Programmable constant current source applying isolation current sampling

Abstract

A programmable constant current source applying isolation current sampling comprises a master control MCU, a bipolar ACDC switching power supply, a capacitor E1, a controllable inversion H bridge, a current sampling unit, an inductor L1 and a load inductor L2, the ACDC, the capacitor E1 and the H bridge are connected in sequence, and the inductor L1 and the load inductor L2 are connected in series and then are in bridge connection with the two ends of the H bridge; the current sampling unit comprises a plurality of shunt branches with the same specification and resolution, and the shunt branches are connected in parallel and then connected in series between the H bridge and the inductor L1; each shunt branch comprises an acquisition module and a relay which are connected in series, the acquisition module comprises a power supply, an IV converter, an ADC converter, an MCU data processor and an optical fiber communication circuit, the power supply provides an independent power supply for the acquisition module, the IV converter converts current into voltage and inputs the voltage into the ADC converter, the ADC converter transmits the voltage to the MCU data processor through SPI communication, and the MCU data processor transmits the voltage to the relay. The MCU data processor establishes a link with the master control MCU through the optical fiber communication circuit and controls the relay to be switched on or switched off.

Description

Technical Field

[0001] The present invention relates to a programmable constant current source applying isolated current sampling. Background Art

[0002] The topology diagram of a high-precision bipolar programmable constant current source is as Figure 1 shown, and it includes a bipolar ACDC switching power supply PW1, a pre-charge resistor R1, a pre-charge bypass relay K1, a capacitor E1, a controllable inverter H-bridge, a current sampling unit, an inductor L1, and a load inductor L2.

[0003] The programmable constant current source performs PID regulation with current as the feedback quantity. Therefore, the accuracy of current sampling determines the output accuracy of the entire system. The current sampling unit is connected in series at the output end of the H-bridge. There are generally two conventional DC current acquisition schemes. One is that the Hall current transformer directly outputs, performs IV conversion, and then ADC conversion. The most obvious disadvantage of this scheme is that the linearity and sensitivity of the sensor are limited, and the higher the linearity, the more expensive the current transformer. The second scheme uses a shunt resistor, performs IV conversion, and then ADC conversion. The linearity and sensitivity of this scheme can be guaranteed. Both of these schemes have an obvious common disadvantage that the ADC resolution will decrease as the measurement current range becomes larger, which affects the final sampling accuracy. For example, when using a 24-bit ADC chip to measure a current of 0 - 10A (1 AD value corresponds to 6 μA), the resolution will be lower than that of measuring a current of 0 - 5A (1 AD value corresponds to 3 μA). Summary of the Invention

[0004] To improve the deficiencies of the prior art, a programmable constant current source applying isolated current sampling is provided, which includes a main control MCU, a bipolar ACDC switching power supply, a capacitor E1, a controllable inverter H-bridge, a current sampling unit, an inductor L1, and a load inductor L2. The bipolar ACDC switching power supply, the capacitor E1, and the controllable inverter H-bridge are connected in sequence. The inductor L1 and the load inductor L2 are connected in series and then connected across both ends of the controllable inverter H-bridge. The current sampling unit includes multiple parallel shunt branches with the same specifications and resolutions. After being connected in parallel, each shunt branch is connected in series between the controllable inverter H-bridge and the inductor L1. Each shunt branch includes an acquisition module and a relay connected in series. The acquisition module includes a power supply, an IV converter, an ADC converter, an MCU data processor, and an optical fiber communication circuit. The power supply provides a separate power supply for the acquisition module. The IV converter converts the current into a voltage and then inputs it to the ADC converter. The ADC converter transmits data to the MCU data processor through SPI communication. The MCU data processor establishes a link with the main control MCU through the optical fiber communication circuit, and controls the closing or opening of the relay.

[0005] Among them, the master MCU regularly sends synchronization signals to each acquisition module. Each acquisition module receives the synchronization signal and triggers the optical fiber to send back data. The master MCU corrects the sampled data based on the transmission and reception delays of the returned data from each acquisition module.

[0006] Among them, the optical fiber communication circuit transmits at a rate of 10M.

[0007] Among them, each sampling module reserves a sampling range of +10%.

[0008] Among them, the acquisition module includes a shunt resistor and an operational amplifier. The shunt resistor shunts the current signal and transmits it to the IV converter. The operational amplifier amplifies the output voltage of the IV converter and sends it to the ADC converter.

[0009] Among them, the power supply is an isolated power supply.

[0010] The present invention designs a multi-module parallel current acquisition method, which can not only ensure the expandability of the test current range but also ensure the resolution, thus ensuring the high precision of large current sampling. Description of the Drawings

[0011] Figure 1 Shows the topology diagram of a bipolar programmable constant current source;

[0012] Figure 2 Shows the block diagram of the current acquisition method;

[0013] Figure 3 Shows the block diagram of a single acquisition module;

[0014] Figure 4 Shows the circuit topology of the acquisition module. Detailed Embodiments

[0015] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0016] The programmable constant current source applying isolated current sampling includes a master MCU, a bipolar ACDC switch 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, an inductor L1, and a load inductor L2.

[0017] The bipolar ACDC switch power supply, the capacitor E1, and the controllable inverter H-bridge are connected in sequence. The pre-charge resistor R1 and the pre-charge bypass relay K1 are connected in parallel and then connected in series to the positive output terminal of the bipolar ACDC switch power supply. The inductor L1 and the load inductor L2 are connected in series and then connected across both ends of the controllable inverter H-bridge.

[0018] Figure 2The block diagram of the present current acquisition method is given. The current sampling unit includes multiple shunt branches connected in parallel with the same specifications and resolution. After being connected in parallel, each shunt branch is serially connected between the controllable inverter H-bridge and the inductor L1. Each shunt branch includes an acquisition module and a relay connected in series. A1 - A5 are individual acquisition modules. Each acquisition module is an independent acquisition system. The circuit design of each module is the same, and the ADC current resolution is the same. Each module can achieve high-precision acquisition of the loop current passing through it. The resolution of a single module determines the system resolution, and the current accuracy of three modules determines the system accuracy. The system can achieve multi-module parallel expansion acquisition according to the output current range. The system will not affect the sampling resolution due to the increase in the number of parallel modules, thus ensuring the accuracy of large current acquisition.

[0019] The block diagram and design diagram of a single acquisition module are as Figure 3 、 4 , including an isolated power supply, a shunt resistor, an IV converter, an operational amplifier, an ADC converter, an MCU data processor, and an optical fiber communication circuit. The isolated power supply provides a separate power supply for the entire module, isolates the input and output at the same time, and provides a good environment for isolating the sampled current. The shunt resistor shunts the current signal of -5.5A - 5.5A and converts it into a small voltage signal of -0.55V - 0.55V through the IV converter. The operational amplifier amplifies the small voltage signal of -0.55V - 0.55V into a voltage of -4.675V - 4.675V, reducing the interference effect by first reducing the conversion and then amplifying. The final amplified voltage signal enters a 24-bit ADC chip for analog-to-digital conversion. The digital signal after ADC conversion is transmitted to the MCU STM32F103 through SPI communication. The MCU chip packages the signal and sends it to the main control MCU in real time through optical fiber communication. The main control MCU sends control, synchronization and other signals to the acquisition module MCU through optical fiber isolation. The optical fiber realizes the communication between the main control MCU and the acquisition module MCU. The acquisition module MCU controls the closing and opening of the relay according to the instructions of the main control MCU, and determines whether the acquisition module is switched on for current sampling.

[0020] Since the current sampling unit is serially connected to the output end of the H-bridge and has a high common-mode voltage, A1 - A5 communicate with the main control MCU through high-speed optical fibers to achieve current isolation acquisition and avoid common-mode interference.

[0021] The specific working mode is as follows. When the output current range of the programmable constant current source is -5A to 5A, the master MCU enables the relay of the A1 current acquisition module to close through the optical fiber, and A2 - A5 are not enabled. The A1 current acquisition module transmits the current sampling data to the master MCU through the optical fiber to achieve closed-loop control. When the output current range of the programmable constant current source is -10A to 10A, the master MCU enables the relays of the A1 and A2 current acquisition modules to close through the optical fiber, and A3 - A5 are not enabled. The A1 and A2 current acquisition modules will equally divide the main circuit current. The current range of the A1 and A2 current acquisition modules is still -5A to 5A. The current sampling data of the A1 and A2 are transmitted to the master MCU through the optical fiber, and the master MCU processes the data of A1 and A2 to achieve closed-loop control. Since the current acquisition range of A1 and A2 has not changed, the ADC resolution remains unchanged, thus ensuring the accuracy. And so on. When the output current range of the programmable constant current source is -25A to 25A, the master MCU enables the relays of the A1 - A5 current acquisition modules to close through the optical fiber. The A1 - A5 current acquisition modules transmit the current sampling data to the master MCU through the optical fiber, and the master MCU processes the data of A1 - A5 to achieve closed-loop control. Whether the A1 - A5 modules are put into the current acquisition circuit is controlled by the master MCU. When the A1 - A5 are put in, the acquired current data is also returned to the master MCU in real time through the optical fiber.

[0022] To ensure the timeliness of data, the optical fiber speed is set at a transmission rate of 10M. Since the acquisition module has completed analog-to-digital conversion, the data sent to the master MCU is the processed data, which reduces the data processing volume of the master MCU. To ensure the synchronous consistency of the data sent by each module, the master MCU periodically sends a synchronization signal to each acquisition module. Each acquisition module triggers the optical fiber to send back the data when it receives the synchronization signal. The master MCU corrects the sampling data based on the transmission and reception delays of the return data of each acquisition module. There will be individual differences in each module. When multiple modules are put into current sampling, there will be a ±5% difference in the current of each module. Therefore, each sampling module reserves a +10% sampling range, and the current acquisition range of each module is -5.5A to 5.5A. The acquisition range of each module is fixed, so the ADC sampling resolution and acquisition accuracy are fixed. The master MCU switches the modules to achieve the purpose of expanding the current acquisition range. In this way, both the current range is expanded and the acquisition accuracy is ensured. For some special application scenarios, considering the sampling redundancy design, several standby acquisition modules can be connected in parallel. When a certain module is damaged, the standby module can be put into use without affecting the normal operation of the system.

[0023] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A programmable constant current source using isolated current sampling, It includes a main control MCU, a bipolar ACDC switching power supply, a capacitor E1, a controllable inverter H-bridge, a current sampling unit, an inductor L1, and a load inductor L2. The bipolar ACDC switching power supply, the capacitor E1, and the controllable inverter H-bridge are connected in sequence, and the inductor L1 and the load inductor L2 are connected in series and then connected across the two ends of the controllable inverter H-bridge. Features: The current sampling unit includes a plurality of parallel shunt branches with the same specifications and resolutions, each shunt branch is connected in parallel and then connected in series between the controllable inverter H bridge and the inductor L1; Each shunt branch includes an acquisition module and a relay connected in series. The acquisition module includes a power supply, an IV converter, an ADC converter, an MCU data processor, and an optical fiber communication circuit. The power supply provides a separate power supply for the acquisition module. The IV converter converts the current into voltage and inputs it into the ADC converter. The ADC converter transmits it to the MCU data processor via SPI communication. The MCU data processor establishes a link with the main control MCU through the optical fiber communication circuit, and controls the relay to close or open.

2. The programmable constant current source according to claim 1, characterized in that: The main control MCU periodically sends synchronization signals to each acquisition module. Each acquisition module receives the synchronization signal and triggers the optical fiber to send return data. The main control MCU corrects the sampled data according to the sending and receiving delay of the return data of each acquisition module.

3. The programmable constant current source according to claim 2, characterized in that: The optical fiber communication circuit uses a 10M transmission rate.

4. The programmable constant current source according to claim 1, characterized in that: Each sampling module reserves +10% of the sampling range.

5. The programmable constant current source according to claim 1, characterized in that: The acquisition module includes a shunt and an operational amplifier. The shunt shunts the current signal and transmits it to the IV converter. The operational amplifier amplifies the output voltage of the IV converter and sends it to the ADC converter.

6. The programmable constant current source according to claim 1, characterized in that: The power supply is an isolated power supply.

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