Space vector modulation method and system based on model predictive control and inverter
阅读说明：本技术 基于模型预测控制的空间矢量调制方法、系统及逆变器 (Space vector modulation method and system based on model predictive control and inverter ) 是由 侯文宝 刘志坚 李德路 张刚 王文杰 于 2020-07-02 设计创作，主要内容包括：本发明属于逆变控制技术领域,公开了一种基于模型预测控制的空间矢量调制方法、系统及逆变器,基于模型预测控制的空间矢量调制方法包括：采用改进的预测模型将指令电流量转换成电压预测量；通过SVPWM的调制进行电压预测值到开关信号的无差转换；且所述转换过程中可实现固定可设的开关频率。本发明基于空间矢量的模型预测电流控制具有参数易于设计,动态响应快,开关频率固定可调,补偿效果好,易于应用非线性系统等优点,本发明能够有效大大减少运算量,但却不影响控制效果,在保证控制精度不变的条件下提高了系统控制的快速性。(The invention belongs to the technical field of inversion control, and discloses a space vector modulation method and system based on model predictive control and an inverter, wherein the space vector modulation method based on the model predictive control comprises the following steps: converting the command current amount into a voltage prediction amount by adopting an improved prediction model; carrying out no-difference conversion from the voltage predicted value to a switching signal through SVPWM modulation; and the switching frequency which can be fixedly set can be realized in the conversion process. The model prediction current control based on the space vector has the advantages of easy parameter design, quick dynamic response, fixed and adjustable switching frequency, good compensation effect, easy application of a nonlinear system and the like.)
1. A space vector modulation method based on model predictive control is characterized by comprising the following steps:
converting the command current amount into a voltage prediction amount by adopting an improved prediction model; carrying out no-difference conversion from the voltage predicted value to a switching signal through SVPWM modulation; and the switching frequency which can be fixedly set can be realized in the conversion process.
2. The model predictive control-based space vector modulation method of claim 1, wherein the improved predictive model is:
wherein, L is a load inductance; t issIs a sampling period; k represents the kth sample;
iα，β(k) is the actual current for the (k +1) th sampling period.
3. The method of claim 1, wherein the method of modulating the space vector based on the model predictive control specifically comprises:
step one, acquiring A, B, C three-phase current magnitude at a load side; performing Clarke transformation on the obtained three-phase current magnitude;
step two, performing phase angle compensation of one period;
converting the instruction current quantity into a voltage prediction quantity by adopting an improved prediction model;
step four, judging the sector; and (5) performing prediction and outputting.
4. The model predictive control-based space vector modulation method according to claim 3, wherein in step two, the phase angle compensation comprises:
5. a model predictive control-based space vector modulation system implementing the model predictive control-based space vector modulation method according to claims 1-4, wherein the model predictive control-based space vector modulation system:
the current amount conversion module is used for converting the instruction current amount into a voltage prediction amount by adopting an improved prediction model;
the non-difference conversion module is used for performing non-difference conversion from the voltage predicted value to the switching signal through SVPWM modulation;
and the switching frequency control module is used for controlling the switching frequency to be fixed and settable in the conversion process.
6. A Z-source inverter carrying the model-predictive-control-based space vector modulation method according to claims 1-4.
7. A microgrid or power generation system carrying an inverter according to claim 6.
8. A computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the model-predictive-control-based space vector modulation method according to any one of claims 1 to 4, comprising: converting the command current amount into a voltage prediction amount by adopting an improved prediction model; carrying out no-difference conversion from the voltage predicted value to a switching signal through SVPWM modulation; and the switching frequency which can be fixedly set can be realized in the conversion process.
Technical Field
The invention belongs to the technical field of inversion control, and particularly relates to a space vector modulation method and system based on model predictive control and an inverter.
Background
At present, a traditional MPC current control method has a faster response speed, can directly output a driving signal, does not need a PWM modulation process, but a switching frequency thereof is not fixed, and a control effect the same as that of other control methods is to be achieved, a control time of the MPC is shorter, but when the traditional MPC method is used for controlling current output, a system needs to calculate predicted values of controlled currents under the influence of 27 switching states respectively in each sampling period, and also needs to calculate differences between the predicted values and command values under the action of 27 switching states respectively in a performance optimization function, if the controlled quantities need to be increased, corresponding calculated quantities are also increased in multiples, and an application effect of an MPC algorithm in current tracking is greatly influenced.
The improved MPC control comprises two key modules, namely an improved prediction control module and an improved optimization performance function module, the tracking effect of the improved prediction control module and the improved optimization performance function module is influenced by the two modules together, wherein the improved prediction model module has the function of quickly and accurately converting the command current into the command voltage, and the improved optimization performance function still has certain error when the closest voltage vector is selected, and a switching signal is directly generated, so that the switching frequency is not fixed, and higher requirements are caused on devices.
The improved MPC method is characterized in that a reference voltage vector to be output is replaced by a closest basic voltage vector, and the method is consistent with the traditional MPC method, and both the two methods have the defect that a certain error still exists between the selected voltage vector and a command output voltage vector, both methods belong to a poor control mode, and the switching frequency of both methods is not fixed, so that higher requirements are generated on a switching device.
Through the above analysis, the problems and defects of the prior art are as follows: in the traditional MPC current control method and the existing improved MPC method, the switching frequency is not fixed, and the requirement on a switching device is high; the calculation amount is large, and errors exist, so that the application effect of the MPC algorithm in current tracking is poor.
The significance of solving the problems and the defects is as follows: when the MPC is applied to a multi-level inverter, the dynamic performance is reduced because the number of the optimization vectors is increased, the method of the invention adopts voltage prediction to replace current prediction, and can simplify the calculation amount in each optimization, thereby improving the dynamic performance of multiple optimization, and being suitable for occasions of multi-level high-power inverters.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a space vector modulation method and system based on model predictive control and an inverter. MPC is a representative model predictive control (MPC-based SVPWM Mechanism).
The invention is realized in such a way that a space vector modulation method based on model predictive control comprises the following steps:
converting the command current amount into a voltage prediction amount by adopting an improved prediction model; carrying out no-difference conversion from the voltage predicted value to a switching signal through SVPWM modulation; and the switching frequency which can be fixedly set can be realized in the conversion process.
Further, the improved prediction model is as follows:
wherein, L is a load inductance; t issIs a sampling period; k denotes the kth sample.
Is the predicted current for the (k +1) th sampling period.
Is the reference current for the (k +1) th sampling period.
Is the predicted voltage for the (k +1) th sampling period.
iα，β(k) Is the actual current of the (k +1) th sampling period。
Further, the space vector-based MPC control method includes:
step one, acquiring A, B, C three-phase current magnitude at a load side; performing Clarke transformation on the obtained three-phase current magnitude;
step two, performing phase angle compensation of one period;
converting the instruction current quantity into a voltage prediction quantity by adopting an improved prediction model;
step four, judging the sector; and (5) performing prediction and outputting.
Further, in step two, the phase angle compensation comprises:
another object of the present invention is to provide a model predictive control-based space vector modulation system that implements the model predictive control-based space vector modulation method, including:
the current amount conversion module is used for converting the instruction current amount into a voltage prediction amount by adopting an improved prediction model;
the non-difference conversion module is used for performing non-difference conversion from the voltage predicted value to the switching signal through SVPWM modulation;
and the switching frequency control module is used for controlling the switching frequency to be fixed and settable in the conversion process.
Another object of the present invention is to provide a Z-source inverter incorporating the space vector based MPC control method.
Another object of the present invention is to provide a microgrid or a power generation system on which the inverter is mounted.
It is another object of the present invention to provide a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the model-predictive-control-based space vector modulation method. The method comprises the following steps: converting the command current amount into a voltage prediction amount by adopting an improved prediction model; carrying out no-difference conversion from the voltage predicted value to a switching signal through SVPWM modulation; and the switching frequency which can be fixedly set can be realized in the conversion process.
By combining all the technical schemes, the invention has the advantages and positive effects that:
the model prediction current control based on the space vector has the advantages of easy parameter design, quick dynamic response, fixed and adjustable switching frequency, good compensation effect, easy application of a nonlinear system and the like,
the invention can effectively and greatly reduce the operation amount without influencing the control effect, and improves the rapidity of system control under the condition of ensuring the unchanged control precision.
In order to verify the feasibility of the three-level Z-source inverter control strategy of the method, a simulation model is established in a Simulink environment. The simulation parameters are as follows: DC power supply Vdc1＝Vdc2The source capacitance C is 1000 μ F, the source inductance L is 2mH, the load R is 10 Ω, and L is 5 mH. The through duty D changes from 0 to 0.3 at 0.25 s.
Fig. 13 shows simulation waveforms of the NPC three-level Z-source inverter. Wherein, the diagram (a) shows the waveform of the output voltage Vi of the Z-source network, when the through state is not added, the output voltage is maintained at the direct-current power voltage, i.e. 50V, the through state is inserted after 0.25s, the through duty ratio is set to 0.3, the inverter realizes the boosting function, and the output voltage of the "X" network is in a series of pulse shapes, as shown in the diagram (b). The graphs (c) and (d) are respectively the line voltage U in the dynamic boosting processabAnd phase voltage U of phase AaIt can be seen from the figure that, when the through duty ratio of 0.25s changes suddenly, the inverter output realizes the boosting function through one period of adjustment, the line voltage peak value is about 250V according to the formula (8), and the simulation result is consistent with the theoretical analysis. The line current waveform of the a-phase load is shown in (e), and in the through duty cycle variation process, the inverter realizes boost output, the load current is increased along with the boost output, the sine degree is high, and the harmonic content is low.
FIG. 14 shows NPC three-level Z-source inverter "X" network capacitance Uc2And (5) simulating a waveform.
The simulation verifies that the NPC three-level Z-source inverter control method provided by the invention has practical significance.
For the conventional SVPWM method based on MPC, 10.03% and 13.91% of time can be saved compared to the conventional SVPWM due to the omission of the method for the complicated triangle calculation. Also, the improved scheme saves 26.25% and 19.25% of the time when D is 0 compared to the conventional SVPWM and MPC based conventional SVPWM, and 28.78% and 17.27% when D is 0.3, due to the subtraction of the current roll optimization calculation.
Drawings
Fig. 1 is a schematic diagram of MPC control based on space vectors according to an embodiment of the present invention.
Fig. 2 is a flowchart of a space vector modulation method based on model predictive control according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a space vector modulation method based on model predictive control according to an embodiment of the present invention.
Fig. 4 is a schematic structural diagram of a space vector modulation system based on model predictive control according to an embodiment of the present invention.
In the figure: 1. a current amount conversion module; 2. a homodyne conversion module; 3. and a switching frequency control module.
Fig. 5 is a schematic diagram of an NPC three-level Z-source inverter circuit according to an embodiment of the present invention.
Fig. 6 is an equivalent circuit schematic diagram of an NPC three-level Z-source inverter provided by an embodiment of the invention.
Fig. 7 is a block diagram of space vector modulation control provided by an embodiment of the present invention.
FIG. 8 is a block diagram of an improved MPC control provided by an embodiment of the present invention.
Fig. 9 is a spatial vector diagram of an NPC three-level Z-source inverter according to an embodiment of the present invention.
Fig. 10 is a spatial vector diagram I provided by an embodiment of the present invention.
Fig. 11 is a schematic diagram of SVPWM operation of a conventional inverter and a Z-source inverter according to an embodiment of the present invention.
Fig. 12 is a schematic diagram of a wave-transmitting sequence in which the reference vector is located in the
Fig. 13 is a schematic diagram of a simulation waveform of an NPC three-level Z-source inverter according to an embodiment of the present invention.
Fig. 14 is a schematic diagram of a simulated waveform of the "X" network capacitor Uc2 according to an embodiment of the present invention.
FIG. 15 is a dynamic waveform of current for a conventional space vector and corresponding harmonic analysis provided by an embodiment of the present invention (FIG. 15(a) phase A current iaWhen D in fig. 15(b) is 0, phase a current iaWhen the harmonic content is 0.3 as shown in fig. 15(c) D, the a-phase current iaHarmonic content).
FIG. 16 is a modified MPC based space vector modulated current dynamic waveform and corresponding harmonic analysis provided by an embodiment of the present invention (FIG. 16(a) phase A current iaWhen D in fig. 16(b) is 0, phase a current iaWhen the harmonic content is 0.3 in fig. 16(c) D, the a-phase current iaHarmonic content).
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In view of the problems in the prior art, the present invention provides a space vector based MPC control method, a control system and an inverter, and the following describes the present invention in detail with reference to the accompanying drawings.
As shown in fig. 1, a space vector modulation method based on model predictive control according to an embodiment of the present invention includes:
converting the command current amount into a voltage prediction amount by adopting an improved prediction model; carrying out no-difference conversion from the voltage predicted value to a switching signal through SVPWM modulation; and the switching frequency which can be fixedly set can be realized in the conversion process.
The embodiment of the invention provides an improved prediction model which comprises the following steps:
wherein, L is a load inductance; t issIs a sampling period; k denotes the kth sample.
As shown in fig. 2 to fig. 3, a space vector modulation method based on model predictive control according to an embodiment of the present invention includes:
s101, acquiring A, B, C three-phase current amount of a load side; and performing Clarke transformation on the obtained three-phase current magnitude.
And S102, performing phase angle compensation for one period.
And S103, converting the instruction current amount into a voltage prediction amount by adopting an improved prediction model.
S104, judging the sector; and (5) performing prediction and outputting.
In step S102, the phase angle compensation provided by the embodiment of the present invention includes:
as shown in fig. 4, the space vector modulation system based on model predictive control according to the embodiment of the present invention includes:
and the current
And the no-
And the switching
The technical solution of the present invention is further illustrated by the following specific examples.