Discrete indirect power control method and device of grid-connected inverter

Abstract

This invention belongs to the fields of AC / DC microgrid "interface converters", energy storage systems and new energy power generation, and active reactive power compensation, and particularly relates to a discrete indirect power control method and device for grid-connected inverters. The control method in this invention is implemented in the αβ stationary coordinate system, eliminating the need for synchronous rotational coordinate transformation calculations. In this invention, the reference value of the grid-connected inverter output current is obtained through calculations using active / reactive power reference values ​​and grid voltage. A current-type pulse train (PT) control method is used to make the output current follow its reference value, thereby achieving the indirect power control objective. Therefore, the control method provided by this invention does not require an error amplifier and its compensation network (proportional-integral controller), the controller parameter design and digital implementation are relatively simple, and it has the advantage of low software cost, possessing certain academic research and engineering application value.

Description

Technical Field

[0001] This invention belongs to the fields of AC / DC microgrid "interface converter", energy storage system and new energy power generation, and active reactive power compensation. In particular, it relates to a discrete indirect power control method and device for grid-connected inverters. Background Technology

[0002] Three-phase grid-connected inverters have the advantages of simple structure, high power density, flexible control and modulation, and controllable output active and reactive power. They are widely used in grid-connected engineering applications of new energy power generation equipment and energy storage devices such as wind power and photovoltaics, and play an important role as "interface converters" to realize active and reactive power dispatch.

[0003] The control objectives of a three-phase grid-connected inverter are as follows: to follow the grid voltage and frequency, and to inject current with controllable amplitude and phase into the grid, thereby achieving active and reactive power control objectives. By controlling active power, the three-phase grid-connected inverter can provide active power support to the grid-connected load and perform peak shaving and valley filling, thus realizing the energy management and dispatch functions of the three-phase grid-connected inverter. By controlling reactive power, the three-phase grid-connected inverter can achieve grid-side power factor regulation, high / low voltage ride-through function for grid-connected equipment, and voltage amplitude regulation at the grid connection point (based on the reactive power-voltage amplitude droop characteristic).

[0004] Currently, the existing current-source control methods for three-phase grid-connected inverters are as follows:

[0005] ① Proportional-Integral Control Method: Proportional-integral control (PI control) can achieve the output current control target of a three-phase grid-connected inverter, and the controller is simple to implement. However, the integral element in the proportional-integral controller has limited gain for power frequency AC quantities, making it difficult to achieve zero steady-state error control of the output current. In the dq synchronous rotating coordinate system, the grid-connected inverter output current is converted into DC quantity. Since the integral element in the PI controller has infinite gain for DC quantity, zero steady-state error control of the output current can be achieved. However, the above control method requires synchronous rotating coordinate transformation calculation, resulting in high software costs.

[0006] ② Proportional-resonant control and quasi-proportional-resonant control methods (i.e., PR and QPR control): Since the PR and QPR controllers contain the internal mode (i.e., resonant element) of the grid current signal in the s-domain, according to the internal mode principle, the PR and QPR controllers have infinite gain for power frequency AC quantities, and can achieve zero steady-state error control of the output current; however, the structure of the PR and QPR controllers is relatively complex (consisting of proportional parameters, resonant parameters, and cutoff frequency parameters), and the design, parameter tuning, and digital programming of the controllers are relatively complex.

[0007] ③ Fuzzy PI control or PR control method: Utilizing fuzzy rules to simulate expert experience, the fuzzy PI controller or PR controller can adjust the controller parameters online to achieve self-tuning when the operating conditions of the grid-connected inverter change. Compared with traditional PI control or PR control, fuzzy PI control or PR control has the advantages of high steady-state accuracy, fast transient response speed, and strong control robustness. However, the control performance of this method is highly dependent on the design of the fuzzy rule base, membership function, etc., and requires more online calculations, which places higher demands on the controller hardware.

[0008] ④ Model Predictive Control (MPC): Based on the mathematical model of the grid-connected inverter control system, MPC uses the system model to predict future behavior and selects the optimal switching state of the grid-connected inverter by minimizing the cost function, thereby achieving the optimal control objective of the output current. This control method has the advantage of high steady-state control accuracy; however, MPC requires the calculation of weighting coefficients and cost functions, resulting in a heavy computational burden. In addition, the control performance of MPC is highly dependent on the modeling accuracy of the grid-connected inverter and has limited robustness to unconsidered stray parameters, thus limiting its engineering applications.

[0009] ⑤ Particle Swarm Optimization (PSO) Control Algorithm: The basic principle of PSO is to treat the controller parameters to be optimized (such as the gain coefficients of PI or PR) as particle positions in the search space. Each particle iteratively updates its velocity and position by tracking its own historical best position and the group's historical best position, gradually approaching the global optimum. In actual operation, a group of random particles is first initialized. The fitness (such as current tracking error, total harmonic distortion, etc.) of each set of parameters is substituted into the inverter simulation model. Then, the individual extreme values ​​and the group extreme values ​​are updated according to the fitness, and the particles are guided to gather towards the optimal region according to the velocity-position update formula. This process is repeated until convergence. This method does not require gradient information, has strong global search capabilities, and can effectively solve the problems of traditional parameter tuning relying on experience and being prone to getting trapped in local optima, significantly improving the dynamic response and steady-state accuracy of grid-connected inverters. However, PSO has problems such as high computational burden, difficulty in achieving online real-time control, unstable convergence performance, difficulty in designing fitness functions, and limited adaptability of offline optimized control parameters to system changes. In addition, the PSO control method has the problem of high software cost.

[0010] In summary, developing a method for controlling the output current and active / reactive power of a three-phase grid-connected inverter with high control precision, simple digital implementation, and low software cost is an academic and engineering problem that urgently needs to be solved by technical personnel in this research field. This method provides key support for improving the control performance of three-phase grid-connected inverters and their engineering applications in power electronic power systems. Summary of the Invention

[0011] The purpose of this invention is to provide a discrete indirect power control method and device for grid-connected inverters. The control method of this invention is implemented in the αβ stationary coordinate system, eliminating the need for synchronous rotational coordinate changes. In this invention, the output current reference value of the grid-connected inverter is obtained through calculations using active / reactive power reference values ​​and grid voltage. A current-mode pulse train (PT) control method is used to make the output current follow its reference value, thereby achieving the indirect power control objective. Therefore, the control method provided by this invention does not require an error amplifier and its compensation network (proportional-integral controller). The controller parameter design and digital implementation are relatively simple, and it has the advantage of low software cost, possessing certain academic research and engineering application value.

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

[0013] A discrete indirect power control method for a grid-connected inverter, implemented in a two-phase stationary coordinate system αβ, includes the following steps:

[0014] S1. At the beginning of each control cycle, sample the input DC voltage u of the three-phase grid-connected inverter. dc Three-phase grid voltage u x (x=a,b,c), three-phase output current i x (x=a,b,c), where x represents the three phases, to obtain the inductance parameters L of the three-phase grid-connected inverter;

[0015] S2 is based on the three-phase grid voltage u x (x=a,b,c), three-phase output current i x (x=a,b,c), determine the grid voltage amplitude U based on the abc / αβ coordinate transformation formula. m And angular frequency ω, and determine grid voltage u y (y=α,β) and inverter output current i y (y=α,β), its expression is: , ;

[0016] S3, based on the grid voltage u y (y=α,β), active power reference value p ref Reactive power reference value q ref Determine the output current i of the grid-connected inverter y Reference value i for (y=α,β) yref (y=α,β), its expression is , ;

[0017] S4, based on the grid voltage u y(y=α,β), Input DC voltage u dc Determine the reference duty cycle component ID yrefI (y=α,β), its expression is: ;

[0018] S5, based on the grid voltage U m And angular frequency ω, grid-connected inverter inductance parameter L, input DC voltage u dc Reference values ​​for active and reactive power p ref q ref The control coefficient ΔD for the current-mode pulse train (PT) is determined by the following expression: ;

[0019] S6. Based on the reference duty cycle component ID yrefI (y=α,β) and the current-mode PT control coefficient ΔD are used to determine the high-power pulse duty cycle D. yH (y=α,β) and low-power pulse duty cycle D yL (y=α,β), its expression is: ;

[0020] S7. At the start of the control cycle, the inverter output current i y (y=α,β) and its reference value i yref (y=α,β) Comparison, if the output current i y (y=α,β) is less than its reference value i yref (y=α,β), select the high-power pulse duty cycle D yH (y=α,β) represents the discrete duty cycle D y (y=α,β); if the output current i y (y=α,β) is greater than its reference value i yref (y=α,β), select a low-power pulse duty cycle D yH (y=α,β) represents the discrete duty cycle D y (y=α,β); its expression is: , ;

[0021] S8. Based on the discrete duty cycle D y (y=α,β), based on the αβ / abc coordinate transformation formula and considering the duty cycle D x Determine the duty cycle D in the abc stationary coordinate system by using the 0.5 DC component in (x=a,b,c). x (x=a,b,c), its expression is: ;

[0022] S9. Based on the duty cycle D in the abc stationary coordinate systemx (x=a,b,c), using the PWM modulation method, determine the driving switching device S. x,p (x=a,b,c) and S x,n The PWM control pulse P for (x=a,b,c) x,p (x=a,b,c) and P x,n (x=a,b,c), where S x,p These are the three upper bridge arm switching devices in a three-phase grid-connected inverter, S x,n These are the three lower bridge arm switching devices in a three-phase grid-connected inverter.

[0023] A discrete indirect power control device for a grid-connected inverter includes a voltage and current sampling module, an abc / αβ coordinate transformation calculation module, an output current reference value calculation module, a reference duty cycle component I calculation module, a high-power and low-power pulse duty cycle calculation module, a discrete duty cycle comparison and selection module, an αβ / abc coordinate transformation calculation module, and a PWM modulation module.

[0024] The voltage and current sampling module is used to execute S1 and sample the input DC voltage u. dc Three-phase grid voltage u x Three-phase output current i x ;

[0025] The abc / αβ coordinate transformation calculation module is used to execute S2, based on the three-phase grid voltage u. x Three-phase output current i x Based on the abc / αβ coordinate transformation formula, the grid voltage amplitude U is determined. m And angular frequency ω, thus determining the grid voltage u y and inverter output current i y ;

[0026] The output current reference value calculation module is used to execute S3, based on the grid voltage u. y Active power reference value p ref Reactive power reference value q ref Obtain the inverter output current i y Reference value i yref ;

[0027] The reference duty cycle component I calculation module is used to execute S4, based on the grid voltage u. y Input DC voltage u dc Determine the reference duty cycle component ID yrefI ;

[0028] The high-power and low-power pulse duty cycle calculation module is used to execute S5 and S6, based on the grid voltage U. mAnd angular frequency ω, grid-connected inverter inductance parameter L, input DC voltage u dc Reference values ​​for active and reactive power p ref q ref Determine the current-mode pulse sequence (PT) control coefficient ΔD, and then based on ID... yrefI The high-power pulse duty cycle D is determined by the control coefficient ΔD. yH and low power pulse duty cycle D yL ;

[0029] The discrete duty cycle comparison and selection module is used to execute S7, which, at the start of the control cycle, sets the inverter output current i... y Its reference value i yref Comparison, if the output current i y Less than its reference value i yref Select a high-power pulse duty cycle D yH As the discrete duty cycle D y If the output current i y Greater than its reference value i yref Select a low-power pulse duty cycle D yH As the discrete duty cycle D y ;

[0030] The αβ / abc coordinate transformation calculation module is used to execute S8, based on the discrete duty cycle D. y Based on the αβ / abc coordinate transformation formula and considering the duty cycle D x Determine the duty cycle D in the abc stationary coordinate system by taking the 0.5 DC component. x ;

[0031] The PWM modulation module is used to execute S9, based on the duty cycle D in the abc stationary coordinate system. x Using the PWM modulation method, the driving switching device S is determined. x,p and S x,n PWM control pulse P x,p and P x,n .

[0032] The beneficial effects of this invention are that the method of this invention can control the output power of the grid-connected inverter without the need for rotational coordinate transformation, and the control algorithm is simple to implement and has low software cost; in addition, the grid-connected inverter current uses a current-type PT control method, which eliminates the need for a proportional-resonant controller, and the parameter design and digital implementation are simple. Attached Figure Description

[0033] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the following drawings are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the structure of a discrete current-type control device for a fast transient response totem pole bridgeless PFC provided in an embodiment of the present invention;

[0035] Figure 1 This is a schematic diagram of the discrete indirect power control method and device for a grid-connected inverter provided in an embodiment of the present invention;

[0036] Figure 2 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p=1500W, reactive power q=1500var) instantaneous output current i α Output current reference value i αref Flag bit, discrete duty cycle D αH and D αL Time-domain simulation waveform;

[0037] Figure 3 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p=1500W, reactive power q=1500var) instantaneous output current i α i β Time-domain simulation waveform;

[0038] Figure 4 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc The three-phase grid voltage u is given by: 400V, active power p=1500W, reactive power q=1500var. x (x=a,b,c), three-phase output current i x (x=a,b,c), time-domain simulation waveforms of grid voltage phase, active power p and reactive power q;

[0039] Figure 5 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc=400V, active power p ramps up from -1500W to 1500W, reactive power q ramps up from -1500var to 1500Var. Active power p and its reference value p. ref Reactive power q and its reference value q ref Time-domain simulation waveform;

[0040] Figure 6 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p ramps up from -1500W to 1500W, reactive power q ramps up from -1500var to 1500Var) three-phase grid voltage u x (x=a,b,c), three-phase output current i x (x=a,b,c), time-domain simulation waveforms of grid voltage phase, active power p and reactive power q;

[0041] Figure 7 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p ramps up from -1500W to 1500W, reactive power q ramps up from -1500var to 1500Var) instantaneous output current i α i β Time-domain simulation waveform;

[0042] Figure 8 This is an embodiment of the present invention providing an operating condition (the effective value of the grid voltage jumps from U=86V to 130V, and the input DC voltage u...). dc =400V, active power reference value p ref =1500W, reactive power reference value q ref The three-phase grid voltage u = 1500var) x (x=a,b,c), three-phase output current i x (x=a,b,c), time-domain simulation waveforms of grid voltage phase, active power p and reactive power q;

[0043] Figure 9 This is an embodiment of the present invention providing an operating condition (the effective value of the grid voltage jumps from U=86V to 130V, and the input DC voltage u...). dc =400V, active power reference value p ref =1500W, reactive power reference value q ref =1500var) instantaneous output current i α i β Time-domain simulation waveform;

[0044] Figure 10 The invention provides an embodiment of an operating condition (the effective value of the mains voltage jumps from U=130 to 86V, and the input DC voltage u) dc =400V, active power reference value p ref =1500W, reactive power reference value q ref The three-phase grid voltage u = 1500var) x (x=a,b,c), three-phase output current i x (x=a,b,c), time-domain simulation waveforms of grid voltage phase, active power p and reactive power q;

[0045] Figure 11 The invention provides an embodiment of an operating condition (the effective value of the mains voltage jumps from U=130 to 86V, and the input DC voltage u) dc =400V, active power reference value p ref =1500W, reactive power reference value q ref =1500var) instantaneous output current i α i β The time-domain simulation waveform diagram. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings and examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0047] The core of this invention is to provide a discrete indirect power control method and device for grid-connected inverters. The control method is implemented in the αβ stationary coordinate system, eliminating the need for synchronous rotational coordinate changes. In this invention, the output current reference value of the grid-connected inverter is obtained through calculations using active / reactive power reference values ​​and grid voltage. A current-mode pulse train (PT) control method is used to make the output current follow its reference value, thereby achieving the indirect power control objective. Therefore, the control method provided by this invention eliminates the need for an error amplifier and its compensation network (proportional-integral controller). The controller parameter design and digital implementation are relatively simple, and it has the advantage of low software cost, making it valuable for academic research and engineering applications.

[0048] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] The control objectives of a three-phase grid-connected inverter are as follows: to follow the grid voltage and frequency, and inject a current with controllable amplitude and phase into the grid, thereby achieving active and reactive power control objectives. Currently, existing current-source control methods for three-phase grid-connected inverters are as follows:

[0050] ① Proportional-Integral Control Method: Proportional-integral control (PI control) can achieve the output current control target of a three-phase grid-connected inverter, and the controller is simple to implement. However, the integral element in the proportional-integral controller has limited gain for power frequency AC quantities, making it difficult to achieve zero steady-state error control of the output current. In the dq synchronous rotating coordinate system, the grid-connected inverter output current is converted into DC quantity. Since the integral element in the PI controller has infinite gain for DC quantity, zero steady-state error control of the output current can be achieved. However, the above control method requires synchronous rotating coordinate transformation calculation, resulting in high software costs.

[0051] ② Proportional-resonant control and quasi-proportional-resonant control methods (i.e., PR and QPR control): Since the PR and QPR controllers contain the internal mode (i.e., resonant element) of the grid current signal in the s-domain, according to the internal mode principle, the PR and QPR controllers have infinite gain for power frequency AC quantities, and can achieve zero steady-state error control of the output current; however, the structure of the PR and QPR controllers is relatively complex (consisting of proportional parameters, resonant parameters, and cutoff frequency parameters), and the design, parameter tuning, and digital programming of the controllers are relatively complex.

[0052] ③ Fuzzy PI control or PR control method: Utilizing fuzzy rules to simulate expert experience, the fuzzy PI controller or PR controller can adjust the controller parameters online to achieve self-tuning when the operating conditions of the grid-connected inverter change. Compared with traditional PI control or PR control, fuzzy PI control or PR control has the advantages of high steady-state accuracy, fast transient response speed, and strong control robustness. However, the control performance of this method is highly dependent on the design of the fuzzy rule base, membership function, etc., and requires more online calculations, which places higher demands on the controller hardware.

[0053] ④ Model Predictive Control (MPC): Based on the mathematical model of the grid-connected inverter control system, MPC uses the system model to predict future behavior and selects the optimal switching state of the grid-connected inverter by minimizing the cost function, thereby achieving the optimal control objective of the output current. This control method has the advantage of high steady-state control accuracy; however, MPC requires the calculation of weighting coefficients and cost functions, resulting in a heavy computational burden. In addition, the control performance of MPC is highly dependent on the modeling accuracy of the grid-connected inverter and has limited robustness to unconsidered stray parameters, thus limiting its engineering applications.

[0054] ⑤ Particle Swarm Optimization (PSO) Control Algorithm: The basic principle of PSO is to treat the controller parameters to be optimized (such as the gain coefficients of PI or PR) as particle positions in the search space. Each particle iteratively updates its velocity and position by tracking its own historical best position and the group's historical best position, gradually approaching the global optimum. In actual operation, a group of random particles is first initialized. The fitness (such as current tracking error, total harmonic distortion, etc.) of each set of parameters is substituted into the inverter simulation model. Then, the individual extreme values ​​and the group extreme values ​​are updated according to the fitness, and the particles are guided to gather towards the optimal region according to the velocity-position update formula. This process is repeated until convergence. This method does not require gradient information, has strong global search capabilities, and can effectively solve the problems of traditional parameter tuning relying on experience and being prone to getting trapped in local optima, significantly improving the dynamic response and steady-state accuracy of grid-connected inverters. However, PSO has problems such as high computational burden, difficulty in achieving online real-time control, unstable convergence performance, difficulty in designing fitness functions, and limited adaptability of offline optimized control parameters to system changes. In addition, the PSO control method has the problem of high software cost.

[0055] Based on the above-mentioned research status, the embodiments of the present invention mainly provide a discrete indirect power control method and device for grid-connected inverters.

[0056] Figure 1 This is a structural block diagram of a discrete indirect power control method and device for a grid-connected inverter provided in an embodiment of the present invention; Figure 1 Includes a three-phase grid-connected inverter topology and a discrete indirect power control block diagram: The discrete indirect power control block diagram consists of a voltage and current sampling module, an abc / αβ coordinate transformation calculation module, an output current reference value calculation module, a reference duty cycle component I calculation module, a high-power and low-power pulse duty cycle calculation module, a discrete duty cycle comparison and selection module, an αβ / abc coordinate transformation calculation module, and a PWM modulation module.

[0057] Depend on Figure 1 The diagram shows a structural block diagram of a discrete indirect power control method and device for a grid-connected inverter. The steps of the discrete indirect power control method for a grid-connected inverter provided in this embodiment of the invention are as follows:

[0058] Step 1: At the beginning of each control cycle, sample the input DC voltage u of the three-phase grid-connected inverter. dc Three-phase grid voltage u x (x=a,b,c), three-phase output current i x (x=a,b,c), obtain the inductance parameters L of the three-phase grid-connected inverter;

[0059] Step 2: Based on the three-phase grid voltage u x(x=a,b,c), three-phase output current i x (x=a,b,c), determine the grid voltage amplitude U based on the abc / αβ coordinate transformation formula. m And angular frequency ω, and determine grid voltage u y (y=α,β) and inverter output current i y (y=α,β):

[0060]

[0061] Step 3: Based on the grid voltage u y (y=α,β), active power reference value p ref Reactive power reference value q ref Determine the inverter output current i y Reference value i for (y=α,β) yref (y=α,β):

[0062]

[0063] Step 4: Based on the grid voltage u y (y=α,β), Input DC voltage u dc Determine the reference duty cycle component ID yrefI (y=α,β):

[0064]

[0065] Step 5: Based on the grid voltage U m And angular frequency ω, grid-connected inverter inductance parameter L, input DC voltage u dc Reference values ​​for active and reactive power p ref q ref Determine the control coefficient ΔD for the current-mode pulse train (PT):

[0066]

[0067] Step Six: Based on the reference duty cycle component ID yrefI (y=α,β) and the current-mode PT control coefficient ΔD are used to determine the high-power pulse duty cycle D. yH (y=α,β) and low-power pulse duty cycle D yL (y=α,β):

[0068]

[0069] Step 7: The principle of discrete indirect power control is as follows: At the beginning of the control cycle, the inverter output current i is... y (y=α,β) and its reference value iyref (y=α,β) Comparison, if the output current i y (y=α,β) is less than its reference value i yref (y=α,β), select the high-power pulse duty cycle D yH (y=α,β) represents the discrete duty cycle D y (y=α,β); if the output current i y (y=α,β) is greater than its reference value i yref (y=α,β), select a low-power pulse duty cycle D yH (y=α,β) represents the discrete duty cycle D y (y=α,β):

[0070]

[0071]

[0072] Step 8: Based on the discrete duty cycle D y (y=α,β), based on the αβ / abc coordinate transformation formula and considering the duty cycle D x Determine the duty cycle D in the abc stationary coordinate system by using the 0.5 DC component in (x=a,b,c). x (x=a,b,c):

[0073]

[0074] Step 9: Based on the duty cycle D in the abc stationary coordinate system x (x=a,b,c), using the PWM modulation method, determine the driving switching device S. x,p (x=a,b,c) and S x,n The PWM control pulse P for (x=a,b,c) x,p (x=a,b,c) and P x,n (x=a,b,c).

[0075] The present invention also provides a discrete indirect power control device for a grid-connected inverter, which has the beneficial effects of the discrete indirect power control method for a grid-connected inverter described above, and will not be repeated here.

[0076] Figures 2-11 This is a simulation result of a discrete indirect power control device for a grid-connected inverter provided in an embodiment of the present invention.

[0077] Figures 2-11 The simulation results shown include the following circuit parameters for the three-phase grid-connected converter: input DC voltage u dc =400V, rated output voltage U N=120V, grid fundamental frequency is 50Hz, grid-connected filter inductor L=3mH, switching frequency f s =20kHz.

[0078] Figures 2-4 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc Simulation results of a discrete indirect power control device for a grid-connected inverter (400V, active power p=1500W, reactive power q=1500var).

[0079] Figure 2 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p=1500W, reactive power q=1500var) instantaneous output current i α Output current reference value i αref Flag bit, discrete duty cycle D αH and D αL The time-domain simulation waveform diagram; by Figure 2 It can be seen that when the instantaneous value of the output current i α Less than the reference value i αref With the flag set to 1, the high-power pulse duty cycle D is selected. αH As the final discrete duty cycle D α Otherwise, the flag is 0, and a low-power pulse duty cycle D is selected. αL As the final discrete duty cycle D α ;Depend on Figure 2 It can be seen that the instantaneous value of the output current i α It can effectively follow its reference value i αref .

[0080] Figure 3 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p=1500W, reactive power q=1500var) instantaneous output current i α i β The time-domain simulation waveform diagram; by Figure 3 It can be seen that the instantaneous value of the output current i α i β The waveform quality is good.

[0081] Figure 4 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dcThe three-phase grid voltage u is given by: 400V, active power p=1500W, reactive power q=1500var. x (x=a,b,c), three-phase output current i x (x=a,b,c), time-domain simulation waveforms of grid voltage phase, active power p, and reactive power q; from Figure 4 It can be seen that the three-phase output current i of the grid-connected inverter x (x=a,b,c) The waveform quality is good, and the active power p and reactive power q can be effectively controlled to follow their reference values ​​of 1500W and 1500Var.

[0082] Figures 5-7 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p ramps up from -1500W to 1500W, reactive power q ramps up from -1500var to 1500Var), simulation results of a discrete indirect power control device for a grid-connected inverter.

[0083] Figure 5 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p ramps up from -1500W to 1500W, reactive power q ramps up from -1500var to 1500Var. Active power p and its reference value p. ref Reactive power q and its reference value q ref The time-domain simulation waveform diagram; by Figure 5 It can be seen that when the active power p increases from -1500W to 1500W and the reactive power q increases from -1500var to 1500Var, the active power p can be compared with its reference value p. ref To achieve good tracking, the reactive power q can be compared with its reference value q. ref Achieve good follow-up.

[0084] Figure 6 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p ramps up from -1500W to 1500W, reactive power q ramps up from -1500var to 1500Var) three-phase grid voltage u x (x=a,b,c), three-phase output current i x (x=a,b,c), time-domain simulation waveforms of grid voltage phase, active power p, and reactive power q; from Figure 6It can be seen that when the active power p increases from -1500W to 1500W and the reactive power q increases from -1500var to 1500Var, the three-phase output current i of the grid-connected inverter... x (x=a,b,c) The waveform quality is good.

[0085] Figure 7 This is an embodiment of the present invention providing an operating condition (grid voltage effective value U=120V, input DC voltage u). dc =400V, active power p ramps up from -1500W to 1500W, reactive power q ramps up from -1500var to 1500Var) instantaneous output current i α i β The time-domain simulation waveform diagram; by Figure 7 It can be seen that when the active power p increases from -1500W to 1500W and the reactive power q increases from -1500var to 1500Var, the instantaneous value of the output current i α i β The waveform quality is good.

[0086] Figures 8-9 This is an embodiment of the present invention providing an operating condition (the effective value of the grid voltage jumps from U=86V to 130V, and the input DC voltage u...). dc =400V, active power reference value p ref =1500W, reactive power reference value q ref =1500var), simulation results of a discrete indirect power control device for a grid-connected inverter.

[0087] Figure 8 This is an embodiment of the present invention providing an operating condition (the effective value of the grid voltage jumps from U=86V to 130V, and the input DC voltage u...). dc =400V, active power reference value p ref =1500W, reactive power reference value q ref The three-phase grid voltage u = 1500var) x (x=a,b,c), three-phase output current i x (x=a,b,c), time-domain simulation waveforms of grid voltage phase, active power p, and reactive power q; from Figure 8 It can be seen that when the effective value of the grid voltage jumps from U=86V to 130V, the active power p and reactive power q exhibit transient overshoot, but eventually converge to the control target p. ref =1500W, q ref =1500var.

[0088] Figure 9This is an embodiment of the present invention providing an operating condition (the effective value of the grid voltage jumps from U=86V to 130V, and the input DC voltage u...). dc =400V, active power reference value p ref =1500W, reactive power reference value q ref =1500var) instantaneous output current i α i β The time-domain simulation waveform diagram; by Figure 9 It can be seen that when the effective value of the grid voltage jumps from U=86V to 130V, the instantaneous value of the output current i α i β It can quickly respond to grid voltage disturbances and rapidly adjust active power p and reactive power q to achieve discrete indirect power control objectives.

[0089] Figures 10-11 This is an embodiment of the present invention providing an operating condition (the effective value of the grid voltage jumps from U=130V to 86V, and the input DC voltage u...). dc =400V, active power reference value p ref =1500W, reactive power reference value q ref =1500var), simulation results of a discrete indirect power control device for a grid-connected inverter.

[0090] Figure 10 This is an embodiment of the present invention providing an operating condition (the effective value of the grid voltage jumps from U=130V to 86V, and the input DC voltage u...). dc =400V, active power reference value p ref =1500W, reactive power reference value q ref The three-phase grid voltage u = 1500var) x (x=a,b,c), three-phase output current i x (x=a,b,c), time-domain simulation waveforms of grid voltage phase, active power p, and reactive power q; from Figure 10 It can be seen that when the effective value of the grid voltage jumps from U=130V to 86V, the active power p and reactive power q exhibit transient overshoot, but eventually converge to the control target p. ref =1500W, q ref =1500var.

[0091] Figure 11 This is an embodiment of the present invention providing an operating condition (the effective value of the grid voltage jumps from U=130V to 86V, and the input DC voltage u...). dc =400V, active power reference value p ref =1500W, reactive power reference value q ref=1500var) instantaneous output current i α i β The time-domain simulation waveform diagram; by Figure 11 It can be seen that when the effective value of the grid voltage jumps from U=130V to 86V, the instantaneous value of the output current i α i β It can quickly respond to grid voltage disturbances and rapidly adjust active power p and reactive power q to achieve discrete indirect power control objectives.

[0092] The above verification process proves the effectiveness and feasibility of the discrete indirect power control of the grid-connected inverter provided in this embodiment.

[0093] The discrete indirect power control method and apparatus for a grid-connected inverter provided by the present invention have been described in detail above. 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 the present invention without departing from the principle of the invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A discrete indirect power control method for a grid-connected inverter, characterized in that, This method is implemented in a two-phase stationary coordinate system αβ and includes the following steps: S1. At the beginning of each control cycle, the input DC voltage u of the three-phase grid-connected inverter is obtained by sampling. dc Three-phase grid voltage u x Three-phase output current i x , where x represents the three phases, x=a,b,c, to obtain the inductance parameters L of the three-phase grid-connected inverter; S2, based on the three-phase power grid voltage u x Three-phase output current i x Based on the abc / αβ coordinate transformation formula, the grid voltage amplitude U is determined. m And angular frequency ω, and determine grid voltage u y and inverter output current i y , where y = α, β: ， S3, based on the grid voltage u y Active power reference value p ref Reactive power reference value q ref Determine the inverter output current i y Reference value i yref : ； S4, based on the grid voltage u y Input DC voltage u dc Determine the reference duty cycle component ID yrefI : ； S5, based on the grid voltage U m And angular frequency ω, grid-connected inverter inductance parameter L, input DC voltage u dc Reference values ​​for active and reactive power p ref q ref Determine the control coefficient ΔD for the current-mode pulse sequence (PT): ； S6. Based on the reference duty cycle component ID yrefI The high-power pulse duty cycle D is determined by the current-type PT control coefficient ΔD. yH and low power pulse duty cycle D yL : ； S7. At the start of the control cycle, the inverter output current i y Its reference value i yref Comparison, if the output current i y Less than its reference value i yref Select a high-power pulse duty cycle D yH As the discrete duty cycle D y If the output current i y Greater than its reference value i yref Select a low-power pulse duty cycle D yH As the discrete duty cycle D y : ， ； S8. Based on the discrete duty cycle D y Based on the αβ / abc coordinate transformation formula and considering the duty cycle D x Determine the duty cycle D in the abc stationary coordinate system by taking the 0.5 DC component. x : ； S9. Based on the duty cycle D in the abc stationary coordinate system x Using the PWM modulation method, the driving switching device S is determined. x,p PWM control pulse P x,p S x,n PWM control pulse P x,n S x,p These are the three upper bridge arm switching devices in a three-phase grid-connected inverter, S x,n These are the three lower bridge arm switching devices in a three-phase grid-connected inverter.

2. A discrete indirect power control device for a grid-connected inverter, used in the control method as described in claim 1, characterized in that, It includes a voltage and current sampling module, an abc / αβ coordinate transformation calculation module, an output current reference value calculation module, a reference duty cycle component I calculation module, a high-power and low-power pulse duty cycle calculation module, a discrete duty cycle comparison and selection module, an αβ / abc coordinate transformation calculation module, and a PWM modulation module. The voltage and current sampling module is used to execute S1 and sample the input DC voltage u. dc Three-phase grid voltage u x Three-phase output current i x ; The abc / αβ coordinate transformation calculation module is used to execute S2, based on the three-phase grid voltage u. x Three-phase output current i x Based on the abc / αβ coordinate transformation formula, the grid voltage amplitude U is determined. m And angular frequency ω, thus determining the grid voltage u y and inverter output current i y ; The output current reference value calculation module is used to execute S3, based on the grid voltage u. y Active power reference value p ref Reactive power reference value q ref Obtain the inverter output current i y Reference value i yref ; The reference duty cycle component I calculation module is used to execute S4, based on the grid voltage u. y Input DC voltage u dc Determine the reference duty cycle component ID yrefI ; The high-power and low-power pulse duty cycle calculation module is used to execute S5 and S6, based on the grid voltage U. m And angular frequency ω, grid-connected inverter inductance parameter L, input DC voltage u dc Reference values ​​for active and reactive power p ref q ref Determine the current-mode pulse sequence (PT) control coefficient ΔD, and then based on ID... yrefI The high-power pulse duty cycle D is determined by the control coefficient ΔD. yH and low power pulse duty cycle D yL ; The discrete duty cycle comparison and selection module is used to execute S7, which, at the start of the control cycle, sets the inverter output current i... y Its reference value i yref Comparison, if the output current i y Less than its reference value i yref Select a high-power pulse duty cycle D yH As the discrete duty cycle D y If the output current i y Greater than its reference value i yref Select a low-power pulse duty cycle D yH As the discrete duty cycle D y ; The αβ / abc coordinate transformation calculation module is used to execute S8, based on the discrete duty cycle D. y Based on the αβ / abc coordinate transformation formula and considering the duty cycle D x Determine the duty cycle D in the abc stationary coordinate system by taking the 0.5 DC component. x ; The PWM modulation module is used to execute S9, based on the duty cycle D in the abc stationary coordinate system. x Using the PWM modulation method, the driving switching device S is determined. x,p and S x,n PWM control pulse P x,p and P x,n .

Images