CN111538243A - Discrete sliding mode control method of three-port flexible multi-state switch - Google Patents

Discrete sliding mode control method of three-port flexible multi-state switch Download PDF

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CN111538243A
CN111538243A CN202010403509.6A CN202010403509A CN111538243A CN 111538243 A CN111538243 A CN 111538243A CN 202010403509 A CN202010403509 A CN 202010403509A CN 111538243 A CN111538243 A CN 111538243A
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CN111538243B (en
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张国荣
王泰文
汤彬
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Hefei University of Technology
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Abstract

The invention discloses a discrete sliding mode control method of a three-port flexible multi-state switch, which comprises the following steps: 1. establishing a mathematical model of a three-port flexible multi-state switch; 2. designing a discrete sliding mode controller; 3. analyzing the system stability and selecting sliding mode control parameters; 4. the designed discrete sliding mode controller is applied to the three-port flexible multi-state switch. According to the invention, the discrete sliding mode control method is applied to the three-port flexible multi-state switch, so that the system has good dynamic property and robustness, and a new solution is provided for the application of the three-port flexible multi-state switch in the power distribution network.

Description

Discrete sliding mode control method of three-port flexible multi-state switch
Technical Field
The invention relates to the technical field of flexible interconnected power distribution networks, in particular to a discrete sliding mode control method of a three-port flexible multi-state switch.
Background
With the rapid advance of power electronic technology, a large number of distributed renewable energy sources are connected into a power distribution network, and a series of challenges such as renewable energy consumption and increasingly complicated power flow control are brought to the power distribution network. The flexible multi-state switch is used as a novel power electronic device capable of replacing a traditional interconnection switch in a power distribution network, the limitation of the traditional mechanical switch action times is avoided, the flexible and various control mode is achieved, and a new solution is provided for the problems.
The study of scholars at home and abroad on the flexible multi-state switch is mainly from the perspective of a power distribution network, the study points are biased to the problems of optimized operation and economy, and the study on the switch equipment control strategy of the flexible multi-state switch is less. Although the conventional PI double-loop control strategy can realize the normal operation of the flexible multi-state switch, for the multi-port flexible multi-state switch, PI parameters are more, and the defects of difficult parameter setting, to-be-improved dynamic performance, poor robustness and the like exist. Although the feedback linearization sliding mode control of the flexible multi-state switch can overcome the defects, the method belongs to the sliding mode control of a continuous time domain, and a digital computer and a DSP controller belong to a discrete system essentially, and control signals of the digital computer and the DSP controller are updated only once at each sampling moment, so that an ideal sliding mode in the continuous time domain sliding mode theory cannot be directly realized, and only a quasi-sliding mode near the field can be reached. If this influence is not considered, the continuous time domain sliding mode control law is directly applied to a discrete system, and adverse effects such as system buffeting or instability can be caused.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a discrete sliding mode control method of a three-port flexible multi-state switch, so that the discrete sliding mode control can be applied to the three-port flexible multi-state switch, the dynamic property and the robustness of a system are improved, and a new solution is provided for the application of the three-port flexible multi-state switch in a power distribution network.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention discloses a discrete sliding mode control method of a three-port flexible multi-state switch, which is characterized by being applied to a system formed by connecting the three-port flexible multi-state switch into a power distribution network and comprising the following steps:
step one, establishing a mathematical model of a three-port flexible multi-state switch;
step 1.1, assuming that the voltage of a power distribution network is a three-phase balanced pure sine wave, and when L filtering is adopted, establishing a discrete mathematical model of one port of the three-port flexible multi-state switch under a dq coordinate system by using the formula (1):
Figure BDA0002490382400000021
in the formula (1), L represents an ac-side filter inductor; r represents the inductance internal resistance; t represents the sampling period of the system; ω represents the phase voltage angular frequency of the distribution network; i.e. id(k) And iq(k) Respectively representing the components of the current of the alternating current side flowing through the inductor on the d axis and the q axis at the kth sampling moment; i.e. id(k +1) and iq(k +1) represents the components of the current value at the (k +1) th sampling time on the d-axis and the q-axis; e.g. of the typed(k) And eq(k) Representing components of the power distribution network side voltage on a d axis and a q axis at the k sampling moment; u. ofd(k) And uq(k) Representing the components of the output voltage of the flexible multi-state switch on the d axis and the q axis at the kth sampling moment;
step 1.2, neglecting the loss of the three-port flexible multi-state switch and the line loss, and establishing the current and power coupling relation of the three-port flexible multi-state switch operation control by using the formula (2) to the formula (4):
Figure BDA0002490382400000022
Pj＝Udcidcj(3)
Figure BDA0002490382400000023
in the formula (2) -formula (4), C represents a dc-side filter capacitor; u shapedcRepresents the dc bus voltage; i.e. ijxIndicating the x phase inductive current of the j port in the flexible multi-state switch; sjxAn xth phase switching function representing a jth port in the flexible multi-state switch; pjThe active power of the alternating current side of the jth port in the flexible multi-state switch is represented; i.e. idcjIndicating a direct current side of a jth port in a flexible multi-state switch；
Designing a discrete sliding mode controller;
step 2.1, determining a discrete sliding mode surface s (k) at the kth sampling time by using the formula (5):
Figure BDA0002490382400000024
in the formula (5), sd(k) And sq(k) Respectively representing discrete integral sliding mode surfaces designed on a d axis and a q axis at the kth sampling moment; ed(k) And Eq(k) Respectively representing the tracking errors of the output current of the kth sampling moment on the d axis and the q axis, and obtaining the tracking errors by an equation (6); m is1And m2For two parameters to be designed and satisfy m1＞0，m2＞0；vd(k) And vq(k) The error integrals of the output currents on the d axis and the q axis at the k-th sampling time are respectively expressed and obtained by equation (7):
Figure BDA0002490382400000025
in the formula (6), the reaction mixture is,
Figure BDA0002490382400000031
and
Figure BDA0002490382400000032
command values respectively representing currents on the d axis and the q axis at the kth sampling time;
Figure BDA0002490382400000033
in the formula (7), G1And G2Is two integral gains, and satisfies G1＞0，G2＞0；
Step 2.2, establishing a discrete sliding mode control law by using the formula (8):
Figure BDA0002490382400000034
the compound of the formula (8),1、2、k1、k2are all approach law control parameters; sat (s (k)) is a saturation function and is obtained from equation (9):
Figure BDA0002490382400000035
in the formula (9), rho is the thickness of the sliding mode boundary layer;
step 2.3, establishing a control equation of the discrete sliding mode controller by using the formula (10) to the formula (11):
Figure BDA0002490382400000036
Figure BDA0002490382400000037
analyzing the system stability and selecting sliding mode control parameters;
step 3.1, determining the stability of the designed discrete sliding mode control system by using the formula (12):
Figure BDA0002490382400000038
step 3.2, determining the value range of the sliding mode control parameter by using the formula (13):
Figure BDA0002490382400000039
step four, applying the designed discrete sliding mode controller to a three-port flexible multi-state switch;
according to different operation scenes of the power distribution network, three control modes of the three-port flexible multi-state switch are set by adopting a double-loop control strategy: u shapedcQ control, PQ control and Uacf, controlling;
step 4.1, determining U by using formula (14)dcVoltage outer loop for Q control mode:
Figure BDA0002490382400000041
in formula (14), idrefA command value of active current of any port; i.e. iqrefA command value for reactive current of the corresponding port; k is a radical ofp、kiControl parameters of the PI controller; u shapedcrefIs a direct current side voltage reference value; qrefIs the reactive power reference value of the corresponding port;
step 4.2, the designed discrete sliding mode controller is utilized, and the formula (15) is utilized to establish UdcCurrent inner loop of Q control mode:
Figure BDA0002490382400000042
and 4.3, determining a power outer loop of the PQ control mode by using the formula (16):
Figure BDA0002490382400000043
in formula (16), PrefThe active power reference value of the corresponding port; k is a radical of1p、k1iControlling a control parameter of the PI controller for the active current; k is a radical of2p、k2iControlling control parameters of the PI controller for the reactive current; p, Q are the active power and reactive power of the corresponding port, and are obtained by equation (17):
Figure BDA0002490382400000044
4.4, establishing a current inner loop of a PQ control mode by using the designed discrete sliding mode controller and an equation (15);
step 4.5, determining U by using the formula (18)acOuter loop control of f control mode:
Figure BDA0002490382400000051
in the formula (18), udlrefAnd uqlrefReference values for the load voltage on the d-axis and the q-axis; p and Q are the active power and the reactive power of the corresponding port load; u. ofdlAnd uqlVoltage components on d-axis and q-axis for the load voltage; k is a radical of3p、k3iControlling a control parameter of the PI controller for the active current; k is a radical of4p、k4iControlling control parameters of the PI controller for the reactive current;
step 4.6, determining U by using the formula (19) -formula (20)acCurrent inner loop of f control mode:
Figure BDA0002490382400000052
Figure BDA0002490382400000053
and 4.7, obtaining active reference current and reactive reference current through the PI regulator of the outer ring, and generating a pulse width modulation switching signal through a current inner ring formed by the discrete sliding mode controller, so that the control of the three-port flexible multi-state switch is realized.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention utilizes the discrete sliding mode control to replace the current inner ring of PI double-ring control, thereby reducing PI control links, simplifying the setting of PI parameters, and simultaneously utilizing the characteristics of good dynamic property and strong robustness of the sliding mode control to improve the dynamic property and the robustness of the system.
2. The discrete sliding mode control can be directly applied to a discrete system, is more beneficial to the realization of the control algorithm in practical engineering, avoids the adverse effects of system buffeting or instability and the like possibly caused in practical application, and improves the running performance of the flexible multi-state switch.
Drawings
FIG. 1 is a schematic diagram of a three-port flexible multi-state switch according to the present invention connected to a power distribution network;
FIG. 2 is a topology of any port of the three-port flexible multi-state switch of the present invention;
FIG. 3 is the present inventionFlexible multi-state switch U with three open portsdcA Q-mode control block diagram;
FIG. 4 is a block diagram of a three port flexible multi-state switch PQ mode control of the present invention;
FIG. 5 shows a three-port flexible multi-state switch U according to the present inventionacf-mode control block diagram.
Detailed Description
In this embodiment, as shown in fig. 1, the three-port flexible multi-state switch is connected to the topology structure of the power distribution network, and the access topology in a back-to-back manner is connected to the tail ends of the feeders, so that flexible interconnection among different feeders can be realized, and the power distribution network has the advantages of open-loop operation and closed-loop operation; as shown in fig. 2, is a topology of any port of the three-port flexible multi-state switch; a discrete sliding mode control method of a three-port flexible multi-state switch is carried out according to the following steps:
step one, establishing a mathematical model of a three-port flexible multi-state switch;
the three ports of the three-port flexible multi-state switch are symmetrical in structure, each port consists of a three-phase voltage type converter, a mathematical model is established by taking the topology of one port as an example, and a three-port current and power coupling relational expression is established according to the access topology of the three-port flexible multi-state switch. Assuming that the system voltage is a pure sine wave balanced by three phases and each port adopts L filtering, a discrete mathematical model of the flexible multi-state switch in a dq coordinate system is determined by equation (1).
In the established flexible multi-state switch discrete mathematical model, the d-axis and q-axis discrete electric quantity relational expression represents the working mechanism of each port of the flexible multi-state switch, and a group of equality constraints represents the energy conservation in the energy scheduling of the flexible multi-state switch.
Step 1.1, assuming that the voltage of a power distribution network is a three-phase balanced pure sine wave, and when L filtering is adopted, establishing a discrete mathematical model of one port of the flexible multi-state switch under a dq coordinate system by using the formula (1):
Figure BDA0002490382400000061
in the formula (1), L represents an ac-side filter inductor; r represents the inductance internal resistance; t represents the sampling period of the system; ω represents the phase voltage angular frequency of the distribution network; i.e. id(k) And iq(k) Respectively representing the components of the current of the alternating current side flowing through the inductor on the d axis and the q axis at the kth sampling moment; i.e. id(k +1) and iq(k +1) represents the components of the current value at the (k +1) th sampling time on the d-axis and the q-axis; e.g. of the typed(k) And eq(k) Representing components of the power distribution network side voltage on a d axis and a q axis at the k sampling moment; u. ofd(k) And uq(k) Representing the components of the output voltage of the flexible multi-state switch on the d axis and the q axis at the kth sampling moment;
step 1.2, neglecting the loss of the three-port flexible multi-state switch and the line loss, and establishing the current and power coupling relation of the three-port flexible multi-state switch operation control by using the formula (2) to the formula (4):
Figure BDA0002490382400000062
Pj＝Udcidcj(3)
Figure BDA0002490382400000071
in the formula (2) -formula (4), C represents a dc-side filter capacitor; u shapedcRepresents the dc bus voltage; i.e. ijxIndicating the x phase inductive current of the j port in the flexible multi-state switch; sjxAn xth phase switching function representing a jth port in the flexible multi-state switch; pjThe active power of the alternating current side of the jth port in the flexible multi-state switch is represented; i.e. idcjIndicating the direct current side current of the j-th port in the flexible multi-state switch;
the following is the derivation of the formula for the established mathematical model of the three-port flexible multi-state switch:
according to the port topology shown in fig. 2, a mathematical model of the continuous time domain of the flexible multi-state switch can be obtained, which is represented by equation (5):
Figure BDA0002490382400000072
in the formula (5), k represents a three phase of a, b and c;
the abc/dq coordinate transformation of equation (5) can be obtained:
Figure BDA0002490382400000073
the formula (6) is arranged to obtain:
Figure BDA0002490382400000074
in formula (7): x ═ idiq]T；
Figure BDA0002490382400000075
u＝[ed-udeq-uq]T；
Figure BDA0002490382400000076
Discretization of equation (7) can yield:
x(k+1)＝Hx(k)+Gu(k) (8)
in formula (8): h ═ eAT；
Figure BDA0002490382400000077
When the system sampling period T is very small, around 1/10 of the system minimum time constant, an approximate expression of H and G can be obtained: h is approximately equal to TA + I; g ≈ TB. Substitution of H and G for formula (8) gives:
Figure BDA0002490382400000081
equation (9) is a discrete mathematical model of one port of the flexible multi-state switch in dq coordinate system.
Designing a discrete sliding mode controller;
step 2.1, determining a discrete sliding mode surface s (k) by using the formula (10):
Figure BDA0002490382400000082
in the formula (10), sd(k) And sq(k) Respectively representing discrete integral sliding mode surfaces designed on a d axis and a q axis at the kth sampling moment; ed(k) And Eq(k) Respectively representing the tracking errors of the output current of the kth sampling moment on the d axis and the q axis, and obtaining the tracking errors by an equation (6); m is1And m2For two parameters to be designed and satisfy m1＞0，m2＞0；vd(k) And vq(k) The error integrals of the output currents on the d axis and the q axis at the k-th sampling time are respectively expressed and obtained by equation (11):
Figure BDA0002490382400000083
in the formula (11), the reaction mixture is,
Figure BDA0002490382400000084
and
Figure BDA0002490382400000085
command values respectively representing currents on the d axis and the q axis at the kth sampling time;
Figure BDA0002490382400000086
in formula (12), G1And G2Is an integral gain and satisfies G1＞0，G2＞0。
Step 2.2, establishing a discrete sliding mode control law by using the formula (13):
Figure BDA0002490382400000087
a compound of the formula (13),1、2、k1、k2are all approach law control parameters; sat (s (k)) is a saturation function and is obtained from equation (14):
Figure BDA0002490382400000088
in equation (14), ρ is the sliding mode boundary layer thickness.
Step 2.3, establishing a control equation of the discrete sliding mode controller by using the formula (15) to the formula (16):
Figure BDA0002490382400000091
Figure BDA0002490382400000092
analyzing the system stability and selecting sliding mode control parameters;
step 3.1, determining the stability of the designed discrete sliding mode control system by using an equation (17):
Figure BDA0002490382400000093
step 3.2, determining the value range of the sliding mode control parameter by using the formula (18):
Figure BDA0002490382400000094
deducing the value range of the obtained sliding mode control parameter as follows:
taking the control of the d axis as an example for analysis, according to the selected discrete sliding mode control law, the following can be obtained:
sd(k+1)-sd(k)＝1sat(sd(k))+(k1-1)sd(k) (19)
if s isd(k) To stabilize the designed discrete sliding mode control system, equation (19) must be satisfied: sd(k+1)-sd(k) Is less than 0. When the sliding mode control parameter meets1＜0，k1When the frequency is less than 1, the discrete sliding mode control system keeps stable.
If s isd(k) < 0, in order to keep the designed discrete sliding mode control system stable, the equation of equation (19) must be satisfied: sd(k+1)-sd(k) Is greater than 0. When the sliding mode control parameter meets1＜0，k1When the frequency is less than 1, the discrete sliding mode control system keeps stable.
In conclusion, when the sliding mode control parameters of the d axis meet the requirements1＜0，k1When the d-axis is less than 1, the control of the d-axis of the designed discrete sliding mode controller can be kept stable. In the same way, when the sliding mode control parameter of the q axis meets2＜0，k2When the control signal is less than 1, the control of the q axis of the designed discrete sliding mode controller can be kept stable.
Step four, applying the designed discrete sliding mode controller to a three-port flexible multi-state switch;
according to different operation scenes of the power distribution network, three control modes of the three-port flexible multi-state switch are set by adopting a double-loop control strategy: u shapedcQ control, PQ control and UacAnd f, controlling. And respectively applying the designed discrete sliding mode controller to the three control modes to realize a control algorithm. Because the three ports of the three-port flexible multi-state switch are symmetrical in structure, each port consists of a three-phase voltage type converter, any one port is taken as an example, the three control modes are respectively realized by double-ring control, and double-ring control of the other two ports is arranged at the same port; u shapedcThe Q-mode control block diagram is shown in fig. 3, and its purpose is to keep the voltage at the dc side stable, independently adjust the reactive power of the corresponding ports, and simultaneously maintain the power balance of the whole three-port flexible multi-state switch; the PQ mode control block diagram is shown in fig. 4, and its purpose is to independently adjust the active power and reactive power of the corresponding ports; u shapeacThe f-mode control block diagram is shown in fig. 5, and aims to provide voltage and frequency support for a power-loss area when a feeder line fault occurs at one port of the three-port flexible multi-state switch, so as to ensure uninterrupted power supply of important loads;
step 4.1, utilizing formula (20)) Determining UdcVoltage outer loop for Q control mode:
Figure BDA0002490382400000101
in the formula (20), idrefIs the command value of the active current of the port; i.e. iqrefIs the command value of the reactive current of the port; k is a radical ofp、kiControl parameters of the PI controller; u shapedcrefIs a direct current side voltage reference value; qrefIs the reactive power reference value for that port.
Step 4.2, utilizing the designed discrete sliding mode controller: formula (15) -formula (16), and in combination with formula (21) to establish UdcCurrent inner loop of Q control mode:
Figure BDA0002490382400000102
and 4.3, determining a power outer loop of the PQ control mode by using the formula (22):
Figure BDA0002490382400000103
in the formula (22), PrefIs the active power reference value of the port; k is a radical of1p、k1iControlling a control parameter of the PI controller for the active current; k is a radical of2p、k2iControlling control parameters of the PI controller for the reactive current; p, Q are the active and reactive power of the port, and are derived from equation (23):
Figure BDA0002490382400000104
step 4.4, utilizing the designed discrete sliding mode controller: equation (15) -equation (16), in combination with equation (21), establish the current inner loop for the PQ control mode.
Step 4.5, determining U by using the formula (24)acOuter loop control of f control mode:
Figure BDA0002490382400000111
in the formula (24), udlrefAnd uqlrefReference values for the load voltage on the d-axis and the q-axis; p and Q are the active power and the reactive power of the port load; u. ofdlAnd uqlVoltage components on d-axis and q-axis for the load voltage; k is a radical of3p、k3iControlling a control parameter of the PI controller for the active current; k is a radical of4p、k4iAnd controlling the control parameters of the PI controller for the reactive current.
Step 4.6, determining U by using the formula (25) to the formula (26)acCurrent inner loop of f control mode:
Figure BDA0002490382400000112
Figure BDA0002490382400000113
in the implementation, a double-loop control strategy is adopted in all three control modes, active reference current and reactive reference current are obtained through a PI regulator of an outer loop, and a pulse width modulation switching signal is generated through a current inner loop formed by a discrete sliding mode controller, so that the control of the three-port flexible multi-state switch is realized.

Claims (1)

1. A discrete sliding mode control method of a three-port flexible multi-state switch is characterized by being applied to a system formed by connecting the three-port flexible multi-state switch to a power distribution network and comprising the following steps:
step one, establishing a mathematical model of a three-port flexible multi-state switch;
step 1.1, assuming that the voltage of a power distribution network is a three-phase balanced pure sine wave, and when L filtering is adopted, establishing a discrete mathematical model of one port of the three-port flexible multi-state switch under a dq coordinate system by using the formula (1):
Figure FDA0002490382390000011
in the formula (1), L represents an ac-side filter inductor; r represents the inductance internal resistance; t represents the sampling period of the system; ω represents the phase voltage angular frequency of the distribution network; i.e. id(k) And iq(k) Respectively representing the components of the current of the alternating current side flowing through the inductor on the d axis and the q axis at the kth sampling moment; i.e. id(k +1) and iq(k +1) represents the components of the current value at the (k +1) th sampling time on the d-axis and the q-axis; e.g. of the typed(k) And eq(k) Representing components of the power distribution network side voltage on a d axis and a q axis at the k sampling moment; u. ofd(k) And uq(k) Representing the components of the output voltage of the flexible multi-state switch on the d axis and the q axis at the kth sampling moment;
step 1.2, neglecting the loss of the three-port flexible multi-state switch and the line loss, and establishing the current and power coupling relation of the three-port flexible multi-state switch operation control by using the formula (2) to the formula (4):
Figure FDA0002490382390000012
Pj＝Udcidcj(3)
Figure FDA0002490382390000013
in the formula (2) -formula (4), C represents a dc-side filter capacitor; u shapedcRepresents the dc bus voltage; i.e. ijxIndicating the x phase inductive current of the j port in the flexible multi-state switch; sjxAn xth phase switching function representing a jth port in the flexible multi-state switch; pjThe active power of the alternating current side of the jth port in the flexible multi-state switch is represented; i.e. idcjIndicating the direct current side current of the j-th port in the flexible multi-state switch;
designing a discrete sliding mode controller;
step 2.1, determining a discrete sliding mode surface s (k) at the kth sampling time by using the formula (5):
Figure FDA0002490382390000014
in the formula (5), sd(k) And sq(k) Respectively representing discrete integral sliding mode surfaces designed on a d axis and a q axis at the kth sampling moment; ed(k) And Eq(k) Respectively representing the tracking errors of the output current of the kth sampling moment on the d axis and the q axis, and obtaining the tracking errors by an equation (6); m is1And m2For two parameters to be designed and satisfy m1＞0，m2＞0；vd(k) And vq(k) The error integrals of the output currents on the d axis and the q axis at the k-th sampling time are respectively expressed and obtained by equation (7):
Figure FDA0002490382390000021
in the formula (6), the reaction mixture is,
Figure FDA0002490382390000027
and
Figure FDA0002490382390000028
command values respectively representing currents on the d axis and the q axis at the kth sampling time;
Figure FDA0002490382390000022
in the formula (7), G1And G2Is two integral gains, and satisfies G1＞0，G2＞0；
Step 2.2, establishing a discrete sliding mode control law by using the formula (8):
Figure FDA0002490382390000023
the compound of the formula (8),1、2、k1、k2are all approach law control parameters; sat (s (k)) is a saturation function and is obtained from equation (9):
Figure FDA0002490382390000024
in the formula (9), rho is the thickness of the sliding mode boundary layer;
step 2.3, establishing a control equation of the discrete sliding mode controller by using the formula (10) to the formula (11):
Figure FDA0002490382390000025
Figure FDA0002490382390000026
analyzing the system stability and selecting sliding mode control parameters;
step 3.1, determining the stability of the designed discrete sliding mode control system by using the formula (12):
Figure FDA0002490382390000031
step 3.2, determining the value range of the sliding mode control parameter by using the formula (13):
Figure FDA0002490382390000032
step four, applying the designed discrete sliding mode controller to a three-port flexible multi-state switch;
according to different operation scenes of the power distribution network, three control modes of the three-port flexible multi-state switch are set by adopting a double-loop control strategy: u shapedcQ control, PQ control and Uacf, controlling;
step 4.1, determining U by using formula (14)dcVoltage outer loop for Q control mode:
Figure FDA0002490382390000033
in formula (14), idrefA command value of active current of any port;iqrefa command value for reactive current of the corresponding port; k is a radical ofp、kiControl parameters of the PI controller; u shapedcrefIs a direct current side voltage reference value; qrefIs the reactive power reference value of the corresponding port;
step 4.2, the designed discrete sliding mode controller is utilized, and the formula (15) is utilized to establish UdcCurrent inner loop of Q control mode:
Figure FDA0002490382390000034
and 4.3, determining a power outer loop of the PQ control mode by using the formula (16):
Figure FDA0002490382390000035
in formula (16), PrefThe active power reference value of the corresponding port; k is a radical of1p、k1iControlling a control parameter of the PI controller for the active current; k is a radical of2p、k2iControlling control parameters of the PI controller for the reactive current; p, Q are the active power and reactive power of the corresponding port, and are obtained by equation (17):
Figure FDA0002490382390000036
4.4, establishing a current inner loop of a PQ control mode by using the designed discrete sliding mode controller and an equation (15);
step 4.5, determining U by using the formula (18)acOuter loop control of f control mode:
Figure FDA0002490382390000041
in the formula (18), udlrefAnd uqlrefReference values for the load voltage on the d-axis and the q-axis; p and Q are the active power and the reactive power of the corresponding port load; u. ofdlAnd uqlVoltages on d-and q-axes for load voltagesA component; k is a radical of3p、k3iControlling a control parameter of the PI controller for the active current; k is a radical of4p、k4iControlling control parameters of the PI controller for the reactive current;
step 4.6, determining U by using the formula (19) -formula (20)acCurrent inner loop of f control mode:
Figure FDA0002490382390000042
Figure FDA0002490382390000043
and 4.7, obtaining active reference current and reactive reference current through the PI regulator of the outer ring, and generating a pulse width modulation switching signal through a current inner ring formed by the discrete sliding mode controller, so that the control of the three-port flexible multi-state switch is realized.
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