Control method of high-power RLC alternating current electronic load
阅读说明：本技术 一种大功率rlc交流电子负载的控制方法 (Control method of high-power RLC alternating current electronic load ) 是由 周玉柱 张永 董浩 唐德平 于 2020-12-30 设计创作，主要内容包括：一种大功率RLC交流电子负载的控制方法属于测量测试用电力电子技术领域,解决如何通过直接控制端口电压的方式,来间接实现待模拟的RLC电路的电流的问题,通过实时控制受控电压源U2实现对RLC交流电子负载特性的模拟,在R、RC、RL三种模式下获取受控电压源U2的指令电压U2n+1；将计算得到的电压指令U2n+1作为H桥的指令电压,通过单电压环开环发波的方式控制输出电压即可得到待模拟的RLC负载的输出电流特性,因为电流是通过电压差来实现的,因此直接电压控制比直接电流控制的动态响应更高,本发明技术方案的方法控制的RLC交流电子负载动态响应高,稳态相移小。(A control method of a high-power RLC alternating current electronic load belongs to the technical field of power electronics for measurement and test, solves the problem of how to indirectly realize the current of an RLC circuit to be simulated by directly controlling port voltage, realizes the simulation of the RLC alternating current electronic load characteristic by controlling a controlled voltage source U2 in real time, and obtains the instruction voltage U2n +1 of the controlled voltage source U2 in three modes of R, RC and RL; the calculated voltage command U2n +1 is used as the command voltage of the H bridge, the output voltage is controlled in a single voltage ring open-loop wave-sending mode, and the output current characteristic of the RLC load to be simulated can be obtained.)
1. A control method of a high-power RLC alternating current electronic load is characterized in that the control method is applied to a high-power RLC alternating current electronic load circuit, and the high-power RLC alternating current electronic load circuit comprises the following steps: the circuit comprises an alternating current voltage source U, a filter inductor L1, an H bridge circuit and a controlled voltage source U2; the output of an alternating current voltage source U is connected to the middle point of two bridge arms of the H-bridge circuit through a filter inductor L1, a controlled voltage source U2 is the voltage output by the middle point of the two bridge arms of the H-bridge circuit, and a power switch tube of the H-bridge circuit adopts an IGBT; according to an ideal model and an actual model of the RLC alternating current electronic load based on voltage control, calculating to obtain an instruction voltage U2n +1 of a controlled voltage source U2 when a constant resistance R load is simulated, a constant RC load is simulated or a constant RL load is simulated to be used as an instruction voltage of an H-bridge circuit, and controlling the controlled voltage source U2 in real time through a single-loop open loop to obtain the output current characteristic of the high-power RLC alternating current electronic load.
2. The method as claimed in claim 1, wherein the equivalent circuit of the RLC ac electronic load ideal model based on voltage control comprises: an alternating current voltage source U and a simulation load; the output end of the alternating current voltage source U is directly connected with the analog load to form a closed loop; the equivalent circuit of the RLC alternating current electronic load actual model based on the voltage control comprises: an alternating current voltage source U, a filter inductor L1 and a controlled voltage source U2; the alternating voltage source U is connected with the controlled voltage source U2 through a filter inductor L1 to form a closed loop.
3. The method for controlling a high-power RLC alternating current electronic load as claimed in claim 2, wherein the calculation method of the command voltage U2n +1 of the controlled voltage source U2 under the condition of simulating a constant resistance Rload is as follows:
when the resistance is constant R load, the ideal model voltage equation is as follows:
U＝R*i (1)
the voltage equation of the actual model at constant resistance Rload is:
the two sides of the formula (1) are derived, and di/dt is taken into the formula (2) and discretized to obtain the formula:
wherein Un is the external alternating current source voltage at the current moment, Un-1 is the external alternating current source voltage at the previous moment, L1 is the inductance of the filter inductor, R is the resistance value of the resistor to be simulated, Δ T is the interrupt period, and U2n +1 is the command voltage calculated at the next moment.
4. The method for controlling a high-power RLC alternating current electronic load as claimed in claim 2, wherein the calculation method of the command voltage U2n +1 of the controlled voltage source U2 under the condition of simulating a constant resistance RC load is as follows:
the voltage equation for an ideal model at constant RC load is:
and (3) performing derivation arrangement on two sides of the formula (4) to obtain:
the voltage equation of the actual model at constant RC load is:
the current differential equation in equation (5) is solved by the two-step Adams method as follows:
Fn＝f(tn,xn)
xn+1＝xn+h(3Fn-Fn-1)/2 (7)
in the formula (7), h is a calculation step length, xn+1Is the state variable, x, at the next momentnIs the state variable at the current time, FnIs the differential at the current time, Fn-1Is the differential amount at the previous time.
Discretizing the step (5) by a two-step Adams method to obtain a specific current differential value, wherein the iteration sequence is as follows:
in+1＝in+ΔT(3Fn＝Fn-1)/2
Fn-1＝Fn
in＝in+1
Un-1＝Un (8)
the command voltage can be obtained by substituting equation (8) for equation (6):
U2n+1＝Un-L1*Fn (9)
in the formulae (8) and (9), FnIs the current differential di/dt value, F, at the present momentn-1Is the current differential value at the previous moment, Δ T is the interruption period, C is the capacitance value of the capacitor to be simulated, R is the resistance value of the resistor to be simulated, in+1Is the current value at the next moment, inIs the current value at the present time, L1 is the filter inductance, UnIs the external AC source voltage value, U, at the present momentn-1Is the voltage value of the external AC source at the previous moment, U2n+1The command voltage at the next time is calculated.
5. The method for controlling a high-power RLC alternating current electronic load as claimed in claim 2, wherein the calculation method of the command voltage U2n +1 of the controlled voltage source U2 under the condition of simulating the constant resistance RL load is as follows:
the voltage equation for an ideal model at constant RL load is:
from formula (10):
the voltage equation for the actual model at constant RL load is:
the specific command voltage can be obtained by discretizing equation (12) by the two steps of Adams, and the iteration sequence is as follows:
in+1＝in+ΔT(3Fn-Fn-1)/2
Fn-1＝Fn
in＝in+1 (13)
the command voltage at the current time can be obtained by substituting equation (13) for equation (12):
U2n+1＝Un-L1*Fn (14)
in the formulae (13) and (14), FnIs the current differential di/dt value, F, at the present momentn-1Is the current differential value at the previous moment, Δ T is the interruption period, L is the inductance to be simulated, R is the resistance value of the resistor to be simulated, in+1Is the current value at the next moment, inIs the current value at the present time, L1 is the filter inductance, UnIs the external AC source voltage at the present time, U2n+1The command voltage at the next time is calculated.
Technical Field
The invention belongs to the technical field of power electronics for measurement and test, and particularly relates to a control method of a high-power RLC alternating current electronic load.
Background
The RLC alternating current electronic load is a power electronic device capable of simulating a traditional impedance load, can simulate resistors, inductors, capacitors and combinations of the resistors, the inductors and the capacitors with different values, and can also simulate certain characteristics of a nonlinear load, and the alternating current electronic load usually achieves the purpose of simulating various loads by controlling input current. The design is originally designed for the factory test of an alternating current power supply or a motor driver, and compared with the defects of high energy consumption, low automation degree and inconvenient regulation of the traditional real RLC device, the alternating current electronic load simulating the RLC characteristic can make the test simpler and more flexible, and the test cost is reduced.
In the current analog alternating current electronic load industry, high-speed switching devices such as MOSFET and SIC are generally adopted as power devices in order to obtain accurate analog effect. However, the current capacity of such a high-speed switching device is low, and in order to meet a high-power test, a parallel-tube or parallel-operation mode needs to be adopted to realize simulation, which causes complex control and high cost. Therefore, the low-speed switching devices such as the IGBT with high current and low cost commonly used in the market are used as the power tube of the analog device, and it is particularly necessary to improve the performance degradation caused by the low control frequency in the control strategy.
The prior art typically implements port characteristics of analog R, RL or RC by controlling port current, i.e., using an implementation based on direct current closed-loop control; for example, in the document "research on a single-phase ac electronic load" (china measurement university, 2016, 6), a port voltage U of an external ac source or a driver may be obtained by sampling, knowing an impedance value of R, RL or an RC circuit to be simulated, a corresponding command current Iref is calculated, and simulation of a corresponding port characteristic may be achieved by closed-loop control of the command current Iref. As shown in fig. 4, the test object of an ac electronic load is typically an ac voltage source, a motor driver. As shown in fig. 5, the ac electronic load based on the RLC principle generally simulates the port characteristics of R, RL and RC. The current instruction is obtained by sampling the voltage U of the external port and calculating according to a given model RLC value, the latest current instruction value Iref is continuously calculated in an iterative mode, and current tracking is achieved through closed-loop control over the Iref. Fig. 6 shows a control block diagram based on current PI control, where Iref is the model command current obtained by the above calculation, L1 is the filter inductor, and IL1 is the output current of the H-bridge. The following of the output current IL1 to the command current Iref is achieved by PI control. For sinusoidal signals Iref, single-loop PI control is difficult to realize the non-static tracking of current; and the switching frequency of the IGBT is generally within 20K. It is difficult to achieve quiet tracking of the sinusoidal command current Iref at lower control frequencies. The other is a hysteresis current control method, a control block diagram is shown in fig. 7, the hysteresis current control has the characteristics of capability of quickly tracking the instruction current and unfixed switching frequency. The smaller the current loop width, the better the waveform quality, but the higher the switching frequency. Therefore, the hysteresis current control is difficult to satisfy the simulation of the alternating current electronic load of the conventional IGBT low switching frequency control.
The prior art has the following disadvantages: (1) in the current industry of simulating alternating current electronic loads, in order to obtain an accurate simulation effect, high-speed switching devices such as MOSFET (metal oxide semiconductor field effect transistor), SIC (semiconductor information technology) and the like are generally adopted as power devices, but the current capacity of the high-speed switching devices is lower; (2) in order to meet the requirement of high-power test, a parallel tube or parallel machine mode is needed to realize simulation, which brings complex control, low stability and high cost. Aiming at the characteristics of low dynamic response and steady-state waveform hysteresis caused by low control frequency of a high-power RLC alternating current electronic load using an IGBT as a switching device, a novel method is provided, so that the dynamic response of the RLC alternating current electronic load is improved, and the hysteresis of the steady-state waveform is improved.
Disclosure of Invention
The technical problem to be solved by the invention is how to indirectly realize the current of the RLC circuit to be simulated by directly controlling the port voltage.
The invention solves the technical problems through the following technical scheme:
a control method of a high-power RLC alternating current electronic load is applied to a high-power RLC alternating current electronic load circuit, and the high-power RLC alternating current electronic load circuit comprises the following steps: the circuit comprises an alternating current voltage source U, a filter inductor L1, an H bridge circuit and a controlled voltage source U2; the output of an alternating current voltage source U is connected to the middle point of two bridge arms of the H-bridge circuit through a filter inductor L1, a controlled voltage source U2 is the voltage output by the middle point of the two bridge arms of the H-bridge circuit, and a power switch tube of the H-bridge circuit adopts an IGBT; according to an ideal model and an actual model of the RLC alternating current electronic load based on voltage control, calculating to obtain an instruction voltage U2n +1 of a controlled voltage source U2 when a constant resistance R load is simulated, a constant RC load is simulated or a constant RL load is simulated to be used as an instruction voltage of an H-bridge circuit, and controlling the controlled voltage source U2 in real time through a single-loop open loop to obtain the output current characteristic of the high-power RLC alternating current electronic load.
The simulation of the characteristics of an RLC alternating current electronic load (R + jX load) is realized by controlling a controlled voltage source U2 in real time, and the command voltage U2n +1 of the controlled voltage source U2 is obtained in three modes of R, RC and RL; the calculated voltage command U2n +1 is used as the command voltage of the H bridge, the output voltage is controlled in a single voltage ring open-loop wave-sending mode, and the output current characteristic of the RLC load to be simulated can be obtained.
As a further improvement of the technical solution of the present invention, the equivalent circuit of the RLC ac electronic load ideal model based on voltage control includes: an alternating current voltage source U and a simulation load; the output end of the alternating current voltage source U is directly connected with the analog load to form a closed loop; the equivalent circuit of the RLC alternating current electronic load actual model based on the voltage control comprises: an alternating current voltage source U, a filter inductor L1 and a controlled voltage source U2; the alternating voltage source U is connected with the controlled voltage source U2 through a filter inductor L1 to form a closed loop.
As a further improvement of the technical solution of the present invention, a calculation method of the command voltage U2n +1 of the controlled voltage source U2 under the condition of simulating the constant resistance R load is as follows:
when the resistance is constant R load, the ideal model voltage equation is as follows:
U＝R*i (1)
the voltage equation of the actual model at constant resistance Rload is:
the two sides of the formula (1) are derived, and di/dt is taken into the formula (2) and discretized to obtain the formula:
wherein Un is the external alternating current source voltage at the current moment, Un-1 is the external alternating current source voltage at the previous moment, L1 is the inductance of the filter inductor, R is the resistance value of the resistor to be simulated, Δ T is the interrupt period, and U2n +1 is the command voltage calculated at the next moment.
As a further improvement of the technical solution of the present invention, a calculation method of the command voltage U2n +1 of the controlled voltage source U2 under the condition of simulating the constant resistance RC load is as follows:
the voltage equation for an ideal model at constant RC load is:
and (3) performing derivation arrangement on two sides of the formula (4) to obtain:
the voltage equation of the actual model at constant RC load is:
the current differential equation in equation (5) is solved by the two-step Adams method as follows: (formula 8)
Fn＝f(tn,xn)
xn+1＝xn+h(3Fn-Fn-1)/2 (7)
In the formula (7), h is a calculation step length, xn+1Is the state variable, x, at the next momentnIs the state variable at the current time, FnIs the differential at the current time, Fn-1Is the differential amount at the previous time.
Discretizing the step (5) by a two-step Adams method to obtain a specific current differential value, wherein the iteration sequence is as follows:
in+1＝in+ΔT(3Fn＝Fn-1)/2
Fn-1＝Fn
in＝in+1
Un-1＝Un (8)
the command voltage can be obtained by substituting equation (8) for equation (6):
U2n+1＝Un-L1*Fn (9)
in the formulae (8) and (9), FnIs the current differential di/dt value, F, at the present momentn-1Is the current differential value at the previous moment, Δ T is the interruption period, C is the capacitance value of the capacitor to be simulated, R is the resistance value of the resistor to be simulated, in+1Is the current value at the next moment, inIs the current value at the present time, L1 is the filter inductance, UnIs the external AC source voltage value, U, at the present momentn-1Is the voltage value of the external AC source at the previous moment, U2n+1The command voltage at the next time is calculated.
As a further improvement of the technical solution of the present invention, a calculation method of the command voltage U2n +1 of the controlled voltage source U2 under the condition of simulating the load of the constant resistance RL is as follows:
the voltage equation for an ideal model at constant RL load is:
from formula (10):
the voltage equation for the actual model at constant RL load is:
the specific command voltage can be obtained by discretizing equation (12) by the two steps of Adams, and the iteration sequence is as follows:
in+1＝in+ΔT(3Fn-Fn-1)/2
Fn-1＝Fn
in＝in+1 (13)
the command voltage at the current time can be obtained by substituting equation (13) for equation (12):
U2n+1＝Un-L1*Fn (14)
in the formulae (13) and (14), FnIs the current differential di/dt value, F, at the present momentn-1Is the current differential value at the previous moment, Δ T is the interruption period, L is the inductance to be simulated, R is the resistance value of the resistor to be simulated, in+1Is the current value at the next moment, inIs the current value at the present time, L1 is the filter inductance, UnIs the external AC source voltage at the present time, U2n+1The command voltage at the next time is calculated.
The invention has the advantages that:
(1) the simulation of the characteristics of an RLC alternating current electronic load (R + jX load) is realized by controlling a controlled voltage source U2 in real time, and the command voltage U2n +1 of the controlled voltage source U2 is obtained in three modes of R, RC and RL; the calculated voltage command U2n +1 is used as the command voltage of the H bridge, the output voltage is controlled in a single voltage ring open-loop wave-sending mode, and the output current characteristic of the RLC load to be simulated can be obtained.
(2) The simulation of the RLC alternating current load is realized by using low control frequency, the IGBT with large current carrying capacity is suitable to be used as a switching device, the single-machine capacity of the alternating current electronic load is improved, the steady-state performance of the system is improved, and the cost is reduced.
(3) And an LCL filter inductor is not needed, and only one L filter inductor is used, so that the system cost is further reduced.
(4) The hardware circuit topology is simple and reliable.
Drawings
FIG. 1 is a circuit diagram of a high power RLC AC electronic load;
FIG. 2 is an equivalent circuit diagram of an ideal model of an RLC AC electronic load based on voltage control;
FIG. 3 is an equivalent circuit diagram of a practical model of an RLC AC electronic load based on voltage control;
FIG. 4 is a schematic diagram of an AC electronic load application;
FIG. 5 is a schematic diagram of the constant impedance principle of an AC electronic load;
FIG. 6 is a block diagram of a prior art current PI control implementation;
fig. 7 is a block diagram of a prior art current hysteresis control implementation.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The technical scheme of the invention is further described by combining the drawings and the specific embodiments in the specification:
example one
As shown in fig. 1, a main circuit of a high-power RLC ac electronic load includes an ac voltage source U, a filter inductor L1, an H-bridge circuit, and a controlled voltage source U2; the output of an alternating current voltage source U is connected to the middle point of two bridge arms of the H-bridge circuit through a filter inductor L1, a controlled voltage source U2 is the voltage output by the middle point of the two bridge arms of the H-bridge circuit, and a power switch tube of the H-bridge circuit adopts an IGBT.
As shown in fig. 2 and 3 corresponding to fig. 1, the RLC alternating current electronic load ideal model and the actual model based on voltage control; the equivalent circuit of the RLC alternating current electronic load ideal model based on voltage control comprises the following components: an alternating current voltage source U and an analog load (R + jX load); and the output end of the alternating current voltage source U is directly connected with the analog load to form a closed loop. The equivalent circuit of the RLC alternating current electronic load actual model based on the voltage control comprises the following components: an alternating current voltage source U, a filter inductor L1 and a controlled voltage source U2; the alternating voltage source U is connected with the controlled voltage source U2 through a filter inductor L1 to form a closed loop.
The simulation of the characteristics of the RLC alternating current electronic load (R + jX load) is realized by controlling the controlled voltage source U2 in real time, so the important point of the embodiment is how to obtain the command voltage U2n +1 of the controlled voltage source U2 in three modes of R, RC and RL; the calculated voltage command U2n +1 is used as the command voltage of the left half H-bridge in fig. 3, and the output voltage is controlled in a single voltage ring open-loop wave-transmitting manner, so that the output current characteristic of the RLC load to be simulated can be obtained. Direct voltage control has a higher dynamic response than direct current control because the current is realized by a voltage difference. The RLC alternating current electronic load controlled by the method has high dynamic response and small steady-state phase shift.
1. For the case of an analog constant resistance Rload
As shown in fig. 2, the imaginary impedance X in the ideal model when the resistor R is loaded is 0, and the voltage equation of the ideal model is:
U＝R*i (1)
as shown in fig. 3, the voltage equation of the actual model at constant resistance rload is:
the two sides of the formula (1) are derived, and di/dt is taken into the formula (2) and discretized to obtain the formula:
wherein Un is the external alternating current source voltage at the current moment, Un-1 is the external alternating current source voltage at the previous moment, L1 is the inductance of the filter inductor, R is the resistance value of the resistor to be simulated, Δ T is the interrupt period, and U2n +1 is the command voltage calculated at the next moment.
2. For the case of simulating a constant RC load
As shown in fig. 2, the voltage equation of the ideal model at constant RC load is:
and (3) performing derivation arrangement on two sides of the formula (4) to obtain:
as shown in fig. 3, the voltage equation of the actual model at constant RC load is:
the current differential equation in equation (5) is solved by the two-step Adams method as follows:
in the formula (7), h is a calculation step length, xn+1Is the state variable, x, at the next momentnIs the state variable at the current time, FnIs the differential at the current time, Fn-1Is the differential amount at the previous time.
Discretizing the step (5) by a two-step Adams method to obtain a specific current differential value, wherein the iteration sequence is as follows:
in+1＝in+ΔT(3Fn＝Fn-1)/2
Fn-1＝Fn
in＝in+1
Un-1＝Un (8)
the command voltage can be obtained by substituting equation (8) for equation (6):
U2n+1＝Un-L1*Fn (9)
in the formulas 8 and 9, FnIs the current differential di/dt value, F, at the present momentn-1Is the current differential value at the previous moment, Δ T is the interruption period, C is the capacitance value of the capacitor to be simulated, R is the resistance value of the resistor to be simulated, in+1Is the current value at the next moment, inIs the current value at the present time, L1 is the filter inductance, UnIs the external AC source voltage value, U, at the present momentn-1Is the voltage value of the external AC source at the previous moment, U2n+1The command voltage at the next time is calculated.
3. For the case of simulating a constant RL load
As shown in FIG. 2, the voltage equation for the ideal model at constant RL load is:
from formula (10):
as shown in FIG. 3, the voltage equation for the actual model at constant RL load is:
the specific command voltage can be obtained by discretizing equation (12) by the two steps of Adams, and the iteration sequence is as follows:
in+1＝in+ΔT(3Fn-Fn-1)/2
Fn-1＝Fn
in＝in+1 (13)
the command voltage at the current time can be obtained by substituting equation (13) for equation (12):
U2n+1＝Un-L1*Fn (14)
in the formulae (13) and (14), FnIs the current differential di/dt value, F, at the present momentn-1Is the current differential value at the previous moment, Δ T is the interruption period, L is the inductance to be simulated, R is the resistance value of the resistor to be simulated, in+1Is the current value at the next moment, inIs the current value at the present time, L1 is the filter inductance, UnIs the external AC source voltage at the present time, U2n+1The command voltage at the next time is calculated.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
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