CN113964858A - Three-phase inverter grid-connected control system based on dual synchronization principle - Google Patents
Three-phase inverter grid-connected control system based on dual synchronization principle Download PDFInfo
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- H—ELECTRICITY
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- H—ELECTRICITY
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Abstract
The invention discloses a three-phase inverter grid-connected control system based on a dual synchronization principle. A synchronous control ring and a voltage stabilizing outer ring are arranged; the synchronous control loop is connected to the input end of the integrator, and the voltage stabilizing outer loop is connected to the input end of the current limiter; the synchronous control loop performs synchronous control by adopting a synchronous control function according to the active power and the active power reference value to obtain angular frequency, establishes braking auxiliary loop diagonal frequency correction according to the q-axis voltage component and the power factor angle, and outputs a phase integrally; and the voltage stabilization outer ring compares the three-phase voltage or power amplitude with a reference value, and outputs a d-axis current reference value by combining the selected voltage control function with the current reference value. The invention provides networking capability and inertia support for the current source three-phase inverter, improves the synchronization performance of the current source three-phase inverter under a weak network, avoids the problem of weak synchronization capability and the problem of transient instability caused by current amplitude limiting, and enables the three-phase inverter to be completely dual with a synchronous machine.
Description
Technical Field
The invention relates to a grid-connected control system and a grid-connected control method in the field of control of grid-connected three-phase inverters, in particular to a dual synchronous machine type three-phase inverter grid-connected control system.
Background
With the development of power electronics technology, more and more renewable energy power generation and direct current transmission are incorporated into the grid through a three-phase inverter. This provides convenience to the grid and also presents new challenges to its safe operation.
At present, common grid-connected three-phase inverters are mainly two types, namely a current source type three-phase inverter with synchronous phase-locked loops and a voltage source type three-phase inverter with virtual synchronous machines. The current source type three-phase inverter with the synchronous phase-locked loop does not have voltage and frequency supporting capacity, the needed inertia of the power grid cannot be provided, and the stability problem is easy to occur under a weak grid due to the coupling of an outer ring and a synchronous control ring. The virtual synchronous machine type voltage source type three-phase inverter simulates the characteristics of a synchronous machine, provides the capability of voltage and frequency support, and is not easy to generate small-interference instability.
However, when the three-phase inverter simulates a synchronous machine, the external characteristic serving as a voltage source is degenerated into a current source due to current amplitude limiting during overload, so that a power angle curve is switched, stability analysis becomes complicated, stability margin is reduced, and transient instability is more likely to occur. Therefore, how to enable the grid-connected three-phase inverter to simultaneously ensure the small-disturbance stability and the transient stability under the weak grid and provide the required inertia for the power system is also provided, and the related technology is relatively lacked in the prior art.
Disclosure of Invention
In order to solve the problems, the invention provides a dual synchronous machine type three-phase inverter grid-connected control system. The three-phase inverter under the control has the advantages of small interference, good stability, no power angle curve switching under the transient state, capability of providing inertia and frequency support for a power grid and the like, and can realize the grid-connected stable operation of the three-phase inverter. The invention adopts active power synchronization to control the outer ring to maintain the voltage and current amplitude, and controls the inner ring to adopt current dq decoupling control. Compared with a virtual synchronous machine, the power angle curve is always a current power angle curve due to the fact that a voltage outer ring is not arranged, the problem of curve switching under current saturation of the virtual synchronous machine is solved, and the transient stability is improved by the aid of a braking auxiliary ring.
In order to achieve the purpose, the invention adopts the technical scheme that:
the three-phase inverter comprises a three-phase inverter, a power grid side structure, a space vector pulse width modulator, a park converter, an integrator and a current inner ring; the three-phase inverter is connected with a power grid side structure, external input signals sequentially pass through the integrator and then are connected and input to the space vector pulse width modulator, the external input signals simultaneously pass through the current limiter and the current inner ring and then are connected and input to the space vector pulse width modulator, and the space vector pulse width modulator is connected and input to a three-phase control end of the three-phase inverter; the method is characterized in that: a synchronous control ring and a voltage stabilizing outer ring are also arranged; the synchronous control loop is connected to the input end of the integrator, and the voltage stabilizing outer loop is connected to the input end of the current limiter.
The power grid side structure comprises an LCL filter, a transformer, a line and a power grid; the power grid is connected with the three-phase input end of the three-phase inverter after sequentially passing through the line, the transformer and the LCL filter.
Thus, the invention is provided with three control loops: a synchronous control loop, a voltage stabilization outer loop and a current inner loop. The current inner loop is controlled in the prior art to ensure the tracking performance of the current. The synchronous control loop is active power synchronization, the dual rocking equation synchronization is adopted to provide inertia for the inverter grid-connected control system, and other transfer functions can be constructed to realize rapid synchronization. And the voltage stabilizing outer ring maintains the amplitude of the voltage and the current by adopting a first-order inertia control or drooping proportional control mode of (1/1+ Ts).
The synchronous control loop receives active power P of the three-phase inverterEQ-axis voltage component V of sum reactive power Q and three-phase inverterqAnd a preset active power reference value PrefThe synchronous control loop is based on the active power PE and the active power reference value PrefSynchronous control is carried out by adopting a synchronous control function to obtain the angular frequency of the three-phase inverter, and meanwhile, the q-axis voltage component V of the three-phase inverter is obtainedqAnd power factor angle
And establishing a brake auxiliary ring to correct the angular frequency of the three-phase inverter, and integrating the angular frequency of the three-phase inverter through an integrator to obtain the output phase of the three-phase inverter and inputting the output phase into the space vector pulse width modulator.
The active power PE and the reactive power Q of the three-phase inverter are obtained by calculating and converting three-phase current and three-phase voltage collected by the three-phase inverter. Q-axis voltage component V of three-phase inverterqThe three-phase voltage is obtained through park conversion processing of a park converter.
In the synchronous control loop, a dual oscillation equation of the following formula is adopted as a synchronous control function:
wherein J is an inertia coefficient, D is a damping coefficient, omega is a per unit value of the angular frequency of the three-phase inverter, omega0Is an angular frequency reference value, PEActive power of three-phase inverter, PrefThe active power reference value of the three-phase inverter is represented by t, and time is represented by t; the formula shows that compared with the dual rocking equation of the synchronous machine, the dual rocking equation has opposite active term signs, and meets the requirement that the three-phase inverter operates at a current power angle of 0-90 degrees.
The dual rocking equation is transformed into a frequency domain expression in a pulling way, and the active power P is obtainedEMinus the active power reference value PrefObtaining a power error, processing the power error by using a frequency domain expression to obtain a per unit value omega of the angular frequency of the three-phase inverter, and multiplying the per unit value omega of the angular frequency of the three-phase inverter by a reference value omegabasicThen obtaining an actual value of the angular frequency of the three-phase inverter; and integrating the actual value of the angular frequency of the three-phase inverter through an integrator to obtain the output phase of the three-phase inverter, inputting the output phase into the space vector pulse width modulator and the park converter, and controlling park conversion through the park converter.
Said synchronous controlThe function adopts inertia control, the synchronous control function is one of the inertia control, and active power P is adoptedEMinus the active power reference value PrefSynchronization is performed and inertial control is configured to provide frequency and inertial support for the power system.
The synchronous control loop is added with a brake auxiliary loop according to a power factor angle
The following reactive criteria are established:
wherein the content of the first and second substances,
representing a limit value of a preset power factor angle, sign is a sign for putting into a brake auxiliary ring;
and judging whether the braking auxiliary ring crosses an unstable limit or not through a power factor angle, and if the braking auxiliary ring crosses the stable limit and enters an unstable area, putting the braking auxiliary ring into braking control to manufacture a transient state balance point to prevent transient state instability.
When sign is 1, a brake assist loop is put in, and q-axis voltage component V of the three-phase inverter is usedqAdded to the synchronization control function, the synchronization control function becomes:
wherein, KqIs the braking coefficient, V, of the auxiliary braking ringqRepresenting the q-axis voltage component of the three-phase inverter.
When sign is equal to 0, the brake assist loop is not put into use, and the synchronous control function is kept unchanged.
It can be seen from the above formula that when the active reference value is greater than the active limit due to voltage drop or overload, the current power angle (the phase angle difference between two current sources) gradually increases to a region exceeding 90 °, triggers the braking control to construct virtual power, constructs a transient balance point, and makes the current power angle not increase any more. When the brake control is triggered, the corresponding power angle curve becomes fig. 5.
The invention improves the transient stability by adopting an additional braking auxiliary ring through a synchronous control ring.
The stable operation range of the dual synchronous machine type three-phase inverter is 0-90 degrees, and the dual synchronous machine type three-phase inverter can be unstable when an operation point exceeds 90 degrees and enters 90-180 degrees due to voltage drop or overload and the like. The synchronous control loop is added with a brake auxiliary loop to prevent transient instability and ensure the transient stability of the three-phase inverter.
The voltage stabilizing outer ring receives a preset voltage reference value V0A predetermined current reference value I0Preset reference value Q of reactive power0The voltage stabilization outer ring compares the three-phase voltage amplitude V or the reactive power amplitude Q with a corresponding reference value, and then selects and presets a current reference value I after being controlled by a voltage control function G(s)0D-axis current reference value I for combined output three-phase inverterdrefReference value I of q-axis current of three-phase inverterqrefTake to zero.
In the voltage stabilization outer ring, the three-phase voltage amplitude V and the corresponding voltage reference value are subtracted and then processed by a voltage control function, and then the current reference value I of the three-phase inverter is added0Obtaining a d-axis current reference value I of the three-phase inverterdref *Specifically, it is represented as:
Idref *＝I0+G(s)(V0-V)
wherein G(s) represents a voltage control function, s represents a Laplace operator, V represents three-phase voltage amplitude of a three-phase inverter, and V represents0Representing the voltage reference of a three-phase inverter, I0Representing the current reference, I, of a three-phase inverterdref *Representing the d-axis current reference of the three-phase inverter.
In the voltage stabilizing outer ring, three-phase power is converted according to the voltage stabilizing outer ringSubtracting the amplitude Q from the corresponding power reference value, processing the subtracted value by a voltage control function, and adding the current reference value I of the three-phase inverter0Obtaining a d-axis current reference value I of the three-phase inverterdref *Specifically, it is represented as:
Idref *＝I0+G(s)(Q0-Q)
wherein G(s) represents a voltage control function, s represents a Laplace operator, Q represents a three-phase power amplitude of a three-phase inverter, and Q represents0Representing the power reference value, I, of a three-phase inverter0Representing the current reference, I, of a three-phase inverterdref *Representing the d-axis current reference of the three-phase inverter.
Reference value I of d-axis current of three-phase inverterdrefReference value of current of x and q axesqrefThe common input is input into a current inner ring after current amplitude limiting, the current inner ring processes and outputs to obtain d-axis and q-axis modulation voltage components of the three-phase inverter, and then the d-axis and q-axis modulation voltage components are input into a space vector pulse width modulator; the current amplitude limiting is to adopt a preset threshold value to carry out truncation processing on an input value, a value larger than the preset threshold value is directly assigned as the preset threshold value, and a value smaller than or equal to the preset threshold value is kept unchanged.
The space vector pulse width modulator outputs the pulse width modulation waveform of the three-phase inverter according to the d-axis and q-axis modulation voltage components of the three-phase inverter output by the current inner loop and the output phase processing of the three-phase inverter output by the synchronous control loop, and then the pulse width modulation waveform is sent to the three-phase inverter to control the work of the three-phase inverter.
According to the invention, the voltage and current amplitude values of the three-phase inverter can be maintained through the voltage stabilizing outer ring according to the given voltage reference value and current reference value of the three-phase inverter.
And the current inner loop adopts dq decoupling control. According to the invention, dq decoupling control is adopted by the current inner loop, and the current inner loop is not coupled with other control loops on a time scale, so that the passive design of parameters can be realized, and the tracking performance and stability of the current inner loop are ensured.
Existing controls typically cause the external characteristics of a three-phase inverter to behave as a constant voltage source. The external characteristics of the three-phase inverter of the invention are represented by constant current sources, so that the impedance of the power grid and the grid side can be equivalent to two parallel current sources through norton during analysis, and equivalent to two voltage sources connected in series to form an external characteristic dual when being connected with a synchronous machine, and an equivalent circuit diagram of the two is shown in fig. 2.
Because the external characteristics of the power-driven synchronous motor are dual with the synchronous motor, the power equation form of the power-driven synchronous motor is the same as that of the synchronous motor. In the synchronous machine, the power angle is defined as the angle at which the voltage at the end of the synchronous machine leads the voltage of the power grid, and the current power angle of the three-phase inverter is defined as the angle at which the current of the three-phase inverter lags the current of the power grid (fig. 3), so that the power angle is dual. Because the definition of the power angle is dual, PE-Pref in the synchronous control of the three-phase inverter is opposite to Pref-PE in a synchronous link in a synchronous machine.
The power angle operation area of the three-phase inverter is the same as that of the synchronous machine, when the current power angle of the three-phase inverter is 0-90 degrees, the power characteristic of the three-phase inverter is the same as that of the three-phase inverter when the current power angle is 0-90 degrees, reactive power is absorbed by light load, and reactive power is emitted by heavy load.
The external characteristics of the three-phase inverter are designed into a current source, namely, the tracking control of an outer loop is eliminated, only the tracking control of an inner loop of the current is reserved, the traditional dq decoupling control is still adopted, and the control block diagram is shown in figure 1. The three-phase inverter grid connection is equivalent to a current source connected in parallel as shown in figure 2. The line impedance and an infinite power grid are converted into an infinite current source parallel line admittance B (the reciprocal of a line reactance X) through the Norton equivalent. This is equivalent to a voltage source connected in series to form a dual with a synchronous machine grid.
Defining the angle of the phase angle of the three-phase inverter current lagging the current phase angle of the reverse network side as the current power angle deltaIThe comparison with the power angle of the synchronous machine is shown in fig. 3, and the power equation is as follows:
wherein, deltaIIs the power angle of the dual synchronous machine, which is defined as the angle of the three-phase inverter current lagging the reverse equivalent network side current, I0Representing the current amplitude, I, of a three-phase invertergRepresents the magnitude of the norton equivalent rear net side current, and B represents the equivalent admittance equal to the inverse of the net side reactance X.
The invention is in phase diagram with the power equation form of the synchronous machine.
The three-phase inverter is designed to operate in the area with the current power angle of 0-90 degrees, so that the requirement that the three-phase inverter can emit reactive power and absorb the reactive power is met, and the dual-connection is formed with the characteristic that the synchronous machine operates at the power angle of 0-90 degrees.
In order to provide the three-phase inverter with inertia providing and frequency supporting capabilities, it is necessary to construct a transfer function of inertia. For the purpose of satisfying the dual operation region, the input of the inertia transfer function is P-P0. P is active power of three-phase inverter, P0Is an active power reference value. Compared with the dual rocking equation of the synchronous machine, the active term has opposite signs, and the requirement that the three-phase inverter operates at a current power angle of 0-90 degrees is met. The system is in a stable operation area at 0-90 degrees and in an unstable operation area at 90-180 degrees.
An additional brake assist loop is employed to improve transient stability. The stable operation range of the dual synchronous machine type three-phase inverter is 0-90 degrees, and the dual synchronous machine type three-phase inverter can be unstable when the operation point exceeds 90 degrees and enters 90-180 degrees due to voltage drop or overload and the like. Therefore, in order to prevent transient instability, a brake auxiliary ring is added in the synchronous control ring to ensure the transient stability of the three-phase inverter.
And (3) giving a three-phase inverter terminal voltage reference value (or a reactive power reference value) and an output current reference value to ensure that the three-phase inverter can maintain the output voltage and current amplitude.
The current inner loop still adopts the traditional dq decoupling control, and because the current inner loop is not coupled with other control loops on a time scale, the passive design of parameters can be realized, and meanwhile, the tracking performance and stability of the current inner loop are ensured.
The invention has the beneficial effects that:
the invention provides inertia for the current source type three-phase inverter, improves the small interference stability of the current source three-phase inverter under a weak network, simultaneously avoids the problem of instability caused by current saturation of the virtual synchronous machine type three-phase inverter, improves the transient stability of the three-phase inverter through the brake auxiliary ring, ensures that the three-phase inverter has good inertia, frequency supporting capability and larger stability margin, and can fully use the theory of a synchronous machine when a plurality of machines analyze.
The control structure provides networking capability and inertia support for the current source three-phase inverter, improves the synchronization performance of the current source three-phase inverter under a weak network, and avoids the problem that the traditional phase-locked loop current source three-phase inverter is weak in synchronization capability under the weak network. Meanwhile, compared with a virtual synchronous machine, the problem of transient instability caused by current amplitude limiting is avoided.
The control structure of the invention enables the three-phase inverter and the synchronous machine to be completely dual: the external characteristics of the voltage source and the current source are dual, the power equation is dual, the dual swing equation is dual, and the power angle operation area is dual.
Drawings
FIG. 1 is a control block diagram of the present invention;
FIG. 2 is a dual equivalent circuit diagram of the present invention and a synchronous machine;
FIG. 3 is a diagram comparing power angle vectors of the present invention and a synchronous machine;
FIG. 4 is a control block diagram of an embodiment of the present invention
FIG. 5 is a graph of power angle for activating the brake assist ring during transient conditions in accordance with an embodiment of the present invention;
FIG. 6 is a waveform diagram of active power, reactive power and frequency under different power reference values according to an embodiment of the present invention;
fig. 7 is a waveform diagram of active power, reactive power and frequency under different inertia coefficients when the network side frequency fluctuates according to the embodiment of the present invention;
fig. 8 is a waveform diagram of active power, reactive power and frequency when the network side voltage drops greatly, and the braking auxiliary loop and the non-braking auxiliary loop are present according to the embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the specific examples.
The specific embodiment of the invention is as follows:
as shown in fig. 1, the system includes a three-phase inverter, a grid-side structure, a space vector pulse width modulator, a park converter, an integrator, and a current inner loop; the three-phase inverter is connected with a power grid side structure, an external input signal is connected and input to the space vector pulse width modulator after sequentially passing through the integrator, the external input signal is connected and input to the space vector pulse width modulator after simultaneously passing through the current limiter and the current inner ring, and the space vector pulse width modulator is connected and input to a three-phase control end of the three-phase inverter; a synchronous control ring and a voltage stabilizing outer ring are also arranged; the synchronous control loop is connected to the input end of the integrator, and the voltage stabilizing outer loop is connected to the input end of the current limiter.
The power grid side structure comprises an LCL filter, a transformer, a line and a power grid; the power grid is connected with the three-phase input end of the three-phase inverter after sequentially passing through the line, the transformer and the LCL filter.
As shown in fig. 4, the control loop includes a synchronous control loop, a reactive-current (Q-I) control outer loop (or a voltage-current (U-I) control outer loop), and a current inner loop.
The synchronous control loop adopts a power dual oscillation equation and transient stability auxiliary control, the current inner loop adopts traditional dq decoupling control, and the control outer loop can be an inertia link 1/(Js + D) or droop control.
In the synchronous control loop, a dual oscillation equation of the following formula is adopted as a synchronous control function:
wherein J is an inertia coefficient, D is a damping coefficient, omega is a per unit value of the angular frequency of the three-phase inverter, omega0Is an angular frequency reference value, PEActive power of three-phase inverter, PrefThe active power reference value of the three-phase inverter is represented by t, and time is represented by t; the formula shows that the active terms of the dual rocking equation are opposite in sign compared with the dual rocking equation of the synchronous machine, and the condition that the three-phase inverter operates in current is metThe power angle is 0-90 degrees.
The dual rocking equation is transformed into a frequency domain expression in a pulling way, and the active power P is obtainedEMinus the active power reference value PrefObtaining a power error, processing the power error by using a frequency domain expression to obtain a per unit value omega of the angular frequency of the three-phase inverter, and multiplying the per unit value omega of the angular frequency of the three-phase inverter by a reference value omegabasicThen obtaining an actual value of the angular frequency of the three-phase inverter; and integrating the actual value of the angular frequency of the three-phase inverter through an integrator to obtain the output phase of the three-phase inverter, inputting the output phase into the space vector pulse width modulator and the park converter, and controlling park conversion through the park converter.
The present embodiment takes the synchronization mode of dual rocking equations as an example, which is called dual rocking equation synchronization in the present invention, and is dual to the dual rocking equation of the synchronous machine. The three-phase inverter is provided with inertia providing and frequency supporting capability, and an inertia transfer function can be adopted in a synchronous control loop.
Specifically, a brake auxiliary ring is added in a synchronous control ring, and the brake auxiliary ring establishes the following reactive criterion according to the reactive power Q:
wherein, I0Representing a current reference value of the three-phase inverter, X representing an equivalent reactance of a power grid side, and sign being a mark for putting into a brake auxiliary loop;
the braking auxiliary ring judges whether the unstable limit is crossed or not through reactive characteristics, and if the unstable limit is crossed, the braking auxiliary ring is thrown into the unstable area to control and manufacture a transient balance point, so that transient instability is prevented.
When sign is 1, a brake assist loop is put in, and q-axis voltage component V of the three-phase inverter is usedqAdded to the synchronization control function, the synchronization control function becomes:
wherein, KqIs the braking coefficient, V, of the auxiliary braking ringqRepresenting the q-axis voltage component of the three-phase inverter.
When sign is equal to 0, the brake assist loop is not put into use, and the synchronous control function is kept unchanged.
The formula shows that when the active reference value is larger than the active limit due to voltage drop or overload, the current power angle is gradually reduced to a 0-90-degree area, the brake control is triggered to construct virtual power, a transient balance point is constructed, and the current power angle is not reduced continuously. When the brake control is triggered, the corresponding power angle curve becomes fig. 5.
The invention improves the transient stability by adopting an additional braking auxiliary ring through a synchronous control ring.
The stable operation range of the dual synchronous machine type three-phase inverter is 0-90 degrees, and the dual synchronous machine type three-phase inverter can be unstable when an operation point exceeds 90 degrees and enters 90-180 degrees due to voltage drop or overload and the like. The synchronous control loop is added with a brake auxiliary loop to prevent transient instability and ensure the transient stability of the three-phase inverter.
In the embodiment, the control outer ring adopts U-I droop as an example to maintain the voltage and current amplitude of the three-phase inverter, and the control expression is a formula.
Idref *＝I0+KV(V0-V)
Wherein, KVIs the droop coefficient of U-I, V represents the three-phase inverter capacitance voltage amplitude, V0Given reference value, I, representing the three-phase inverter voltage0Given reference value, I, representing the current of a three-phase inverterrefAnd the three-phase inverter current reference value of the U-I droop output to the current inner ring is represented.
The current inner loop still adopts dq decoupling control, and due to the fact that coupling does not exist between the current inner loop and other control loops on the time scale, passive design of parameters can be achieved, and meanwhile tracking performance and stability of the current inner loop are guaranteed.
A single-machine infinite system shown in figure 1 is built in Matlab/Simulink software and is used for simulation analysis. The definitions and physical meanings of some of the variables are shown in table 1 below.
Table 1 example simulation verification of parameter values of partial system variables
Fig. 6 is a waveform diagram of active power, reactive power, frequency and current power angle of a three-phase inverter at different power reference values in simulation verification according to an embodiment of the present invention. FIG. 6 shows that at light load, the three-phase inverter absorbs reactive power; when the load is heavy, the three-phase inverter sends out reactive power, which is consistent with theoretical analysis. The three-phase inverter has good dynamic response capability, and when the active power reference value changes, the three-phase inverter can track the change of the active power in real time and ensure the stability of the frequency.
Fig. 7 shows waveforms of active power, reactive power and frequency of the three-phase inverter when the grid frequency changes under different inertia coefficients J. As can be seen from FIG. 6, after the inertia coefficient is increased, the change speed of the frequency and the active power can be delayed, so that the inertia support can be provided for the system
Fig. 8 shows the power and frequency curves with and without auxiliary brake loop in the case of a severe grid-side voltage drop. As can be seen from fig. 8, when a voltage drop occurs, the conventional control has no auxiliary brake loop, and when a voltage drop fault occurs in the power grid, the three-phase inverter has transient instability; after the control with the brake auxiliary ring is adopted, the three-phase inverter can still keep stable when the voltage of the power grid drops. The change and the stabilization mechanism of the current power angle conform to theoretical analysis, and the temporary state stability of the system can be improved by the aid of the auxiliary braking ring.
Therefore, the dual synchronous control three-phase inverter can provide inertia and frequency support for a system, has good small interference stability, and has good transient stability after an auxiliary brake ring is adopted.
The present invention is limited only by the following modifications and variations, which fall within the spirit of the invention and the scope of the appended claims.
Claims (9)
1. A dual synchronization principle-based three-phase inverter grid-connected control system comprises a three-phase inverter, a power grid side structure, a space vector pulse width modulator, a park converter, an integrator and a current inner ring; the method is characterized in that: a synchronous control ring and a voltage stabilizing outer ring are also arranged; the synchronous control loop is connected to the input end of the integrator, and the voltage stabilizing outer loop is connected to the input end of the current limiter.
2. The grid-connected control system of the three-phase inverter based on the dual synchronization principle of claim 1, characterized in that: the synchronous control loop receives active power P of the three-phase inverterEQ-axis voltage component V of sum reactive power Q and three-phase inverterqAnd a preset active power reference value PrefThe synchronous control loop is based on the active power PE and the active power reference value PrefSynchronous control is carried out by adopting a synchronous control function to obtain the angular frequency of the three-phase inverter, and meanwhile, the q-axis voltage component V of the three-phase inverter is obtainedqAnd power factor angle
And establishing a brake auxiliary ring to correct the angular frequency of the three-phase inverter, and integrating the angular frequency of the three-phase inverter through an integrator to obtain the output phase of the three-phase inverter and inputting the output phase into the space vector pulse width modulator.
3. The grid-connected control system of the three-phase inverter based on the dual synchronization principle of claim 1, characterized in that:
in the synchronous control loop, a dual oscillation equation of the following formula is adopted as a synchronous control function:
wherein J is the inertia coefficient, D is the damping coefficient, omega*Is the per unit value, omega, of the angular frequency of a three-phase inverter0Is an angular frequency reference value, PEActive power of three-phase inverter, PrefThe active power reference value of the three-phase inverter is represented by t, and time is represented by t;
the dual rocking equation is transformed into a frequency domain expression in a pulling way, and the active power P is obtainedEMinus the active power reference value PrefObtaining power error, and processing the power error by using a frequency domain expression to obtain a per unit value omega of the angular frequency of the three-phase inverter*The per unit value omega of the angular frequency of the three-phase inverter*Multiplied by a reference value ωbasicThen obtaining an actual value of the angular frequency of the three-phase inverter; and integrating the actual value of the angular frequency of the three-phase inverter by an integrator to obtain the output phase of the three-phase inverter, and inputting the output phase into the space vector pulse width modulator and the park converter.
4. The grid-connected control system of the three-phase inverter based on the dual synchronization principle of claim 3, characterized in that: the synchronous control loop is added with a brake auxiliary loop according to a power factor angle
The following reactive criteria are established:
wherein the content of the first and second substances,
representing a limit value of a preset power factor angle, sign is a sign for putting into a brake auxiliary ring;
when sign is 1, a brake assist loop is put in, and q-axis voltage component V of the three-phase inverter is usedqAdding the synchronization control function, the synchronization control function becomes:
wherein, KqIs the braking coefficient, V, of the auxiliary braking ringqRepresenting the q-axis voltage component of the three-phase inverter.
When sign is equal to 0, the brake assist loop is not put into use, and the synchronous control function is kept unchanged.
5. The grid-connected control system of the three-phase inverter based on the dual synchronization principle of claim 1, characterized in that: the voltage stabilizing outer ring receives a preset voltage reference value V0A predetermined current reference value I0A preset reference value Q of reactive power0The voltage stabilization outer ring compares the three-phase voltage amplitude V or the reactive power amplitude Q with a corresponding reference value, and then selects and presets a current reference value I after being controlled by a voltage control function G(s)0D-axis current reference value I for combined output three-phase inverterdref *。
6. The grid-connected control system of the three-phase inverter based on the dual synchronization principle of claim 5, wherein:
in the voltage stabilization outer ring, the three-phase voltage amplitude V and the corresponding voltage reference value are subtracted and then processed by a voltage control function, and then the current reference value I of the three-phase inverter is added0Obtaining d-axis current reference value I of three-phase inverterdref *Specifically, it is represented as:
Idref *＝I0+G(s)(V0-V)
wherein G(s) represents a voltage control function, and s represents LaplacianA s operator, V representing the three-phase voltage amplitude of the three-phase inverter, V0Representing the voltage reference of a three-phase inverter, I0Representing the current reference value, I, of a three-phase inverterdref *Representing the d-axis current reference of the three-phase inverter.
7. The grid-connected control system of the three-phase inverter based on the dual synchronization principle of claim 5, wherein: in the voltage stabilization outer ring, the three-phase power amplitude Q and the corresponding power reference value are subtracted and then processed by a voltage control function, and then the current reference value I of the three-phase inverter is added0Obtaining d-axis current reference value I of three-phase inverterdref *Specifically, it is represented as:
Idref *＝I0+G(s)(Q0-Q)
wherein G(s) represents a voltage control function, s represents a Laplace operator, Q represents a three-phase power amplitude of a three-phase inverter, and Q represents0Representing the power reference value, I, of a three-phase inverter0Representing the current reference value, I, of a three-phase inverterdref *Representing the d-axis current reference of the three-phase inverter.
8. The grid-connected control system of the three-phase inverter based on the dual synchronization principle of claim 1, characterized in that: reference value I of d-axis current of three-phase inverterdref *And q-axis current reference value Iqref *The common input is input into a current inner ring after current amplitude limiting, the current inner ring processes and outputs to obtain d-axis and q-axis modulation voltage components of the three-phase inverter, and then the d-axis and q-axis modulation voltage components are input into a space vector pulse width modulator; the space vector pulse width modulator outputs the pulse width modulation waveform of the three-phase inverter according to the d-axis and q-axis modulation voltage components of the three-phase inverter output by the current inner loop and the output phase processing of the three-phase inverter output by the synchronous control loop, and then the pulse width modulation waveform is sent to the three-phase inverter to control the work of the three-phase inverter.
9. The grid-connected control system of the three-phase inverter based on the dual synchronization principle of claim 1, characterized in that: and the current inner loop adopts dq decoupling control.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116599125A (en) * | 2023-05-04 | 2023-08-15 | 国网江苏省电力有限公司电力科学研究院 | New energy station simulation optimization method, device, equipment and storage medium |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102914325A (en) * | 2012-10-19 | 2013-02-06 | 南京信息工程大学 | Dissipation synchronization-based detection method of small signal under chaos background |
| CN105356783A (en) * | 2015-10-28 | 2016-02-24 | 浙江大学 | Enhanced current-limiting control method aimed at drop-controlled inverter |
| CN110380451A (en) * | 2019-06-24 | 2019-10-25 | 上海交通大学 | A kind of double-fed fan motor unit with active inertia responding ability |
| CN110729929A (en) * | 2019-10-21 | 2020-01-24 | 南京航空航天大学 | Double-winding permanent magnet motor starting power generation system and fault-tolerant control method thereof |
| CN112018804A (en) * | 2019-05-29 | 2020-12-01 | 郑州大学 | AC-DC hybrid micro-grid coupling inverter cascade control implementation method |
| CN112968466A (en) * | 2021-02-02 | 2021-06-15 | 四川大学 | Grid-connected inverter transient control method based on power angle estimation |
-
2021
- 2021-07-09 CN CN202110776826.7A patent/CN113964858B/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102914325A (en) * | 2012-10-19 | 2013-02-06 | 南京信息工程大学 | Dissipation synchronization-based detection method of small signal under chaos background |
| CN105356783A (en) * | 2015-10-28 | 2016-02-24 | 浙江大学 | Enhanced current-limiting control method aimed at drop-controlled inverter |
| CN112018804A (en) * | 2019-05-29 | 2020-12-01 | 郑州大学 | AC-DC hybrid micro-grid coupling inverter cascade control implementation method |
| CN110380451A (en) * | 2019-06-24 | 2019-10-25 | 上海交通大学 | A kind of double-fed fan motor unit with active inertia responding ability |
| CN110729929A (en) * | 2019-10-21 | 2020-01-24 | 南京航空航天大学 | Double-winding permanent magnet motor starting power generation system and fault-tolerant control method thereof |
| CN112968466A (en) * | 2021-02-02 | 2021-06-15 | 四川大学 | Grid-connected inverter transient control method based on power angle estimation |
Non-Patent Citations (2)
| Title |
|---|
| LINBIN HUANG 等: "Interconnecting Very Weak AC Systems by Multiterminal VSC-HVDC Links With a Unified Virtual Synchronous Control", 《IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS》, vol. 06, no. 03, 30 September 2018 (2018-09-30), pages 1041 - 1053 * |
| LUYAO XU 等: "Symmetric Admittance Modeling for Stability Analysis of Grid-Connected Converters", 《IEEE TRANSACTIONS ON ENERGY CONVERSION》, vol. 35, no. 01, 31 March 2020 (2020-03-31), pages 434 - 444 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116599125A (en) * | 2023-05-04 | 2023-08-15 | 国网江苏省电力有限公司电力科学研究院 | New energy station simulation optimization method, device, equipment and storage medium |
| CN116599125B (en) * | 2023-05-04 | 2023-11-24 | 国网江苏省电力有限公司电力科学研究院 | New energy station simulation optimization method, device, equipment and storage medium |
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