CN112255453A - V2G-oriented electric automobile bidirectional electric energy metering method - Google Patents

Abstract

The invention provides a V2G-oriented bidirectional electric energy metering method for an electric automobile, and belongs to the field of electric energy metering of electric automobiles. The method comprises the following steps: establishing a bidirectional interaction model of the electric automobile connected to a power grid; wherein the two-way interaction model comprises: grid voltage u (t), grid line load Z_l1、Z_l2、Z_l3Other loads Z in the power grid, electric automobile bidirectional inverter, electric automobile battery electromotive force E and electric automobile internal load Z_ev(ii) a Network voltage series connection Z_l2、Z_l3Then, the two-way inverter of the electric automobile is connected, Z_evE is connected in series and then connected in parallel with two ends of a bidirectional inverter of the electric automobile, Z and Z_l1After being connected in series, the two ends of the grid voltage are connected in parallel; and determining the electric energy measured during charging and the electric energy measured during discharging of the electric automobile under the distortion signal according to the established two-way interaction model. By adopting the invention, the aberration of the electric automobile can be realizedAnd bidirectional electric energy metering during charging and discharging under variable signals.

Description

V2G-oriented electric automobile bidirectional electric energy metering method

Technical Field

The invention relates to the field of electric automobile electric energy metering, in particular to a V2G-oriented electric automobile bidirectional electric energy metering method.

Background

The environmental and resource problems generated by the traditional fuel oil automobile are increasingly prominent, the fuel oil automobile is limited by successive strict measures in each country, and the new energy automobile plays an important role in relieving the pressure of oil shortage, reducing the emission of automobile tail gas, and promoting the transformation and upgrading of the automobile manufacturing industry and the sustainable development of the transportation industry. However, large-scale electric vehicle access to the grid also presents several challenges to the operation of the grid.

The electric Vehicle networking technology (V2G) describes a system in which an electric Vehicle is connected to a power Grid for bidirectional charging and discharging. The electric automobile can be used as a load to influence the power grid on one hand, and can be used as distributed energy storage equipment to provide electric energy for other users of the power grid during power utilization peak on the other hand. At present, the V2G technology has been widely concerned by scholars at home and abroad, and has achieved a series of achievements. Most researchers focus on intelligent scheduling, battery life, charging and discharging strategies and the like, and few documents relate to the problem of electric energy metering of V2G charging and discharging. Due to the nonlinear characteristic of a charging and discharging system of the electric automobile, the current electric energy metering method has unreasonable problems, and according to statistics of an electric power department, each charging pile has about 5% -30% of electric energy loss (the electric meter count is inconsistent with the charging amount of the electric automobile), and the reason is that the current electric energy meter metering principle is based on sine signal hypothesis. However, a large number of nonlinear loads are connected to the power grid nowadays, so that distorted signals exist in the power grid. The fundamental wave meter has not been able to meet the power metering in the current grid environment. Harmonic power is negative and is fed back to the power grid to become power grid garbage, the part of electric energy is converted from fundamental wave electric energy which is extracted from the power grid by the nonlinear load, the part of electric energy is useless and harmful, and the current electric energy metering method deducts the part of electric energy from the fundamental wave electric energy which is extracted from the power grid by the nonlinear load. At present, most electric vehicle charging models established by vast scholars at home and abroad are used for analyzing the influence of electric vehicles on a power grid or the aspects of optimized dispatching, economic benefit and the like of the power grid. These models are all built from a system perspective and cannot be used directly for power metering.

The signal types in the current power grid are very complex due to the access of a large number of nonlinear loads. Besides harmonic signals and simple harmonic signals, distortion signals of other forms exist in the power grid, and especially unstable distortion signals such as impact signals cannot be described by a harmonic model at all. Typical unsteady distortion signals in the grid are surge signals and ripple signals, assuming that for the kth surge or ripple, the current i in the grid circuit_k(t) is

i_k(t)＝(1+α_k(t))I_mk sin(ω₀t+φ_k) (1)

In the formula, alpha_k(t) is the kth impact function, I_mk、φ_kCurrent amplitude and current phase, omega, respectively₀And t represents the time, which is the standard power frequency angular frequency. For the convenience of metering, the zero point of the metering time is alpha_kThe time at which (t) occurs is standard. If the signal is an impulsive signal, alpha_k(t) can be approximately represented as

Wherein M is_k＞0 (2)

In the formula, M_kThe amplitude of the k-th impact signal is obtained; t is t_kThe duration of the kth impact signal;

if the signal is a wobble signal, α_k(t) can be approximately represented as

In the formula, M_kIs the amplitude of the kth fluctuation signal; t is t_kThe kth wobble signal duration.

Since the time at which the fluctuations occur is uncertain, the duration t_kIs random. When M is_kWhen the voltage is more than 1, the amplitude of the fluctuation current is more than that of the fundamental wave current, and the voltage drops; when M is_k<At 1, the amplitude of the ripple current is smaller than that of the fundamental current, and the voltage rises.

Under the condition of distorted signals, the voltage u (t) at a certain metering point in the power grid and the current i (t) flowing into the metering point can be expressed by the following formula:

u(t)＝u_I(t)+u_S(t) (4)

i(t)＝i_I(t)+i_S(t) (5)

in the formula u_I(t)、u_S(t) fundamental voltage and distortion voltage at the measurement point, i_I(t)、i_S(t) are the fundamental current and the distortion current at the metering point, respectively.

On the basis, scholars establish a charging model and a discharging model of the electric automobile in a power grid, and provide an electric energy metering formula during charging or discharging.

Taking the charging of the electric vehicle in the power grid as an example, fig. 1 is a charging model of the electric vehicle in the power grid. As shown in fig. 1, the left side of the circuit is a Power grid (Power grid) simplified model. u (t) is the grid instantaneous voltage; i (t) is the instantaneous current in the line; z_lAs a line load on the grid side during charging; on the right side of the circuit, an electric vehicle (electric vehicle) simplified model is provided, and the electric vehicle is equivalent to a pure load Z during charging. The design time is T, and for the sake of discussion, T is assumed to be N.T₀，T₀The fundamental wave period is N, which represents the number of impacts/undulations and is an integer. At the kth impact or surge, the instantaneous power p at point a is measured_ak(t) is

p_ak(t)＝u_ak(t)·i_k(t) (6)

In the formula u_ak(t) represents the point voltage at metering point a at the kth bump or surge; u. of_ak(t) represents the voltage at the kth shock or fluctuation metering point a;

combining the formulas (4) and (5), one can obtain

Wherein, U_akI(t) is the fundamental voltage at the metering point a at the time of the kth surge or fluctuation, i_kI(t) is the fundamental current at the kth surge or surge, u_akS(t) is the distortion voltage at the metering point a at the kth impact or fluctuation, i_kS(t) is a distortion current at the time of the kth impact or fluctuation.

So the average power (active power) P at the metering point a at the kth surge or fluctuation_akComprises the following steps:

in the formula, P_akI、P_akIs、P_aksI、P_aksThe fundamental wave power at the point a, the power generated by the action of the fundamental wave voltage and the distortion current, the power generated by the action of the distortion voltage and the fundamental wave current and the distortion power are measured when the shock or the fluctuation occurs at the kth time respectively.

Assuming that there are N impacts or fluctuations within the power metering time T, where N is a random positive integer, the average power P at the metering point a_aComprises the following steps:

in the formula, P_I、P_IS、P_SI、P_SAnd respectively measuring the fundamental wave power at the point a, the power generated by the action of the fundamental wave voltage and the distortion current, the power generated by the action of the distortion voltage and the fundamental wave current and the distortion power.

Various researches are integrated, and the conclusion that the electric automobile is connected in the power grid for charging is obtained:

P_Igreater than 0, fundamental waveThe power generated by the voltage and the fundamental wave current is positive, that is, the fundamental wave power is positive, which indicates that the electric energy generated by the fundamental wave power belongs to the electric energy absorbed by the electric vehicle from the power grid during the charging time of the electric vehicle in the power grid.

P_ISNot less than 0, the power generated by the fundamental voltage and the distortion current is not negative (only containing the harmonic wave is 0), namely the electric energy absorbed by the electric automobile from the power grid.

P_SIThe power generated by the distortion voltage and the fundamental wave current is not positive (0 when only the harmonic wave is contained), which indicates that the part of electric energy flows into the power grid, but is fed back to the power grid in a mode of the fundamental wave current, and the power grid is not polluted.

P_S<0, the distortion power is negative, and the part of electric energy also flows into the power grid and is fed back to the power grid in a distortion current mode to pollute the power grid. The part of electric energy is not ignored, and is charged by the user of the electric automobile without metering.

In combination with the above analysis, the power to be measured when the electric vehicle is charged in the power grid is as follows:

P＝P_I+P_IS+P_SI (10)

＝(P_I+P_IS+P_SI+P_S)-P_S

＝P_a-P_S

where P represents the total power that should be metered;

in fact, the process of discharging the electric vehicle on the power grid is opposite to that of charging the electric vehicle, and the influence of the distorted signal on the circuit needs to be considered. However, the above-mentioned energy metering formula is only applicable to the case where the electric vehicle is only charged or only discharged in the grid. The charging and discharging behaviors of the electric automobile connected in the power grid have higher randomness, and the establishment of a uniform two-way interaction model has more practical significance for V2G electric energy metering.

In the prior art, a charging model and a discharging model of an electric vehicle in a power grid are established, and an electric energy metering formula during charging or discharging is provided, but the electric energy metering modes have limitations and are only suitable for the situation that the electric vehicle is only charged or only discharged in the power grid. At present, a bidirectional interaction model aiming at electric automobile electric energy metering does not exist, and charging and discharging bidirectional electric energy metering cannot be realized.

Disclosure of Invention

The embodiment of the invention provides a V2G-oriented bidirectional electric energy metering method for an electric vehicle, which can realize bidirectional electric energy metering during charging and discharging of the electric vehicle under a distorted signal. The technical scheme is as follows:

the embodiment of the invention provides a V2G-oriented bidirectional electric energy metering method for an electric vehicle, which comprises the following steps:

establishing a bidirectional interaction model of the electric automobile connected to a power grid; wherein the two-way interaction model comprises: grid voltage u (t), grid line load Z_l1、Z_l2、Z_l3Other loads Z in the power grid, electric automobile bidirectional inverter, electric automobile battery electromotive force E and electric automobile internal load Z_ev(ii) a Network voltage series connection Z_l2、Z_l3Then, the two-way inverter of the electric automobile is connected, Z_evE is connected in series and then connected in parallel with two ends of a bidirectional inverter of the electric automobile, Z and Z_l1After being connected in series, the two ends of the grid voltage are connected in parallel;

and determining the electric energy measured during charging and the electric energy measured during discharging of the electric automobile under the distortion signal according to the established two-way interaction model.

Further, under the condition of the distorted signal, the grid voltage u (t) is:

u(t)＝U_m sin(ω₀t+ψ_k)

wherein, U_mIs the grid voltage amplitude; omega₀Is the standard power frequency angular frequency; psi_kVoltage phase for the kth surge or fluctuation; t is the time.

Furthermore, in the power grid, at Z_l2、Z_l3The point on the line between is the metering point a;

is provided with Z_l2、Z_l3Are all pure resistive loads R_lWhen the electric automobile is charged in the power grid or the electric automobile is discharged into the power grid,the voltage at metering point a is:

u_a(t)＝u(t)-R_li_a(t)

wherein u is_a(t) is the voltage at metering point a; i.e. i_a(t) is the current at metering point a;

with electric automobile charge direction as the positive direction, when electric automobile discharges to the electric wire netting, to k impact or undulant under the distortion signal condition, current is in metering point a:

i_ak(t)＝-(1+α_k(t))I_mk sin(ω₀t+φ_k)

wherein i_ak(t) represents the current at the kth impact or fluctuation metering point a; alpha is alpha_k(t) denotes the kth-time impact function; i is_mk、φ_kThe current amplitude and the current phase of the kth impact or fluctuation are respectively.

Further, for the kth impact or fluctuation, the voltage at the metering point a is:

u_ak(t)＝u(t)-R_li_ak(t)

＝U_m sin(ω₀t+ψ_k)+R_l[1+α_k(t)]I_mk sin(ω₀t+φ_k)

＝U_m sin(ω₀t+ψ_k)+R_lI_mk sin(ω₀t+φ_k)+R_lα_k(t)I_mk sin(ω₀t+φ_k)

＝U_m sinω₀tcosψ_k+U_m sinψ_k cosω₀t+R_lI_mk sinω₀tcosφ_k

+R_lI_mk sinφ_k cosω₀t+R_lI_mka_k(t)sin(ω₀t+φ_k)

＝u_akI(t)+u_akS(t)

u_akI(t)＝U_m sinω₀tcosψ_k+U_m sinψ_k cosω₀t+R_lI_mk sinω₀tcosφ_k

+R_lI_mk sinφ_k cosω₀t

＝(U_m cosψ_k+R_lI_mk cosφ_k)sinω₀t

+(U_m sinψ_k+R_lI_mk sinφ_k)cosω₀t

＝U_akIm sin(ω₀t+θ_k)

u_akS(t)＝R_lI_mkα_k(t)sin(ω₀t+φ_k)

wherein u is_ak(t) represents the voltage at the kth shock or fluctuation metering point a; u. of_akI(t)、u_akS(t) the fundamental voltage and the distortion voltage at the k-th impact or fluctuation metering point a respectively; u shape_akImThe fundamental voltage amplitude at the k-th impact or fluctuation metering point a is obtained; theta_kIs the fundamental voltage phase;

fundamental current i at k-th impact or fluctuation metering point a_akI(t) is:

i_akI(t)＝-I_mk sin(ω₀t+φ_k)

distortion current i at k-th impact or fluctuation metering point a_aks(t) is:

i_akS(t)＝-I_mkα_k(t)sin(ω₀t+φ_k)。

further, the determining, according to the established bidirectional interaction model, the electric energy measured during charging and the electric energy measured during discharging of the electric vehicle under the distortion signal includes:

according to the established two-way interaction model, determining the average power at the metering point a in the metering time:

wherein, P_aIs the average power at metering point a over the metering time T; p_akThe average power at the metering point a in the time when the kth impact exists; p is a radical of_ak(t) measuring the instantaneous power at the point a during the time when the kth impact exists; t is N.T₀，T₀The fundamental wave period is N represents the impact times; t is₁＝N₁T₀，T₁Metering time for charging, N₁Representing the number of times the impact occurred during the charging process; t is₂＝N₂T₀，T₂For measuring time of discharge, N₂Indicating the number of times the impact occurred during the discharge; p_{a_charge}The average power at the metering point a in the charging metering time is; p_{a_discharge}Is the average power at metering point a during the discharge metering time; p_{I_charge}、P_{IS_charge}、P_{SI_charge}、P_{S_charge}The power generated by the action of the fundamental wave power, the fundamental wave voltage and the distortion current during charging, and the work and the distortion power generated by the action of the distortion voltage and the fundamental wave current are respectively; p_{I_discharge}、P_{IS_discharge}、P_{SI_discharge}、P_{S_discharge}The power generated by the action of the fundamental wave power, the fundamental wave voltage and the distortion current during discharging, the power generated by the action of the distortion voltage and the fundamental wave current and the distortion power are respectively;

according to the obtained P_{a_charge}And P_{S_charge}Determining the electric energy W measured during charging_charge；

According to the obtained P_{a_discharge}And P_{S_discharge}Determining the electric energy W measured during discharge_discharge。

Further, P_{S_discharge}Expressed as:

further, W_chargeExpressed as:

W_charge＝(P_{I_charge}+P_{IS_charge}+P_{SI_charge})T₁

＝(P_{a_charge}-P_{S_charge})T₁

＝W_{a_charge}-W_{S_charge}

wherein, W_{a_charge}Measuring the charging power at point a, W_{a_charge}＝P_{a_charge}*T₁；W_{S_charge}Distortion of electric energy during charging, W_{S_charge}＝P_{S_charge}*T₁。

Further, W_dischargeExpressed as:

W_discharge＝(P_{I_discharge}+P_{IS_discharge}+P_{SI_discharge})T₂

＝(P_{a_discharge}-P_{S_discharge})T₂

＝W_{a_discharge}-W_{S_discharge}

wherein, W_{a_discharge}Measuring the discharge power at point a, W_{a_discharge}＝P_{a_discharge}*T₂；W_{S_discharge}Electric energy distorted during discharge, W_{S_discharge}＝P_{S_discharge}*T₂。

Further, the method further comprises:

and summing the determined electric energy measured during charging and the determined electric energy during discharging to obtain the total electric energy measured by bidirectional charging and discharging.

The technical scheme provided by the embodiment of the invention has the beneficial effects that at least:

in the embodiment of the invention, aiming at the fact that the charging and discharging behaviors of the electric automobile connected to the power grid have high randomness, a uniform two-way interaction model of the electric automobile connected to the power grid is established; and according to the established bidirectional interaction model, bidirectional electric energy metering of the electric automobile during charging and discharging under the distorted signal is realized.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a schematic diagram of a charging model of an electric vehicle in a power grid;

FIG. 2 is a schematic diagram of a bidirectional interaction model of an electric vehicle connected to a power grid according to an embodiment of the present invention;

fig. 3 is a schematic flow chart of a V2G-oriented electric vehicle bidirectional electric energy metering method according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in fig. 2 and fig. 3, an embodiment of the present invention provides a bidirectional electric energy metering method for a V2G-oriented electric vehicle, where the method includes:

s101, establishing a bidirectional interaction model of the electric automobile connected to a power grid; wherein the two-way interaction model comprises: grid voltage u (t), grid line load Z_l1、Z_l2、Z_l3Other loads Z in the power grid, electric automobile bidirectional inverter, electric automobile battery electromotive force E and electricityInternal load Z of motor vehicle_ev(ii) a Network voltage series connection Z_l2、Z_l3Then, the two-way inverter of the electric automobile is connected, Z_evE is connected in series and then connected in parallel with two ends of a bidirectional inverter of the electric automobile, Z and Z_l1After being connected in series, the two ends of the grid voltage are connected in parallel;

and S102, determining the electric energy measured during charging and the electric energy measured during discharging of the electric automobile under the distortion signal according to the established two-way interaction model.

According to the V2G-oriented bidirectional electric energy metering method for the electric automobile, a uniform bidirectional interaction model of the electric automobile connected to a power grid is established aiming at the fact that the charging and discharging behaviors of the electric automobile connected to the power grid have high randomness; and according to the established bidirectional interaction model, bidirectional electric energy metering of the electric automobile during charging and discharging under the distorted signal is realized.

In this example, Z_l1、Z_l2、Z_l3Both represent grid line loads, and other loads Z in the grid include: loads other than line loads and electric vehicles in the power grid, for example, lighting loads, household loads such as air conditioners and refrigerators, and loads such as industrial electric appliances.

In fig. 2, the simplified model of the power grid is shown on the left side of the circuit, and the electric vehicle is shown on the right side of the circuit. Taking the current direction shown in fig. 2 as the positive direction, when the electric vehicle is charged, the Bi-directional inverter (Bi-directional Converter) of the electric vehicle controls the current to flow into the electric vehicle from the point b; when the electric automobile discharges, the bidirectional inverter controls the current to flow out to the point b from the electric automobile, and the current and the grid voltage are the load (comprising: Z) in the grid_l1、Z_l2、Z_l3And Z) power supply.

In FIG. 2, in the power grid, at Z_l2、Z_l3The points on the line between the points are metering points a, i (t) are network currents, u_a(t) is the voltage at the measurement point a, i_a(t) is the current at metering point a, u_evAnd (t) is the output voltage of the electric automobile when discharging to the power grid.

Under distorted signal conditions, the grid voltage u (t) can be expressed as:

u(t)＝U_m sin(ω₀t+ψ_k) (11)

wherein, U_mIs the grid voltage amplitude; omega₀Is the standard power frequency angular frequency; psi_kFor the phase of the voltage of the kth surge or surge, psi_kIs a random variable; t is the time.

Taking the current direction shown in fig. 2 as the positive direction, that is, the charging direction of the electric vehicle as the positive direction, the current flowing into the metering point a during the charging of the electric vehicle can be obtained according to the equation (1):

i_a(t)＝(1+α(t))I_msin(ω₀t+φ) (12)

wherein i_a(t) is the current at the metering point a, α (t) is the impulse function, I_mPhi is the current amplitude and current phase, respectively.

In this embodiment, the expression of α (t) depends on whether the signal is an impulse signal or a ripple signal, as shown in equations (2) and (3).

Similarly, the current flowing into the metering point a during the discharge of the electric automobile is as follows:

i_a(t)＝-(1+α(t))I_msin(ω₀t+φ) (13)

when the electric automobile is charged in a power grid, the voltage at the point a of the metering point is as follows:

u_a(t)＝u(t)-Z_l2i_a(t) (14)

wherein u is_a(t) is the voltage at metering point a;

when the electric automobile discharges to the power grid, the voltage at the point a is measured

u_a(t)＝u_ev(t)-Z_l3i_a(t) (15)

Wherein u is_ev(t) is the output voltage of the electric vehicle discharging to the power grid;

in fact, the output voltage u of the electric vehicle when discharging into the grid_ev(t) is practically the same as the grid voltage u (t), which is a standard sinusoidal voltage, then:

u_ev(t)＝u(t) (16)

suppose Z_l2、Z_l3Are all pure resistive loads R_lMeasuring the voltage u at point a in the case of charging or discharging V2G_a(t) can be expressed in the form:

u_a(t)＝u(t)-R_li_a(t) (17)

taking the electric vehicle discharge as an example for analysis, under the condition of distorted signals, for the kth impact or fluctuation, the current at the metering point a is as follows:

i_ak(t)＝-(1+α_k(t))I_mk sin(ω₀t+φ_k) (18)

wherein i_ak(t) represents the current at the kth impact or fluctuation metering point a; alpha is alpha_k(t) denotes the kth-time impact function; i is_mk、φ_kThe current amplitude and the current phase of the kth impact or fluctuation are respectively;

for the kth bump or fluctuation, the voltage at metering point a is:

wherein u is_ak(t) represents the voltage at the kth shock or fluctuation metering point a; u. of_akI(t)、u_akS(t) the fundamental voltage and the distortion voltage at the k-th impact or fluctuation metering point a respectively;

according to equation (19), the voltage at the metering point a can be divided into a fundamental voltage u_akI(t) and distortion voltage u_aks(t), wherein the fundamental voltage is:

wherein, U_akImThe fundamental voltage amplitude at the k-th impact or fluctuation metering point a is obtained; theta_kIs the fundamental voltage phase;

the distortion voltage at the measurement point a is:

u_akS(t)＝R_lI_mkα_k(t)sin(ω₀t+φ_k) (23)

according to equation (23), the current at measurement point a can be divided into fundamental current i_akI(t) and a distortion current i_aks(t) wherein the fundamental current i at the kth impact or fluctuation metering point a_akI(t) is:

i_akI(t)＝-I_mk sin(ω₀t+φ_k) (24)

distortion current i at k-th impact or fluctuation metering point a_aks(t) is:

i_akS(t)＝-I_mkα_k(t)sin(ω₀t+φ_k) (25)

for convenience of description, it is assumed that T is N · T during the measurement time T₀，T₀N represents the number of impacts, and essentially, N represents the sum of the number of impacts and undulations. The charging metering time of the electric automobile is T₁Discharge metering time of T₂. Theoretically, T₁＞T₂For convenience of measurement, assume that within the measurement time T, N₁When the secondary impact occurs in the charging process, the charging metering time is T₁＝N₁T₀；N₂The sub-impact occurs in the discharge process, and the discharge metering time is T₂＝N₂T₀(ii) a The average power (active power) P at the metering point a during the metering time can be obtained_aComprises the following steps:

wherein, P_aIs the average power at metering point a over the metering time; p_akThe average power at the metering point a in the time when the kth impact exists; p is a radical of_ak(t) is the time during which the kth impact is present, the meterThe instantaneous power at quantity point a;

wherein, P_{a_charge}Is the average power at metering point a over the charge metering time; p_{a_discharge}Is the average power at metering point a during the discharge metering time;

as can be seen from equation (27), the power at the metering point a can be divided into four parts in the charging metering time and the discharging metering time:

wherein, P_{I_charge}、P_{IS_charge}、P_{SI_charge}、P_{S_charge}The power generated by the action of the fundamental wave power, the fundamental wave voltage and the distortion current during charging, and the work and the distortion power generated by the action of the distortion voltage and the fundamental wave current are respectively; p_{I_discharge}、P_{IS_discharge}、P_{SI_discharge}、P_{S_discharge}The power generated by the action of the fundamental wave power, the fundamental wave voltage and the distortion current during discharging, the power generated by the action of the distortion voltage and the fundamental wave current and the distortion power are respectively;

take the discharging process of the electric vehicle as an example, P is sequentially paired_{I_discharge}、P_{IS_discharge}、P_{SI_discharge}、P_{S_discharge}The four parts of power are analyzed:

1. fundamental power P during discharge_{I_discharge}

As can be seen from equations (20) and (24), the fundamental instantaneous power at the measurement point a is:

wherein, the first term is alternating current component, the mean value is zero, and represents power second harmonic; the second term is a direct current component, which indicates the average power of the fundamental voltage and the fundamental current, and must be positive.

2. Power P generated by action of wave voltage and distorted current during discharge_{IS_discharge}

As can be seen from equations (20) and (25), the instantaneous power generated by the action of the fundamental voltage and the distortion current at the measurement point a is:

for a surge signal or a surge signal, the energy accumulation time can be regarded as infinitely long, so that the total electrical energy E generated in the metering time_{IS_discharge}Comprises the following steps:

1) if the signal is a wobble signal, then

Wherein, I_mkThe current amplitude of the kth fluctuation signal is obtained; t is t_kFor the duration of the kth wobble signal

Then the formula (32) is

Wherein, the first term and the second term are random terms, and the sum of multiple fluctuations tends to zero. Third term cos (θ)_k-φ_k) The one must be positive and is generally not very small, less than 0.5, not uncommon under current constraints on the power factor of the grid. The third term is therefore positive. Thus is provided with

E_{IS_diacharge}≤0 (35)

2) If the signal is an impact signal, then:

wherein, γ_kIn a simplified form, the method specifically comprises the following steps:

therefore, formula (32) can be written as

When t is_kOn a time scale of → 0,

E_{IS_discharge}→0 (39)

when t is_k＞T₀When the temperature of the water is higher than the set temperature,

2ω₀t_kis greater than 1, so

Where the first term is a positive value and the second term is a random variable, the sum of multiple hits will tend to zero. Therefore, it is not only easy to use

Combine formula (35) and (41) to know

E_{IS_discharge}≤0 (42)

Energy E generated by action of fundamental voltage and distortion current_{IS_discharge}Must not be greater than zero, and because,

so the average power P_{IS_discharge}Must also be no greater than 0, so there is:

P_{IS_discharge}≤0 (43)

3. power P generated by action of distortion voltage and fundamental current during discharge_{SI_discharge}

As is clear from the equations (23) and (24), the instantaneous power generated by the action of the distortion voltage and the fundamental current at the measurement point a is

The average power is:

thus, the sum of the first term and the second term is not greater than 0, i.e.

P_{SI_discharge}≤0 (46)

4. Distortion power P at discharge_{S_discharge}

As is clear from the expressions (23) and (25), the distortion instantaneous power at the measurement point a is

Average power:

thus, the sum of the first term and the second term is less than 0, i.e.

P_{S_discharge}<0 (49)

In combination with the above analysis, the electric vehicle has the following conclusions during the discharging process:

P_{I_discharge}<0, the fundamental power is negative, and the electric automobile supplies power to a power grid and needs to be measured.

P_{IS_discharge}Less than or equal to 0, the power generated by the action of the fundamental voltage and the distortion current is not positive (0 when only the harmonic is contained), and the electric automobile provides electric quantity and needs to be measured.

P_{SI_discharge}Less than or equal to 0, the power generated by the action of the distortion voltage and the fundamental wave current is not positive (0 when only the harmonic wave is contained), and the power grid absorbs energy and needs to be measured.

P_{S_discharge}<0, the distortion power is negative, and the electric automobile supplies power to the power grid, but flows into the power grid in a distortion current mode, so that the power grid is polluted and is not measured.

Therefore, a reasonable formula for electricity metering at discharge should be:

wherein, W_dischargeThe electric energy is measured during discharging; w_{a_discharge}To measure the discharge power at point a, W_{a_discharge}＝P_{a_discharge}*T₂；W_{S_discharge}For distorting electric energy during discharge, W_{S_discharge}＝P_{S_discharge}*T₂；

The formula derivation of the charging process of the electric vehicle is similar to the discharging process, and only the current direction needs to be noticed to be opposite, and the description is omitted here. Therefore, it can be concluded when the electric vehicle is charged:

P_{I_charge}and if the power is more than 0, the fundamental wave power is positive, and the power grid supplies power to the electric automobile and needs to measure.

P_{IS_charge}Not less than 0, the power generated by the action of the fundamental voltage and the distortion current is not negative (only containing the harmonic wave, the power is 0), and the power grid supplies power to the electric automobile and needs to be measured.

P_{SI_charge}Less than or equal to 0, the power generated by the action of the distortion voltage and the fundamental wave current is not positive (0 when only the harmonic wave is contained), but the power is fed back to the power grid in a mode of the fundamental wave current, and the power grid is not polluted.

P_{S_charge}<And 0, the distortion power is negative and is fed back to the power grid in a distortion current mode, and although the part feeds back electric energy to the power grid, the part pollutes the power grid and is not measured.

In this example, P_{S_charge}Expressed as:

therefore, a reasonable formula for measuring the electric quantity during charging is

Wherein, W_chargeElectric energy measured during charging; w_{a_charge}For measuring the charging power at point a, W_{a_charge}＝P_{a_charge}*T₁；W_{S_charge}For distorting electric energy during charging, W_{S_charge}＝P_{S_charge}*T₁；

In the metering time T, the electricity metering formula at the metering point a is as follows:

wherein, W_aTo measure the quantity of electricity at point a, W_IAs fundamental electric energy, W_ISElectric energy produced for fundamental voltage and distortion current action, W_ISElectric energy produced for the action of distorted voltage and fundamental current, W_SIs distortion power;

in the foregoing embodiment of the V2G-oriented bidirectional electric energy metering method for the electric vehicle, further, the method further includes:

and summing the determined electric energy measured during charging and the determined electric energy during discharging to obtain the total electric energy measured by bidirectional charging and discharging.

In this embodiment, in combination with equations (50) and (51), the rational measure equation should be:

wherein W represents the total electric energy measured by bidirectional charge and discharge, and W_a＝P_{a_charge}T₁+P_{a_discharge}T₂，W_S＝P_{a_charge}T₁+P_{a_discharge}T₂。

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (9)

1. A V2G-oriented bidirectional electric energy metering method for an electric automobile is characterized by comprising the following steps:

establishing a bidirectional interaction model of the electric automobile connected to a power grid; wherein the two-way interaction model comprises: grid voltage u (t), grid line load Z_l1、Z_l2、Z_l3Other loads Z in the power grid, electric automobile bidirectional inverter, electric automobile battery electromotive force E and electric automobile internal load Z_ev(ii) a Network voltage series connection Z_l2、Z_l3Then, the two-way inverter of the electric automobile is connected, Z_evE is connected in series and then connected in parallel with two ends of a bidirectional inverter of the electric automobile, Z and Z_l1After being connected in series, the two ends of the grid voltage are connected in parallel;

and determining the electric energy measured during charging and the electric energy measured during discharging of the electric automobile under the distortion signal according to the established two-way interaction model.

2. The V2G-oriented electric vehicle bidirectional electric energy metering method according to claim 1, wherein under the condition of distorted signals, the grid voltage u (t) is:

u(t)＝U_m sin(ω₀t+ψ_k)

wherein, U_mIs the grid voltage amplitude; omega₀Is the standard power frequency angular frequency; psi_kVoltage phase for the kth surge or fluctuation; t is the time.

3. The V2G-oriented electric vehicle bidirectional electric energy metering method according to claim 2, wherein the power grid is located at Z_l2、Z_l3The point on the line between is the metering point a;

is provided with Z_l2、Z_l3Are all pure resistive loads R_lWhen the electric automobile is charged in the power grid or discharged into the power grid, the voltage at the metering point a is as follows:

u_a(t)＝u(t)-R_li_a(t)

wherein u is_a(t) is the voltage at metering point a; i.e. i_a(t) is the current at metering point a;

with electric automobile charge direction as the positive direction, when electric automobile discharges to the electric wire netting, to k impact or undulant under the distortion signal condition, current is in metering point a:

i_ak(t)＝-(1+α_k(t))I_mk sin(ω₀t+φ_k)

wherein i_ak(t) represents the current at the kth impact or fluctuation metering point a; alpha is alpha_k(t) denotes the kth-time impact function; i is_mk、φ_kThe current amplitude and the current phase of the kth impact or fluctuation are respectively.

4. The V2G-oriented electric vehicle bidirectional electric energy metering method according to claim 3, wherein for the kth impact or fluctuation, the voltage at the metering point a is:

u_ak(t)＝u(t)-R_li_ak(t)

＝U_m sin(ω₀t+ψ_k)+R_l[1+α_k(t)]I_mk sin(ω₀t+φ_k)

＝U_m sin(ω₀t+ψ_k)+R_lI_mk sin(ω₀t+φ_k)+R_lα_k(t)I_mk sin(ω₀t+φ_k)

＝U_m sinω₀tcosψ_k+U_m sinψ_k cosω₀t+R_lI_mk sinω₀tcosφ_k+R_lI_mk sinφ_k cosω₀t+R_lI_mkα_k(t)sin(ω₀t+φ_k)

＝u_akI(t)+u_akS(t)

u_akI(t)＝U_m sinω₀tcosψ_k+U_m sinψ_k cosω₀t+R_lI_mk sinω₀tcosφ_k+R_lI_mk sinφ_k cosω₀t

＝(U_m cosψ_k+R_lI_mk cosφ_k)sinω₀t+(U_m sinψ_k+R_lI_mk sinφ_k)cosω₀t

＝U_akIm sin(ω₀t+θ_k)

u_akS(t)＝R_lI_mkα_k(t)sin(ω₀t+φ_k)

wherein u is_ak(t) represents the voltage at the kth shock or fluctuation metering point a; u. of_akI(t)、u_akS(t) the fundamental voltage and the distortion voltage at the k-th impact or fluctuation metering point a respectively; u shape_akImIs as followsThe fundamental voltage amplitude at the k times of impact or fluctuation metering point a; theta_kIs the fundamental voltage phase;

fundamental current i at k-th impact or fluctuation metering point a_akI(t) is:

i_akI(t)＝-I_mk sin(ω₀t+φ_k)

distortion current i at k-th impact or fluctuation metering point a_aks(t) is:

i_akS(t)＝-I_mkα_k(t)sin(ω₀t+φ_k)。

5. the V2G-oriented electric vehicle bidirectional electric energy metering method according to claim 4, wherein the determining of the electric vehicle under the distorted signal, the electric energy metered during charging and the electric energy metered during discharging according to the established bidirectional interaction model comprises:

according to the established two-way interaction model, determining the average power at the metering point a in the metering time:

wherein, P_aIs the average power at metering point a over the metering time T; p_akThe average power at the metering point a in the time when the kth impact exists; p is a radical of_ak(t) measuring the instantaneous power at the point a during the time when the kth impact exists; t is N.T₀，T₀The fundamental wave period is N represents the impact times; t is₁＝N₁T₀，T₁The time is measured for the purpose of charging,N₁representing the number of times the impact occurred during the charging process; t is₂＝N₂T₀，T₂For measuring time of discharge, N₂Indicating the number of times the impact occurred during the discharge; p_{a_charge}The average power at the metering point a in the charging metering time is; p_{a_discharge}Is the average power at metering point a during the discharge metering time; p_{I_charge}、P_{IS_charge}、P_{SI_charge}、P_{S_charge}The power generated by the action of the fundamental wave power, the fundamental wave voltage and the distortion current during charging, and the work and the distortion power generated by the action of the distortion voltage and the fundamental wave current are respectively; p_{I_discharge}、P_{IS_discharge}、P_{SI_discharge}、P_{S_discharge}The power generated by the action of the fundamental wave power, the fundamental wave voltage and the distortion current during discharging, the power generated by the action of the distortion voltage and the fundamental wave current and the distortion power are respectively;

according to the obtained P_{a_charge}And P_{S_charge}Determining the electric energy W measured during charging_charge；

According to the obtained P_{a_discharge}And P_{S_discharge}Determining the electric energy W measured during discharge_discharge。

6. The V2G-oriented electric vehicle bidirectional electric energy metering method according to claim 5, wherein P is P_{S_discharge}Expressed as:

7. the V2G-oriented electric vehicle bidirectional electric energy metering method according to claim 5, wherein W is W_chargeExpressed as:

W_charge＝(P_{I_charge}+P_{IS_charge}+P_{SI_charge})T₁

＝(P_{a_charge}-P_{S_charge})T₁

＝W_{a_charge}-W_{S_charge}

wherein, W_{a_charge}Measuring the charging power at point a, W_{a_charge}＝P_{a_charge}*T₁；W_{S_charge}Distortion of electric energy during charging, W_{S_charge}＝P_{S_charge}*T₁。

8. The V2G-oriented electric vehicle bidirectional electric energy metering method according to claim 5, wherein W is W_dischargeExpressed as:

W_discharge＝(P_{I_discharge}+P_{IS_discharge}+P_{SI_discharge})T₂

＝(P_{a_discharge}-P_{S_discharge})T₂

＝W_{a_discharge}-W_{S_discharge}

wherein, W_{a_discharge}Measuring the discharge power at point a, W_{a_discharge}＝P_{a_discharge}*T₂；W_{S_discharge}Electric energy distorted during discharge, W_{S_discharge}＝P_{S_discharge}*T₂。

9. The V2G-oriented electric vehicle bidirectional electric energy metering method according to claim 1, characterized in that the method further comprises:

and summing the determined electric energy measured during charging and the determined electric energy during discharging to obtain the total electric energy measured by bidirectional charging and discharging.

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