CN110962666A

CN110962666A - Electric vehicle charging equipment based on load virtual synchronous machine technology and control method

Info

Publication number: CN110962666A
Application number: CN201911232249.4A
Authority: CN
Inventors: 周珊; 吕志鹏; 吴鸣; 孙丽敬; 宋振浩; 刘国宇
Original assignee: China Electric Power Research Institute Co Ltd CEPRI
Current assignee: China Electric Power Research Institute Co Ltd CEPRI
Priority date: 2019-12-04
Filing date: 2019-12-04
Publication date: 2020-04-07

Abstract

The invention discloses electric vehicle charging equipment and a control method based on a load virtual synchronous machine technology, wherein a charging circuit of the electric vehicle charging equipment adopts a two-pole converter circuit; the two-pole converter circuit comprises an active digital Vienna rectifier and a digital full-bridge LLC resonant converter. Controlling an active digital vienna rectifier in an electric vehicle charging installation, comprising: obtaining a given value of active power through PI control based on the direct current side voltage and a reference value of the direct current side voltage; the given value of the active power is controlled by an active control loop, a reactive control loop and a voltage and current double closed loop to obtain a reference instruction value of a current inner loop; after the reference instruction value of the current inner loop is compared with the current value of the feedback inductor, a voltage modulation wave signal is generated through a proportion link; and the voltage modulation wave signal is modulated to generate a PWM signal to drive the on-off of the switching tube. The invention enables the charging equipment of the electric automobile to follow the fluctuation of the voltage on the direct current side.

Description

Electric vehicle charging equipment based on load virtual synchronous machine technology and control method

Technical Field

The invention relates to the field of electrical engineering, in particular to electric automobile charging equipment based on a load virtual synchronous machine technology and a control method.

Background

The existing power system has the following three defects: firstly, it is estimated that 90% of the power of a new generation of power system needs to be used after power electronic conversion in the future, and power electronic equipment with higher and higher proportions is connected into the power system, so that the trend of diversification of power conversion interface devices and strong load nonlinearity is more obvious, meanwhile, the loss of system inertia is caused, and the safety and stability of a large power grid face huge challenges; secondly, with the continuous development of the renewable energy distributed power generation technology, a large amount of renewable energy is connected into the power system, and compared with the traditional thermal power generation, the renewable energy distributed power generation has the advantages that the output is influenced by natural factors such as illumination intensity, wind power intensity and the like, and the uncertainty, the uncontrollable property, the random fluctuation and the discontinuity are very strong. Because the renewable energy power system has the problems of voltage stability, wind and light abandonment, reduction of rotational inertia, oscillation of a weak power grid and the like, the natural variability of renewable energy sources needs to be compensated through other energy storage systems, and the power grid is promoted to better accept fluctuating renewable energy sources; thirdly, the power balance of the existing power system is maintained by the rotation of a large synchronous generator at the same frequency, and with the improvement of the permeability of new energy technologies represented by wind power generation and electric automobiles in a power grid, the installed proportion of the traditional thermal power generator is gradually reduced, which means that a rotation synchronization mechanism in the power system is gradually weakened and the stability of the power system is endangered. The requirement for power grid stability cannot be met only by a ' source ' side peak shaving unit, and load ' coordination and participation are urgently needed and a ' source-network-load ' efficient and friendly interaction mechanism is established. The conventional control only focuses on the adjustment of the internal characteristics of the control ring, the adjustment of the external characteristics cannot be realized, and the traditional load side does not have an adjustment mechanism, so that the interactivity, controllability and flexibility of the load are gradually enhanced along with the introduction of diversified loads. The electric vehicle load belongs to a typical active load, and the charging and discharging process of the electric vehicle load can bring fluctuation to the tide of a power grid. The traditional load handling mode of the power grid is mainly switching off and power limiting, the social and economic benefits are poor, and a mechanism for efficient interaction of the load and the power grid is urgently needed to be established.

Due to the problems of the three aspects, a plurality of problems occur to the power grid directly or indirectly, and most importantly, the frequency of the power grid is unstable.

Disclosure of Invention

In order to solve the above-mentioned deficiencies in the prior art, the present invention provides an electric vehicle charging apparatus and a control method based on a load virtual synchronous machine technology, in order to achieve the following objectives:

(1) the scheme is provided for solving the problem of system inertia loss in a new generation of power system.

(2) The problems that a renewable energy power system has voltage stability, wind and light abandonment, rotational inertia reduction, weak power grid connection oscillation and the like are solved to a certain extent.

(3) The requirement for power grid stability cannot be met only by a ' source ' side peak shaving unit, and load ' coordination and participation are urgently needed and a ' source-network-load ' efficient and friendly interaction mechanism is established.

The invention provides an electric automobile charging device, which comprises: the charging circuit of the electric vehicle charging equipment adopts a two-pole converter circuit; the two-pole converter circuit comprises an active digital Vienna rectifier and a digital full-bridge LLC resonant converter.

Preferably, the active digital vienna rectifier is a three-level voltage source type rectifier, and the load virtual synchronous machine technology is combined with the converter autonomous control to rectify the grid voltage into a direct-current voltage of 400 VDC-800 VDC.

Preferably, the digital full-bridge LLC resonant converter is a three-level DC/DC direct-current voltage conversion circuit, and the output voltage of the three-level DC/DC direct-current voltage conversion circuit is 200 VDC-750 VDC.

Based on the same inventive concept, the invention also provides a control method of the electric vehicle charging equipment, which is used for controlling the active digital vienna rectifier in the electric vehicle charging equipment and comprises the following steps:

obtaining a given value of active power through PI control based on the direct current side voltage and a reference value of the direct current side voltage;

the given value of the active power is controlled by an active control loop, a reactive control loop and a voltage and current double closed loop to obtain a reference instruction value of a current inner loop;

after the reference instruction value of the current inner loop is compared with the current value of the feedback inductor, a voltage modulation wave signal is generated through a proportion link;

and the voltage modulation wave signal is modulated to generate a PWM signal to drive the on-off of the switching tube, and a reference value of the direct current side voltage is output.

Preferably, the given value of the active power is calculated according to the following formula:

P_m＝-U_dc ^*(U_dc ^*-U_dc)(K_p+K_i/s)

wherein, P_mThe method comprises the following steps of (1) setting a given value of active power of a load virtual synchronous machine; u shape_dc ^*The reference value is the DC side voltage of the load virtual synchronous machine; u shape_dcThe voltage of the direct current side of the virtual synchronous machine is a load; k_pThe proportional coefficient of a PI controller of a direct-current side voltage loop of the load virtual synchronous machine is obtained; k_iAnd the integral coefficient of the PI controller of the direct-current side voltage loop of the load virtual synchronous machine is shown.

Preferably, the obtaining of the reference command value of the current inner loop by the control of the active control loop, the reactive control loop and the voltage-current double closed loop includes:

introducing a rotor motion equation into an active control loop based on the given value of the active power to obtain a power angle of the load virtual synchronous machine;

obtaining an output voltage amplitude of a reactive power control loop based on the obtained actual value of the reactive power of the load virtual synchronous machine and the actual capacitor voltage effective value;

constructing an electromagnetic equation in a voltage-current double-closed loop based on the output voltage amplitude of the reactive control loop and the power angle of the load virtual synchronous machine;

and obtaining a reference command value of the current inner ring according to the electromagnetic equation.

Preferably, the introducing a rotor motion equation into an active control loop based on the given value of the active power to obtain the power angle of the load virtual synchronous machine includes:

in the control link of the converter, an electromechanical transient equation of a synchronous motor is adopted, and a control algorithm of an active control loop is obtained based on the given value of the active power;

and introducing a rotor motion equation into a control algorithm of the active control loop to obtain the power angle of the load virtual synchronous machine.

Preferably, the control algorithm of the active control loop is as follows:

in the formula: omega is the mechanical angular velocity, omega_nFor synchronizing angular speed, T, of the grid_mFor loading the mechanical torque of a virtual synchronous machine, T_eFor loading the electromagnetic torque of a virtual synchronous machine, T_dFor loading the damping torque, T, of a virtual synchronous machine₀For nominal torque command, Δ T for frequency deviation feedback command, P_eIs the actual value of active power, P_mThe reference value is the mechanical power reference value of the load virtual synchronous machine, and theta is the power angle of the load virtual synchronous machine;

wherein, the power angle θ of the load virtual synchronous machine is calculated according to the following formula:

θ＝(P_m-P_e+D_pω_n)/s/(Js+D_p)

in the formula: theta is the power angle of the virtual synchronous machine, J is the moment of inertia of the virtual synchronous machine, D_pThe damping coefficient of the load virtual synchronous machine.

Preferably, the obtaining of the output voltage amplitude of the reactive power control loop based on the obtained actual value of the reactive power of the load virtual synchronous machine and the actual effective value of the capacitor voltage includes:

simulating a synchronous motor excitation current control method to obtain a control equation of the midpoint voltage of a bridge arm of the rectifier based on the effective value of the reference voltage of the capacitor of the rectifier and the effective value of the actual capacitor voltage;

constructing a primary voltage regulation equation of the synchronous generator based on the obtained actual value of the reactive power of the load virtual synchronous machine, the set given value of the reactive power and the rated effective value of the output voltage;

and simultaneously establishing the control equation and the primary voltage regulation equation to obtain the output voltage amplitude of the reactive power control loop.

Preferably, the constructing an electromagnetic equation in the voltage-current double closed loop based on the reactive control loop output voltage amplitude and the power angle of the load virtual synchronous machine includes:

constructing a three-phase modulation wave signal based on the reactive control loop output voltage amplitude and the power angle of the load virtual synchronous machine;

constructing an electromagnetic equation based on the three-phase modulation wave signal and the terminal voltage of the load virtual synchronous machine;

and obtaining the instantaneous reactive power output by regulating the terminal voltage and the terminal of the alternating current interface by regulating the virtual potential of the load virtual synchronous machine based on an electromagnetic equation.

Preferably, the electromagnetic equation is expressed by the following formula:

i_abc＝(e_abc-u_abc)/(Ls+R)

in the formula: e.g. of the type_abcFor loading the virtual synchronous machine potential u_abcFor loading the terminal voltage, i, of a virtual synchronous machine_abcThe output current of the load virtual synchronous machine is L, and the stator inductance R of the load virtual synchronous machine is the resistance of the load virtual synchronous machine.

Preferably, the virtual potential of the load virtual synchronous machine is as follows:

E_p＝E₀+ΔE_Q+ΔE_U

in the formula: e_pTo load the virtual potential of a virtual synchronous machine, E₀Is the effective value of the internal potential, delta E, of the load virtual synchronous machine in a steady state_QIs deficiency of loadReactive power regulation potential, delta E, of a quasi-synchronous machine_UAdjusting the potential for the reactor terminal voltage of the load virtual synchronous machine;

wherein the potential Δ E of the load virtual synchronous machine reactive power regulation_QAs shown in the following formula:

ΔE_Q＝K_q(Q_ref-Q_e)

in the formula: k_qFor loading virtual synchronous machine reactive regulation coefficient, Q_refFor loading reactive commands, Q, of the AC interface of a virtual synchronous machine_eInstantaneous reactive power output by the AC interface machine end of the load virtual synchronous machine;

instantaneous reactive power Q output by the AC interface machine end of the load virtual synchronous machine_eAs shown in the following formula:

in the formula: u. of_a、u_bAnd u_cThe three-phase machine terminal voltages of the load virtual synchronous machine are respectively;

the reactor terminal voltage regulation potential Delta E_UAs shown in the following formula:

ΔE_U＝D_q(U_ref-U_n)

wherein, U_refFor the command value, U, of the effective value of the line voltage of the terminal of a load-virtual synchronous machine_nIs the true value, D, of the effective value of the terminal line voltage of the load virtual synchronous machine_qAnd adjusting the voltage regulating coefficient of the load virtual synchronous machine, namely the droop coefficient of the reactive ring of the load virtual synchronous machine.

Preferably, after the voltage modulation wave signal is modulated to generate a PWM signal to drive the switching tube to be turned on or off and output a reference value of the dc-side voltage, the method further includes:

adding small disturbance at a direct current working point of electric vehicle charging equipment, and constructing a small signal model of an active power inner ring without considering the active and reactive coupling relation;

analyzing small signal models of a direct current side voltage loop, a voltage outer loop and an active power inner loop in a voltage and current double-closed loop, and determining the value range of the rotational inertia of the load virtual synchronous machine based on the stability of the direct current side voltage loop;

and further determining the value range of the rotational inertia and the value range of the damping coefficient in the value range of the rotational inertia of the load virtual synchronous machine based on the parameter characteristics of the rectification side system.

Preferably, the small signal model of the active power inner loop is shown as follows:

in the formula:

respectively corresponding to small disturbance quantities near the direct current working point; t is_m0The torque is the torque of the load virtual synchronous machine during steady-state work; t is_e0The electromagnetic torque is the electromagnetic torque of the load virtual synchronous machine during steady-state operation; omega₀The angular frequency of the output voltage when the load virtual synchronous machine works in a steady state; delta₀The power angle of the output voltage when the load virtual synchronous machine works in a steady state is used as the power angle of the output voltage; e₀The effective value of the internal potential is the effective value of the internal potential of the load virtual synchronous machine in a steady state; p_e0The active power is output when the load virtual synchronous machine works in a steady state; q₀The reactive power is output when the load virtual synchronous machine works in a steady state;

the small disturbance of the mechanical power of the virtual synchronous machine near a steady-state working point is loaded.

Preferably, the analyzing the dc-side voltage ring, the voltage outer ring in the voltage-current double closed loop, and the small signal model of the active power inner ring, and determining the value range of the rotational inertia of the load virtual synchronous machine based on the stability of the dc-side voltage ring include:

obtaining a closed loop transfer function of the power inner loop based on the small signal model of the active power inner loop, and designing the power inner loop as a critical damping system;

constructing a small signal model of a voltage outer ring based on a constraint relation between direct-current side current and power and load virtual synchronous machine electromagnetic power;

obtaining an open-loop transfer function at the rectifying side based on the small-signal model of the voltage outer ring and the closed-loop transfer function of the power inner ring;

analyzing the open-loop transfer function of the rectifying side based on the stability and amplitude-frequency characteristic curve of the direct-current side voltage loop to obtain the value range of the cut-off frequency;

and determining the value range of the rotational inertia of the load virtual synchronous machine based on the value range of the cut-off frequency.

Preferably, the closed loop transfer function of the power inner loop is shown as follows:

in the formula: g_VSM(s) is the closed loop transfer function of the power inner loop,

for small disturbance quantities of the actual active power on the ac side of the rectifier near the dc operating point,

for small disturbances of the mechanical power of the load virtual synchronous machine in the vicinity of the steady-state operating point, E₀Is the effective value of the internal potential omega of the load virtual synchronous machine in the steady state₀For the angular frequency of the output voltage during steady-state operation of the load virtual synchronous machine, D_pIs damping coefficient, X is the sum of impedance between the converter and AC system, J is moment of inertia, U_GThe effective value of the AC power grid phase voltage of the load virtual synchronous machine is obtained; zeta is damping ratio, omega_nIs a natural oscillation frequency;

wherein the natural oscillation frequency ω_nAnd a damping ratio ζ, calculated as:

preferably, the constraint relationship between the direct-current side current and power and the electromagnetic power of the load virtual synchronous machine is as follows:

in the formula: i is_dcThe total current flowing into the converter from the direct current bus; u shape_dcIs a dc bus voltage; r_invIs a rectifier side equivalent resistance; p_eIs the actual active power on the ac side of the rectifier.

Preferably, the small signal model of the voltage outer loop is as follows:

in the formula:

the small disturbance quantity of the direct current side voltage near a steady-state working point is obtained; u shape_dc0Is the initial value of the voltage on the dc side,

c is a small disturbance quantity of the actual active power of the alternating current side of the rectifier near a steady-state working point, and is a filter capacitor of the direct current side; r_invIs the rectifier side equivalent resistance.

Preferably, the open-loop transfer function of the rectifying side is as follows:

in the formula: g_Vo(s) is the complete open-loop transfer function on the commutation side, ω_nAt a nominal angular frequency, ω₀For the angular frequency, R, of the output voltage of the load virtual synchronous machine during steady-state operation_invIs a rectifier side equivalent resistance, k_pIs the voltage outer ring ratioExample section adjustment coefficient, k_iAdjusting coefficient of a reactive loop of a voltage outer loop integral link; zeta is damping ratio, C is filter capacitance on DC side, U_dc0Is the initial value of the dc side voltage.

Preferably, after constructing the small-signal model of the active power inner loop without considering the active and reactive coupling relations, the method further includes:

setting a droop coefficient of a reactive ring based on a power grid standard;

setting a reactive power regulation coefficient based on a constraint that a system loop gain amplitude is equal to 1 at a cut-off frequency;

and designing open-loop gain of the reactive loop based on the obtained droop coefficient of the reactive loop, and designing the turning frequency of the first-order low-pass filter based on the reactive regulation coefficient and the droop coefficient of the reactive loop.

Preferably, the turning frequency of the first-order low-pass filter is as follows:

in the formula: d_qIs the sag factor, f_LQIs the transition frequency, K, of a first-order low-pass filter_qIs a reactive power regulating coefficient.

Preferably, the inertia coefficient of the reactive loop is calculated according to the following formula:

in the formula: k_qFor the reactive regulation coefficient, f, of the loaded virtual synchronous machine_cqIs the cut-off frequency of the reactive loop, X is the sum of the impedances between the converter of the load virtual synchronous machine and the AC system, E₀Is the effective value of the internal potential of the load virtual synchronous machine in a steady state, U_gIs the effective value of the grid voltage, f₀At power frequency, D_qThe droop coefficient of the reactive ring of the load virtual synchronous machine is shown.

Preferably, the method further determines a value range of the moment of inertia and a value range of the damping coefficient in the value range of the moment of inertia of the load virtual synchronous machine based on the parameter characteristics of the rectification side system, and includes:

determining the stable condition of the active ring based on the open-loop transfer function and the closed-loop transfer function of the active ring of the load virtual synchronous machine;

obtaining a phase angle stability margin and an overshoot of the active loop based on the stability condition of the active loop;

determining the value range of the damping coefficient based on the value range of the phase angle stability margin of the active ring;

and further determining the value range of the moment of inertia based on the value range of the overshoot of the active ring.

Preferably, the open-loop transfer function and the closed-loop transfer function of the active ring of the load virtual synchronous machine are as follows:

in the formula: h_P(s) is the open loop transfer function of the active ring of the load virtual synchronous machine, G_P(s) is the closed-loop transfer function of the active ring of the load virtual synchronous machine, E_nIs the effective value of the neutral-point voltage fundamental wave, U, of the bridge arm of the load virtual synchronous machine_gAs effective value of the grid voltage, omega_nAt nominal angular frequency, J is moment of inertia, X_sIs the sum of the converter output impedance and the line impedance, D_pIs the damping coefficient.

Preferably, the active ring has a stable condition as shown in the following formula:

in the formula: e_nIs the effective value of the fundamental wave of the midpoint voltage of the bridge arm, U_gAs effective value of the grid voltage, omega_nAt nominal angular frequency, J is moment of inertia, X_sIs the sum of the converter output impedance and the line impedance, and Dp is a damping coefficient.

Preferably, the phase angle stability margin of the active loop is as follows:

in the formula: gamma is the phase angle stability margin; e_nThe effective value of the midpoint voltage fundamental wave of the bridge arm is obtained; u shape_gThe effective value of the voltage of the power grid is; omega_nIs the rated angular frequency; j is moment of inertia; x_sIs the sum of the converter output impedance and the line impedance; d_pIs the damping coefficient.

Preferably, when the phase angle stability margin of the active ring is 30 ° to 60 °, the value range of the damping coefficient is as follows:

preferably, the active loop overshoot is as follows:

in the formula: sigma% is the overshoot of the active loop; ζ is the damping ratio;

wherein

T_gAnd K_gIs a parameter defined in ζ; e_nThe effective value of the midpoint voltage fundamental wave of the bridge arm of the load virtual synchronous machine is obtained; u shape_gThe effective value of the voltage of the power grid is; omega_nIs the rated angular frequency; j is moment of inertia; x_sIs the sum of the converter output impedance and the line impedance; d_pIs the damping coefficient.

Preferably, the range of the moment of inertia is as follows:

in the formula: e_nThe effective value of the midpoint voltage fundamental wave of the bridge arm of the load virtual synchronous machine is obtained; u shape_gThe effective value of the voltage of the power grid is; omega_nIs the rated angular frequency; j is moment of inertia; x_sIs the sum of the converter output impedance and the line impedance; d_pIs the damping coefficient.

Preferably, after the value range of the moment of inertia is further determined based on the value range of the overshoot of the active ring, the method further includes:

measuring the rotational inertia of the load virtual synchronous machines with different power levels by using an inertia time constant;

drawing a root locus diagram based on the inertia time constant and the damping coefficient, and analyzing the root locus diagram to obtain the operation boundary of the active ring;

obtaining a critical value of a rotational inertia, a damping coefficient, a voltage outer ring proportion link regulating coefficient and a reactive ring regulating coefficient of a voltage outer ring integral link based on the operation boundary of the active ring and the obtained reference parameter of the electric vehicle charging equipment;

wherein, the reference parameter of the electric automobile charging equipment comprises: direct current side voltage, alternating current power grid voltage, rated power, rated frequency, direct current capacitor, direct current side resistance, filter inductance and inductance parasitic resistance.

Preferably, inertia time constants are used to measure the rotational inertia of the load virtual synchronous machine with different power levels according to the following formula:

in the formula: h is the time from the idle starting to the rated rotating speed of the load virtual synchronous machine under the rated torque; s_nThe rated capacity of the virtual synchronous machine is the load; j is moment of inertia, ω₀The angular frequency of the output voltage when the load virtual synchronous machine works in a steady state is adopted.

Compared with the prior art, the invention has the beneficial effects that:

(1) the charging circuit of the electric vehicle charging equipment adopts a two-pole converter circuit; the two-pole converter circuit comprises an active digital Vienna rectifier and a digital full-bridge LLC resonant converter, and the output voltage is DC 200V-750V.

(2) The technical scheme provided by the invention controls the active digital Vienna rectifier in the electric automobile charging equipment, and comprises the following steps: obtaining a given value of active power through PI control based on the direct current side voltage and a reference value of the direct current side voltage; the given value of the active power is controlled by an active control loop, a reactive control loop and a voltage and current double closed loop to obtain a reference instruction value of a current inner loop; after the reference instruction value of the current inner loop is compared with the current value of the feedback inductor, a voltage modulation wave signal is generated through a proportion link; and the voltage modulation wave signal is modulated to generate a PWM signal to drive the on-off of the switching tube, and a reference value of the direct current side voltage is output. The electric automobile charging equipment can autonomously participate in the operation and management of the power grid, and makes corresponding response under the abnormal conditions of power grid frequency/voltage and active/reactive power for coping with the dynamic adjustment of the power grid, so that the stability of the power grid frequency is improved.

(3) According to the technical scheme provided by the invention, a load virtual synchronous machine technology is adopted in electric vehicle charging equipment to simulate the swing characteristic of a synchronous motor, so that the load power can be controlled in real time according to the change of the frequency and the voltage of a power grid, and the stability of the frequency of the power grid is improved.

(4) According to the technical scheme provided by the invention, the electric vehicle charging equipment applying the load virtual synchronous machine technology converts the charging pile load response from a simple load shedding mode into an inertia supporting mode and a demand side scheduling mode, has a power following characteristic, can autonomously determine the amount and speed of absorbed power according to the state of a power grid, dynamically adjusts along with the power grid, and stabilizes the over-fast change of the state of the power grid, so that the stability of the frequency of the power grid is improved.

(5) According to the technical scheme provided by the invention, the inertia and the damping of the load virtual synchronous machine technology are utilized to improve the capability of an electric vehicle charging system for coping with the parameter change of a power grid; the electric vehicle charging equipment applying the load virtual synchronous machine technology has an inertia control mechanism, has torsion and damps oscillation, improves the self-adaptive capacity of regional loads under the abnormal conditions of voltage sag, frequency mutation and the like, reduces the impact of abnormal quitting of the loads on a power grid, and strengthens the perception and participation of the loads on the power grid, thereby realizing friendly interaction of the power grid and the loads and improving the stability, autonomy and friendliness of a power system.

Drawings

FIG. 1 is a flow chart of a control method of an electric vehicle charging apparatus according to the present invention;

FIG. 2 is a control structure diagram of the charging equipment of the electric vehicle based on the load virtual synchronous machine technology according to the present invention;

FIG. 3 is a power frequency small signal model of the electric vehicle charging equipment based on the load virtual synchronous machine technology according to the present invention;

FIG. 4 is a model diagram of an active loop power frequency small signal of an electric vehicle charging device of the present invention without consideration of a coupled load virtual synchronous machine technique;

FIG. 5 is a voltage outer loop control block diagram of an electric vehicle charging apparatus without consideration of the coupled load virtual synchronous machine technique of the present invention;

FIG. 6 is a voltage open loop amplitude-frequency characteristic curve of the electric vehicle charging apparatus of the load virtual synchronous machine technology of the present invention;

FIG. 7 is a reactive loop power frequency small signal model of an electric vehicle charging apparatus of the present invention without consideration of the coupled load virtual synchronous machine technique;

fig. 8 is an operation boundary of the electric vehicle charging equipment based on the load virtual synchronous machine technology according to the present invention.

Detailed Description

For a better understanding of the present invention, reference is made to the following description taken in conjunction with the accompanying drawings and examples.

The invention provides electric vehicle charging equipment based on a load virtual synchronous machine technology, aiming at the problem that a traditional charging pile cannot participate in power grid regulation.

The charging circuit of the electric automobile charging equipment of the load virtual synchronous machine adopts a two-pole converter circuit; the two-pole converter circuit comprises an active digital Vienna rectifier and a digital full-bridge LLC resonant converter. The active digital Vienna rectifier is a three-level voltage source type rectifier, adopts a load virtual synchronous machine technology combined with converter autonomous control, and is used for rectifying the power grid voltage into a direct current voltage of 400 VDC-800 VDC. The digital full-bridge LLC resonant converter is a three-level DC/DC direct-current voltage conversion circuit, and the output voltage of the three-level DC/DC direct-current voltage conversion circuit is 200 VDC-750 VDC.

Based on the same inventive concept, as shown in fig. 1, the present invention further provides a method for controlling an electric vehicle charging apparatus, for controlling an active digital vienna rectifier in the electric vehicle charging apparatus, comprising:

s1, obtaining a given value of active power through PI control based on the direct current side voltage and a reference value of the direct current side voltage;

s2, controlling the given value of the active power through an active control loop, a reactive control loop and a voltage and current double closed loop to obtain a reference instruction value of a current inner loop;

s3, comparing the reference instruction value of the current inner loop with the current value of the feedback inductor, and generating a voltage modulation wave signal through a proportion link;

and S4, the voltage modulation wave signal is modulated to generate a PWM signal to drive the switching tube to be switched on and off, and the reference value of the direct current side voltage is output.

Fig. 2 is a control structure diagram of an electric vehicle charging device based on a load virtual synchronous machine technology, and the control is mainly divided into five parts: direct current side voltage loop, rotor equation of motion, reactive loop, electromagnetic equation and current inner loop control.

The control method of the load virtual synchronous machine directly controls the output voltage and frequency through the active control loop and the reactive control loop, and unification of the off-grid and grid-connected control modes is achieved. The active control loop is essentially a rotor equation of motion, and is also called a rotor equation of motion control loop and an active power inner loop. In order to quickly and accurately control the voltage and the current of the system and improve the dynamic characteristics of the system, voltage and current double closed-loop control is further cascaded on the basis of a power loop of the load virtual synchronous machine. The essence of the voltage-current double closed-loop control is to introduce an electromagnetic equation, so the voltage-current double closed-loop control is also called an electromagnetic equation control loop. And the voltage and current double closed-loop control takes the reactive loop output voltage amplitude as a reference instruction value of the voltage outer ring, the reference instruction value of the voltage outer ring is compared with the fed-back capacitor voltage value, and the deviation is output as a reference instruction value of the current inner ring control after PI regulation. And comparing a reference instruction value controlled by the current inner loop with a current value of the feedback inductor, generating a voltage modulation wave signal through a proportion link (PR), and finally generating a PWM signal through modulation of the voltage modulation wave signal to drive the on-off of the switch tube. The non-difference regulation of an alternating current system is realized by combining abc-dq coordinate transformation with a PI regulator, and the cross decoupling of the d-axis electric quantity and the q-axis electric quantity is realized by coupling item feedback.

S1, obtaining the given value of active power through PI control based on the direct current side voltage and the reference value of the direct current side voltage, and the method comprises the following steps:

the active digital Vienna rectifier is controlled by combining a load virtual synchronous technology with a converter autonomous control, in the load virtual synchronous machine technology, the voltage on the direct current side is controlled by a PI to obtain a direct current given value, and the direct current given value is multiplied by the inverse number of the voltage given value to obtain a given value P of active power_m：

P_m＝-U_dc ^*(U_dc ^*-U_dc)(K_p+K_i/s) (1)

Wherein, P_mThe method comprises the following steps of (1) setting a given value of active power of a load virtual synchronous machine; u shape_dc ^*The reference value is the DC side voltage of the load virtual synchronous machine; u shape_dcThe voltage of the direct current side of the virtual synchronous machine is a load; k_pAnd K_iProportional and integral coefficients of a direct-current side voltage loop PI controller of the load virtual synchronous machine are respectively; s is the laplace transform of the time domain equation.

S2, the given value of the active power is controlled by an active control loop, a reactive control loop and a voltage and current double closed loop to obtain a reference instruction value of a current inner loop, and the reference instruction value comprises the following steps:

the active loop control of the control method of the load virtual synchronous machine adopts an electromechanical transient equation of a synchronous motor in the control link of a converter, and a mechanical motion equation can be expressed as follows:

wherein: j is the moment of inertia of the load virtual synchronous machine, kg.m 2; omega is mechanical angular velocity, namely the electrical angular velocity of the load virtual synchronous machine, rad/s; omega_nIs the synchronous angular velocity of the power grid, rad/s; t is_m、T_eAnd T_dMechanical torque, electromagnetic torque and damping torque of the load virtual synchronous machine, N.m, T₀A rated torque command, N · m; Δ T is a frequency deviation feedback command, N · m; d_pThe damping coefficient is N.m/s/rad of the load virtual synchronous machine.

The active loop part control algorithm of the direct power control mode is as follows:

wherein, P_eFor loading the virtual synchronous machine active power actual value, P_mThe reference value is the mechanical power of the virtual synchronous machine of the load, and theta is the phase angle, rad, of the virtual synchronous machine of the load.

By introducing a rotor motion equation, obtaining a phase angle theta of the load virtual synchronous machine in an active ring:

θ＝(P_m-P_e+D_pω_n)/s/(Js+D_p) (4)

in the reactive loop control of the load virtual synchronous machine control method, a synchronous motor exciting current control method is simulated, and a control equation of the midpoint voltage of a bridge arm of a rectifier can be obtained as follows:

wherein: e is the effective value of the output phase voltage of the bridge arm of the rectifier, namely the effective value of the electromotive force of the virtual synchronous machine of the load; u shape_refThe reference voltage effective value is the capacitance reference voltage effective value of the load virtual synchronous machine rectifier; u shape₀The effective value of the actual capacitor voltage of the load virtual synchronous machine is the effective value of the output voltage of the load virtual synchronous machine; g(s) is the transfer function of the load virtual synchronizer power control regulator. Compared with the active control loop of the rectifier, the excitation control link can be analogized to an inertia integral link in the active loop, and meanwhile, in order to realize no-difference regulation, a PI controller is selected for G(s).

The primary voltage regulation equation for a synchronous generator is as follows:

wherein: q_eThe reactive power is actually output by the load virtual synchronous machine; q_refA reactive instruction of an alternating current interface of the load virtual synchronous machine; d_qThe reactive-voltage droop coefficient of the load virtual synchronous machine is obtained; u shape_nThe load virtual synchronous machine outputs a rated effective value of voltage.

The two equations of the formula (5) and the formula (6) are combined to eliminate the common variable U_refAfter that, there are

Considering the similarity with the active loop control structure, let D_q/G(s)＝K_qs，K_qFor the excitation regulation coefficient, i.e. the reactive regulation coefficient, of the load virtual synchronous machine, equation (7) can be written as

The output voltage amplitude of the rectifier is obtained by simulating the reactive loop of the synchronous motor:

wherein: e_mThe effective value of the electromotive force of the virtual synchronous machine of the load.

The phase angle value theta calculated by the active control loop and the voltage value E calculated by the reactive control loop_mThree-phase modulation wave signal for constructing load virtual synchronous control algorithm, abc three-phase modulation signal E_am、E_bm、E_cmThe expression is as follows:

the electromagnetic equation of the load virtual synchronous machine can be expressed as:

i_abc＝(e_abc-u_abc)/(Ls+R) (11)

wherein e is_abcLoad virtual synchronous machine potential, i.e. rectifier port voltage; wherein e_abc＝E_am+E_bm+E_cm；u_abcThe method comprises the following steps of (1) loading a machine end voltage of a virtual synchronous machine, namely a PCC three-phase voltage; i.e. i_abcOutputting current, namely three-phase alternating-current side current, for the load virtual synchronous machine; l is the stator inductance of the load virtual synchronous machine, namely the filter inductance of the port of the rectifier; and R is the resistance of the load virtual synchronous machine, namely the parasitic resistance of the port filter of the rectifier.

According to kirchhoff principle, the electromagnetic equation of the load virtual synchronous machine is expressed as:

the synchronous motor adjusts the reactive output and the terminal voltage thereof through the excitation controller. Similarly, the virtual potential E of the virtual synchronous machine model can be adjusted by adjusting the load_pTo regulate its terminal voltage and reactive power. Virtual potential instruction E of load virtual synchronous machine_pThe method comprises the following steps: no-load potential E of the motor₀Reactive power regulation potential delta E_QAnd the voltage regulation potential Delta E at the end of the reactor_U。

The virtual potential of the load virtual synchronous machine is as follows:

E_p＝E₀+ΔE_Q+ΔE_U(13)

reactive power regulated partial potential Δ E_QExpressed as:

ΔE_Q＝K_q(Q_ref-Q_e) (14)

wherein, K_qFor loading virtual synchronous machine excitation regulating coefficient, i.e. reactive regulating coefficient, Q_refFor loading reactive commands, Q, of the AC interface of a virtual synchronous machine_eInstantaneous reactive power, Q, output at the AC interface terminal of a load virtual synchronous machine_eExpressed as:

wherein: u. of_a、u_bAnd u_cThe three-phase machine terminal voltages of the load virtual synchronous machine are respectively;

reactor terminal voltage regulation potential Delta E_U，ΔE_UEquivalent to an automatic excitation regulator (AVR) of a load virtual synchronous machine, wherein the AVR is simplified into a proportional link, and then the delta E is calculated_UExpressed as:

ΔE_U＝D_q(U_ref-U_n) (16)

wherein, U_refAnd U is the instruction value and the true value of the effective value of the terminal line voltage of the load virtual synchronous machine, D_qAnd adjusting the voltage regulating coefficient of the load virtual synchronous machine, namely the droop coefficient of the reactive ring of the load virtual synchronous machine.

Obtaining a reference value i of the current of the load virtual synchronous machine according to an electromagnetic equation_abcrefAnd under the action of the PR controller, a three-phase modulation signal is obtained, so that the on-off of a switching tube of the rectifier is controlled. The actual value of the current tracks the given value quickly and accurately, and the harmonic current of the power grid interaction current can be effectively reduced.

In the current inner ring control in the load virtual synchronous machine technology, when the loss of a converter reactor is ignored and a power grid connected with a rectifier is considered as an infinite system, the famous value active power P and the reactive power Q transmitted between an alternating current power grid and the rectifier are respectively

In the formula: u shape_GThe effective value of the AC power grid phase voltage of the load virtual synchronous machine is obtained; e is the effective value of the voltage of the alternating current side phase of the load virtual synchronous machine rectifier; delta is U_GAnd E; and X is the sum of the impedances between the load virtual synchronous machine converter and the alternating current system.

The steady-state components and the secondary disturbance in the equations (2), (3) and (17) are eliminated, and the phase difference between the AC side voltage of the converter and the grid voltage in the steady-state condition is not large, and the following approximate relationship is considered: sin delta_n≈δ_n，cosδ_n≈1，U₀E is approximately distributed, direct current quantity is eliminated on two sides of an equation, disturbance quantity more than two times is ignored, and a small signal model of the active power inner ring load virtual synchronous machine without considering the active and reactive coupling relation is obtained, wherein the expression is as follows:

in the formula (I), the compound is shown in the specification,

respectively corresponding to small disturbance quantities near the direct current working point; t is_m0、T_e0、ω₀、δ₀、E₀、P_e0、Q₀Respectively setting torque, electromagnetic torque, angular frequency of output voltage, power angle, effective value of midpoint voltage of a bridge arm, and output active power and reactive power when the load virtual synchronous machine works in a steady state;

small disturbance of mechanical power of the load virtual synchronous machine near a steady-state working point; e₀The effective value of the internal potential is the effective value of the internal potential when the load virtual machine is in a steady state. For time after linearizationThe domain equation is subjected to laplace transform, and a transfer function block diagram of the power inner loop can be obtained as shown in fig. 3.

In the load virtual synchronization technology, the coupling between the active loop and the reactive loop is weak, and the active loop and the reactive loop can be approximately considered as decoupling, so that the parameters of the active loop and the reactive loop can be respectively and independently designed. The analysis of the active loop is performed through two aspects of the voltage outer loop and the power inner loop.

From fig. 4, the closed loop transfer function of the power inner loop can be calculated:

wherein the natural oscillation frequency and the damping ratio are

The power inner loop open loop transfer function is an I-type system, and the mechanical power P can be realized as long as the system is stable_mFor electromagnetic power P_eNo difference control of (2). The method is characterized in that a load virtual synchronous machine technology is adopted, parameters of the load virtual synchronous machine can be adjusted randomly within a reasonable range without being limited by a physical system, and an inner ring is designed into a critical damping system.

According to the conservation of power, when the influence of the parasitic resistance of the converter reactor is neglected, the power on the direct current side should be equal to the power on the alternating current side. DC side current and power and load virtual synchronous machine electromagnetic power P_eThere are the following constraints:

in the formula: i is_dcRepresenting the total current flowing into the converter from the direct current bus; u shape_dcRepresents the dc side voltage; r_invIs a rectifier side equivalent resistance; p_eThe power of the alternating current side of the rectifier is also the electromagnetic power of the load virtual synchronous machine.

Establishing P from equation (21)_eAnd a DC side voltage U_dcSmall signal mode ofType and transfer function:

thus, a transfer function block diagram of the voltage outer loop of the coupled load virtual synchronous machine technology electric vehicle charging equipment without considering the active and reactive coupling relation is obtained as shown in fig. 5.

From the control block 5, a complete open-loop transfer function on the rectification side can be obtained as

Cut-off frequency omega of open-loop transfer function for ensuring stability of DC-side voltage loop_cThe frequency response curve is in a slope section of-20 dB; in addition, in order to reduce the influence of high frequency noise on system control, the gain of the high frequency band should be rapidly attenuated. According to the open-loop amplitude-frequency characteristic curve of FIG. 6, k can be taken_i/k_p＜ω_c＜ω_n，ω_nThe cross-over frequency of the power inner loop second-order system is also the natural oscillation frequency. According to the formula (20) for calculating the natural oscillation frequency, the value of the inertia coefficient J of the load virtual synchronous machine should satisfy:

as can be seen from equations (9) and (18), the transfer function block diagram of the reactive loop of the electric vehicle charging installation without consideration of the coupled load virtual synchronous machine technology is shown in fig. 7.

As can be seen from FIG. 7, the reactive ring contains a proportional link 3 (2E)₀-U_G) the/X and first-order low-pass filtering link is 0.707/(K)_qs+D_q). Wherein the sag factor D of the reactive ring_qDetermining open loop gain and reactive power regulation coefficient K of reactive power loop_qAnd sag factor D of the reactive ring_qDetermining the turning frequency f of a first-order low-pass filter_LQThe expression is

Wherein D_qDetermined by grid standards, and hence by design K_qThe system meets the requirements of stability and dynamic performance, and because the first-order low-pass filtering link in the reactive loop introduces-90 DEG phase shift at the position of cut-off frequency at most, the phase angle margin of the reactive loop is 90 DEG at least, the phase angle margin requirement is always met, and K is solved only according to the constraint that the system loop gain amplitude is equal to 1 at the cut-off frequency_qAnd (4) finishing. At the reactive loop cut-off frequency f_cqHere, the magnitude of the loop gain of the system is equal to 1, which is obtained according to equation (25):

the equation (25-1) is discussed in two cases:

1) if the expression result in the root is greater than zero, K can be calculated according to the expression (25-1)_qIt should be noted that, in order to suppress the influence of the double power frequency pulsating quantity in the instantaneous reactive power on the amplitude of the output voltage, the cut-off frequency f of the reactive loop_cqTypically within 2 times the power frequency of 1/10.

2) And if the expression result in the root sign is less than zero, the reactive loop does not have cut-off frequency, and the loop gain of the reactive loop is lower than 0dB in the full frequency band. In order to meet the requirement of inhibiting the double power frequency pulsating quantity in the reactive power, the turning frequency f of a first-order low-pass filter in the reactive loop_LQGenerally, within 1/10 of 2 times the power frequency, there are:

in the formula f₀Is the power frequency.

The formula (25-2) can be obtained by arranging:

the latter stage digital full bridge LLC resonant conversion circuit is realized by voltage and frequency droop control.

Generally, the inertia time constant H is used to measure the inertia of synchronous generators of different power levels. Wherein H is defined as

In the formula, S_nThe rated capacity of the virtual synchronous machine is the load; h is the time of the load virtual synchronous machine from the static starting to the rated rotating speed under the rated torque without load.

The following description will be made of the operation boundaries H and D of the electric vehicle charging apparatus using the load virtual synchronous machine technique_pAnd (5) determining a value range.

Open loop transfer function H of active ring of load virtual synchronous machine_P(s) and closed loop transfer function G_P(s) are respectively as follows:

wherein E is_nIs the effective value of the fundamental wave of the midpoint voltage of the bridge arm, U_gAs effective value of the grid voltage, omega_nAt nominal angular frequency, J is moment of inertia, X_sIs the sum of the converter output impedance and the line impedance.

The stable conditions of the active loop are known by the Laus judge to be:

namely, it is

The phase angle stability margin of the active ring is obtained as follows:

when the phase angle margin gamma is 30 DEG to 60 DEG, satisfactory performance can be obtained, i.e.

The overshoot of the active ring is expressed as

Wherein

When zeta is 0.4-0.8, sigma% is 1.5-25.4%

Standard EN50438 specifies the condition of a micro power plant in parallel with a public low-voltage distribution network as follows: the frequency of the power grid voltage is between 49Hz and 51Hz, and the amplitude of the power grid voltage is between 90 percent and 110 percent of the rated voltage amplitude. According to the requirements of the standard, D_pThe design principle of (2) is as follows: the voltage frequency of the power grid changes by 1Hz, and the output active power of the converter changes by 100 percent (10 kW). Then there is D_p≤5。

In summary, after converting J to H, the operation boundary of the active loop is determined as shown by the shaded portion in fig. 8, and the damping coefficient D in fig. 8_pThe value of (2) is obtained according to a formula (30), and the value range of the boundary is further narrowed according to the requirement of power grid adjustment and characteristic parameters.

Reference parameters in the table are taken and respectively correspond to the moment of inertia J and the damping coefficient D_pVoltage outer ring proportion link regulating coefficient K_pReactive ring adjusting coefficient K of voltage outer ring integral link_iAnalyzing the root locus diagram as a parameter to obtain a critical value of the moment of inertia J of 0.722 damping coefficient D_pTaking a critical value of 1.39 and a voltage outer ring proportion link adjustment coefficient K_pTaking a critical value of 1.39 and a reactive loop regulation coefficient K of a voltage outer loop integral link_iWhen the critical value is 30.1, U_dcThe step response curve is in full agreement with the stable condition of the root trajectory analysis.

Basic parameter table of electric vehicle charging equipment based on load virtual synchronous machine technology

The electric automobile charging equipment based on the load virtual synchronous machine technology is different from the electric automobile charging equipment applying conventional rectification control, power grid frequency and voltage information is introduced, and the capability of an electric automobile charging system for coping with power grid parameter changes is improved by utilizing inertia and damping of the load virtual technology.

The electric vehicle charging equipment can be a charging pile.

The concept of the present invention is different from the paper published by rivason entitled "research on charging key technologies of electric vehicles", in that: the thesis of electric vehicle charging key technology research does not take the algorithm and performance of a load virtual synchronous machine as main research objects, focuses more on optimizing and improving the circuit of the direct-current part of the electric vehicle charging pile, a half-bridge LLC resonant converter is adopted in the fourth chapter, detailed analysis is carried out on the performance of the part, the voltage output realized by the charging pile in the thesis is DC48V, the direct-current part in the application adopts a full-bridge LLC resonant converter, and the voltage output realized by the charging pile is DC 200V-750V.

As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

The present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the scope of the claims of the present invention which are filed as the application.

Claims

1. The utility model provides an electric automobile equipment of charging based on virtual synchrodyne technique of load which characterized in that includes: the charging circuit of the electric vehicle charging equipment adopts a two-pole converter circuit; the two-pole converter circuit comprises an active digital Vienna rectifier and a digital full-bridge LLC resonant converter.

2. The electric vehicle charging apparatus of claim 1, wherein the active digital vienna rectifier is a three-level voltage source type rectifier, employing load virtual synchronous machine technology in combination with converter autonomous control, for rectifying the grid voltage to a dc voltage of 400VDC to 800 VDC.

3. The electric vehicle charging apparatus of claim 1, wherein the digital full bridge LLC resonant converter is a three-level DC/DC voltage conversion circuit, the three-level DC/DC voltage conversion circuit outputting a voltage of 200VDC to 750 VDC.

4. A control method for electric vehicle charging equipment based on a load virtual synchronous machine technology is characterized in that an active digital Vienna rectifier in the electric vehicle charging equipment is controlled, and the method comprises the following steps:

5. The method of claim 4, wherein the given value of active power is calculated as:

P_m＝-U_dc ^*(U_dc ^*-U_dc)(K_p+K_i/s)

6. The method of claim 4, wherein the obtaining the reference command value of the current inner loop by controlling the active control loop, the reactive control loop and the voltage-current double closed loop according to the given value of the active power comprises:

7. The method of claim 6, wherein the introducing a rotor motion equation in an active control loop based on the given value of the active power to obtain the power angle of the load virtual synchronous machine comprises:

8. The method of claim 7, wherein the control algorithm of the active control loop is represented by the following equation:

θ＝(P_m-P_e+D_pω_n)/s/(Js+D_p)

9. The method of claim 6, wherein obtaining the output voltage amplitude of the reactive control loop based on the obtained actual value of the reactive power of the load virtual synchronous machine and the actual effective value of the capacitor voltage comprises:

10. The method of claim 6, wherein constructing the electromagnetic equation in a voltage current double closed loop based on the reactive control loop output voltage magnitude and the power angle of the load virtual synchronous machine comprises:

11. The method of claim 10, wherein the electromagnetic equation is expressed as:

i_abc＝(e_abc-u_abc)/(Ls+R)

12. The method of claim 10, wherein the virtual potential of the load virtual synchronous machine is as follows:

E_p＝E₀+ΔE_Q+ΔE_U

in the formula: e_pTo load the virtual potential of a virtual synchronous machine, E₀Is the effective value of the internal potential, delta E, of the load virtual synchronous machine in a steady state_QAdjusting the potential, Delta E, for reactive power of a load virtual synchronous machine_UAdjusting the potential for the reactor terminal voltage of the load virtual synchronous machine;

wherein the content of the first and second substances,potential delta E for reactive power regulation of the load virtual synchronous machine_QAs shown in the following formula:

ΔE_Q＝K_q(Q_ref-Q_e)

ΔE_U＝D_q(U_ref-U_n)

13. The method of claim 4, wherein the voltage modulation wave signal is modulated to generate a PWM signal to drive the switching tube to be switched on and off, and after outputting the reference value of the DC side voltage, the method further comprises:

14. The method of claim 13, wherein the small signal model of the active power inner loop is represented by:

in the formula:

15. The method of claim 13, wherein analyzing the small-signal models of the dc-side voltage loop, the voltage outer loop in the voltage-current double closed loop, and the active power inner loop, and determining the range of the moment of inertia of the loaded virtual synchronous machine based on the stability of the dc-side voltage loop comprises:

16. The method of claim 15, wherein the closed loop transfer function of the power inner loop is represented by:

for small disturbances of the mechanical power of the load virtual synchronous machine in the vicinity of the steady-state operating point, E₀Is the effective value of the internal potential omega of the load virtual synchronous machine in the steady state₀For the angular frequency of the output voltage during steady-state operation of the load virtual synchronous machine, D_pIs damping coefficient, X is the sum of impedance between the converter and AC system, J is moment of inertia, U_GThe effective value of the AC power grid phase voltage of the load virtual synchronous machine is obtained; zeta dampingRatio, ω_nIs a natural oscillation frequency;

17. the method of claim 15, wherein the constraint relationship between the dc-side current and power and the electromagnetic power of the load virtual synchronous machine is as follows:

18. The method of claim 15, wherein the small signal model of the voltage outer loop is represented by:

in the formula:

19. The method of claim 15, wherein the open loop transfer function of the rectifying side is represented by the following equation:

in the formula: g_Vo(s) is the complete open-loop transfer function on the commutation side, ω_nAt a nominal angular frequency, ω₀For the angular frequency, R, of the output voltage of the load virtual synchronous machine during steady-state operation_invIs a rectifier side equivalent resistance, k_pAdjusting the coefficient, k, for the voltage outer loop proportional element_iAdjusting coefficient of a reactive loop of a voltage outer loop integral link; zeta is damping ratio, C is filter capacitance on DC side, U_dc0Is the initial value of the dc side voltage.

20. The method of claim 13, wherein after constructing the small-signal model of the active power inner loop without taking into account active and reactive coupling relationships, further comprising:

setting a droop coefficient of a reactive ring based on a power grid standard;

21. The method of claim 20, wherein the first order low pass filter has a transition frequency as follows:

in the formula: d_qIs the sag factor, f_LQIs the transition frequency, K, of a first-order low-pass filter_qIs the inertia coefficient of the reactive loop.

22. The method of claim 20, wherein the reactive power regulation factor is calculated as:

23. The method of claim 13, wherein the further determining a range of the moment of inertia and a range of the damping coefficient based on the parameter characteristics of the rectifier-side system over the range of the moment of inertia of the virtual synchronous machine of the load comprises:

24. The method of claim 23, wherein the open-loop transfer function and the closed-loop transfer function of the active loop of the load virtual synchronous machine are expressed by the following equations:

in the formula: h_P(s) is the open loop transfer function of the active ring of the load virtual synchronous machine, G_P(s) is the closed-loop transfer function of the active ring of the load virtual synchronous machine, E_nIs the effective value of the fundamental wave of the midpoint voltage of the bridge arm, U_gAs effective value of the grid voltage, omega_nAt nominal angular frequency, J is moment of inertia, X_sIs the sum of the converter output impedance and the line impedance, D_pIs the damping coefficient.

25. The method of claim 23, wherein the active loop is stabilized under the following formula:

in the formula: e_nIs the effective value of the fundamental wave of the midpoint voltage of the bridge arm, U_nAs effective value of the grid voltage, omega_nAt nominal angular frequency, J is moment of inertia, X_sIs the sum of the converter output impedance and the line impedance, D_pIs the damping coefficient.

26. The method of claim 23, wherein the phase angle stability margin of the active loop is as follows:

27. The method of claim 26, wherein when the phase angle stability margin of the active loop is 30 ° to 60 °, the damping coefficient is in a range as follows:

28. the method of claim 23, wherein the active loop overshoot is represented by the following equation:

wherein

T_gAnd K_gAre all intermediate variables in the zeta damping ratio; e_nThe effective value of the midpoint voltage fundamental wave of the bridge arm of the load virtual synchronous machine is obtained; u shape_gThe effective value of the voltage of the power grid is; omega_nIs the rated angular frequency; j is moment of inertia; x_sIs the sum of the converter output impedance and the line impedance; d_pIs the damping coefficient.

29. The method of claim 23, wherein the range of values of the moment of inertia is as follows:

30. The method of claim 23, wherein after further determining a value range of the moment of inertia based on the value range of the active loop overshoot, the method further comprises:

31. The method of claim 30, wherein the moment of inertia of the loaded virtual synchronous machine at different power levels is measured using an inertia time constant as follows: