Patent Description:
With the development of new electric power technology, people introduce a microgrid structure to adjust an external power grid, which is beneficial to an interconnection of distributed power supply and large scale access of the distributed power supply to medium and low voltage distribution systems. A microgrid is a group of system units comprising a control device, an energy storage device, a load and a micro power, to supply power to the load. The microgrid can be operated in a state of grid-connected with an external power grid or in isolation. <CIT> discloses a control system of a microgrid, comprising a grid-connection switch, a power converter, a first controller and a second controller, wherein the first controller controls connection and disconnection of the grid-connection switch and sends a first control instruction based on a state of the control system of the microgrid and the second controller receives the first control instruction from the first controller and controls the power converter in response to the first control instruction.

However, a real-time performance of the existing microgrid depends on communication and response speeds of downstream devices, and operation stability of the microgrid system is poor and needs to be improved.

An object of the present disclosure is to provide a control system of a microgrid and a microgrid, which enhance operation stability of the microgrid by hierarchical control.

A control system of a microgrid is provided as defined in claim <NUM>.

A microgrid is provided as defined in claim <NUM>, which includes the control system of the microgrid described above, an energy storage unit and a load.

The control system of the microgrid and the microgrid of the present disclosure enhance the operation stability of the microgrid by hierarchical control, and achieve an ability of applying <NUM>% unbalanced load in an off-grid state by double closed loop control of voltage and current.

The above and other objects, characteristics and advantages will be more clear according to following detailed descriptions in conjunction with drawings, wherein:.

Various exemplary embodiments of the present disclosure are fully described hereinafter in conjunction with drawings, and some of the exemplary embodiments are illustrated in the drawings.

A control system of a microgrid and a microgrid according to embodiments of the present disclosure are described hereinafter by referring to <FIG>.

As illustrated in <FIG>, the control system of the microgrid according to an embodiment of the present disclosure includes a grid-connection switch <NUM>, a first controller <NUM>, a second controller <NUM> and an energy router <NUM>. The grid-connection switch <NUM>, the first controller <NUM>, the second controller <NUM> and the energy router <NUM> are communicated via optical fibers. Here, a fiber optic communication protocol may be a custom private protocol, to maximize real-time performance. As an example, fiber optic communication coding and decoding may be performed by a field programmable gate array (FPGA).

The first controller <NUM> controls connection and disconnection of the grid-connection switch <NUM> and sends a first control instruction based on a state of the control system of the microgrid. The second controller <NUM> receives the first control instruction from the first controller <NUM>, and controls the energy router <NUM> in response to the first control instruction.

It should be understood that when the grid-connection switch <NUM> is connected, the control system of the microgrid is in a grid-connected state, and when the grid-connection switch <NUM> is disconnected, the control system of the microgrid is in an off-grid state.

Here, the second controller <NUM> includes a digital signal processor (DSP). The second controller <NUM> may be configured to be in a VSG control mode when the digital signal processor runs a VSG algorithm, and in a PQ control mode when the digital signal processor runs a PQ algorithm.

It should be understood that the first controller <NUM> may also include a digital signal processor to apply a control algorithm.

Preferably, data exchange may be performed by the field programmable gate array and the digital signal processor.

In an embodiment, when the grid-connection switch <NUM> is disconnected, the first controller <NUM> generates a first frequency regulation instruction and a first voltage regulation instruction based on actual voltage and frequency of the power grid, determines a first active power instruction and a first reactive power instruction based on a three-phase voltage of the power grid and a three-phase voltage of the microgrid, and takes the first frequency regulation instruction, the first voltage regulation instruction, the first active power instruction and the first reactive power instruction as the first control instruction; the second controller <NUM> is in the VSG (virtual synchronous generator) control mode.

That is to say, when the grid-connection switch <NUM> is disconnected, the control system of the microgrid is in the off-grid state, and the first controller <NUM> takes the first frequency regulation instruction, the first voltage regulation instruction, the first active power instruction and the first reactive power instruction as the first control instruction to send. The second controller <NUM> is in the VSG control mode, and controls the energy router <NUM> in response to the received first control instruction.

A control process of the first controller <NUM> in the off-grid state is described in detail hereinafter.

The first controller <NUM> determines a voltage amplitude Uoutg of the power grid and an angular frequency of the power grid, takes the voltage amplitude Uoutg of the power grid as the first voltage regulation instruction Uref, and takes the angular frequency of the power grid as the first frequency regulation instruction ωref. In addition, the first controller <NUM> further determines the frequency Freqg of the power grid, the frequency Freqm of the microgrid and the voltage amplitude Uoutm of the microgrid; perfroms PI (Proportional Integral) adjustment on a difference between the frequency Freqg of the power grid and the frequency Freqm of the microgrid and determines the difference after the PI adjustment as the first active power instruction Pref; and performs PI adjustment on a difference between the voltage amplitude Uoutg of the power grid and the voltage amplitude Uoutm of the microgrid and determines the difference after the PI adjustment as the first reactive power instruction Qref.

Here, the above two PI adjustments simulate processes of voltage regulation and frequency regulation of a synchronous generator, cause the voltage amplitude and the frequency outputted by the microgrid to be consistent with the voltage amplitude and the frequency outputted by the power grid and cause a voltage phase outputted by the microgrid and a voltage phase outputted by the power grid to be inconsistent in the off-grid state.

Preferably, the first controller <NUM> collects the three-phase voltage of the power grid, calculates the voltage amplitude Uoutg of the power grid, the frequency Freqg of the power grid and the voltage phase Thetag of the power grid through a software phase-locked loop (PLL), and determines a product of 2π and the frequency Freqg of the power grid as the angular frequency of the power grid.

Preferably, the first controller <NUM> collects the three-phase voltage of the power grid, calculates the voltage amplitude Uoutm of the microgrid, the frequency Freqm of the microgrid and the voltage phase Thetam of the microgrid through a software phase-locked loop.

A control process of the second controller <NUM> in the off-grid state is described in detail hereinafter.

The second controller <NUM> receives the first voltage regulation instruction Uref and the first frequency regulation instruction ωref, and controls the energy router <NUM> in response to the first voltage regulation instruction Uref and the first frequency regulation instruction ωref, to make the voltage amplitude and the frequency outputted by the microgrid consistent with the voltage amplitude and the frequency outputted by the power grid. In addition, the second controller <NUM> receives the first active power instruction Pref and the first reactive power instruction Qref, and controls the energy router <NUM> in response to the first active power instruction Pref and the first reactive power instruction Qref, to make the energy router <NUM> output an active power and a reactive power that match the load.

As illustrated in <FIG>, the second controller <NUM> determines an actual output active power Pout and an actual output reactive power Qout based on an output voltage of the energy router <NUM> (i.e., an output voltage of the microgrid), and determines angles θ of a positive sequence rotation coordinate transformation and a negative sequence rotation coordinate transformation of the output voltage and the output current of the energy router <NUM> by invoking a rotor motion equation and an original mover regulation equation in combination with the actual output active power Pout, the first active power instruction Pref and the first frequency regulation instruction ωref.

As illustrated in <FIG>, the second controller <NUM> determines d axis and q axis component given values Udref, Uqref of the positive sequence output voltage of the energy router <NUM> based on the actual output reactive power Qout, the first reactive power instruction Qref and the first voltage regulation instruction Uref, and sets d axis and q axis component given values of the negative sequence output voltage of the energy route <NUM> as zero.

As illustrated in <FIG> and <FIG>, the second controller <NUM> is configured to: perform a positive sequence rotation coordinate transformation and a negative sequence rotation coordinate transformation on the output voltage of the energy router <NUM> to obtain positive sequence components Ud, Uq and negative sequence components Udn, Uqn of the output voltage; obtain direct current components UdNotch, UqNotch of the positive sequence components Ud, Uq and direct current components UdnNotch, UqnNotch of the negative sequence components Udn, Uqn of the output voltage by a notch filter; perform a positive sequence rotation coordinate transformation and a negative sequence rotation coordinate transformation on the output current of the energy router <NUM> to obtain positive sequence components Id, Iq and negative sequence components Idn, Iqn of the output current; obtain direct current components IdNotch, IqNotch of the positive sequence components Id, Iq and direct current components IdnNotch, IqnNotch of the negative sequence components Idn, Iqn of the output current by a notch filter; calculate an instantaneous active power and an instantaneous reactive power of the energy router <NUM> based on the direct current components UdNotch, UqNotch, UdnNotch, UqnNotch of the positive sequence component and the negative sequence component of the output voltage and the direct current components IdNotch, IqNotch, IdnNotch, IqnNotch of the positive sequence component and the negative sequence component of the output current; and pass the instantaneous active power and the instantaneous reactive power through a low pass filter (LPF) to obtain the actual output active power Pout and the actual output reactive power Qout.

Preferably, in order to suppress unbalanced output voltage caused by unbalanced load, the second controller <NUM> is further configured to: pass the positive sequence components Ud, Uq and the negative sequence components Udn, Uqn of the output voltage through a notch filter with a center frequency being twice times of the output frequency, to obtain the direct current components UdNotch, UqNotch of the positive sequence components Ud, Uq of the output voltage and direct current components UdnNotch, UqnNotch of the negative sequence components Udn, Uqn of the output voltage. <FIG> is a waveform of an experiment of applying an unbalanced load in the VSG control mode according to an embodiment of the present disclosure. As illustrated in <FIG>, curve <NUM> is a line voltage Uab outputted by the energy router <NUM>, curve <NUM> is a line voltage Ubc outputted by the energy router <NUM>, and curves <NUM>, <NUM>, <NUM> are three phase currents Ia, Ib, Ic outputted by the energy router <NUM>, respectively. It can be known from <FIG> that the technology solution may control the output voltage to be balanced under the off-grid state when applying an unbalanced load, without being affected by the unbalanced load, thus verifying correction of the control algorithms.

Herein, the instantaneous active power may be calculated by following equation:
<MAT>
where UdNotch is the d axis direct current component of the positive sequence component of the output voltage, UqNotch is the q axis direct current component of the positive sequence component of the output voltage, IdNotch is the d axis direct current component of the positive sequence component of the output current, and IqNotch is the q axis direct current component of the positive sequence component of the output current.

The instantaneous reactive power may be calculated by following equation:
<MAT>.

It should be understood that the second controller <NUM> passes the instantaneous active power and the instantaneous reactive power through the low pass filter to obtain the actual output active power Pout and the actual output reactive power Qout, thereby improving stability of the VSG control mode of the second controller in the off-grid state.

Herein, the rotor motion equation is:
<MAT>
where ωref is the first frequency regulation instruction, ωout is the angular frequency of the output voltage, Pout is the actual output active power, Pm is a virtual mechanical power given value of the VSG, J is a virtual rotational inertia, D is a virtual damping factor, θ is the angle of positive sequence rotation coordinate transformation and negative sequence rotation coordinate transformation of the output voltage and the output current of the energy router <NUM>.

The prime mover regulation equation is:
<MAT>
where Pref is the first active power instruction, Kp is an active power difference coefficient, Pm is the virtual mechanical power given value of the VSG, which consists of the first active power instruction and an adjustment power outputted by a virtual governor based on an angular frequency deviation, and is provided by simulating a prime mover of a synchronous machine via a distributed power supply and an energy storage unit.

Voltage regulating of the second controller <NUM> in the VSG control mode is simulating a reactive voltage sag relationship of the synchronous generator to obtain a VSG output voltage, as shown in following equation:
<MAT>.

Eref is the VSG output voltage, Uref is the first voltage regulation instruction, Qref is the first reactive power instruction, Qout is the actual output reactive power, and Kq is a reactive power difference coefficient.

In order to stabilize a parallel operation of multi-machine, a virtual impedance ωLv is added, such that the d axis and q axis component given values Udref, Uqref of the positive sequence output voltage of the energy router <NUM> may be determined by following equation:
<MAT>.

In order to achieve applying an unbalance load in the off-grid state, the d axis and q axis component given values of the negative sequence output voltage of the energy route <NUM> are set as zero.

To enable the energy router <NUM> have an off-grid black start function, the second controller <NUM> invokes a ramp function to add the first voltage regulation instruction Uref to an output of a reactive power deviation regulation to realize a function of stepping up from zero, to gradually increase the output voltage of the energy router (i.e., the output voltage of the microgrid) from zero to a preset value. <FIG> is a waveform of an experiment of black-start of the energy router according to an embodiment of the present disclosure. As illustrated in <FIG>, curve <NUM> is the line voltage Uab outputted by the energy router <NUM>, and curve <NUM> is the line voltage Ubc outputted by the energy router <NUM>. It can be known from <FIG> that the voltage of the microgrid is gradually increased from zero to a given voltage, thereby reducing an magnetizing inrush current of a distribution transformer and ensuring stability of the frequency and voltage of the microgrid.

As illustrated in <FIG>, the second controller <NUM> is further configured to: perform PI adjustment on differences between the d axis component given value and q axis component given value of a positive sequence output voltage and a negative sequence output voltage of the energy router <NUM> and the direct current components UdNotch, UqNotch, UdnNotch, UqnNotch of the positive sequence component and the negative sequence component of the output voltage, and takes the differences after the PI adjustment as the positive sequence and negative sequence output current component given values Idref, Iqref, Idnref, Iqnref of the energy router <NUM>; determines positive sequence and negative sequence output voltage component given values Ualfapref, Ubetapref, Ualfanref, Ubetanref of the energy router <NUM> in the static coordinate system based on differences between the positive sequence and negative sequence output current component given values Idref, Iqref, Idnref, Iqnref of the energy router <NUM> and the direct current components IdNotch, IqNotch, IdnNotch, IqnNotch of the positive sequence and negative sequence components of the output current after the PI adjustment, to realize double closed loop control of voltage and current and thus realize applying <NUM>% unbalance load in the off-grid state.

Preferably, the second controller <NUM> controls differences between the positive sequence and negative sequence output current component given values Idref, Iqref, Idnref, Iqnref of the energy router <NUM> and the direct current components IdNotch, IqNotch, IdnNotch, IqnNotch of the positive sequence and negative sequence components of the output current to suffer a PI adjustment, an addition of a voltage coupling term generated by an electric reactor and an inverse transformation, to obtain the positive sequence and negative sequence output voltage component given values Ualfapref, Ubetapref, Ualfanref, Ubetanref of the energy router <NUM> in the static coordinate system.

In a case of applying a nonlinear load in an off-grid state, odd harmonics will be contained in the output voltage of the energy router <NUM> if harmonic suppression is not performed, which will result in overproof of harmonic distortion THD of the output voltage and thus requirement on power quality of powering a sensitive load cannot be met. Therefore, the second controller <NUM> detects the odd harmonics in the output voltage of the energy router <NUM>, determines a direct current component of each of the harmonic voltages, performs PI adjustment on difference between the direct current component of each of the harmonic voltages and zero, and performs inverse transform on the differences after the PI adjustment to obtain a given value of each of the harmonic voltages Ualfahref, Ubetahref, to suppress harmonics in the output voltage of the energy router <NUM>.

As an example, in a case of applying an uncontrolled rectifier nonlinear load in an off-grid state, the active power is 90kW, the reactive power is 30kW. If there is no harmonic suppression, content of fifth harmonic contained in the output voltage of the energy router <NUM> calculated by FFT is <NUM>%, content of seventh harmonic is <NUM>%, content of eleventh harmonic is <NUM>%, and content of thirteenth harmonic is <NUM>%. If harmonic suppression is performed, content of fifth harmonic contained in the output voltage of the energy router <NUM> calculated by FFT is <NUM>%, content of the seventh harmonic is <NUM>%, content of the eleventh harmonic is <NUM>%, and content of the thirteenth harmonic is <NUM>%. Therefore, the fifth, seventh, eleventh and thirteenth harmonics in the output voltage of the power router <NUM> are well suppressed, and thus effectiveness of the harmonic suppression control algorithm is verified.

As illustrated in <FIG>, the second controller <NUM> detects the fifth, seventh, eleventh and thirteenth harmonics in the output voltage of the power router <NUM>, and performs rotation coordinate transformation on the output voltage of the energy router <NUM> to obtain the corresponding harmonic components. It should be understood that in a general balanced load application, the fifth and eleventh harmonics appear as negative sequence components, and the seventh and thirteenth harmonics appear as positive sequence components. Therefore, negative sequence rotation coordinate transformation with rotation angles of -5xθ and -11xθ are respectively performed on the fifth and eleventh harmonics, and positive sequence rotation coordinate transformation with rotation angles of 7xθ and 13xθ are respectively performed on the seventh and thirteenth harmonics, to obtain the corresponding harmonic components. Then, the second controller <NUM> passes the harmonic component through the low pass filter to obtain direct current component of the harmonic current, performs PI adjustment on differences between the direct current component of each harmonic voltage and zero, and performs inverse transform on the differences after the PI adjustment to obtain the given value of each harmonic voltage (Ualfahref, Ubetahref(h=<NUM>, <NUM>, <NUM>, <NUM>)).

As illustrated in <FIG>, the second controller <NUM> obtains feedforward amounts Ualfa, Ubeta of the output voltage by performing a static coordinate transformation on the output voltage of the energy router <NUM>, and generates a modulated wave by invoking an SVPWM (space vector pulse width modulation) modulation wave generation function in combination with a sum of the positive sequence and negative sequence output voltage component given values Ualfapref, Ubetapref, Ualfanref, Ubetanref in the static coordinate system, each harmonic voltage given values Ualfahref, Ubetahref and the feedforward amounts Ualfa, Ubeta of the output voltage, to control operation of the energy router <NUM>.

In another embodiment, when the grid-connection switch <NUM> is disconnected, the first controller <NUM> determines the voltage amplitude Uoutg of the power grid, the voltage phase Thetag of the power grid, the voltage phase Thetam of the microgrid and an angular frequency of the microgrid, and detects whether a difference between the voltage phase Thetag of the power grid and the voltage phase Thetam of the microgrid reaches a predetermined threshold; and the first controller <NUM>, when detecting that the difference reaches the predetermined threshold, controls the grid-connection switch <NUM> to be closed, thus achieving smooth switch from the off-grid state to the grid-connected state.

Specifically, the first controller <NUM> superimposes a predetermined multiple of the difference onto the angular frequency of the microgrid to obtain a second frequency regulation instruction, and takes the voltage amplitude Uoutg of the power grid as the second voltage regulation instruction, and also determines a second active power instruction and a second reactive power instruction which match the load, and takes the second frequency regulation instruction, the second voltage regulation instruction, the second active power instruction and the second reactive power instruction as the first control instruction.

Preferably, the predetermined multiple is <NUM>, which is not limited in the present disclosure.

As illustrated in <FIG>, in the off-grid state, the active power is 100kw, the reactive power is 90kw; in the grid-connected state, the active power is 10kw, the reactive power is 0kw. Curves <NUM> and <NUM> are the line voltages Uab, Ubc outputted by the energy router <NUM>, curves <NUM>, <NUM>, <NUM> are the three phase currents Ia, Ib, Ic outputted by the energy router <NUM>, respectively, and curve <NUM> is the state of the grid-connection switch <NUM>. As illustrated in <FIG>, when the off-grid state is switched to the grid-connected state, the voltage and current outputted by the energy router <NUM> are shock-free, and after grid connection the power quickly tracks active and reactive instructions of the grid-connected state.

In another embodiment, when the grid-connection switch <NUM> is closed, the first controller <NUM> generates a third active power instruction and a third reactive power instruction as the first control instruction based on a power of the load and a state of an energy storage unit; and the second controller <NUM> is in the PQ (active and reactive) control mode.

That is to say, when the grid-connection switch <NUM> is closed, the control system of the microgrid is in the grid-connected state, the first controller <NUM> takes the third active power instruction and the third reactive power instruction as the first control instruction to send. The second controller <NUM> is in the PQ control mode, and controls the energy router <NUM> in response to the received first control instruction.

In the grid-connected state, the second controller <NUM> does not perform voltage closed-loop control and voltage harmonic suppression control. Furthermore, the second controller <NUM> sets the negative sequence output current component given values Idnref, Iqnref of the energy router <NUM> as <NUM>.

As illustrated in <FIG>, the second controller <NUM>, based on the positive sequence and negative sequence output current component given values Idref, Iqref, Idnref, Iqnref of the energy router <NUM> and the direct current components IdNotch, IqNotch, IdnNotch, IqnNotch of the positive sequence and negative sequence components of the output current of the energy router <NUM>, determines the positive sequence and negative sequence output voltage component given values Ualfapref, Ubetapref, Ualfanref, Ubetanref in the static coordinate system, and generates a modulated wave by invoking an SVPWM modulation wave generation function in combination with a sum of the positive sequence and negative sequence output voltage component given values Ualfapref, Ubetapref, Ualfanref, Ubetanref in the static coordinate system and the feedforward amounts Ualfa, Ubeta of the output voltage of the energy router <NUM>, to control the operation of the energy router.

Specifically, the second controller <NUM> controls the differences between the positive sequence and negative sequence output current component given values Idref, Iqref, Idnref, Iqnref of the energy router <NUM> and the direct current components IdNotch, IqNotch, IdnNotch, IqnNotch of the positive sequence and negative sequence components of the output current of the energy router <NUM> to suffer a PI adjustment, an addition of a voltage coupling term generated by an electric reactor and an inverse transformation, to obtain the positive sequence and negative sequence output voltage component given values Ualfapref, Ubetapref, Ualfanref, Ubetanref in the static coordinate system, and generates a modulated wave by invoking an SVPWM modulation wave generation function in combination with a sum of the positive sequence and negative sequence output voltage component given values Ualfapref, Ubetapref, Ualfanref, Ubetanref in the static coordinate system and the feedforward amounts Ualfa, Ubeta of the output voltage of the energy router <NUM>.

In another embodiment, the first controller <NUM>, if detecting fault of the power grid in a case that the control system of the microgrid is in the grid-connected state, controls the grid-connection switch <NUM> to be disconnected.

In another embodiment, in a case that the grid-connection switch <NUM> is closed, the first controller <NUM>, if detecting that a current flowing through the grid-connection switch <NUM> reaches a predetermined current threshold, controls the grid-connection switch <NUM> to be disconnected, thereby achieving smooth switching from the grid-connected state to the off-grid state.

Specifically, the first controller generates a fourth active power instruction and a fourth reactive power instruction according to the current flowing through the grid-connection switch, and then takes the four active power instruction and the fourth reactive power instruction as the first control instruction.

As illustrated in <FIG>, in the off-grid state, the active power is 100kw, and the reactive power is 90kw. Curves <NUM> and <NUM> are the line voltages Uab, Ubc outputted by the energy router <NUM>, curves <NUM>, <NUM>, <NUM> are the three phase currents Ia, Ib, Ic outputted by the energy router <NUM>, and curve <NUM> is the state of the grid-connection switch <NUM>. As illustrated in <FIG>, an output power of the energy router <NUM> has been matched with the load before off-grid, thereby ensuring that the current flowing through the grid-connection switch <NUM> is small and thus the voltage and current are shock free in process of switching from the grid-connected state to the off-grid state.

The microgrid system according to the embodiments of the present disclosure is described hereinafter in conjunction with <FIG>.

As illustrated in <FIG>, a microgrid system is further provided according to an embodiment of the present disclosure. The microgrid system includes the control system of the microgrid as described above, the energy storage unit <NUM> and the load <NUM>; the energy storage unit <NUM> is connected to an end of the energy router <NUM>, and another end of the power router <NUM> is connected to the power grid <NUM> via the grid-connection switch <NUM>; the energy router <NUM> supplies power to the load <NUM>; the energy storage unit <NUM> and the grid-connection switch <NUM> are connected to the first controller <NUM> through an optical network; the energy router <NUM> is connected to the second controller <NUM> through an optical network, and the second controller <NUM> is connected to the first controller <NUM> through an optical network.

In a case that the microgrid is in the off-grid state, the control system of the microgrid converts a direct current of the energy storage unit <NUM> into an alternating current to supply power to the load <NUM>. In a case that the microgrid is in the grid-connected state, the control system of the microgrid converts an alternating current of the power grid <NUM> into a direct current to charge the energy storage unit <NUM>.

In addition, the control system of the microgrid and the microgrid according to the embodiment of the present disclosure enhance operation stability of the microgrid through hierarchical control, and achieve an ability of applying <NUM>% unbalanced load in the off-grid state through double closed loop control of voltage and current.

Claim 1:
A control system of a microgrid, comprising: a grid-connection switch (<NUM>), an energy router (<NUM>), a first controller (<NUM>) and a second controller (<NUM>),
wherein the first controller (<NUM>) is configured to control connection and disconnection of the grid-connection switch (<NUM>) and send a first control instruction based on a state of the control system of the microgrid; and
the second controller (<NUM>) is configured to receive the first control instruction from the first controller (<NUM>) and control the energy router (<NUM>) in response to the first control instruction;
wherein the second controller (<NUM>) is further configured to detect odd harmonics in the output voltage of the energy router (<NUM>), and determine a direct current component of each of the harmonic voltages, perform proportional integral PI adjustment on a difference between the direct current component of each of the harmonic voltages and zero, and perform inverse transformation on the difference after the PI adjustment to obtain a given value of each of the harmonic voltages to suppress harmonics in the output voltage of the energy router (<NUM>).