CN106300396A - Realize charging electric vehicle switching device and the charging method of three-phrase burden balance - Google Patents

Abstract

The invention belongs to the technical field of electric vehicle charging control, and in particular relates to an electric vehicle charging switch device and a charging method for realizing three-phase load balance, including sequentially connected: a miniature measuring voltage converter, a signal conditioning module, and an A/D sampling module , CPU module, three-choose-one interlocking solid-state switch and charger unit; the input terminal of the miniature measurement voltage converter is connected to a three-phase power supply; the three-phase power supply is a three-phase four-wire system, which are A phase, B phase, C phase and N phase line; the input terminal of the three-choice one interlock solid state switch is also connected to the A phase, B phase, and C phase of the three-phase power supply; the charger unit is respectively connected to the output terminal of the three-choice one interlock solid state switch and the N line of the three-phase power supply Connection; according to the result of A/D conversion, select the phase with the highest voltage among the phases A, B, and C, and conduct the phase with the highest voltage by a three-choice interlock solid-state switch as an electric vehicle The charging power supply realizes the three-phase load balance of the distribution network.

Description

Electric vehicle charging switch device and charging method for realizing three-phase load balance

technical field

The invention belongs to the technical field of electric vehicle charging control, and in particular relates to an electric vehicle charging switch device and a charging method for realizing three-phase load balance.

Background technique

Energy crisis and environmental pollution are two major problems facing the development of the world today, and a large number of traditional vehicles have brought a non-negligible impact on energy crisis and environmental pollution. Electric vehicles do not directly consume primary energy, and because of their advantages of high efficiency and low pollution, they have incomparable advantages over traditional vehicles in solving the above problems. Household commuter electric vehicles (private electric vehicles) usually stop driving during the day and park in the garage of the community at night. They have a long charging period to choose from, and usually use the conventional slow charging method, that is, single-phase 220V power supply for charging.

Three-phase unbalance means that the magnitude of the current/voltage of each phase line in the three-phase power supply line is not equal or the phase angle difference is not 120 degrees. Three-phase balance is the basis for the safe and economical operation of the power grid. Serious three-phase imbalance will not only lead to unqualified voltage quality, but also increase power grid loss (line, transformer loss), and even cause power grid safety accidents.

When large-scale private electric vehicles are charged at a slow speed in the community garage, if no control measures are taken, the most obvious problems are: 1) increase the maximum load value of the regional power grid and further increase the load peak-valley difference; 2) cause three-phase load imbalance , so that the three-phase voltage unbalance of the local low-voltage distribution network is unqualified, the network loss increases, and even threatens the safe operation of electrical equipment.

Through literature analysis, it can be seen that most of the current research on the orderly and slow charging method of private electric vehicles is based on the modeling and analysis of the single-phase charging system, ignoring the analysis and treatment of the three-phase imbalance problem of the low-voltage distribution network.

In the prior art, there are also studies on the control method of load imbalance in the low-voltage distribution network (but not for electric vehicle charging). The above method detects the load of each phase of the low-voltage line at the bus outlet (the part circled by the dotted line in Figure 1), forms the user's electricity consumption plan (which phase electricity is used by each user), and then sends the control command through wired or wireless communication A phase selection switch for the user.

This low-voltage distribution network load imbalance management method has the following disadvantages: 1) When the load imbalance occurs in the system, the number of phase selection switches participating in the action is relatively large, and the phase selection switch operates frequently; There will be power supply interruption or voltage drop, which will affect the user's power supply reliability and electricity safety. 3) A communication medium is required to realize the distribution of control signals.

Contents of the invention

In view of the above problems, the present invention proposes an electric vehicle charging switch device and a charging method for realizing three-phase load balance.

A charging access switch device for electric vehicles that realizes three-phase load balance, the device includes: a miniature measuring voltage converter, a signal conditioning module, an A/D sampling module, a CPU module, an interlocking solid-state switch for selecting one of three, and a charger unit;

The input terminal of the miniature measurement voltage converter is connected to a three-phase power supply, and the output terminal of the miniature measurement voltage converter is connected to the input terminal of the signal conditioning module; the three-phase power supply is a three-phase four-wire system, which are respectively A phase, B phase, C phase and N line;

The input terminal of the A/D sampling module is connected to the output terminal of the signal conditioning module, and the output terminal is connected to the CPU module;

The output end of the CPU module is connected to the input end of the three-choice interlocking solid state switch, and the input end of the three-choice one interlocking solid state switch is also connected to the A phase, B phase, and C phase of the three-phase power supply. connect;

The charger unit is respectively connected to the output terminal of the three-select-one interlocking solid-state switch and the N line of the three-phase power supply.

The miniature measuring voltage converter is a 220V/5V miniature measuring voltage converter.

The A/D sampling module specifically includes three parts: sampling and holding, multiplexing and A/D conversion.

A method for charging an electric vehicle using the device described in any one of the above, said method comprising the following steps:

S1, converting the power supply voltage into a signal acquisition voltage;

S2, converting the output voltage of the miniature measurement voltage converter to the A/D input voltage range, and filtering the sampling signal;

S3, performing sampling and holding, multiplexing and A/D conversion on the filtered signal;

S4, according to the result of A/D conversion, select the phase with the highest voltage among the phases A, B, and C, and turn on the phase with the highest voltage by a three-choice interlock solid-state switch as an electric vehicle power plug.

The step S4 further includes: according to the input control signal, cutting off the other two phases except the phase with the highest voltage.

The beneficial effects of the present invention are:

The invention designs an electric vehicle charger access switch device that realizes three-phase load balance. Using the travel rules (travel and home time, daily mileage) data and charging data of private electric vehicles, the actual application of the device was simulated, and the device was verified to achieve charging load balance and improve three-phase voltage imbalance. And reduce the effect of distribution network line loss.

Description of drawings

Figure 1 is a schematic diagram of real-time regulation of three-phase load imbalance in the low-voltage power grid;

Fig. 2 is a diagram of an automatic load balancing electric vehicle charging access switch device;

Figure 3 is a schematic diagram of the low-voltage distribution network wiring for centralized slow charging in the underground garage of a private electric vehicle community;

Figure 4 is a schematic diagram of the centralized charging low-voltage distribution network wiring in the underground garage of the private electric vehicle community;

Figure 5 is a probability distribution diagram of the return time of the last trip of a private vehicle;

Figure 6 is a probability distribution map of the daily mileage of private vehicles;

Figure 7 is a constant current-constant voltage two-stage slow charging timing diagram;

Fig. 8 is a timing diagram of the charging power of each phase of Scheme 1;

Fig. 9 is a timing diagram of the three-phase voltage unbalance degree of scheme 1;

Fig. 10 is a time sequence diagram of the voltage amplitudes of each phase node at the terminal node of scheme 1;

Fig. 11 is a timing diagram of charging power of each phase of scheme 2;

Fig. 12 is a time sequence diagram of three-phase voltage unbalance in scheme 2;

Fig. 13 is a time sequence diagram of the voltage amplitudes of each phase node at the terminal node of scheme 2.

detailed description

The embodiments will be described in detail below in conjunction with the accompanying drawings.

Aiming at the demand characteristics of the slow charging load in the private electric vehicle community (single-phase 220V charging), an electric vehicle charger access switch device that automatically realizes three-phase load balance by detecting the voltage of the power supply access point is designed, as shown in Figure 2 shown.

The TV module is a miniature measurement voltage converter, which converts the 220V power supply voltage to a lower voltage to facilitate signal collection. This device uses a 220V/5V miniature measurement voltage converter;

Signal conditioning module: convert the TV output voltage to the A/D input voltage range, and at the same time filter the sampled signal to suppress interference to improve the measurement accuracy and stability of the system;

A/D sampling module: It mainly includes three parts: sampling and holding, multi-channel selection and A/D conversion, to realize the digitization of analog voltage.

CPU module: The control system coordinates the work, completes A/D conversion and data processing, selects the phase with the highest voltage, and then controls the three-choice interlocking solid-state switch to turn on the phase with the highest voltage as the charging power supply for electric vehicles.

Three-choice interlocking solid-state switch: It is a three-phase interlocking solid-state switch. According to the input control signal, one of the phases is selected to be turned on, and the other two are turned off.

The switchgear has the following features:

1) Automatically detect the voltages of U _AN , U _BN , and U _CN , and select the phase with the highest voltage as the charging power source for electric vehicles;

2) Phase selection is carried out before the load (electric vehicle charging load) is connected, and the phase power is continuously used as the charging power source after the connection, until the charging is completed, and no other phases are switched as the charging power source in the middle, so there is no power supply interruption or voltage drop Phenomenon;

3) No need for remote control, easy to use.

A schematic diagram of a slow charging system for a parking lot in a residential area based on the "automatic load balancing switch" of the present invention is shown in FIG. 3 .

In order to verify the validity of this patent, a simulation verification was carried out according to the design scheme of centralized slow charging of electric vehicles in the underground garage of the actual community (currently, the number of private electric vehicles is small, and only simulation verification can be carried out). Based on Figure 3, the low-voltage distribution network wiring diagram for centralized charging in the underground garage of the private electric vehicle community is shown in Figure 4, and the electrical equipment and low-voltage distribution line parameters in the figure are shown in Table 1.

Table 1 Parameters of electrical equipment of low-voltage power distribution system

According to the classification methods of household compact electric vehicles, mid-to-high-end electric vehicles and SUV electric vehicles in the relevant literature and the proportion of fuel private cars to compact cars, mid-to-high-end cars and SUVs, the parameters and models of each model are obtained The ratio is shown in Table 2, and the reference car series are Nissan Leaf, Changan E30, and BYDE6.

Table 2 Parameters and model ratios of each car series

Three-phase unbalance means that the current/voltage amplitudes of each phase of the three-phase power supply line are not equal or the phase angle difference is not 120 degrees. Three-phase balance is the basis for the safe and economical operation of the power grid. Serious three-phase imbalance will not only lead to unqualified voltage quality, but also increase power grid loss (line, transformer loss), and even cause power grid safety accidents. Unbalanced current (produced by unbalanced load) is an important cause of asymmetric voltage, and voltage unbalance is one of the power quality assessment parameters, that is, when the power grid is in normal operation, the negative sequence voltage unbalance degree of the public connection point of the power system (national standard value) does not exceed 2%, and does not exceed 4% for a short time.

Based on the centralized charging system in the underground garage of the private electric vehicle community shown in Figure 3 (50 charging parking spaces per phase, a total of 150) and the electrical equipment parameters shown in Table 1 and Table 2, the travel rules of private electric vehicles in relevant literature are used and the probability density distribution function of mileage, the timing simulations of the two schemes without and with the automatic load balancing electric vehicle charging access switch device were carried out (5 minutes as a time interval). The detailed process is as follows:

According to the usage habits of private electric vehicles, the assumed conditions for orderly charging of private electric vehicles during off-peak hours are as follows:

(1) The charging start time of an electric vehicle is the return time of the last trip, and the charging start time satisfies the following normal distribution, and its probability density function is:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \&lsqb;</span><span\; class="notranslate">\; -</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; ,</span>& <span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; twenty\; four</span>}\\ \frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \&lsqb;</span><span\; class="notranslate">\; -</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; twenty\; four</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \&le;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, μ _S =17.6; σ _S =3.4.

The probability distribution map of the return time of the last trip of the private vehicle is shown in Figure 5.

(2) The daily mileage satisfies the following lognormal distribution, and its probability density function is:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; x\&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \&lsqb;</span><span\; class="notranslate">\; -</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; ln</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula, μ _D =3.20; σ _D =0.88.

The probability distribution map of the daily mileage of private vehicles is shown in Figure 6.

(3) The power battery capacity of domestic electric vehicles is usually evenly distributed in the range of 20-30kWh. At present, the power batteries of electric vehicles are mainly lithium batteries, and the three-stage slow and small current charging method is generally adopted in the community. The three-stage charging stages are pre-charging stage, constant-current charging stage and constant-voltage charging stage, as shown in Figure 3. shown. Private electric vehicle community charging uses on-board chargers. When using slow charging, only a parking space is required to provide a charging pile with a rated current of 16A (or greater) AC 220V power supply, that is, automatic load balancing electric vehicle charging access Switching Device The output of a solid-state switch.

The distribution of power battery capacity of household electric vehicles is usually normally distributed in the range of 20-30kWh (there are also those with larger capacity). At present, the power battery of household electric vehicles is mainly charged by constant current-constant voltage two-stage slow and small current charging method. The charging power PC of each electric vehicle is 0.1C or 0.2C (C is the battery capacity, unit kWh), that is, 2- 6kW (the charging power of large-capacity batteries will also be larger) the charging process will be approximately constant power characteristics, as shown in Figure 7.

The simulation process uses the slow charging power of each electric vehicle shown in Table 2 for constant power charging, that is, P _C =3kW/4.8kW/15kW

(4) The formula for calculating the charging time of electric vehicles is as follows:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; LW</span>}}_{\mathrm{<span\; class="notranslate">\; 100</span>}}}{\mathrm{<span\; class="notranslate">\; 100</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In the formula, T _C is the length of charging time, unit (h); L is the daily mileage, unit (km); W ₁₀₀ is the power consumption per hundred kilometers, unit (kWh); P _C is the charging power, unit (kW) .

Simulation result analysis:

Option 1: Do not use automatic load balancing electric vehicle charging access switch device

The distribution of charging private electric vehicles obtained by simulation is as follows: a total of 145 vehicles participated in charging that day, of which, phase A: 48 vehicles, phase B: 50 vehicles, phase C: 47 vehicles; the total mileage of these vehicles: 8434 kilometers, Total charging capacity: 1380.4kWh; the timing diagram of the obtained charging power is shown in Figure 8.

The three-phase voltage unbalance value of the node with the most serious three-phase voltage unbalance at each moment is counted, and the time sequence diagram of the three-phase voltage unbalance value of the system obtained is shown in Figure 9. The timing diagram of the voltage amplitude of each phase node at the end node is shown in Fig. 10 .

ABC three-phase 24-hour network loss and system network loss rate are as follows:

Phase A: 8.39kWh, Phase B: 9.96kWh, C: 7.04kWh; ΔP% = 1.8%

Solution 2: Adopt automatic load balancing electric vehicle charging access switch device

The distribution of charging private electric vehicles obtained by simulation is as follows: a total of 146 vehicles participated in charging that day, of which, phase A: 49 vehicles, phase B: 47 vehicles, phase C: 50 vehicles; the total mileage of these vehicles: 8329 kilometers, Total charging capacity: 1398.6kWh; the timing diagram of the obtained charging power is shown in Figure 11.

The three-phase voltage unbalance value of the node with the most serious three-phase voltage unbalance at each time is counted, and the time sequence diagram of the three-phase voltage unbalance value of the system obtained is shown in Figure 12. The timing diagram of the voltage amplitude of each phase node at the end node is shown in Fig. 13 .

ABC three-phase 24-hour network loss and system network loss rate are as follows:

Phase A: 7.81kWh, Phase B: 6.02kWh, C: 7.91kWh; ΔP% = 1.6%

Comparative analysis of scheme 1 and scheme 2

It can be seen from Fig. 8 and Fig. 11 that when the charging vehicles are equivalent, when the three-phase balanced charging mode of the device of the present invention is not used, the B phase has an overload of nearly 8kW, and the A and C two phases have a slight overload (FIG. 8), while using the three-phase balanced charging mode of the device of the present invention, the loads are relatively balanced, not only no overload occurs, but also a certain load range remains.

As can be seen from Figures 9 and 12, when the three-phase balanced charging mode of the device of the present invention is not used, the system has an obvious three-phase voltage unbalance (exceeding the allowable value of the national standard by 2%), while using the three-phase charging mode of the device of the present invention In the phase balance charging mode, there is no phenomenon that the three-phase voltage imbalance exceeds the standard.

It can be seen from Fig. 10 and Fig. 13 that after adopting the three-phase balanced charging mode of the device of the present invention, the minimum value of the terminal node voltage (212.5V) is obviously better than that without using the three-phase balanced charging mode of the device of the present invention. value (208.5V), the voltage quality has also been improved.

In addition, after adopting the three-phase balanced charging mode of the device of the present invention, the system network loss rate is also reduced from 1.8% before adopting to 1.6% after adopting.

The switching device of the present invention has the following features: 1) Automatically detect the voltages of U _AN , U _BN , and U _CN , and select the phase with the highest voltage as the electric vehicle charging power supply; 2) Select the phase before the load (electric vehicle charging load) is connected, After connecting, continue to use the phase power as the charging power source until the charging is completed, and do not switch to other phases as the charging power source in the middle, so there is no power supply interruption or voltage drop phenomenon; 3) No remote control is required, and the application is simple.

The invention designs an electric vehicle charger access switch device that realizes three-phase load balance. Using the travel rules (travel and home time, daily mileage) data and charging data of private electric vehicles, the actual application of the device was simulated, and the device was verified to achieve charging load balance and improve three-phase voltage imbalance. And reduce the effect of distribution network line loss.

This embodiment is only a preferred specific implementation of the present invention, but the scope of protection of the present invention is not limited thereto. Any skilled person in the technical field can easily think of changes or substitutions within the technical scope disclosed in the present invention. , should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (5)

1. the charging electric vehicle realizing three-phrase burden balance accesses switching device, it is characterised in that described device includes: Miniature measurement voltage changer, Signal-regulated kinase, A/D sampling module, CPU module, one-out-three interlocking solid-state switch and charging Machine unit；

Described miniature measurement voltage changer input termination three phase mains, described miniature measurement voltage converter output connects described The input of Signal-regulated kinase；Described three phase mains is three-phase four-wire system, respectively A phase, B phase, C phase and N line；

The input of described A/D sampling module terminates the outfan of described Signal-regulated kinase, and output terminates described CPU mould Block；

The outfan of described CPU module is connected with the input of described one-out-three interlocking solid-state switch, and described one-out-three locks mutually The input of state switch is also connected with the A phase of described three phase mains, B phase, C；

Described charger unit connects with the outfan of described one-out-three interlocking solid-state switch and the N line of described three phase mains respectively Connect.

Device the most according to claim 1, it is characterised in that described miniature measurement voltage changer is that 220V/5V is miniature Measure voltage changer.

Device the most according to claim 1, it is characterised in that described A/D sampling module specifically includes: sampling keep, many Road selects and A/D changes three parts.

4. the device used described in any one of the claim 1-3 method to charging electric vehicle, it is characterised in that described Method comprises the steps:

S1, is transformed to signals collecting voltage by supply voltage；

S2, transforms to A/D input voltage range by the output voltage of described miniature measurement voltage changer, and enters sampled signal Row filtering；

S3, carries out sampling holding, multi-path choice and A/D conversion to filtered signal；

S4, according to the result of A/D conversion, selects the phase that in described A phase, B phase, C phase, voltage is the highest, and is locked mutually by one-out-three Voltage described in state switch conduction the highest one as charging electric vehicle power supply.

Method the most according to claim 4, it is characterised in that described step S4 also includes: according to input control signal, will Other biphase cut-off in addition to the phase that described voltage is the highest.