Current source system

Abstract

A current source system comprises a waveform generation unit, a first circuit, a power tube, a primary switching circuit, a current conversion unit, a small current direct coupling amplification circuit and a power supply unit. The primary switching circuit is used to switch to the current conversion unit when the current output by the power tube is greater than a preset current, and switch to the small current direct coupling amplification circuit when the current is less than or equal to the preset current. The small current direct coupling amplification circuit is used to switch to a matching gear according to the current output by the power tube to output the current and feed back to the pre-circuit through feedback sampling. The power supply unit is used to monitor the current output by the current conversion unit or the small current direct coupling amplification circuit as a current source system output current signal and adjust the power supply frequency. The current source system provided by the embodiment of the application can significantly improve the performance index of a high-end electric energy meter calibration device in terms of small current output stability and power factor accuracy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power measurement, in particular to a current source system. BACKGROUND

[0002] With the accelerated construction of new power systems, high-level gateway electric energy meters as the core measuring instruments for electric power trade settlement, the precision and adaptability of their calibration devices are facing higher requirements. The traditional electric energy meter calibration device has significant limitations in key technical links such as small current stability and power factor control, mainly embodied in:

[0003] 1) The small current output stability problem is prominent: the existing calibration device mostly adopts a single current generation mode of current booster + transformer structure, and in the small current segment below 0.1A, it is limited by hysteresis effect and signal-to-noise ratio degradation, and the output amplitude fluctuation is usually more than ±0.05%, which is difficult to meet the calibration requirements of 0.2S level and above electric energy meters at 1% rated current point (3mA or 15mA);

[0004] 2) The power factor control precision is limited: the traditional calibration device scheme relies on DAC chip to directly generate phase signal, which is limited by device resolution (usually 12-14 bits) and clock jitter (>1ns), and the voltage and current phase adjustment step can only reach 0.01°, and the power factor output error is about ±0.001 (cosφ=1.0). In the extreme low power factor scene (such as 0.1 inductive / capacitive), the phase deviation cumulative effect is significant, which cannot meet the calibration requirements of high-level gateway electric energy meters;

[0005] 3) The device beat frequency interference: the calibration device contains various instruments and wiring slots inside, and the interaction of various frequency signals will produce "beat frequency signals". The signal is superimposed on the current signal to form electromagnetic interference, which is superimposed in the current in the form of "periodic fluctuation", causing the originally smooth current amplitude to fluctuate up and down with the beat frequency, causing error jump. In order to reduce interference, most of the existing calibration devices have made some processing on the wiring, such as using shielded wire for signal line, but for 0.01 level device, the error bias requirement is within 0.002%, which still cannot meet the measurement stability under small current.

[0006] Although there are some researches trying to improve the power supply topology or increase the calibration link to alleviate the above problems, but due to the rigidity of hardware architecture and the lack of algorithm adaptability, it is still difficult to meet the comprehensive needs of high stability and micro phase resolution. SUMMARY

[0007] In view of this, the present application provides a current source system, which aims to solve one or more of the technical problems mentioned in the background technology section.

[0008] In a first aspect, an embodiment of the present application provides a current source system, comprising: a waveform generation unit configured to receive input parameters, generate an analog signal based on the received input parameters, and send the analog signal to a first circuit; the first circuit configured to obtain a driving signal based on the analog signal and a feedback signal, and send the driving signal to a power tube; the power tube configured to output a current based on the driving signal; a primary switching circuit configured to switch to a current conversion unit when the current output by the power tube is greater than a preset current, and switch to a small-current direct-coupled amplification circuit when the current output by the power tube is less than or equal to the preset current; the current conversion unit configured to switch to a matching gear to output a current according to the size of the current output by the power tube, and feed back the output current to the first circuit as a feedback signal; the small-current direct-coupled amplification circuit comprising a main amplification circuit, a push-pull circuit, a feedback sampling operational amplifier circuit, and a feedback sampling switching circuit connected in sequence, and configured to switch to a matching gear to output a current according to the size of the current output by the power tube through the feedback sampling switching circuit, and feed back the output current to the first circuit as a feedback signal; and a power supply unit configured to monitor the current output by the current conversion unit or the small-current direct-coupled amplification circuit as a current source system output current signal, and supply power to the current source system after adjusting the frequency of the power supply according to the current source system output current signal.

[0009] Further, the first circuit comprises: a preamplifier circuit configured to obtain a preamplifier signal based on the analog signal and the feedback signal, and send the preamplifier signal to a driving circuit; and the driving circuit configured to obtain a driving signal based on the preamplifier signal, and send the driving signal to the power tube.

[0010] Further, the waveform generation unit comprises: an MCU configured to receive input parameters, obtain a waveform frequency to be generated by a CPLD based on the received input parameters, send the waveform frequency to the CPLD, and output waveform point data to a signal conditioning circuit according to a received waveform signal; the CPLD configured to receive the waveform frequency, generate a waveform signal based on the waveform frequency, and send the generated waveform signal to the MCU; a magnetic isolation unit arranged between the MCU and the signal conditioning circuit, and configured to suppress mutual interference between digital signals of the MCU and analog signals of the signal conditioning circuit; and the signal conditioning circuit configured to receive the waveform point data of the MCU, and convert the waveform point data into an analog signal output to the first circuit.

[0011] Further, the MCU comprises: a man-machine interface MCU, configured to receive an input parameter in response to a setting operation, and send the received input parameter to the waveform generation MCU; and the waveform generation MCU, configured to receive the input parameter, obtain a waveform frequency required by the CPLD based on the input parameter, and send the waveform frequency to the CPLD, and output waveform point data according to the received waveform signal to the signal conditioning circuit.

[0012] Further, the input parameter comprises an input voltage, an input current, an input phase and an input frequency, and the waveform generation MCU is further configured to: initialize waveform data, obtain sine waveform points and store the sine waveform points in a BaseData[i]=sin(θ×i) array, where θ is a phase angle resolution, i is a waveform point number, i=1, 2…M, and M=360 / θ; obtain initial sequences of the voltage and the current based on the received input voltage, input current and input phase; obtain the waveform frequency required by the CPLD based on the received input frequency, and send the waveform frequency to the CPLD to generate a waveform signal; and output the waveform point data of the voltage and the current in the initial sequences of the voltage and the current to the conditioning circuit based on the received waveform signal generated by the CPLD.

[0013] Further, the obtaining of the waveform frequency required by the CPLD based on the received input frequency comprises: obtaining an output waveform frequency f_out of the CPLD as follows: f_out=3600×f_in, where f_in is the received input frequency.

[0014] Further, the sending of the waveform frequency to the CPLD to generate a waveform signal comprises: sending the waveform frequency to the CPLD, so that the CPLD generates a 0-360KHz waveform signal by performing frequency multiplication f_out=3600×f_in through a phase-locked loop logic.

[0015] Further, the waveform generation MCU is equipped with an FPU unit and a DSP unit.

[0016] Further, the preamplifier circuit is further configured to: superimpose and compare and amplify the analog signal and the feedback signal to obtain a preamplifier signal, and send the preamplifier signal to the driving circuit.

[0017] Further, the driving circuit is further configured to: filter and shape the preamplifier signal, and process the filtered and shaped signal by using a push-pull amplifier to obtain a driving signal, and send the driving signal to the power tube.

[0018] Further, the current conversion unit adopts any one of a current booster or a current transformer.

[0019] Further, the feedback sampling switch circuit comprises N feedback sampling resistors and N-1 relays connected in series, wherein N is a positive integer greater than 1; each feedback sampling resistor is connected in parallel with a relay, except for the feedback sampling resistor connected to the current input end; the current input end and the current output end of the feedback sampling switch circuit are connected to the two input ends of the feedback sampling operational amplifier circuit respectively; the current input end of the feedback sampling switch circuit is also connected to the output end of the push-pull circuit; the output end of the main amplification circuit is connected to the input end of the push-pull circuit; one input end of the main amplification circuit is connected to the output end of the feedback sampling operational amplifier circuit, and the other input end is connected to the ground.

[0020] Further, the small-current direct-coupled amplification circuit comprises N gears, and when the current gear is at the jth gear, j-1 relays close to the current input end are disconnected, and the remaining relays are attracted; wherein j is a positive integer, 1≤j≤N.

[0021] Further, the power supply unit comprises a frequency capture unit, a main control MCU, an IGBT driver, an IGBT, a voltage transformer, and a single-phase rectifier circuit; the frequency capture unit is configured to collect a current source system output current signal, obtain an instantaneous frequency based on the current source system output current signal, and send the instantaneous frequency to the main control MCU; the main control MCU is configured to obtain the instantaneous frequency output by the frequency capture unit and a weak current signal fed back by the voltage transformer, generate and output two-way SPWM drive signals to the IGBT driver based on the instantaneous frequency and the weak current signal; the IGBT driver is configured to receive the two-way SPWM drive signals, perform signal amplification and level matching on the received two-way SPWM drive signals, obtain amplified SPWM drive signals, and output the amplified SPWM drive signals to the IGBT; the IGBT is configured to perform switching actions in response to the amplified SPWM drive signals, output a pulse voltage signal to the low-pass filter; the low-pass filter is configured to receive the pulse signal output by the IGBT, filter the pulse signal output by the IGBT, and output a sinusoidal voltage to power the current source system; the voltage transformer is configured to collect the sinusoidal voltage output by the low-pass filter, convert the collected sinusoidal voltage into a weak current signal, and feed back the weak current signal to the main control MCU; the single-phase rectifier circuit is configured to convert commercial power into a direct-current voltage to provide working power for the IGBT.

[0022] Further, the frequency capture unit is further configured to collect a current source system output current signal to obtain a discrete sampling sequence; based on the discrete sampling sequence, zero-crossing detection and interpolation are adopted to obtain a zero-crossing time; based on the zero-crossing time, an instantaneous frequency is obtained, and the instantaneous frequency is sent to the main control MCU.

[0023] Further, the master MCU is further configured to: acquire an instantaneous frequency output by a frequency capture unit; obtain a minimum frequency difference threshold based on the instantaneous frequency; select a feasible frequency set from a candidate frequency set based on the minimum frequency difference threshold; select an optimal power supply frequency from the feasible frequency set; limit the speed of the optimal power supply frequency to obtain a power supply frequency that needs to be modulated; process a weak electric signal fed back by a voltage transformer based on the power supply frequency that needs to be modulated to obtain an estimated value of a voltage amplitude; perform amplitude closed-loop adjustment based on the estimated value of the voltage amplitude to obtain a control amount of the voltage amplitude; generate and output two-way SPWM driving signals to an IGBT driver based on the power supply frequency that needs to be modulated and the control amount of the voltage amplitude; and return to the step of acquiring the instantaneous frequency output by the frequency capture unit to enter a next control cycle.

[0024] Further, the minimum frequency difference threshold is obtained based on the instantaneous frequency, including: obtaining an estimated value of the instantaneous frequency by exponential smoothing filtering based on the instantaneous frequency; and obtaining the minimum frequency difference threshold based on the estimated value of the instantaneous frequency.

[0025] Further, the optimal power supply frequency is selected from the feasible frequency set, including: calculating a cost function for each frequency in the feasible frequency set, and selecting a frequency that minimizes the cost function as the optimal power supply frequency.

[0026] Further, the estimated value of the voltage amplitude is obtained by processing the weak electric signal fed back by the voltage transformer based on the power supply frequency that needs to be modulated, including: obtaining the estimated value of the voltage amplitude by quadrature demodulation of the weak electric signal fed back by the voltage transformer based on the power supply frequency that needs to be modulated by using a synchronous detection method.

[0027] The current source system provided by the embodiment of the application comprises a waveform generation unit, a first circuit, a power tube, a primary switching circuit, a current conversion unit, a small-current direct-coupled amplification circuit and a power supply unit. Through the cooperation of the above units, the beat frequency interference of the power supply of the testing device on the small-current loop can be effectively eliminated, the performance index of the high-end electric energy meter testing device in terms of small-current output stability and power factor precision can be significantly improved, the testing level of the electric measurement device can be improved, the high-precision, high-stability and high-reliability measurement demand under the background of new power system construction can be supported, the construction of high-level measurement equipment quality evaluation system can be assisted, and the upgrading of high-end electric energy metering device manufacturing can be empowered. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A structure schematic diagram of the current source system according to the embodiment of the application is shown;

[0029] Figure 2Fig. 1 shows a structural schematic diagram of a waveform generating unit according to an embodiment of the present application;

[0030] Figure 3 Fig. 2 shows a structural schematic diagram of a dual-channel 16-bit D / A chip according to an embodiment of the present application;

[0031] Figure 4 Fig. 3 shows an exemplary flow chart of actions performed by a waveform generating MCU according to an embodiment of the present application;

[0032] Figure 5 Fig. 4 shows a structural schematic diagram of a small-current direct-coupled amplification circuit according to an embodiment of the present application;

[0033] Figure 6 Fig. 5 shows a structural schematic diagram of a power supply unit according to an embodiment of the present application;

[0034] Figure 7 Fig. 6 shows an exemplary flow chart of actions performed by a master MCU according to an embodiment of the present application. DETAILED DESCRIPTION

[0035] Reference will now be made to the exemplary embodiments of the present application with reference to the accompanying drawings, however, the present application can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, provided that the present application is fully disclosed and the scope of the present application is sufficiently conveyed to those skilled in the art. The terminology used herein is not intended to limit the present application. In the drawings, the same elements / elements are denoted by the same reference numerals.

[0036] Unless otherwise defined, the terms (including technical terms) used herein have meanings commonly understood by those skilled in the art. In addition, it is to be understood that the terms defined by commonly used dictionaries are to be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art, and are not to be interpreted in an idealized or overly formal sense.

[0037] Figure 1 Fig. 7 shows a structural schematic diagram of a current source system according to an embodiment of the present application.

[0038] As Figure 1 shown, the current source system comprises:

[0039] The waveform generating unit 101 is configured to receive input parameters, generate an analog signal according to the received input parameters, and send the analog signal to the first circuit 102.

[0040] Figure 2 Fig. 1 shows a structural schematic diagram of a waveform generating unit according to an embodiment of the present application. As Figure 2 shown, the waveform generating unit comprises:

[0041] MCU 201, configured to receive input parameters, obtain a waveform frequency required by the CPLD according to the received input parameters, and send the waveform frequency to the CPLD, and output waveform point data according to a received waveform signal to a signal conditioning circuit.

[0042] Further, the MCU 201 comprises:

[0043] The human-machine interface MCU 2011 is configured to receive input parameters in response to a setting operation, and send the received input parameters to the waveform generation MCU.

[0044] The waveform generation MCU 2012 is configured to receive input parameters, obtain a waveform frequency required by the CPLD based on the input parameters, and send the waveform frequency to the CPLD, and output waveform point data according to a received waveform signal to a signal conditioning circuit.

[0045] Specifically, the human-machine interface MCU is configured to realize parameter display and touch interaction, support Modbus RTU / TCP remote communication protocol, process voltage, current and angle values set by the human-machine interface, and send these parameters to the waveform generation MCU.

[0046] The waveform generation MCU is equipped with an FPU unit and a DSP unit, supports floating point operation acceleration, runs a waveform generation algorithm (with a maximum sampling rate of 1.8 MSPS), implements a PID feedback control algorithm, and manages synchronous communication with the CPLD. The waveform generation MCU calculates a square wave frequency required by the CPLD according to a rise source frequency value, and sends the square wave frequency to the CPLD chip. The waveform generation MCU outputs waveform points according to a square wave frequency output by the CPLD.

[0047] The CPLD 202 is configured to receive a waveform frequency, generate a waveform signal based on the waveform frequency, and send the generated waveform signal to the MCU.

[0048] Specifically, the CPLD generates a reference clock based on a 24 MHz crystal oscillator, generates a 0-360 KHz square wave signal according to a rise source frequency, f_out=3600×f_in, f_out is a square wave frequency output by the CPLD, and f_in is a set rise source frequency. The CPLD phase-locked loop (PLL) logic realizes frequency multiplication, ensures frequency division / multiplication accuracy, and avoids phase noise.

[0049] The magnetic isolation unit 203 is arranged between the MCU and the signal conditioning circuit, and is configured to suppress mutual interference between digital signals of the MCU and analog signals of the signal conditioning circuit.

[0050] Specifically, the magnetic isolation unit is used to realize the electrical isolation between the waveform generation MCU and the signal conditioning circuit, suppress common-mode interference, and improve the system anti-electromagnetic interference (EMI) capability.

[0051] The signal conditioning circuit 204 is used to receive the waveform point data of the MCU and convert the waveform point data into an analog signal output to the first circuit.

[0052] Further, the signal conditioning circuit 204 includes a three-phase voltage control signal conditioning circuit 2041 and a three-phase current control signal conditioning circuit 2042.

[0053] Specifically, the three-phase voltage control signal conditioning circuit and the three-phase current control signal conditioning circuit each include a 3-channel dual-channel D / A chip. The D / A chip converts the waveform point data, i.e., voltage and current digital signals, output by the waveform generation MCU into analog signals, such as three-phase voltage and three-phase current waveforms of 0-5V, to provide the required input signals for the current source system.

[0054] Figure 3 A structural schematic diagram of a dual-channel 16-bit D / A chip according to an embodiment of the present application is shown. As shown in Figure 3 The waveform generation MCU sends digital signals to the dual-channel D / A chip through a 16-bit data bus, and the D / A chip converts the digital signals into analog signals. The dual-channel 16-bit D / A chip forms an equivalent 32-bit high-precision digital-to-analog conversion module, and the original signal adjustment fineness is improved from 100ppm to 10ppm. The output signal Us= (D / 2 31 -1) × V ref × R4 / R3, where D is the data amount, V ref is the reference voltage of the D / A chip.

[0055] Further, the input parameters include input voltage, current, phase, and frequency, and the waveform generation MCU is further used to:

[0056] Initialize waveform data to obtain sinusoidal waveform points and store them in a BaseData [i]=sin(θ×i) array, where θ is the phase angle resolution, i is the waveform point number, i=1,2…M, and M=360 / θ.

[0057] Based on the received input voltage, current, and phase, initial sequence points of voltage and current are obtained, and based on the received input frequency, a waveform frequency required by the CPLD to generate a waveform signal is obtained and sent to the CPLD to generate the waveform signal.

[0058] Based on the received waveform signal generated by the CPLD, the waveform point data of voltage and current in the initial sequence of voltage and current are sequentially output to the conditioning circuit.

[0059] Further, based on the received input frequency, the waveform frequency that the CPLD needs to generate is obtained, including:

[0060] The output waveform frequency f_out of the CPLD is obtained as follows:

[0061] f_out=3600×f_in;

[0062] Wherein, f_in is the received input frequency.

[0063] Further, the waveform frequency is sent to the CPLD to generate a waveform signal, including:

[0064] The waveform frequency is sent to the CPLD, so that the CPLD generates a 0-360KHz waveform signal by realizing frequency multiplication f_out=3600×f_in through phase-locked loop logic.

[0065] Figure 4 An exemplary flowchart of the actions performed by the waveform generation MCU according to an embodiment of the present application is shown as follows: Figure 4 As shown, the specific flow of the actions performed by the waveform generation MCU is as follows:

[0066] Step S401: Initialize waveform data.

[0067] Specifically, the discrete data base sequence of the waveform control can be represented as BaseDataXY[i]. Wherein: X (U or I) represents the voltage or current output signal, Y (A, B, C) represents the phase sequence, i represents the waveform point number, i=1, 2…M, M=360 / θ, θ is the phase angle resolution, in order to improve the phase resolution, θ is 0.001°, M takes 360000 points, each point is different by 0.001°, realizing high-precision phase resolution.

[0068] First, the waveform data is initialized, the sine wave waveform points are calculated and stored in the BaseData [i]=sin(θ×i) array, θ is the phase angle resolution, and i is the waveform point number.

[0069] Step S402: Wait for the input parameters of the man-machine interface MCU.

[0070] Specifically, the input parameters of the man-machine interface MCU are waited for, i.e. the upgrade source command, when there is an upgrade source command, step S403 is executed, otherwise the waiting for receiving is continued.

[0071] Step S403: Calculate the initial sequence of each-phase voltage and current.

[0072] Specifically, according to the voltage and current amplitude and phase angle in the received source command, the initial sequence of each phase voltage and current BaseDataUA[i], BaseDataUB[i+ubθ], BaseDataUC[i+ucθ], BaseDataIA[i+iaθ], BaseDataIB[i+ibθ], BaseDataIC[i+icθ] is calculated, wherein ubθ represents the phase angle of voltage UB and UA, ucθ represents the phase angle of voltage UC and UA, iaθ represents the phase angle of current IA and UA, ibθ represents the phase angle of current IB and UB, and icθ represents the phase angle of current IC and UC. At the same time, according to the received frequency parameter, the CPLD generates a pulse signal of 0-360 kHz, f_out=3600xf_in, wherein f_out is the output square wave frequency of the CPLD, and f_in is the source frequency.

[0073] Step S404: outputting the waveform point data to the conditioning circuit.

[0074] Specifically, according to the CPLD control square wave signal, the waveform sequence BaseDataXY is sequentially sent to the conditioning circuit to be converted into an analog signal output.

[0075] The waveform generation unit provided by the above embodiment relies on the double MCU chip cooperative processing architecture and the CPLD logic chip, improves the waveform generation point number, and can effectively solve the technical problem of insufficient accuracy of the conventional 0.02% level and below electric energy meter calibration device waveform generation unit when outputting a low power factor (0.25 and below). The voltage and current phase angle resolution is improved to 0.001°, and under a low power factor, the power factor adjustment fineness can reach 0.000017, so that the accuracy is improved to within 0.01%, and accurate power factor control is realized.

[0076] The first circuit 102 is configured to obtain a driving signal based on the analog signal and the feedback signal, and send the driving signal to the power tube.

[0077] Further, the first circuit 102 comprises:

[0078] The pre-circuit 1021 is configured to obtain a pre-signal based on the analog signal and the feedback signal, and send the pre-signal to the driving circuit.

[0079] Further, the pre-circuit 1021 is further configured to:

[0080] The analog signal and the feedback signal are superimposed, compared, amplified, and the pre-signal is obtained, and the pre-signal is sent to the driving circuit.

[0081] Specifically, the preamplifier circuit is configured to superimpose and amplify the analog signal Vin output by the waveform generating unit and the feedback signal Vfk (a current or voltage feedback signal output by the current converting unit or the small-current direct-coupled amplification circuit) to obtain a driving signal, where Vout=(Vin-Vfk) x Ain, Vout is the output signal, Vin is the analog signal, Vfk is the feedback signal, and Ain is the amplification factor. The signal amplitude is increased to drive the circuit.

[0082] The driving circuit 1022 is configured to obtain a driving signal based on the preamplifier signal and send the driving signal to the power tube.

[0083] Further, the driving circuit is further configured to:

[0084] filter and shape the preamplifier signal, process the filtered and shaped signal using a push-pull amplifier to obtain a driving signal, and send the driving signal to the power tube.

[0085] Specifically, the driving circuit is configured to filter and shape the signal output by the preamplifier circuit to remove high-frequency noise and ensure that the driving signal is clean and reliable. A push-pull amplifier is used to improve the current driving capability of the signal to drive the power tube.

[0086] The power tube 103 is configured to output a current based on the driving signal.

[0087] Specifically, the power tube is configured to convert the DC power energy into the required AC power under the control of the driving signal and output the current through a current conversion mode or a direct-coupled mode.

[0088] The primary switching circuit 104 is configured to switch to the current converting unit when the current output by the power tube is greater than a preset current, and switch to the small-current direct-coupled amplification circuit when the current output by the power tube is less than or equal to the preset current.

[0089] Specifically, the primary switching circuit is configured to automatically switch to the appropriate circuit according to the size of the output current. Preferably, the preset current value is 20 mA, when the current is greater than 20 mA, the power tube output signal is switched to the current converting unit; when the current is less than or equal to 20 mA, the power tube output signal is switched to the small-current direct-coupled amplification circuit.

[0090] The current converting unit 105 is configured to switch to a matching gear to output a current according to the size of the current output by the power tube, and feed back the current output as a feedback signal to the preamplifier circuit.

[0091] Further, the current converting unit uses any one of a current booster or a current transformer.

[0092] Specifically, the output current of the current transformer is between 0.1A-100A, and multiple range gears are built-in, and the appropriate gear is automatically switched according to different currents to ensure the accuracy of the output current.

[0093] The small-current direct-coupled amplification circuit 106 comprises a main amplification circuit, a push-pull circuit, a feedback sampling operational amplifier circuit and a feedback sampling switching circuit connected in sequence, and is used for switching to a matching gear through the feedback sampling switching circuit according to the current size of the power tube output to output the current, and feeding back the current output as a feedback signal to the preamplifier circuit.

[0094] Further, the feedback sampling switching circuit comprises N feedback sampling resistors and N-1 relays connected in series, wherein N is a positive integer greater than 1.

[0095] Among them, except for the feedback sampling resistor of the current input end, each of the remaining feedback sampling resistors is connected in parallel with a relay.

[0096] Among them, the current input end and the current output end of the feedback sampling switching circuit are connected with two input ends of the feedback sampling operational amplifier circuit respectively, the current input end of the feedback sampling switching circuit is also connected with the output end of the push-pull circuit, the output end of the main amplification circuit is connected with the input end of the push-pull circuit, one input end of the main amplification circuit is connected with the output end of the feedback sampling operational amplifier circuit, and the other input end is grounded.

[0097] Further, the small-current direct-coupled amplification circuit comprises N gears, and the small-current direct-coupled amplification circuit is also used for:

[0098] When the current gear is in the jth gear, j-1 relays close to the current input end are disconnected, and the remaining relays are attracted; wherein j is a positive integer, 1≤j≤N.

[0099] Preferably, the number of feedback sampling resistors N=5.

[0100] Figure 5 The structure schematic diagram of the small-current direct-coupled amplification circuit according to one embodiment of the present application is shown. Figure 5As shown, Rf1-Rf5 are feedback sampling resistors, K1-K4 are gear relays, Rf1-Rf5 and K1-K4 constitute a feedback sampling switching circuit 501, operational amplifier A1 and R5, R6 constitute a main amplification circuit 502, operational amplifier A2 and R1-R4 constitute a feedback sampling operational amplifier circuit 503, and the push-pull output of the power tube and R7 constitute a push-pull circuit 504. The total small current is divided into five gears, which are 20 mA, 10 mA, 5 mA, 1 mA and 0.1 mA, and are controlled by K1-K4 relays. When the current gear is 20 mA, the relays K1-K4 are all attracted, and the feedback sampling resistor Rf1 works; when the current gear is 10 mA, the relay K1 is disconnected, and the relays K2-K4 are attracted, and the feedback sampling resistors Rf1 and Rf2 work; when the current gear is 5 mA, the relays K1 and K2 are disconnected, and the relays K3 and K4 are attracted, and the feedback sampling resistors Rf1, Rf2 and Rf3 work; when the current gear is 1 mA, the relays K1-K3 are disconnected, and the relay K4 is attracted, and the feedback sampling resistors Rf1, Rf2, Rf3 and Rf4 work; when the current gear is 0.1 mA, the relays K1-K4 are all disconnected, and the feedback sampling resistors Rf1-Rf5 work; the operational amplifier A1 is a differential operational amplifier, which takes the voltage at the front end of Rf1 and the voltage at the rear end of Rf5, respectively, and R1-R4 and C1, C2 constitute a second-order low-pass filter to reduce the noise input of the feedback signal.

[0101] The power supply unit 107 is used for monitoring the output current of the current conversion unit or the small current direct-coupled amplification circuit, and adjusting the frequency of the power supply after monitoring the output current, and then supplying power to the current source system.

[0102] The above embodiment can effectively solve the problem of frequent small current output "jumping" of the current output unit of the traditional 0.02% level and below electric energy meter calibration device adopting a single current booster or transformer technology route, adapt to the measurement and detection of 1% rated current or below in the scene of gateway meter and high-level electric energy meter, and provide a reference detection capability with an error of less than 0.01%.

[0103] Figure 6 A structure diagram of the power supply unit according to an embodiment of the present application is shown. As shown in the figure, Figure 6 The power supply unit comprises:

[0104] The frequency capture unit 601 is used for acquiring the output current signal of the current source system, obtaining the instantaneous frequency based on the output current signal of the current source system, and sending the instantaneous frequency to the master control MCU.

[0105] Further, the frequency capture unit 601 is also used for:

[0106] acquiring the output current signal of the current source system to obtain a discrete sampling sequence;

[0107] Based on the discrete sampling sequence, zero-crossing detection and interpolation are adopted to obtain the zero-crossing time;

[0108] Based on the zero-crossing time, the instantaneous frequency is obtained, and the instantaneous frequency is sent to the main control MCU.

[0109] Specifically, the sampling rate is f s The current source system outputs the current signal to obtain the discrete sampling sequence x [ n ]When the adjacent sampling points in the sequence satisfy x [ n ]≤0 and x [ n +1]>0, the accurate zero-crossing time is calculated by using the linear interpolation formula t zc As follows:

[0110] ;

[0111] Wherein, T s =1 / f s The sampling interval.

[0112] The period is obtained from the continuous two same direction zero-crossing time t zc,1 、 t zc,2 = T = t zc,1 ― t zc,2 Then the instantaneous frequency is f out =1 / T .

[0113] The main control MCU 602 is used for acquiring the instantaneous frequency output by the frequency capture unit and the weak current signal fed back by the voltage transformer, and generating and outputting two-way SPWM driving signals to the IGBT driver based on the instantaneous frequency and the weak current signal.

[0114] Figure 7 An exemplary flowchart of the actions performed by the main control MCU according to an embodiment of the application is shown as follows: Figure 7 As shown in the flowchart, the main control MCU is also used for:

[0115] Step S701: Acquire the instantaneous frequency output by the frequency capture unit.

[0116] Further, before step S701, it further includes:

[0117] Step S700: initialize system parameters.

[0118] Specifically, according to the need, set the appropriate lower limit of power supply frequency f L , upper limit f H , frequency step Δf , maximum frequency change Δf max , proportional coefficient ρ , absolute threshold δ abs , weight coefficient w 1, w 2, w 3, filter coefficient α , defined frequency f nom , reference amplitude U ref , proportional and integral coefficient K p and K i . The system parameter constraints are as follows:

[0119] Power supply frequency f supply ( f sup ) allowed range: f supply ∈[ f L , f H ];

[0120] Beat frequency f beat Definition: f beat =| f supply ― f out |;

[0121] Control cycle and sampling rate: control update cycle T c 20ms, sampling rate f s 200kS / s;

[0122] Frequency adjustment step and speed limit: frequency step Δf 0.02, maximum change per cycle Δf max 0.1Hz.

[0123] Step S702: based on the instantaneous frequency, get the minimum frequency difference threshold.

[0124] Further, step S702 comprises:

[0125] obtaining an estimated value of the instantaneous frequency by exponential smoothing filtering based on the instantaneous frequency;

[0126] obtaining the minimum frequency difference threshold based on the estimated value of the instantaneous frequency.

[0127] Specifically, the estimated value of the instantaneous frequency is obtained according to the formula

[0128] The minimum frequency difference threshold required at present is calculated according to the formula

[0129] Step S703: screening a feasible frequency set from the candidate frequency set based on the minimum frequency difference threshold.

[0130] Specifically, the candidate frequency set is obtained in advance by the following way: generating a discrete candidate frequency set f L , f H with a step size Δf in the interval . All frequencies not satisfying are eliminated from to obtain the feasible frequency set .

[0131] Step S704: selecting the optimal power supply frequency from the feasible frequency set.

[0132] Further, step S704 comprises:

[0133] calculating a cost function for each frequency in the feasible frequency set, and selecting the frequency making the cost function minimum as the optimal power supply frequency.

[0134] Specifically, the cost function of each frequency is calculated by the following formula:

[0135] ;

[0136] wherein ɛ is a positive constant, preferably ɛ =10 -3 , f nom is the defined frequency w 1、 w 2、 w 3 is a weight coefficient;

[0137] The optimal power supply frequency is selected by the formula .​​

[0138] Step S705: limiting the optimal power supply frequency to obtain the power supply frequency to be modulated.

[0139] Specifically, the difference between the frequency of the previous cycle and the frequency of the current cycle is limited to [-1, 1] to obtain the power supply frequency to be modulated in the current cycle f sup k -1) is limited to [-1, 1] to obtain the power supply frequency to be modulated in the current cycle Δf max Δf max ] to obtain the power supply frequency to be modulated in the current cycle f sup k ) is limited to [-1, 1] to obtain the power supply frequency to be modulated in the current cycle

[0140]

[0141] sat x Δ x limited to [-1, 1]. Δ Δ

[0142] In the above embodiment, by performing the above processes such as exponential smoothing filtering on the instantaneous frequency calculated by the frequency capture unit according to the collected current source system output current signal and cost function selection, the optimal power supply frequency is obtained, and the optimal power supply frequency is limited to output the power supply frequency to be modulated, which effectively avoids the influence of beat frequency.

[0143] Step S706: based on the power supply frequency to be modulated, processing the weak electric signal fed back by the voltage transformer to obtain the estimated value of the voltage amplitude.

[0144] Further, step S706 includes:

[0145] Using the synchronous detection method, the weak electric signal fed back by the voltage transformer is quadrature demodulated based on the power supply frequency to be modulated to obtain the estimated value of the voltage amplitude.

[0146] Specifically, based on the power supply frequency to be modulated in the current cycle f sup k , the quadrature reference is constructed and synchronous detection is performed. Assuming that the window length is N, the angular frequency is , and the weak electric signal fed back by the voltage transformer is the output voltage sampling signal, then the output voltage amplitude estimation value is obtained by the following formula:

[0147] ​​​​​​​​​​​​​

[0148] wherein, U c is the projection component of the output voltage sampling signal in the cosine direction, representing the similarity degree of the component with frequency f sup in the output voltage and the reference cosine signal, U s is the projection component of the output voltage sampling signal in the sine direction, representing the similarity degree of the component with frequency f sup in the output voltage and the reference sine signal.

[0149] Step S707: Based on the estimated value of the voltage amplitude, the amplitude closed-loop adjustment is performed to obtain the control quantity of the voltage amplitude.

[0150] Specifically, the amplitude error is calculated, and the voltage amplitude control quantity u(k) is updated by a discrete PI controller, and the specific updating method is as follows:

[0151] ;

[0152] wherein, the proportional and integral coefficients K p and K i can be set by experiments.

[0153] In the above embodiment, through the voltage amplitude feedback closed-loop adjustment, the influence of the amplitude of the voltage output when adjusting the frequency is effectively avoided, and the amplitude deviation caused by the remaining ripple and the load / temperature drift is suppressed.

[0154] Step S708: Based on the power supply frequency to be modulated and the control quantity of the voltage amplitude, two-way SPWM driving signals are generated and output to the IGBT driver, and the step of acquiring the instantaneous frequency output by the frequency capture unit is returned to enter the next control cycle.

[0155] In the above embodiment, through the real-time monitoring of the current source system output current signal, and based on the monitoring situation, the power supply frequency and the voltage amplitude are adjusted by the frequency adjustment algorithm, which effectively eliminates the beat frequency interference of the power supply of the test device on the small current loop, and significantly improves the small current stability.

[0156] The IGBT driver 603 is used for receiving two-way SPWM driving signals, performing signal amplification and level matching on the received two-way SPWM driving signals, obtaining and outputting amplified SPWM driving signals to the IGBT.

[0157] The IGBT 604 is used for switching in response to the amplified SPWM driving signals, and outputs a pulse voltage signal to the low-pass filter.

[0158] Specifically, the IGBT, as a power switching device, amplifies the SPWM drive signal and outputs a pulse voltage signal.

[0159] The low-pass filter 605 receives the pulse signal output by the IGBT and filters the pulse signal output by the IGBT to output a sinusoidal voltage for powering the current source system.

[0160] Specifically, the low-pass filter is used to filter the high-frequency pulse signal output by the IGBT, filter out the high-order harmonics, extract the fundamental component, and output a pure sinusoidal voltage.

[0161] The voltage transformer 606 is used to collect the sinusoidal voltage output by the low-pass filter and convert the collected sinusoidal voltage into a weak signal and feed it back to the main control MCU.

[0162] Specifically, the voltage transformer is used to sample the output sinusoidal voltage and convert the high-voltage signal into a weak signal through electromagnetic induction principle.

[0163] The single-phase rectifier circuit 607 is used to convert the mains into a direct current voltage to provide a working power supply for the IGBT.

[0164] Specifically, the power supply unit is used to output a frequency-adjustable voltage after rectification, inversion, and low-pass filtering of the mains to power the entire current source. The power supply system adopts an intelligent frequency conversion method, monitors the frequency of the output current in real time, and adjusts the frequency of the current source power supply to minimize the interference of the mains on the current.

[0165] Specific implementation process: The mains input is converted into a direct current voltage by the single-phase rectifier circuit to provide a working power supply for the IGBT. The main control MCU generates two SPWM drive signals to the IGBT driver based on the voltage signal and frequency signal fed back by the voltage transformer to control the switching action of the IGBT module. After processing by the low-pass filter, a 220V, 45-55Hz continuously adjustable alternating voltage is output to power the current source. The voltage transformer converts the output 220V voltage signal into a weak signal in real time for the main control MCU to collect and monitor with high precision. The main control MCU dynamically adjusts the output frequency of the power supply voltage by tracking the actual frequency of the current source output current in real time to ensure that the frequency of the current source power supply and the frequency of the output current maintain a frequency difference of about 5%, fundamentally suppressing the beat frequency interference under small current conditions and ensuring the stability of the output current.

[0166] The above embodiment provides a current source system, which comprises a waveform generation unit, a first circuit, a power tube, a primary switching circuit, a current conversion unit, a small current direct-coupled amplification circuit and a power supply unit. Through the cooperation of the above units, the beat frequency interference of the power supply of the testing device on the small current loop can be effectively eliminated, the performance index of the high-end electric energy meter testing device in terms of small current output stability and power factor accuracy can be significantly improved, the electric measurement device testing level is improved, the high-precision, high-stability and high-reliability measurement demand under the background of new power system construction is supported, the high-level measurement equipment quality evaluation system is constructed, and the high-end electric energy metering device manufacturing is upgraded.

[0167] The application has been described by reference to a few embodiments. However, as will be apparent to those skilled in the art in light of the disclosure, some modifications thereof can be made without departing from the scope of the application as defined in the appended patent claims.

[0168] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a" or "an" means "at least one" unless otherwise clearly indicated by the context of the only language "the". The steps of any method disclosed herein need not be performed in the exact order disclosed, unless explicitly stated.

[0169] Those skilled in the art will appreciate that embodiments of the application can be supplied as a method, a system, or a computer program product. Accordingly, the application can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the application can take the form of a computer program product on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) embodying computer readable program code thereon.

[0170] The application is described with reference to the flowcharts and / or block diagrams of the methods, apparatus (systems) and computer program products according to embodiments of the application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, as well as combinations of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing apparatus to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing apparatus produce a means for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 The flow or multiple flows and / or blocks Figure 1 The device that implements the functions specified in the flow or multiple flows and / or blocks

[0171] These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the flow Figure 1 The functions specified in the flow or flows and / or blocks Figure 1 The functions specified in the flow or flows and / or blocks

[0172] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flow Figure 1 The functions specified in the flow or flows and / or blocks Figure 1 The functions specified in the flow or flows and / or blocks

[0173] Finally, it should be noted that the above-mentioned embodiments are merely used to illustrate the technical solutions of the present application, rather than limit the present application. Although the present application has been described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and any modification or replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.

Claims

1. A current source system, characterized in that, include: A waveform generation unit is used to receive input parameters, generate an analog signal based on the received input parameters, and send the analog signal to the first circuit. The first circuit is used to obtain a drive signal based on the analog signal and the feedback signal, and send the drive signal to the power transistor; The power transistor is used to output current based on the drive signal; A switching circuit is used to switch to the current conversion unit when the current output by the power transistor is greater than the preset current, and to switch to the low-current direct-coupled amplifier circuit when the current output by the power transistor is less than or equal to the preset current. The current conversion unit is used to switch to the matching range according to the magnitude of the current output by the power transistor to output current, and feeds the output current back to the preamplifier circuit as a feedback signal. The low-current direct-coupled amplifier circuit includes a main amplifier circuit, a push-pull circuit, a feedback sampling operational amplifier circuit, and a feedback sampling switching circuit connected in sequence. It is used to switch to the matching range to output current according to the magnitude of the current output by the power transistor, and feed the output current back to the preamplifier circuit as a feedback signal. The power supply unit is used to monitor the current output by the current conversion unit or the small current direct coupling amplifier circuit as the output current signal of the current source system, and to supply power to the current source system after adjusting the power supply frequency according to the output current signal of the current source system. The power supply unit includes: The frequency acquisition unit is used to acquire the output current signal of the current source system, obtain the instantaneous frequency based on the output current signal of the current source system, and send the instantaneous frequency to the main control MCU; The main control MCU is used to acquire the instantaneous frequency output by the frequency acquisition unit and the weak current signal fed back by the voltage transformer. Based on the instantaneous frequency and the weak current signal, it generates and outputs two SPWM drive signals to the IGBT driver. The IGBT driver is used to receive two SPWM drive signals, amplify and level match the received two SPWM drive signals, and then output the amplified SPWM drive signal to the IGBT. IGBT is used to switch in response to the amplified SPWM drive signal and output pulse voltage signal to low-pass filter; The low-pass filter is used to receive the pulse signal output by the IGBT and filter the pulse signal output by the IGBT, and output a sinusoidal voltage to power the current source system. The voltage transformer is used to acquire the sinusoidal voltage output from the low-pass filter and convert the acquired sinusoidal voltage into a weak electrical signal before feeding it back to the main control MCU. A single-phase rectifier circuit is used to convert AC power into DC voltage to provide operating power to IGBTs.

2. The current source system according to claim 1, characterized in that, The first circuit includes: A preamplifier circuit is used to obtain a preamplifier signal based on the analog signal and the feedback signal, and to send the preamplifier signal to the drive circuit. A driving circuit is used to obtain a driving signal based on the preamplifier signal and send the driving signal to the power transistor.

3. The current source system according to claim 1, characterized in that, The waveform generating unit includes: The MCU is used to receive input parameters, obtain the waveform frequency to be generated by the CPLD based on the received input parameters, send the waveform frequency to the CPLD, and output waveform point data to the signal conditioning circuit based on the received waveform signal. The CPLD is used to receive the waveform frequency, generate a waveform signal based on the waveform frequency, and send the generated waveform signal to the MCU. A magnetic isolation unit is placed between the MCU and the signal conditioning circuit to suppress mutual interference between the digital signals of the MCU and the analog signals of the signal conditioning circuit. The signal conditioning circuit is used to receive waveform point data from the MCU and convert the waveform point data into an analog signal for output to the first circuit.

4. The current source system according to claim 3, characterized in that, The MCU includes: The human-machine interface MCU is used to respond to setting operations, receive input parameters, and send the received input parameters to the waveform generation MCU. The waveform generating MCU is used to receive the input parameters, obtain the waveform frequency to be generated by the CPLD based on the input parameters, send the waveform frequency to the CPLD, and output waveform point data to the signal conditioning circuit according to the received waveform signal.

5. The current source system according to claim 4, characterized in that, The input parameters include input voltage, current, phase, and frequency. The waveform generator MCU is also used for: Initialize waveform data, obtain sine wave waveform points and store them in the array BaseData[i]=sin(θ×i), where θ is the phase angle resolution, i is the number of waveform points, i=1,2…M, M=360 / θ; Based on the received input voltage, current and phase, an initial sequence of voltage and current is obtained, and based on the received input frequency, the waveform frequency to be generated by the CPLD is obtained, and the waveform frequency is sent to the CPLD to generate a waveform signal; Based on the waveform signal received from the CPLD, the waveform data of voltage and current in the initial sequence of voltage and current are sequentially output to the conditioning circuit.

6. The current source system according to claim 5, characterized in that, The process of obtaining the waveform frequency to be generated by the CPLD based on the received input frequency includes: The output waveform frequency f_out of the CPLD is obtained as follows: f_out = 3600 × f_in; Where f_in is the received input frequency.

7. The current source system according to claim 6, characterized in that, Sending the waveform frequency to the CPLD to generate a waveform signal includes: The waveform frequency is sent to the CPLD, so that the CPLD can perform frequency multiplication f_out=3600×f_in through phase-locked loop logic to generate a 0-360KHz waveform signal.

8. The current source system according to claim 4, characterized in that, The waveform generating MCU is equipped with an FPU unit and a DSP unit.

9. The current source system according to claim 2, characterized in that, The preamplifier circuit is also used for: The analog signal and the feedback signal are superimposed, compared, and amplified to obtain a preamplifier signal, which is then sent to the drive circuit.

10. The current source system according to claim 2, characterized in that, The driving circuit is also used for: The preamplifier signal is filtered and shaped, and a push-pull amplifier is used to process the filtered and shaped signal to obtain a drive signal, which is then sent to the power transistor.

11. The current source system according to claim 1, characterized in that, The current conversion unit can be either a current booster or a current transformer.

12. The current source system according to claim 1, characterized in that, The feedback sampling switching circuit includes: N feedback sampling resistors and N-1 relays connected in series, where N is a positive integer greater than 1; Except for the feedback sampling resistor at the current input terminal, each of the other feedback sampling resistors is connected in parallel with a relay. The current input and current output terminals of the feedback sampling switching circuit are connected to the two input terminals of the feedback sampling operational amplifier circuit, respectively. The current input terminal of the feedback sampling switching circuit is also connected to the output terminal of the push-pull circuit. The output terminal of the main amplifier circuit is connected to the input terminal of the push-pull circuit. One input terminal of the main amplifier circuit is connected to the output terminal of the feedback sampling operational amplifier circuit, and the other input terminal is grounded.

13. The current source system according to claim 12, characterized in that, The low-current direct-coupled amplifier circuit includes N ranges, and is also used for: When the current setting is at the j-th setting, the j-1 relays closest to the current input terminal are disconnected, and the remaining relays are energized; where j is a positive integer, 1≤j≤N.

14. The current source system according to claim 1, characterized in that, The frequency acquisition unit is further configured to: The output current signal of the current source system is acquired to obtain a discrete sampling sequence; Based on the discrete sampling sequence, zero-crossing detection and interpolation are used to obtain the zero-crossing time. Based on the zero-crossing moment, the instantaneous frequency is obtained and sent to the main control MCU.

15. The current source system according to claim 1, characterized in that, The main control MCU is also used for: Acquire the instantaneous frequency output by the frequency capture unit; Based on the instantaneous frequency, the minimum frequency difference threshold is obtained; Based on the minimum frequency difference threshold, a feasible frequency set is obtained by filtering from the candidate frequency set; The optimal power supply frequency is selected from the set of feasible frequencies; The optimal power supply frequency is speed-limited to obtain the power supply frequency that needs to be modulated; Based on the power supply frequency that needs to be modulated, the weak electrical signal fed back by the voltage transformer is processed to obtain an estimated value of the voltage amplitude. Based on the estimated voltage amplitude, closed-loop amplitude regulation is performed to obtain the control quantity of the voltage amplitude; Based on the required modulation power supply frequency and the control quantity of the voltage amplitude, two SPWM drive signals are generated and output to the IGBT driver. Return to the step of acquiring the instantaneous frequency output by the frequency acquisition unit and proceed to the next control cycle.

16. The current source system according to claim 15, characterized in that, The process of obtaining the minimum frequency difference threshold based on the instantaneous frequency includes: Based on the instantaneous frequency, an estimated value of the instantaneous frequency is obtained through exponential smoothing filtering; Based on the estimated instantaneous frequency, the minimum frequency difference threshold is obtained.

17. The current source system according to claim 15, characterized in that, Selecting the optimal power supply frequency from the set of feasible frequencies includes: For each frequency in the feasible frequency set, calculate the cost function and select the frequency that minimizes the cost function as the optimal power supply frequency.

18. The current source system according to claim 15, characterized in that, Based on the required modulated power supply frequency, the weak current signal fed back from the voltage transformer is processed to obtain an estimated value of the voltage amplitude, including: Using the synchronous detection method, the weak electrical signal fed back from the voltage transformer is quadraturely demodulated based on the power supply frequency that needs to be modulated, and an estimated value of the voltage amplitude is obtained.

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