Capacity configuration method for household photovoltaic energy storage system
阅读说明：本技术 一种家庭光伏储能系统的容量配置方法 (Capacity configuration method for household photovoltaic energy storage system ) 是由 蒋建彗 倪志春 魏青竹 陈成锦 蔡霞 柯坡 陆文华 曹海波 余嫦 吴镇 于 2019-09-20 设计创作，主要内容包括：本发明公开了一种家庭光伏储能系统的容量配置方法,为不同条件的用户提供家庭光伏储能系统方案指导。一种家庭光伏储能系统的容量配置方法,包括如下步骤：A、根据当地居民电价政策选择运行模式,所述运行模式包括通用模式和经济模式；若当地居民电价政策无峰谷电价时,选择所述通用模式；若当地居民电价政策有峰谷电价时,选择所述经济模式；B、获取家庭用户的日用电量及日用电规律；C、依据家庭用户的需求及所选择的运行模式设计方案,所述方案包括光伏容量及储能电池容量。(The invention discloses a capacity configuration method of a household photovoltaic energy storage system, which provides scheme guidance of the household photovoltaic energy storage system for users under different conditions. A capacity configuration method of a household photovoltaic energy storage system comprises the following steps: A. selecting an operation mode according to a local resident electricity price policy, wherein the operation mode comprises a general mode and an economic mode; if the local resident electricity price policy has no peak-valley electricity price, selecting the general mode; if the local resident electricity price policy has peak-valley electricity prices, selecting the economic mode; B. acquiring daily electricity consumption and daily electricity consumption rules of a household user; C. and designing a scheme according to the requirements of the household user and the selected operation mode, wherein the scheme comprises photovoltaic capacity and energy storage battery capacity.)
1. A capacity configuration method of a household photovoltaic energy storage system is characterized by comprising the following steps:
A. selecting an operation mode according to a local resident electricity price policy, wherein the operation mode comprises a general mode and an economic mode; if the local resident electricity price policy has no peak-valley electricity price, selecting the general mode; if the local resident electricity price policy has peak-valley electricity prices, selecting the economic mode;
B. acquiring daily electricity consumption and daily electricity consumption rules of a household user;
C. and designing a scheme according to the requirements of the household user and the selected operation mode, wherein the scheme comprises photovoltaic capacity and energy storage battery capacity.
2. The capacity configuration method of claim 1,
when the operation mode is a general mode, the photovoltaic capacity W in the step C satisfies the following conditions:
wherein P is the daily electric quantity of a household user, PR is the system conversion efficiency from a direct current end to an alternating current end of the household photovoltaic energy storage system, and h is the daily average peak sunshine hours;
the capacity V of the energy storage battery in the step C meets the following requirements:
wherein, PNightThe power consumption of the household user at night is shown as omega, the battery discharge efficiency is shown as mu, the battery energy conversion efficiency is shown as mu, and epsilon is the battery discharge depth.
3. The capacity configuration method of claim 1,
when the operation mode is the economy mode, the photovoltaic capacity W in the step C satisfies the following conditions:
wherein P is the daily electricity consumption of a household user, V is the capacity of an energy storage battery, PR is the system conversion efficiency from a direct current end to an alternating current end of the household photovoltaic energy storage system, and h is the average peak sunshine hours per day;
the capacity V of the energy storage battery in the step C meets the following requirements:
wherein, PNightThe power consumption of the household user at night is shown as omega, the battery discharge efficiency is shown as mu, the battery energy conversion efficiency is shown as mu, and epsilon is the battery discharge depth.
4. The capacity allocation method according to claim 1, wherein: the operation mode further comprises an off-grid mode, and if the local area is a remote area, the off-grid mode is selected.
5. The capacity configuration method of claim 4,
when the operation mode is an off-grid mode, the photovoltaic capacity W in the step C satisfies the following condition:
the method comprises the following steps that P is daily electricity consumption of a household user, d is the number of days of local continuous overcast and rainy, PR is system conversion efficiency from a direct current end to an alternating current end of the household photovoltaic energy storage system, h is the average peak sunlight hour per day, and t is the number of days required for charging a storage battery;
the capacity V of the energy storage battery in the step C meets the following requirements:
where ω is the battery discharge efficiency, μ is the battery energy conversion efficiency, and ε is the battery depth of discharge.
6. The capacity configuration method of claim 1,
in the step C, a plurality of schemes to be selected are designed according to different requirements of the family user and the selected operation mode;
the capacity configuration method further comprises the following steps:
D. and respectively analyzing investment income of each scheme, selecting the scheme with the best economy, and configuring the photovoltaic capacity and the energy storage battery capacity of the household photovoltaic energy storage system according to the selected scheme.
7. The capacity allocation method according to claim 6, wherein the step D specifically comprises:
calculating the income C of each scheme under the selected operation mode;
investment C for obtaining total cost of household grid-connected optical energy storage systemThrow-in；
Calculating the total income C in the life cycle of each scheme according to the income C and the total investment cost Ctotal；
And calculating the project recovery period and the internal yield, and selecting an economic optimal scheme.
8. The capacity allocation method according to claim 7, wherein the profit C is a monthly profit and the total profit C in the life cycletotal＝12*c*n-cThrow-inWherein n is the life cycle of the project.
9. The capacity allocation method according to claim 7 or 8, wherein the profit C in the general mode is calculated according to the following formula:
C＝Q1*(E1+S)+Q2*(E2+S)+Q3*(E3+S)+Q*(E+S)
the device comprises a power supply module, a power supply module and a controller, wherein E1 is a first-step power price, E2 is a second-step power price, E3 is a third-step power price, Q1 is first-step photovoltaic self-power consumption, Q2 is second-step photovoltaic self-power consumption, Q3 is third-step photovoltaic self-.
10. The capacity allocation method according to claim 7 or 8, wherein the profit C in the economy mode is calculated according to the following formula:
C＝Q1*(E1+S)+Q2*(E2+S)+Q3*(E3+S)+V*(Ppeak(s)-PGrain)+Q*(E+S)
Wherein E1 is first ladder electricity price, E2 is second ladder electricity price, E3 is third ladder electricity price, Q1 is first ladder photovoltaic self-using electricity quantity, Q2 is second ladder photovoltaic self-using electricity quantity, Q3 is third ladder photovoltaic self-using electricity quantity, S is photovoltaic electricity price subsidy, Q is surplus online electricity quantity, E is local desulfurization coal electricity price, P is the first ladder electricity price, E is the second ladder electricity price, and the second ladder electricity price is the second ladder photovoltaic self-using electricity quantity, and thePeak(s)Represents the peak electricity rate, P, of the peak-to-valley electricity ratesGrainIndicates a valley power rate among peak-to-valley power rates.
Technical Field
The invention belongs to the field of photovoltaics, and relates to a capacity configuration method for a household photovoltaic energy storage system.
Background
With the technical development of the photovoltaic industry and the change of national subsidy policies, the price of the photovoltaic module rapidly decreases in recent years. The reduction of the price of the component enables a household photovoltaic system to come to spring, aiming at rural and villa users, the reduction of the price of the photovoltaic component is converted from the original high input to the low input high recovery, and simultaneously, in 2019, the photovoltaic new political affairs aim at the independent division of the subsidies of the household photovoltaic system, so that the household photovoltaic market is greatly stimulated. The household photovoltaic system can flexibly select a self-service and surplus power internet surfing mode or a full internet surfing mode, so that economic benefits are maximized.
While the price of the photovoltaic industry is reduced, the industry has been discussed about the way of coming photovoltaic, and most persuasive is that the combination of photovoltaic and energy storage is the indispensable way of coming photovoltaic. And from 2018, the improvement of the lithium battery technology in China causes the great reduction of the battery cost, and the photovoltaic and energy storage are combined to have good economical efficiency. At present, in germany, italy and other european countries with fast photovoltaic development and australia with higher residential electricity prices, the household photovoltaic energy storage system is rapidly developed in two years, and the countries have various advantages and subsidies on the household photovoltaic energy storage system, so that the development of the household photovoltaic energy storage system is greatly promoted. Although no relevant policy specially aiming at a household photovoltaic energy storage system exists in China at present, the photovoltaic energy storage system has the advantages of improving the electric energy quality of a power grid, reducing the impact of the photovoltaic system on the power grid, reducing the peak-valley power utilization difference value of the power grid and the like, and can flexibly adjust the working mode of the energy storage system, so that the economy of photovoltaic energy storage users is maximized, the power utilization stability of the users is guaranteed (the energy storage system can be used for supplying power to household common electrical appliances when the power grid is powered off, and the uninterrupted power supply is realized), and the photovoltaic energy storage system has a great application prospect.
From 2018, the energy storage system enters an industrial explosion period, and only one year in 2018, the installed capacity is rapidly doubled, so that the power battery enterprises and the photovoltaic enterprises are promoted to be arranged in an energy storage direction in a dispute. However, since energy storage is just rising, the main markets aimed by various large manufacturers are power grid side and user side energy storage systems, but the household photovoltaic energy storage systems are not further distributed. Because the market of the household photovoltaic energy storage system is small at present, a standard design scheme and definite economic analysis aiming at the household photovoltaic energy storage system are not available. Although the installed capacity of a user is small, the household photovoltaic energy storage system inevitably occupies a place in the future energy storage market along with the reduction of the energy storage cost due to the advantages of wider user group, simple installation and construction and the like.
Disclosure of Invention
Aiming at the technical problems, the invention aims to provide a capacity configuration method specially aiming at different working modes and different profit manners of a household photovoltaic energy storage system, and provides scheme guidance of the household photovoltaic energy storage system for users under different conditions.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a capacity configuration method of a household photovoltaic energy storage system comprises the following steps:
A. selecting an operation mode according to a local resident electricity price policy, wherein the operation mode comprises a general mode and an economic mode; if the local resident electricity price policy has no peak-valley electricity price, selecting the general mode; if the local resident electricity price policy has peak-valley electricity prices, selecting the economic mode;
B. acquiring daily electricity consumption and daily electricity consumption rules of a household user;
C. the scheme is designed according to the requirements of the electricity consumption and the electricity consumption law of a household user and the selected operation mode, and comprises photovoltaic capacity and energy storage battery capacity.
Preferably, when the operation mode is a general mode, the photovoltaic capacity W in the step C satisfies:
wherein P is the daily electric quantity of a household user, PR is the system conversion efficiency from a direct current end to an alternating current end of the household photovoltaic energy storage system, and h is the daily average peak sunshine hours;
the capacity V of the energy storage battery in the step C meets the following requirements:
wherein, PNightThe power consumption of the household user at night is shown as omega, the battery discharge efficiency is shown as mu, the battery energy conversion efficiency is shown as mu, and epsilon is the battery discharge depth.
Preferably, when the operation mode is the economy mode, the photovoltaic capacity W in the step C satisfies:
wherein P is the daily electricity consumption of a household user, V is the capacity of an energy storage battery, PR is the system conversion efficiency from a direct current end to an alternating current end of the household photovoltaic energy storage system, and h is the average peak sunshine hours per day;
the capacity V of the energy storage battery in the step C meets the following requirements:
wherein, PNightThe power consumption of the household user at night is shown as omega, the battery discharge efficiency is shown as mu, the battery energy conversion efficiency is shown as mu, and epsilon is the battery discharge depth.
Preferably, the operation mode further comprises an off-grid mode, and the off-grid mode is selected if the local area is a remote area.
More preferably, when the operation mode is an off-grid mode, the photovoltaic capacity W in the step C satisfies:
the method comprises the following steps that P is daily electricity consumption of a household user, d is the number of days of local continuous overcast and rainy, PR is system conversion efficiency from a direct current end to an alternating current end of the household photovoltaic energy storage system, h is the average peak sunlight hour per day, and t is the number of days required for charging a storage battery;
the capacity V of the energy storage battery in the step C meets the following requirements:
where ω is the battery discharge efficiency, μ is the battery energy conversion efficiency, and ε is the battery depth of discharge.
Preferably, in the step C, a plurality of schemes to be selected are designed according to different power consumption and power consumption law requirements of the home user and the selected operation mode (the specific design is mainly photovoltaic capacity and battery capacity design, and the design method is according to the description in the step C);
the capacity configuration method further comprises the following steps:
D. and respectively analyzing investment income of each scheme, selecting the scheme with the best economy, and configuring the photovoltaic capacity and the energy storage battery capacity of the household photovoltaic energy storage system according to the selected scheme.
Preferably, the step D specifically includes:
calculating the income C of each scheme under the selected operation mode;
investment C for obtaining total cost of household grid-connected optical energy storage systemThrow-in；
Calculating the total income C in the life cycle of each scheme according to the income C and the total investment cost Ctotal；
And calculating the project recovery period and the internal yield, and selecting an economic optimal scheme.
Further, the income C is monthly income, and the total income C in the life cycletotal＝12*C*n-CThrow-inWherein n is the life cycle of the project.
Further, the profit C in the general mode is calculated according to the following formula:
C＝Q1*(E1+S)+Q2*(E2+S)+Q3*(E3+S)+Q*(E+S)
the device comprises a power supply module, a power supply module and a controller, wherein E1 is a first-step power price, E2 is a second-step power price, E3 is a third-step power price, Q1 is first-step photovoltaic self-power consumption, Q2 is second-step photovoltaic self-power consumption, Q3 is third-step photovoltaic self-.
Further, the profit C in the economy mode is calculated according to the following formula:
C＝Q1*(E1+S)+Q2*(E2+S)+Q3*(E3+S)+V*(Ppeak(s)-PGrain)+Q*(E+S)
Wherein E1 is first ladder electricity price, E2 is second ladder electricity price, E3 is third ladder electricity price, Q1 is first ladder photovoltaic self-using electricity quantity, Q2 is second ladder photovoltaic self-using electricity quantity, Q3 is third ladder photovoltaic self-using electricity quantity, S is photovoltaic electricity price subsidy, Q is surplus online electricity quantity, E is local desulfurization coal electricity price, P is the first ladder electricity price, E is the second ladder electricity price, and the second ladder electricity price is the second ladder photovoltaic self-using electricity quantity, and thePeak(s)Represents the peak electricity rate, P, of the peak-to-valley electricity ratesGrainIndicates a valley power rate among peak-to-valley power rates.
Compared with the prior art, the invention has the following advantages by adopting the scheme:
the capacity allocation method is a capacity allocation scheme and an economic analysis method specially aiming at different working modes and different profit modes of the household photovoltaic energy storage system, and can provide optimal household photovoltaic energy storage system scheme guidance and expected economic measurement and calculation for users under different conditions.
Drawings
In order to more clearly illustrate the technical solution 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 the drawings without creative efforts.
FIG. 1 is a schematic diagram of a home photovoltaic energy storage system;
fig. 2 is a flow chart of capacity allocation of a household photovoltaic energy storage system according to an embodiment;
fig. 3 is a flowchart of an economic analysis of a household photovoltaic energy storage system according to an embodiment.
Wherein the content of the first and second substances,
1. a photovoltaic array; 2. a photovoltaic controller; 3. a bidirectional charger; 4. an energy storage battery; 5. a bidirectional inverter; 6. a load; 7. a bidirectional electric meter; 8. a power grid; 9. a power control system.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the advantages and features of the invention may be more readily understood by those skilled in the art. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, the household photovoltaic energy storage system includes a photovoltaic array 1, a photovoltaic controller 2, a
When the household photovoltaic energy storage system operates in a universal mode, the working sequence of the household photovoltaic energy storage system is 'load priority, battery second time and residual electricity on the internet'. Namely, when a load works in the household photovoltaic energy storage system, the generated energy of the photovoltaic module is preferentially supplied to the load for use, if the photovoltaic power generation is less than the load power, the energy storage battery is required to supply the electric quantity (load power-photovoltaic power generation) to the load for use, and if the battery has no redundant electric quantity, the electric quantity (load power-photovoltaic power generation) provided by the power grid is required to be supplied to the load for use; if the photovoltaic power generation is larger than the load power, redundant electric quantity (photovoltaic power generation-load power) is preferentially supplied to the battery to charge the battery, and if the battery is full, the redundant electric quantity is supplied to a power grid, namely, a residual power grid-surfing mode.
When the household photovoltaic energy storage system operates in an economic mode, the working principle is that charging is carried out at the valley price and discharging is carried out at the peak price. The method comprises the following steps: the system can adjust the power to the energy storage battery from the power grid when the electricity price is in the valley, and discharges the energy storage battery to supply power for the load or surf the internet when the electricity price is in the peak. The local resident electricity prices on the premise of this mode have peak-to-valley electricity prices, and the larger the peak-to-valley price difference, the better the economy of this mode, so the economic profit is closely related to the electricity price policy of different countries or regions.
When the household photovoltaic energy storage system operates in an off-grid mode, the mode is mainly used in remote areas, islands and other areas isolated from a large power grid, so that the mode has certain limitation in use, and the capacity configuration of the mode is mainly based on the local power utilization condition and continuous rainy days. The system needs to meet daily power consumption requirements of off-grid users during design, all power consumption is provided by the photovoltaic system, if the electric quantity of the photovoltaic system is larger than the load power consumption, redundant electric quantity charges the energy storage battery, and if the battery is fully charged, the redundant electric quantity is wasted, so that the best capacity is designed.
As shown in fig. 2, the capacity configuration method of the household photovoltaic energy storage system of the embodiment includes the following steps:
1. the method comprises the steps of collecting project sites and local resident electricity price policies (whether peak-valley electricity prices are executed, the electricity price difference is large, whether step electricity prices are executed or not), and calculating the average daily peak sunlight hours h by using professional software according to the project sites, so that the photovoltaic power generation amount can be conveniently calculated later. Selecting which operation mode to adopt according to the local resident electricity price policy, wherein the selection principle is as follows: if the local peak-valley free electricity price is yes, selecting a general mode; selecting an economic mode if the local area has obvious peak-valley electricity prices; if the local area is a remote area, only the off-grid mode can be selected for design.
2. Survey household user's power consumption condition and law, mainly include daily electric quantity P, daily load power curve of basic information such as electricity consumption law, carry out photovoltaic and energy storage system capacity design according to daily electric quantity, the design principle does: on the premise of considering the conversion efficiency of the system, the photovoltaic power generation can be ensured to meet the power consumption requirement of a user. And meanwhile, photovoltaic and energy storage capacity setting needs to be carried out by combining different operation modes.
3. According to the research result, the capacities of the photovoltaic cell and the energy storage cell are respectively designed according to different operation modes.
3-1, Universal mode Capacity design
Firstly, photovoltaic capacity design is carried out, and the photovoltaic capacity W should satisfy at least:
the PR value is the system conversion efficiency from the direct current end to the alternating current end of the photovoltaic and energy storage system, and the empirical value of the PR value is selected to be in the range of 80% -85%. P is daily electric quantity, and h is daily average peak sunshine hours obtained by software simulation calculation.
And then, designing the capacity V of the energy storage battery, wherein the battery capacity needs to meet the following requirements:
in the formula, PNightFor the household user, the power consumption at night, ω is the battery discharge efficiency (bidirectional charger operating efficiency), μ is the battery energy conversion efficiency (battery discharge/battery charge), and ε is the battery discharge depth (percentage of battery discharge to battery rated capacity).
3-2, economic mode capacity design
And when the electricity prices of residents in the project place have peak and valley electricity prices, the use of the economic mode can be considered, and finally, the economic performance of the economic mode and the general mode is compared and analyzed, and a better scheme is selected. Generally, the larger the peak-to-valley electricity price difference, the better the economy, and the more recommended the economy mode is.
Firstly, photovoltaic capacity design is carried out, and the photovoltaic capacity W should satisfy at least:
wherein each symbol is as defined above.
And then, designing the capacity V of the energy storage battery, wherein the battery capacity needs to meet the following requirements:
in the formula, PNightThe power consumption of the user is the same as the above meaning.
The range is adopted in the above formula instead of ═ mainly because the above formula is the most basic requirement that needs to be achieved under different modes of the household photovoltaic system, and certain changes can be made according to project characteristics and customer requirements.
3-3, off-grid mode capacity design
If the project only supports the off-grid mode, the off-grid system needs to be designed according to project characteristics, and the off-grid project photovoltaic system capacity design meets the following requirements:
in the formula, d is the number of days of continuous overcast and rainy in the local area, h is the average peak daily sunshine hours obtained by software simulation calculation, and t is the number of days required for charging the storage battery.
The design of energy storage battery capacity V, battery capacity needs to satisfy:
4. according to different project places and customer requirements, selecting a proper operation mode, and calculating several schemes to be selected according to a related formula.
5. The investment income analysis is carried out on a plurality of different scale schemes (because the curves of the power consumption and the power consumption law of each user are inconsistent, and the planned investment quantity is diversified, a plurality of different capacity schemes need to be designed according to the actual requirements of different customers, the main difference of each scheme is that the capacities of photovoltaic and energy storage batteries are different, the customers can conveniently select according to the actual power consumption and the investment condition, and the scheme design provides the investment income analysis for the customers aiming at each scheme simultaneously so as to provide the reference selection for the customers), so that the scheme with the best economical efficiency is selected. The project investment can be estimated according to market price, the income analysis needs to calculate basic information such as income, recovery time limit, internal earning rate and the like according to different project places and different residential electricity requirements, and the optimal and most economic scheme is selected.
Referring to fig. 3, the specific steps of the economic analysis of this embodiment are as follows:
1. the income of the household photovoltaic energy storage system is influenced by a local electricity price policy and a system working mode, and the system income calculation needs to be analyzed according to the specific working mode.
1-2, calculating the monthly income in a general mode:
C＝Q1*(E1+S)+Q2*(E2+S)+Q3*(E3+S)+Q*(E+S)
in the above formula, C is income, E1 is first ladder electricity price, E2 is second ladder electricity price, E3 is third ladder electricity price, Q1 is first ladder photovoltaic self-using electricity quantity, Q2 is second ladder photovoltaic self-using electricity quantity, Q3 is third ladder photovoltaic self-using electricity quantity, S is photovoltaic electricity price subsidy, Q is surplus online electricity quantity, and E is local desulfurization coal electricity price.
In the above formula, the gain calculation is performed by considering the factor of the stepped electricity price, and if the electricity consumption of the user only reaches the second step, the value of Q3 is 0, and the calculation result is not affected. At the same time, peak-to-valley price differences are not considered in this calculation.
1-2, calculating the monthly income of the economic model:
CQ1*(E1+S)+Q2*(E2+S)+Q3*(E3+S)+V*(Ppeak(s)-PGrain)+Q*(E+S)
In the formula, PPeak(s)Represents the peak electricity rate, P, of the peak-to-valley electricity ratesGrainIndicates a valley power rate among peak-to-valley power rates.
In the calculation of the formula, the peak-to-valley electricity price difference and the step electricity price factor are comprehensively considered, and a detailed and income calculation method is provided.
2. Total cost investment C for project completionThrow-inAnd (5) information collection and calculation.
3. Calculating Total earnings C within the Life cycletotal：
Ctotal＝12*C*n-CThrow-in
Where n is the life cycle of the project.
4. And finally calculating the project recovery period and the internal yield through the factors, selecting an economic optimal scheme aiming at different schemes, and configuring the photovoltaic capacity and the energy storage battery capacity according to the selected economic optimal scheme.
The project recovery period calculation method comprises the following steps: i.e. investing in C when the total cost of the projectThrow-inTotal profit in life cycle CtotalThe time required.
Internal rate of return: the Internal Rate of Return (IRR), which is the discount Rate when the total amount of the capital inflow and the total amount of the capital outflow are equal and the net present value is equal to zero, is financial information, and is calculated as follows:
IRR＝a+[NPVa/(NPVa-NPVb)]*(b-a)
wherein: a. b is the discount rate, a>b；NPVaWhen the discount rate is a, the net current value calculated is a positive number NPVbWhen the discount rate is b, the net present value calculated is a negative number.
In the capacity configuration method, 1, a consistent calculation method is given to photovoltaic and energy storage capacity configuration of a household photovoltaic energy storage system according to different working modes through analysis; 2. according to different operation modes, an economic calculation method under each mode is provided, influence factors of peak-valley electricity prices and step electricity prices are considered in the calculation in detail, and a general calculation formula is provided.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and are preferred embodiments, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the scope of the present invention. All equivalent changes or modifications made according to the principles of the present invention should be covered within the protection scope of the present invention.
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