Multiple-Load Series Resonant Inverter for Induction Cooking Application with Pulse Density Modulation

Transcription

1 Multiple-Load Series Resonant Inverter for Induction Cooking Application with Pulse Density Modulation P. Sharath Kumar Dept. of Electrical Engineering Rajarambapu Institute of echnology Islampur, Maharashtra, India N. Vishwanathan 2 2 Dept. of Electrical Engineering 2 National Institute of echnology Warangal Warangal, elangana, India Abstract Multiple-load induction cooking applications are suitable using with multi output inverters or multi inverters are needed for multiple-load operation. By using some common approaches and modifications are needed in inverter configuration for multiple-load application. his paper presents an inverter configuration with two loads by using pulse density modulation control technique. It allows the output power control of each load independently with constant switching frequency and constant duty-ratio. he pulse density modulation control technique is obtained using phase on-off control between two legs of the inverter to reduce acoustic noise. he proposed configuration provides reducing the component count for extension of multiple-loads. he control technique provides wide range of output power control. In addition, it can achieve efficient and stable ZVS operation in the whole load range. he proposed configuration and control scheme is simulated and experimentally verified. Keywords Induction cooking; Multiple-load; Series resonant inverter; ZVS; Pulse density modulation control; I. INRODUCION Induction heating method is a far better approach than other conventional methods. In conventional methods, the heat is transferred from heat source to load by conduction or radiation. In induction heating, the heat is developed inside the load due to generation of eddy currents at skin depth level from the surface []. In recent times, considerable progress is made in control schemes and inverter configurations. Induction cooking is one of the several applications of induction heating. Fig., shows a typical arrangement of high frequency induction heating circuit. AC UFAC Source Diode Rectifier LS Cdc DC Link HF Inverter Fig.. ypical arrangement of induction cooking resonant inverter IH Coil and Load Resonant inverter is commonly used as a source of high frequency AC supply. he DC input to it is derived by rectifying the utility AC source. High frequency AC flowing in the load coil results in eddy currents induced in the vessel at skin depth level resulting in heating effect. Commonly used topologies for induction cooking application are quasi resonant, half-bridge, and full bridge inverter [2]. Out of these, full bridge inverter is preferred for high power applications. In induction cooking application Variable Frequency (VF) scheme, Pulse Frequency Modulation (PFM), Pulse Amplitude Modulation (PAM), Phase Shift Modulation (PSM), and Asymmetrical Duty-cycle Control technique are used for output power control [3]-[8]. In VF scheme to control the output power for a constant load by varying the normalized switching frequency, in case of below resonance operation filter components are large for the low-frequency range [3]. PFM control has ZVS soft switching operating region is relatively narrow. In PAM control for constant load amplitude of the source voltage is varied to control the output power. PSM control gives high efficiency at higher duty-ratio [4]. ADC control gives ZVS at higher duty ratios in full-bridge inverter configuration [5]. For reducing switching losses, it is mainly used in half-bridge topology. AVC control gives ZVS at lower duty ratios also in full-bridge inverter configuration. AVC control technique is mainly used in full-bridge topology [5]-[7]. In induction cooking application, one inverter feeds power to a single load. For multiple load application, there is a need to develop inverter circuits and control techniques which can minimize component count and provide independent control of each load [8]. Certain techniques are available in the literature. his paper proposes multiple-load series resonant inverter for induction cooking application with pulse density modulation control technique. he proposed inverter configuration powers two loads with independent output power control of each load. In this configuration, for PDM control technique [9]-[4] is used with phase on-off control between two legs of inverter for load output power control. he phase on-off control has no acoustic noise; due to inverter switching frequency is more than audible range. But in general PDM technique the duration of inverter gate pulse density is should be less than audible range. It can be overcome with phase on-off control technique. his configuration can be extended to multiple-loads also.

2 II. OPERAING PRINCIPLE OF IH AND LOAD CHARACERISICS A. Operating Principle of Induction Heating Operating principle of IH is that when induction heating coil is energized by high frequency current, it produces magnetic flux. It causes eddy currents that occur in heating load and this result in heating effect. he induced eddy currents are concentrated in the vessel bottom layer at skin depth (δ) level [2], which is explained by δ = ρ ρ 4π = () πμ f s μ r f s where, ρ is electrical resistivity, µ is magnetic permeability and µ r is relative magnetic permeability of load material and f s is switching frequency of the inverter circuit. he load surface resistance (R L ) is determined by the load skin depth and its material specific resistance is shown in below expression, R L = ρ = k ρμ δ rf s (2) where k is constant = he load parameters depends on several variables including the shape of the heating coil, the spacing between the heating coil and cooking vessel (load), load electrical conductivity and magnetic permeability, and the inverter switching frequency. B. Equivalent Circuit of IH Coil and Load A linear equivalent model of the IH coil and load represented by the effective equivalent inductance (L eq ) in series with effective equivalent resistance (R eq ) is referred to the input side of IH coil. R L L0 Req R eq = R +A 2 R L (7) L r = L A 2 L 0 (8) where, M 0 = M 0 = M III. and A= (ωm ) R L 2 +(ωl0 ) 2 = M L 0 at ωl 0 R L PROPOSED INVERER CONFIGURAION AND CONROL SCHEME his section describes the proposed inverter configuration and control scheme for two load induction cooking application. Fig. 3, shows the circuit diagram of proposed three-leg inverter configuration. he two loads are connected across the inverter output voltages v AB, and v AC respectively. he concept of series resonance is used with each load. he resonant load circuits are connected to leg-, which is common leg for both loads. hey are marked as leg-, leg-2 and leg-3 respectively. Load- consists of C r, L r, and R eq which are resonant capacitor, inductance of the load- and equivalent load resistance in series with resonant tank respectively, which is connected between leg- and leg-2. Similarly for load-2, C r2, L r2, and R eq2 are resonant capacitor, inductance of the load-2 and equivalent load resistance in series with resonant tank respectively, which is connected between leg- and leg-3. V DC Q Leg- Leg-2 Leg-3 A D Cr i L r R eq C r2 L r2 R eq2 Q 4 B Q 6 D 4 D 6 C v O i i0 M0 M0 RL v O Lr Q 2 D 2 i 2 Q 3 D 3 Q 5 D 5 Fig. 2. Equivalent circuit of IH coil with load Fig. 2, shows the equivalent circuits for IH coil with load parameters. Load parameters are taken as single turn short circuited secondary winding. he circuit elements are represented as: ) R L surface resistance of the load 2) L 0 inductance of the load 3) R resistance of IH coil 4) L inductance of IH coil 5) i 0, i load current and IH coil current 6) M 0, M 0 the mutual inductance between IH coil and load. he voltage equations for the above equivalent circuit: di v 0 = i R + L + M di 0 0 dt dt di 0 = i 0 R L + L 0 + M di 0 0 dt dt From (3) and (4) equations, (3) (4) R eq = R + (ωm )2.R L R L 2 +(ωl0 ) 2 (5) L r = L (ωm )2.L 0 R L 2 +(ωl0 ) 2 (6) Q Q 2 Q 4 Q 3 Q 6 Q 5 Fig. 3. Proposed two load inverter configuration A. Characteristics of resonant tank Switching Signals he resonant tank circuit of each load in three-leg inverter circuit is shown in Fig. 3. It can be described by the following parameters: he resonant angular frequency is ω r = (9) L r C r he normalized switching frequency is ω n = ω s ω r (0) where ω s = switching angular frequency = 2π f s f s = switching frequency

3 he characteristic impedance is Z 0 = L r C r = ω r C r = ω r L r () he IH load quality factor is Q = ω rl r = = Z 0 (2) R eq ω r C r R eq R eq he resonant tank circuit impedance is given by Z eq = R eq + j ω s L r (3) ω s C r = R eq + jq ω n ω n (4) Z eq = R eq Q 2 ω n 2 (5) ω n he phase-angle between output voltage and current is = tan Q ω n (6) ω n B. Pulse density modulation control technique Pulse density modulation control is obtained using phase on-off control technique. By making phase-in and phase-out sequence of switching pulses between two legs of full-bridge inverter circuit, we get phase on-off control technique. Fig. 4 shows the switching pulses of an inverter circuit and inverter output voltage with its respective load current for a full-bridge circuit. Q 3 switching pulses are phase-in and phase-out sequence with Q switching pulses. Similarly, Q 4 switching pulses are w.r.t. Q 2 switching pulses. When switching pulses are in phase-in sequence, inverter output voltage V AB applied across load and switching pulses are in phase-out sequence, inverter output voltage V AB becomes zero. he similar phase-in and phase-out sequence of switching pulses is applied for load-2 to obtain inverter output voltage V AC. Q Q 2 Q 3 Q 4 V AB 0 τ = 2L = 2Q R eq ω he envelope i e of resonant tank current is given by (7) i e (t) = I m e t τ +Ie t τ for 0 t on (8) i e (t) = I( on ) e t on τ for on t (9) e where, I = I on τ m e τ I m : max. current in full-power operation I : initial value of the envelope i e he average power is obtained by multiplying V DC and i e, as follows P = on 0 2 = 2 π V DCI m on +τe π V DCi e t dt on τ τ + 2 π V DCI m τe on τ e τ (20) e on τ If the periodic time of the PDM control operation is much smaller than the time constant τ, no fluctuation occurs in the amplitude of the resonant tank current and becomes continuous waveform. If the periodic time is much greater than the time constant τ, the output power is in proportion to the pulse density because the resonant tank current becomes a discontinuous waveform. hus, the input power is in proportion to the pulse density is given by lim τ 0 P = 2 V on π DCI m (2) Assuming, the inverter circuit losses are constant. Because of the inverter circuit operates with constant switching frequency and constant duty-ratio. hus, the output power is also in proportion to the pulse density is given by P out = I 2 R on = P eq max D y (22) where, I is the r.m.s. value of load current R eq is the equivalent load resistance. D y is the pulse density ratio. P max is the full output power under continuous condition In this paper, both loads have same component values and their resonant frequencies are same. Hence, their power rating is also same and operated at a switching frequency of 30 khz. Resonant frequency of each load circuit is, f r = 2π L r C r. Switching frequency of each leg is slightly higher than their resonant frequency. Hence, inverter switching frequency (f s ) can be chosen 5 to 0% higher than the resonant frequency (f r ) for ZVS operation. i 0 on Fig. 4. Inverter output voltage and load current with PDM control he time constant of the envelope of load current is given by IV. RESULS OF PROPOSED CONFIGURAION Proposed configuration of full-bridge series resonant inverter for two load induction cooking application with 3-leg is designed and operated at constant switching frequency of 30 khz. Proposed inverter configuration with PDM of phase on-off control technique is simulated and experimentally verified using the parameters shown in table I.

4 ABLE I. PARAMEERS OF PROPOSED CONFIGURAION Item Symbol Value Source voltage V DC 3 Equivalent resistance of each load R eq.95ω Equivalent inductance of each load L r 68μH Resonant capacitance of each load C r 0.45μF Dead time in each leg t d 450 nsec ime period for one PDM cycle 0.0sec Resonant frequency of load circuit f r 28.77kHz Switching frequency of each leg f s 30kHz P max 226 W MOSFEs used IRFP40PbF 0, 8 Experimental setup of proposed inverter configuration is shown in Fig. 5. Fig. 6. wo loads are operating at 00% D y 5-5 Fig. 5. Experimental setup of proposed inverter configuration A. Simulation and experimental results he simulation and experimental results of proposed configuration with PDM of phase on-off control technique are shown in Figs. 6 to 9 for different % D y combinations of load- and load ms 2.2ms 2.4ms 2.6ms 2.8ms 3.0ms 3.2ms 3.4ms 3.6ms 3.8ms 4.0ms ime ms.2ms.4ms.6ms.8ms 2.0ms 2.2ms 2.4ms ime 2.6ms 2.8ms 3.0ms Fig. 7. First load is operating at % D y

5 ms 2.2ms 2.4ms 2.6ms 2.8ms 3.0ms 3.2ms 3.4ms 3.6ms 3.8ms 4.0ms ime Fig. 8. First load is operating at 2% D y ms 2.6ms 2.8ms 3.0ms 3.2ms 3.4ms 3.6ms 3.8ms 4.0ms 4.2ms ime Fig. 9. Both loads are operating at 50% D y Simulation waveforms of inverter output voltage and load currents are shown in Figs. 6 to 9 at different % D y combinations. hese waveforms are shown under experimental condition in Figs. 6 to 9. Simulation and experimental waveforms are in good agreement. B. Control of output power In proposed configuration, both loads are similar and each load output power (P out ) can be controlled independently with the phase on-off control technique. In proposed phase on-off control technique, the time constant τ is 0.7% only of one PDM cycle periodic time. So, the load current will be in discontinuous mode. he output power (P out ) can be derived from eqs. (2) and (22). he output power (P out ) with percentage of pulse density (%D y ) is shown in table II. ABLE II. Output POWER CONROL WIH PDM S. No % D y P out W W W W W W W W PDM is used with phase on-off control between two legs of inverter for load output power control. At zero inverter output voltage, inverter operates in freewheeling mode and the total stored energy in load will be discharged. PDM control technique offers smooth variation of power control from minimum to maximum value. From eq. (22), the prototype P max is 226 W. he periodic time for one PDM cycle is taken 0.0sec. i.e., 00 Hz is chosen and the switching pulses are generating without any discontinuous mode to reduce acoustic noise. C. ZVS opearation In wide range of power control, the inverter operates with maximum and constant duty-ratio with PDM control

6 technique. For getting ZVS, at turn-on of inverter output voltage the load current should be negative. [4] L. Grajales, J. A. Sabate, K. R. Wang, W. A. abisz, F. C. Lee, Design of a 0 kw, 500 khz Phase-Shift Controlled Series-Resonant Inverter for Induction Heating, Industry Applications Society Annual Meeting, vol. 2, 993, pp Fig. 0. Both loads are operating with ZVS Fig. 0 shows that both loads operating with constant and maximum duty-ratio and load currents are in negative at inverter output voltage turn-on position. In whole wide range, the inverter is operated with ZVS and the inverter efficiency is also at 96%. V. CONCLUSION wo load three leg series resonant inverter configuration with PDM control technique for induction cooking application was proposed. PDM is used with phase on-off control between two legs of inverter for load output power control. With the phase on-off control technique the acoustic noise is reduced in the audible range of PDM frequency also. At zero inverter output voltage, inverter operates in freewheeling mode and the total stored energy in load is to be discharged. In this configuration, each load output power controlled independently. he two load inverter configuration is generalized into n-output series resonant inverter configuration with saving of switching devices. i.e., 2n+2 switching devices are required instant of 4n switching devices for a full-bridge configuration. In whole wide range of inverter operation, ensures ZVS with constant and maximum duty-ratio and constant switching frequency of 30 khz. Simulation and experimental results of the proposed configuration are in good agreement. Overall efficiency of this configuration is 96%. he proposed configuration can be extended to multiple loads. [5] D. V. Bhaskar, N. Yagnyaseni, N. Vishwanathan, and. Maity, Comparison of Control Methods for High Frequency IH Cooking Applications, Power and Energy Systems Conference: owards Sustainable Energy, 204, Page(s): 6. [6] J. M. Burdio, L. A. Barragan, F. Monterde, D. Navarro, J. Acero, Asymmetrical voltage-cancellation control for full-bridge series resonant inverters, IEEE rans. Power Electronics, vol. 9, no. 2, 2004, pp [7] Jose M. Burdio, Fernando Monterde, Jose R. Garcia, Luis A. Barragan, Abelardo Martinez, A wo-output Series-Resonant Inverter for Induction-Heating Cooking Appliances, IEEE rans. Power Electronics, vol. 20, no. 4, 2005, pp [8] Oscar Lucia, Claudio Carretero, J.M. Burdio, Jesus Acero, and Fernando Almazan, Multiple-Output Resonant Matrix Converter for Multiple Induction Heaters, IEEE ransactions on Industry Applications, vol. 48, no. 4, July/August 202, pp [9] Nam-Ju Park, Dong-Yun Lee, and Dong-Seok Hyun, A Power-Control Scheme With Constant Switching Frequency in Class-D Inverter for Induction-Heating Jar Application, IEEE ransactions on Industrial Electronics, vol. 54, no. 3, June 2007, pp [0] Jinfei Shen, Hongbin Ma,Wenxu Yan, Jing Hui, Lei Wu, PDM and PSM Hybrid Power Control of a Series-Resonant Inverter for Induction Heating Applications, IEEE Conference on Industrial Electronics and Applications, ICIEA [] Oscar Lucia, J.M. Burdio, I. Millan, J. Acero, D. Puyal, Load-Adaptive Control Algorithm of Half-Bridge Series Resonant Inverter for Domestic Induction Heating, IEEE ransactions on Industrial Electronics, vol.56, no. 8, August 2009, pp [2] H. Fujita, H. Akagi, K. Sano, K. Mita, R. H. Leonard, Pulse Density Modulation Based Power Control of a 4kW 400kHz Voltage-Source Inverter for Induction Heating Applications, Power Conversion Conference, Yokohama, 993, pp. -6. [3] Lichan Meng, Ka Wai Eric Cheng, and Ka Wing Chan, Systematic Approach to High-Power and Energy-Efficient Industrial Induction Cooker System: Circuit Design, Control Strategy, and Prototype Evaluation, IEEE ransactions on Power Electronics, vol. 26, no. 2, December 20, pp [4] Hector Sarnago, Oscar Lucia, Arturo Mediano, J.M. Burdio, Class D/DE Dual-Mode-Operation Resonant Converter for Improved- Efficiency Domestic Induction Heating System, IEEE ransactions on Power Electronics, vol. 28, no. 3, March 203, pp REFERENCES [] W. C. Moreland, he induction range: Its performance and its development problems, IEEE rans. Industry Applications, vol. IA-9, no., 973, pp [2] Mokhtar Kamli, Shigehiro Yamamoto, and Minoru Abe, A khz Half-Bridge Inverter for Induction Heating Applications, IEEE rans. Industrial Electronics, vol. 43, no., 996, pp [3] Young-Sup Kwon, Sang-Bong Yoo, Dong-Seok Hyun, Half-Bridge Series Resonant Inverter for Induction Heating Applications with Load- Adaptive PFM Control Strategy, 4th Applied Power Electronics Conference and Exposition, APEC 99, vol., 999, pp