digital control system. It is a flowchart of the main program of the digital control system of this invention. 6 is a flowchart of a digital control AD conversion completion interrupt program. It is a flowchart of a pilot current measurement program. It is a flowchart of a pilot current transmission control program. It is a flowchart of the program of feedforward control + load characteristic compensation. It is a flowchart of the program of feedback control. It is a flowchart of the program of another method of pilot current measurement. This is a conventional circuit configuration in which a current detection operational amplifier capable of detecting current with high accuracy can be configured with a single power source.

A constant current digital power supply device according to 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.
1 includes an input power supply 11, a capacitor 12, a switching element 13, a foil diode 14, an inductor 15, a capacitor 16, a current detection circuit (shunt resistor) 17, a differential amplifier 19, and a control circuit 20. Consists of. A load 18 is connected to the output of the constant current digital power supply device 10.
In addition to the shunt resistor, a Hall element, a current transformer, or the like is used for the current detection circuit 17.

  The constant current digital power supply apparatus 10 supplies the load 18 with an output current subjected to constant current control 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 noise of the input power supply 11 and noise caused by 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, output current flows from the switching element 13 to the inductor 15, the shunt resistor 17, and the load 18, and power is stored in the inductor 15. During the period when the switching element 13 is off, the output current flows to the foil 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 constitute 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, a constant current controlled from 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 from the outside of the constant current digital power supply 10 to the set current input unit 25 by, for example, SPI (Serial Peripheral Interface) communication. 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 constituted by a CPU, a ROM, a RAM, and the like, and realizes constant current control by executing a program stored in the ROM.

FIG. 3 is a diagram for explaining that the control method varies depending on 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 for controlling the output current range that becomes the dead zone of AD conversion.
The present invention outputs a constant current by feedback (FB) control if the set current value is equal to or greater than the predetermined current value, and feedforward (FF) control and load characteristic compensation if the set current value is less than the predetermined current value. A constant current is output 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 linearity in the vicinity of GND. For this reason, if the current value is less than the predetermined current value, the constant current control is performed by a combination of feedforward control and load characteristic compensation.
In this embodiment, the predetermined current value is 0.5 A, but it may be a current value other than 0.5 A depending on the difference in performance of the differential amplifier 19, the control range of the power supply device, and the like.

  The constant current control of the combined method of feedforward control and load characteristic compensation of the present invention obtains a command value corresponding to the output current by sampling and measuring the output current in advance with a specific load connected to the power supply device 10 in advance. The relation between the set current value and the command value is approximated by a polynomial (a pseudo circuit is emulated from the polynomial). Then, a command value is calculated by substituting a specific set value of feedforward control into the polynomial, 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, although feedforward control approximates the load characteristics when a specific load is connected in advance by a polynomial, the output current based on the command value calculated by the polynomial is different from the load specified in advance, 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, for a difference in output current due to a difference between the load specified in advance and an actual load or an environmental change such as temperature, a short-term test current (hereinafter, (Referred to as “pilot current”) is applied to the load, and the relationship between the pilot current and the output current is measured. A compensation coefficient is calculated by obtaining a PI control command value at the time when the output current due to the pilot current reaches a target value (hereinafter, the target value of the output current due to the pilot current is referred to as “measurement threshold”). The compensation coefficient is multiplied by the feedforward control command value to obtain a specified value for compensating for a load difference, temperature change, and the like.
Here, the pilot current is a periodic value used to calibrate 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. This is the current that is output to the load for a short time.

The pilot current measurement is obtained by sampling the command value of PI control of feedback control by switching from the previous feedforward control to feedback control.
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 slew rate controller (to be described later) uses a sampling cycle (in this embodiment, the cycle is approximately 15 μs at 66 kHz. Since the target current for each) is suppressed to 0.18A, the target value is obtained after 6 sampling periods of 0.18A, 0.36A, 0.54A, 0.72A, 0.90A, 1.0A. To reach. On the other hand, if the measurement threshold value of the output current is 0.5 A, the pilot current measurement ends when the output current reaches the measurement threshold value of 0.5 A.

  Note that 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 PI control command value when the output current reaches the target value is a more accurate value. It becomes.

Next, a pilot current sending method will be described with reference to FIG.
FIG. 4 is a diagram illustrating changes in command values for pilot current measurement and feedforward control before and after that. The horizontal axis represents time, and the vertical axis represents an If command value for feedforward control (hereinafter, the command value for feedforward control is referred to as “If command value”).

  As shown in FIG. 4, a current stop period is provided before the pilot current is sent from the next sampling period of the feedforward control immediately before the pilot current measurement. Thereby, it is possible to prevent the set 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 (1.0 A in this embodiment), and measurement is started. The pilot current rises stepwise for each sampling period by the function of the slew rate controller.
The pilot current measurement is performed by feedback control, and when the output current reaches the measurement threshold value (0.5 A in this embodiment), the command value of the PI control arithmetic unit for feedback control (hereinafter, the command value of feedback control is “Ipi Command value)) and used as an input value for calculating a compensation coefficient. Pilot current measurement is performed periodically, and a moving average value of Ipi command values obtained continuously is used as an input value for calculating a compensation coefficient.

  When the compensation coefficient is calculated, the Iff command value of the next feedforward control after the end of the pilot current measurement is the compensated If command obtained by multiplying the If 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 compensation coefficient calculation method will be described with reference to FIG.
FIG. 5 is a diagram for explaining acquisition of a command value and calculation of a compensation coefficient by pilot current measurement. The horizontal axis is the set current, and the vertical axis is the Iff command value for feedforward control. The solid curve is a load characteristic specified in advance and 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 value obtained by the pilot current measurement and the Iff command value (hereinafter referred to as “reference value”) of the measurement threshold value calculated by the polynomial is a change in the command value with respect to the load current. Therefore, a new command value for feedforward control with respect to load fluctuation is obtained by compensating this change to an Iff command value calculated by a polynomial.

  The set current in the feedforward control is normally calculated by substituting the set current value (A in FIG. 5) into a polynomial (solid curve shown in FIG. 5) and an Iff command value (a in FIG. 5) for the feedforward control. Then, the If command value is multiplied by a voltage variation coefficient or PWM gain of the input power source 11 described later, and set in the digital PWM generator 24.

Since the pilot current measurement is executed by feedback control, the pilot current is transmitted, and the Ipi command value (b1 in FIG. 5) when the output current reaches 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, since the Iff command value (b0 in FIG. 5) based on the polynomial of the measurement threshold (B in FIG. 5) is a reference value, the compensation coefficient is obtained by the following equation.
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, and the feedforward control is performed. An Iff command value (c0 in FIG. 5) is calculated, and this If command value is multiplied by a compensation coefficient obtained by pilot current measurement. That is,
Command value after compensation of feedforward control = specified value obtained from polynomial (c0) * 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 a 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, “Ipi average value−reference value” in Expression (1) is a negative value.
Note that the dotted 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 expression. That is, after the compensation coefficient is calculated, the command value of the set current If command value is calculated by the polynomial indicated by the dotted line, and it is possible to cope 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, functions and signal flows constituting the control circuit 20 shown in FIG. 2 will be described.
FIG. 6 is a signal processing flowchart of the digital control system control circuit 20 for realizing the current control method of the present invention.

  The functions relating to pilot current measurement are as follows: pilot current measurement timing controller 31, pilot current measurement controller 40, switch 46, switch 47, moving average calculator 43, deviation calculator 44, AGC gain multiplier 45, switch 48, 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, a function related to control in which load characteristic compensation is combined with feedforward control is realized by a set current detector 33, a switch 48, a slew rate controller 39, a switch 49, a converter 42, a digital PWM generator 24, and a driver 37. The

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

It should be noted that the function relating 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 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 “×” is superimposed on “◯” is a multiplier.
Further, the switch 49 and the converter 41 have a function of adding a command value by 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 with specific load characteristics such as LD (Laser Diode), for example, it is necessary to reduce the load of the program related to feedback control as much as possible. is there. Therefore, the ratio of the input voltage to the constant reference voltage value (hereinafter referred to as “reference DC voltage”) with respect to the fluctuation of the input voltage of the input power supply 11 is calculated as a voltage fluctuation coefficient. The command value is multiplied by the voltage variation coefficient to reduce the load of the feedback control program as the PWM control command value.

That is, if the input voltage increases, the current increases by the amount of voltage increase. In order to suppress the increase, the command value input to the digital PWM generator 24 is multiplied by this voltage variation coefficient (the reference DC voltage is divided by the input voltage, so if the voltage increases, the command value is multiplied by 1). By reducing the value, the output current can be suppressed regardless of the feedback control.
In the present embodiment, the reference DC voltage value is 55 V, 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 a PWM count value corresponding to the command value. 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 a pulse width modulation (PWM) signal control amount.

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 diagram shown in FIG.
The pilot current measurement timing controller 31 outputs a pilot current measurement start signal for every fixed circumference. Upon receiving this signal, the pilot current measurement controller 40 connects the switch 48 to the pilot current measurement side. Further, since the pilot current measurement is performed by feedback control, the switch 46 is connected. 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 period if there is a difference between the set current value and the previous set value (the previous sampling period). )

  The pilot current measurement controller 40 determines a current stop period, a pilot current transmission period, and a pilot current measurement end, and controls the pilot current according to the periods. The pilot current output from the pilot current measurement controller 40 is input to the deviation calculator 38 after the change of the set current exceeding the slew rate value is suppressed by the function of the slew rate controller 39. 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 a 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 fluctuation 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.

  In addition, since the pilot current measurement is performed at regular intervals, a plurality of Ipi designated values when the output current reaches the measurement threshold are obtained by continuous pilot current measurement, and the moving average is calculated as a moving average calculator. 43.

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

Next, functions related to a combination system of low-current (set 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 flowchart 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 while the change of the set current exceeding the slew rate value is suppressed by the function of the slew rate controller 39.
The switch 49 is connected to the load characteristic compensation side by a polynomial, and the converter 42 calculates an If command value from the set current value by a polynomial. The calculated If command value is multiplied by the compensation coefficient calculated by the pilot current measurement, and further multiplied by the voltage fluctuation coefficient of the converter 34 and the PWM gain of the PWM gain multiplier 35, and then input to the digital PWM generator 24. . Thereby, the current control corresponding to the difference between the load specified in advance and the actual load and the temperature change is performed.

Next, the signal flow and each function of normal feedback control (set current is 0.5 A or more) will be described.
9 is a diagram showing a signal processing flow of feedback control in the signal processing flowchart 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 equal to or greater than the predetermined current value, the switch 46 is turned on to form a control loop, and feedback control is 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 side of the deviation calculator 38. The other input terminal receives an output current signal detected by the current detection circuit 17 and AD-converted by the AD converter 21 via the differential amplifier 19. The deviation calculator 38 calculates the difference 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 fluctuation 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 control the output current.

Here, the switch 49 is connected to the converter 41 as shown in FIG. 9, and the output of the slew rate controller 39 is changed to the Ipi command value by feedback control via the converter 41 (function to output the input as it is). The signal processing flow is added.
That is, a signal processing flow of a combined output of feedback control and feedforward control is shown. Note that the switch 49 is not connected in the case of control based only on the Ipi command value of 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 providing the upper limit value and the lower limit value of the signal is omitted. For example, a limiter provided before and after the PI control arithmetic unit 36 has a function of preventing the control system from becoming unstable.

The description of the respective functions of the digital signal processing flow of the present invention shown in FIG. 6 is finished, 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 executed by the CPU of the digital signal processing circuit 23.

FIG. 10 is a flowchart of the main program of the digital control system 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 initial values are set to various parameters necessary for controlling the constant current digital power supply device 10.

Next, pilot current measurement activation processing is performed at a constant cycle (S11). An initialization flag is set every time the specified time arrives, and the sequence counter is cleared to “0” (S11). The main program repeats this process, and when an interrupt occurs, it shifts to that interrupt program.
Here, the numerical value of the sequence counter is used in the following meaning.
0-13 ... Current stop period 14-255 ... Pilot current sending period 256 ... Pilot current measurement end value

FIG. 11 is a flowchart of a digitally controlled AD conversion completion interrupt program. This program is executed when an AD conversion completion interrupt is generated when the output current is AD converted every sampling period. 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, a voltage variation coefficient is calculated, and 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 subroutine program of feedforward control + load characteristic compensation in 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), a pilot current measurement subroutine program is executed (S107). When the program ends, the interrupt processing program ends and returns to the main program.

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

  In step S204, the set current value is set to 0 A, the sequence count value is set to “1”, and the initialization flag is cleared. Since the pilot current measurement is executed by feedback control, a subroutine program of feedback control 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 stopped. 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 set to 0A.

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

On the other hand, if the output current has reached the target value (S207, YES), the pilot current Ipi command value is acquired in step S210, and the pilot current measurement Ipi designated value in this sampling period and the previous sampling period Ipi are obtained. A moving average value with respect to the command value (moving average value of two Ipi command values) is obtained, and a compensation coefficient is calculated by equation (1).
The compensation coefficient is stored in the memory of the digital signal processing circuit 23.
In this program, the Ipi command value is two moving average values, but may be a moving average value of 3 or more, or may be a weighted average value of Ipi command values acquired continuously.

  In the next step S211, if the output current has reached the target value (measurement threshold) 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 256 as the measurement end value. .

FIG. 13 is a flowchart of a pilot current transmission control program. It is a detail 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 the pilot current target value is smaller than the set value of the set current of the feedforward control of the previous time (the previous sampling cycle).

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

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

FIG. 14 is a flowchart of a program of 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 a polynomial to obtain an If command value. Here, the polynomial for calculating the If command value from the set current value is, for example,
If 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 shown in Formula (3) is an example, and there are various polynomials depending on the characteristics of the load specified in advance.
In step S402, the If 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.
This is the details of the subroutine program executed in step S205 in FIG. 12 and step S305 in FIG. 13 in addition to step S104 in 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) = Ipi command value (previous) + k0 * deviation (current)
+ K1 * deviation (previous) ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ （4）
Can be expressed as Here, the deviation is “set current value−output current value”, and k0 and k1 are coefficients. Further, as described above, the previous time and the current time are the previous sampling cycle and the sampling cycle of the currently executed program.

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 and set in 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, it is possible to take out a constant current from a low current region where feedback control cannot be performed only by program control in a power supply circuit used with a single power supply.

(Second pilot current measurement method)
FIG. 16 is a flowchart of a program of another 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 for feedback control of the sampling period when the output current converges to a certain range. To get. A compensation coefficient is calculated according to equation (1) from a reference value calculated by substituting an average value of a plurality of Ipi command values obtained successively and a target current value into a 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 (down in some cases) Rather than acquiring the Ipi command value when the output current reaches the target value (crossing the target value), the Ipi command value when the output current converges to a certain range of the target value is acquired. is there.

  In the pilot current measurement shown in FIG. 16, it is determined whether or not 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 is completed.
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 transmission period of step S605.

If it is not the pilot current sending period (S605, NO), the pilot current measurement end processing in 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 certain value (for example, 0.01 A) (S606, NO), it is determined that the output current is not yet stable, and the subroutine program for pilot current transmission control in step S607 is executed. When the program ends, the program for pilot current measurement in 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 step S608, the pilot current Ipi command value is acquired, the command value (current value), the Ipi command value (previous value) in the previous sampling cycle, and the moving average value are obtained. ) Is calculated.
The compensation coefficient is stored in a memory because it is used in a program of feedforward control + load characteristic compensation.

  Next, 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 transmission period in step S609, even if the sequence count value is still smaller than 255, the sequence count value Is set to a measurement end value of 256 (S609). When the processing is completed, the pilot current measurement program in this sampling period is completed.

  Note that 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 the pilot current Ipi command value (for example, 25 by the sequence count value). In this case, the elapsed period is determined by evaluating actual load characteristics.

DESCRIPTION OF SYMBOLS 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 ... Setting 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.

Claims (8)

A current control method for a constant current digital power supply device that performs on / off control of a switching element by a pulse width modulation signal that is digitally controlled, and outputs a predetermined output current to a load based on an input voltage,
When the set current value is equal to or greater 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 command of the feedforward control is substituted by substituting the set current value into the polynomial. A constant current digital power supply apparatus current control method characterized in that the control value of the pulse width modulation signal is obtained 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 apparatus, wherein the compensation coefficient is obtained from a behavior of the output current when a 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,
The test current is changed stepwise at a predetermined sampling period and output to the load, and the compensation coefficient is calculated based on a feedback control command value when the output current reaches a predetermined measurement threshold value. A 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 command value of the feedforward control calculated by substituting the measurement threshold as the set current value into the polynomial is used as a reference value,
Obtaining an average value by successively obtaining a command value for feedback control of a sampling period when the output current has reached the measurement threshold value a plurality of times, and calculating the compensation coefficient from a difference between the reference value and the average value A current control method for 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,
A current control method for a constant-current digital power supply apparatus, characterized in that a current stop period for stopping the output current is provided before outputting the test current. A current control method for a constant current digital power supply device according to claim 2,
The test current is output to the load, and the command value of the feedback control of the sampling period in which the output current has converged to a certain range of the target current value is continuously obtained a plurality of times to obtain an average value, and the target current value is set. A constant current digital power supply apparatus characterized in that a command value of the feedback control calculated by substituting 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,
For 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 defined as a voltage fluctuation coefficient, and the command fluctuation value is multiplied by the voltage fluctuation coefficient to generate a pulse width modulation signal. A current control method for a constant current digital power supply device, characterized in that the control amount is used.   A constant-current digital power supply apparatus comprising the constant-current digital power supply apparatus current control method according to claim 1.

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