Square wave current control method

Abstract

The invention relates to a square wave current control method. The method comprises the steps that S1, the resonant frequency of a PR controller is determined according to the voltage frequency of a power grid; determining a repetitive control period according to the square wave current period; s2, when the power grid voltage frequency changes, adjusting the resonant frequency; when the square wave current period changes, the repetitive control period is adjusted; s3, determining an inductive current deviation value of the current control period; s4, respectively calculating a PI control output value, a PR control output value and a repetitive control output value based on the inductive current deviation value, the resonant frequency and the repetitive control period; s5, determining the total output quantity of the current loop; and in the next control period, repeatedly executing the steps S2 to S5. According to the square wave current control method provided by the invention, periodic regular or irregular disturbance is effectively inhibited through PI + PR + repetition compound control, and accurate tracking of the square wave current of the digital ballast is realized.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and particularly to a method for controlling square-wave current. Background Art

[0002] The working principle of a digital ballast is as follows: the alternating-current sinusoidal current is converted into a constant DC bus voltage through a rectification link, and then inverted through a BUCK circuit and an H-bridge circuit to generate an alternating-current square-wave current with adjustable amplitude and frequency. The circuit design generally adopts a three-pole structure, which consists of a PFC circuit, a BUCK circuit, and an H-bridge circuit.

[0003] Currently, the conventional control strategy is to adjust the BUCK inductor current through PI control. However, due to the coupling of the H-bridge switching circuit and the RCD buffer circuit, the complexity of the circuit transient switching is increased, and periodic irregular interference is introduced. In addition, the PFC link of the digital ballast introduces periodic bus voltage fluctuations, which will generate periodic current disturbances in the square-wave current. In short, during the process of controlling the square-wave current, there are problems of periodic regular and irregular interference. First, there are overshoot and oscillation problems during the rising or falling process of the square-wave current. These periodic irregular interferences will lead to a decrease in current tracking accuracy and an extension of the adjustment time. In addition, the periodic bus voltage fluctuations further deteriorate the tracking performance of the square-wave current. In summary, due to the existence of periodic regular and irregular disturbances, the traditional PI controller cannot accurately track the square-wave current of the digital ballast and urgent improvement is needed. Summary of the Invention

[0004] Based on this, it is necessary to provide a method for controlling square-wave current, which can suppress periodic regular or irregular disturbances and achieve accurate tracking of the square-wave current.

[0005] This application provides a method for controlling square-wave current, including: S1. Determine the resonant frequency of the PR controller according to the grid voltage frequency; determine the repetitive control period according to the square-wave current period; S2. When the grid voltage frequency changes, adjust the resonant frequency; when the square-wave current period changes, adjust the repetitive control period; S3. Determine the deviation value of the inductor current in the current control period; S4. Calculate the PI control output value, the PR control output value, and the repetitive control output value respectively based on the inductor current deviation value, the resonant frequency, and the repetitive control period; S5. Determine the total output of the current loop.

[0006] Wherein, is the total output, is the PI control output value, is the PR control output value, is the repetitive control output value, is the PI control weight coefficient, is the PR control weight coefficient, is the repetitive control weight coefficient; in the next control cycle, steps S2 to S5 are repeatedly executed.

[0007] Preferably, the calculation formula for the PI control output value is:

[0008] where, is the inductor current deviation value, is a complex variable, is the first proportional gain coefficient, is the integral gain coefficient.

[0009] Preferably, the calculation formula for the PR control output value is:

[0010] where, is the second proportional gain coefficient, is the resonant gain coefficient, is the cut-off frequency, is the resonant frequency.

[0011] Preferably, the calculation formula for the repetitive control output value is:

[0012] where, is a low-pass filter, is a compensation link, is the natural constant, is the repetitive control cycle.

[0013] Preferably, 0 < < 1, 0 < < 1, 0 < < 1.

[0014] Preferably, the resonant frequency is:

[0015] where, is the bus voltage disturbance frequency, is the grid voltage frequency.

[0016] Preferably, the repetitive control cycle is:

[0017] where, is the square wave current period.

[0018] Preferably, the inductor current deviation value is the difference between the reference value of the inductor current and the sampled value of the inductor current in the current control period.

[0019] Preferably, the total output is the duty cycle of the PWM drive.

[0020] The square-wave current control method provided by this application effectively suppresses periodic regular or irregular disturbances through the composite control of "PI + PR + repetition", and realizes the accurate tracking of the square-wave current of the digital ballast. Specifically, the PR control can effectively suppress the periodic regular disturbances of the bus voltage, and can also adjust its own resonance frequency accordingly according to the change of the bus voltage disturbance frequency, so that the ballast has good voltage adaptability; the repetitive control can suppress the periodic irregular disturbances of the DC current and effectively track the periodic signal. In addition, the corresponding weight coefficients are assigned to the three control terms to adjust the weight and influence of each control term in the entire control system, so as to achieve precise regulation and optimization of the system performance. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of this application or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0022] Figure 1 It is the circuit topology diagram of a three-stage digital ballast.

[0023] Figure 2 It is the control block diagram of the embodiment of this application.

[0024] Figure 3 It is the flowchart of the square-wave current control method of the embodiment of this application.

[0025] Figure 4 It is the transient waveform diagram of a single PI control.

[0026] Figure 5 It is the transient waveform diagram of the embodiment of this application.

[0027] Figure 6 It is the steady-state waveform diagram of a single PI control.

[0028] Figure 7 It is the steady-state waveform diagram of the embodiment of this application. Detailed Embodiments

[0029] To facilitate the understanding of this application, the following will provide a more comprehensive description of this application with reference to the relevant drawings. Embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of this application more thorough and comprehensive.

[0030] It can be understood that in the following embodiments, "connection", if there is a transfer of electrical signals or data between the connected circuits, modules, units, etc., should be understood as "electrical connection", "communication connection", etc.

[0031] The hardware platform to which the square-wave current control method of this embodiment is applied is a three-level digital ballast, and the circuit topology is as Figure 1 shown. The input is an AC power supply, and the current flows sequentially through the PFC high-frequency transistor module 1, the PFC low-frequency transistor module 2, the BUCK circuit 3, the RCD buffer circuit 4, and the H-bridge circuit 5. The output of the H-bridge circuit 5 is connected to a dysprosium lamp. The PFC high-frequency transistor module 1 includes: multiple high-frequency transistors and an inductor, and its main function is to rectify the AC power supply and perform power factor correction. The PFC low-frequency transistor module 2 includes: multiple low-frequency transistors to further process the current. The BUCK circuit 3 is used for step-down, reducing the input voltage to the required voltage level. The RCD buffer circuit 4 is used to protect the switching device, effectively reducing the voltage and current stress during the switching process. The H-bridge circuit 5 is used to control the current direction of the output current to achieve AC inverter control.

[0032] The square-wave current control method of this embodiment is designed for the inductor current loop of the BUCK circuit 3, and the control block diagram is as Figure 2 shown.

[0033] As Figure 2 and Figure 3 shown, this embodiment provides a square-wave current control method, including the following steps.

[0034] S1. Determine the resonant frequency of the PR controller according to the grid voltage frequency ; determine the repetitive control period according to the square-wave current period ; ; .

[0035] In this embodiment, based on the grid voltage frequency determine the bus voltage disturbance frequency , specifically, the bus voltage disturbance frequency is twice the grid voltage frequency . Based on this, set the resonant frequency of the PR controller to be:

[0036] As an example, the grid voltage frequency is 50 Hz or 60 Hz.

[0037] Preferably, the repetitive control period is determined according to the set value of the square-wave current period , and since irregular periodic disturbances occur during the switching process of the positive and negative half-cycles of the square-wave current, the repetitive control period is determined as: T to ensure that the repetitive control can adapt to the new square-wave current period and continue to effectively track periodic signals and suppress disturbances. As an example, = 1 / 75 = 0.133. =1 / 75=0.133。

[0038] S2. When the grid voltage frequency changes, adjust the resonant frequency ; when the square-wave current period changes, adjust the repetitive control period .

[0039] PR control has an infinite gain at the resonant frequency . Utilizing this characteristic, PR control can effectively suppress the periodic disturbances of the bus voltage; moreover, it can adjust its own resonant frequency correspondingly according to the change of the bus voltage disturbance frequency , thereby enabling the ballast to have good voltage adaptability.

[0040] Applying the PR controller to the DC current control scenario, it can compensate for the double-frequency DC bus voltage disturbances, significantly improving the stability of the square-wave current envelope.

[0041] In addition, the PR controller can also flexibly adjust its own resonant frequency for different grid voltage frequencies (such as the common 50 Hz and 60 Hz) to meet the control requirements in different grid environments.

[0042] S3. Determine the inductor current deviation value of the current control period .

[0043] Preferably, within the current control period, the difference between the inductor current reference value and the inductor current sampled value is used as the inductor current deviation value .

[0044] Here, the inductor current reference value is a set value and serves as the given signal of the current loop; the inductor current sampled value It is obtained by sampling and calculating with a Hall sensor and a DSP, and serves as the feedback signal of the current loop.

[0045] S4. Based on the inductance current deviation value , the resonance frequency and the repetitive control period calculate the proportional-integral (PI) control output value, the PR control output value, and the repetitive control output value respectively.

[0046] Preferably, the calculation formula of the proportional-integral control output value is:

[0047] Wherein, is a complex variable, is the first proportional gain coefficient (i.e., the proportional gain coefficient of PI control), is the integral gain coefficient. Here, the specific values of the two coefficients and are determined according to the controlled object. As an example, = 0.05, = 0.001.

[0048] The PI controller consists of a proportional link (P) and an integral link (I). When the system is disturbed or the reference value of the inductance current changes, an inductance current deviation will occur. The proportional link immediately generates a control action according to the inductance current deviation, making the output of the system change in the direction of reducing the deviation. At the same time, the integral link also starts to integrate the inductance current deviation. As time goes by, the integral action gradually strengthens, further adjusting the output of the system until the deviation is reduced to zero or close to zero. At steady state, the inductance current deviation value approaches zero, and the output of the proportional link also approaches zero. However, due to the cumulative effect of the deviation by the integral link during the dynamic process, its output will remain at a stable value, enabling the system to maintain an accurate output at steady state and eliminating the steady-state error.

[0049] Preferably, the calculation formula of the PR control output value is:

[0050] Wherein, is a complex variable, is the second proportional gain coefficient (i.e., the proportional gain coefficient of PR control), is the resonance gain coefficient, is the cut-off frequency, is the resonance frequency of the PR controller. As an example, = 0.01, = 3, = 0.2.

[0051] The PR control is based on the internal model principle. By introducing a resonant link in the controller, the controller has an infinite gain for signals at the resonant frequency so as to achieve the static error-free tracking of AC signals.

[0052] In the steady state, through the combined action of the proportional link and the resonant link, the PR controller enables the output of the system to accurately suppress the AC interference signal and achieve static error-free control.

[0053] Preferably, the calculation formula for the output value of the repetitive control is:

[0054] where is a low-pass filter or a constant between 0 and 1; is a compensation link, , is a gain coefficient used to scale the compensation link proportionally, is a time delay link. The three parts constitute the compensation link of the system; is a complex variable, is the natural constant; is a delay link representing a delay with a period of T. As an example, = 0.95, .

[0055] Based on the periodicity and irregularity of the inductor current disturbance during the H-bridge switching, this embodiment introduces repetitive control to suppress harmonic interference and adaptively adjust the repetitive control period to achieve effective suppression of disturbances with different periods, thereby achieving higher control precision and smaller steady-state error.

[0056] S5. Determine the total output of the current loop : .

[0057] where is the PI control weight coefficient, is the PR control weight coefficient, is the repetitive control weight coefficient. PI control, PR control, and repetitive control are all assigned corresponding weight coefficients, which are used to adjust the weight and influence of each control term in the entire control system, so as to achieve precise regulation and optimization of the system performance to meet the diverse control objectives and complex operating conditions requirements.

[0058] In this embodiment, the total output is the duty cycle of PWM drive. By adjusting the duty cycle, the on-off time of the MOS transistor is controlled, thereby regulating the magnitude of the inductor current to achieve closed-loop control.

[0059] Here, the magnitudes of the three weight coefficients are related to the characteristics of the controlled object and the magnitude of the periodic disturbance. Preferably, 0 < < 1, 0 < < 1, 0 < < 1. As an example, = 0.25, = 0.3, = 0.1.

[0060] In the next control cycle, the above steps S2 to S5 are repeatedly executed.

[0061] Figure 4 shows the transient waveform of the existing single PI control, Figure 5 shows the transient waveform of the "PI + PR + repetitive" composite control according to the embodiment of the present application. In Figure 4 and Figure 5 , purple is the transient waveform of the output voltage, and blue is the transient waveform of the output current. Figure 4 and Figure 5 By comparison, it can be obtained that after adopting the "PI + PR + repetitive" composite control square wave according to the embodiment of the present application, the overshoot of the square wave current decreases, the steady-state error decreases, and the fluctuation of the square wave current is significantly suppressed; thus, it shows that the square wave current control method according to the embodiment of the present application not only improves the dynamic characteristics of the controller but also effectively suppresses the periodic irregular disturbance.

[0062] Figure 6 shows the steady-state waveform of the existing single PI control, Figure 7 shows the steady-state waveform of the "PI + PR + repetitive" composite control according to the embodiment of the present application. In Figure 6 and Figure 7 , green is the steady-state waveform of the input current, purple is the steady-state waveform of the output voltage, and blue is the steady-state waveform of the output current. Figure 6 and Figure 7 By comparison, it can be obtained that by adopting the "PI + PR + repetitive" composite control according to the embodiment of the present application, there is no second-harmonic periodic disturbance in the envelope of the square wave current; thus, it shows that the square wave current control method according to the embodiment of the present application effectively suppresses the periodic regular disturbance, that is, the influence of the second-harmonic disturbance of the DC bus voltage on the square wave current.

[0063] The square-wave current control method provided by this application effectively suppresses periodic regular or irregular disturbances through the composite control of "PI + PR + repetitive", and realizes accurate tracking of the square-wave current of the digital ballast. Specifically, the PR control can effectively suppress the periodic regular disturbances of the bus voltage, and can also adjust its own resonance frequency accordingly according to the change of the disturbance frequency of the bus voltage, so that the ballast has good voltage adaptability; the repetitive control can suppress the periodic irregular disturbances of the DC current and effectively track the periodic signal. In addition, the corresponding weight coefficients are assigned to the three control terms to adjust the weight and influence of each control term in the entire control system, so as to realize the precise regulation and optimization of the system performance.

[0064] The above embodiments only represent several implementation manners of this application, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of this application. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several deformations and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of this application should be subject to the appended claims.

Claims

1. A square-wave current control method, characterized in that, It includes the following steps: S1. Determine the resonant frequency of the PR controller according to the grid voltage frequency; determine the repetitive control period according to the square-wave current period; S2. When the grid voltage frequency changes, adjust the resonant frequency; when the square-wave current period changes, adjust the repetitive control period; S3. Determine the inductor current deviation value of the current control period; S4. Calculate the PI control output value, the PR control output value and the repetitive control output value respectively based on the inductor current deviation value, the resonant frequency and the repetitive control period; S5. Determine the total output of the current loop; Among them, is the total output,[[]]END]] is the PI control output value,[[]]END]] is the PR control output value,[[]]END]] is the repetitive control output value,[[]]END]] is the PI control weight coefficient,[[]]END]] is the PR control weight coefficient,[[]]END]] is the repetitive control weight coefficient;[[]]END]] In the next control period, repeat steps S2 to S5 above.

2. The square wave current control method according to claim 1, wherein The calculation formula of the PI control output value is: Among them, is the inductor current deviation value, is a complex variable, is the first proportional gain coefficient, is the integral gain coefficient.

3. The square-wave current control method according to claim 2, characterized in that The calculation formula of the PR control output value is: Among them, is the second proportional gain coefficient, is the resonance gain coefficient, is the cut-off frequency, is the said resonance frequency.

4. The square-wave current control method according to claim 3, wherein The calculation formula of the repetitive control output value is: Among them, is a low-pass filter, is a compensation link, is the natural constant, is the repetition control period.

5. The square-wave current control method according to claim 1, wherein 0＜ ＜1，0＜ ＜1，0＜ ＜1。 6. The square wave current control method according to claim 1, characterized in that The resonant frequency is: Among them, is the bus voltage disturbance frequency, is the grid voltage frequency.

7. The square-wave current control method according to claim 1, wherein The repetitive control period is: Among them, is the square-wave current period.

8. The square wave current control method according to claim 1, wherein, The inductor current deviation value is the difference between the inductor current reference value and the inductor current sampled value of the current control period.

9. The square-wave current control method according to claim 1, wherein The total output is the duty cycle of the PWM drive.

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