CN111817595A - quasi-Z-source inverter model prediction control method without weight coefficient - Google Patents

quasi-Z-source inverter model prediction control method without weight coefficient Download PDF

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CN111817595A
CN111817595A CN202010572451.8A CN202010572451A CN111817595A CN 111817595 A CN111817595 A CN 111817595A CN 202010572451 A CN202010572451 A CN 202010572451A CN 111817595 A CN111817595 A CN 111817595A
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CN111817595B (en
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吴春
杨佳磊
陈强
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Zhejiang University of Technology ZJUT
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H02M7/53873—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with digital control

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Abstract

A quasi-Z source inverter model prediction control method without weight coefficients aims at a Z source inverter to collect voltage and current signals; establishing a mathematical model of the quasi-Z source inverter; therefore, a prediction model of each control object of the quasi-Z source inverter is established, and a delay compensation strategy is added; calculating a reference value of each control object; and the priority of the quasi Z-source inverter control object is determined according to a cascade model prediction control method and by combining the specificity of the inductive current. Compared with the traditional finite set model predictive control method, the cascade model predictive control method effectively eliminates the weight coefficient, makes the control method simpler and reduces the calculated amount of a digital processor.

Description

quasi-Z-source inverter model prediction control method without weight coefficient
Technical Field
The invention discloses a quasi Z-source inverter model prediction control method without a weight coefficient, and belongs to the field of control of quasi Z-source inverters.
Background
The quasi-Z-source inverter (qZSI) is used as a novel inverter topology, can overcome the defects of the traditional inverter, has a boosting function, and is very suitable for new energy power generation occasions such as photovoltaic and the like. At present, the research of control methods aiming at a Z-source inverter is mainly divided into two categories, one category is a traditional modulation method, and the other category is mainly a Sinusoidal Pulse Width Modulation (SPWM) method and a space vector modulation (SVPWM) method; the other type is a nonlinear control method mainly based on model predictive control (model predictive control). Compared with the traditional modulation method, the model prediction control method has the characteristics of no modulation, simple control method, excellent dynamic performance and the like. Therefore, the model prediction control method of the quasi-Z source inverter has important research significance.
Document "High-Performance Predictive Control of Quasi-Impedance Source Inverter" (Mostafa Mosa, Robert S.Balog et al. IEEE TRANSACTIONS POWER APPARATUS CS 2012,32 (04)). In this document, a finite set model predictive control (FCS-MPC) method is used to control a Z-source inverter, and the predicted values of the inductive current, the capacitive voltage and the output current corresponding to 8 output voltage vectors are substituted into a cost function to calculate, so as to obtain an optimal voltage vector. Although the method can realize good control of the quasi-Z source inverter, 3 weight coefficients exist in the cost function and need to be adjusted simultaneously, and no proper design rule is available at present to guide the design of the weight coefficients, so that when one cost function has a plurality of weight coefficients, the adjustment of the weight coefficients becomes extremely complicated, and if the weight coefficients are not designed properly, the quasi-Z source inverter cannot work normally.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a cascade model predictive control (S-MPC) method, which adopts a cascade thought, so that a quasi-Z source inverter model predictive control method without a weight coefficient is designed, and the defect that the weight coefficient needs to be designed in the traditional finite set model predictive control method is effectively overcome. In addition, by using the predicted value of the inductance current, the state of the next control period of the Z-source inverter can be judged, so that the calculated amount of the digital processor is effectively reduced.
The technical scheme proposed for solving the technical problems is as follows:
a quasi-Z source inverter model prediction control method without weight coefficients comprises the following steps:
step 1, aligning a voltage signal and a current signal of a Z-source inverter to sample;
the current is recorded as the kth sampling moment, the voltage signal and the current signal of the Z-source inverter are sampled, and the sampling content comprises the following steps: inductor current iL1(k) And a capacitor voltage vC1(k) And outputting the load three-phase current ia(k)、ib(k) And ic(k) Then converting the three-phase current of the load from the three-phase static coordinate system to an alpha beta coordinate system to obtain ioα(k) And ioβ(k)；
Step 2, establishing a mathematical model of the quasi-Z source inverter, wherein the process is as follows:
2.1, establishing an output voltage equation of the AC side of the quasi-Z source inverter
The minimum 8 output voltage vectors required for the qZSI system are first listed in Table 1
Figure BDA0002550140830000021
TABLE 1
8 output voltage vectors V of qZSIx(k) Is shown as
Figure BDA0002550140830000022
Wherein a ═ ej2π/3；x＝[0～7]；vdcThe peak voltage of a direct current side bus connected to the inverter bridge; s1、S3、S5Switch states of A, B, C phases, respectively;
the output voltage equation of the qZSI AC side is
Figure BDA0002550140830000023
Wherein R, L is the load phase resistance and phase inductance, Vxα、VxβFor the voltage component of the output voltage vector on the α β axis, ioα(k)、ioβ(k) To output currentA current component of the vector on the α β axis;
2.2, establishing an inductance current and capacitance voltage equation of the quasi-Z source impedance network in a non-direct-through state and a direct-through state respectively;
2.2.1) non-pass-through state:
Figure BDA0002550140830000031
in the formula, L1、C1Respectively, the inductance and capacitance values in the impedance network; rL1Is an inductance L1The stray resistance of (2); v. ofin(k) Is the input voltage; i.e. iL1(k) And vC1(k) Sampling values of the inductive current and the capacitor voltage at the kth sampling moment respectively; i.e. iinv(k)＝iA(k)S1+iB(k)S3+iC(k)S5；iA(k)、iB(k) And iC(k) Current values of the phase A, the phase B and the phase C at the kth sampling moment;
2.2.2) straight-through state:
Figure BDA0002550140830000032
in the formula, L1、C1Respectively, the inductance and capacitance values in the impedance network; rL1Is an inductance L1The stray resistance of (2); i.e. iL1(k) And vC1(k) Sampling values of the inductive current and the capacitor voltage at the kth sampling moment respectively;
step 3, establishing a prediction model of the quasi-Z source inverter, wherein the process is as follows:
3.1) adopting a forward Euler method to control each control variable with a control period TsUnder the conditions of (1) discretization
Figure BDA0002550140830000033
Substituting the formula (5) into the formulas (2), (3) and (4) respectively to obtain a predicted value of the output current, a predicted value of the inductive current and a predicted value of the capacitive voltage:
predicted value of output current:
Figure BDA0002550140830000041
in the formula ioα(k) And ioβ(k) Component i on the α β axis of the current sample value at the k-th sampling instantoα(k +1) and ioβ(k +1) is a component of a current predicted value at the k +1 th sampling moment on an alpha beta axis;
predicted values of inductor current and capacitor voltage in non-shoot-through state:
Figure BDA0002550140830000042
in the formula iL1(k +1) and vC1(k +1) are respectively the predicted values of the inductive current and the capacitive voltage at the (k +1) th sampling moment in a non-direct-connection state;
predicted values of inductor current and capacitor voltage in the shoot-through state:
Figure BDA0002550140830000043
in the formula iL1(k +1) and vC1(k +1) are respectively the predicted values of the inductive current and the capacitive voltage in the direct-connection state at the (k +1) th sampling moment;
3.2) Compensation method for adding delay
Carrying out cost function calculation by adopting the predicted value of the (k +2) th sampling moment to compensate output delay;
substituting k in the formulas (6), (7) and (8) by k +1 to obtain the predicted value of each control object at the time of k +2, and then substituting the predicted value into a cost function to calculate;
step 4, calculating the reference value of each control object, wherein the process is as follows:
4.1) calculation of reference values for the inductor current and the capacitor voltage
Figure BDA0002550140830000044
In the formula, Po_refAs an output power reference value, iL1_ref(k) Is the reference value v of the inductor currentC1_ref(k) The reference value of the capacitor voltage is a constant value;
4.2) calculating the phase current amplitude of the reference output current
Figure BDA0002550140830000051
In the formula Iom_refIs the phase current amplitude of the reference output current and is a constant value;
step 5, designing a cascade model prediction control method suitable for a quasi-Z source inverter
In the quasi-Z source inverter, the control objects are inductive current, capacitance voltage and output current, the inductive current control represents the control of input power, the capacitance voltage control represents the control of boosting on the DC side, the output current control represents the control of inversion on the AC side,
5.1) judging the state of the next control period according to the predicted value of the inductive current
Because of the particularity of the inductive current, the inductive current predicted values corresponding to 7 non-through vectors are the same as 1 value, while 1 through vector corresponds to 1 inductive current predicted value, and the inductive current predicted value in the non-through state is recorded as iL1_ns(k +2) and the predicted value of the inductor current in the through state is iL1_s(k+2)；
Figure BDA0002550140830000052
5.2) obtaining the optimal voltage vector for the capacitor voltage and the output current according to the cascade thought
5.2.1) remember that the method of calculating the capacitor voltage first and then the output current is S-MPC1
Firstly, 7 non-straight-through vectors are substituted into a (12) capacitor voltage cost function g C2 optimal voltage vectors are selected, and then the 2 voltages are usedVector substitution to the output current cost function g of equation (12)iFinally selecting an optimal voltage vector;
Figure BDA0002550140830000053
in the formula ioα_ref(k) And ioβ_ref(k) Respectively outputting components of three-phase current on an alpha beta axis for reference;
5.2.2) remember that the method of calculating the output current first and then the capacitor voltage is S-MPC2
Firstly, 7 non-straight-through vectors are substituted into an output current cost function g of a formula (12)i2 optimal voltage vectors are selected, and then the 2 optimal voltage vectors are substituted into a capacitance voltage cost function g of an equation (12)CFinally selecting an optimal voltage;
and 6, taking the optimal switching state obtained by calculation in the step 5 as the switching state at the k +1 th moment, and obtaining the switching state at the k +2 th moment from the steps so as to circulate continuously.
Further, in said 5.1), the cost function g in the formula (11)nsAnd gsAll take the form of absolute values; at this time, by comparing gnsAnd gsCan judge what state the next control cycle is, if gns<gsIf the state is judged to be a non-straight-through state, 5.2) is entered; if g isns>gsIf the direct vector is judged to be in the direct state, the direct vector is directly output.
Still further, in the 5.2.1), the capacitance-voltage cost function g in the formula (12)CIn the form of absolute values, and a current cost function g is outputiIn the form of a square.
According to the method, a quasi-Z-source inverter model predictive control method without weight coefficients is designed according to a cascade model predictive control method and by combining the particularity of inductive current, the defect that the weight coefficients need to be designed in a finite set model predictive control method is overcome, and the calculated amount of a digital processor is effectively reduced.
The technical conception of the invention is as follows: aiming at the problem that the adjustment of the weight coefficient is complicated in the Z-source inverter finite set model prediction control method, the invention adopts the cascade model prediction control method, and compared with the traditional finite set model prediction control method, the weight coefficient is effectively eliminated, so that the control method is simpler; in addition, the predicted value of the inductive current is judged, and the calculation amount of the digital processor is effectively reduced.
The invention has the beneficial effects that: the Z-source inverter is controlled by adopting a cascade model predictive control method, so that the weight coefficient is effectively eliminated, and the calculation amount of a digital processor is reduced.
Drawings
FIG. 1 is a circuit diagram of a quasi-Z-source inverter;
FIG. 2 is an equivalent circuit diagram of a quasi-Z-source inverter in a non-shoot-through state;
FIG. 3 is an equivalent circuit diagram of a quasi-Z-source inverter in a shoot-through state;
FIG. 4 is a basic flow diagram of the S-MPC1 method of the present invention;
FIG. 5 is a basic flow diagram of the S-MPC2 method of the present invention;
FIG. 6 is a graph of experimental waveforms for the FCS-MPC method;
FIG. 7 is a graph of experimental waveforms for the S-MPC1 method;
FIG. 8 is a graph of experimental waveforms for the S-MPC2 method.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Referring to fig. 1 to 8, a quasi-Z source inverter model predictive control method without a weight coefficient includes the following steps:
step 1, aligning a voltage signal and a current signal of a Z-source inverter to sample;
the current is recorded as the kth sampling moment, the voltage signal and the current signal of the Z-source inverter are sampled, and the sampling content comprises the following steps: inductor current iL1(k) And a capacitor voltage vC1(k) And outputting the load three-phase current ia(k)、ib(k) And ic(k) Then converting the three-phase current of the load from the three-phase static coordinate system to an alpha beta coordinate system to obtain ioα(k) Andioβ(k)；
step 2, establishing a mathematical model of the quasi-Z source inverter, wherein the process is as follows:
2.1, establishing an output voltage equation of the AC side of the quasi-Z source inverter
The minimum 8 output voltage vectors required for the qZSI system are first listed in Table 1
Figure BDA0002550140830000071
TABLE 1
8 output voltage vectors V of qZSIx(k) Is shown as
Figure BDA0002550140830000072
Wherein a ═ ej2π/3；x＝[0～7]；vdcThe peak voltage of a direct current side bus connected to the inverter bridge; s1、S3、S5Switch states of A, B, C phases, respectively;
the output voltage equation of the qZSI AC side is
Figure BDA0002550140830000073
Wherein R, L is the load phase resistance and phase inductance, Vxα、VxβFor the voltage component of the output voltage vector on the α β axis, ioα(k)、ioβ(k) Is the current component of the output current vector on the α β axis;
2.2, establishing an inductance current and capacitance voltage equation of the quasi-Z source impedance network in a non-direct-through state and a direct-through state respectively;
2.2.1) non-pass-through state:
Figure BDA0002550140830000074
in the formula, L1、C1Respectively, the inductance and capacitance values in the impedance network; rL1Is an inductance L1The stray resistance of (2); v. ofin(k) Is the input voltage; i.e. iL1(k) And vC1(k) Sampling values of the inductive current and the capacitor voltage at the kth sampling moment respectively; i.e. iinv(k)＝iA(k)S1+iB(k)S3+iC(k)S5；iA(k)、iB(k) And iC(k) Current values of the phase A, the phase B and the phase C at the kth sampling moment;
2.2.2) straight-through state:
Figure BDA0002550140830000081
in the formula, L1、C1Respectively, the inductance and capacitance values in the impedance network; rL1Is an inductance L1The stray resistance of (2); i.e. iL1(k) And vC1(k) Sampling values of the inductive current and the capacitor voltage at the kth sampling moment respectively;
step 3, establishing a prediction model of the quasi-Z source inverter, wherein the process is as follows:
3.1), adopting a forward Euler method to control each control variable with a control period TsUnder the conditions of (1) discretization
Figure BDA0002550140830000082
Substituting the formula (5) into the formulas (2), (3) and (4) respectively to obtain a predicted value of the output current, a predicted value of the inductive current and a predicted value of the capacitive voltage:
predicted value of output current:
Figure BDA0002550140830000083
in the formula ioα(k) And ioβ(k) Component i on the α β axis of the current sample value at the k-th sampling instantoα(k +1) and ioβ(k +1) is a component of a current predicted value at the k +1 th sampling moment on an alpha beta axis;
predicted values of inductor current and capacitor voltage in non-shoot-through state:
Figure BDA0002550140830000084
in the formula iL1(k +1) and vC1(k +1) are respectively the predicted values of the inductive current and the capacitive voltage at the (k +1) th sampling moment in a non-direct-connection state;
predicted values of inductor current and capacitor voltage in the shoot-through state:
Figure BDA0002550140830000091
in the formula iL1(k +1) and vC1(k +1) are respectively the predicted values of the inductive current and the capacitive voltage in the direct-connection state at the (k +1) th sampling moment;
3.2) Compensation method for adding delay
Because of a large amount of calculation in the digital control system, the calculated switching state is output in the next control period, and the last switching state is continuously applied before the calculation, so that the output delay of the system is caused, and the normal work of the system is influenced; carrying out cost function calculation by adopting the predicted value of the (k +2) th sampling moment to compensate output delay;
substituting k in the formulas (6), (7) and (8) by k +1 to obtain the predicted value of each control object at the time of k +2, and then substituting the predicted value into a cost function to calculate;
step 4, calculating the reference value of each control object, wherein the process is as follows:
4.1) calculation of reference values for the inductor current and the capacitor voltage
Figure BDA0002550140830000092
In the formula, Po_refAs an output power reference value, iL1_ref(k) Is the reference value v of the inductor currentC1_ref(k) The reference value of the capacitor voltage is a constant value;
4.2) calculating the phase current amplitude of the reference output current
Figure BDA0002550140830000093
In the formula Iom_refIs the phase current amplitude of the reference output current and is a constant value;
step 5, designing a cascade model prediction control method suitable for a quasi-Z source inverter
In the quasi-Z source inverter, the control objects comprise inductive current, capacitor voltage and output current, the inductive current control represents the control of input power, the capacitor voltage control represents the control of boosting on a direct current side, and the output current control represents the control of inversion on an alternating current side;
5.1, judging the state of the next control period according to the predicted value of the inductive current
Because of the particularity of the inductive current, the inductive current predicted values corresponding to 7 non-through vectors are the same as 1 value, while 1 through vector corresponds to 1 inductive current predicted value, and the inductive current predicted value in the non-through state is recorded as iL1_ns(k +2) and the predicted value of the inductor current in the through state is iL1_s(k+2)；
Figure BDA0002550140830000101
Cost function g in equation (11)nsAnd gsAll take the form of absolute values; at this time, by comparing gnsAnd gsCan judge what state the next control cycle is, if gns<gsIf the state is judged to be a non-straight-through state, 5.2) is entered; if g isns>gsIf the direct current state is judged, the direct current vector is directly output;
5.2) obtaining the optimal voltage vector for the capacitor voltage and the output current according to the cascade thought
5.2.1) remember that the method of calculating the capacitor voltage first and then the output current is S-MPC1
Firstly, 7 non-straight-through vectors are substituted into a (12) capacitance-voltage cost functionNumber g C2 optimal voltage vectors are selected, and then the 2 optimal voltage vectors are substituted into an output current cost function g of a formula (12)iFinally, an optimal voltage vector is selected.
Figure BDA0002550140830000102
In the formula ioα_ref(k) And ioβ_ref(k) Respectively outputting components of three-phase current on an alpha beta axis for reference;
capacitance voltage cost function g in equation (12)CIn the form of absolute values, and a current cost function g is outputiIn the form of a square;
5.2.2) remember that the method of calculating the output current first and then the capacitor voltage is S-MPC2
Firstly, 7 non-straight-through vectors are substituted into an output current cost function g of a formula (12)i2 optimal voltage vectors are selected, and then the 2 optimal voltage vectors are substituted into a capacitance voltage cost function g of an equation (12)CFinally selecting an optimal voltage;
and 6, taking the optimal switching state obtained by calculation in the step 5 as the switching state at the k +1 th moment, and obtaining the switching state at the k +2 th moment from the steps so as to circulate continuously.

Claims (3)

1. A quasi-Z-source inverter model predictive control method without weight coefficients is characterized by comprising the following steps:
step 1, aligning a voltage signal and a current signal of a Z-source inverter to sample;
the current is recorded as the kth sampling moment, the voltage signal and the current signal of the Z-source inverter are sampled, and the sampling content comprises the following steps: inductor current iL1(k) And a capacitor voltage vC1(k) And outputting the load three-phase current ia(k)、ib(k) And ic(k) Then converting the three-phase current of the load from the three-phase static coordinate system to an alpha beta coordinate system to obtain ioα(k) And ioβ(k)；
Step 2, establishing a mathematical model of the quasi-Z source inverter, wherein the process is as follows:
2.1, establishing an output voltage equation of the AC side of the quasi-Z source inverter
The minimum 8 output voltage vectors required for the qZSI system are first listed in Table 1
Figure FDA0002550140820000011
TABLE 1
8 output voltage vectors V of qZSIx(k) Is shown as
Figure FDA0002550140820000012
Wherein a ═ ej2π/3；x＝[0～7]；vdcThe peak voltage of a direct current side bus connected to the inverter bridge; s1、S3、S5Switch states of A, B, C phases, respectively;
the output voltage equation of the qZSI AC side is
Figure FDA0002550140820000013
Wherein R, L is the load phase resistance and phase inductance, Vxα、VxβFor the voltage component of the output voltage vector on the α β axis, ioα(k)、ioβ(k) Is the current component of the output current vector on the α β axis;
2.2, establishing an inductance current and capacitance voltage equation of the quasi-Z source impedance network in a non-direct-through state and a direct-through state respectively;
2.2.1) non-pass-through state:
Figure FDA0002550140820000021
in the formula, L1、C1Respectively, the inductance and capacitance values in the impedance network; rL1Is an inductance L1The stray resistance of (2); v. ofin(k) Is input intoA voltage; i.e. iL1(k) And vC1(k) Sampling values of the inductive current and the capacitor voltage at the kth sampling moment respectively; i.e. iinv(k)＝iA(k)S1+iB(k)S3+iC(k)S5；iA(k)、iB(k) And iC(k) Current values of the phase A, the phase B and the phase C at the kth sampling moment;
2.2.2) straight-through state:
Figure FDA0002550140820000022
in the formula, L1、C1Respectively, the inductance and capacitance values in the impedance network; rL1Is an inductance L1The stray resistance of (2); i.e. iL1(k) And vC1(k) Sampling values of the inductive current and the capacitor voltage at the kth sampling moment respectively;
step 3, establishing a prediction model of the quasi-Z source inverter, wherein the process is as follows:
3.1) adopting a forward Euler method to control each control variable with a control period TsUnder the conditions of (1) discretization
Figure FDA0002550140820000023
Substituting the formula (5) into the formulas (2), (3) and (4) respectively to obtain a predicted value of the output current, a predicted value of the inductive current and a predicted value of the capacitive voltage:
predicted value of output current:
Figure FDA0002550140820000024
in the formula ioα(k) And ioβ(k) Component i on the α β axis of the current sample value at the k-th sampling instantoα(k +1) and ioβ(k +1) is a component of a current predicted value at the k +1 th sampling moment on an alpha beta axis;
predicted values of inductor current and capacitor voltage in non-shoot-through state:
Figure FDA0002550140820000031
in the formula iL1(k +1) and vC1(k +1) are respectively the predicted values of the inductive current and the capacitive voltage at the (k +1) th sampling moment in a non-direct-connection state;
predicted values of inductor current and capacitor voltage in the shoot-through state:
Figure FDA0002550140820000032
in the formula iL1(k +1) and vC1(k +1) are respectively the predicted values of the inductive current and the capacitive voltage in the direct-connection state at the (k +1) th sampling moment;
3.2) Compensation method for adding delay
Carrying out cost function calculation by adopting the predicted value of the (k +2) th sampling moment to compensate output delay;
substituting k in the formulas (6), (7) and (8) by k +1 to obtain the predicted value of each control object at the time of k +2, and then substituting the predicted value into a cost function to calculate;
step 4, calculating the reference value of each control object, wherein the process is as follows:
4.1) calculation of reference values for the inductor current and the capacitor voltage
Figure FDA0002550140820000033
In the formula, Po_refAs an output power reference value, iL1_ref(k) Is the reference value v of the inductor currentC1_ref(k) The reference value of the capacitor voltage is a constant value;
4.2) calculating the phase current amplitude of the reference output current
Figure FDA0002550140820000034
In the formula Iom_refIs the phase current amplitude of the reference output current and is a constant value;
step 5, designing a cascade model prediction control method suitable for a quasi-Z source inverter
In the quasi-Z source inverter, the control objects are inductive current, capacitance voltage and output current, the inductive current control represents the control of input power, the capacitance voltage control represents the control of boosting on the DC side, the output current control represents the control of inversion on the AC side,
5.1) judging the state of the next control period according to the predicted value of the inductive current
Because of the particularity of the inductive current, the inductive current predicted values corresponding to 7 non-through vectors are the same as 1 value, while 1 through vector corresponds to 1 inductive current predicted value, and the inductive current predicted value in the non-through state is recorded as iL1_ns(k +2) and the predicted value of the inductor current in the through state is iL1_s(k+2)；
Figure FDA0002550140820000041
5.2) obtaining the optimal voltage vector for the capacitor voltage and the output current according to the cascade thought
5.2.1) remember that the method of calculating the capacitor voltage first and then the output current is S-MPC1
Firstly, 7 non-straight-through vectors are substituted into a (12) capacitor voltage cost function gC2 optimal voltage vectors are selected, and then the 2 optimal voltage vectors are substituted into an output current cost function g of a formula (12)iFinally selecting an optimal voltage vector;
Figure FDA0002550140820000042
in the formula ioα_ref(k) And ioβ_ref(k) Respectively outputting components of three-phase current on an alpha beta axis for reference;
5.2.2) remember that the method of calculating the output current first and then the capacitor voltage is S-MPC2
Firstly, 7 non-straight-through channels are connectedVector substitution formula (12) output current cost function gi2 optimal voltage vectors are selected, and then the 2 optimal voltage vectors are substituted into a capacitance voltage cost function g of an equation (12)CFinally selecting an optimal voltage;
and 6, taking the optimal switching state obtained by calculation in the step 5 as the switching state at the k +1 th moment, and obtaining the switching state at the k +2 th moment from the steps so as to circulate continuously.
2. The quasi-Z-source inverter model predictive control method without weight coefficients as claimed in claim 1, characterized in that in 5.1), the cost function g in formula (11) isnsAnd gsAll take the form of absolute values; at this time, by comparing gnsAnd gsCan judge what state the next control cycle is, if gns<gsIf the state is judged to be a non-straight-through state, 5.2) is entered; if g isns>gsIf the direct vector is judged to be in the direct state, the direct vector is directly output.
3. The quasi-Z-source inverter model predictive control method without weight coefficients as claimed in claim 1 or 2, characterized in that in 5.2.1), the capacitance-voltage cost function g in formula (12)CIn the form of absolute values, and a current cost function g is outputiIn the form of a square.
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