Micro inverter based on PI and repetitive control and control method thereof
By combining a dual closed-loop control strategy of PI and repetitive control in the microinverter, the current inner loop of the flyback microinverter is optimized, solving the problem of high grid-connected current distortion rate and achieving high-quality grid-connected current and improved dynamic performance.
Patent Information
- Application Number
- CN202511482661.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-16
- Publication Date
- 2025-12-12
AI Technical Summary
Traditional PI control methods cannot achieve zero steady-state error tracking of sinusoidal signals in flyback micro-inverters, resulting in high grid current distortion rate and complex control. Existing repetitive control has poor dynamic performance.
Combining PI control and repetitive control, a dual closed-loop control strategy is adopted, in which the voltage outer loop uses PI control and the current inner loop uses PI+repetitive control. By designing compensators and low-pass filters, the dynamic performance and harmonic suppression capability of the control system are optimized.
Without changing the inverter topology, it significantly reduces the grid-connected current distortion rate, improves the grid-connected current quality, has good dynamic performance and harmonic suppression capabilities, and does not increase hardware costs.
Smart Images
Figure CN121124602A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of micro-inverter technology, specifically relating to a micro-inverter based on PI and repetitive control and its control method. Background Technology
[0002] In grid-connected photovoltaic power generation systems, power generation systems with smaller inverter power are called microinverters. Microinverters have the following characteristics: 1) High reliability, each photovoltaic panel works independently without affecting each other; 2) Modular architecture, flexible power expansion; 3) Safe to use, there is no high-voltage DC terminal in the system; 4) Each photovoltaic panel has an independent MPPT, resulting in high utilization of the photovoltaic panels; 5) Easy installation, microinverters can be used immediately upon plugging and playing.
[0003] Microinverters can be broadly categorized into three types based on the type of DC bus: DC bus structure, pseudo-DC bus structure, and no DC bus structure. Among these, the flyback microinverter with a pseudo-DC bus structure is the most common topology, offering advantages such as simple structure, electrical isolation, and low cost. Addressing the leakage inductance in a flyback microinverter is crucial; passive clamping circuits are characterized by high losses and are unsuitable for low-power output in microinverters.
[0004] Traditional control strategies do not consider the nonlinear time-varying characteristics of flyback grid-connected inverters. Therefore, when using traditional PI control methods, zero steady-state error tracking of sinusoidal signals cannot be achieved, often resulting in poor control performance and high grid current distortion. Repetitive control can ensure high steady-state accuracy and harmonic suppression capability, improving grid current quality, but its dynamic performance is poor. PI control is often used to improve the dynamic performance of the system. To address the problems of high grid current distortion and complex control, the inventors aim to design a control method combining PI control and repetitive control for flyback microinverters. Summary of the Invention
[0005] To address the problem of excessively high grid-connected current distortion rate in micro-inverters when using traditional control methods, the present invention aims to propose a micro-inverter and its control method that combines PI control and repetitive control without changing the topology of the interleaved parallel flyback micro-inverter, taking into account the characteristics of the intermittent conduction mode. This control method can effectively reduce the grid-connected current distortion rate of the flyback micro-inverter.
[0006] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:
[0007] This invention provides a micro inverter based on PI and repetitive control, including a solar photovoltaic panel, an active clamping circuit I, an active clamping circuit II, a flyback circuit I, a flyback circuit II, a full-bridge inverter circuit, a filter circuit, and a control circuit.
[0008] After the flyback circuit I and flyback circuit II are connected in parallel with alternating configurations, their input terminals are connected to the solar photovoltaic panels, and their output terminals are connected to the grid access terminal via a full-bridge inverter circuit.
[0009] Both the active clamping circuit I and the active clamping circuit II include a clamping capacitor, an auxiliary switching transistor, and an auxiliary diode. The auxiliary switching transistor and the auxiliary diode are connected in parallel to form a series branch with the clamping capacitor. The series branch is connected in parallel across the primary winding of the transformer in the flyback circuit.
[0010] The control circuit has an outer voltage loop and an inner current loop, wherein the outer voltage loop uses PI control and the inner current loop uses PI+ repetitive control.
[0011] The pulse width modulation signal PWM1 generated by the control circuit controls the flyback circuit I through the flyback drive circuit I, and the pulse width modulation signal PWM2 generated by the control circuit controls the flyback circuit II through the flyback drive circuit II, so that it outputs a sinusoidal half-wave current.
[0012] The full-bridge inverter circuit consists of four switching transistors. By switching the polarity at the zero-crossing point, it outputs a sine wave of grid current, where the output voltage is clamped by the grid voltage.
[0013] The present invention also provides a control method for a micro inverter, comprising the following steps:
[0014] S1, the voltage output by the photovoltaic panel. V pv and current I pv Sampling is performed, and the reference value of the grid-connected current amplitude is obtained through the MPPT perturbation observation method. I ref ;
[0015] S2, Set the reference value of the grid-connected current amplitude I ref The grid-connected current reference value is obtained by multiplying the phase of the grid voltage obtained from the phase-locked loop. i ref ;
[0016] S3, Grid-connected current reference value i ref With grid current i gAfter comparison, the pulse width modulation signals of the two flyback circuits are obtained by PI+ repetitive control and then added to the current sharing loop control. Based on the pulse width modulation signals, the pulse width modulation signals of the two active clamp circuits are obtained by active clamp control circuit.
[0017] S4. In repetitive control, a non-ideal internal model structure is used. Based on the transfer function of PI+ repetitive control, the repetitive control gain, phase lead compensation, and low-pass filter of the compensator are reasonably designed to enhance the ability of the micro inverter to suppress harmonics.
[0018] Furthermore, step S1 specifically includes the following sub-steps:
[0019] S101, The voltage of the photovoltaic panel is sampled through the sampling circuit. V pv and current I pv Perform sampling;
[0020] S102, Sampled voltage V pv and current I pv The voltage outer loop reference value is obtained through MPPT. V ref ;
[0021] S103, Voltage Outer Loop Reference Value V ref With the voltage of the photovoltaic panel V pv Subtract the values to obtain the error value;
[0022] S104. Input the error value into the PI controller to obtain the reference value of the grid-connected current amplitude. I ref .
[0023] Furthermore, step S2 specifically includes the following sub-steps:
[0024] S201, The amplitude of the mains voltage is sampled by the sampling circuit. u g The phase of the grid voltage sin(ωt) is sampled;
[0025] S202. Obtain the grid voltage phase sin(ωt) through a phase-locked loop;
[0026] S203, Reference values for grid voltage phase and grid-connected current amplitude I ref Multiply to obtain the grid-connected current reference value. i ref .
[0027] Furthermore, step S3 specifically includes the following sub-steps:
[0028] S301. The grid-connected current is sampled through the sampling circuit to obtain the grid-connected current. i g ;
[0029] S302, Grid-connected current i g Compared with the grid-connected current reference value i ref Subtract the values to obtain the error value;
[0030] S303. Input the error value into the PI+ repetitive controller to obtain the current inner loop output duty cycle D;
[0031] S304. The sampling circuit samples the primary current values of the two flyback circuits to obtain the two flyback currents. i p1 and i p2 The duty cycle correction is obtained through the flow equalization loop control;
[0032] S305. Add the duty cycle D of the inner current loop output to the duty cycle correction amount obtained through the current sharing loop control, and use it as the pulse width modulation signal of the flyback circuit.
[0033] S306. Based on the pulse width modulation signal, the turn-on and turn-off times of the auxiliary switching transistor are calculated, and a reasonable dead time is set so that the control signal of the active clamp passes through the active clamp drive circuit I and the active clamp drive circuit II respectively. The two control signals are 180° out of phase, so that the active clamp circuit works.
[0034] Furthermore, step S4 specifically includes the following sub-steps:
[0035] S401, the internal model of the repetitive controller appears in discrete form, using a non-ideal internal model structure:
[0036]
[0037] in, For a low-pass filter with a gain less than 1, a value of 0.95 is used.
[0038] S402, Transfer function of PI+ repetitive control:
[0039]
[0040] From the characteristic equation of the transfer function, we can see the sufficient condition for system stability:
[0041]
[0042] Where Ts is the system sampling time;
[0043] S403. The design of the compensator provides amplitude and phase compensation for the entire control system. The compensator design method is a phase compensation method based on a leading element, and its characteristics are:
[0044]
[0045] S404, A low-pass filter needs to be introduced in the high-frequency band. To further attenuate the amplitude, a fourth-order Butterworth low-pass filter is selected.
[0046] S405, Design Phase Advance Compensation We choose k=15 as the lead time.
[0047] Further, in step S402, the conditions for system stability are determined, and the equivalent object of the repetitive controller is defined:
[0048]
[0049] Furthermore, in step S403, the compensator mainly comprises three parts: repetitive control gain. Phase advance compensation and low-pass filter Repetitive control gain Take 0.05.
[0050] The beneficial effects of this invention are:
[0051] This invention addresses the high distortion rate of grid-connected current in microinverters by employing a dual closed-loop control strategy. The inner current loop utilizes a PI control combined with repetitive control. PI control enhances the dynamic performance of the microinverter, while repetitive control improves its harmonic suppression capability. Combining PI and repetitive control achieves high grid-connected current quality with excellent dynamic performance and harmonic suppression. This invention requires no changes to the topology of the flyback microinverter and incurs no additional hardware costs. It only requires improvements to the inner current loop, enabling the microinverter to exhibit good harmonic suppression and significantly reduce the distortion rate of the grid-connected current.
[0052] Of course, any product implementing this invention does not necessarily need to achieve all of the above advantages at the same time. Attached Figure Description
[0053] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0054] Figure 1 This is a topology diagram of the interleaved parallel flyback microinverter in the embodiment;
[0055] Figure 2 This is a control block diagram of the interleaved parallel flyback microinverter in the embodiment;
[0056] Figure 3 This is a structural diagram of the repetitive control system in the embodiment;
[0057] Figure 4 This is a structural diagram of the PI+ repetitive control system in the embodiment;
[0058] Figure 5 The Bode plot of the fourth-order Butterworth low-pass filter in the embodiment is shown.
[0059] Figure 6 The diagram shows the phase frequency curves for different values of k in the example.
[0060] Figure 7 The Bode plot of the transfer function of the grid-connected system under composite control in the embodiment;
[0061] Figure 8 The THD diagram of the grid-connected current in the embodiment uses traditional PI control for the inner current loop;
[0062] Figure 9 The current inner loop in this embodiment uses PI+ repetitive control to generate the grid current THD diagram. Detailed Implementation
[0063] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.
[0064] like Figure 1 As shown, this embodiment provides a micro-inverter based on PI and repetitive control. The micro-inverter device includes two flyback circuits, two flyback drive circuits, and a full-bridge inverter and drive circuit. The two identical flyback circuits are connected in parallel with each other, and their input terminals are connected to the solar photovoltaic panel. Their output terminals are connected to the grid access terminal via the full-bridge inverter circuit. Both active clamping circuit I and active clamping circuit II include a clamping capacitor, an auxiliary switch, and an auxiliary diode. The auxiliary switch and the auxiliary diode are connected in parallel and then form a series branch with the clamping capacitor. The series branch is connected in parallel across the primary winding of the transformer in the flyback circuit.
[0065] like Figure 2As shown, the control circuit has an outer voltage loop and an inner current loop. The outer voltage loop uses PI control, and the inner current loop uses PI+ repetitive control. The control circuit generates a pulse width modulation signal PWM1, which controls flyback circuit I through flyback drive circuit I. The control circuit generates a pulse width modulation signal PWM2, which controls flyback circuit II through flyback drive circuit II, causing it to output a sinusoidal half-wave current. The full-bridge inverter circuit consists of four switching transistors. By using zero-crossing polarity reversal, it outputs a sinusoidal current to the grid, where the output voltage is clamped by the grid voltage.
[0066] The control circuit of the interleaved parallel microinverter generates pulse width modulation signals PWM1 and PWM2, whose triangular wave carriers are 180° out of phase and have the same modulation wave. This causes the two flyback circuits to be interleaved and conduct at a 180° phase difference, and also improves the power level of the flyback circuit.
[0067] The active clamping circuit, based on the pulse width modulation signals PWM1 and PWM2, calculates the turn-on and turn-off times of the auxiliary switching transistors and sets a reasonable dead time, so that the control signals of the active clamping pass through the active clamping drive circuit I and the active clamping drive circuit II respectively. The two control signals are 180° out of phase, so that the active clamping circuit works.
[0068] like Figure 2 As shown, this embodiment employs dual closed-loop control: an inner current loop and an outer voltage loop. First, the voltage of the photovoltaic panel is sampled using a sampling circuit. V pv and current I pv Sampling is performed, and the sampled voltage is obtained. V pv and current I pv The voltage outer loop reference value is obtained through MPPT. V ref Voltage outer loop reference value V ref With the voltage of the photovoltaic panel V pv The difference is calculated to obtain the error value, which is then input into the PI controller to obtain the reference value for the grid-connected current amplitude. I ref The amplitude of the grid voltage is sampled by the sampling circuit. u g The grid voltage phase sin(ωt) is sampled and obtained through a phase-locked loop. This provides a reference value for the grid voltage phase and the amplitude of the grid-connected current. I ref Multiply to obtain the grid-connected current reference value. i ref The grid-connected current is obtained by sampling the grid-connected current through a sampling circuit.i g Grid-connected current i g Compared with the grid-connected current reference value i ref The difference is calculated to obtain the error value. This error value is then input into the PI+ repetitive controller to obtain the duty cycle D of the inner current loop output. The sampling circuit samples the primary current values of the two flyback circuits to obtain the two flyback currents. i p1 and i p2 The duty cycle correction is obtained through current sharing loop control. The duty cycle D output by the inner current loop is added to the duty cycle correction obtained through current sharing loop control, which serves as the pulse width modulation signal for the flyback circuit. Based on the pulse width modulation signal, the turn-on and turn-off times of the auxiliary switch are calculated, and a reasonable dead time is set so that the active clamp control signal passes through active clamp drive circuit I and active clamp drive circuit II respectively. The two control signals are 180° out of phase, enabling the active clamp circuit to work.
[0069] To achieve better control performance in the current loop control of the microinverter, circuit modeling and analysis are required, resulting in:
[0070]
[0071] Traditional PI control is insufficient in suppressing harmonics, while repetitive control can effectively suppress them. In practical applications, the internal model of a repetitive controller often appears in a discrete form, as follows:
[0072]
[0073] The above equation represents the ideal repetitive control internal model structure. The integral element based on the fundamental period can achieve zero steady-state error tracking of the command signal. However, the N unit circular poles introduced by the ideal internal model structure in the control system will cause the open-loop system to reach a critical stable state. To enhance the system robustness, the internal model is improved, and its transfer function is as follows:
[0074]
[0075] in, This is a low-pass filter with a gain of less than 1. In practical engineering, it is usually taken as 0.95, and in this embodiment, it is taken as 0.95.
[0076] In practical engineering applications of repetitive controllers, due to bandwidth constraints and environmental disturbances, steady-state errors inevitably occur in their tracking accuracy. To suppress these steady-state errors and enhance system stability and robustness, a compensation element is introduced. This element adjusts and optimizes the repetitive controller based on the system's transfer function characteristics to meet the system's performance indicators and requirements. An example is a grid-connected flyback micro-inverter system with a repetitive controller incorporating a compensation element, internal model filter, and periodic delay element. Figure 3 As shown. With the addition of PI control, the flyback microinverter grid-connected system is as follows: Figure 4 As shown, based on the PI control and repetitive control structure diagrams, the derivation is... i out (z) to i ref (z) is as follows:
[0077]
[0078] To find the conditions for system stability, we can define the equivalent object of the repetitive controller as follows:
[0079]
[0080] From the characteristic equation of the transfer function, we know that the sufficient condition for system stability is as follows:
[0081]
[0082] In the above formula, Ts is the system sampling time. To meet the stability conditions of the system, each component needs to be designed.
[0083] The compensator plays a decisive role in the performance of the entire control system and is designed based on the amplitude-frequency characteristics of the controlled object. The purpose of the compensator is to ensure that the compensated controlled object has zero phase shift and unity-gain characteristics. Its main task is to provide amplitude and phase compensation for the entire control system. For effective error compensation, the given control quantity must have appropriate phase and amplitude. If the phase or amplitude of the given control quantity is inappropriate, the stability of the entire system will be severely affected. The most commonly used compensator design method is a phase compensation method based on a lead element, with the following characteristics:
[0084]
[0085] The compensator mainly consists of three parts: repetitive control gain. Phase advance compensation and low-pass filter Repetitive control gain The magnitude of the error will affect the convergence speed, steady-state error, and system stability.
[0086] The low-to-mid-frequency range of the controlled object is corrected to 1, while the high-frequency range is attenuated to ensure system stability. A low-pass filter needs to be introduced in the high-frequency range. To further attenuate the amplitude, a fourth-order Butterworth low-pass filter is chosen. Its cutoff frequency is typically selected to be less than one-tenth of the sampling frequency; here, a low-pass filter with a cutoff frequency of 1.8 kHz is selected. The Bode plot of this fourth-order Butterworth low-pass filter is shown below. Figure 5 As shown, adding a low-pass filter results in increased phase lag, which affects the system's dynamic response speed and control accuracy. Therefore, phase lead compensation is necessary. The design is necessary. Within the 2.5kHz frequency range, when the phase lead time k is 14, 15, 16, and 17, the compensated phase frequency curve remains within the range of [-90°, 90°], satisfying the system's stability requirements. Figure 6 As shown, when k is 15, the compensated phase frequency curve is closest to 0°, so k=15 is chosen as the lead time.
[0087] After discretization using the zero-order hold method, the Bode plot of the transfer function of the grid-connected system under composite control can be obtained, as follows: Figure 7 As shown, it is clear that after using composite control, the system has a large amplitude gain at n times the fundamental frequency of the input signal (50Hz), significantly improving the system's ability to suppress harmonics and reducing the steady-state error of the system's output signal. Therefore, the composite control combining repetitive control and PI control integrates the advantages of both control methods, enabling the entire flyback microinverter system to both reduce steady-state error and improve the system's dynamic characteristics. Figure 8 For grid-connected current THD using traditional PI control, Figure 9 To achieve better grid-connected current quality (THD) by using PI+ repetitive control, the figure clearly shows that using PI+ repetitive control in the inner current loop can obtain better grid-connected current quality.
[0088] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A micro inverter based on PI and repetitive control, characterized in that, It includes solar photovoltaic panels, active clamp circuit I, active clamp circuit II, flyback circuit I, flyback circuit II, full-bridge inverter circuit, filter circuit and control circuit; After the flyback circuit I and flyback circuit II are connected in parallel with alternating configurations, their input terminals are connected to the solar photovoltaic panels, and their output terminals are connected to the grid access terminal via a full-bridge inverter circuit. Both the active clamping circuit I and the active clamping circuit II include a clamping capacitor, an auxiliary switching transistor, and an auxiliary diode. The auxiliary switching transistor and the auxiliary diode are connected in parallel to form a series branch with the clamping capacitor. The series branch is connected in parallel across the primary winding of the transformer in the flyback circuit. The control circuit has an outer voltage loop and an inner current loop, wherein the outer voltage loop uses PI control and the inner current loop uses PI+ repetitive control. The pulse width modulation signal PWM1 generated by the control circuit controls the flyback circuit I through the flyback drive circuit I, and the pulse width modulation signal PWM2 generated by the control circuit controls the flyback circuit II through the flyback drive circuit II, so that it outputs a sinusoidal half-wave current. The full-bridge inverter circuit consists of four switching transistors. By switching the polarity at the zero-crossing point, it outputs a sine wave of grid current, where the output voltage is clamped by the grid voltage.
2. The control method for a micro-inverter according to claim 1, characterized in that, Includes the following steps: S1, the voltage output by the photovoltaic panel. V pv and current I pv Sampling is performed, and the reference value of the grid-connected current amplitude is obtained through the MPPT perturbation observation method. I ref ; S2, Set the reference value of the grid-connected current amplitude I ref The grid-connected current reference value is obtained by multiplying the phase of the grid voltage obtained from the phase-locked loop. i ref ; S3, Grid-connected current reference value i ref With grid-connected current i g After comparison, the pulse width modulation signals of the two flyback circuits are obtained by PI+ repetitive control and then added to the current sharing loop control. Based on the pulse width modulation signals, the pulse width modulation signals of the two active clamp circuits are obtained by active clamp control circuit. S4. In repetitive control, a non-ideal internal model structure is used. Based on the transfer function of PI+ repetitive control, the repetitive control gain, phase lead compensation, and low-pass filter of the compensator are reasonably designed to enhance the ability of the micro inverter to suppress harmonics.
3. The control method according to claim 2, characterized in that, Step S1 specifically includes the following sub-steps: S101, The voltage of the photovoltaic panel is sampled through the sampling circuit. V pv and current I pv Perform sampling; S102, Sampled voltage V pv and current I pv The voltage outer loop reference value is obtained through MPPT. V ref ; S103, Voltage Outer Loop Reference Value V ref Voltage of photovoltaic panels V pv The difference is calculated to obtain the error value; S104. Input the error value into the PI controller to obtain the reference value of the grid-connected current amplitude. I ref。 4. The control method according to claim 3, characterized in that, Step S2 specifically includes the following sub-steps: S201, The amplitude of the mains voltage is sampled by the sampling circuit. u g The phase of the grid voltage sin(ωt) is sampled; S202. Obtain the grid voltage phase sin(ωt) through a phase-locked loop; S203, Reference values for grid voltage phase and grid-connected current amplitude I ref Multiply to obtain the grid-connected current reference value. i ref .
5. The control method according to claim 4, characterized in that, Step S3 specifically includes the following sub-steps: S301. The grid-connected current is sampled through the sampling circuit to obtain the grid-connected current. i g ; S302, Grid-connected current i g Compared with the grid-connected current reference value i ref The difference is calculated to obtain the error value; S303. Input the error value into the PI+ repetitive controller to obtain the current inner loop output duty cycle D; S304. The sampling circuit samples the primary current values of the two flyback circuits to obtain the two flyback currents. i p1 and i p2 The duty cycle correction is obtained through the flow equalization loop control; S305. Add the duty cycle D of the inner current loop output to the duty cycle correction amount obtained through the current sharing loop control, and use it as the pulse width modulation signal of the flyback circuit. S306. Based on the pulse width modulation signal, the turn-on and turn-off times of the auxiliary switching transistor are calculated, and a reasonable dead time is set so that the control signal of the active clamp passes through the active clamp drive circuit I and the active clamp drive circuit II respectively. The two control signals are 180° out of phase, so that the active clamp circuit works.
6. The control method according to claim 5, characterized in that, Step S4 specifically includes the following sub-steps: S401, the internal model of the repetitive controller appears in discrete form, using a non-ideal internal model structure: ； in, For a low-pass filter with a gain less than 1, a value of 0.95 is used. S402, Transfer function of PI+ repetitive control: ； From the characteristic equation of the transfer function, we can see the sufficient condition for system stability: ； Where Ts is the system sampling time; S403. The design of the compensator provides amplitude and phase compensation for the entire control system. The compensator design method is a phase compensation method based on a leading element, and its characteristics are: ； S404, A low-pass filter needs to be introduced in the high-frequency band. To further attenuate the amplitude, a fourth-order Butterworth low-pass filter is selected. S405, Design Phase Advance Compensation We choose k=15 as the lead time.
7. The control method according to claim 6, characterized in that, In step S402, the conditions for system stability are determined, and the equivalent object of the repetitive controller is defined: 。 8. The control method according to claim 7, characterized in that, In step S403, the compensator mainly consists of three parts: repetitive control gain. Phase advance compensation and low-pass filter Repetitive control gain Take 0.05.