High-precision ac electronic load control system and method

Abstract

The application provides a high-precision AC electronic load control system and method, and belongs to the field of test equipment of AC electronic load simulation, which comprises the following steps: obtaining the capacitor voltage U on the capacitor C of an LC filter c ; calculating the current instruction value of the inductance L of the LC filter 10 to obtain the current sampling value i of the inductance L of the LC filter L ; comparing the current instruction value of the inductance L with the current sampling value i of the inductance L L ; inputting the PR controller for calculation; obtaining the voltage U of the bus capacitor C2 d ; performing proportional calculation on U c and U d ; taking the ratio of U c to U d as compensation and adding and subtracting the ratio from the output value of the PR controller to output the duty ratio for controlling the on-off of the switch tube; the inductance current single-loop control is combined with the output voltage compensation, and the external output current does not need to be sampled.

Description

Technical Field

[0001] This invention relates to the field of testing equipment technology for AC electronic load simulation, specifically to a control system and method for a high-precision AC electronic load. Background Technology

[0002] AC electronic load simulation testing equipment is widely used in applications such as load testing of AC motor controllers, frequency converters, and AC analog power supplies, specific power factor load simulation, and aging testing. An AC electronic load is essentially a power electronic device capable of controlling the amplitude and phase of AC current. Compared to traditional energy-consuming loads such as R / RC / RL, AC electronic loads offer flexible applications such as constant current, constant resistance, and constant power, while also feeding energy back to the grid, achieving energy conservation and environmental protection. The paper "Research on Single-Phase Energy-Feeding AC Electronic Loads" (Communication Power Technology, Li Zhao, Shi Yanfei, Rizhao No.1 Middle School, Rizhao Key Laboratory, January 25, 2017) addresses the problems of low accuracy, slow dynamic response, and poor simulation effect of traditional control methods for energy-feeding AC electronic loads by applying repetitive +P control to the design of the load simulation side current controller. The analog converter uses single-current-loop control, while the grid-connected converter uses a dual closed-loop control system with an inner current loop and an outer voltage loop incorporating a secondary notch filter. This allows the energy-feeding AC electronic load to accurately simulate a real load and feed energy back to the grid at a unit power factor, achieving energy conservation.

[0003] Its original design purpose was for factory testing of AC power supplies or motor controllers. Compared with the disadvantages of traditional real RLC devices, such as high energy consumption, low automation, and unchanging adjustment, AC electronic loads that simulate RLC characteristics can make testing simpler, more flexible, and reduce test costs.

[0004] High dynamic performance and high steady-state accuracy are core indicators for AC electronic loads. To reduce output current ripple and improve external voltage sampling accuracy, electronic loads typically use an external LC filter. High-precision output current control is achieved by sampling the external load's output current. Most control methods employ an outer loop for output current and an inner loop for inductor current. This approach offers high accuracy in current amplitude and phase, using a dual-loop control strategy to control both the output current amplitude and phase. However, this method suffers from low current control gain, large output current amplitude and phase errors, and poor dynamic performance. Improving current dynamics by using fast power devices such as SiC / MOSFETs significantly increases system cost. Another approach is to directly control the amplitude and phase of the inductor current. This method offers high current dynamics, but the presence of the LC filter introduces a phase difference between the inductor current and the output current, making it difficult to guarantee the output current's phase. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to achieve high dynamic and high precision control of the output current amplitude and phase by sampling the capacitor voltage and inductor current of the filter of the AC electronic load.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0007] A high-precision AC electronic load control system, characterized in that it includes: an AC power supply under test e1 or a motor controller, an AC electronic load circuit, and a power grid e2;

[0008] The AC electronic load circuit includes: an LC filter, a PWM full-bridge inverter circuit, a PWM full-bridge rectifier circuit, and a bus capacitor C2;

[0009] The PWM full-bridge inverter circuit and the LC filter serve as a simulated load for testing the AC power supply e1 under test. The voltage U across the bus capacitor C2 is measured by the PWM full-bridge rectifier circuit. d Voltage regulation is implemented, and excess energy is fed back to the grid (e2).

[0010] A control method for a high-precision AC electronic load control system, the control method comprising:

[0011] S1. Obtain the capacitor voltage U across the capacitor C of the LC filter. c ;

[0012] S2. Calculate the current command value of the inductor L of the LC filter.

[0013] S3. Obtain the current sampling value i of the inductor L of the LC filter. L The current command value of the inductor L The current sampling value i of the inductor L L After comparison, the data is input into the PR controller for calculation;

[0014] S4. Obtain the voltage U of the bus capacitor C2. d The capacitor voltage U c and the voltage U of the bus capacitor C2 d Perform proportional calculations and convert the capacitor voltage U c The voltage U of the bus capacitor C2 d The ratio is used as the output voltage feedforward compensation. After adding or subtracting the output value of the PR controller, the output duty cycle is used to control the on / off state of the switching transistor in the PWM full-bridge inverter circuit of the AC electronic load.

[0015] Beneficial effects: This invention transforms the amplitude and phase control of the external output current into the amplitude and phase control of the internal inductor current; it changes the dual-loop control (outer loop of output current, inner loop of current sensing) to single-loop control (closed loop of current sensing only), making the control simple and reliable, and ensuring that the amplitude and phase errors of the controlled variable are minimized; the addition of output voltage compensation control reduces the burden on the PR controller and further improves the accuracy of the controlled current. The control method mainly uses single-loop PR control of the inductor current, which improves the dynamic performance of the current; combined with output voltage compensation, it improves the rapid response to voltage disturbances. The single-loop inductor current uses a PR controller, supplemented by output voltage feedforward compensation, which is simple to control, has high current dynamic performance, and small error.

[0016] Further, in step S1, the capacitor voltage U across the capacitor C of the LC filter is obtained. c The method is as follows:

[0017] The capacitor voltage U across capacitor C is obtained through sampling and phase-locking. c ;

[0018]

[0019] In the formula U rms ω is the effective voltage value of the external AC voltage source, w is the voltage angular frequency, and wt+θ1 is the phase-locked phase of the external AC source.

[0020] Further, in step S2, the current command value I of the inductor L of the LC filter is calculated. Lref The method is as follows:

[0021] S21. The user inputs the power factor PF value of the load current, and then calculates the corresponding power factor angle θ, or the user directly provides the power factor angle θ:

[0022] θ = acos(PF) Formula (2)

[0023] Among them, PF is greater than 0 for inductive load, PF is less than 0 for capacitive load, and PF = 1 for resistive load;

[0024] S22, User input current RMS value command I rms Then the corresponding instantaneous value instruction I oref for

[0025]

[0026] In the formula, θ is the capacitor voltage U across the capacitor C of the LC filter obtained by formula (2). c The phase difference of the current;

[0027] S23. Calculate the reactive current consumed by the capacitor C of the LC filter:

[0028]

[0029] Substituting formula (1) into formula (4) yields:

[0030]

[0031] In the formula, C is the capacitance value of the LC filter, and the unit is farad;

[0032] S24. Calculate the current command value of the inductor L of the LC filter. for:

[0033]

[0034] Substituting formulas (3) and (5) into formula (6) yields:

[0035]

[0036] In the formula I rms The effective value of the input current is given by the user, wt+θ1 is the phase lock phase of the external AC source, w is the voltage angular frequency, λ is the power factor angle, and C is the capacitance value of the LC filter.

[0037] Beneficial Effects: This invention proposes a novel control strategy. A current conversion method converts an output current command with one amplitude and phase into an inductor current command with another amplitude and phase. By sampling the capacitor voltage and inductor current of the LC filter of the AC electronic load, high dynamic and high-precision control of the output current amplitude and phase is achieved. Simultaneously, eliminating the need for output current sampling reduces system costs. Indirect control of the output current amplitude and phase at the front end of the LC filter is achieved through direct control of the inductor current at the back end of the AC electronic load's LC filter. This eliminates the need for an output current sampling sensor; the output side only samples the capacitor voltage and inductor current of the LC filter to achieve amplitude and phase control of the output current. The topology is simple, reliable, and low-cost.

[0038] Furthermore, the transfer function of the PR controller in step S3 is:

[0039]

[0040] In the formula, Kp is the proportional coefficient of the controller, Kr is the resonant term coefficient, w0 is the resonant frequency, and w c It is the ring width frequency.

[0041] Beneficial effects: In this invention, the PR controller has an infinite control gain at the center frequency, ensuring that the amplitude and phase error of the current induction control are minimized.

[0042] Furthermore, the switching transistor in the AC electronic load circuit is an IGBT.

[0043] Beneficial effects: This invention uses IGBTs, which have low cost and high current carrying capacity, as switching devices to increase the single-unit capacity of AC electronic loads, improve system steady-state performance, and reduce system costs. Using commonly used low-switching-frequency, conventional IGBTs (compared to MOSFETs / SiCs) as power devices to simulate high-power load current simplifies hardware and software driving, further reduces costs, facilitates market promotion, and provides a simple and reliable control loop.

[0044] Compared with the prior art, the present invention provides a high-precision control method for AC electronic loads, which has the following advantages:

[0045] 1. This invention transforms the amplitude and phase control of the external output current into the amplitude and phase control of the internal inductor current; it changes the dual-loop control (outer loop of output current, inner loop of current sensing) to single-loop control (closed loop of current sensing only), making the control simple and reliable, and ensuring that the amplitude and phase errors of the controlled variable are minimized; the addition of output voltage compensation control reduces the burden of PR control and further improves the accuracy of the controlled current. The control method mainly uses single-loop PR control of the inductor current, which improves the dynamic performance of the current; combined with output voltage compensation, it improves the fast response to voltage disturbances. The single-loop inductor current uses PR control, supplemented by output voltage feedforward compensation, which is simple to control, has high current dynamic performance, and small error.

[0046] 2. This invention proposes a novel control strategy: a current conversion method that converts an output current command with one amplitude and phase into an inductor current command with another amplitude and phase. By sampling the capacitor voltage and inductor current of the LC filter of the AC electronic load, high dynamic and high-precision control of the output current amplitude and phase is achieved. Simultaneously, eliminating the need for output current sampling reduces system costs. Indirect control of the output current amplitude and phase at the front end of the LC filter is achieved through direct control of the inductor current at the back end of the AC electronic load's LC filter. This eliminates the need for an output current sampling sensor; the output side only samples the capacitor voltage and inductor current of the LC filter to achieve amplitude and phase control of the output current. The topology is simple, reliable, and low-cost.

[0047] 3. In this invention, the PR controller has an infinite control gain at the center frequency, which can ensure that the amplitude and phase error of the current sensing control are minimized.

[0048] 4. This invention uses IGBTs, which have low cost and high current carrying capacity, as switching devices to increase the single-unit capacity of AC electronic loads, improve system steady-state performance, and reduce system costs. Using commonly used low-switching-frequency, conventional IGBTs (compared to MOSFETs / SiCs) as power devices to simulate high-power load current simplifies hardware and software driving, further reduces costs, facilitates market adoption, and provides a simple and reliable control loop. Attached Figure Description

[0049] Figure 1 This is a schematic diagram illustrating the application of the AC electronic load of the present invention;

[0050] Figure 2 This is a topology diagram of the AC electronic load of the present invention;

[0051] Figure 3 This is a block diagram of the inductor current control of the AC electronic load in Embodiment 2 of the present invention;

[0052] Figure 4 This is a block diagram of the inductor current control of an AC electronic load with added output voltage feedforward compensation in Embodiment 3 of the present invention;

[0053] Figure 5 This is the simulation waveform diagram corresponding to the closed-loop control block diagram of the inductor current of the AC electronic load in Embodiment 2 of the present invention;

[0054] Figure 6 This is the simulation waveform diagram corresponding to the inductor current control block diagram of the AC electronic load with added output voltage feedforward compensation in Embodiment 3 of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0057] Example 1

[0058] like Figure 1-2 As shown, the application of AC electronic load consists of three parts: AC power supply or motor controller under test, AC electronic load, and power grid, with energy fed back to the power grid.

[0059] A high-precision AC electronic load control system includes: an AC power supply under test e1 or a motor controller, an AC electronic load circuit, and a power grid e2;

[0060] The AC electronic load circuit includes: an LC filter 10, a PWM full-bridge inverter circuit 20, a PWM full-bridge rectifier circuit 30, and a bus capacitor C2;

[0061] The PWM full-bridge inverter circuit 20 and LC filter 10 are used as simulated loads to test the AC power supply e1 under test. The voltage U of the PWM full-bridge rectifier circuit 30 to the bus capacitor C2 is... d Voltage regulation is implemented, and excess energy is fed back to the grid (e2).

[0062] Example 2

[0063] A control method for a high-precision AC electronic load control system, the control method comprising:

[0064] Step 1: Calculate the current command value of inductor L of LC filter 10.

[0065] Specifically, the current command value of the inductor L of the LC filter 10 is calculated. The method is as follows:

[0066] A. The user inputs the power factor PF value of the load current, and then calculates the corresponding power factor angle θ, or the user directly provides the power factor angle θ:

[0067] θ = acos(PF) Formula (2)

[0068] Among them, PF is greater than 0 for inductive load, PF is less than 0 for capacitive load, and PF = 1 for resistive load.

[0069] B. User input current RMS value command I rms Then the corresponding instantaneous value instruction I oref for

[0070]

[0071] In the formula, λ is the phase difference of the current obtained by formula (2) (relative to the capacitor voltage Y on capacitor C of LC filter 10). c ).

[0072] C. Calculate the reactive current consumed by capacitor C of LC filter 10:

[0073]

[0074] Substituting formula (1) into formula (4) yields:

[0075]

[0076] In the formula, C is the capacitance value of the LC filter 10, and the unit is farad.

[0077] D. Calculate the current command value of inductor L of LC filter 10. for:

[0078]

[0079] Substituting formulas (3) and (5) into formula (6) yields:

[0080]

[0081] In the formula I rms The input current is the effective value, wt+θ1 is the phase of the external AC source, w is the voltage angular frequency, θ is the power factor angle, and C is the capacitance value of the capacitor C of the LC filter 10.

[0082] Step Two, Refer to Figure 3 Obtain the current sampling value i of the inductor L of LC filter 10. L The current command value of inductor L The current sampling value i of inductor L L After comparison, the input is processed by the PR controller, which outputs the duty cycle to control the switching of the transistors in the PWM full-bridge inverter circuit 20 of the AC electronic load. The PR controller has infinite control gain at the center frequency, ensuring that the amplitude and phase error of the current-sensing control are minimized.

[0083] The transfer function of the PR controller is:

[0084]

[0085] In the formula, Kp is the proportional coefficient of the controller, Kr is the resonant term coefficient, w0 is the resonant frequency, and w c It is the ring width frequency.

[0086] In practice, e1 might be an SPWM square wave emitted by a motor controller, etc. This SPWM square wave cannot be sampled to obtain its actual corresponding voltage. Typically, an LC filter is used to filter the SPWM square wave into a sine wave for easier sampling; therefore, LC filters have wider applicability. Furthermore, even if the external voltage e1 is a standard sine wave, due to the large amount of interference in high-power power supplies, a capacitor C is used at the load end to filter out some interference noise. The U of this application... c This corresponds to the voltage of the external source e1 after noise is filtered out.

[0087] This invention proposes a novel control strategy: a current conversion method that converts an output current command with one amplitude and phase into an inductor current command with another amplitude and phase. By sampling the capacitor voltage and inductor current of the LC filter of the AC electronic load, high dynamic and high-precision control of the output current amplitude and phase is achieved. Simultaneously, eliminating the need for output current sampling reduces system cost. Furthermore, by directly controlling the inductor current at the downstream end of the LC filter of the AC electronic load, indirect control of the output current amplitude and phase at the upstream end of the LC filter is achieved. This eliminates the need for an output current sampling sensor; the output side only samples the capacitor voltage and inductor current of the LC filter to achieve amplitude and phase control of the output current. The topology is simple, reliable, and low-cost.

[0088] This invention employs IGBTs, which have low cost and high current carrying capacity, as switching devices to increase the single-unit capacity of AC electronic loads, improve system steady-state performance, and reduce system costs. Using commonly used low-switching-frequency, conventional IGBTs (compared to MOSFETs / SiCs) as power devices to simulate high-power load current simplifies hardware and software driving, further reduces costs, facilitates market adoption, and provides a simple and reliable control loop.

[0089] Example 3

[0090] See Figure 4 This embodiment provides a control method for a high-precision AC electronic load control system, the control method comprising:

[0091] Step 1: Obtain the capacitor voltage U across capacitor C of LC filter 10. c ;

[0092] Specifically, the capacitor voltage U across capacitor C of LC filter 10 is obtained. c The method is as follows: the capacitor voltage U across capacitor C is obtained through sampling and phase-locked loop. c ;

[0093]

[0094] In the formula U rms ω is the effective voltage value of the external AC voltage source, w is the voltage angular frequency, and wt+θ1 is the phase-locked phase of the external AC source.

[0095] Step 2: Calculate the current command value of inductor L of LC filter 10.

[0096] Specifically, the current command value of the inductor L of the LC filter 10 is calculated. The method is as follows:

[0097] A. The user inputs the power factor PF value of the load current, and then calculates the corresponding power factor angle θ, or the user directly provides the power factor angle θ:

[0098] θ = acos(PF) Formula (2)

[0099] Among them, PF is greater than 0 for inductive load, PF is less than 0 for capacitive load, and PF = 1 for resistive load.

[0100] B. User input current RMS value command I rms Then the corresponding instantaneous value instruction I oref for

[0101]

[0102] In the formula, θ is the phase difference of the current obtained by formula (2) (relative to the capacitor voltage U on capacitor C of LC filter 10). c ).

[0103] C. Calculate the reactive current consumed by capacitor C of LC filter 10:

[0104]

[0105] Substituting formula (1) into formula (4) yields:

[0106]

[0107] In the formula, C is the capacitance value of the LC filter 10, and the unit is farad.

[0108] D. Calculate the current command value of inductor L of LC filter 10. for:

[0109]

[0110] Substituting formulas (3) and (5) into formula (6) yields:

[0111]

[0112] In the formula I rms The input current is the effective value, wt+θ1 is the phase of the external AC source, w is the voltage angular frequency, λ is the power factor angle, and C is the capacitance value of the LC filter 10.

[0113] Step 3, Refer to Figure 3 Obtain the current sampling value i of the inductor L of LC filter 10. L The current command value of inductor L The current sampling value i of inductor L LAfter comparison, the data is input to the PR controller for calculation. The PR controller has infinite control gain at the center frequency, which ensures that the amplitude and phase error of the current induction control are minimized.

[0114] The transfer function of the PR controller is:

[0115]

[0116] In the formula, Kp is the proportional coefficient of the controller, Kr is the resonant term coefficient, w0 is the resonant frequency, and w c It is the ring width frequency.

[0117] Step 4: Obtain the voltage U of bus capacitor C2. d , the capacitor voltage U c The voltage U of the bus capacitor C2 d Perform proportional calculations and assign U c / U d The output duty cycle is calculated by adding or subtracting the output value of the PR controller to compensate for the output voltage feedforward, and then controls the switching of the switching transistors in the PWM full-bridge inverter circuit 20 in the AC electronic load.

[0118] In practice, e1 might be an SPWM square wave emitted by a motor controller, etc. This SPWM square wave cannot be sampled to obtain its actual corresponding voltage. Typically, an LC filter is used to filter the SPWM square wave into a sine wave for easier sampling, thus making the LC filter more adaptable. Furthermore, even if the external voltage e1 is a standard sine wave, due to the large amount of interference in high-power power supplies, a capacitor C is used at the load end to filter out some interference noise. The U of this application... c This corresponds to the voltage of the external source e1 after noise is filtered out.

[0119] This invention proposes a novel control strategy: a current conversion method that converts an output current command with one amplitude and phase into an inductor current command with another amplitude and phase. By sampling the capacitor voltage and inductor current of the LC filter of the AC electronic load, high dynamic and high-precision control of the output current amplitude and phase is achieved. Simultaneously, eliminating the need for output current sampling reduces system cost. Furthermore, by directly controlling the inductor current at the downstream end of the LC filter of the AC electronic load, indirect control of the output current amplitude and phase at the upstream end of the LC filter is achieved. This eliminates the need for an output current sampling sensor; the output side only samples the capacitor voltage and inductor current of the LC filter to achieve amplitude and phase control of the output current. The topology is simple, reliable, and low-cost.

[0120] This invention employs IGBTs, which have low cost and high current carrying capacity, as switching devices to increase the single-unit capacity of AC electronic loads, improve system steady-state performance, and reduce system costs. Using commonly used low-switching-frequency, conventional IGBTs (compared to MOSFETs / SiCs) as power devices to simulate high-power load current simplifies hardware and software driving, further reduces costs, facilitates market adoption, and provides a simple and reliable control loop.

[0121] The voltage U of the bus capacitor C2 d The voltage U of the bus capacitor C2 during operation often originates from another PWM rectifier. d In reality, it fluctuates; the voltage U of the bus capacitor C2 fluctuates. d This will cause disturbances to the control of AC electronic loads. Capacitor voltage U c Divide by the voltage U of the bus capacitor C2 d It refers to the inverter modulation corresponding to the current output voltage, which is achieved by superimposing U. c / U d The link can eliminate U c and U d The disturbance can greatly reduce the burden on the PR controller in the inductor current control loop.

[0122] In this embodiment, the amplitude and phase control of the external output current are transformed into the amplitude and phase control of the internal inductor current; the dual-loop control (outer loop of output current, inner loop of current sensing) is changed to single-loop control (current sensing closed loop only), which is simple and reliable, ensuring that the amplitude and phase errors of the controlled variable are minimized; the addition of output voltage compensation control reduces the burden of PR control and further improves the accuracy of the controlled current. The control method mainly uses single-loop PR control of the inductor current, which improves the dynamic performance of the current; combined with output voltage compensation, it improves the fast response to voltage disturbances. The single-loop inductor current uses PR control, supplemented by output voltage feedforward compensation, which is simple to control, has high current dynamic performance, and small error. (See reference...) Figure 6 , has U c and U d During compensation control, the voltage U of bus capacitor C2 d Even under large fluctuations, the output current waveform remains undistorted.

[0123] Simulation verification

[0124] The voltage U of the bus capacitor C2 is obtained by sampling. d =700V, capacitor voltage When the voltage U of the bus capacitor C2 d The voltage changes abruptly from 700V to 400V at time t1, and then abruptly from 400V to 700V at time t2. When the control method in Example 1 is used, that is, without U...c and U d Compensation control, the corresponding simulation waveform is as follows Figure 5 As shown, when U d When there are large fluctuations, the output current waveform is distorted. When using the control method in Example 2, please refer to... Figure 6 That is, having U c and U d Compensation control, when U d Even under large fluctuations, the output current waveform remains undistorted.

[0125] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-precision AC electronic load control system, characterized in that, include: The components are: AC power supply under test (e1) or motor controller, AC electronic load circuit, and mains power (e2); the AC electronic load circuit includes an LC filter, a PWM full-bridge inverter circuit, a PWM full-bridge rectifier circuit, and a bus capacitor (C2); the PWM full-bridge inverter circuit and LC filter serve as a simulated load to test the AC power supply under test (e1), and the voltage across the bus capacitor (C2) is measured by the PWM full-bridge rectifier circuit. Voltage regulation control is implemented, and excess energy is fed back to the grid (e2). Control methods applied to high-precision AC electronic load control systems include: S1. Obtain the capacitor voltage across capacitor C of the LC filter. ; S2. Calculate the current command value of the inductor L of the LC filter. ; S3. Obtain the current sampling value of the inductor L of the LC filter. The current command value of inductor L Current sampling value of inductor L After comparison, the data is input into the PR controller for calculation; S4. Obtain the voltage of bus capacitor C2. , capacitor voltage and the voltage of bus capacitor C2 Perform proportional calculations and convert the capacitor voltage... Voltage of bus capacitor C2 The ratio is used as the output voltage feedforward compensation. After adding or subtracting the output value of the PR controller, the output duty cycle is used to control the on / off state of the switching transistor in the PWM full-bridge inverter circuit of the AC electronic load.

2. The high-precision AC electronic load control system according to claim 1, characterized in that, In step S1, the capacitor voltage across capacitor C of the LC filter is obtained. The method is as follows: The capacitor voltage across capacitor C is obtained through sampling and phase-locking. ; Official (1) In the formula The effective value of the voltage from the external AC voltage source. It is the voltage angular frequency. It is a phase-locked phase for an external AC source.

3. The high-precision AC electronic load control system according to claim 1, characterized in that, In step S2, the current command value of the inductor L of the LC filter is calculated. The method is as follows: S21. The user inputs the power factor (PF) value of the load current, and then calculates the corresponding power factor angle. Or the user can directly provide the power factor angle. : Official (2) Among them, PF is greater than 0 for inductive load, PF is less than 0 for capacitive load, and PF is 1 for resistive load; S22, User input current RMS value command Then the corresponding instantaneous value instruction for: Official (3) In the formula The capacitor voltage across the capacitor C of the LC filter obtained by formula (2) The phase difference of the current; S23. Calculate the reactive current consumed by capacitor C of the LC filter: Official (4) Substituting formula (1) into formula (4) yields: Official (5) In the formula, C is the capacitance of the LC filter, and the unit is farad; S24. Calculate the current command value of the inductor L of the LC filter. for: Official (6) Substituting formulas (3) and (5) into formula (6) yields: - Official (7) In the formula Input the effective value of the current for the user. For external AC source phase-locked phase, It is the voltage angular frequency. The power factor angle.

4. The high-precision AC electronic load control system according to claim 1, characterized in that, The transfer function of the PR controller in step S3 is: Official (8) In the formula, Kp is the proportional coefficient of the controller, Kr is the resonant term coefficient, w0 is the resonant frequency, and w c It is the ring width frequency.

5. The high-precision AC electronic load control system according to claim 1, characterized in that, In AC electronic load circuits, the switching transistor is an IGBT.

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