CN117792027A - High-precision bipolar programmable constant current source based on delay AD conversion - Google Patents
High-precision bipolar programmable constant current source based on delay AD conversion Download PDFInfo
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Abstract
The invention relates to a high-precision bipolar programmable constant current source based on delay AD conversion, which comprises a bipolar ACDC switching power supply, a pre-charging resistor R1, a pre-charging bypass relay K1, a capacitor E1, a controllable inversion H bridge, a current sampling unit A1, a controller, an inductor L1 and a load inductor L2, wherein the pre-charging bypass relay K1 is connected with the capacitor E1; the current sampling unit A1 is configured to comprise at least one AD conversion chip, an input signal of the AD conversion chip is output current of the controllable inversion H bridge, the controller controls the AD conversion chip to start first-wheel AD conversion at the highest point or the lowest point of output current ripple of the controllable inversion H bridge, after conversion is finished, the controller stores sampling values of the first-wheel, then starts second-wheel AD conversion after N/2 switching period is delayed, after conversion is finished, the controller reads the sampling values of the first-wheel and the sampling values of the upper-wheel to be added to obtain an average value, and the average value is used as current value feedback, wherein N is a positive integer and is an odd number.
Description
Technical Field
The invention relates to power electronics, in particular to a high-precision bipolar programmable constant current source based on delay AD conversion.
Background
The high-precision bipolar programmable constant current source main circuit consists of an ACDC switching power supply, a pre-charging resistor, a pre-charging bypass relay, a capacitor, an inversion H bridge (Q1-Q4), current sampling, an inductor, an input terminal, an output terminal and the like. The power supply needs to have the following functions and technical indexes:
1) The bipolar current output can not only change the current direction arbitrarily, but also output zero current;
2) The output current is programmable, the target output current can be set at will within-25.0000A to +25.0000A, and the current reaches the newly set target current from the current;
3) High-precision current output is carried out, the output range is 0.1 mA-25A, and the resolution is 0.1mA;
4) Peak-to-peak ripple current is less than or equal to 5mA;
5) The output current accuracy is less than or equal to 1mA.
In the electrical topological diagram of the bipolar constant current source shown in fig. 1, A1 is a current sensor, the output current is sampled, the controller takes the output current as a feedback signal and compares the feedback signal with a given current to form a closed loop, the output power of the H bridge is orderly controlled after PI regulation, and finally the actual output current is changed according to the given current. The output current response time may be optimized by modifying the PI parameter. A closed loop control block diagram is shown in fig. 2.
From the above method for generating constant current output, it can be seen that to make the power supply output high precision current, firstly, the current sampling precision is very high, and the current is basically 24 bit AD sampling at a higher level; and the sampling speed is higher than the switching control frequency of the H bridge. However, for the high-precision bipolar programmable constant current source, in order to achieve the precision of the output current, the switching frequency needs to be set relatively high, for example, the switching frequency of an H-bridge is 20kHz, while a 24-bit AD conversion chip (generally at a sampling rate of about 20 kHz) and a singlechip matched with the high-precision bipolar programmable constant current source obviously cannot achieve high sampling speed, which results in that the output direct current is not a standard direct current waveform, but has ripple current with the same frequency as the switching frequency, as shown in fig. 3. If the AD sampling frequency cannot be higher than the H-bridge switching frequency, but is the same or smaller, current sampling may be inaccurate. If the sampled value is the highest point of the normal output current ripple, the controller considers that the output current is higher than the given current, and the H bridge is controlled to reduce the output current; if the sampled values are the lowest points of the normal output current ripple, the controller will turn up the output current. The current that is normally output is deviated from the given current due to sampling value errors.
From the above, it can be seen that whether the bipolar programmable constant current source can output high-precision current or not, and high-precision current sampling is critical.
Disclosure of Invention
The invention aims at: the high-precision bipolar programmable constant current source is realized, and particularly, the high-precision current output of the constant current source is ensured by improving the current sampling precision.
In order to achieve the above purpose, a high-precision bipolar programmable constant current source based on delay AD conversion is provided, which comprises a bipolar ACDC switching power supply, a pre-charging resistor R1, a pre-charging bypass relay K1, a capacitor E1, a controllable inversion H bridge, a current sampling unit A1, a controller, an inductor L1 and a load inductor L2; the ACDC switching power supply PW1 takes electricity from the outside; the pre-charging resistor R1 and the pre-charging bypass relay K1 are connected in parallel and then connected in series to a direct current bus at the output end of the ACDC switching power supply; the capacitor E1 is connected across the direct current bus; the controllable inversion H bridge takes electricity from the direct current bus and is configured to achieve constant current output through closed loop control of the controller, and the current sampling unit A1 is used for collecting output current of the controllable inversion H bridge and feeding the output current back to the controller; the inductor L1 and the load inductor L2 are connected in series in sequence and then connected across the two output ends of the controllable inversion H bridge; the current sampling unit A1 is configured to comprise at least one AD conversion chip, an input signal of the AD conversion chip is output current of the controllable inversion H bridge, the controller controls the AD conversion chip to start first-wheel AD conversion at the highest point or the lowest point of output current ripple of the controllable inversion H bridge, after conversion is finished, the controller stores sampling values of the first-wheel, then starts second-wheel AD conversion after N/2 switching cycles are delayed, after conversion is finished, the controller reads the sampling values of the first-wheel and adds the sampling values of the upper-wheel to obtain an average value, and the average value is used as current value feedback, wherein N is a positive integer and is an odd number.
Further, after the second-round AD conversion is finished, the lower-round AD conversion is started after the N/2 switching period, sampling values of the upper-round AD conversion and the lower-round AD conversion are calculated to be used as new feedback, and continuous feedback is obtained repeatedly in a circulating mode.
Further, the current detection interval is shortened, the feedback sensitivity is improved, and the above N is configured to be 1.
Further, the AD conversion chip adopts 24 bits.
Further, the switching frequency of the controllable inversion H bridge is larger than or equal to 20kHz.
The invention has the advantages that:
1) The invention adopts a conventional hardware current sampling circuit, combines the characteristics of output current ripple and accurately samples the output current value;
2) The cost is low.
Drawings
Fig. 1 shows a bipolar constant current source electrical topology.
Fig. 2 shows a closed-loop control block diagram.
Fig. 3 shows a dc current output waveform.
Fig. 4 shows a sample point identification map.
Fig. 5 shows a power supply composition block diagram.
Detailed Description
The technical scheme of the invention is further described below with reference to the attached drawings and specific embodiments.
As shown in fig. 1, the hardware topology of the high-precision bipolar programmable power supply is composed of a bipolar ACDC switching power supply, a pre-charging resistor R1, a pre-charging bypass relay K1, a capacitor E1, controllable inversion H-bridges (Q1-Q4), a current sampling unit A1, an inductor L1, an input/output terminal and the like, and a load inductor L2 is a key component of the power supply. The ACDC switching power supply PW1 takes electricity from the outside; the pre-charging resistor R1 and the pre-charging bypass relay K1 are connected in parallel and then connected in series to a direct current bus at the output end of the ACDC switching power supply; the capacitor E1 is connected across the direct current bus; the controllable inversion H bridge takes electricity from a direct current bus, the switching frequency is greater than or equal to 20kHz, the controllable inversion H bridge is configured to achieve constant current output through closed loop control of a controller, and a current sampling unit A1 is used for collecting output current of the controllable inversion H bridge and feeding the output current back to the controller; the inductor L1 and the load inductor L2 are connected in series in sequence and then connected across the two output ends of the controllable inversion H bridge.
The high-precision bipolar programmable power supply outputs constant current of-25.0000A to +25.0000A, the resolution is 0.1mA, the output precision is less than or equal to 1mA, and the peak-to-peak ripple current is less than or equal to 5mA. In order to meet the requirement of such high performance indexes, the invention adopts a 24-bit AD conversion chip. From the aspect of the number of sampling bits, 24 bits can represent the range of 0-16777216, can completely cover the current requirement range of 0-250000, and can greatly meet the requirement of current sampling precision. However, the conversion rate of the 24-bit AD conversion chip is not high, and is generally about 20kHz. As described in the background, the sampling frequency of the output current is far higher than the switching control frequency of the H-bridge to ensure the current accuracy. If the switching speed of the H bridge is 20kHz (basically approaches to the limit conversion speed of a 24-bit AD single chip), the AD sampling speed can meet the requirement only when the conversion speed peak-to-peak ripple current reaches 200 kHz; otherwise, if the AD sampling frequency cannot be much higher than the H-bridge switching frequency, but is the same or smaller, current sampling may be inaccurate. Referring to fig. 3, if the sampled value is the highest point (0.033A) of the ripple of the normal output current (0.03A), the controller considers that the output current is higher than the given current (0.03A), and the H-bridge is controlled to reduce the output current; if the sampled values are all the lowest points (0.027A) of the ripple of the normal output current (0.03A), the controller will boost the output current. The current (current with 0.03A as the central waveform) which is normally output originally, is deviated from the given current due to sampling value errors.
The switching frequency of the bipolar constant current source is high, and the conversion speed of the AD sampling cannot far exceed the switching frequency. In contrast, the invention does not directly increase the AD conversion speed, but repeatedly adjusts the sampling time interval according to the ripple rule of the output current, and skillfully samples the correct current. Specifically, the current sampling unit A1 is configured to include at least one AD conversion chip, an input signal of the AD conversion chip is an output current of the controllable inversion H-bridge, after power-up, the controller controls the AD conversion chip to start the first-round AD conversion at the highest point or the lowest point of the output current ripple of the controllable inversion H-bridge, after the start conversion is finished, a conversion result is output, and a sampling value of the first round is read and stored by the controller. At this time, the next AD conversion is started after the 1/2 switching period without being urgent to start the AD conversion again, after the conversion is completed, the second sampling value is read and added with the upper sampling value to obtain an average value, and the average value can be used as a feedback current value. Then, after a delay of 1/2 of the switching period, the AD conversion of the lower wheel is started again to obtain the sampling value of the upper wheel as new feedback, and the feedback current value can be obtained continuously and accurately by repeating the steps.
For ease of understanding, the detailed description is provided in connection with fig. 4. Referring to fig. 4, when the AD conversion is started at the position (1), a sampling result of the position (1) is obtained at the position (2) after one period T, and is recorded as a sampling value 1; and starting AD sampling at the position (3) after the delay of 1/2 period, and obtaining a sampling result at the position (3) when the AD sampling is performed at the position (4), and recording the sampling result as a sampling value 2. At this time, the sampling value 1 and the sampling value 2 are added to obtain an average value, and the average value is the feedback current which can participate in H-bridge control. And simultaneously, the value of the sampling value 2 is replaced by the sampling value 1 and is recorded as the sampling value 1, then the AD sampling is started when the time is delayed by 1/2 period to the position (5), the current value of the position (5) is obtained at the position (6), the current value is recorded as the sampling value 2, and the average value is obtained after the current value is added with the sampling value 1 to be used as the feedback current value of H bridge control. By cycling, the correct current can be output according to the given current.
The sampling interval is repeatedly adjusted, so that the first sampling value and the second sampling value are different by 1.5T period, if the first sampling value is the positive half cycle of the ripple, the first sampling value is the lower half cycle of the ripple after 1.5T, and the actual direct current output current is obtained after the average of the two times of addition. If the first sampling value is 0.033A and the second sampling value after 1.5T period time is 0.027A, which is the minimum value of the lower half period, 0.03A is obtained after the two sampling values are added, compared with the current of 0.03A, the PID still controls the H bridge according to the last duty ratio.
As shown in fig. 5, the power supply control center is composed of a detection circuit 5, a drive circuit 4, a controller 3, an AD conversion circuit 6, an operation panel 7, and the like. The detection module 5 mainly comprises voltage detection and temperature detection, and detection signals are processed by a circuit and then sent to the controller 3; the controller 3 samples the current of the AD conversion chip 6, and outputs the sampled current data as a feedback signal through the driving circuit 4 to drive the CMOS transistor. The operation panel 7 can output the current magnitude and direction of the device at any time, and display the current voltage, current, temperature and other data of the power supply.
The invention has the advantages that:
1) The invention adopts a conventional hardware current sampling circuit, combines the characteristics of output current ripple and accurately samples the output current value;
2) The cost is low.
The above-described embodiments are merely preferred embodiments of the present invention, and many alternative modifications and combinations of the above-described embodiments can be made by those skilled in the art based on the technical solutions of the present invention and the related teachings of the above-described embodiments.
Claims (5)
1. A high-precision bipolar programmable constant current source based on delay AD conversion is characterized in that:
the device comprises a bipolar ACDC switching power supply, a pre-charging resistor R1, a pre-charging bypass relay K1, a capacitor E1, a controllable inversion H bridge, a current sampling unit A1, a controller, an inductor L1 and a load inductor L2; the ACDC switching power supply PW1 takes electricity from the outside; the pre-charging resistor R1 and the pre-charging bypass relay K1 are connected in parallel and then connected in series to a direct current bus at the output end of the ACDC switching power supply; the capacitor E1 is connected across the direct current bus; the controllable inversion H bridge takes electricity from the direct current bus and is configured to achieve constant current output through closed loop control of the controller, and the current sampling unit A1 is used for collecting output current of the controllable inversion H bridge and feeding the output current back to the controller; the inductor L1 and the load inductor L2 are connected in series in sequence and then connected across the two output ends of the controllable inversion H bridge;
the current sampling unit A1 is configured to comprise at least one AD conversion chip, an input signal of the AD conversion chip is output current of the controllable inversion H bridge, the controller controls the AD conversion chip to start first-wheel AD conversion at the highest point or the lowest point of output current ripple of the controllable inversion H bridge, after conversion is finished, the controller stores sampling values of the first-wheel, then starts second-wheel AD conversion after N/2 switching cycles are delayed, after conversion is finished, the controller reads the sampling values of the first-wheel and adds the sampling values of the upper-wheel to obtain an average value, and the average value is used as current value feedback, wherein N is a positive integer and is an odd number.
2. The high precision bipolar programmable constant current source according to claim 1, wherein: after the AD conversion of the second round is finished, the AD conversion of the lower round is started after the N/2 switching period is delayed to obtain the sampling value of the upper round as new feedback, and the continuous feedback is obtained repeatedly in a circulating way.
3. The high-precision bipolar programmable constant current source according to claim 1 or 2, characterized in that: n is configured to be 1.
4. The high precision bipolar programmable constant current source according to claim 1, wherein: the AD conversion chip adopts 24 bits.
5. The high precision bipolar programmable constant current source according to claim 4, wherein: the switching frequency of the controllable inversion H bridge is larger than or equal to 20kHz.
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| CN202311855232.0A CN117792027A (en) | 2023-12-29 | 2023-12-29 | High-precision bipolar programmable constant current source based on delay AD conversion |
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| CN202311855232.0A CN117792027A (en) | 2023-12-29 | 2023-12-29 | High-precision bipolar programmable constant current source based on delay AD conversion |
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