A nonlinear control method for a three-phase voltage source inverter

Abstract

This invention belongs to the field of inverter technology, specifically relating to a nonlinear control method for a three-phase voltage source inverter, including detecting inductor current I. Labc Detect the output voltage V oabc ; By transforming from the abc coordinate system to the αβ coordinate system, we obtain I Lαβ V oαβ ; Set the outer voltage loop parameter K2 and the inner current loop parameter K1; obtain the filter inductor current reference value through the outer voltage loop, input the current reference value into the inner current loop control, and obtain the inverter modulation signal S in the αβ coordinate. invx(x＝α,β) The modulated signal is transformed into an abc coordinate system as S. invz(z＝a,b,c) The invention outputs PWM drive signals for the inverter's switching devices via carrier modulation to drive the inverter to output three-phase AC power. This invention effectively solves the chattering problem caused by the sliding phase term in the current inner loop control, introduces a nonlinear control term, enhances the system's robustness, and enables the inverter to compensate for both low-order and high-order harmonic voltages.

Description

Technical Field

[0001] This invention belongs to the field of inverter technology, specifically relating to a nonlinear control method for a three-phase voltage source inverter. Background Technology

[0002] For three-phase voltage source inverters, Zhao Ensheng's paper, "Research on Multi-scale Instability Mechanism and Robust Passive Control Method for Islanded Microgrids," from the University of Electronic Science and Technology of China, designed a passive control method with an outer voltage loop and an inner current loop. Compared to the traditional proportional-integral dual closed-loop control method, the passive control method is insensitive to parameter perturbations. Even when the filter inductance or capacitance parameters change within a certain range, the passive control method can still function normally.

[0003] However, when inverters are connected to nonlinear loads such as uncontrolled rectifier bridges and LED lights, the nonlinear current caused by the load leads to a common problem of inverter output voltage distortion. Traditional proportional-integral dual-loop control methods and passive dual-loop control methods cannot effectively compensate for the distorted output voltage. Furthermore, there is a chattering problem caused by the sliding phase term in the inner current loop control. While traditional proportional-resonant control methods can compensate for a finite number of harmonic voltages such as the 5th, 7th, and 11th orders, they cannot compensate for higher-order harmonic voltages due to the insufficient control bandwidth of the control system. Summary of the Invention

[0004] The present invention aims to provide a nonlinear control method for a three-phase voltage source inverter to solve the chattering problem caused by the sliding phase in the current inner loop control, so as to achieve compensation for low-order and high-order harmonic voltages.

[0005] To achieve the above objectives, the present invention provides a nonlinear control method for a three-phase voltage source inverter, comprising the following steps:

[0006] Voltage and current detection: Detecting inductor current Detect output voltage ;

[0007] Coordinate system transformation: The coordinate system is transformed from abc to αβ to obtain the coordinates required for dual closed-loop control. , ;

[0008] Parameter tuning: Tune the outer voltage loop parameter K2 and the inner current loop parameter K1 to optimize the system control effect;

[0009] Voltage outer loop control: The reference value of the filter inductor current is obtained through the voltage outer loop. The control equations for the outer voltage loop are:

[0010]

[0011] Current inner loop control: The current reference value is input to the current inner loop control, and the inverter modulation signal in the αβ coordinate is obtained through the inner loop control. The governing equation for the inner current loop is:

[0012]

[0013] Three-phase AC output: Converts the modulated signal to an abc coordinate system. The inverter outputs PWM drive signals for its switching devices via carrier modulation to drive the inverter to output three-phase AC power.

[0014] Optionally, in the voltage and current detection step, the inductor current is detected using a filter inductor current sensor. The output voltage is detected using a filter capacitor voltage sensor. .

[0015] Optionally, in the parameter tuning step, the filter KVL equations are used to tune the inner current loop parameter K1 and the outer voltage loop parameter K2:

[0016] .

[0017] Optionally, in the parameter tuning step, based on the Input-to-State Stability (ISS) theory, a Lyapunov function is constructed. The Lyapunov function is as follows:

[0018]

[0019] The theoretical expression for ISS is:

[0020]

[0021] Where e is the voltage error and r is the parasitic resistance. This is an external disturbance.

[0022] Optionally, during the parameter tuning step, the system differential equation is linearized near the steady-state operating point, and the linearized system differential equation becomes:

[0023]

[0024] Its time constant is:

[0025] .

[0026] The working principle of this invention is as follows: the filter inductor current sensor detects the inductor current. Filter capacitor voltage sensor detects output voltage By transforming from the abc coordinate system to the αβ coordinate system, the control method required can be obtained. , The reference value of the filter inductor current is obtained through the voltage outer loop. Input the current reference value into the inner current loop, and input the absolute value of the voltage error. It was introduced into the inner current loop and used It replaced the inner loop of the original passive control method. This addresses the chattering problem caused by the sliding membrane term. Here, `sign` is the sign function, which is defined when... hour ,when hour The modulation signal in the αβ coordinate is obtained through current inner loop control. The modulated signal is converted to an abc coordinate system. Finally, the PWM drive signal for the inverter's switching devices is output via carrier modulation. This PWM drive signal enables the inverter to output three-phase AC power.

[0027] The beneficial effects of this plan are as follows:

[0028] 1. Regardless of load changes and switching, and regardless of output current distortion, the inverter output voltage quality remains high even with a 50% fluctuation in filter parameters (LC inductor and capacitor parameters), with total harmonic distortion (THD) controlled below 0.5%. Even with a 30% perturbation in filter parameters, the THD of the output voltage can still be limited to below 3% without controlling the connection of nonlinear loads such as the rectifier bridge.

[0029] 2. Global system stability can be achieved simply by adjusting the two control gains K1 and K2 of the voltage and current dual closed loops, simplifying parameter design. Parameter tuning can be achieved through simulation or by constructing Lyapunov functions; see the parameter tuning steps in the embodiment for details.

[0030] 3. This method has very strong versatility and applicability, and can be used in any three-phase voltage source inverter, including but not limited to two-level three-phase voltage source inverters, three-level three-phase voltage source inverters and multi-level three-phase voltage source inverters.

[0031] 4. Based on the passive dual-loop inverter, the absolute value of the voltage error is introduced, which differs from the traditional super-spiral sliding diaphragm control method where the sliding surface and the absolute value term are consistent. This reduces the chattering caused by the sliding term in traditional sliding diaphragm control, and by introducing the outer-loop voltage error into the nonlinear control part, the robustness of the system can be further increased, enabling the control method to better compensate for harmonic voltages.

[0032] 5. Using inductor current Replacement LC filter output current This reduces the number of sensors and auxiliary circuits, and involves fewer control parameters, simplifying system design. Attached Figure Description

[0033] Figure 1 This is the overall control framework of a nonlinear control method for a three-phase voltage source inverter in an embodiment of the present invention;

[0034] Figure 2 This is a system control block diagram of a nonlinear control method for a three-phase voltage source inverter according to an embodiment of the present invention;

[0035] Figure 3 This is a topology of a three-phase voltage source inverter in an embodiment of the present invention;

[0036] Figure 4 This is a simulation of the output performance of a nonlinear control method for a three-phase voltage source inverter in an embodiment of the present invention when the filter parameters are not perturbed.

[0037] Figure 5 This invention relates to an embodiment of a nonlinear control method for a three-phase voltage source inverter, focusing on the output voltage tracking effect and quality under filter parameter perturbation. Detailed Implementation

[0038] The following detailed examples illustrate this further.

[0039] Example

[0040] This embodiment is basically as follows: Figure 1 and Figure 2 As shown: A nonlinear control method for a three-phase voltage source inverter. The basic parameters verified by experiments are as follows:

[0041] , , , , , , , , , , .

[0042] The output voltage angular frequency, For the output voltage frequency, DC voltage, Reference voltage, Switching frequency, For filtering inductors, It is a Snubber resistor. It is a filter inductor parasitic resistance, DC-side capacitor, Controller parameters

[0043] The entire method includes the following steps:

[0044] Voltage and current detection: Filter inductor current sensor detects inductor current. Filter capacitor voltage sensor detects output voltage ;

[0045] Coordinate system transformation: The coordinate system is transformed from abc to αβ to obtain the coordinates required for dual closed-loop control. , ;

[0046] Parameter tuning: Tune the inner current loop parameter K1 and the outer voltage loop parameter K2; the specific process is as follows:

[0047] Filter KVL equations:

[0048] (1)

[0049] In this embodiment, no power control loop is included. Therefore, for the control method in this embodiment, the α-axis and β-axis are the same and independent of each other. Thus, subscripts are omitted in the stability proof. and The simultaneous current inner loop control equations and equation (1) are: (2)

[0051] Let voltage error , Combine the voltage outer loop control equations and equation (2):

[0052] (3)

[0053] Substituting the actual reference voltage into equation (3), where , , :

[0054] (4)

[0055] In equation (4), both the linear and nonlinear parts contain sine or cosine perturbation terms. Because the nonlinear part contains a perturbation term in its sign function... This means the system can only guarantee bounded stability, meaning it can only tolerate errors. Fluctuating within a very small range, i.e. ,in is a given positive constant.

[0056] The bounded stability of the system's differential equations is shown below:

[0057] In the theory of input-to-state stability (ISS), when At that time, the system is stable from input to state, that is, the system state is stable. The influence of the disturbance is bounded, indicating that the system possesses robust stability in the presence of the disturbance. It is a positive definite function, representing the decay term of the system state. It's about disturbances. A positive definite function.

[0058] Define the Lyapunov function of the system:

[0059] (5)

[0060] but Substituting equation (5) into:

[0061] (6)

[0062] The perturbation term in the sign function sign Consider it as an external disturbance:

[0063] (7)

[0064] in The maximum magnitude of the disturbance term in the linear term is Therefore, after separating the disturbance term:

[0065] (8)

[0066] Then the system attenuation term Disturbance term amplitude Therefore, as long as the magnitude of the attenuation term is greater than the magnitude of the disturbance term, the system is globally bounded stable, that is:

[0067] (9)

[0068] Parasitic resistance And because Let's assume here. Therefore, we can deduce:

[0069] (10)

[0070] The error accuracy can be obtained from equation (10). The smaller, the more It will get bigger and bigger, when hour, However, due to system bandwidth limitations and the impact of latency in the DSP, and Further optimization is needed.

[0071] The system differential equations are then linearized near the steady-state operating point, and the following is given in conjunction with the system control bandwidth. and The range of values ​​for .

[0072] Since the system has been proven to remain stable under the influence of disturbance terms, and linearization analysis primarily focuses on performance optimization, the disturbance terms are ignored. The linearized system differential equation becomes:

[0073] (11)

[0074] This is a first-order linear system with the following time constant:

[0075] (12)

[0076] To ensure that the effect of delay on the system's phase is acceptable at the bandwidth frequency, typically ,and Considering that the actual control system delay in this study is The system time constant can be calculated to be approximately In the stability analysis Substituting into equation (12), we can calculate .

[0077] Voltage outer loop control: , The reference value of the filter inductor current is obtained through the voltage outer loop. The control equations for the outer voltage loop are:

[0078]

[0079] Current inner loop control: The current reference value... The input is fed into the inner loop control method, and the inverter modulation signal in the αβ coordinate system is obtained through the inner loop control method. The governing equation for the inner current loop is:

[0080]

[0081] Three-phase AC output: Converts the modulated signal to the abc coordinate system. The inverter outputs PWM drive signals for its switching devices via carrier modulation to drive the inverter to output three-phase AC power.

[0082] The inverter topology used in the experiment is as follows: Figure 3 As shown in the figure. This embodiment uses a 10kW GaN / Si hybrid ANPC inverter prototype to verify the proposed control method. The solid elliptical box contains the GaN MOSFET, and the dashed rectangular box contains the Si MOSFET. It should be noted that, firstly, since the control method proposed in this embodiment does not involve a modulation module, it is also applicable to other three-phase voltage source inverters, including two-level inverters and other types of three-level inverters such as TNPC or NPC inverters. Secondly, the ANPC prototype used in this embodiment employs an LCL filter. Because a snubber resistor is added to the filter capacitor of the LCL filter in this embodiment, the resonance peak of the LCL is effectively suppressed. Furthermore, only the filter inductor is used in the derivation and simulation of the above control method equations. The current and voltage across the filter capacitor C are not involved; the filter inductor is not considered. Therefore, it is reasonable and effective to use a GaN / Si hybrid ANPC with a snubber resistor to experimentally verify the proposed control method in this embodiment.

[0083] Figure 4 This represents the inverter's output performance when the filter parameters are not perturbed. Figure 4 In step a, from 0-0.05s, the inverter load is a nonlinear load consisting of a three-phase uncontrolled rectifier bridge, inductor, capacitor, and resistor; from 0.05-0.1s, it is a nonlinear load connected in parallel with an unbalanced load; from 0.1-0.15s, it is an unbalanced load; and from 0.15-0.2s, it is a resistive balanced load. It can be observed that different load types cause different output current distortions. For example, from 0-0.05s, the load current is an intermittent pulse current; from 0.05-0.1s, it is an unbalanced pulse current; and from 0.1-0.15s, it is an unbalanced current. Regardless of how the load conditions change and switch, the three-phase voltage source inverter using the control method proposed in this embodiment can always guarantee a high output voltage quality. Figure 4 d shows that the total harmonic distortion of the output line voltage during the time interval 0-0.2s is 0.14%. Figure 4 b is a magnified view of the inverter output voltage following the reference voltage. It can be seen that the error between the output voltage and the reference voltage is about 0.5V. Figure 4 c shows that the inverter output inductor current follows the reference inductor current with a tracking error within 1A, which is consistent with the bounded stability in the stability analysis. Simulations verify that the proposed nonlinear dual-loop control method has a good compensatory effect on harmonic voltages under various load conditions.

[0084] Figure 5 (a) and (b) show the inverter output voltage following the reference voltage under filter parameter perturbation. As the filter parameters change more, the output voltage contains more high-frequency components, which is mainly due to the deterioration of filter performance. The control method proposed in this embodiment can still track the reference voltage well, proving that the proposed control method has strong robustness to filter parameter perturbation. Figure 5 When (c) and (d) correspond to cases (a) and (b) respectively, in Figure 4 Under operating conditions, the total harmonic distortion (THD) of the inverter line voltage is as follows. Even with a 50% perturbation of the filter parameters, the control method proposed in this embodiment can still control the THD to 0.72%, which is lower than the 5% THD of the grid voltage specified by national and IEEE standards, demonstrating good control performance.

Claims

1. A nonlinear control method for a three-phase voltage source inverter, characterized in that: Includes the following steps: Voltage and current detection: Detecting inductor current Detect output voltage ; Coordinate system transformation: The coordinate system is transformed from abc to αβ to obtain the coordinates required for dual closed-loop control. , ; Parameter tuning: Tune the outer voltage loop parameter K2 and the inner current loop parameter K1 to optimize the system control effect; During the parameter tuning step, the system differential equation is linearized near the steady-state operating point. The linearized system differential equation becomes: ； Its time constant is: ； Voltage outer loop control: The reference value of the filter inductor current is obtained through the voltage outer loop. The control equations for the outer voltage loop are: ； Current inner loop control: The current reference value is input to the current inner loop control, and the inverter modulation signal in the αβ coordinate is obtained through the inner loop control. The governing equation for the inner current loop is: ； Three-phase AC output: Converts the modulated signal to an abc coordinate system. The inverter outputs PWM drive signals for its switching devices via carrier modulation to drive the inverter to output three-phase AC power. L1 is the filter inductor; r is the parasitic resistance of the filter inductor L1; e is the voltage error; C is the filter capacitor.

2. The nonlinear control method for a three-phase voltage source inverter according to claim 1, characterized in that: In the voltage and current detection step, the inductor current is detected using a filter inductor current sensor. The output voltage is detected using a filter capacitor voltage sensor. .

3. The nonlinear control method for a three-phase voltage source inverter according to claim 2, characterized in that: In the parameter tuning step, the inner current loop parameter K1 and the outer voltage loop parameter K2 are tuned using the filter KVL equation: 。 4. The nonlinear control method for a three-phase voltage source inverter according to claim 3, characterized in that: In the parameter tuning step, based on the Input-to-State Stability (ISS) theory, a Lyapunov function is constructed. The Lyapunov function is as follows: ； The theoretical expression for ISS is: ； Where e is the voltage error and r is the parasitic resistance. This is an external disturbance.

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