System and method for reducing voltage harmonic distortion of off-grid inverter

Abstract

The invention provides a system for reducing the voltage harmonic distortion of an off-grid inverter, and the system comprises an extended state observation unit, a linear control law unit, a disturbance compensation unit, and a three-dimensional space vector modulation unit. The off-grid voltage and the preset expected voltage of the inverter topology circuit are input into the expansion state observation unit, the linear control law unit and the disturbance compensation unit to obtain a bridge arm circuit unit comprehensive control signal, and the three-dimensional space vector modulation unit is used for carrying out space vector modulation processing on the bridge arm circuit unit comprehensive control signal. And the bridge arm circuit unit generates an off-grid voltage of the inverter topology circuit through the filter unit under the control of the bridge arm circuit unit switching signal. Errors caused by a topology circuit are reduced through a disturbance compensation correction value, the disturbance compensation unit is responsible for restraining disturbance caused by factors such as load changes, and the system can effectively reduce total harmonic distortion (THD) of output voltage.

Description

Technical Field

[0001] The present invention relates to the technical field of off-grid inverter control, and in particular to a system and method for reducing voltage harmonic distortion of an off-grid inverter. Background Art

[0002] With the rapid development of renewable energy technology, off-grid inverters are an important part of solar photovoltaic power generation systems, wind power generation systems and independent power systems. Their performance is directly related to the overall operating efficiency and power quality of the system. LC off-grid inverters have been widely used in renewable energy power generation systems due to their simple structure, high efficiency and good reliability.

[0003] However, due to factors such as changes in load, fluctuations in environmental conditions, and differences in the inverter's own parameters, the output voltage will fluctuate and produce harmonic distortion, thus affecting the power quality.

[0004] At present, the control strategy of off-grid inverters is mainly proportional-integral control. Although this control strategy has a simple structure and is widely used, it has slow dynamic response, poor anti-interference ability, and weak ability to suppress harmonic distortion. Summary of the invention

[0005] The purpose of the present invention is to provide a system and method for reducing voltage harmonic distortion of an off-grid inverter in view of the defects of the prior art.

[0006] The present invention provides a system for reducing voltage harmonic distortion of an off-grid inverter, comprising: an extended state observation unit, a linear control law unit, a disturbance compensation unit and a three-dimensional space vector modulation unit;

[0007] The extended state observation unit is used to perform state observation and disturbance estimation according to the off-grid voltage of the inverter topology circuit, and obtain an off-grid voltage observation value, an off-grid voltage change rate observation value, and a disturbance estimation value;

[0008] The linear control law unit includes a first gain channel, a second gain channel and a control law value calculator. The control law value calculator firstly performs a difference between a preset expected voltage of the inverter topology circuit and an off-grid voltage observation value to obtain a first difference value. The first gain channel is used to perform a linear transformation process on the first difference value to obtain a first control law value. The second gain channel is used to perform a linear transformation process on the off-grid voltage change rate observation value to obtain a second control law value. The control law value calculator then performs a difference between the first control law value and the second control law value to obtain a second difference.

[0009] The disturbance compensation unit is used to obtain a third difference by subtracting the second difference from the disturbance estimation value, obtain a fourth difference by subtracting the third difference from the disturbance compensation correction value, and obtain a comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit by performing scaling compensation processing on the fourth difference;

[0010] The three-dimensional space vector modulation unit is used to perform space vector modulation processing on the comprehensive control signal of the bridge arm circuit unit to obtain a bridge arm circuit unit switching signal. The bridge arm circuit unit generates an off-grid voltage of the inverter topology circuit via the filter unit under the control of the bridge arm circuit unit switching signal.

[0011] Furthermore, it also includes: an iterative calculation unit, which is used to sequentially cycle the expanded state observation unit, the linear control law unit, the disturbance compensation unit and the three-dimensional space vector modulation unit, wherein, in the first round of iteration, the expanded state observation unit performs state observation and disturbance estimation according to the off-grid voltage, and starting from the second round of iteration, the expanded state observation unit performs state observation and disturbance estimation according to the off-grid voltage and the comprehensive control signal of the bridge arm circuit unit obtained in the previous round of iteration, and establishes the iteration end condition:

[0012] |Off-grid voltage observation value - preset expected voltage|≤Δi

[0013] Wherein, Δi represents the preset voltage error value.

[0014] Furthermore, in the three-dimensional space vector modulation unit, the specific method for the bridge arm circuit unit to generate the off-grid voltage of the inverter topology circuit via the filter unit under the control of the bridge arm circuit unit switch signal is:

[0015] The bridge arm circuit unit controls the on and off of the IGBT in the bridge arm circuit unit according to the switch signal, and outputs the initial voltage to the filter unit. The filter unit filters the initial voltage and outputs an off-grid voltage with reduced total harmonic distortion.

[0016] Furthermore, the expanded state space expression of the filter unit is constructed as follows:

[0017]

[0018] Among them, p 1 =-1 / L f C f , p 2 =-1 / RC f , b 0 =1 / L f C f , x 1 =y=v c , x 3 =f,

[0019] In the formula, x 1 is the first variable, is the rate of change of the first variable, x 2is the second variable, is the rate of change of the second variable, x 3 is the third variable, is the rate of change of the third variable, y is the output value of the filter unit, u is the input value of the filter unit, h is the replacement factor of the rate of change of the disturbance, v c is the off-grid voltage, is the off-grid voltage change rate, is the second-order derivative of the off-grid voltage, f is the disturbance of the off-grid voltage, is the change rate of the off-grid voltage disturbance, L f is the inductance of the filter, C f is the capacitance of the filter, R is the linear load connected to the filter, and p 1 is the first disturbance compensation correction parameter, p 2 is the second disturbance compensation correction parameter, b 0 is the compensation factor.

[0020] Furthermore, in the expanded state observation unit, the specific method of performing state observation and disturbance estimation on the off-grid voltage of the inverter topology circuit to obtain the off-grid voltage observation value, the off-grid voltage change rate observation value, and the disturbance estimation value is as follows:

[0021] The observation formula of the extended state observer is established as follows

[0022]

[0023] in:

[0024]

[0025] In the formula, is the off-grid voltage observation value, is the rate of change of off-grid voltage observation value, is the observed value of the off-grid voltage change rate, is the first-order derivative of the off-grid voltage change rate observation, is the disturbance estimate, is the rate of change of the disturbance estimate, A is the state matrix, B is the compensation matrix, C is the observation matrix, L is the error feedback matrix, and l 1 is the first error feedback parameter, l 2 is the second error feedback parameter, l 3 The third error feedback parameter, ω o is the bandwidth of the extended state observer.

[0026] Further, in the linear control law unit, the control law value calculator first subtracts the preset expected voltage of the inverter topology circuit from the off-grid voltage observation value to obtain a first difference, the first gain channel is used to perform a linear transformation process on the first difference to obtain a first control law value, the second gain channel is used to perform a linear transformation process according to the off-grid voltage change rate observation value to obtain a second control law value, and the control law value calculator then subtracts the first control law value from the second control law value to obtain a second difference. The specific method is as follows:

[0027] The formula for establishing the linear control law unit is as follows:

[0028]

[0029] Among them, k d =2ω c , k p =ω c 2 ;

[0030] In the formula, r is the expected voltage, k p is the first gain of the linear control law, k d is the second gain of the linear control law, is the off-grid voltage observation value, is the observed value of the off-grid voltage change rate, Defined as the first difference, Defined as the first control law value, Defined as the second control law value, ω c is the bandwidth of the controller, is the second-order derivative of the off-grid voltage. Defined as the second difference.

[0031] Further, in the disturbance compensation unit, the second difference is subtracted from the disturbance estimation value to obtain a third difference, the third difference is subtracted from the disturbance compensation correction value to obtain a fourth difference, and the fourth difference is scaled and compensated to obtain the comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit. The specific method is as follows:

[0032] The formula for establishing the disturbance compensation unit is as follows:

[0033]

[0034] Among them, p 1 =-1 / L f C f , p 2 =-1 / RC f , b 0 =1 / L f C f ;

[0035] In the formula, F 1 is the disturbance compensation correction value, F 2 is the comprehensive control signal of the bridge arm circuit unit, is the disturbance estimate, Defined as the third difference, Defined as the fourth difference.

[0036] A method for reducing voltage harmonic distortion of an off-grid inverter, comprising:

[0037] Step 1: The expanded state observation unit performs state observation and disturbance estimation according to the off-grid voltage of the inverter topology circuit to obtain an off-grid voltage observation value, an off-grid voltage change rate observation value, and a disturbance estimation value;

[0038] Step 2: The control law value calculator of the linear control law unit first subtracts the preset expected voltage of the inverter topology circuit from the off-grid voltage observation value to obtain a first difference value; the first gain channel of the linear control law unit performs linear transformation processing on the first difference value to obtain a first control law value; the second gain channel of the linear control law unit performs linear transformation processing according to the off-grid voltage change rate observation value to obtain a second control law value; the control law value calculator of the linear control law unit then subtracts the first control law value from the second control law value to obtain a second difference;

[0039] Step 3: The disturbance compensation unit subtracts the second difference from the disturbance estimation value to obtain a third difference, subtracts the third difference from the disturbance compensation correction value to obtain a fourth difference, and performs scaling compensation processing on the fourth difference to obtain a comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit;

[0040] Step 4: The three-dimensional space vector modulation unit performs space vector modulation processing on the comprehensive control signal of the bridge arm circuit unit to obtain a switching signal of the bridge arm circuit unit. The bridge arm circuit unit generates an off-grid voltage of the inverter topology circuit through the filter unit under the control of the switching signal of the bridge arm circuit unit.

[0041] Furthermore, the method further comprises: step 5, looping step 1 to step 4 in sequence;

[0042] Among them, in the first round of iteration, step 1 performs state observation and disturbance estimation based on the off-grid voltage. Starting from the second round of iteration, step 1 performs state observation and disturbance estimation based on the off-grid voltage and the comprehensive control signal obtained in the previous round of iteration, and establishes the iteration end condition:

[0043] |Off-grid voltage observation value - preset expected voltage|≤Δi

[0044] Wherein, Δi represents the preset voltage error value.

[0045] A computer program product comprises a computer program / instruction, wherein when the computer program / instruction is executed by a processor, the method for reducing voltage harmonic distortion of an off-grid inverter is implemented.

[0046] The beneficial effects of the present invention are:

[0047] 1. Compared with the output voltage of the proportional integral control based on the existing common technology, the output voltage waveform of the technical solution of the present invention is smoother, the THD is lower, and the voltage output waveform is more stable during load switching. In the nonlinear load simulation, the steady-state output voltage THD of the present invention can reach 1.46%, while the steady-state output voltage THD under proportional integral control is 4.85%. Further, in the simulation of linear load switching, the two algorithms are used for comparison under the same conditions. The present invention can well cope with the load switching, and the output voltage THD of one phase is 0.69% in the cycle before the load switching, and the output voltage THD of one cycle after the load change is 0.73%. When the proportional integral control faces linear load switching, the output voltage fluctuates greatly. When the output voltage of one phase is analyzed, the THD of one phase is 1.31% in the cycle before the load switching, and the output voltage THD of one cycle after the load change is 2.95%. Furthermore, in the linear load switching experiment, the present invention showed an excellent switching effect. The off-grid output voltage fluctuated slightly before and after the switching. At the same time, the THD was calculated to be 2.34% when any one-phase steady-state output voltage was selected. However, when the proportional-integral control was used for load switching, the off-grid output voltage fluctuated greatly. At the same time, the THD was calculated to be 4.97% when any one-phase steady-state output voltage was selected. The simulation and experiments showed that the present invention can suppress the disturbance caused by factors such as load changes and effectively reduce the total harmonic distortion (THD) of the output voltage.

[0048] 2. The controller in the present invention comprises an extended state observation unit, a linear control law unit, a disturbance compensation unit, a disturbance compensation correction unit and a three-dimensional space vector modulation unit. The disturbance compensation correction unit reduces the error caused by the disturbance of the topological circuit itself, while the disturbance compensation unit is responsible for suppressing the disturbance caused by factors such as load changes, and combined with other units in the controller, the total harmonic distortion (THD) of the output voltage is effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a system structure block diagram of the present invention.

[0050] Figure 2 The voltage and current output waveforms and THD (simulation) with nonlinear load under proportional-integral control.

[0051] Figure 3The voltage and current output waveforms and THD (simulation) with nonlinear load under the control of the present invention.

[0052] Figure 4 The voltage and current output waveforms and THD (simulation) of the linear load switching under proportional-integral control.

[0053] Figure 5 The voltage and current output waveforms and THD (simulation) of the linear load switching under the control of the present invention.

[0054] Figure 6 The voltage and current output waveforms and THD (experimental) of linear load switching under proportional-integral control.

[0055] Figure 7 The voltage and current output waveforms and THD (experimental) of the linear load switching under the control of the present invention.

[0056] Figure 8 It is a schematic diagram of the present invention. DETAILED DESCRIPTION

[0057] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0058] Example 1

[0059] refer to Figure 1 , a system for reducing voltage harmonic distortion of an off-grid inverter, comprising: an extended state observation unit, a linear control law unit, a disturbance compensation unit and a three-dimensional space vector modulation unit;

[0060] The extended state observation unit is used to perform state observation and disturbance estimation according to the off-grid voltage of the inverter topology circuit, and obtain an off-grid voltage observation value, an off-grid voltage change rate observation value, and a disturbance estimation value;

[0061] The linear control law unit includes a first gain channel, a second gain channel and a control law value calculator. The control law value calculator firstly performs a difference between a preset expected voltage of the inverter topology circuit (the rated voltage of the inverter) and an off-grid voltage observation value to obtain a first difference value. The first gain channel is used to perform a linear transformation process on the first difference value to obtain a first control law value. The second gain channel is used to perform a linear transformation process on the off-grid voltage change rate observation value to obtain a second control law value. The control law value calculator then performs a difference between the first control law value and the second control law value to obtain a second difference value.

[0062] The disturbance compensation unit is used to obtain a third difference by subtracting the second difference from the disturbance estimation value, obtain a fourth difference by subtracting the third difference from the disturbance compensation correction value, and obtain a comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit by performing scaling compensation processing on the fourth difference;

[0063] The three-dimensional space vector modulation unit is used to perform space vector modulation processing on the comprehensive control signal of the bridge arm circuit unit to obtain a bridge arm circuit unit switching signal. The bridge arm circuit unit generates an off-grid voltage of the inverter topology circuit via the filter unit under the control of the bridge arm circuit unit switching signal.

[0064] The iterative calculation unit is used to sequentially cycle the extended state observation unit, the linear control law unit, the disturbance compensation unit and the three-dimensional space vector modulation unit, wherein, in the first round of iteration, the extended state observation unit performs state observation and disturbance estimation according to the off-grid voltage, and starting from the second round of iteration, the extended state observation unit performs state observation and disturbance estimation according to the off-grid voltage and the comprehensive control signal of the bridge arm circuit unit obtained in the previous round of iteration, and establishes the iteration end condition:

[0065] |Off-grid voltage observation value - preset expected voltage|≤Δi

[0066] Wherein, Δi represents the preset voltage error value.

[0067] The extended state observation unit is used to observe and estimate the internal state and external disturbance of the system. Through continuous cycle observation, the accuracy and response speed of estimation are improved. After the first difference is amplified by the first gain, the first control law value is output, which is used to adjust the output voltage to be close to the expected voltage. The off-grid voltage change rate state observation value is input into the second gain channel of the linear control law to output the second control law value. The first control law value is subtracted from the second control law value to obtain the second difference. According to the second difference, a more comprehensive control signal can be obtained, which can simultaneously consider the voltage deviation and the voltage change rate. By subtracting the second difference from the disturbance estimate to obtain the third difference, the control signal can be further adjusted to better match the dynamic response of the system. This step is actually to add a correction to the original control signal based on the voltage change rate. The third difference is then subtracted from the disturbance compensation correction value to obtain the fourth difference, which is used to compensate the topological circuit and reduce the influence of the topological circuit's own error on the control effect. The disturbance compensation correction value is the output value of the disturbance compensation correction unit. The comprehensive control signal not only considers the state and external disturbance of the system, but also considers the topological circuit error, so it can control the system more effectively. Feeding the integrated control signal back to the extended state observer during iteration can help the extended state observer to more accurately estimate the state of the topology circuit and external disturbances. Finally, through continuous iterations, the off-grid voltage is infinitely close to the expected voltage, achieving the purpose of reducing voltage harmonic distortion.

[0068] (1) In the three-dimensional space vector modulation unit, the specific method for the bridge arm circuit unit to generate the off-grid voltage of the inverter topology circuit via the filter unit under the control of the bridge arm circuit unit switch signal is:

[0069] The bridge arm circuit unit controls the on and off of the IGBT in the bridge arm circuit unit according to the switch signal, and outputs the initial voltage to the filter unit. The filter unit filters the initial voltage and outputs an off-grid voltage with reduced total harmonic distortion.

[0070] (2) The present invention is based on a three-phase four-bridge-arm inverter, which can be regarded as self-decoupling into three single-phase inverters. Therefore, the present invention uses a certain phase in the three-phase circuit for theoretical analysis and adopts the technical solution of the present invention. The principles of the other two phases are the same. The technical solution of the present invention can also be applied to single-phase off-grid inverters.

[0071] The state space expression for constructing the filter unit is as follows:

[0072]

[0073] Among them, p 1 =-1 / L f C f , p 2 =-1 / RC f , b 0 =1 / L f C f , x 1 =y=v c , x 3 =f,

[0074] In the formula, x 1 is the first variable, is the rate of change of the first variable, x 2 is the second variable, is the rate of change of the second variable, x 3 is the third variable, is the rate of change of the third variable, y is the output value of the filter unit, u is the input value of the filter unit, h is the replacement factor of the rate of change of the disturbance, v c is the off-grid voltage, is the off-grid voltage change rate, is the second-order derivative of the off-grid voltage, f is the disturbance of the off-grid voltage, is the change rate of the off-grid voltage disturbance, L f is the inductance of the filter, C f is the capacitance of the filter, R is the linear load connected to the filter, and p 1 is the first disturbance compensation correction parameter, p2 is the second disturbance compensation correction parameter, b 0 is the compensation factor.

[0075] (3) In the expanded state observation unit, the specific method of performing state observation and disturbance estimation on the off-grid voltage of the inverter topology circuit to obtain the off-grid voltage observation value, the off-grid voltage change rate observation value, and the disturbance estimation value is as follows:

[0076] The observation formula of the extended state observer is established as follows

[0077]

[0078] in:

[0079]

[0080] In the formula, is the off-grid voltage observation value, is the rate of change of off-grid voltage observation value, is the observed value of the off-grid voltage change rate, is the first-order derivative of the off-grid voltage change rate observation, is the disturbance estimate, is the rate of change of the disturbance estimate, A is the state matrix, B is the compensation matrix, C is the observation matrix, L is the error feedback matrix, and l 1 is the first error feedback parameter, l 2 is the second error feedback parameter, l 3 The third error feedback parameter, ω o is the bandwidth of the extended state observer.

[0081] (4) In the linear control law unit, the control law value calculator firstly performs a subtraction between the preset expected voltage of the inverter topology circuit and the off-grid voltage observation value to obtain a first difference value, the first gain channel is used to perform a linear transformation process on the first difference value to obtain a first control law value, the second gain channel is used to perform a linear transformation process according to the off-grid voltage change rate observation value to obtain a second control law value, and the control law value calculator then performs a subtraction between the first control law value and the second control law value to obtain a second difference value. The specific method is as follows:

[0082] The formula for establishing the linear control law unit is as follows:

[0083]

[0084] Among them, k d =2ω c , k p =ω c 2 ;

[0085] In the formula, r is the expected voltage, k p is the first gain of the linear control law, k d is the second gain of the linear control law, is the off-grid voltage observation value, is the observed value of the off-grid voltage change rate, Defined as the first difference, Defined as the first control law value, Defined as the second control law value, ω c is the bandwidth of the controller, is the second-order derivative of the off-grid voltage. Defined as the second difference.

[0086] (5) In the disturbance compensation unit, the method of obtaining a third difference by subtracting the second difference from the disturbance estimation value, obtaining a fourth difference by subtracting the third difference from the disturbance compensation correction value, and performing scaling compensation processing on the fourth difference to obtain a comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit is as follows:

[0087] The formula for establishing the disturbance compensation unit is as follows:

[0088]

[0089] Among them, p 1 =-1 / L f C f , p 2 =-1 / RC f , b 0 =1 / L f C f ;

[0090] In the formula, F 1 is the disturbance compensation correction value, F 2 is the comprehensive control signal of the bridge arm circuit unit, is the disturbance estimate, Defined as the third difference, Defined as the fourth difference.

[0091] Simulation Verification

[0092] The structure diagram is as follows Figure 8 As shown, the specific parameters are: DC voltage source voltage is 700V, voltage fundamental frequency is 50Hz, PWM switching frequency is 20KHz, sampling frequency is 20KHz, filter inductance is 3.2mH, filter capacitance is 5uF, resistance is 4Ω, and rated output voltage is 310sin(100πt)V. In Matlab simulation, the control parameters of the proportional integral controller are set to P=14, I=6. The parameters of the controller of the present invention are set to ωc =2800rad / s,ω o =5600rad / s. When performing nonlinear load simulation, detect the a-phase voltage THD and a-phase voltage and current waveform. When performing load switching simulation, detect the three-phase voltage and current output waveforms. In the experimental stage, a load switching experiment is performed based on the PTS-3000 experimental platform to detect the three-phase voltage output waveform and the steady-state output voltage THD.

[0093] First by Figure 2 and Figure 3 It can be seen that in the nonlinear load simulation, the voltage waveform of the technical solution of the present invention is smooth, and the THD of the output voltage is 1.46%, while the output voltage waveform of the proportional-integral control based on the existing common technology is rough, and the THD is 4.85%.

[0094] Secondly, by Figure 4 and Figure 5 It can be seen that in the load switching simulation, the technical solution of the present invention can well cope with the load switching, and the THD of the output voltage of any one phase is 0.69% in the cycle before the load switching, and the THD of the output voltage of the cycle after the load change is 0.73%. However, the output voltage of the proportional integral control has a large fluctuation when facing the linear load switching, and the THD of the output voltage of any one phase is 1.31% in the cycle before the load switching, and the THD of the output voltage of the cycle after the load change is 2.95%.

[0095] Finally by Figure 6 and Figure 7 It can be seen that in the linear load switching experiment, the present invention shows an excellent switching effect, the off-grid output voltage fluctuates slightly before and after the switching, and the THD is calculated to be 2.34% when any one-phase steady-state output voltage is selected. However, when the proportional-integral control is performing load switching, the off-grid output voltage fluctuates greatly, and the THD is calculated to be 4.97% when any one-phase steady-state output voltage is selected.

[0096] Example 2

[0097] A method for reducing voltage harmonic distortion of an off-grid inverter, comprising:

[0098] Step 1: The expanded state observation unit performs state observation and disturbance estimation according to the off-grid voltage of the inverter topology circuit to obtain an off-grid voltage observation value, an off-grid voltage change rate observation value, and a disturbance estimation value;

[0099] Step 2: The control law value calculator of the linear control law unit first subtracts the preset expected voltage of the inverter topology circuit (the rated voltage of the inverter) from the off-grid voltage observation value to obtain a first difference value; the first gain channel of the linear control law unit performs a linear transformation process on the first difference value to obtain a first control law value; the second gain channel of the linear control law unit performs a linear transformation process according to the off-grid voltage change rate observation value to obtain a second control law value; the control law value calculator of the linear control law unit then subtracts the first control law value from the second control law value to obtain a second difference value;

[0100] Step 3: The disturbance compensation unit subtracts the second difference from the disturbance estimation value to obtain a third difference, subtracts the third difference from the disturbance compensation correction value to obtain a fourth difference, and performs scaling compensation processing on the fourth difference to obtain a comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit;

[0101] Step 4: The three-dimensional space vector modulation unit performs space vector modulation processing on the comprehensive control signal of the bridge arm circuit unit to obtain a switching signal of the bridge arm circuit unit. The bridge arm circuit unit generates an off-grid voltage of the inverter topology circuit through the filter unit under the control of the switching signal of the bridge arm circuit unit.

[0102] Step 5, looping steps 1 to 4 in sequence;

[0103] Among them, in the first round of iteration, step 1 performs state observation and disturbance estimation based on the off-grid voltage. Starting from the second round of iteration, step 1 performs state observation and disturbance estimation based on the off-grid voltage and the comprehensive control signal obtained in the previous round of iteration, and establishes the iteration end condition:

[0104] |Off-grid voltage observation value - preset expected voltage|≤Δi

[0105] Wherein, Δi represents the preset voltage error value.

[0106] The extended state observation unit is used to observe and estimate the internal state and external disturbance of the system. Through continuous cycle observation, the accuracy and response speed of estimation are improved. After the first difference is amplified by the first gain, the first control law value is output, which is used to adjust the output voltage to be close to the expected voltage. The off-grid voltage change rate state observation value is input into the second gain channel of the linear control law to output the second control law value. The first control law value is subtracted from the second control law value to obtain the second difference. According to the second difference, a more comprehensive control signal can be obtained, which can simultaneously consider the voltage deviation and the voltage change rate. By subtracting the second difference from the disturbance estimate to obtain the third difference, the control signal can be further adjusted to better match the dynamic response of the system. This step is actually to add a correction to the original control signal based on the voltage change rate. The third difference is then subtracted from the disturbance compensation correction value to obtain the fourth difference, which is used to compensate the topological circuit and reduce the influence of the topological circuit's own error on the control effect. The disturbance compensation correction value is the output value of the disturbance compensation correction unit. The comprehensive control signal not only considers the state and external disturbance of the system, but also considers the topological circuit error, so it can control the system more effectively. Feeding the integrated control signal back to the extended state observer during iteration can help the extended state observer to more accurately estimate the state of the topology circuit and external disturbances. Finally, through continuous iterations, the off-grid voltage is infinitely close to the expected voltage, achieving the purpose of reducing voltage harmonic distortion.

[0107] (1) In step 4, the specific method for the bridge arm circuit unit to generate the off-grid voltage of the inverter topology circuit via the filter unit under the control of the bridge arm circuit unit switch signal is:

[0108] The bridge arm circuit unit controls the on and off of the IGBT in the bridge arm circuit unit according to the switch signal, and outputs the initial voltage to the filter unit. The filter unit filters the initial voltage and outputs an off-grid voltage with reduced total harmonic distortion.

[0109] (2) The present invention is based on a three-phase four-bridge-arm inverter, which can be regarded as self-decoupling into three single-phase inverters. Therefore, the present invention uses a certain phase in the three-phase circuit for theoretical analysis and adopts the technical solution of the present invention. The principles of the other two phases are the same. The technical solution of the present invention can also be applied to single-phase off-grid inverters.

[0110] The state space expression for constructing the filter unit is as follows:

[0111]

[0112] Among them, p 1 =-1 / L f C f , p 2 =-1 / RC f , b0 =1 / L f C f , x 1 =y=v c , x 3 =f,

[0113] In the formula, x 1 is the first variable, is the rate of change of the first variable, x 2 is the second variable, is the rate of change of the second variable, x 3 is the third variable, is the rate of change of the third variable, y is the output value of the filter unit, u is the input value of the filter unit, h is the replacement factor of the rate of change of the disturbance, v c is the off-grid voltage, is the off-grid voltage change rate, is the second-order derivative of the off-grid voltage, f is the disturbance of the off-grid voltage, is the change rate of the off-grid voltage disturbance, L f is the inductance of the filter, C f is the capacitance of the filter, R is the linear load connected to the filter, and p 1 is the first disturbance compensation correction parameter, p 2 is the second disturbance compensation correction parameter, b 0 is the compensation factor.

[0114] (3) In step 1, the specific method of performing state observation and disturbance estimation on the off-grid voltage of the inverter topology circuit to obtain the off-grid voltage observation value, the off-grid voltage change rate observation value, and the disturbance estimation value is as follows:

[0115] The observation formula of the extended state observer is established as follows

[0116]

[0117] in:

[0118]

[0119] In the formula, is the off-grid voltage observation value, is the rate of change of off-grid voltage observation value, is the observed value of the off-grid voltage change rate, is the first-order derivative of the off-grid voltage change rate observation, is the disturbance estimate, is the rate of change of the disturbance estimate, A is the state matrix, B is the compensation matrix, C is the observation matrix, L is the error feedback matrix, and l 1 is the first error feedback parameter, l 2 is the second error feedback parameter, l 3 The third error feedback parameter, ω o is the bandwidth of the extended state observer.

[0120] (4) In step 2, the control law value calculator firstly performs a subtraction between the preset expected voltage of the inverter topology circuit and the off-grid voltage observation value to obtain a first difference value, the first gain channel is used to perform a linear transformation process on the first difference value to obtain a first control law value, the second gain channel is used to perform a linear transformation process according to the off-grid voltage change rate observation value to obtain a second control law value, and the control law value calculator then performs a subtraction between the first control law value and the second control law value to obtain a second difference value. The specific method is as follows:

[0121] The formula for establishing the linear control law unit is as follows:

[0122]

[0123] Among them, k d =2ω c , k p =ω c 2 ;

[0124] In the formula, r is the expected voltage, k p is the first gain of the linear control law, k d is the second gain of the linear control law, is the off-grid voltage observation value, is the observed value of the off-grid voltage change rate, Defined as the first difference, Defined as the first control law value, Defined as the second control law value, ω c is the bandwidth of the controller, is the second-order derivative of the off-grid voltage. Defined as the second difference.

[0125] (5) In step 3, the method of subtracting the second difference from the disturbance estimation value to obtain a third difference, subtracting the third difference from the disturbance compensation correction value to obtain a fourth difference, and performing scaling compensation processing on the fourth difference to obtain the comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit is as follows:

[0126] The formula for establishing the disturbance compensation unit is as follows:

[0127]

[0128] Among them, p 1 =-1 / L f C f , p 2 =-1 / RC f , b 0 =1 / L f C f ;

[0129] In the formula, F 1 is the disturbance compensation correction value, F 2 is the comprehensive control signal of the bridge arm circuit unit, is the disturbance estimate, Defined as the third difference, Defined as the fourth difference.

[0130] Simulation Verification

[0131] The structure diagram is as follows Figure 8 As shown, the specific parameters are: DC voltage source voltage is 700V, voltage fundamental frequency is 50Hz, PWM switching frequency is 20KHz, sampling frequency is 20KHz, filter inductance is 3.2mH, filter capacitance is 5uF, resistance is 4Ω, and rated output voltage is 310sin(100πt)V. In Matlab simulation, the control parameters of the proportional integral controller are set to P=14, I=6. The parameters of the controller of the present invention are set to ω c =2800rad / s,ω o =5600rad / s. When performing nonlinear load simulation, detect the a-phase voltage THD and a-phase voltage and current waveform. When performing load switching simulation, detect the three-phase voltage and current output waveforms. In the experimental stage, a load switching experiment is performed based on the PTS-3000 experimental platform to detect the three-phase voltage output waveform and the steady-state output voltage THD.

[0132] First by Figure 2 and Figure 3 It can be seen that in the nonlinear load simulation, the voltage waveform of the technical solution of the present invention is smooth, and the THD of the output voltage is 1.46%, while the output voltage waveform of the proportional-integral control based on the existing common technology is rough, and the THD is 4.85%.

[0133] Secondly, by Figure 4 and Figure 5It can be seen that in the load switching simulation, the technical solution of the present invention can well cope with the load switching, and the THD of the output voltage of any one phase is 0.69% in the cycle before the load switching, and the THD of the output voltage of the cycle after the load change is 0.73%. However, the output voltage of the proportional integral control has a large fluctuation when facing the linear load switching, and the THD of the output voltage of any one phase is 1.31% in the cycle before the load switching, and the THD of the output voltage of the cycle after the load change is 2.95%.

[0134] Finally by Figure 6 and Figure 7 It can be seen that in the linear load switching experiment, the present invention shows an excellent switching effect, the off-grid output voltage fluctuates slightly before and after the switching, and the THD is calculated to be 2.34% when any one-phase steady-state output voltage is selected. However, when the proportional-integral control is performing load switching, the off-grid output voltage fluctuates greatly, and the THD is calculated to be 4.97% when any one-phase steady-state output voltage is selected.

[0135] Example 3

[0136] A computer program product includes a computer program / instruction, wherein when the computer program / instruction is executed by a processor, the method for reducing the voltage harmonic distortion of an off-grid inverter in embodiment 2 is implemented.

[0137] The contents not described in detail in this specification belong to the prior art known to those skilled in the art. It should be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0138] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0139] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0140] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit its protection scope. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that after reading the present invention, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation methods of the invention, but these changes, modifications or equivalent substitutions are all within the protection scope of the pending claims of the invention.

Claims

1. A system for reducing voltage harmonic distortion of an off-grid inverter, characterized in that: include: Extended state observation unit, linear control law unit, disturbance compensation unit and three-dimensional space vector modulation unit; The extended state observation unit is used to perform state observation and disturbance estimation according to the off-grid voltage of the inverter topology circuit, and obtain an off-grid voltage observation value, an off-grid voltage change rate observation value, and a disturbance estimation value; The linear control law unit includes a first gain channel, a second gain channel and a control law value calculator. The control law value calculator firstly performs a difference between a preset expected voltage of the inverter topology circuit and an off-grid voltage observation value to obtain a first difference value. The first gain channel is used to perform a linear transformation process on the first difference value to obtain a first control law value. The second gain channel is used to perform a linear transformation process on the off-grid voltage change rate observation value to obtain a second control law value. The control law value calculator then performs a difference between the first control law value and the second control law value to obtain a second difference. The disturbance compensation unit is used to obtain a third difference by subtracting the second difference from the disturbance estimation value, obtain a fourth difference by subtracting the third difference from the disturbance compensation correction value, and obtain a comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit by performing scaling compensation processing on the fourth difference; The three-dimensional space vector modulation unit is used to perform space vector modulation processing on the comprehensive control signal of the bridge arm circuit unit to obtain a bridge arm circuit unit switching signal. The bridge arm circuit unit generates an off-grid voltage of the inverter topology circuit via the filter unit under the control of the bridge arm circuit unit switching signal.

2. The system for reducing voltage harmonic distortion of an off-grid inverter according to claim 1, characterized in that: Also includes: The iterative calculation unit is used to sequentially cycle the extended state observation unit, the linear control law unit, the disturbance compensation unit and the three-dimensional space vector modulation unit, wherein, in the first round of iteration, the extended state observation unit performs state observation and disturbance estimation according to the off-grid voltage, and starting from the second round of iteration, the extended state observation unit performs state observation and disturbance estimation according to the off-grid voltage and the comprehensive control signal of the bridge arm circuit unit obtained in the previous round of iteration, and establishes the iteration end condition: |Off-grid voltage observation value - preset expected voltage|≤Δi Wherein, Δi represents the preset voltage error value.

3. The system for reducing voltage harmonic distortion of an off-grid inverter according to claim 1, characterized in that: In the three-dimensional space vector modulation unit, the specific method for the bridge arm circuit unit to generate the off-grid voltage of the inverter topology circuit via the filter unit under the control of the bridge arm circuit unit switch signal is: The bridge arm circuit unit controls the on and off of the IGBT in the bridge arm circuit unit according to the switch signal, and outputs the initial voltage to the filter unit. The filter unit filters the initial voltage and outputs an off-grid voltage with reduced total harmonic distortion.

4. The system for reducing voltage harmonic distortion of an off-grid inverter according to claim 1, characterized in that: The expanded state space expression for constructing the filter unit is as follows: Where p1 = -1 / L f C f , p2=-1 / RC f , b0=1 / L f C f , x1=y=v c , In the formula, x1 is the first variable, is the rate of change of the first variable, x2 is the second variable, is the rate of change of the second variable, x3 is the third variable, is the rate of change of the third variable, y is the output value of the filter unit, u is the input value of the filter unit, h is the replacement factor of the rate of change of the disturbance, v c is the off-grid voltage, is the off-grid voltage change rate, is the second-order derivative of the off-grid voltage, f is the disturbance of the off-grid voltage, is the change rate of the off-grid voltage disturbance, L f is the inductance of the filter, C f is the capacitance of the filter, R is the linear load connected to the filter, p1 is the first disturbance compensation correction parameter, p2 is the second disturbance compensation correction parameter, and b0 is the compensation factor.

5. The system for reducing voltage harmonic distortion of an off-grid inverter according to claim 4, characterized in that: In the extended state observation unit, the specific method of performing state observation and disturbance estimation on the off-grid voltage of the inverter topology circuit to obtain the off-grid voltage observation value, the off-grid voltage change rate observation value, and the disturbance estimation value is as follows: The observation formula of the extended state observer is established as follows in: In the formula, is the off-grid voltage observation value, is the rate of change of off-grid voltage observation value, is the observed value of the off-grid voltage change rate, is the first-order derivative of the off-grid voltage change rate observation, is the disturbance estimate, is the rate of change of the disturbance estimate, A is the state matrix, B is the compensation matrix, C is the observation matrix, L is the error feedback matrix, l1 is the first error feedback parameter, l2 is the second error feedback parameter, l3 is the third error feedback parameter, ω o is the bandwidth of the extended state observer.

6. The system for reducing voltage harmonic distortion of an off-grid inverter according to claim 5, characterized in that: In the linear control law unit, the control law value calculator firstly performs a difference between the preset expected voltage of the inverter topology circuit and the off-grid voltage observation value to obtain a first difference value, the first gain channel is used to perform a linear transformation process on the first difference value to obtain a first control law value, the second gain channel is used to perform a linear transformation process according to the off-grid voltage change rate observation value to obtain a second control law value, and the control law value calculator then performs a difference between the first control law value and the second control law value to obtain a second difference. The specific method is as follows: The formula for establishing the linear control law unit is as follows: Among them, k d =2ω c , k p =ω c 2 ; In the formula, r is the expected voltage, k is p is the first gain of the linear control law, k d is the second gain of the linear control law, is the off-grid voltage observation value, is the observed value of the off-grid voltage change rate, Defined as the first difference, Defined as the first control law value, Defined as the second control law value, ω c is the bandwidth of the controller, is the second-order derivative of the off-grid voltage. Defined as the second difference.

7. The system for reducing voltage harmonic distortion of an off-grid inverter according to claim 6, characterized in that: In the disturbance compensation unit, the method of obtaining a third difference by subtracting the second difference from the disturbance estimation value, obtaining a fourth difference by subtracting the third difference from the disturbance compensation correction value, and performing scaling compensation processing on the fourth difference to obtain a comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit is as follows: The formula for establishing the disturbance compensation unit is as follows: Where p1 = -1 / L f C f , p2=-1 / RC f , b0=1 / L f C f ; In the formula, F1 is the disturbance compensation correction value, F2 is the comprehensive control signal of the bridge arm circuit unit, is the disturbance estimate, Defined as the third difference, Defined as the fourth difference.

8. A method for reducing voltage harmonic distortion of an off-grid inverter, characterized in that: include: Step 1: The expanded state observation unit performs state observation and disturbance estimation according to the off-grid voltage of the inverter topology circuit to obtain an off-grid voltage observation value, an off-grid voltage change rate observation value, and a disturbance estimation value; Step 2: The control law value calculator of the linear control law unit first subtracts the preset expected voltage of the inverter topology circuit from the off-grid voltage observation value to obtain a first difference value; the first gain channel of the linear control law unit performs linear transformation processing on the first difference value to obtain a first control law value; the second gain channel of the linear control law unit performs linear transformation processing according to the off-grid voltage change rate observation value to obtain a second control law value; the control law value calculator of the linear control law unit then subtracts the first control law value from the second control law value to obtain a second difference; Step 3: The disturbance compensation unit subtracts the second difference from the disturbance estimation value to obtain a third difference, subtracts the third difference from the disturbance compensation correction value to obtain a fourth difference, and performs scaling compensation processing on the fourth difference to obtain a comprehensive control signal of the bridge arm circuit unit of the inverter topology circuit; Step 4: The three-dimensional space vector modulation unit performs space vector modulation processing on the comprehensive control signal of the bridge arm circuit unit to obtain a switching signal of the bridge arm circuit unit. The bridge arm circuit unit generates an off-grid voltage of the inverter topology circuit through the filter unit under the control of the switching signal of the bridge arm circuit unit.

9. The method for reducing voltage harmonic distortion of an off-grid inverter according to claim 8, characterized in that: Also includes: Step 5, repeat step 1 to step 4 in sequence; Among them, in the first round of iteration, step 1 performs state observation and disturbance estimation based on the off-grid voltage. Starting from the second round of iteration, step 1 performs state observation and disturbance estimation based on the off-grid voltage and the comprehensive control signal obtained in the previous round of iteration, and establishes the iteration end condition: |Off-grid voltage observation value - preset expected voltage|≤Δi Wherein, Δi represents the preset voltage error value.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the method for reducing voltage harmonic distortion of an off-grid inverter as described in any one of claims 8 to 9 is implemented.

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