A high-precision bipolar programmable constant current source based on multi-chip AD time-sharing sampling

Abstract

The application relates to a high-precision bipolar programmable constant current source based on multi-piece AD time-sharing sampling, which comprises a bipolar ACDC switching power supply, a pre-charging resistor R1, a pre-charging bypass relay K1, a capacitor E1, a controllable inverter H bridge, a current sampling unit A1, a total controller, an inductor L1 and a load inductor L2; wherein the sampling speed of the current sampling unit A1 is configured to be N times higher than the switching frequency of the controllable inverter H bridge; the A1 comprises a control chip and N pieces of AD conversion chips, the input signals of the AD conversion chips are all the output currents of the controllable inverter H bridge, the AD conversion chips are configured to time-sharingly and sequentially sample the current signals at equal intervals, and the sampling results are sequentially sent into the control chip according to time sequence; after one round of sampling is completed, the control chip immediately starts the next round of equal-interval current sampling, and the average value of the data sampled in the last round is sent to the total controller as feedback.

Description

Technical Field

[0001] This invention relates to power electronics, and more particularly to a high-precision bipolar programmable constant current source based on time-division sampling of multiple AD converters. Background Technology

[0002] The high-precision bipolar programmable constant current source main circuit consists of an AC-DC switching power supply, a pre-charge resistor, a pre-charge bypass relay, capacitors, an inverter H-bridge (Q1~Q4), current sampling, inductors, and input / output terminals. The power supply needs to have the following functions and technical specifications:

[0003] 1) Bipolar current output, which not only allows for arbitrary changes in current direction, but also enables zero-current output;

[0004] 2) The output current is programmable. The target output current can be set arbitrarily within the range of -25.0000A to +25.0000A, and the current will increase from the current to the newly set target current.

[0005] 3) High-precision current output, output range 0.1mA~25A, resolution 0.1mA;

[0006] 4) Peak-to-peak ripple current ≤ 5mA;

[0007] 5) Output current accuracy ≦1mA.

[0008] Figure 1 The diagram shows the electrical topology of a bipolar constant current source. A1 is a current sensor that samples the output current. The main controller uses the output current as a feedback signal and compares it with the given current to form a closed loop. After PI regulation, the output power of the H-bridge is controlled in an orderly manner, ultimately making the actual output current change according to the given current. The output current response time can be optimized by modifying the PI parameters. The closed-loop control block diagram is shown below. Figure 2 As shown.

[0009] From the methods for generating constant current output described above, it can be seen that to achieve high-precision current output from a power supply, the current sampling accuracy must first be very high, with 24-bit AD sampling being a current-level standard. Furthermore, the sampling speed must be higher than the switching control frequency of the H-bridge. However, for high-precision bipolar programmable constant current sources, to achieve output current accuracy, the switching frequency needs to be set relatively high, for example, an H-bridge switching frequency of 20kHz. A 24-bit AD conversion chip (typically with a sampling rate of around 20kHz) and its associated microcontroller obviously cannot achieve such a high sampling speed. This results in the output DC current not being a standard DC waveform, but rather exhibiting ripple current at the same frequency as the switching frequency, such as... Figure 3As shown. If the AD sampling frequency cannot be higher than the H-bridge switching frequency, but is the same as or lower, it will lead to inaccurate current sampling. If each sampled value is the highest point of the normal output current ripple, the main controller will think that the output current is higher than the given current and will control the H-bridge to reduce the output current; if the sampled values ​​are the lowest points of the normal output current ripple, the main controller will increase the output current. The normally normal output current deviates from the given current due to incorrect sampling.

[0010] As can be seen from the above, high-precision current sampling is the key to whether a bipolar programmable constant current source can output high-precision current. Summary of the Invention

[0011] The purpose of this invention is to realize a high-precision bipolar programmable constant current source, especially to ensure high-precision output current of the constant current source by improving the current sampling accuracy.

[0012] To achieve the above objectives, a high-precision bipolar programmable constant current source based on multi-chip AD time-division sampling is provided, including a bipolar AC-CDC switching power supply, a pre-charge resistor R1, a pre-charge bypass relay K1, a capacitor E1, a controllable inverter H-bridge, a current sampling unit A1, a main controller, an inductor L1, and a load inductor L2; the AC-CDC switching power supply PW1 is powered externally; the pre-charge resistor R1 and the pre-charge bypass relay K1 are connected in parallel and then connected in series with the DC bus at the output terminal of the AC-CDC switching power supply; the capacitor E1 is connected across the DC bus; the controllable inverter H-bridge is powered from the DC bus and configured to achieve constant current output through closed-loop control of the main controller; the current sampling unit A1 is used to collect the output current of the controllable inverter H-bridge. Feedback is sent to the main controller; inductor L1 and load inductor L2 are connected in series across the output of the controllable inverter H-bridge; wherein, the sampling rate of the current sampling unit A1 is configured to be N times higher than the switching frequency of the controllable inverter H-bridge, where N is an integer; the current sampling unit A1 includes a control chip and N AD conversion chips, the input signal of each AD conversion chip is the output current of the controllable inverter H-bridge, each AD conversion chip is configured to sample the current signal at equal intervals in a time-division manner, and the sampling results are sent to the control chip in chronological order; after one round of sampling is completed, the control chip immediately starts the next round of equal-interval current sampling, and takes the average value of the data from the previous round of sampling as the feedback and sends it to the main controller.

[0013] Furthermore, N is configured to be greater than or equal to 10.

[0014] Furthermore, the AD conversion chip is 24-bit.

[0015] Furthermore, the switching frequency of the controllable inverter H-bridge is greater than or equal to 20kHz.

[0016] Furthermore, the control chip is configured as an FPGA.

[0017] Furthermore, each AD conversion chip has a follower at its input terminal, and the output current of the controllable inverter H-bridge enters each AD conversion chip through each follower.

[0018] Advantages of this invention:

[0019] 1. High sampling accuracy: Multiple current samples are taken within each ripple cycle. Even if individual sampling points are incorrect, the average will not have much impact.

[0020] 2. Fast sampling speed, with high-precision feedback current in each switching cycle, which greatly improves the dynamic response of the output current and can cope with situations of rapid load changes. Attached Figure Description

[0021] Figure 1 The electrical topology of a bipolar constant current source is shown.

[0022] Figure 2 A closed-loop control block diagram is shown.

[0023] Figure 3 The DC current output waveform is shown.

[0024] Figure 4 The sampling topology diagram with equal time intervals is shown.

[0025] Figure 5 A block diagram of the power supply is shown. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown, the hardware topology of the high-precision bipolar programmable power supply consists of a bipolar AC-DC switching power supply, a pre-charge resistor R1, a pre-charge bypass relay K1, a capacitor E1, a controllable inverter H-bridge (Q1~Q4), a current sampling unit A1, an inductor L1, and input / output terminals. The load inductor L2 is a key component of the power supply. The AC-DC switching power supply PW1 is powered externally; the pre-charge resistor R1 and the pre-charge bypass relay K1 are connected in parallel and then connected in series with the DC bus at the output of the AC-DC switching power supply; the capacitor E1 is connected across the DC bus; the controllable inverter H-bridge is powered from the DC bus, with a switching frequency greater than or equal to 20kHz, and is configured to achieve constant current output through closed-loop control of the main controller. The current sampling unit A1 is used to collect the output current of the controllable inverter H-bridge and feed it back to the main controller; the inductor L1 and the load inductor L2 are connected in series across the output of the controllable inverter H-bridge.

[0028] A high-precision bipolar programmable power supply needs to output a constant current of -25.0000A to +25.0000A, with a resolution of 0.1mA, output accuracy ≤1mA, and peak-to-peak ripple current ≤5mA. To meet these high performance requirements, this invention employs a 24-bit AD converter chip. In terms of sampling bit depth, 24 bits can represent a range of 0 to 16,777,216, completely covering the current requirement range of 0 to 250,000, far exceeding the current sampling accuracy requirements. However, the conversion rate of 24-bit AD converter chips is not high, typically around 20kHz. As mentioned in the background, the sampling frequency of the output current must be much higher than the switching control frequency of the H-bridge to ensure current accuracy. If the H-bridge switching speed is 20kHz (close to the limit conversion rate of a single 24-bit AD chip), then the AD sampling speed must reach a conversion speed of 200kHz to meet the peak-to-peak ripple current requirements.

[0029] The switching frequency of a bipolar constant current source is very high, and the conversion speed of AD sampling cannot far exceed the switching frequency. To address this, the bipolar constant current source current AD sampling method of this invention can accurately and quickly sample the output current. It not only has high accuracy but also a fast sampling speed. This fast sampling speed can greatly improve the dynamic response speed of the bipolar constant current source output current.

[0030] The current sampling method of this invention employs a method of sampling at equal time intervals using multiple AD conversion chips, such as... Figure 4 As shown, adhering to the principle that the sampling rate is configured to be N times (N being an integer) higher than the switching frequency of the controllable inverter H-bridge, a single control chip (FPGA) manages N AD conversion chips, sequentially starting and reading data from the AD conversion chips. The input signal of the AD conversion chips is the same current signal, which is the output current of the controllable inverter H-bridge. That is, the same signal is sampled sequentially by each AD conversion chip at equal time intervals, and the sampling results enter the control chip in chronological order. After one round of sampling is completed, the control chip immediately starts the second round of equally spaced current sampling, while simultaneously averaging the data from the previous round of sampling. The resulting data is sent to the next-level control chip (DSP) for closed-loop adjustment of the H-bridge's PWM value, thereby regulating the output of the constant current source.

[0031] Bipolar constant current sources have very high requirements for ripple and accuracy, and a wide output current range. Therefore, the higher the switching frequency of the bipolar power supply, the easier it is to achieve low ripple and high-precision current output. However, a high switching frequency will inevitably generate high ripple current. Following the principle that the sampling speed should be a multiple of the switching frequency, we will use a switching frequency of 20kHz for the H-bridge, the fastest conversion speed of a single AD chip of 20kHz, and a total current sampling conversion speed of 200kHz for explanation.

[0032] When the H-bridge switching frequency is 20kHz, the period T = 50µs, which is also the period of the output ripple current. Dividing the period T into 10 equal parts, we get a current sampling period t = 5µs. This means there is a current sampling (AD conversion) result every 5µs. After power-on, the FPGA first controls AD converter chip 1 to start, then AD converter chip 2 after 5µs, then AD converter chip 3 after another 5µs, and so on, finally starting AD converter chip 10. Since the single AD conversion time period is also 50µs, after AD converter chip 10 starts, it will begin to receive the conversion result from AD converter chip 1. At this time, the FPGA reads the conversion value from AD converter chip 1 and restarts AD converter chip 1; after 5µs, it will receive the conversion value from AD converter chip 2 and restarts AD converter chip 2; and so on. After receiving the conversion value from AD converter chip 10, the FPGA can calculate the average value of 10 samples, which is the DC output current within one switching frequency cycle (50µs). This cyclical sampling results in a real-time current value update in each switching frequency cycle.

[0033] Bipolar programmable constant current sources using multiple AD conversion chips and other sampling intervals not only have low output current ripple and high accuracy, but also have a fast dynamic response speed.

[0034] like Figure 5 As shown, the power control center of this invention consists of a detection circuit 5, a drive circuit 4, a main controller 3, and an operation panel 6. The detection module 5 mainly includes voltage and temperature detection; the detection signals are processed by the circuit and then sent to the main controller 3. The main controller 3 reads the current value from the FPGA control center 7, uses the current data as a feedback signal, and drives the CMOS transistor in the power supply through the drive circuit 4. The operation panel 6 allows setting the magnitude and direction of the output current at any time and displays the current voltage, current, and temperature data of the power supply. 7 is the control center of the FPGA, mainly responsible for the orderly management of the AD conversion chip 8, indirectly improving the conversion speed of the AD conversion. Simultaneously, the FPGA's logic processing capability is faster than that of a regular MCU, and this type of solution, which is sensitive to speed, can further improve the sampling speed.

[0035] As an improvement, each AD conversion chip is equipped with a follower at its input terminal. The output current of the controllable inverter H-bridge enters each AD conversion chip through each follower. In this way, the signal of each AD conversion chip can be reverse isolated from the same current signal, preventing a fault in one AD chip from affecting the current collected in turn, and thus affecting other AD chips.

[0036] Advantages of this invention:

[0037] 1. High sampling accuracy: Multiple current samples are taken within each ripple cycle. Even if individual sampling points are incorrect, the average will not have much impact.

[0038] 2. Fast sampling speed, with high-precision feedback current in each switching cycle, which greatly improves the dynamic response of the output current and can cope with situations of rapid load changes.

[0039] The above specific embodiments are merely preferred embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A high-precision bipolar programmable constant current source based on time-division sampling of multiple AD chips, characterized in that: The system includes a bipolar AC-DC switching power supply, a pre-charge resistor R1, a pre-charge bypass relay K1, a capacitor E1, a controllable inverter H-bridge, a current sampling unit A1, a main controller, an inductor L1, and a load inductor L2. The AC-DC switching power supply PW1 is powered externally. The pre-charge resistor R1 and the pre-charge bypass relay K1 are connected in parallel and then connected in series with the DC bus at the output of the AC-DC switching power supply. The capacitor E1 is connected across the DC bus. The controllable inverter H-bridge is powered from the DC bus and configured to achieve constant current output through closed-loop control by the main controller. The current sampling unit A1 is used to collect the output current of the controllable inverter H-bridge and feed it back to the main controller. The inductor L1 and the load inductor L2 are connected in series and then connected across the output of the controllable inverter H-bridge. The sampling rate of the current sampling unit A1 is configured to be N times higher than the switching frequency of the controllable inverter H-bridge, where N is an integer. The current sampling unit A1 includes a control chip and multiple AD conversion chips. The input signal of each AD conversion chip is the output current of the controllable inverter H-bridge. Each AD conversion chip is configured to sample the current signal at equal intervals in a time-division manner, and the sampling results are sent to the control chip in chronological order. After one round of sampling is completed, the control chip immediately starts the next round of equal-interval current sampling and takes the average value of the data from the previous round of sampling as the feedback and sends it to the main controller. N is configured to be greater than or equal to 10. The AD conversion chip is 24-bit. The switching frequency of the controllable inverter H-bridge is greater than or equal to 20kHz.

2. The high-precision bipolar programmable constant current source according to claim 1, characterized in that: The control chip is configured as an FPGA.

3. The high-precision bipolar programmable constant current source according to claim 1, characterized in that: Each AD converter chip has a follower at its input terminal, and the output current of the controllable inverter H-bridge enters each AD converter chip through each follower.

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