阅读说明：本技术 一种基于lcl谐振补偿的电动汽车双向无线充电控制方法 (electric automobile bidirectional wireless charging control method based on LCL resonance compensation ) 是由 庄慧敏 刘兴茂 张江林 张绍全 何西凤 邓昌建 谢晓娜 于 2019-10-24 设计创作，主要内容包括：本发明公开了一种基于LCL谐振补偿的电动汽车双向无线充电控制方法,具体涉及无线充电技术领域,具体控制方法如下：S1、建立LCL-BWPT系统的数学模型及控制构架：一、二次侧的高频变换器均采用全控型H桥,功率控制器安装在二次侧,根据BMS电池能量管理系统提供的电池状态、电价及车主的意愿计算控制参数,并通过无线通信将一次侧所需的调控参数α传到一次侧；S2、控制方案由两大模块构成：充/放电功率整定和控制参数设计。本发明以LCL-BWPT系统为研究对象,从车主的角度出发,实现了系统自治、独立运行,不需要集中控制器,考虑车主的意愿、电价以及EV电池的荷电状态等,基于模糊控制理论推算出EV充/放电功率的参考值。(The invention discloses electric vehicle bidirectional wireless charging control methods based on LCL resonance compensation, and particularly relates to the technical field of wireless charging, wherein the control method comprises the following steps of S1, building a mathematical model and a control framework of an LCL-BWPT system, , adopting a full-control H bridge for a high-frequency converter on a secondary side, installing a power controller on the secondary side, calculating control parameters according to a battery state, an electricity price and the intention of a vehicle owner provided by a BMS battery energy management system, transmitting a control parameter α required by the side to a side through wireless communication, and S2, forming a control scheme by two modules, namely, setting charging/discharging power and designing the control parameters.)

The LCL resonance compensation-based electric automobile bidirectional wireless charging control method is characterized by comprising the following specific control methods:

s1, establishing a mathematical model and a control framework of the LCL-BWPT system;

s1.1, adopting an LCL-BWPT system and a control framework;

s1.2, establishing an accurate mathematical model of the LCL-BWPT system:

the secondary side outputs power as follows:

in the formula, P_s、Q_sActive power and reactive power output by the secondary side respectively, α and β are and the internal phase shift angle of the control signal of the secondary converter respectively, delta is the external phase shift angle between the control signals of the two converters, V_dc、V_b secondary side DC bus voltage and battery voltage respectively;

the maximum output active power is:

s2, adopting the mathematical model and control framework of the LCL-BWPT system, the control scheme is composed of two modules: the method comprises the following steps of setting charge/discharge power and designing control parameters, wherein the specific control steps are as follows:

s2.1, setting charge/discharge power based on a fuzzy theory:

when the vehicle owner does not consider the charging economy, directly calculating a charging power setting value;

when the vehicle owner considers the charging economy, according to the size of the charging/discharging capacity and the psychological price c of the vehicle owner_exWith the current price of electricity c_tSetting the charging/discharging power by applying a fuzzy mathematical theory;

s2.2, designing control parameters based on an LCL-BWPT system accurate mathematical model:

when designing controller parameters, the BWPT system works in UPF mode, i.e. delta-delta_Q0Close to but not equal to +/-90 DEG, and an initial value delta of delta is taken first₀The control parameters α and β are predicted at 90 ° or-90 °, initial values thereof are obtained, and then iterative correction is performed.

2. The LCL resonance compensation-based electric vehicle bidirectional wireless charging control method according to claim 1, wherein the LCL-BWPT system and the control architecture are characterized in that the converter times and the secondary converter are arranged on two sides and connected through a loosely coupled coil with LCL resonance compensation, the converter times and the secondary converter are both high frequency converters and both adopt a fully controlled H-bridge, a power controller is installed and connected on the secondary converter side, the input end of the power controller is connected with the BMS battery energy management system, control parameters are calculated according to the battery state, the electricity price and the owner's will provided by the BMS battery energy management system, and the control parameters α required by the converter times are transmitted to the converter times through wireless communication.

3. The electric vehicle bidirectional wireless charging control method based on LCL resonance compensation of claim 2, wherein the power controller is installed on the secondary side and connected to the PPM modulation circuit via wireless communication to achieve the transmission of the regulation parameters α.

4. The LCL resonance compensation-based electric vehicle bidirectional wireless charging control method of claim 1, wherein in step S1.2, due to the effect of harmonics, when the system is operated in UPF unit power factor mode, i.e. the output reactive power is 0, the phase angle δ is shifted outwards_Q0No longer equal to ± 90 °, but is:

5. the electric vehicle bidirectional wireless charging control method based on LCL resonance compensation of claim 1, wherein in step S2.1, when the vehicle owner does not consider the economy of charging, the formula for calculating the setting value of charging power is as follows:

in the formula, t₀、t_ndEV charge/discharge start time and end time, SoC respectively₀、SoC_exRespectively start and end of charge/dischargeState of charge of the battery during electricity, E_Nη are the rated capacity and charge/discharge efficiency of the battery, respectively.

6. The electric vehicle bidirectional wireless charging control method based on LCL resonance compensation of claim 1, wherein in step S2.1, when the vehicle owner considers the economy of charging, the specific method of setting the charging/discharging power is as follows:

two input variables:

output variables:

① fuzzy space partitioning of input and output variables:

both input variables are divided into three fuzzy subsets: high, normal, low; wherein high is represented by H, normal by N, and low is represented by L; the output variables are divided into 5 fuzzy subsets: NB, NS, ZE, PS, PB, wherein NB represents negative large, NS represents negative small, ZE represents zero, PS represents positive small, PB represents positive large; the variable membership functions all adopt trapezoidal functions;

② employ fuzzy control rules;

③ fuzzy inference, using Mamdani inference method, determining the fuzzy relation of input and output by control rule, then using fuzzy synthesis operation to obtain fuzzy output by actual fuzzy input inference;

④, deblurring and precision processing, wherein after fuzzy reasoning obtains the fuzzy value of the control variable, the fuzzy value is deblurred by adopting an area gravity center method, so as to obtain the precise value of the control variable;

delta P inferred by fuzzy control rules_refSo as to obtain the compound with the characteristics of,

if P_ref＞P_maxThen let P_ref＝P_max(ii) a If P_ref＜P_minThen let P_ref＝P_min。

7. The LCL resonance compensation-based electric vehicle bidirectional wireless charging control method according to claim 1, wherein in step S2.2, for simplifying calculation, α - β is taken, and the specific steps are as follows:

① according to the selected charging mode, will be₀Finding P by substituting formula (3) at 90 ° or-90 °_max，δ₀When the phase angle is equal to 90 °, charge is represented, and when the phase angle is equal to 90 °, discharge is represented, the initial value of the phase angle is obtained:

α₀＝β₀＝cos^-1(1-2P_ref/P_max) (6)

② substituting the k-th iteration value of control parameter for equation (2) to obtain the reactive power Q_s，kThen, by the operating conditions of the UPF mode: q_s，kAt 0, the δ value for the k +1 th iteration is found:

δ_k+1＝δ_k+Δδ_k+1(8)

③ will be substituted into α_k＝β_k、δ_k+1Formula (1) is substituted to obtain active power P_s，kThen, α, β for the k +1 th iteration are solved:

α_k+1＝β_k+1＝β_k+Δβ_k+1(10)

④ and substituting the modified α and β into formula (4) to obtain delta_Q0And judging whether the convergence condition is met: | δ_k+1-δ_Q0Epsilon is less than or equal to | or k is more than or equal to k_max，k_maxIf the maximum iteration number is met, outputting the final value of delta, turning to the ③ step to obtain the final values of α and β, and ending the iteration, otherwise, turning to the ② step to continue the iterationAnd (4) calculating.

Technical Field

The invention relates to the technical field of wireless charging, in particular to electric automobile bidirectional wireless charging control methods based on LCL resonance compensation.

Background

In recent years, with the increasing energy crisis and environmental problems, hybrid electric vehicles and pure Electric Vehicles (EVs) are rapidly developed at home and abroad, at present, the biggest obstacle to the popularization of electric vehicles is the problem of charging, compared with a wired charging mode, the wireless charging of the electric vehicles has the characteristics of convenience, rapidness, safety, stability and strong environmental adaptability, and the space occupied by charging piles can be saved, so that the wireless charging has a more application prospect than wired charging.

In the field of EV wireless charging, most of current research is mainly directed to a one-way transmission system, and with the proposal of an energy internet concept and the development of an internet of vehicles technology, an electric vehicle will serve as a important mobile energy storage system in a future intelligent Power distribution network to provide important auxiliary services for an intelligent Power grid.

The resonant network is also called a compensation network, and at present, the resonant network mainly comprises Series (S) compensation, Parallel (Parallel, P) compensation, Series-Parallel (LCL) compensation and other compensation networks derived on the basis.

Regarding the BWPT system, at present, domestic research is few, and foreign research mainly focuses on the establishment of a system mathematical model, the analysis of transmission characteristics, the synchronization method of control signals, and the realization of energy bidirectional flow. In the aspect of control strategies, a PI control algorithm is generally adopted, is simple and easy to implement, and is weak in anti-interference capability and poor in robustness. In addition, the current control strategies all use the precondition that a superior control system gives a charge and discharge power reference value.

The patent application publication No. CN 108544935A discloses a electric vehicle bidirectional wireless charging system transmission power control method, which includes the following steps of calculating mutual inductance between a primary coil and a secondary coil of the system, calculating an internal phase shift angle of a primary converter and a secondary converter according to an output power instruction value, adjusting phases of bridge arm switching signals in the primary converter and the secondary converter respectively by the primary controller and the secondary controller by taking respective clock signals as references, decoupling control of the direction and the magnitude of transmission power, realizing phase synchronization of control signals of the primary converter and the secondary converter by tracking an extreme value of output current, and controlling the direction of the transmission power of the system.

However, in practical application, the technical scheme still has disadvantages, such as the adoption of a dual SP resonant circuit topology, the premise of taking a given power reference value as a premise, no consideration of the actual charging requirement of an owner, or the need of giving the power reference value by a central controller, and inconvenient use, and in addition, the invention realizes the control of the power transmission direction by adopting a method of applying disturbance to a control signal, and the method is complex.

Disclosure of Invention

In order to overcome the above-mentioned drawbacks of the prior art, an embodiment of the present invention provides electric vehicle bidirectional wireless charging control methods based on LCL resonance compensation, which take an LCL-BWPT system as a research target, and from the perspective of a vehicle owner, implement system autonomous and independent operation, do not require an integrated controller, and calculate a reference value of EV charging/discharging power based on a fuzzy control theory, taking into account the will, electricity price, and state of charge of an EV battery, so as to solve the technical problems proposed in the background art.

In order to achieve the purpose, the invention provides the following technical scheme that electric automobile bidirectional wireless charging control methods based on LCL resonance compensation comprise the following specific control methods:

s1, establishing a mathematical model and a control framework of the LCL-BWPT system;

s1.1, adopting an LCL-BWPT system and a control framework;

s1.2, establishing an accurate mathematical model of the LCL-BWPT system:

the secondary side outputs power as follows:

in the formula, P_s、Q_sActive power and reactive power output by the secondary side respectively, α and β are and the internal phase shift angle of the control signal of the secondary converter respectively, delta is the external phase shift angle between the control signals of the two converters, V_dc、V_b secondary side DC bus voltage and battery voltage respectively;

is the resonant frequency, L_pi、L_si, secondary side filter inductance, L_sc、C_sCoil self-inductance and compensation capacitance, R, of secondary side respectively_siThe equivalent resistance of the secondary side resonance circuit; (ii) a M is the mutual inductance coefficient of the coils at two sides;

the maximum output active power is:

s2, adopting the mathematical model and control framework of the LCL-BWPT system, the control scheme is composed of two modules: the method comprises the following steps of setting charge/discharge power and designing control parameters, wherein the specific control steps are as follows:

s2.1, setting charge/discharge power based on a fuzzy theory:

when the vehicle owner does not consider the charging economy, directly calculating a charging power setting value;

when the vehicle owner considers the charging economy, according to the size of the charging/discharging capacity and the psychological price c of the vehicle owner_exWith the current price of electricity c_tSetting the charging/discharging power by applying a fuzzy mathematical theory;

s2.2, designing control parameters based on an LCL-BWPT system accurate mathematical model:

when designing controller parameters, the BWPT system is operated in UPF mode (delta-delta)_Q0Close to but not equal to + -90 deg.), the initial value delta of delta is taken first₀The control parameters α and β are predicted at 90 ° (charge mode) or-90 ° (discharge mode), and the initial values are obtained, followed by iterative correction.

In preferred embodiments, the LCL-BWPT system and the control framework are characterized in that the secondary converters and the secondary converters are arranged on two sides and connected through a loose coupling coil with LCL resonance compensation, the secondary converters and the secondary converters are all high-frequency converters and all adopt a fully-controlled H bridge, a power controller is installed and connected on the side of the secondary converters, the input end of the power controller is connected with the BMS battery energy management system, control parameters are calculated according to the battery state, the electricity price and the intention of a vehicle owner provided by the BMS battery energy management system, and the control parameters α required by the secondary converters are transmitted to the secondary converters through wireless communication.

In preferred embodiments, the power controller is installed on the secondary side and is connected with the secondary side PPM modulation circuit through wireless communication, so that the transmission of the regulation and control parameters α is realized.

In preferred embodiments, in step S1.2, due to the influence of harmonics, when the system is operated in the UPF unit power factor mode, i.e. the output reactive power is 0, the out-shift angle δ is obtained_Q0No longer equal to ± 90 °, but is:

in preferred embodiments, in step S2.1, when the vehicle owner does not consider the economy of charging, the formula for calculating the charging power setting value is as follows:

in the formula, t₀、t_ndEV charge/discharge start time and end time, SoC respectively₀、SoC_exThe state of charge of the battery at the start and end of charging/discharging, respectively, E_Nη are the rated capacity and charge/discharge efficiency of the battery, respectively.

In preferred embodiments, in step S2.1, when the vehicle owner considers the economy of charging, the specific method of setting the charging/discharging power is as follows:

two input variables:

output variables:

① fuzzy space partitioning of input and output variables:

to simplify the rule description, both input variables are divided into three fuzzy subsets: high (H), normal (N), low (L), the output variables are divided into 5 fuzzy subsets: NB (negative large), NS (negative small), ZE (zero), PS (positive small), PB (positive large); the variable membership functions all adopt trapezoidal functions;

② employ fuzzy control rules;

③ fuzzy inference, using Mamdani inference method, determining the fuzzy relation of input and output by control rule, then using fuzzy synthesis operation to obtain fuzzy output by actual fuzzy input inference;

④, deblurring and precision processing, wherein after fuzzy reasoning obtains the fuzzy value of the control variable, the fuzzy value is deblurred by adopting an area gravity center method, so as to obtain the precise value of the control variable;

delta P inferred by fuzzy control rules_refSo as to obtain the compound with the characteristics of,

if P_ref＞P_maxThen let P_ref＝P_max(ii) a If P_ref＜P_minThen let P_ref＝P_min。

In preferred embodiments, in step S2.2, for simplicity of calculation, α is β, and the specific steps are as follows:

① according to the selected charging mode, will be₀Finding P by substituting formula (3) at 90 ° or-90 °_max，δ₀When the phase angle is equal to 90 °, charge is represented, and when the phase angle is equal to 90 °, discharge is represented, the initial value of the phase angle is obtained:

α₀＝β₀＝cos^-1(1-2P_ref/P_max) (6)

② substituting the k-th iteration value of control parameter for equation (2) to obtain the reactive power Q_s，kThen, by the operating conditions of the UPF mode: q_s，kAt 0, the δ value for the k +1 th iteration is found:

δ_k+1＝δ_k+Δδ_k+1(8)

③ will be substituted into α_k＝β_k、δ_k+1Formula (1) is substituted to obtain active power P_s，kThen, α, β for the k +1 th iteration are solved:

α_k+1＝β_k+1＝β_k+Δβ_k+1(10)

④ and substituting the modified α and β into formula (4) to obtain delta_Q0And judging whether the convergence condition is met: | δ_k+1-δ_Q0Epsilon is less than or equal to | or k is more than or equal to k_max(maximum iteration times), if yes, outputting the final value of delta, turning to the ③ step to obtain the final values of α and β, and ending the iteration, otherwise, turning to the ② step to continue the iteration calculation.

The invention has the technical effects and advantages that:

1. the invention takes the LCL-BWPT system as a research object, starts from the angle of a vehicle owner, realizes the autonomous and independent operation of the system, does not need an integrated controller, considers the will, the price of electricity of the vehicle owner, the charge state of an EV battery and the like, and deduces a reference value of EV charging/discharging power based on a fuzzy control theory;

2. the invention applies an accurate LCL-BWPT system mathematical model, takes the improvement of energy transmission efficiency and the reduction of switching loss as starting points, designs a second layer power controller, and realizes the efficient, rapid and stable tracking of a power reference value;

3. the invention changes the power transmission direction by changing the positive and negative signs of the phase shift angle, and obtains the value of the control parameter by iterative calculation based on the accurate system mathematical model, so that the reference power can be quickly trackedP _refAnd the transmission efficiency is high, the switching loss is small, and the anti-interference capability is strong.

Drawings

FIG. 1 is a schematic diagram of an LCL-BWPT system structure and control architecture according to the present invention.

Fig. 2 is a block diagram of a control scheme of the present invention.

FIG. 3 is a diagram illustrating the structure of membership functions for input and output variables according to the present invention.

Fig. 4 is an overall control flow chart of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only partial embodiments of of the present invention, rather than all embodiments.

According to electric vehicle bidirectional wireless charging control methods based on LCL resonance compensation shown in FIGS. 1-4, the specific control method is as follows:

s1, establishing a mathematical model and a control framework of the LCL-BWPT system, as shown in FIG. 1;

s1.1, adopting an LCL-BWPT system and a control framework;

the LCL-BWPT system is characterized in that the -time converter and the secondary converter are arranged on two sides and are connected through a loose coupling coil with LCL resonance compensation, and the -time converter and the secondary converter are both high-frequency converters and all adopt a fully-controlled H bridge;

the control framework is characterized in that a power controller is installed and connected on the side of the secondary converter, the input end of the power controller is connected with a BMS battery energy management system, control parameters are calculated according to the battery state, the electricity price and the intention of a vehicle owner provided by the BMS battery energy management system, and the control parameters α required by the -time converter side are transmitted to the -time converter side through wireless communication, wherein the -time converter is connected with a -time PPM modulation circuit, the secondary converter is connected with a secondary-side PPM modulation circuit, the output end of the power controller is connected with the input end of the secondary-side PPM modulation circuit, and the -time PPM modulation circuit is connected with the secondary-side controller through wireless communication to realize the;

s1.2, establishing an accurate mathematical model of the LCL-BWPT system:

the secondary side outputs power as follows:

in the formula, P_s、Q_sActive power and reactive power output by the secondary side respectively, α and β are and the internal phase shift angle of the control signal of the secondary converter respectively, delta is the external phase shift angle between the control signals of the two converters, V_dc、V_b secondary side DC bus voltage and battery voltage respectively;is the resonant frequency, L_pi、L_si, secondary side filter inductance, L_sc、C_sCoil self-inductance and compensation capacitance, R, of secondary side respectively_siThe equivalent resistance of the secondary side resonance circuit; m is the mutual inductance coefficient of the coils at two sides;

the maximum output active power is:

due to the influence of harmonic wave, when the system operates in a UPF unit power factor mode, namely the output reactive power is 0, the phase angle delta is shifted outwards_Q0No longer equal to ± 90 °, but is:

s2, adopting the mathematical model and control framework of the LCL-BWPT system, the control scheme is composed of two modules: the specific implementation process of each module is shown in fig. 2, and the specific control steps are as follows:

s2.1, setting charge/discharge power based on a fuzzy theory:

when the vehicle owner does not consider the charging economy, the charging power setting value is directly calculated, and the formula is as follows:

in the formula, t₀、t_ndEV charge/discharge start time and end time, SoC respectively₀、SoC_exThe state of charge of the battery at the start and end of charging/discharging, respectively, E_Nη are the rated capacity and charge/discharge efficiency of the battery, respectively;

when the vehicle owner considers the charging economy, the charging cost is lower while the charging requirement is expected to be met from the vehicle owner's perspective, and therefore, the charging cost is lower according to the magnitude of the charging/discharging capacity and the psychological price c of the vehicle owner_exWith the current price of electricity c_tThe difference of (2) is to set the charging/discharging power by applying fuzzy mathematical theory, and the specific method is as follows:

two input variables:

output variables:

① fuzzy space partitioning of input and output variables:

to simplify the rule description, both input variables are divided into three fuzzy subsets: high (H), normal (N), low (L), the output variables are divided into 5 fuzzy subsets: NB (negative large), NS (negative small), ZE (zero), PS (positive small), PB (positive large); the variable membership functions are all trapezoidal functions, as shown in FIG. 3;

②, using fuzzy control rules, as shown in tables 1 and 2 below:

TABLE 1 fuzzy control rules for charging power settings

TABLE 2 fuzzy control rules for discharge power settings

③ fuzzy inference, using Mamdani inference method, determining the fuzzy relation of input and output by control rule, then using fuzzy synthesis operation to obtain fuzzy output by actual fuzzy input inference;

④, deblurring and precision processing, wherein after fuzzy reasoning obtains the fuzzy value of the control variable, the fuzzy value is deblurred by adopting an area gravity center method, so as to obtain the precise value of the control variable;

delta P inferred by fuzzy control rules_refSo as to obtain the compound with the characteristics of,

if P_ref＞P_maxThen let P_ref＝P_max(ii) a If P_ref＜P_minThen let P_ref＝P_min；

S2.2, designing control parameters based on an LCL-BWPT system accurate mathematical model:

simulation analysis and experimental verification show that: the closer the phase angle delta is to +/-90 degrees, the higher the theoretical transmission efficiency between the coils can be; however, when δ is equal to ± 90 °, half of the switching tubes in the BWPT system will operate in the hard on state, which is not favorable for the optimal operation of the converter. Therefore, when designing the controller parameters, the BWPT system is operated in the UPF mode (δ ═ δ -_Q0Close to but not equal to ± 90 °), thereby improving wireless energy transfer efficiency and reducing switching loss of the converter. Based on this, the initial value delta of delta is first taken₀Predicting control parameters α and β at 90 degrees (charging mode) or-90 degrees (discharging mode) to obtain initial values, then iteratively correcting, and taking α at β for simplifying calculation, wherein the specific steps are as follows:

① depending on the charging mode selected,will delta₀Calculation of P by substituting formula (3) for 90 ° (charging) or-90 ° (discharging)_maxThen, the initial value of the phase shift angle is obtained:

α₀＝β₀＝cos^-1(1-2P_ref/P_max) (6)

② substituting the k-th iteration value of control parameter for equation (2) to obtain the reactive power Q_s，kThen, by the operating conditions of the UPF mode: q_s，kAt 0, the δ value for the k +1 th iteration is found:

δ_k+1＝δ_k+Δδ_k+1(8)

③ will be substituted into α_k＝β_k、δ_k+1Formula (1) is substituted to obtain active power P_s，kThen, α, β for the k +1 th iteration are solved:

α_k+1＝β_k+1＝β_k+Δβ_k+1(10)

④ and substituting the modified α and β into formula (4) to obtain delta_Q0And judging whether the convergence condition is met: | δ_k+1-δ_Q0Epsilon is less than or equal to | or k is more than or equal to k_max(maximum iteration times), if yes, outputting the final value of delta, turning to the ③ step to obtain the final values of α and β, and ending the iteration, otherwise, turning to the ② step to continue the iteration calculation, and the whole control flow chart is shown in fig. 4.

Description of the drawings: 1. the mathematical model of the LCL-BWPT system is the reference [1 ]: ahmed A.S.M., AlbertoBerzoy, 0sama A.M.Experimental Validation of Comprehensive step-State analytical Model of Bidirectional WPT System in EVs Applications [ J ]. IEEETransactions On Vehicular Technology, 66(7), pp.5584-5594, 2017.

First, in the description of the present application, it should be noted that, unless otherwise specified and limited, the terms "mounted," "connected," and "connected" should be understood as meaning either mechanically or electrically connected, or communication between two elements, or directly connected, and "up," "down," "left," and "right" are used only to indicate relative positional relationships, and when the absolute position of the object to be described changes, the relative positional relationships may change;

in the drawings of the disclosed embodiment of the invention, only the structures related to the disclosed embodiment are referred to, other structures can refer to common design, and the same embodiment and different embodiments of the invention can be combined with each other without conflict;

and finally: 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 are within the spirit and principle of the present invention are intended to be included in the scope of the present invention.