A method and device for suppressing discrete harmonic of grid-connected current of single-phase inverter

Abstract

The present application belongs to the single-phase grid-connected inverter control technical field, specifically relates to a kind of single-phase inverter's grid-connected current discrete harmonic suppression method and device.Control technology in the present application does not need multiple proportional-resonance controller and multiple wave traps, control loop is simple, and control technology software overhead is low;Control technology in the present application can suppress 3, 5, 7 times etc. major harmonic components in grid-connected current, so as to be favorable to optimize the power quality of single-phase grid-connected inverter;In addition, by giving the dq component of grid-connected current reference value, the control technology of the present application can realize the control to grid-connected current active and reactive component;As described above, the present application has certain academic research and engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of single-phase grid-connected inverter control technology, specifically relating to a method and device for suppressing discrete harmonics in the grid-connected current of a single-phase inverter. Background Technology

[0002] Due to the prevalence of nonlinear loads in distributed generation systems, grid voltage distortion is widespread in power systems. Harmonic voltages directly cause distortion in the grid-connected current waveform of single-phase grid-connected inverters, thereby polluting the public power grid and affecting the operational stability of nearby power equipment. Therefore, researching grid-connected current harmonic suppression technology under grid distortion conditions can enable inverters to output high-quality sinusoidal current even under non-ideal grid conditions, thus increasing the operational reliability and grid applicability of single-phase inverters and ensuring they meet stringent grid connection standards.

[0003] Currently, the existing grid-connected current harmonic suppression technologies for single-phase grid-connected inverters are as follows:

[0004] ① Multi-proportional-resonant control technology: By connecting multiple resonant controllers in parallel at specific harmonic frequencies, the main harmonic components such as the 3rd, 5th, and 7th harmonics in the grid-connected current can be suppressed in a targeted manner; however, since multiple proportional-resonant controllers are required, the control loop of this control technology is complex and difficult to implement in software.

[0005] ② Repetitive control technology: Based on the internal model principle, the repetitive controller can effectively suppress periodic harmonic disturbances. Therefore, it can specifically suppress the main harmonic components such as the 3rd, 5th, and 7th harmonics in the grid-connected current. However, due to the presence of a delay element in the repetitive controller, the transient response performance is limited.

[0006] ③ Specific harmonic compensation technology: Notch filters are used to extract the 3rd, 5th, and 7th harmonic components in the grid-connected current, and the grid-connected current is compensated according to the harmonic component information, thereby achieving the harmonic suppression target of the grid-connected current; however, this method requires the use of multiple notch filters to extract the 3rd, 5th, and 7th harmonics, which increases the complexity of the control loop, the software overhead of the control system, and the difficulty of implementation.

[0007] ④ Model predictive control technology: It uses system models to predict the future behavior of single-phase grid-connected inverters and directly selects the optimal switching state of the inverter through rolling optimization, so as to achieve fast grid-connected current tracking while effectively suppressing harmonics; however, the performance of model predictive control depends on factors such as the modeling accuracy of the control system and the setting of evaluation functions, which makes it difficult to apply in actual engineering.

[0008] ⑤ Adaptive PI Control Technology: In weak power grids (with high grid impedance), traditional fixed-parameter PI controllers may lead to system instability or harmonic amplification. Adaptive PI controllers can sense changes in grid impedance and adjust control parameters to ensure system stability and avoid current distortion caused by instability. However, an adaptive PI controller is essentially a low-pass or band-pass filter with limited gain for specific frequency harmonics, unlike repetitive or multi-resonant PR controllers which can provide extremely high gain at specific harmonic frequencies. Therefore, for severe periodic voltage distortion, the suppression effect of using an adaptive PI controller alone is not ideal.

[0009] ⑥ Full feedforward control technology for grid voltage: This control technology introduces all frequency components (including fundamental and harmonics) of the grid voltage into the feedforward path, thereby completely eliminating the disturbance effect of grid background harmonics on the grid-connected current. However, ideal full feedforward requires the introduction of a differential term (compensation for sL), which amplifies high-frequency noise.

[0010] In summary, developing a control method for single-phase grid-connected inverters that features a simple control loop, low software cost, strong control robustness, and effective harmonic suppression is an academic and engineering problem that urgently needs to be solved by technical personnel in this research field. This method provides key technical support for applications in harmonic mitigation and power quality optimization control of single-phase grid-connected inverters. Summary of the Invention

[0011] To address the above problems, this invention proposes a method and apparatus for suppressing discrete harmonics in the grid-connected current of a single-phase inverter.

[0012] The technical solution of this invention is as follows:

[0013] A method for suppressing discrete harmonics in grid-connected current of a single-phase inverter includes the following steps:

[0014] Step 1: At the beginning of each control cycle, sample the input DC voltage u of the single-phase grid-connected inverter. dc Given the grid voltage u and the grid-connected current i, obtain the inductance parameter L and the parasitic resistance parameter R of the single-phase grid-connected inverter. L ; Obtain the fundamental frequency f1 and the maximum allowable frequency deviation Δf max Equivalent harmonic suppression bandwidth f bw,eff ;

[0015] Step 2: Based on the fundamental frequency f1 and the maximum allowable frequency deviation Δf max Equivalent harmonic suppression bandwidth f bw,eff To obtain the damping coefficient k:

[0016]

[0017] Step 3: Based on the grid voltage u, fundamental frequency f1, and damping coefficient k, obtain the grid voltage fundamental angular frequency ω1 and αβ component u using a second-order generalized integrator (SOGI). α and u β :

[0018]

[0019] Step 4: Based on the fundamental component u of the grid voltage α and u β To obtain the phase θ1 of the fundamental component of the grid voltage:

[0020]

[0021] Step 5: Based on the input DC voltage u dc Single-phase grid voltage u, angular frequency ω1, inductance parameters L and parasitic resistance parameters R of the single-phase grid-connected inverter. L and the dq component of the grid-connected current reference value i dref and i qref Calculate the duty cycle D of high and low power pulses. H and D L :

[0022]

[0023] Step Six: Based on the dq component i of the grid-connected current reference value dref and i qref The grid voltage component phase θ1 is calculated based on dq / αβ coordinate transformation and grid-connected current reference calculation to obtain the grid-connected current reference value i. ref :

[0024]

[0025] Step 7: The discrete duty cycle generation module (composed of a comparator and a selector) works as follows: At the beginning of the control cycle, the inverter grid-connected current i is compared with the reference value i ref Comparison: If i ref Select a high-power pulse duty cycle D H Use the discrete duty cycle D; otherwise, choose the low-power pulse duty cycle D. L As the discrete duty cycle D:

[0026]

[0027]

[0028] ​Step 8: Based on the discrete duty cycle D and the SPWM modulation module, the PWM control pulse P of the switching devices in the single-phase grid-connected inverter can be obtained. 1,2,3,4 .

[0029] Preferably, the damping coefficient k of the SOGI includes:

[0030] Based on the fundamental frequency f1 and the maximum allowable frequency deviation Δf max Equivalent harmonic suppression bandwidth f bw,eff The damping coefficient k is obtained, and its expression is: ;

[0031] Preferably, the fundamental angular frequency ω1 and αβ component u of the power grid voltage α and u β ,include:

[0032] Based on the grid voltage u, fundamental frequency f1, and damping coefficient k, the fundamental angular frequency ω1 and αβ component u of the grid voltage are obtained using a second-order generalized integrator (SOGI). α and u β Its expression is: ;

[0033] Preferably, the fundamental component phase θ1 of the grid voltage includes:

[0034] According to the fundamental component u of the grid voltage α and u β The phase θ1 of the fundamental component of the grid voltage is obtained, and its expression is: ;

[0035] Preferably, the duty cycle D of the high and low power pulses H and D L ,include:

[0036] Based on the input DC voltage u dc Single-phase grid voltage u, angular frequency ω1, inductance parameters L and parasitic resistance parameters R of the single-phase grid-connected inverter. L and the dq component of the grid-connected current reference value i dref and i qref Calculate the duty cycle D of high and low power pulses. H and D L Its expression is: ;

[0037] Preferably, the grid-connected current reference value i ref ,include:

[0038] Based on the dq component of the grid-connected current reference valuedref and i qref The grid voltage component phase θ1 is calculated based on dq / αβ coordinate transformation and grid-connected current reference calculation to obtain the grid-connected current reference value i. ref Its expression is: ;

[0039] Preferably, the discrete duty cycle D includes:

[0040] At the start of the control cycle, the inverter grid-connected current i is compared with the reference value i. ref Comparison: If i ref Select a high-power pulse duty cycle D H Use the discrete duty cycle D; otherwise, choose the low-power pulse duty cycle D. L The expression for the discrete duty cycle D is: ;

[0041] Preferably, the PWM control pulse P of the single-phase grid-connected inverter switching device 1,2,3,4 ,include:

[0042] Based on the discrete duty cycle D and the SPWM modulation module, the PWM control pulse P of the switching devices in a single-phase grid-connected inverter can be obtained. 1,2,3,4 .

[0043] The present invention also provides a grid-connected current discrete harmonic suppression device for a single-phase inverter, comprising a voltage and current sampling module and a circuit parameter acquisition module, a second-order generalized integrator, a grid voltage fundamental component phase calculation module, a high / low power pulse duty cycle calculation module, a dq / αβ coordinate transformation calculation and grid-connected current reference calculation module, a discrete duty cycle generation module, and an SPWM modulation module, used to execute various steps in the method.

[0044] The beneficial effects of this invention are as follows: the control technology of this invention does not require multiple proportional-resonant controllers and multiple notch filters, the control loop is simple, and the software overhead of the control technology is low; the control technology of this invention can suppress the main harmonic components such as the 3rd, 5th, and 7th orders in the grid-connected current, thereby helping to optimize the power quality of single-phase grid-connected inverters; in addition, by giving the dq component of the grid-connected current reference value, the control technology of this invention can achieve control of the active and reactive components of the grid-connected current; in summary, this invention has certain academic research and engineering application value. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the structure of a grid-connected current discrete harmonic suppression method and device for a single-phase inverter provided in an embodiment of the present invention;

[0046] Figure 2 ​This is a time-domain waveform and spectrum analysis diagram of the grid voltage u under a certain operating condition (the effective values ​​of the grid voltage fundamental u1, 3rd harmonic u3, 5th harmonic u5 and 7th harmonic u7 are 120V, 9.6V, 6V and 3.6V respectively) provided by an embodiment of the present invention.

[0047] Figure 3 This embodiment of the invention provides the grid voltage u and the grid voltage fundamental αβ component u under a specific operating condition (the effective values ​​of the grid voltage fundamental u1, 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 are 120V, 9.6V, 6V, and 3.6V, respectively). α and u β Time-domain simulation waveform of the fundamental component phase θ1 of the grid voltage;

[0048] Figure 4 The dq component i of the grid-connected current reference value under a certain operating condition (the effective values ​​of the grid voltage fundamental u1, 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 are 120V, 9.6V, 6V, and 3.6V, respectively) is provided in an embodiment of the present invention. dref and i qref αβ component i αref and i βref Grid-connected current reference value i ref Time-domain simulation waveform;

[0049] Figure 5 This invention provides a grid-connected current i and its reference value i under a specific operating condition (with effective values ​​of the grid voltage fundamental u1, 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 being 120V, 9.6V, 6V, and 3.6V, respectively). ref Flag bit, high / low power pulse duty cycle D H and D L Time-domain simulation waveform;

[0050] Figure 6 This invention provides an embodiment of an operating condition (with a grid voltage fundamental value of u1 of 120V, t=1.003s, the effective values ​​of the grid voltage third harmonic u3, fifth harmonic u5, and seventh harmonic u7 step from 0V to 9.6V, 6V, and 3.6V respectively), and the dq component i of the grid-connected current reference value. dref =10A and i qref The time-domain simulation waveforms of the grid voltage u (=0A), the third harmonic u3, the fifth harmonic u5 and the seventh harmonic u7 of the grid voltage, and the grid current i are shown.

[0051] Figure 7This invention provides an embodiment of an operating condition (with a grid voltage fundamental value of u1 of 120V, t=1.003s, the effective values ​​of the grid voltage third harmonic u3, fifth harmonic u5, and seventh harmonic u7 step from 0V to 9.6V, 6V, and 3.6V respectively), and the dq component i of the grid-connected current reference value. dref =10A and i qref The grid voltage u, the third harmonic u3, the fifth harmonic u5 and the seventh harmonic u7 of the grid voltage, and the grid current i are obtained from the spectrum analysis simulation waveform diagram.

[0052] Figure 8 When using the traditional proportional-resonant control method, under a certain operating condition, the effective value of the fundamental grid voltage u1 is 120V. At t=1.003s, the effective values ​​of the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage step from 0V to 9.6V, 6V, and 3.6V, respectively. The dq component i of the grid-connected current reference value... dref =10A and i qref The time-domain simulation waveforms of the grid voltage u (=0A), the third harmonic u3, the fifth harmonic u5 and the seventh harmonic u7 of the grid voltage, and the grid current i are shown.

[0053] Figure 9 When using the traditional proportional-resonant control method, under a certain operating condition, the effective value of the fundamental grid voltage u1 is 120V. At t=1.003s, the effective values ​​of the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage step from 0V to 9.6V, 6V, and 3.6V, respectively. The dq component i of the grid-connected current reference value... dref =10A and i qref The time-domain simulation waveforms of the grid voltage u (=0A), the third harmonic u3, the fifth harmonic u5 and the seventh harmonic u7 of the grid voltage, and the grid current i are shown.

[0054] Figure 10 This invention provides an embodiment of an operating condition (with a grid voltage fundamental value of u1 of 120V, t=1.003s, the effective values ​​of the grid voltage third harmonic u3, fifth harmonic u5, and seventh harmonic u7 step from 0V to 9.6V, 6V, and 3.6V respectively), and the dq component i of the grid-connected current reference value. dref =0A and i qref The simulation waveforms of the grid voltage u (=8A), the 3rd harmonic u3, 5th harmonic u5 and 7th harmonic u7 of the grid voltage, and the grid current i are obtained from the spectrum analysis. Detailed Implementation

[0055] 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 of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0056] Example:

[0057] Figure 1 This is a structural block diagram of a method and device for suppressing discrete harmonics in the grid-connected current of a single-phase inverter, as provided in this embodiment. Figure 1 The control block diagram includes a single-phase inverter topology and a method for suppressing discrete harmonics in grid-connected current. The control block diagram for the method for suppressing discrete harmonics in grid-connected current consists of a voltage and current sampling module and a circuit parameter acquisition module, a second-order generalized integrator (SOGI), a grid voltage fundamental component phase calculation module, a high / low power pulse duty cycle calculation module, a dq / αβ coordinate transformation calculation and grid-connected current reference calculation module, a discrete duty cycle generation module (comparator and selector), and an SPWM modulation module.

[0058] Depend on Figure 1 The diagram shows a structural block diagram of a method and device for suppressing discrete harmonics in the grid-connected current of a single-phase inverter. The steps of the method for suppressing discrete harmonics in the grid-connected current of a single-phase inverter provided in this embodiment of the invention are as follows:

[0059] Step 1: At the beginning of each control cycle, sample the input DC voltage u of the single-phase grid-connected inverter. dc Given the grid voltage u and the grid-connected current i, obtain the inductance parameter L and the parasitic resistance parameter R of the single-phase grid-connected inverter. L ; Obtain the fundamental frequency f1 and the maximum allowable frequency deviation Δf max Equivalent harmonic suppression bandwidth f bw,eff ;

[0060] Step 2: Based on the fundamental frequency f1 and the maximum allowable frequency deviation Δf max Equivalent harmonic suppression bandwidth f bw,eff To obtain the damping coefficient k:

[0061]

[0062] Step 3: Based on the grid voltage u, fundamental frequency f1, and damping coefficient k, obtain the grid voltage fundamental angular frequency ω1 and αβ component u using a second-order generalized integrator (SOGI). αand u β :

[0063]

[0064] Step 4: Based on the fundamental component u of the grid voltage α and u β To obtain the phase θ1 of the fundamental component of the grid voltage:

[0065]

[0066] Step 5: Based on the input DC voltage u dc Single-phase grid voltage u, angular frequency ω1, inductance parameters L and parasitic resistance parameters R of the single-phase grid-connected inverter. L and the dq component of the grid-connected current reference value i dref and i qref Calculate the duty cycle D of high and low power pulses. H and D L :

[0067]

[0068] Step Six: Based on the dq component i of the grid-connected current reference value dref and i qref The grid voltage component phase θ1 is calculated based on dq / αβ coordinate transformation and grid-connected current reference calculation to obtain the grid-connected current reference value i. ref :

[0069]

[0070] Step 7: The discrete duty cycle generation module (composed of a comparator and a selector) works as follows: At the beginning of the control cycle, the inverter grid-connected current i is compared with the reference value i ref Comparison: If i ref Select a high-power pulse duty cycle D H Use the discrete duty cycle D; otherwise, choose the low-power pulse duty cycle D. L As the discrete duty cycle D:

[0071]

[0072]

[0073] Step 8: Based on the discrete duty cycle D and the SPWM modulation module, the PWM control pulse P of the switching devices in the single-phase grid-connected inverter can be obtained. 1,2,3,4 .

[0074] ​The present invention also provides a grid-connected current discrete harmonic suppression device for a single-phase inverter, which has the beneficial effects of the above-mentioned grid-connected current discrete harmonic suppression method for a single-phase inverter, and will not be described in detail here.

[0075] Figures 2-10 This is a simulation result of a grid-connected current discrete harmonic suppression device for a single-phase inverter provided in an embodiment of the present invention.

[0076] Figures 2-10 The simulation results shown include the following circuit parameters for the three-phase grid-connected converter: input DC voltage u dc =400V, the rated output voltage is U N =120V, grid fundamental frequency is 50Hz, grid-connected filter inductor L=5mH, switching frequency f s =20kHz. When the grid voltage is distorted, the effective values ​​of the fundamental voltage u1, the 3rd harmonic u3, the 5th harmonic u5, and the 7th harmonic u7 are 120V, 9.6V, 6V, and 3.6V, respectively.

[0077] Figures 2-5 The following are simulation results of a grid-connected current discrete harmonic suppression device for a single-phase inverter under grid voltage distortion conditions (the effective values ​​of the grid voltage fundamental u1, 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 are 120V, 9.6V, 6V, and 3.6V, respectively):

[0078] Figure 2 This is a time-domain waveform and spectrum analysis diagram of the grid voltage u under a specific operating condition (the effective values ​​of the grid voltage fundamental u1, 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 are 120V, 9.6V, 6V, and 3.6V, respectively). This is provided by an embodiment of the present invention. Figure 2 It can be seen that due to the presence of the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 in the grid voltage u, the waveform of the grid voltage u is significantly distorted, and the THD is 9.90%.

[0079] Figure 3 This embodiment of the invention provides the grid voltage u and the grid voltage fundamental αβ component u under a specific operating condition (the effective values ​​of the grid voltage fundamental u1, 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 are 120V, 9.6V, 6V, and 3.6V, respectively). α and u β The time-domain simulation waveform of the fundamental component phase θ1 of the grid voltage; by Figure 3 It can be seen that SOGI is used to obtain the fundamental αβ component u of the grid voltage. α and u β Then, the phase θ1 of the fundamental component of the grid voltage can be calculated;

[0080] Figure 4 The dq component i of the grid-connected current reference value under a certain operating condition (the effective values ​​of the grid voltage fundamental u1, 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 are 120V, 9.6V, 6V, and 3.6V, respectively) is provided in an embodiment of the present invention. dref and i qref αβ component i αref and i βref Grid-connected current reference value i ref The time-domain simulation waveform diagram; by Figure 4 It can be seen that, based on the dq component i of the grid-connected current reference value dref and i qref The grid voltage component phase θ1 is calculated based on dq / αβ coordinate transformation and grid-connected current reference calculation to obtain the grid-connected current reference value i. ref : ;

[0081] Figure 5 This invention provides a grid-connected current i and its reference value i under a specific operating condition (with effective values ​​of the grid voltage fundamental u1, 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 being 120V, 9.6V, 6V, and 3.6V, respectively). ref Flag bit, high / low power pulse duty cycle D H and D L The time-domain simulation waveform diagram; by Figure 5 It can be seen that at the beginning of the control cycle, the inverter grid-connected current i is compared with the reference value i ref Comparison: If i ref Select a high-power pulse duty cycle D H Use the discrete duty cycle D; otherwise, choose the low-power pulse duty cycle D. L As the discrete duty cycle D:

[0082] Figures 6-7 This invention provides an embodiment of an operating condition (with a grid voltage fundamental value of u1 of 120V, t=1.003s, the effective values ​​of the grid voltage third harmonic u3, fifth harmonic u5, and seventh harmonic u7 step from 0V to 9.6V, 6V, and 3.6V respectively), and the dq component i of the grid-connected current reference value. dref =10A and i qref Simulation results of a grid-connected current discrete harmonic suppression device for a single-phase inverter (=0A):

[0083] Figure 6 ​This invention provides an embodiment of an operating condition (with a grid voltage fundamental value of u1 of 120V, t=1.003s, the effective values ​​of the grid voltage third harmonic u3, fifth harmonic u5, and seventh harmonic u7 step from 0V to 9.6V, 6V, and 3.6V respectively), and the dq component i of the grid-connected current reference value. dref =10A and i qref The time-domain simulation waveforms of the grid voltage u (=0A), the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage, and the grid-connected current i are shown. Figure 6 It can be seen that, due to the use of the grid-connected current discrete harmonic suppression method for a single-phase inverter proposed in this invention, the grid-connected current i waveform is highly sinusoidal when the grid voltage u is distorted;

[0084] Figure 7 This invention provides an embodiment of an operating condition (with a grid voltage fundamental value of u1 of 120V, t=1.003s, the effective values ​​of the grid voltage third harmonic u3, fifth harmonic u5, and seventh harmonic u7 step from 0V to 9.6V, 6V, and 3.6V respectively), and the dq component i of the grid-connected current reference value. dref =10A and i qref Simulation waveforms of the grid voltage u (=0A), the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage, and the grid-connected current i; (from...) Figure 7 It can be seen that, due to the use of the grid-connected current discrete harmonic suppression method for a single-phase inverter proposed in this invention, when the grid voltage u is distorted, the harmonic components of the grid-connected current i are limited to below 0.10, the THD is 2.81%, which is limited to within 3%, and the waveform quality is good.

[0085] Figures 8-9 When using the traditional proportional-resonant control method, under a certain operating condition, the effective value of the fundamental grid voltage u1 is 120V. At t=1.003s, the effective values ​​of the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage step from 0V to 9.6V, 6V, and 3.6V, respectively. The dq component i of the grid-connected current reference value... dref =10A and i qref Simulation results for (=0A):

[0086] Figure 8 When using the traditional proportional-resonant control method, under a certain operating condition, the effective value of the fundamental grid voltage u1 is 120V. At t=1.003s, the effective values ​​of the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage step from 0V to 9.6V, 6V, and 3.6V, respectively. The dq component i of the grid-connected current reference value... dref =10A and i qrefThe time-domain simulation waveforms of the grid voltage u (=0A), the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage, and the grid-connected current i are shown. Figure 8 It can be seen that when using the traditional proportional-resonant control method, the waveform of the grid current i is significantly distorted when the grid voltage u is distorted.

[0087] Figure 9 When using the traditional proportional-resonant control method, under a certain operating condition, the effective value of the fundamental grid voltage u1 is 120V. At t=1.003s, the effective values ​​of the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage step from 0V to 9.6V, 6V, and 3.6V, respectively. The dq component i of the grid-connected current reference value... dref =10A and i qref The time-domain simulation waveforms of the grid voltage u (=0A), the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage, and the grid-connected current i are shown. Figure 9 It can be seen that when using the traditional proportional-resonant control method, the THD of the grid-connected current i is 25.58% when the grid voltage u is distorted;

[0088] contrast Figures 6-7 and Figures 8-9 Simulation results show that, compared with the traditional proportional-resonant control method, the grid-connected current discrete harmonic suppression method for single-phase inverters proposed in this invention has the beneficial effect of suppressing grid-connected current harmonic components.

[0089] Figure 10 This invention provides an embodiment of an operating condition (with a grid voltage fundamental value of u1 of 120V, t=1.003s, the effective values ​​of the grid voltage third harmonic u3, fifth harmonic u5, and seventh harmonic u7 step from 0V to 9.6V, 6V, and 3.6V respectively), and the dq component i of the grid-connected current reference value. dref =0A and i qref The grid voltage u (e.g., 8A), the 3rd harmonic u3, 5th harmonic u5, and 7th harmonic u7 of the grid voltage, and the simulated waveforms of the grid-connected current i are analyzed by spectrum analysis. Figure 10 It can be seen that, due to the use of the grid-connected current discrete harmonic suppression method for a single-phase inverter proposed in this invention, the waveform of the grid-connected current i is highly sinusoidal when the grid voltage u is distorted; in addition, the above method can adjust the power factor of the grid-connected current i and the grid voltage fundamental u1.

[0090] The above verification process proves the correctness of the working principle, the feasibility of software implementation, and the effectiveness of the control performance of the grid-connected current discrete harmonic suppression method for a single-phase inverter provided in this embodiment.

[0091] The foregoing has provided a detailed description of a method and apparatus for suppressing discrete harmonics in the grid-connected current of a single-phase inverter, as provided by this invention. The various embodiments in the specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section. It should be noted that those skilled in the art can make several improvements and modifications to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A method for suppressing discrete harmonics in the grid-connected current of a single-phase inverter, characterized in that, Includes the following steps: S1. At the beginning of each control cycle, sample the input DC voltage u of the single-phase grid-connected inverter. dc Given the grid voltage u and the grid-connected current i, obtain the inductance parameter L and the parasitic resistance parameter R of the single-phase grid-connected inverter. L Obtain the fundamental frequency f1 and the maximum allowable frequency deviation Δf. max Equivalent harmonic suppression bandwidth f bw,eff ; S2. Based on the fundamental frequency f1, the maximum allowable frequency deviation Δf max Equivalent harmonic suppression bandwidth f bw,eff To obtain the damping coefficient k: ； S3. Based on the grid voltage u, fundamental frequency f1, and damping coefficient k, the fundamental angular frequency ω1 and αβ component u of the grid voltage are obtained using a second-order generalized integrator. α and u β : ； S4. Based on the fundamental component u of the grid voltage α and u β To obtain the phase θ1 of the fundamental component of the grid voltage: ； S5, based on the input DC voltage u dc Single-phase grid voltage u, angular frequency ω1, inductance parameters L and parasitic resistance parameters R of the single-phase grid-connected inverter. L and the dq component of the grid-connected current reference value i dref and i qref Calculate the duty cycle D of high and low power pulses. H and D L : ； S6. Based on the dq component of the grid-connected current reference value, i dref and i qref The grid voltage component phase θ1 is calculated based on dq / αβ coordinate transformation and grid-connected current reference calculation to obtain the grid-connected current reference value i. ref : ； S7. At the start of the control cycle, the inverter grid-connected current i is compared with the reference value i ref Comparison: If i ref Select a high-power pulse duty cycle D H Use the discrete duty cycle D; otherwise, choose the low-power pulse duty cycle D. L As the discrete duty cycle D:​ ； S8. Obtain the PWM control pulse P of the switching devices in the single-phase grid-connected inverter based on the discrete duty cycle D. 1,2,3,4 .

2. A grid-connected current discrete harmonic suppression device for a single-phase inverter, used in the grid-connected current discrete harmonic suppression method for a single-phase inverter as described in claim 1, characterized in that, It includes a voltage and current sampling module and a circuit parameter acquisition module, a second-order generalized integrator, a grid voltage fundamental component phase calculation module, a high / low power pulse duty cycle calculation module, a dq / αβ coordinate transformation calculation and grid-connected current reference calculation module, a discrete duty cycle generation module, and an SPWM modulation module; The voltage and current sampling module and the circuit parameter acquisition module are used to sample the input DC voltage u of the single-phase grid-connected inverter at the beginning of each control cycle. dc Given the grid voltage u and the grid-connected current i, obtain the inductance parameter L and the parasitic resistance parameter R of the single-phase grid-connected inverter. L ; Obtain the fundamental frequency f1 and the maximum allowable frequency deviation Δf max Equivalent harmonic suppression bandwidth f bw,eff ; The second-order generalized integrator is used to determine the fundamental frequency f1 and the maximum allowable frequency deviation Δf. max Equivalent harmonic suppression bandwidth f bw,eff The damping coefficient k is obtained, and its expression is: Based on the grid voltage u, fundamental frequency f1, and damping coefficient k, the fundamental angular frequency ω1 and αβ component u of the grid voltage are obtained. α and u β Its expression is: ; The grid voltage fundamental component phase calculation module is used to calculate the phase of the grid voltage fundamental component u. α and u β The phase θ1 of the fundamental component of the grid voltage is obtained by the following expression: ; The high / low power pulse duty cycle calculation module is used to calculate the input DC voltage u. dc Single-phase grid voltage u, angular frequency ω1, inductance parameters L and parasitic resistance parameters R of the single-phase grid-connected inverter. L and the dq component of the grid-connected current reference value i dref and i qref Calculate the duty cycle D of high and low power pulses. H and D L The expression is: ; The dq / αβ coordinate transformation calculation and grid-connected current reference calculation module is used to calculate the dq component i of the grid-connected current reference value. dref and i qref The grid voltage component phase θ1 is calculated based on dq / αβ coordinate transformation and grid-connected current reference calculation to obtain the grid-connected current reference value i. ref Its expression is: ; The discrete duty cycle generation module is used to, at the start of the control cycle, compare the inverter grid-connected current i with the reference value i ref Comparison: If i ref Select a high-power pulse duty cycle D H As the discrete duty cycle D;​ Otherwise, choose a low-power pulse duty cycle D. L The expression for the discrete duty cycle D is: ; The SPWM modulation module is used to obtain the PWM control pulse P of the switching devices of the single-phase grid-connected inverter based on the discrete duty cycle D. 1,2,3,4 .

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