Circuit for improving current sampling precision of inverter
By combining a differential sampling circuit and a low-pass filter, the problem of insufficient current sampling accuracy in the inverter was solved, achieving higher control accuracy and stability, and simplifying the hardware design.
Patent Information
- Application Number
- CN202522562954.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-03
- Publication Date
- 2026-01-06
- Estimated Expiration
- 2035-12-03
AI Technical Summary
In existing technologies, the current sampling accuracy of inverters is affected by high-frequency switching noise and channel delay errors, resulting in insufficient control accuracy, especially with significant errors at low currents, and increasing the sampling rate becomes more complicated.
A combination of differential sampling circuit and low-pass filter is used to filter out high-frequency switching noise. The differential sampling circuit outputs two signals: one goes directly to the DSP, and the other is processed by the low-pass filter before going to the DSP for calibration, thereby improving sampling accuracy.
It effectively filters out high-frequency switching ripple, enables sampling of current signals closer to the average value, improves inverter control accuracy, simplifies hardware design, and reduces the requirements for ADC and processor.
Smart Images
Figure CN223770284U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of inverter technology, specifically relating to a circuit for improving the current sampling accuracy of inverters. Background Technology
[0002] In photovoltaic-storage hybrid inverters, the sampling accuracy of the inductor current plays a crucial role in the inverter's control and power dispatch. The commonly used PWM modulation strategy in power electronics results in a square pulse voltage across the inductor, leading to a corresponding triangular current. Due to the characteristics of digital sampling, the acquired voltage signal is directly sent to the DSP for control. However, in practical applications, when acquiring the triangular current waveform, high-frequency switching harmonics cause waveform distortion, and the intermittent operation at low currents leads to unavoidable errors due to channel delay, which are significant enough to severely impact control. Current patents address this by using a multi-sample technique, increasing the number of samples within a switching cycle and then averaging the sampled values to improve accuracy. Therefore, a larger sample count results in higher accuracy, but errors cannot be eliminated, and control becomes more complex. Utility Model Content
[0003] The purpose of this invention is to address the problems existing in the prior art by providing a circuit that improves the current sampling accuracy of inverters. It processes high-frequency switching noise at the hardware level, greatly improving the sampling accuracy of inductor current and making the power control of the inverter more precise during actual operation.
[0004] The technical solution is as follows:
[0005] A circuit for improving the current sampling accuracy of an inverter includes a differential sampling circuit, a filtering circuit, and a DSP. The current signal at the inverter sampling point is output as two signals after passing through the differential sampling circuit. One signal is directly output to the AD1 interface of the DSP, and the other signal is processed by a low-pass filter of the filtering circuit and then output to the AD2 interface of the DSP. The DSP uses the filtered value to calibrate the sampled value to improve the current sampling accuracy of the inverter. The differential sampling circuit includes resistors R1-R4 and an operational amplifier. The non-inverting input terminal Vp of the operational amplifier is connected in series with resistor R3 at the sampling point, and its inverting input terminal Vn is connected in series with resistor R1 at the reference voltage. Resistor R2 is connected in series between Vn and the output Vo of the operational amplifier, and pull-down resistor R4 is connected in parallel between Vi and R3.
[0006] Furthermore, the current signal at the inverter sampling point is a triangular wave current controlled by PWM, and the signal output by the differential sampling circuit is a voltage signal.
[0007] Furthermore, the low-pass filter in the filtering circuit is one of three types: a first-order RC filter, a second-order RC filter, or a Sallen-Key filter.
[0008] Furthermore, the first-order RC filter includes a resistor R5 and a capacitor C1; one end of R5 is connected between Vo and the AD1 interface of the DSP, and the other end is connected to the AD2 interface of the DSP; C1 is connected between the AD2 interface of the DSP and the signal ground.
[0009] Furthermore, the second-order RC filter includes resistors R5 and R6, and capacitors C1 and C2; one end of R5 is connected between Vo and the AD1 interface of the DSP, and the other end is connected in series with R6 to the AD2 interface of the DSP; one end of C1 is connected at the connection between R5 and R6, and the other end is connected to signal ground; C2 is connected between signal ground and the AD2 interface of the DSP.
[0010] Furthermore, the Sallen-Key filter includes an operational amplifier, resistors R5 and R6, and capacitors C1 and C2. One end of R5 is connected between Vo and the AD1 interface of the DSP, and the other end is connected in series with R6 to the non-inverting input Vp of the operational amplifier. One end of C1 is connected at the junction of R5 and R6, and the other end is connected to the inverting input Vn of the operational amplifier. One end of C2 is connected to the non-inverting input Vp of the operational amplifier, and the other end is connected to signal ground. The output of the operational amplifier is connected to the AD2 interface of the DSP.
[0011] Beneficial effects:
[0012] 1) This utility model adds a filter circuit to attenuate high-frequency signals, which can effectively filter out the high-frequency switching ripples and glitches superimposed in the sampling signal, making the signal collected by the ADC closer to the "average value" or "low-frequency component" of the current, and using the filtered value to calibrate the sampling value, thereby achieving more precise control.
[0013] 2) Based on a circuit design, the filtered values are used to calibrate the real-time channel current value to achieve high-precision sampling.
[0014] 3) It requires only a small number of resistors and capacitors, making the hardware implementation simple. It does not require support for higher sampling rate ADCs or more powerful processors, and it has good robustness. Attached Figure Description
[0015] Figure 1 This is a circuit diagram illustrating the present invention for improving the current sampling accuracy of an inverter.
[0016] Figure 2 The circuit diagram of the filter circuit of this utility model uses a first-order RC filter as a low-pass filter.
[0017] Figure 3 The circuit diagram of the filter circuit of this utility model uses a second-order RC filter as a low-pass filter;
[0018] Figure 4 This is a circuit diagram showing the use of a Sallen-Key filter as a low-pass filter in the filtering circuit of this utility model.
[0019] Figure 5 This is a schematic diagram illustrating the principle of this utility model. Detailed Implementation
[0020] To make the objectives, technical solutions, and advantages of this utility model clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the utility model and are not intended to limit it. Terms such as "upper," "lower," "front," "rear," "left," "right," "bottom," "inner," and "outer," indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the utility model. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the utility model.
[0021] like Figures 1 to 4 The circuit shown is for improving the current sampling accuracy of an inverter. It includes a differential sampling circuit, a filter circuit, and a DSP. The current signal at the inverter sampling point is output as two signals after passing through the differential sampling circuit. One signal is directly output to the AD1 interface of the DSP, and the other signal is processed by the low-pass filter of the filter circuit and output to the AD2 interface of the DSP. The DSP uses the filtered value to calibrate the sampled value to improve the current sampling accuracy of the inverter. The differential sampling circuit includes resistors R1-R4 and an operational amplifier. The non-inverting input terminal Vp of the operational amplifier is connected in series with resistor R3 at the sampling point, and its inverting input terminal Vn is connected in series with resistor R1 at the reference voltage. Resistor R2 is connected in series between Vn and the output Vo of the operational amplifier, and pull-down resistor R4 is connected in parallel between Vi and R3.
[0022] The current signal at the inverter sampling point is a triangular wave current controlled by PWM, and the signal output by the differential sampling circuit is a voltage signal.
[0023] The low-pass filter in the filtering circuit is one of three types: a first-order RC filter, a second-order RC filter, or a Sallen-Key filter. The first-order RC filter includes resistor R5 and capacitor C1; one end of R5 is connected between Vo and the AD1 interface of the DSP, and the other end is connected to the AD2 interface of the DSP; C1 is connected between the AD2 interface of the DSP and signal ground. The second-order RC filter includes resistors R5 and R6, and capacitors C1 and C2; one end of R5 is connected between Vo and the AD1 interface of the DSP, and the other end is connected in series with R6 to the AD2 interface of the DSP; one end of C1 is connected at the junction of R5 and R6, and the other end is connected to signal ground; C2 is connected between signal ground and the AD2 interface of the DSP. The Sallen-Key filter includes an operational amplifier, resistors R5 and R6, and capacitors C1 and C2. One end of R5 is connected between Vo and the AD1 interface of the DSP, and the other end is connected in series with R6 to the non-inverting input Vp of the operational amplifier. One end of C1 is connected at the junction of R5 and R6, and the other end is connected to the inverting input Vn of the operational amplifier. One end of C2 is connected to the non-inverting input Vp of the operational amplifier, and the other end is connected to signal ground. The output of the operational amplifier is connected to the AD2 interface of the DSP.
[0024] Example: A simple, robust, and highly reliable first-order RC filter is used. The acquired voltage signal is processed by a differential sampling circuit and output through an operational amplifier. One signal is directly output to the AD1 interface of the DSP, while the other signal is processed by a first-order RC filter and output to the AD2 interface. The DSP then uses the filtered value to calibrate the sampled value internally.
[0025] like Figure 5 As shown, at times T0 and T1, the current sample values without the filter circuit are both 0, while the sample values with the filter circuit are both greater than 0. These two values are transmitted to the DSP, and by calibrating the sample values using the filtered values, stable power control of the inverter under low current conditions can be achieved. The red dashed line in the figure illustrates the comparison between the current sample values without the filter circuit projected onto the filtered circuit during the T0-T1 time period.
[0026] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions and improvements made within the principles and spirit of the present utility model should be included within the protection scope of the present utility model.
Claims
1. A circuit for improving the accuracy of inverter current sampling, characterized by: The current signal of the inverter sampling point is outputted two ways after the differential sampling circuit, one way is directly outputted to the AD1 interface of the DSP, the other way is outputted to the AD2 interface of the DSP after the low-pass filter of the filter circuit, the sampling value is calibrated by the DSP using the filtered value to improve the inverter current sampling accuracy; wherein the differential sampling circuit comprises resistors R1-R4 and an operational amplifier, the non-inverting input terminal Vp of the operational amplifier is connected in series with the resistor R3 at the sampling point, the inverting input terminal Vn of the operational amplifier is connected in series with the resistor R1 at the reference voltage, the resistor R2 is connected in series between Vn and the output Vo of the operational amplifier, the pull-down resistor R4 is connected in parallel between Vi and R3.
2. The circuit for improving the accuracy of the inverter current sampling of claim 1, wherein: The current signal of the inverter sampling point is a PWM controlled triangular wave current, and the signal outputted by the differential sampling circuit is a voltage signal.
3. The circuit for improving the accuracy of the inverter current sampling of claim 1, wherein: The low-pass filter in the filter circuit is one of a first-order RC filter, a second-order RC filter and a Sallen-Key filter.
4. The circuit for improving the accuracy of the inverter current sampling of claim 3, wherein: The first-order RC filter comprises a resistor R5 and a capacitor C1; wherein one end of R5 is connected between Vo and the AD1 interface of the DSP, and the other end is connected to the AD2 interface of the DSP; C1 is connected between the AD2 interface of the DSP and the signal ground.
5. The circuit for improving the accuracy of the inverter current sampling of claim 3, wherein: The second-order RC filter comprises resistors R5 and R6, and capacitors C1 and C2; wherein one end of R5 is connected between Vo and the AD1 interface of the DSP, and the other end is connected to the AD2 interface of the DSP in series with R6; one end of C1 is connected at the connection of R5 and R6, and the other end is connected to the signal ground, and C2 is connected between the signal ground and the AD2 interface of the DSP.
6. The circuit for improving the precision of the sampling of the inverter current as recited in claim 3, wherein: The Sallen-Key filter comprises an operational amplifier, resistors R5 and R6, and capacitors C1 and C2; wherein one end of R5 is connected between Vo and the AD1 interface of the DSP, and the other end is connected to the non-inverting input terminal Vp of the operational amplifier in series with R6; one end of C1 is connected at the connection of R5 and R6, and the other end is connected to the inverting input terminal Vn of the operational amplifier; one end of C2 is connected to the non-inverting input terminal Vp of the operational amplifier, and the other end is connected to the signal ground; the output of the operational amplifier is connected to the AD2 interface of the DSP.