DC Micro-Grid Contactless Power Supply System with Load Detecting Control Method

Transcription

1 MicroGrid ontactless Power upply yste with Load etectin ontrol Method on Xu, a, eiji Hashioto,b and Wei Jian,c ivision of Electronics and inforatics, Guna University, Kiryu, Guna, Japan epartent of Electrical Enineerin, Yanzhou University, Yanzhou, hina a <xuson9@63.co>, b < hashiotos@unau.ac.jp>, c <jianwei@yzu.edu.cn> Keywords: contactless power transfer, dc icro rid, load detectin control. Abstract. icrorid is ainin an increasin attention in the field of power oranization because of its hih efficiency and intellience in power oranizin and usin abilities. In this paper, a contactless power supply syste for the obile active load in the icrorid has been desined and analyzed. Moreover, for the enery savin purpose, the load detection function has been added to the transfer syste. The theoretic analysis of the power transfer syste is proposed and the siulation has been carried out in MATLAB/IMULINK to test the control ethod. The experient platfor is built with a dspi controller, and then experients are perfored to verify the control efficiency of the load detectin control ethod.. Introduction icrorid is ainin ore and ore attention, because of the rapid developent of new enery and distributed power eneration technoloy. However, the isolated syste protection between rid and the source load still need to be iproved. The wireless power transfer technoloy provides a feasible way for the isolated protection. The technoloy uses the anetic enery to transfer the electric power, and accordin to the way of power transfer, it can be divided into three parts: electroanetic power transfer, resonance power transfer and radiation power transfer. Its benefits can be shortly concluded as no contact, safe and reliable, continuous power supply [][4]. This paper desins a contactless power supply syste applied to the source load of icrorid. The syste is based on the principle of electroanetic induction, and use the series L resonant tank to realize the noncontact power transission. ue to the characteristics of the source load, the power adjustent unit is desined to atch the different voltae levels of the load. The syste takes the icrorid as the ain power input, and in order to siulate the source load of the rid, the 48V battery is taken as the ain load of the syste. The syste can realize the contactless power supply fro the ird to the battery. In this paper, focusin on the load detectin function of the syste, the cobination of theory and experient is used to evaluate the load detectin control ethod.. yste tructure The syste frae and scheatic diara are shown in Fi.. The proposed syste ainly includes four parts: input power, power conversion unit, resonant network unit, power adjustent unit and enery storae battery. The power conversion unit coprises the priary / A conversion unit and the secondary A / conversion unit. The resonant network is ainly

2 coposed of a series L resonant network. Power adjustent unit is cobined by the boost converter, takin 48V battery as the ain load to siulate the source load of icrorid. + Priary oil econdary coil Bettery A A ouplin Tank P V PWM 3 PWM3 4 I L L 3 B 5 V V 3 L G V PWM5 H 3 V V 4 P PWM PWM4 MU MU Fi.. yste frae and scheatic diara Fro the scheatic diara, the / A converter unit in priary side and the A/ converter unit in secondary side both use the full bride topoloy, and the resonant tank in both side are the sae L series resonant net. The typical resonant network of both side of the syste is shown in Fi.. Assuin that is the priary resonant capacitor, L is the resonant inductance, is the secondary resonant capacitor, L is the resonant inductance. In order to achieve the hihest power transission efficiency, the resonant frequency of the priary side f and secondary side f need to be sae, as show in Eq. (). f = f = = () π L π L i i + + v L v 3. Inductance urrent Analysis Fi.. Typical L series resonant net The series resonant couplin tank is applied and the boost converter is used as the power adjustent unit, which can atch the voltae level and ake the syste to have constant current in the resonant inductance. To analysis the characteristic of this syste, the whole circuit topoloy can be equaled to a Ttype siplified circuit as shown in Fi. 3. i ( i ( u ( L M R M L M R u ( Vin R L Fi. 3 iplified Ttype circuit

3 With this siplified circuit, assuin that k is the couplin coefficient between priary resonant inductance L and secondary resonant inductance L, the input voltae is E, the syste anular frequency is ω, the utual inductance between the priary and secondary coils is M, as described in Eq. () and Eq. (3) L L () M k L L (3) Accordin to the principle of full bride inverter, the relationship between u( and the input voltae E can be calculated as Eq. (4), also the relationship between u( and the input voltae of the Boost converter input voltae Vin can be calculated as Eq. (5). 4E ( sin t (4) ( 4V in u sin t (5) u Accordin to Kirchhoff's law of voltae, the voltae identities of the priary side and secondary side are obtained as Eq. (6) and Eq. (7) i ( L R j Mi( u( j i( L R j Mi ( u( j (6) (7) When the syste is workin under the resonant frequency, due to the priary and secondary coil resistance R, R can be neliible, the syste state eets the Eq. (8) L L (8) o that we can et the current in the priary coil i( as Eq. (9) and the current in secondary coil i( as Eq. () u( i( (9) M 4V sin t M in i ( Fro the Eq. (9) and Eq. (), two ain characteristics of the couplin syste can be obtained. First, the current in the priary coil only can be influenced by the input voltae of the Boost converter, so if the voltae is controlled, the current in priary coil will be constant and independent of the input voltae. econd, the current in the secondary coil is only related to the voltae of the input. When the syste is under the condition that the input voltae is constant, the current is not affected by the transission power. These characteristics is naed as the syste coil current constant. 4. ontrol yste esin In order to eet the load instability and save enery, the syste should just work when there is load connected. That is, only when the load is accessed, the syste is workin continuously, if the load is absent, the syste should be cut down and worked in the detectin ode, and no enery transission is required. For this purpose, in the priary side of the syste, the load detection ()

4 > control ethod was desined. The control block is shown in Fi. 4, where the axiu current in the priary coil is used to jude the load state, Moreover, the iddle point saplin ethod is applied to et the axiu current. E(s)>A yste Enable Y(s) + E(s) I L (s) Y(s) E(s)<A yste isable H(s) Fi.4. all sinal equivalent circuit In Fi. 4, Y(s) is the realtie output of the current saplin circuit, Y(s) is previous output of the saplin circuit, E(s) is the error between the previous saple and the current saple value, H(s) is the transfer function of the saplin circuit, and IL(s) is the current in the priary coil. Accordin to the couplin theory, the axiu current error is set to A. o that, when E(s)>A, it can be seen that the load is connected, then syste bein to work continuously and to transfer the power fro icrorid to the source load. When E(s)<A, it can be considered that the load has been cut off, then, the syste chanes the workin odel into detectin odel. The detection state of the syste is set to detect s per s, so as to jude whether there is no load access, and control the syste to achieve load detection control. 5. MATLAB/IMULINK iulation Accordin to the above analysis, the whole closed loop syste is built in MATLAB / IMULINK, ainly to verify the load detection function and the transfer power control. The ain siulation circuit and each odule are shown in Fi. 5. In this siulation, set the siulation tie.6s, and the load is connected at.3s. After the load connection, the input voltae of the boost converter is controlled at 8V. Accordin to the theoretical analysis, before.3s, the syste should be workin in the detection ode, after.3s, the syste should work continuously. The siulation result is shown in Fi. 6. the syste works as the load detection state before.3s, and works continuously and transfer power after.3s. cope Mosfet4 Ground iscrete, Ts = e6 s. eries RL Branch powerui M M3 Ground Mosfet Mosfet o Vin p ouplin s bus + v VinBoost M5 o Bettery M M4 Mosfet Mosfet3 witch Ideal witch Ground4 PWMH PWML PWMH PWML f ref EN 4 onstant Vref Verror PWM tep witchin Network 8 PZ controlor Fi. 5. MATLAB/IMULINK iulation ircuit

5 6. Experients and analysis Fi. 6. iulation Result An experiental platfor with a 6bit dspi as its controller is shown in Fi. 7. An adjustable bench power supply with 3V and A is selected as the input source to siulate the icrorid. The load is a leadacid battery pack rated at 48V and Ah. The ajor syste paraeters are listed in Table. Table yste Paraeters oponent/ Value operation condition L 6uH.98uF L 8.5uH.88uF f s 3.5kHz us T s Fi. 7. Experient Platfor The load detection is divided into three conditions: First, there is no load connected, the syste just work under detectin odel. econd, the syste startup with load connected, the syste detectin the load and work continuously after start. Third, the syste work at detectin odel at beinnin, when the load connected, the syste chanes into continuous workin odel. Fi. 8 shows the first condition s experiental result. There is no load connected to the syste, and the syste was workin at load detectin ode. The second condition s experiental result is shown in Fi. 9, where the syste startup with load already connected. After startup, the syste works continuously and transfers the power. The experiental result for last condition is shown in

6 Fi.. As is said, the syste works at detectin ode, and after the load connected, it chanes into continuous workin ode and transfer the power. Output current sensor Priary coil current /A Output rive sinal Load detectin ode Output current sensor tartup load connected Priary coil current rive sinal Fi. 8. First condition Fi. 9. econd condition /A Output Output current sensor Priary coil current Load onnected rive sinal 7. onclusion Fi.. Third condition In this paper, a contactless power supply syste applied to the source load of icrorid has been proposed. Focusin on the syste load detection function, a load detectin control ethod has been proposed to realize this function. The whole syste is siulated in MATLAB/IMULINK, and the experients have been carried out to verify the effectiveness of the load detectin control ethod. References [] M. Budhia and G. A. ovic and J. T. Boys, esin and optiization of circular anetic structures for luped inductive power transfer systes, IEEE Trans. Power Electron., vol. 6, no., pp ,. []. Wan and G. A. ovic and O. H. tielau, Power transfer capability and bifurcation phenoena of loosely coupled inductive power transfer systes, IEEE Trans. Ind. Electron., vol. 5, no., pp. 4857, 4. [3]. J. hen, and T. H. hu and. L. Lin and Z.. Jou, A study of loosely coupled coils for wireless power transfer, IEEE Trans. ircuits yst., vol. 57, no. 7, pp ,. [4] O. H. tielau and G. A. ovic, esin of loosely coupled inductive power transfer systes, in Proc. Int. onf. Power yst. Technol., vol., pp. 859,.