Combined non-isolated three-phase inverter, island operation control method and system, electronic equipment and product

Abstract

The invention belongs to the technical field of electric energy conversion, and aims to provide a combined non-isolated three-phase inverter, an isolated island operation control method and system, electronic equipment and a product. According to the combined non-isolated three-phase inverter, generation of common-mode current can be reduced, the use of a transformer is omitted by configuring the three single-phase Helic inverters, and compared with a traditional combined three-phase inverter, the equipment cost is reduced. According to the island operation control method, an updated active-frequency equation is constructed based on a hyperbolic tangent function, and due to the fact that the hyperbolic tangent function is provided with an upper boundary and a lower boundary, according to the characteristic, the frequency can be limited to change within a specified range, and the control accuracy is improved. In other words, no matter how the load and the output power change, the frequency does not exceed the preset range, and therefore the frequency out-of-limit problem which cannot be solved by traditional droop control is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric energy conversion, and specifically relates to a combined non-isolated three-phase inverter, an island operation control method, system, electronic equipment and products. Background Art

[0002] The traditional combined three-phase inverter is composed of three single-phase full-bridge inverters connected in star shape. This modular structure design makes the system easy to implement and maintain. At the same time, the combined three-phase inverter supports independent control of voltage and current dual closed loops, which allows each phase to be controlled separately, thereby improving the flexibility and control accuracy of the system. In addition, the combined three-phase inverter can also realize the parallel operation of multiple devices, which not only improves the redundancy and reliability of the system, but also facilitates the expansion of the system scale. Based on this, the combined three-phase inverter is widely used in high-power power supply occasions.

[0003] The instability of the power grid will cause the inverter to be disconnected from the grid and enter an island state (also known as "off-grid"), and in order to ensure that the inverter outputs a good sinusoidal three-phase voltage without a communication line, and to achieve power sharing and voltage balance among multiple inverters, the combined three-phase inverter usually adopts a droop control scheme in the island state. Taking one phase of a combined three-phase inverter as an example, the general process of the traditional droop control scheme is: collect the output voltage and output current of the inverter in real time, and perform power calculation on them to obtain the output active power and reactive power of the inverter; then, through the traditional active-frequency (also active power-frequency, which can be abbreviated as) used for droop control P - f ) equation and the traditional reactive-voltage (that is, reactive power-frequency, which can be abbreviated as Q - U ) equation to obtain the amplitude and angular frequency of the reference voltage, and then obtain the three-phase reference voltage; finally, based on the three-phase reference voltage, the drive signal of the power switch tube in the combined three-phase inverter is obtained, and the inverter operation is controlled based on the drive signal. The above control process is used for the other two phases of the inverter at the same time, so that the combined three-phase inverter can output a three-phase voltage.

[0004] However, in the process of using the prior art, the inventors found that the prior art has at least the following problems: Compared with other types of inverters, traditional combined three-phase inverters use more power switch tubes, resulting in larger size and higher cost.

[0005] In addition, if Figure 1 The following are based on the traditional active power-frequency ( P - f ) equation and the traditional reactive-voltage ( Q - U) equation, refer to Figure 1 It can be seen that in traditional droop control, active power and frequency are in a linear relationship. This means that when the inverter is connected to a large load, the frequency will exceed the specified range (also known as "frequency over-limit"), affecting the safe operation of the inverter and the load. Summary of the invention

[0006] The present invention aims to solve the above technical problems at least to a certain extent. The present invention provides a combined non-isolated three-phase inverter, an island operation control method, a system, an electronic device and a product.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a combined non-isolated three-phase inverter, comprising a combined three-phase inverter and three single-phase Heric inverters, wherein the input end of the combined three-phase inverter constitutes a DC input end of the combined non-isolated three-phase inverter, the output end of the combined three-phase inverter is respectively connected to the input ends of the three single-phase Heric inverters, and the output ends of the three single-phase Heric inverters constitute a three-phase grid-connected output end of the combined non-isolated three-phase inverter.

[0008] In a second aspect, the present invention provides an island operation control method for a combined non-isolated three-phase inverter, comprising: The three-phase output voltage value, the three-phase output current value and the three-phase inductor current value of the combined non-isolated three-phase inverter in the island state are collected in real time, and power calculation is performed according to the three-phase output voltage value and the three-phase output current value to obtain the three-phase output active power value and the three-phase reactive power value of the combined non-isolated three-phase inverter; constructing updated active-frequency equations of the three phases for droop control based on active power values ​​of the three phases and a hyperbolic tangent function, and obtaining specified reactive-voltage equations of the three phases based on reactive power values ​​of the three phases; According to the updated active-frequency equation of the three phases and the specified reactive-voltage equation of the three phases, a reference amplitude and a reference angular frequency are obtained; Obtaining three-phase reference voltage values ​​according to the reference amplitude and the reference angular frequency; Perform voltage and current double closed-loop control according to the three-phase reference voltage value, the three-phase output voltage value and the three-phase inductor current value to obtain a regulating signal; A driving signal is generated according to the adjustment signal and a preset triangular carrier, and the combined non-isolated three-phase inverter is controlled to operate based on the driving signal.

[0009] In a possible design, among the updated active power-frequency equations of the three phases, the updated active power-frequency equation of any phase is: ; In the formula, f is the reference angular frequency; f o is the preset angular frequency given value; P is the active power value of any phase; P o It is the preset active power given value; m 1 is the preset boundary coefficient, m 2 is the preset droop coefficient; Among the three-phase specified reactive power-voltage equations, the specified reactive power-voltage equation for any phase is: ; In the formula, u is the reference amplitude; Q o is the preset reactive power given value; Q is the reactive power value of any phase; n is the preset reactive power droop coefficient; u o is the output voltage value of any phase.

[0010] In a possible design, among the updated active power-frequency equations of the three phases, the updated active power-frequency equation of any phase is: ; In the formula, f is the reference angular frequency; f o is the preset angular frequency given value; P avg is the average value of the three-phase active power, , P a , P b and P c The active power values ​​of phase A, phase B and phase C in the three phases respectively; P o It is the preset active power given value; m 1 is the preset boundary coefficient, m 2 is the preset droop coefficient; Among the three-phase specified reactive power-voltage equations, the specified reactive power-voltage equation for any phase is: ; In the formula, u is the reference amplitude; Q o is the preset reactive power given value; Qavg is the average value of the three-phase reactive power, , Q a , Q b and Q c Reactive power values ​​of phase A, phase B and phase C respectively among the three phases; n is the preset reactive power droop coefficient; u o is the output voltage value of any phase.

[0011] In a possible design, among the updated active power-frequency equations of the three phases, the updated active power-frequency equation of any phase is: ; In the formula, f is the reference angular frequency; f o is the preset angular frequency given value; P avg is the average value of the three-phase active power, , P a , P b and P c The active power values ​​of phase A, phase B and phase C in the three phases respectively; P o It is the preset active power given value; m 1 is the preset boundary coefficient, m 2 is the preset droop coefficient; Among the three-phase specified reactive power-voltage equations, the specified reactive power-voltage equation for any phase is: ; In the formula, u is the reference amplitude; Q o is the preset reactive power given value; Q avg is the average value of the three-phase reactive power, , Q a , Q b and Q c Reactive power values ​​of phase A, phase B and phase C respectively among the three phases; n is the preset reactive power droop coefficient; u o is the output voltage value of any phase; is the voltage compensation amount, ,U ref is the reference voltage value; k is the preset compensation coefficient.

[0012] In one possible design, the three-phase reference voltage values ​​are U ref It includes the reference voltage value of phase A, the reference voltage value of phase B and the reference voltage value of phase C, among which the reference voltage value of phase A is: U refa =usinf ; In the formula, u is the reference amplitude; f is the reference angular frequency; The reference voltage value of phase B is: U refb =usin(f-2π / 3) ; The reference voltage value of phase C is: U refc =usin(f+2π / 3) .

[0013] In a possible design, voltage and current dual closed-loop control is performed according to the three-phase reference voltage value, the three-phase output voltage value and the three-phase inductor current value to obtain a regulation signal, including: The voltage loop is used as an outer loop, the reference voltage values ​​of the three phases are used as input data of the voltage loop, and the output voltage values ​​of the three phases are used as feedback signals of the voltage loop to obtain the difference between the reference voltage values ​​of the three phases and the output voltage values ​​of the corresponding three phases, and the reference current of the three phases is obtained based on the difference; wherein the voltage loop adopts proportional integral control; The current loop is used as an inner loop, and the three-phase inductor current values ​​are used as feedback signals of the current loop to compare the three-phase inductor current values ​​with the three-phase reference currents, and obtain adjustment signals based on a proportional controller; wherein the current loop adopts proportional control.

[0014] In a third aspect, the present invention provides an island operation control system for implementing any of the island operation control methods described above; the island operation control system comprises: A signal acquisition module, used for real-time acquisition of the three-phase output voltage value, the three-phase output current value and the three-phase inductance current value of the combined non-isolated three-phase inverter in an island state, and performing power calculation according to the three-phase output voltage value and the three-phase output current value to obtain the three-phase output active power value and the three-phase reactive power value of the combined non-isolated three-phase inverter; A droop control module, in communication with the signal acquisition module, for constructing an updated three-phase active power-frequency equation for droop control based on the three-phase active power values ​​and the hyperbolic tangent function, and obtaining a specified three-phase reactive power-voltage equation based on the three-phase reactive power values; A reference voltage synthesis module is communicatively connected with the droop control module, and is used to obtain a reference amplitude and a reference angular frequency according to the updated active power-frequency equation of the three phases and the specified reactive power-voltage equation of the three phases; and is also used to obtain a reference voltage value of the three phases according to the reference amplitude and the reference angular frequency; A voltage-current dual-loop control module is connected to the reference voltage synthesis module for performing voltage-current dual closed-loop control according to the three-phase reference voltage value, the three-phase output voltage value and the three-phase inductor current value to obtain a regulation signal; A drive module is communicatively connected to the voltage-current dual-loop control module, and is used to generate a drive signal according to the adjustment signal and a preset triangular carrier, and control the operation of the combined non-isolated three-phase inverter based on the drive signal.

[0015] In a fourth aspect, the present invention provides an electronic device, comprising: a memory for storing computer program instructions; and, A processor is used to execute the computer program instructions to complete the operation of the island operation control method as described in any one of the above.

[0016] In a fifth aspect, the present invention provides a computer program product, including a computer program or instructions, which, when executed by a computer, implements the island operation control method as described in any one of the above.

[0017] The beneficial effects of the present invention are: 1) The combined non-isolated three-phase inverter disclosed in the present invention is composed of a combined three-phase inverter and three single-phase inverters with Heric topology. Two power switch tubes are added to each phase of the AC side of the traditional combined three-phase inverter, including a total of 18 power switch tubes, and the filter circuit adopts LC type filtering. During operation, the combined three-phase inverter using the Heric topology structure can achieve electrical isolation between the DC side and the power grid. Compared with the traditional combined three-phase inverter, the six new power switch tubes on the AC side can suppress the generation of common-mode current, and no transformer is required, so that the equipment cost can be reduced. In addition, compared with the common three-phase full-bridge inverter, three-phase four-bridge arm inverter, etc., the combined non-isolated three-phase inverter in the present invention uses more power switch tubes, is easier to achieve high-power operation, has a higher power level, and is more suitable for high-power scenarios. The Heric topology structure can further achieve electrical isolation between the inverter and the power grid to prevent current breakdown of the power switch tube.

[0018] 2) In the island operation control method of the combined non-isolated three-phase inverter disclosed in the present invention, the active power-frequency equation used for droop control adopts an updated active power-frequency equation constructed based on the hyperbolic tangent function. Since the hyperbolic tangent function has upper and lower boundaries, according to this feature, the present invention can limit the frequency change within a specified range, that is, no matter how the load and output power change, the frequency will not exceed the preset range, thereby solving the frequency over-limit problem that traditional droop control cannot solve.

[0019] Other beneficial effects of the present invention will be further described in the specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is based on the traditional active-frequency ( P - f ) equation and the traditional reactive-voltage ( Q - U ) Schematic diagram of the traditional sag curve obtained by the equation; Figure 2 is a circuit schematic diagram of the combined non-isolated three-phase inverter in Example 1; Figure 3 is a flow chart of the island operation control method in Example 2; Figure 4 is the updated active power-frequency in Example 3 ( P - f ) Schematic diagram of the comparison between the updated droop curve obtained by the equation and the traditional droop curve; Figure 5 It is a schematic diagram of output voltage and current when two phases are unloaded using traditional droop control and improved droop control of this embodiment obtained by simulation experiments; Figure 6 It is a schematic diagram of the frequency waveforms of the conventional droop control and the improved droop control of this embodiment when two phases are unloaded, obtained through simulation experiments; Figure 7 It is a schematic diagram of output voltage and current when three phases are loaded and unbalanced using conventional droop control and improved droop control of this embodiment; Figure 8 It is a schematic diagram of the frequency waveform when the three-phase is loaded and unbalanced using the traditional droop control and the improved droop control of this embodiment; Fig. 9 It is a module block diagram of the island operation control system in Example 6. DETAILED DESCRIPTION

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be briefly introduced below in combination with the drawings and the description of the embodiments or the prior art. Obviously, the following description of the structure of the drawings is only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0022] Embodiment 1: This embodiment discloses a combined non-isolated three-phase inverter. Figure 2 As shown, it includes a combined three-phase inverter and three single-phase Heric inverters, the input end of the combined three-phase inverter constitutes the DC input end of the combined non-isolated three-phase inverter, the output end of the combined three-phase inverter is respectively connected to the input ends of the three single-phase Heric inverters, and the output ends of the three single-phase Heric inverters constitute the three-phase grid-connected output end of the combined non-isolated three-phase inverter. It should be noted that, in this embodiment, the combined three-phase inverter is composed of three full-bridge units connected in parallel, the two bridge arms of each full-bridge unit are connected in parallel, and each bridge arm includes two power switch tubes connected in series. In addition, in the present embodiment, the output ends of the three single-phase Heric inverters are connected in a star shape, and each can be independently controlled, so that the combined non-isolated three-phase inverter in the present embodiment can be operated in single phase or three phase, and the control is simple. It only needs to control the three single-phase inverters separately, so that the phases of the inverters are 120 degrees apart, and each group of bridge arms of each single-phase inverter is alternately turned on for 180 degrees, so that the three-phase voltage can be output.

[0023] During the implementation of this embodiment, the DC input end of the combined non-isolated three-phase inverter can be connected to a DC power source such as an energy storage battery and a solar panel, and the three-phase grid-connected output end can be connected to the power grid via a transmission line. Figure 2 A, B, C and N refer to the A phase line, B phase line, C phase line and N neutral line of the power grid respectively.

[0024] It should be noted that the combined non-isolated three-phase inverter in this embodiment is composed of a combined three-phase inverter and three single-phase inverters of Heric topology structure. Two power switch tubes are added to each phase of the AC side of the traditional combined three-phase inverter, including a total of 18 power switch tubes, and the filter circuit adopts LC type filtering. Compared with the traditional combined three-phase inverter, the combined non-isolated three-phase inverter in this embodiment can reduce the generation of common-mode current and solve the problems of electromagnetic interference and current distortion caused by common-mode current. In addition, compared with the common three-phase full-bridge inverter, three-phase four-bridge arm inverter, etc., the combined non-isolated three-phase inverter in this embodiment uses more power switch tubes, is easier to achieve high-power operation, has a higher power level, and is more suitable for high-power scenarios. It can also further realize electrical isolation between the inverter and the power grid through the Heric topology structure to prevent current breakdown of the power switch tube.

[0025] Embodiment 2: This embodiment discloses an island operation control method for a combined non-isolated three-phase inverter as in Embodiment 1, which can be executed by, but is not limited to, a computer device or controller with certain computing resources, such as a personal computer, an industrial computer, an embedded development system, etc.

[0026] like Figure 3 As shown, an island operation control method, Figure 3 The topological structure of the combined non-isolated three-phase inverter is simplified in ( Figure 3 The three square boxes in the figure correspond to three full-bridge units), and a specific process of the method is given. The method may include but is not limited to the following steps: S1. Real-time collection of the three-phase output voltage values ​​of the combined non-isolated three-phase inverter in the island state u o , three-phase output current value i o And the three-phase inductor current values i L , and according to the three-phase output voltage value u o And the three-phase output current value i o Perform power calculation to obtain the output active power value of the three phases of the combined non-isolated three-phase inverter P And the three-phase reactive power value Q .

[0027] S2. Active power value based on three phases P The updated active power-frequency ( P - f) equation and obtain the reactive power value based on the three phases Q The specified reactive power-voltage of the three phases is obtained ( Q - U ) equation; it should be noted that after the update, the active power-frequency ( Pf ) equation and specify the reactive-voltage ( Q - U ) equation constitutes the improved droop control equation proposed in this embodiment.

[0028] S3. According to the updated active power-frequency of the three phases ( P - f ) equation and the specified reactive power-voltage ( Q - U ) equation, and obtain the reference amplitude u and the reference angular frequency f .

[0029] S4. According to the reference amplitude u and the reference angular frequency f , get the three-phase reference voltage value U ref Specifically, in this embodiment, the three-phase reference voltage value U ref It includes the reference voltage value of phase A, the reference voltage value of phase B and the reference voltage value of phase C, among which the reference voltage value of phase A is: U refa =usinf , the reference voltage value of phase B is: U refb =usin(f-2π / 3) , the C phase reference voltage value is: U refc =usin(f+2π / 3) ; In the formula, u is the reference amplitude; f is the reference angular frequency.

[0030] S5. According to the three-phase reference voltage value U ref , three-phase output voltage value u o And the three-phase inductor current values i L Perform voltage and current dual closed-loop control to obtain regulation signals.

[0031] Specifically, in step S5, according to the reference voltage values ​​of the three phases U ref , three-phase output voltage value u o And the three-phase inductor current values i LPerform voltage and current double closed-loop control to obtain regulation signals, including: S501. Use the voltage loop as the outer loop and set the three-phase reference voltage value U ref As the input data of the voltage loop, the three-phase output voltage value u o As the voltage loop feedback signal, to obtain the three-phase reference voltage value U ref The output voltage value of the corresponding three phases u o The difference between the two phases is calculated, and a reference current of the three phases is obtained based on the difference; wherein the voltage loop adopts proportional integral control, and the proportional integral control function is realized based on a preset PI (Proportional Integral) controller; S502. Use the current loop as the inner loop and set the three-phase inductor current values i L As the feedback signal of the current loop, the three-phase inductor current value i L The current loop is compared with the three-phase reference current and a regulating signal is obtained based on a proportional controller; wherein the current loop adopts proportional control.

[0032] Specifically, in step S5 of this embodiment, voltage and current dual closed-loop control is adopted to collect capacitor voltage values, that is, the output voltage values ​​of the three phases. u o As the feedback signal of the voltage loop, the inductor current value i L It is used as the feedback signal of the current loop for control, where the voltage outer loop adopts proportional integral control and the current inner loop adopts proportional control.

[0033] S6. Generate a drive signal according to the adjustment signal and the preset triangular carrier, and control the operation of the combined non-isolated three-phase inverter based on the drive signal. Specifically, in this embodiment, the triangular carrier is a fixed-frequency reference signal for PWM (Pulse-Width Modulation) modulation. By comparing it with the adjustment signal, the duty cycle of PWM can be obtained, and then a drive signal is generated; the drive signal can be used to control the power switch tube in the combined non-isolated three-phase inverter, so as to achieve control of the combined non-isolated three-phase inverter.

[0034] It should be noted that, in this embodiment, the active power-frequency ( P - f ) equation is constructed based on the hyperbolic tangent function tanh(x) to construct the updated active power-frequency ( P- f ) equation, since the hyperbolic tangent function tanh(x) has upper and lower boundaries, based on this feature, the present embodiment can limit the frequency change within a specified range, that is, no matter how the load and output power change, the frequency will not exceed the preset range, thereby solving the frequency over-limit problem that traditional droop control cannot solve.

[0035] Embodiment 3: This embodiment is a technical solution based on Embodiment 2.

[0036] Specifically, the updated active power-frequency of the three phases ( P - f ) equation, the updated active power-frequency ( P - f ) equation is: ; In the formula, f is the reference angular frequency; f o is the preset angular frequency given value; P is the active power value of any phase; P o It is the preset active power given value; m 1 is the boundary coefficient of the preset hyperbolic tangent function tanh(x), m 2 is the preset droop coefficient; It should be noted that in the implementation process, by changing the boundary coefficient m 1 and droop coefficient m 2, the frequency range can be changed. P - f The comparison between the updated droop curve obtained by the equation and the traditional droop curve is shown in the figure below. Figure 4 As shown, the frequency range is between the upper and lower boundaries, that is, no matter how the load and output power change, the frequency will not exceed the preset range; in addition, refer to Figure 4 , it can be seen that at the power given point P o Nearby, the curvature of the updated droop curve is greater than that of the traditional active power-frequency ( P - f ) equation, therefore, based on the updated active power-frequency ( P - f ) equation to achieve a faster frequency response.

[0037] The specified reactive power-voltage of three phases ( Q - U) equation, the specified reactive power-voltage ( Q - U ) equation is: ; In the formula, u is the reference amplitude; Q o is the preset reactive power given value; Q is the reactive power value of any phase; n It is the preset reactive power droop coefficient, which is a fixed value; u o is the output voltage value of any phase.

[0038] Embodiment 4: This embodiment is a technical solution based on Embodiment 2.

[0039] Since the combined three-phase inverter has the characteristic of independent control of each phase, when the load connected to the inverter is a balanced load, the output power of each phase is equal, so that the reference voltage of each phase output by the traditional droop control is consistent. At this time, the combined three-phase inverter can output symmetrical three-phase voltage. However, in the prior art, when the combined three-phase inverter is connected to an unbalanced load, since the loads carried by each phase are different, the output power of each phase of the inverter is no longer equal. Figure 1 It can be seen that the unequal active power of each phase will produce three unequal frequencies, making the phase of the synthesized reference voltage inconsistent. Similarly, the unequal reactive power will lead to inconsistent amplitudes of the reference voltage. Finally, due to the inconsistency of phase and amplitude, the synthesized reference voltage becomes asymmetric, resulting in asymmetric three-phase voltage output by the inverter. To this end, this embodiment further makes the following improvements: the updated active power-frequency ( P - f ) equation, the updated active power-frequency ( P - f ) equations are: ; In the formula, f is the reference angular frequency; f o is the preset angular frequency given value; P avg is the average value of the three-phase active power, , P a , P b and P c The active power values ​​of phase A, phase B and phase C in the three phases respectively; P oIt is the preset active power given value; m 1 is the boundary coefficient of the preset hyperbolic tangent function tanh(x), m 2 is the preset droop coefficient; The specified reactive power-voltage of three phases ( Q - U ) equation, the specified reactive power-voltage ( Q - U ) equation is: ; In the formula, u is the reference amplitude; Q o is the preset reactive power given value; Q avg is the average value of the three-phase reactive power, , Q a , Q b and Q c Reactive power values ​​of phase A, phase B and phase C respectively among the three phases; n It is the preset reactive power droop coefficient, which is a fixed value; u o is the output voltage value of any phase.

[0040] It should be noted that in this embodiment, in order to solve the problem that each phase of the combined non-isolated three-phase inverter cannot obtain a balanced three-phase reference voltage independently, the average active power output by the inverter is calculated. P avg and the average reactive power Q avg The traditional droop control is improved to obtain the updated active power-frequency ( P - f ) equation and the specified reactive power-voltage ( Q - U ) equation, the A, B, and C phases of the combined non-isolated three-phase inverter share the same P avg -f The sag curve and Q avg -U The droop curve, that is, each phase of the combined non-isolated three-phase inverter adopts the same droop curve, so that the reference voltage of each phase remains consistent.

[0041] Embodiment 5: This embodiment is a technical solution based on Embodiment 2.

[0042] Since the output voltage of the combined three-phase inverter is not only affected by the reference voltage, but also related to the output impedance, when the reference voltages of each phase of the inverter are consistent, the output voltage of the inverter is determined by the output impedance. In the prior art, when the output impedances of the inverters of each phase in the combined three-phase inverter are different, the problem of asymmetric three-phase voltage output by the inverter still occurs. In order to further solve the problem of asymmetric inverter output voltage caused by the inverter output impedance, the present embodiment further makes the following improvements: the updated active power-frequency ( P - f ) equation, the updated active power-frequency ( P - f ) equations are: ; In the formula, f is the reference angular frequency; f o is the preset angular frequency given value; P avg is the average value of the three-phase active power, , P a , P b and P c The active power values ​​of phase A, phase B and phase C in the three phases respectively; P o It is the preset active power given value; m 1 is the boundary coefficient of the preset hyperbolic tangent function tanh(x), m 2 is the preset droop coefficient; The specified reactive power-voltage of three phases ( Q - U ) equation, the specified reactive power-voltage ( Q - U ) equation is: ; In the formula, u is the reference amplitude; Q o is the preset reactive power given value; Q avg is the average value of the three-phase reactive power, , Q a , Q b and Q c Reactive power values ​​of phase A, phase B and phase C respectively among the three phases; n It is the preset reactive power droop coefficient, which is a fixed value;u o is the output voltage value of any phase; is the voltage compensation amount, , U ref is the reference voltage value; k is the preset compensation coefficient.

[0043] Specifically, in this embodiment, a voltage amplitude compensator is used to perform corresponding voltage drop compensation on the reference voltage, so that the inverter outputs a symmetrical three-phase voltage. Taking any phase as an example, the updated active power-frequency ( P - f ) equation to obtain the reference angular frequency of the reference voltage, and according to the constant reactive power-voltage ( Q - U ) equation to obtain the reference angular frequency of the reference voltage, and then obtain the reference voltage value of any phase according to the reference angular frequency and the reference angular frequency, and compare the difference between the obtained reference voltage value and the output voltage value and multiply it by a preset compensation coefficient to obtain the voltage compensation value. In this embodiment, the voltage compensation amount By performing voltage drop compensation on the output voltage value, the problem of output voltage asymmetry caused by the output impedance of the inverter can be further solved, so that the three-phase reference voltages of the combined non-isolated three-phase inverter are equal.

[0044] A combined non-isolated three-phase inverter simulation model was built in Matlab / Simulink to verify the correctness of the control strategy proposed in the embodiment, and two-phase no-load and three-phase loaded and unbalanced experiments were carried out respectively.

[0045] The output voltage, current and frequency waveforms of the inverter using the traditional droop control and the improved droop control of this embodiment when the two phases are unloaded are as follows: Figure 5 and Figure 6 shown. Figure 5 middle, U a , U b and U c Represent the output voltage of phase A, phase B and phase C respectively, i a , i b and i c Represent the output current of phase A, phase B and phase C respectively; Figure 6 middle, f a , f b and f cRepresent the frequencies of phase A, phase B, and phase C respectively.

[0046] At 0.5s, the loads of phases B and C are disconnected. Figure 5 It can be found that the traditional droop control still cannot output a symmetrical three-phase voltage. The frequency of phases B and C changes from 50Hz to 50.5Hz, which is not equal to the frequency of phase A. The improved droop control can still ensure the symmetry of the output voltage when the two phases are unloaded, so that the frequency change of the system remains consistent.

[0047] The output voltage, current and frequency waveforms of the inverter using the traditional droop control and the improved droop control of this embodiment when the three phases are loaded and unbalanced are as follows: Figure 7 and Figure 8 shown.

[0048] At 0.5s, the loads of phases B and C suddenly change. The voltage output by the traditional droop control is asymmetrical, and gradually intensifies over time. The frequencies of each phase are not equal, and the frequencies of phases B and C have exceeded the specified range (50±0.5Hz). The improved droop control can not only output symmetrical three-phase voltages, but also ensure that the frequency changes within the preset range due to the boundedness of the hyperbolic tangent curve.

[0049] Embodiment 6: This embodiment discloses an island operation control system for implementing the island operation control method in Embodiment 6; Fig. 9 As shown, the island operation control system includes: A signal acquisition module, used for real-time acquisition of the three-phase output voltage value, the three-phase output current value and the three-phase inductance current value of the combined non-isolated three-phase inverter in an island state, and performing power calculation according to the three-phase output voltage value and the three-phase output current value to obtain the three-phase output active power value and the three-phase reactive power value of the combined non-isolated three-phase inverter; A droop control module, in communication with the signal acquisition module, for constructing an updated three-phase active power-frequency equation for droop control based on the three-phase active power values ​​and the hyperbolic tangent function, and obtaining a specified three-phase reactive power-voltage equation based on the three-phase reactive power values; A reference voltage synthesis module is communicatively connected with the droop control module, and is used to obtain a reference amplitude and a reference angular frequency according to the updated active power-frequency equation of the three phases and the specified reactive power-voltage equation of the three phases; and is also used to obtain a reference voltage value of the three phases according to the reference amplitude and the reference angular frequency; A voltage-current dual-loop control module is connected to the reference voltage synthesis module for performing voltage-current dual closed-loop control according to the three-phase reference voltage value, the three-phase output voltage value and the three-phase inductor current value to obtain a regulation signal; A drive module is communicatively connected to the voltage-current dual-loop control module, and is used to generate a drive signal according to the adjustment signal and a preset triangular carrier, and control the operation of the combined non-isolated three-phase inverter based on the drive signal.

[0050] It should be noted that the working process, working details and technical effects of the island operation control system provided in this embodiment 6 can be found in embodiment 2 and will not be described in detail here.

[0051] Embodiment 7: Based on Embodiment 1 or 6, this embodiment discloses an electronic device, which may be a smart phone, a tablet computer, a laptop computer, or a desktop computer, etc. The electronic device may be called a user terminal, a portable terminal, a desktop terminal, etc. The electronic device includes: a memory for storing computer program instructions; and, A processor is used to execute the computer program instructions to complete the operation of the island operation control method as described in any one of Example 2.

[0052] Embodiment 8: Based on any one of Embodiments 1 to 7, this embodiment discloses a computer program product, including a computer program or an instruction, wherein when the computer program or the instruction is executed by a computer, the island operation control method as described in any one of Embodiment 2 is implemented. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices.

[0053] Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, and optionally, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A combined non-isolated three-phase inverter, characterized in that: The invention comprises a combined three-phase inverter and three single-phase Heric inverters, wherein the input end of the combined three-phase inverter constitutes the DC input end of the combined non-isolated three-phase inverter, the output end of the combined three-phase inverter is respectively connected to the input ends of the three single-phase Heric inverters, and the output ends of the three single-phase Heric inverters constitute the three-phase grid-connected output end of the combined non-isolated three-phase inverter.

2. A method for controlling island operation of a combined non-isolated three-phase inverter as claimed in claim 1, characterized in that: include: The three-phase output voltage value, the three-phase output current value and the three-phase inductor current value of the combined non-isolated three-phase inverter in the island state are collected in real time, and power calculation is performed according to the three-phase output voltage value and the three-phase output current value to obtain the three-phase output active power value and the three-phase reactive power value of the combined non-isolated three-phase inverter; constructing updated active-frequency equations of the three phases for droop control based on active power values ​​of the three phases and a hyperbolic tangent function, and obtaining specified reactive-voltage equations of the three phases based on reactive power values ​​of the three phases; According to the updated active-frequency equation of the three phases and the specified reactive-voltage equation of the three phases, a reference amplitude and a reference angular frequency are obtained; Obtaining three-phase reference voltage values ​​according to the reference amplitude and the reference angular frequency; Perform voltage and current double closed-loop control according to the three-phase reference voltage value, the three-phase output voltage value and the three-phase inductor current value to obtain a regulating signal; A driving signal is generated according to the adjustment signal and a preset triangular carrier, and the combined non-isolated three-phase inverter is controlled to operate based on the driving signal.

3. The island operation control method according to claim 2, characterized in that: Among the updated active power-frequency equations of the three phases, the updated active power-frequency equation of any phase is: ； In the formula, f is the reference angular frequency; f o is the preset angular frequency given value; P is the active power value of any phase; P o It is the preset active power given value; m 1 is the preset boundary coefficient, m 2 is the preset droop coefficient; Among the three-phase specified reactive power-voltage equations, the specified reactive power-voltage equation for any phase is: ； In the formula, u is the reference amplitude; Q o is the preset reactive power given value; Q is the reactive power value of any phase; n is the preset reactive power droop coefficient; u o is the output voltage value of any phase.

4. The island operation control method according to claim 2, characterized in that: Among the updated active power-frequency equations of the three phases, the updated active power-frequency equation of any phase is: ； In the formula, f is the reference angular frequency; f o is the preset angular frequency given value; P avg is the average value of the three-phase active power, , P a , P b and P c The active power values ​​of phase A, phase B and phase C in the three phases respectively; P o It is the preset active power given value; m 1 is the preset boundary coefficient, m 2 is the preset droop coefficient; Among the three-phase specified reactive power-voltage equations, the specified reactive power-voltage equation for any phase is: ； In the formula, u is the reference amplitude; Q o is the preset reactive power given value; Q avg is the average value of the three-phase reactive power, , Q a , Q b and Q c Reactive power values ​​of phase A, phase B and phase C respectively among the three phases; n is the preset reactive power droop coefficient; u o is the output voltage value of any phase.

5. The island operation control method according to claim 2, characterized in that: Among the updated active power-frequency equations of the three phases, the updated active power-frequency equation of any phase is: ； In the formula, f is the reference angular frequency; f o is the preset angular frequency given value; P avg is the average value of the three-phase active power, , P a , P b and P c The active power values ​​of phase A, phase B and phase C in the three phases respectively; P o It is the preset active power given value; m 1 is the preset boundary coefficient, m 2 is the preset droop coefficient; Among the three-phase specified reactive power-voltage equations, the specified reactive power-voltage equation for any phase is: ； In the formula, u is the reference amplitude; Q o is the preset reactive power given value; Q avg is the average value of the three-phase reactive power, , Q a , Q b and Q c Reactive power values ​​of phase A, phase B and phase C respectively among the three phases; n is the preset reactive power droop coefficient; u o is the output voltage value of any phase; is the voltage compensation amount, , U ref is the reference voltage value; k is the preset compensation coefficient.

6. The island operation control method according to claim 2, characterized in that: Three-phase reference voltage value U ref It includes the reference voltage value of phase A, the reference voltage value of phase B and the reference voltage value of phase C, among which the reference voltage value of phase A is: U refa =usinf ； In the formula, u is the reference amplitude; f is the reference angular frequency; The reference voltage value of phase B is: U refb =usin(f-2π / 3) ； The reference voltage value of phase C is: U refc =usin(f+2π / 3) 。 7. The island operation control method according to claim 2, characterized in that: According to the three-phase reference voltage value, the three-phase output voltage value and the three-phase inductor current value, the voltage and current double closed-loop control is performed to obtain the adjustment signal, including: The voltage loop is used as an outer loop, the reference voltage values ​​of the three phases are used as input data of the voltage loop, and the output voltage values ​​of the three phases are used as feedback signals of the voltage loop to obtain the difference between the reference voltage values ​​of the three phases and the output voltage values ​​of the corresponding three phases, and the reference current of the three phases is obtained based on the difference; wherein the voltage loop adopts proportional integral control; The current loop is used as an inner loop, and the three-phase inductor current values ​​are used as feedback signals of the current loop to compare the three-phase inductor current values ​​with the three-phase reference currents, and obtain adjustment signals based on a proportional controller; wherein the current loop adopts proportional control.

8. An island operation control system, characterized in that: Used to implement the island operation control method as described in any one of claims 2 to 7; The island operation control system comprises: A signal acquisition module, used for real-time acquisition of the three-phase output voltage value, the three-phase output current value and the three-phase inductance current value of the combined non-isolated three-phase inverter in an island state, and performing power calculation according to the three-phase output voltage value and the three-phase output current value to obtain the three-phase output active power value and the three-phase reactive power value of the combined non-isolated three-phase inverter; A droop control module, in communication with the signal acquisition module, for constructing an updated three-phase active power-frequency equation for droop control based on the three-phase active power values ​​and the hyperbolic tangent function, and obtaining a specified three-phase reactive power-voltage equation based on the three-phase reactive power values; A reference voltage synthesis module is communicatively connected with the droop control module, and is used to obtain a reference amplitude and a reference angular frequency according to the updated active power-frequency equation of the three phases and the specified reactive power-voltage equation of the three phases; and is also used to obtain a reference voltage value of the three phases according to the reference amplitude and the reference angular frequency; A voltage-current dual-loop control module is connected to the reference voltage synthesis module for performing voltage-current dual closed-loop control according to the three-phase reference voltage value, the three-phase output voltage value and the three-phase inductor current value to obtain a regulation signal; A drive module is communicatively connected to the voltage-current dual-loop control module, and is used to generate a drive signal according to the adjustment signal and a preset triangular carrier, and control the operation of the combined non-isolated three-phase inverter based on the drive signal.

9. An electronic device, characterized in that: include: a memory for storing computer program instructions; as well as, A processor is used to execute the computer program instructions to complete the operation of the island operation control method as described in any one of claims 2 to 7.

10. A computer program product comprising a computer program or instructions, characterized in that When the computer program or the instruction is executed by a computer, the island operation control method according to any one of claims 2 to 7 is implemented.

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