CN110365038B - Microgrid inverter and control method and control device thereof - Google Patents
Microgrid inverter and control method and control device thereof Download PDFInfo
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Abstract
The invention provides a control method and a control device of a microgrid inverter and the microgrid inverter, wherein the microgrid inverter comprises a power device, and the control method comprises the following steps: a detection step: detecting the output voltage, the working voltage and the working current of the microgrid inverter in an off-grid state of the microgrid; a double closed loop control step: determining each harmonic in the detected output voltage of the microgrid inverter, and executing double closed-loop control based on each harmonic and the detected working voltage and working current; a driving pulse signal generating step: and generating a driving pulse signal for controlling the power device according to the result of the double closed-loop control so as to enable the micro-grid inverter to output power consistent with the micro-grid load. By adopting the control method and the control device of the microgrid inverter and the microgrid inverter, the capability of the microgrid inverter with nonlinear load can be improved.
Description
Technical Field
The present invention relates generally to the field of new energy technologies, and in particular, to a method and an apparatus for controlling a microgrid inverter, and a microgrid inverter.
Background
The micro-grid is a system unit formed by a group of control devices, an energy storage device, a load and a micro-power source, and supplies electric energy to the load. The micro-grid can be operated in a grid-connected mode with an external power grid, and can also be operated in an isolated mode. In a microgrid, it is often necessary to access an external grid or load through a microgrid inverter (i.e. a power electronic converter).
Typically, in an off-grid condition of the microgrid, the microgrid inverter supplies harmonic currents to the nonlinear load. However, the harmonic current output by the microgrid inverter may generate a harmonic voltage drop on the output impedance, which further causes the output voltage of the microgrid inverter to generate a harmonic voltage, and the power quality of the microgrid inverter is deteriorated.
Disclosure of Invention
The invention aims to provide a control method and a control device of a microgrid inverter and the microgrid inverter, which can improve the nonlinear load carrying capacity of the microgrid inverter.
An aspect of the present invention provides a method of controlling a microgrid inverter, the microgrid inverter including a power device, the method comprising: a detection step: detecting the output voltage, the working voltage and the working current of the microgrid inverter in an off-grid state of the microgrid; a double closed loop control step: determining each harmonic in the detected output voltage of the microgrid inverter, and executing double closed-loop control based on each harmonic and the detected working voltage and working current; a driving pulse signal generating step: and generating a driving pulse signal for controlling the power device according to the result of the double closed-loop control so as to enable the micro-grid inverter to output power consistent with the micro-grid load.
Optionally, the microgrid inverter further comprises a reactor and a filter capacitor, wherein the detecting step further comprises: detecting direct-current bus voltage, output three-phase voltage of the microgrid inverter, inductance three-phase current of the reactor and capacitance three-phase current of the filter capacitor in an off-grid state of the microgrid; the double closed-loop control step further comprises: determining each harmonic in the detected output three-phase voltage, and executing double closed loop control based on each odd harmonic and the detected inductance three-phase current and capacitance three-phase current; the driving pulse signal generating step further includes: and generating a driving pulse signal for controlling the power device according to the result of the double closed-loop control and the voltage of the direct current bus so as to enable the micro-grid inverter to output power consistent with the load of the micro-grid.
Optionally, the double closed-loop controlling step further includes: determining a voltage given value of a voltage loop in the double closed-loop control based on the output three-phase voltage, the inductance three-phase current and the capacitance three-phase current; determining the given value of each harmonic voltage of the output three-phase voltage; determining a current set value of a current loop in the double closed-loop control based on the voltage set value and the output three-phase voltage; wherein the driving pulse signal generating step further comprises: and generating a driving pulse signal for controlling the power device based on the current set value, the inductance three-phase current, the capacitance three-phase current and the direct-current bus voltage.
Optionally, the double closed-loop controlling step further includes: adding the inductance three-phase current and the capacitance three-phase current to obtain an output three-phase current of the inverter; performing Park conversion on the output three-phase voltage, the inductance three-phase current and the output three-phase current respectively to obtain a direct-current component of the output three-phase voltage, a direct-current component of the inductance three-phase current and a direct-current component of the output three-phase current; and enabling the direct-current components of the output three-phase current to sequentially pass through the two cascaded wave traps to obtain the filtering value of the output three-phase current.
Optionally, the double closed-loop controlling step further includes: determining the output voltage of the virtual synchronous generator model; and determining the voltage set value of the voltage loop according to the output voltage, the virtual impedance and the filtered value of the output three-phase current.
Optionally, the double closed-loop controlling step further includes: performing Park conversion on each subharmonic voltage, and performing moving average filtering on a conversion result to obtain a direct current component of each subharmonic voltage; and calculating the opposite value of the direct current component of each subharmonic voltage, performing proportional integral adjustment on the opposite value, and performing Ipark transformation including angle compensation on the result of the proportional integral adjustment to obtain the given value of each subharmonic voltage.
Optionally, the double closed-loop controlling step further includes: subtracting the direct-current component of the output three-phase voltage from the voltage given value, performing proportional-integral regulation on the subtraction result, and taking the proportional-integral regulation result as the current given value of the current loop; performing proportional-integral regulation on the difference between the given current value and the direct-current component of the three-phase current of the inductor, adding the result of the proportional-integral regulation and a voltage coupling term generated by the reactor, and performing Imark transformation on the added result to obtain a given voltage value under a two-phase static coordinate system; superposing the voltage given value under the two-phase static coordinate system to each subharmonic voltage given value to obtain a total voltage given value for space vector pulse width modulation control; wherein the driving pulse signal generating step further comprises: and generating a driving pulse signal for controlling the power device according to the total voltage given value and the direct-current bus voltage.
Optionally, the rotation angle of the Park transformation is an angle generated by power frequency adjustment of the virtual synchronous generator model.
Optionally, a center frequency of one of the two traps is 6 times an output frequency of the inverter, and a center frequency of the other trap is 12 times the output frequency of the inverter.
Optionally, the control method compensates for harmonics caused by a delay introduced by a control command period in a digital control manner.
Another aspect of the present invention also provides a control apparatus of a microgrid inverter, the microgrid inverter including a power device, the control apparatus including: a detection unit configured to detect an output voltage, an operating voltage, and an operating current of the microgrid inverter in an off-grid state of a microgrid; a double closed-loop control unit configured to determine harmonics in an output voltage of the microgrid inverter, and perform double closed-loop control based on the harmonics and a working voltage and a working current of the microgrid inverter detected by the detection unit; and the driving pulse signal generating unit is used for generating a driving pulse signal for controlling the power device according to the result of the double closed-loop control so as to enable the micro-grid inverter to output power consistent with the load of the micro-grid.
Optionally, the microgrid inverter further comprises a reactor and a filter capacitor, wherein the detection unit is further configured to detect a direct current bus voltage, an output three-phase voltage of the microgrid inverter, an inductance three-phase current of the reactor, and a capacitance three-phase current of the filter capacitor in an off-grid state of the microgrid; the double closed-loop control unit is further configured to determine each harmonic in the output three-phase voltage detected by the detection unit, and perform double closed-loop control based on each odd harmonic and the inductance three-phase current and the capacitance three-phase current detected by the detection unit; the driving pulse signal generating unit is further configured to generate a driving pulse signal for controlling the power device according to a result of the double closed-loop control and the direct current bus voltage, so that the microgrid inverter outputs power consistent with a microgrid load.
Optionally, the dual closed-loop control unit is further configured to: determining a voltage given value of a voltage loop in the double closed-loop control based on the output three-phase voltage, the inductance three-phase current and the capacitance three-phase current; determining the given value of each harmonic voltage of the output three-phase voltage; determining a current set value of a current loop in the double closed-loop control based on the voltage set value and the output three-phase voltage; wherein the drive pulse signal generation unit is further configured to: and generating a driving pulse signal for controlling the power device based on the current set value, the inductance three-phase current, the capacitance three-phase current and the direct-current bus voltage.
Optionally, the dual closed-loop control unit is further configured to: adding the inductance three-phase current and the capacitance three-phase current to obtain an output three-phase current of the inverter; performing Park conversion on the output three-phase voltage, the inductance three-phase current and the output three-phase current respectively to obtain a direct-current component of the output three-phase voltage, a direct-current component of the inductance three-phase current and a direct-current component of the output three-phase current; and enabling the direct-current components of the output three-phase current to sequentially pass through two cascaded wave traps arranged in the double closed-loop control unit to obtain the filtering value of the output three-phase current.
Optionally, the dual closed-loop control unit is further configured to: determining the output voltage of the virtual synchronous generator model; and determining the voltage set value of the voltage loop according to the output voltage, the virtual impedance and the filtered value of the output three-phase current.
Optionally, the dual closed-loop control unit is further configured to: performing Park conversion on each subharmonic voltage, and performing moving average filtering on a conversion result to obtain a direct current component of each subharmonic voltage; and calculating the opposite value of the direct current component of each subharmonic voltage, performing proportional integral adjustment on the opposite value, and performing Ipark transformation including angle compensation on the result of the proportional integral adjustment to obtain the given value of each subharmonic voltage.
Optionally, the dual closed-loop control unit is further configured to: subtracting the direct-current component of the output three-phase voltage from the voltage given value, performing proportional-integral regulation on the subtraction result, and taking the proportional-integral regulation result as the current given value of the current loop; performing proportional-integral regulation on the difference between the given current value and the direct-current component of the three-phase current of the inductor, adding the result of the proportional-integral regulation and a voltage coupling term generated by the reactor, and performing Imark transformation on the added result to obtain a given voltage value under a static coordinate system; superposing the voltage given value under the static coordinate system to the harmonic voltage given values to obtain a total voltage given value for space vector pulse width modulation control; wherein the drive pulse signal generation unit is further configured to: and generating a driving pulse signal for controlling the power device according to the total voltage given value and the direct-current bus voltage.
Optionally, the rotation angle of the Park transformation is an angle generated by power frequency adjustment of the virtual synchronous generator model.
Optionally, a center frequency of one of the two traps is 6 times an output frequency of the inverter, and a center frequency of the other trap is 12 times the output frequency of the inverter.
Optionally, the double closed-loop control unit comprises a digital controller, wherein the digital controller compensates for harmonics caused by delays introduced by control command periods by means of digital control.
Another aspect of the present invention also provides a microgrid inverter comprising a control device as described above.
According to the control method and the control device of the microgrid inverter and the microgrid inverter, double closed-loop control is executed based on each harmonic of the output voltage of the microgrid inverter, and phase compensation is carried out on each harmonic based on Ipeak conversion including angle compensation, so that each harmonic in the output voltage of the microgrid inverter caused by nonlinear load is restrained, and the capacity of the microgrid inverter with the nonlinear load is improved. In addition, the output of the micro-grid inverter has inertia and damping by simulating the external characteristics of the synchronous generator, and the output frequency is insensitive to the fluctuation of the load, so that the operation stability of the micro-grid inverter is improved.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:
fig. 1 shows a block diagram of a control arrangement of a microgrid inverter according to an embodiment of the present invention;
fig. 2 shows a schematic of a topology of a microgrid inverter according to an embodiment of the present invention;
FIG. 3 illustrates a schematic diagram of determining DC components of output three-phase voltages in accordance with an embodiment of the present invention;
FIG. 4 illustrates a schematic diagram of determining DC components of inductive three-phase currents in accordance with an embodiment of the present invention;
FIG. 5 illustrates a schematic diagram of determining filtered values of output three-phase currents, according to an embodiment of the invention;
FIG. 6 shows a schematic diagram of determining filtered values of active and reactive power according to an embodiment of the invention;
FIG. 7 shows a schematic diagram of determining a rotation angle according to an embodiment of the invention;
FIG. 8 shows a schematic diagram for determining a voltage set-point for a voltage loop in dual closed-loop control according to an embodiment of the invention;
FIG. 9 illustrates a schematic diagram for determining a set point for each harmonic voltage in accordance with an embodiment of the present invention;
FIG. 10 shows a control schematic of a digital controller;
FIG. 11 shows a schematic diagram of determining a voltage setpoint in a two-phase stationary coordinate system according to an embodiment of the present invention;
FIG. 12 shows a schematic diagram of generating a drive pulse signal according to an embodiment of the invention;
fig. 13 shows an experimental output waveform of a microgrid inverter without harmonic suppression in the case of a conventional microgrid inverter with a nonlinear load;
figure 14 shows experimental output waveforms of a microgrid inverter when harmonic suppression is performed with the microgrid inverter loaded non-linearly according to an embodiment of the present invention;
fig. 15 shows a flow chart of a method of controlling a microgrid inverter according to an embodiment of the present invention.
Detailed Description
Various example embodiments will now be described more fully with reference to the accompanying drawings, in which some example embodiments are shown.
A control apparatus of a microgrid inverter, a control method of a microgrid inverter, and a microgrid inverter according to embodiments of the present invention are described below with reference to fig. 1 to 15.
Fig. 1 shows a block diagram of a control device of a microgrid inverter according to an embodiment of the present invention, and fig. 2 shows a topological schematic of the microgrid inverter according to an embodiment of the present invention.
Referring to fig. 1, a control apparatus of a microgrid inverter according to an embodiment of the present invention includes: a detection unit 100, a double closed-loop control unit 200, and a driving pulse signal generation unit 300.
Referring to fig. 2, the microgrid inverter includes a power device 400, a reactor 500, a filter capacitor 600, and a control device (not shown).
Here, the reactor 500 and the filter capacitor 600 constitute an LC filter circuit, which can filter high frequency harmonics generated by the power device 400 and maintain excellent power quality.
Returning to fig. 1, the detection unit 100 detects the output voltage, the operating voltage, and the operating current of the microgrid inverter in an off-grid state of the microgrid.
As an example, the output voltage of the microgrid inverter may be the output three-phase voltage U of the microgrid inverteroabcThe working voltage of the micro-grid inverter can be the DC bus voltage UdcThe working current of the micro-grid inverter can be the inductive three-phase current I of the reactor 500LabcAnd the capacitance three-phase current I of the filter capacitor 600Cabc。
As an example, the detection unit 100 may include a three-phase voltage sensor and a three-phase current transformer.
The double closed-loop control unit 200 determines harmonics in the output voltage of the microgrid inverter detected by the detection unit 100, and performs double closed-loop control based on the harmonics in the output voltage of the microgrid inverter and the operating voltage and operating current of the microgrid inverter detected by the detection unit 100.
Preferably, the dual closed-loop control unit 200 determines the output three-phase voltage U detected by the detection unit 100oabcBased on each odd harmonic and the inductive three-phase current I detected by the detection unit 100LabcAnd capacitance three-phase current ICabcA double closed loop control is performed.
The driving pulse signal generating unit 300 generates a driving pulse signal for controlling the power device 400 according to the result of the double closed-loop control, so that the microgrid inverter outputs power in accordance with the microgrid load.
Preferably, the driving pulse signal generating unit 300 generates the dc bus voltage U according to the result of the double closed loop controldcA drive pulse signal for controlling the power device 400 is generated to cause the microgrid inverter to output power in accordance with the microgrid load.
Further, the dual closed-loop control unit 200 outputs a three-phase voltage U based onoabcInductance three-phase current ILabcAnd capacitance three-phase current ICabcDetermining voltage set value U of voltage ring in double closed-loop controlodref、Uoqref(ii) a Determining output three-phase voltage UoabcGiven value U of each harmonic voltagealfahref、Ubetahref(ii) a Based on voltage set value Uodref、UoqrefAnd outputs three-phase voltage UoabcDetermining a current setpoint value I of a current loop in a dual closed-loop controldref、Iqref. The driving pulse signal generating unit 300 generates a driving pulse signal based on the given current value Idref、IqrefInductance three-phase current ILabcThree-phase current I of capacitorCabcAnd DC bus voltage UdcA driving pulse signal for controlling the power device 400 is generated.
A process in which the control device of the microgrid inverter performs double closed-loop control to generate the driving pulse signal according to the embodiment of the present invention is described in detail below with reference to fig. 3 to 11.
Fig. 3 illustrates a schematic diagram of determining the dc components of the output three-phase voltages according to an embodiment of the present invention, fig. 4 illustrates a schematic diagram of determining the dc components of the inductive three-phase currents according to an embodiment of the present invention, and fig. 5 illustrates a schematic diagram of determining the filtered values of the output three-phase currents according to an embodiment of the present invention.
Referring to fig. 3 to 5, the dual closed-loop control unit 200 converts the inductive three-phase current ILabcThree-phase current I with capacitorCabcAdding to obtain the output three-phase current I of the micro-grid inverteroabc(ii) a To output three-phase voltage UoabcInductance three-phase current ILabcAnd outputs three-phase current IoabcRespectively carrying out Park transformation (namely, transformation from a three-phase static coordinate system abc to a two-phase synchronous rotating coordinate system dq, also called rotation transformation) to obtain an output three-phase voltage UoabcD.c. component U ofod、UoqInductance three-phase current ILabcDirect current component I ofLd、ILqAnd outputs three-phase current IoabcDirect current component I ofod、Ioq(ii) a Make the output three-phase current IoabcDirect current component I ofod、IoqTwo cascaded wave traps sequentially arranged in the double closed-loop control unit 200 to obtain output three-phase current IoabcOf the filtered value Iodflt、Ioqflt。
When the microgrid inverter is under the condition of being off-grid of the microgrid and is provided with a nonlinear load, harmonic components caused by the nonlinear load exist in the output voltage and the output current of the microgrid inverter, typical harmonic components of 5 th order and 7 th order are expressed as 6-frequency-multiplication alternating-current components of the output frequency of the microgrid inverter in direct-current components after rotation conversion, and harmonic components of 11 th order and 13 th order are expressed as 12-frequency-multiplication alternating-current components of the output frequency of the microgrid inverter in direct-current components after rotation conversion. Therefore, in order to eliminate the DC component I of the output current by the 6-frequency multiplication AC component and the 12-frequency multiplication AC componentod、IoqIn a preferred embodiment, the center frequency through the cascade is the microgrid inverter output frequencyThe 6 times frequency trap Notch6 and the 12 times frequency trap Notch12, the center frequency of which is the output frequency of the microgrid inverter, are used for filtering out 6 times frequency alternating current components and 12 times frequency alternating current components.
Specifically, the transfer function of the trap is:
where s is Laplace operator, ωnQ is the trap quality factor for the center frequency of the trap. Taking Q as the actual value
ωnIs 6 x omegaoutOr 12 x ωout。ωoutThe angular frequency output for power frequency adjustment (i.e., controlling the output frequency according to the power adjustment) of the virtual synchronous generator model. Because the virtual synchronous generator model is adopted for control, the primary frequency modulation function is achieved, the output frequency of the microgrid inverter can change along with the size of an active load, and in order to ensure the accuracy of the center frequency of the wave trap, the value of the center frequency needs to be tracked in real time.
Fig. 6 shows a schematic diagram of determining filtered values of active and reactive power according to an embodiment of the invention.
Referring to fig. 6, in one example, the instantaneous active power P output by the microgrid inverter can be calculated from the instantaneous power theory1And instantaneous reactive power Q1：
P1＝1.5×(Uod×Iod+Uoq×Ioq)，
Q1＝1.5×(Uoq×Iod-Uod×Ioq)，
The instantaneous active power P calculated by the above formula1And instantaneous reactive power Q1When the micro-grid inverter is provided with a nonlinear load in an off-grid state of the micro-grid, harmonic components caused by the nonlinear load also occur, so that transient state is causedReal active power P1And instantaneous reactive power Q1The 6 times multiplied AC component and the 12 times multiplied AC component occur, and for the stability of active control and reactive control in virtual synchronous generator model control, in a preferred embodiment, the calculated instantaneous active power P is made1And instantaneous reactive power Q1Sequentially passing through a cascade wave trap with the center frequency of 6 times the output frequency of the microgrid inverter and a wave trap with the center frequency of 12 times the output frequency of the microgrid inverter, and then passing the output of the two cascade wave traps through a Low Pass Filter (LPF) to obtain a filtering value P of the active power output by the microgrid inverteroutAnd the filtered value Q of the reactive powerout。
Fig. 7 shows a schematic diagram of determining a rotation angle according to an embodiment of the invention.
Referring to fig. 7, the rotation angle θ of the Park conversion is a phase angle of the output voltage of the microgrid inverter.
In a preferred embodiment, the microgrid inverter is controlled based on a virtual synchronous generator model, and the rotation angle θ can be generated through power frequency adjustment of the virtual synchronous generator model.
The primary frequency modulation control of the virtual synchronous generator model consists of a rotor motion equation and a prime motor regulation equation. The equation of motion of the rotor is:
wherein, ω isrefFor nominal voltage angular frequency (i.e. for off-grid operation given angular frequency), ωoutFor virtual synchronous generator output voltage angular frequency, PoutFiltered value, P, of active power output by a microgrid invertermGiving virtual mechanical power of the virtual synchronous generator, J is virtual moment of inertia, D is a virtual damping coefficient, and theta is a rotating angle of Park transformation.
The prime mover regulation equation is:
Pm＝Pref+Kp(ωref-ωout)，
wherein, PrefAs an active power command, KpThe active adjustment coefficient. Virtual synchronous generator virtual mechanical power given PmBy active power command PrefAnd the virtual speed regulator outputs the regulating power according to the angular frequency deviation, and the regulating power is provided by simulating a prime motor of the synchronous machine by a distributed power supply and an energy storage unit.
FIG. 8 shows a schematic diagram for determining a voltage set-point for a voltage loop in dual closed-loop control, according to an embodiment of the invention.
Referring to fig. 8, the dual closed-loop control unit 200 determines an output voltage E of the virtual synchronous generator modelref(ii) a According to the output voltage ErefVirtual impedance ω LV、RVAnd outputs three-phase current IoabcOf the filtered value Iodflt、IoqfltDetermining a voltage setpoint value U of a voltage loopodref、Uoqref。
In one example, the primary voltage regulation control of the virtual synchronous generator model is to simulate the reactive voltage droop relationship of the synchronous generator to obtain the output voltage E of the virtual synchronous generator modelrefSpecifically, the formula is shown as follows:
Eref＝Kq(Qref-Qout)+Uref，
wherein, UrefOutputting a voltage command, Q, for a microgrid inverterrefFor reactive power command, QoutFiltered value, K, of reactive power output by a microgrid inverterqAnd the reactive difference adjustment coefficient is obtained.
Preferably, virtual impedance omega is increased for stabilizing the parallel operation of multiple machinesLv、RvTherefore, voltage set value U of voltage loop in double closed loop controlodref、UoqrefCan be determined by the following formula:
preferably, in order to make the microgrid inverter have an off-grid black start function, the off-grid black start function can be performedSo that the micro-grid inverter outputs a voltage command UrefPass through a ramp function, and output U passing through the ramp functionrampAnd the voltage is added to the output of the reactive deviation regulation, so that the zero-start boosting function can be realized, and the output voltage of the micro-grid inverter is gradually increased from zero to a given value.
Fig. 9 shows a schematic diagram of determining a given value of a voltage of each subharmonic according to an embodiment of the present invention.
Referring to fig. 9, the double closed-loop control unit 200 performs Park conversion on each subharmonic voltage and performs Moving Average Filtering (MAF) on the conversion result to obtain a direct current component U of each subharmonic voltagedhnflt、Uqhnflt(h ═ 5, 7, 11, 13); calculating the opposite value of the DC component of each subharmonic voltage, performing proportional integral adjustment on the opposite value, and performing Ipark transformation (i.e. transformation from two-phase synchronous rotating coordinate system dq to two-phase static coordinate system alpha beta) including angle compensation on the result of the proportional integral adjustment to obtain a given value U of each subharmonic voltagealfahref、Ubetahref。
When the microgrid inverter is provided with a nonlinear load in an off-grid state of the microgrid, if voltage harmonic suppression is not performed, the output voltage of the microgrid inverter contains odd harmonics of 5, 7, 11, 13 and the like, so that the harmonic distortion rate THD of the output voltage of the microgrid inverter exceeds the standard and the requirement of the power quality of power supply of sensitive loads is not met, and therefore suppression of the odd harmonics of 5, 7, 11, 13 and the like is required.
In a preferred embodiment, the detection unit 100 detects 5, 7, 11, and 13 th harmonics in the output voltage of the microgrid inverter, and performs multi-synchronous rotating coordinate transformation on the output voltage of the microgrid inverter by using a multi-synchronous rotating coordinate system method to obtain a component U of each harmonic in a two-phase synchronous rotating coordinate systemdhn、Uqhn. Then, the component Udhn、UqhnThen the DC component U of each subharmonic voltage is obtained through a moving average filterdhnflt、Uqhnflt。
In a typical balanced load application, the 5, 11 th harmonic appears as a negative sequence component, 7,The 13 th harmonic is expressed as a positive sequence component, and for this reason, in a preferred embodiment, 5 and 11 times of negative sequence rotational coordinate transformation with rotational angles of-5 × theta and-11 × theta, 7 and 13 times of positive sequence rotational coordinate transformation with rotational angles of 7 × theta and 13 × theta are performed, the direct current components of each of the decomposed harmonics are compared with 0, the difference between them is subjected to proportional integral adjustment, and Ipark transformation including angle compensation is performed on the result of the proportional integral adjustment to obtain a given voltage value U of each harmonicalfahref、UbetahrefThereby suppressing harmonics in the output voltage of the microgrid inverter.
Preferably, the angle in the Ipark transform including angle compensation may be h θ +. DELTA.h.
Preferably, the dual closed-loop control unit 200 comprises a digital controller. The digital controller compensates for harmonics caused by delays introduced by control command cycles through a digital control scheme.
Fig. 10 shows a control schematic of a digital controller.
It should be understood that the feature of the digital control is that the control command is updated every certain period, the update period of the control command is greater than or equal to the sampling period of the system, and from the moment when the control command is changed in the current period to the moment when the control command is changed in the next period, the control signal of the system remains unchanged and does not change along with the change of the control object, which is another more serious delay introduced by the digital controller.
Referring to fig. 10, ω is the inverter output voltage angular frequency. For a digital controller, an operation time of at least one sampling period T is required, and a PWM output of the inverter also requires a time of T to build a voltage. Thus, there is at least a delay time of T from the voltage sampling to the control loop output PWM update. During the delay time T, the h-th harmonic voltage rotates by Δ θ during this time T, as shown in the following equation:
Δθ＝hωT＝2hπfT
here, f is the fundamental frequency of the inverter output voltage. If this delay time is not compensated for, the coordinate transformation in fig. 9 is no longer an identity transformation. In severe cases, the control of a certain higher harmonic may even form a positive feedback, so that through the output of the control loop, the higher harmonic cannot be eliminated, but becomes larger and larger, thereby causing the system control to fail. It can be seen that compensation of the delay time is important in the control of the voltage harmonics. In the present embodiment, when the proportional-integral control output of the harmonics 5, 7, 11, and 13 is converted into the two-phase stationary coordinate system, the conversion angle is compensated, and the angle of each inverse conversion is h θ +. DELTA.h (h is 5, 7, 11, and 13).
Fig. 11 shows a schematic diagram of determining a voltage set-point in a two-phase stationary coordinate system according to an embodiment of the present invention, and fig. 12 shows a schematic diagram of generating a driving pulse signal according to an embodiment of the present invention.
Referring to fig. 11 and 12, the double closed-loop control unit 200 sets a voltage given value Uodref、UoqrefAnd outputs three-phase voltage UoabcD.c. component U ofod、UoqSubtracting, performing proportional integral adjustment on the subtraction result, and taking the result of the proportional integral adjustment as the given current value I of the current loopdref、Iqref(ii) a For given value of current Idref、IqrefAnd inductance three-phase current ILabcDirect current component I ofLd、ILqPerforms proportional-integral adjustment, and couples the result of the proportional-integral adjustment with the voltage generated by the reactor by a term ω LgAdding the voltage values and the given voltage value U in a two-phase static coordinate system, and carrying out Imark transformation on the result of the additionalfaref、Ubetaref(ii) a Setting a voltage value U under a two-phase static coordinate systemalfaref、UbetarefSuperposed to each harmonic voltage set value Ualfahref、UbetahrefTo obtain a total voltage set point PWM for Space Vector Pulse Width Modulation (SVPWM) controlalfaref、PWM_betaref. The driving pulse signal generating unit 300 generates PWM u according to the total voltage set valuealfaref、PWM_betarefAnd DC bus voltage UdcA drive pulse signal for controlling the power device is generated.
Fig. 13 shows an experimental output waveform of the microgrid inverter when harmonic suppression is not performed in the case where the conventional microgrid inverter is loaded with a nonlinear load, and fig. 14 shows an experimental output waveform of the microgrid inverter when harmonic suppression is performed in the case where the microgrid inverter is loaded with a nonlinear load according to an embodiment of the present invention.
Referring to fig. 13 and 14, an experiment that a microgrid inverter with a rated power of 210kW has 90kW of active power, 30kW of reactive power and uncontrolled rectification nonlinear load in an off-grid state of the microgrid is taken as an example. Fig. 13 shows three line voltage waveforms output without harmonic suppression by the microgrid inverter. The content of 5 th harmonic, 3.5% of 7 th harmonic, 2.2% of 11 th harmonic and 1.8% of 13 th harmonic in the output voltage of the microgrid inverter are calculated through FFT analysis. Fig. 14 shows three line voltage waveforms output with the microgrid inverter performing harmonic suppression. The content of 5 th harmonic in the output voltage of the microgrid inverter is 0.23%, the content of 7 th harmonic in the output voltage of the microgrid inverter is 0.14%, the content of 11 th harmonic in the output voltage of the microgrid inverter is 0.10%, and the content of 13 th harmonic in the output voltage of the microgrid inverter is 0.08%, so that 5 th harmonic, 7 th harmonic, 11 th harmonic and 13 th harmonic in the output voltage caused by nonlinear loads can be well inhibited, and the electric energy quality of the output voltage of the microgrid inverter is improved.
A control method of the microgrid inverter according to an embodiment of the present invention is described below with reference to fig. 15.
Fig. 15 shows a flow chart of a method of controlling a microgrid inverter according to an embodiment of the present invention. Here, the microgrid inverter includes a power device, a reactor, and a filter capacitor.
In step S10 (i.e., the detection step), the output voltage and the operating current of the microgrid inverter are detected in the microgrid off-grid state.
In one embodiment of step S10, the dc bus voltage U is detected in the off-grid state of the microgriddcOutput three-phase voltage U of micro-grid inverteroabcInductance three-phase current I of reactorLabcCapacitance three-phase current I of filter capacitorCabc。
In step S20 (i.e., the double closed-loop control step), harmonics in the detected output voltage of the microgrid inverter are determined, and double closed-loop control is performed based on the harmonics in the output voltage of the microgrid inverter and the detected operating voltage and operating current of the microgrid inverter.
In one embodiment of step S20, the detected output three-phase voltage U is determinedoabcEach odd harmonic in the inductor, and the detected three-phase current I of the inductor based on each odd harmonicLabcAnd capacitance three-phase current ICabcA double closed loop control is performed.
Preferably based on the output three-phase voltage UoabcInductance three-phase current ILabcAnd capacitance three-phase current ICabcDetermining voltage set value U of voltage ring in double closed-loop controlodref、Uoqref(ii) a Determining output three-phase voltage UoabcGiven value U of each harmonic voltagealfahref、Ubetahref(ii) a Based on voltage set value Uodref、UoqrefAnd outputs three-phase voltage UoabcDetermining a current setpoint value I of a current loop in a dual closed-loop controldref、Iqref。
Further, the three-phase current I of the inductorLabcThree-phase current I with capacitorCabcAdding to obtain the output three-phase current I of the inverteroabc(ii) a To output three-phase voltage UoabcInductance three-phase current ILabcAnd outputs three-phase current IoabcRespectively carrying out Park conversion to obtain output three-phase voltage UoabcD.c. component U ofod、UoqInductance three-phase current ILabcDirect current component I ofLd、ILqAnd outputs three-phase current IoabcDirect current component I ofod、Ioq(ii) a Make the output three-phase current IoabcDirect current component I ofod、IoqSequentially passing through two cascaded wave traps to obtain output three-phase current IoabcOf the filtered value Iodflt、Ioqflt. Determining an output voltage E of a virtual synchronous generator modelref(ii) a According to the output voltage ErefVirtual impedance ω LV、RVAnd outputs three-phase current IoabcOf the filtered value Iodflt、IoqfltDetermining a voltage setpoint value U of a voltage loopodref、Uoqref。
Here, the rotation angle of the Park transformation is an angle generated by power frequency adjustment of the virtual synchronous generator model.
Here, the center frequency of one of the two traps is 6 times the output frequency of the inverter, and the center frequency of the other trap is 12 times the output frequency of the inverter.
Further, performing Park conversion on each subharmonic voltage, and performing moving average filtering on a conversion result to obtain a direct current component of each subharmonic voltage; calculating the opposite value of the DC component of each subharmonic voltage, performing proportional integral adjustment on the opposite value, and performing Ipark transformation including angle compensation on the result of the proportional integral adjustment to obtain the given value U of each subharmonic voltagealfahref、Ubetahref。
Further, the voltage is given by a given value Uodref、UoqrefAnd outputs three-phase voltage UoabcD.c. component U ofod、UoqSubtracting, performing proportional integral adjustment on the subtraction result, and taking the result of the proportional integral adjustment as the given current value I of the current loopdref、Iqref(ii) a For given value of current Idref、IqrefAnd inductance three-phase current ILabcDirect current component I ofLd、ILqPerforms proportional-integral adjustment, and couples the result of the proportional-integral adjustment with the term ω L of the voltage generated by reactor 500gAdding the voltage values and the given voltage value U in a two-phase static coordinate system, and carrying out Imark transformation on the result of the additionalfaref、Ubetaref(ii) a Setting a voltage value U under a two-phase static coordinate systemalfaref、UbetarefSuperposed to each harmonic voltage set value Ualfahref、UbetahrefTo obtain a total voltage set value PWM _forspace vector pulse width modulation controlalfaref、PWM_betaref。
In step S30 (i.e., a drive pulse signal generation step), a drive pulse signal for controlling the power device 400 is generated based on the result of the double closed-loop control so that the microgrid inverter outputs power in accordance with the microgrid load.
In one embodiment of step S30, the DC bus voltage U is determined according to the result of the dual closed loop controldcA drive pulse signal for controlling the power device 400 is generated to cause the microgrid inverter to output power in accordance with the microgrid load.
Preferably, step S30 is based on a given value of current Idref、IqrefInductance three-phase current ILabcThree-phase current I of capacitorCabcAnd DC bus voltage UdcA driving pulse signal for controlling the power device 400 is generated.
Further, step S30 is performed according to the total voltage set value PWM _alfaref、PWM_betarefAnd DC bus voltage UdcA driving pulse signal for controlling the power device 400 is generated.
Preferably, the control method compensates for harmonics caused by delays introduced by control command cycles through a digital control scheme.
In addition, the control device and the control method for the microgrid inverter and the microgrid inverter according to the embodiments of the present invention perform double closed loop control based on each harmonic of the detected output voltage of the microgrid inverter and perform phase compensation on each harmonic based on the Ipark conversion including angle compensation, thereby suppressing each harmonic in the output voltage of the microgrid inverter caused by a nonlinear load and improving the capability of the microgrid inverter to carry the nonlinear load. In addition, the output of the micro-grid inverter has inertia and damping by simulating the external characteristics of the synchronous generator, and the output frequency is insensitive to the fluctuation of the load, so that the operation stability of the micro-grid inverter is improved.
Furthermore, it should be understood that the respective units in the control apparatus of the microgrid inverter according to an exemplary embodiment of the present invention may be implemented as hardware components and/or software components. The individual units may be implemented, for example, using Field Programmable Gate Arrays (FPGAs) or Application Specific Integrated Circuits (ASICs), depending on the processing performed by the individual units as defined by the skilled person.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
Claims (19)
1. A method of controlling a microgrid inverter, the microgrid inverter comprising a power device, the method comprising:
a detection step: detecting the output voltage, the working voltage and the working current of the microgrid inverter in an off-grid state of the microgrid;
a double closed loop control step: determining each harmonic in the detected output voltage of the microgrid inverter, and executing double closed-loop control based on each harmonic and the detected working voltage and working current;
a driving pulse signal generating step: generating a driving pulse signal for controlling the power device according to the result of the double closed-loop control so as to enable the micro-grid inverter to output power consistent with the micro-grid load;
the microgrid inverter also comprises a reactor and a filter capacitor,
wherein, the detection step further comprises: detecting output three-phase voltage of the microgrid inverter, inductance three-phase current of the reactor and capacitance three-phase current of the filter capacitor in an off-grid state of the microgrid;
the double closed-loop control step further comprises: determining each harmonic in the detected output three-phase voltage, and executing double closed loop control based on each odd harmonic and the detected inductance three-phase current and capacitance three-phase current;
the double closed-loop control step further comprises:
performing Park conversion on each subharmonic voltage, and performing moving average filtering on a conversion result to obtain a direct current component of each subharmonic voltage;
calculating the opposite value of the direct current component of each harmonic voltage, carrying out proportional integral adjustment on the opposite value, and carrying out Ipark conversion including angle compensation on the result of the proportional integral adjustment to obtain a given value of each harmonic voltage, wherein the angle in the Ipark conversion including angle compensation is h theta plus delta h, h is the harmonic frequency, theta is the rotating angle of Park conversion, and delta h is the rotating angle of the h harmonic voltage in a sampling period;
subtracting the voltage given value of a voltage ring in the double closed-loop control from the direct-current component of the output three-phase voltage, performing proportional-integral regulation on the subtraction result, and taking the proportional-integral regulation result as the current given value of a current ring in the double closed-loop control;
performing proportional-integral regulation on the difference between the given current value and the direct-current component of the three-phase current of the inductor, adding the result of the proportional-integral regulation and a voltage coupling term generated by the reactor, and performing Ipeak transformation on the added result to obtain a given voltage value under a two-phase static coordinate system;
and superposing the voltage given value under the two-phase static coordinate system to each subharmonic voltage given value to obtain a total voltage given value for space vector pulse width modulation control.
2. The control method according to claim 1,
the detecting step further comprises: detecting the voltage of a direct current bus in an off-grid state of the microgrid;
the driving pulse signal generating step further includes: and generating a driving pulse signal for controlling the power device according to the result of the double closed-loop control and the voltage of the direct current bus so as to enable the micro-grid inverter to output power consistent with the load of the micro-grid.
3. The control method of claim 2, wherein the dual closed-loop-control step further comprises:
determining a voltage given value of a voltage loop in the double closed-loop control based on the output three-phase voltage, the inductance three-phase current and the capacitance three-phase current;
wherein the driving pulse signal generating step further comprises:
and generating a driving pulse signal for controlling the power device based on the current set value, the inductance three-phase current, the capacitance three-phase current and the direct-current bus voltage.
4. The control method of claim 3, wherein the dual closed-loop-control step further comprises:
adding the inductance three-phase current and the capacitance three-phase current to obtain an output three-phase current of the inverter;
performing Park conversion on the output three-phase voltage, the inductance three-phase current and the output three-phase current respectively to obtain a direct-current component of the output three-phase voltage, a direct-current component of the inductance three-phase current and a direct-current component of the output three-phase current;
and enabling the direct-current components of the output three-phase current to sequentially pass through the two cascaded wave traps to obtain the filtering value of the output three-phase current.
5. The control method of claim 4, wherein the dual closed-loop-control step further comprises:
determining the output voltage of the virtual synchronous generator model;
and determining the voltage set value of the voltage loop according to the output voltage, the virtual impedance and the filtered value of the output three-phase current.
6. The control method according to claim 5, wherein the drive pulse signal generating step further comprises:
and generating a driving pulse signal for controlling the power device according to the total voltage given value and the direct-current bus voltage.
7. The control method according to claim 4,
the rotation angle of Park transformation is an angle generated by power frequency adjustment of the virtual synchronous generator model.
8. The control method according to claim 4,
one of the two traps has a center frequency 6 times the output frequency of the inverter and the other trap has a center frequency 12 times the output frequency of the inverter.
9. The control method according to any one of claims 1 to 8, wherein the control method compensates for harmonics caused by delays introduced by control command periods by means of digital control.
10. A control apparatus of a microgrid inverter, the microgrid inverter comprising a power device, characterized in that the control apparatus comprises:
a detection unit configured to detect an output voltage, an operating voltage, and an operating current of the microgrid inverter in an off-grid state of a microgrid;
a double closed-loop control unit configured to determine harmonics in an output voltage of the microgrid inverter, and perform double closed-loop control based on the harmonics and a working voltage and a working current of the microgrid inverter detected by the detection unit;
the driving pulse signal generating unit is used for generating a driving pulse signal for controlling the power device according to the result of the double closed-loop control so as to enable the micro-grid inverter to output power consistent with the load of the micro-grid;
the microgrid inverter also comprises a reactor and a filter capacitor,
the detection unit is further configured to detect an output three-phase voltage of the microgrid inverter, an inductance three-phase current of the reactor and a capacitance three-phase current of the filter capacitor in an off-grid state of a microgrid;
the double closed-loop control unit is further configured to determine each harmonic in the output three-phase voltage detected by the detection unit, and perform double closed-loop control based on each odd harmonic and the inductance three-phase current and the capacitance three-phase current detected by the detection unit;
the dual closed-loop control unit is further configured to:
performing Park conversion on each subharmonic voltage, and performing moving average filtering on a conversion result to obtain a direct current component of each subharmonic voltage;
calculating the opposite value of the direct current component of each harmonic voltage, carrying out proportional integral adjustment on the opposite value, and carrying out Ipark conversion including angle compensation on the result of the proportional integral adjustment to obtain a given value of each harmonic voltage, wherein the angle in the Ipark conversion including angle compensation is h theta plus delta h, h is the harmonic frequency, theta is the rotating angle of Park conversion, and delta h is the rotating angle of the h harmonic voltage in a sampling period;
subtracting the voltage given value of a voltage ring in the double closed-loop control from the direct-current component of the output three-phase voltage, performing proportional-integral regulation on the subtraction result, and taking the proportional-integral regulation result as the current given value of a current ring in the double closed-loop control;
performing proportional-integral regulation on the difference between the given current value and the direct-current component of the three-phase current of the inductor, adding the result of the proportional-integral regulation and a voltage coupling term generated by the reactor, and performing Ipeak transformation on the added result to obtain a given voltage value under a two-phase static coordinate system;
and superposing the voltage given value under the two-phase static coordinate system to each subharmonic voltage given value to obtain a total voltage given value for space vector pulse width modulation control.
11. The control device of claim 10,
the detection unit is also configured to detect a direct current bus voltage in an off-grid state of the microgrid;
the driving pulse signal generating unit is further configured to generate a driving pulse signal for controlling the power device according to a result of the double closed-loop control and the direct current bus voltage, so that the microgrid inverter outputs power consistent with a microgrid load.
12. The control apparatus of claim 11, wherein the dual closed-loop control unit is further configured to:
determining a voltage given value of a voltage loop in the double closed-loop control based on the output three-phase voltage, the inductance three-phase current and the capacitance three-phase current;
wherein the drive pulse signal generation unit is further configured to:
and generating a driving pulse signal for controlling the power device based on the current set value, the inductance three-phase current, the capacitance three-phase current and the direct-current bus voltage.
13. The control apparatus of claim 12, wherein the dual closed-loop control unit is further configured to:
adding the inductance three-phase current and the capacitance three-phase current to obtain an output three-phase current of the inverter;
performing Park conversion on the output three-phase voltage, the inductance three-phase current and the output three-phase current respectively to obtain a direct-current component of the output three-phase voltage, a direct-current component of the inductance three-phase current and a direct-current component of the output three-phase current;
and enabling the direct-current components of the output three-phase current to sequentially pass through two cascaded wave traps arranged in the double closed-loop control unit to obtain the filtering value of the output three-phase current.
14. The control apparatus of claim 13, wherein the dual closed-loop control unit is further configured to:
determining the output voltage of the virtual synchronous generator model;
and determining the voltage set value of the voltage loop according to the output voltage, the virtual impedance and the filtered value of the output three-phase current.
15. The control device according to claim 14, wherein the drive pulse signal generation unit is further configured to:
and generating a driving pulse signal for controlling the power device according to the total voltage given value and the direct-current bus voltage.
16. The control device of claim 13,
the rotation angle of Park transformation is an angle generated by power frequency adjustment of the virtual synchronous generator model.
17. The control device of claim 13,
one of the two traps has a center frequency 6 times the output frequency of the inverter and the other trap has a center frequency 12 times the output frequency of the inverter.
18. The control apparatus of any of claims 10-17, wherein the dual closed-loop control unit comprises a digital controller,
wherein the digital controller compensates for harmonics caused by delays introduced by control command cycles in a digital control manner.
19. A microgrid inverter comprising a control device according to any of claims 10-17.
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