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Application of Magnetic Energy Recovery Switch (MERS) for Power Factor Correction IPEC-Niigata 2005 April 4-8, 2005 Toki Messe Niigata, Japan Jun Narushima, Kouta Inoue, Taku Takaku, Takanori Isobe, Tadayuki Kitahara, Ryuichi Shimada (Tokyo Institute of Technology) Table of contents Operation principles of MERS Power factor correction of singlephase induction motor PWM control of MERS Energy saving by MERS 1 Magnetic Energy Recovery Switch S2 MERS S1 (Magnetic Energy Recovery Switch) L S3 Power Source S4 R Load Connected in series Simple circuit, simple control Bi-directional current switch Can shut off current in any phase MERS has a fucnction of automatic power factor correction regardless of the load inpedance 2 Operational mode (a)(b) i S1 ON i S4 S1 L OFF C L C + ON S2 S4 R S3 v (a) On condition When the capacitor is not charged, Current flows in parallel OFF S1 S3 turn off S2 R S3 v (b) Magnetic energy is absorbed The current charges the capacitor through diodes Current decreases rapidly 3 Operational Mode (c)(d) i i S1 OFF S4 S1 L ON C L C + - + OFF S2 S4 R S3 v (c) Off condition The magnetic energy is completely converted to capacitor energy ON S1 S3 turn on S2 R S3 v (d) Capacitor energy is discharged The capacitor discharges the energy to load Current incleases rapidly 4 Reactance voltage compensation S2 S1 S1 S3 is on Vc Vc L Vc L L S3 VL R S4 R S2 S4 is on VC is generated by LC resonance VL is compensated by switching S1~S4 The power factor becomes R VL Computed waveforms (X C > X L ) S1,S3 ON Voltages (V) 200 δ vc vc v id vd v -200 40 Current (A) S2,S4 ON vd 20 40 id -40 20 time (ms) 40 Discharging time of C is shorter than the switching cycle When vc is the maximum value, i d becomes zero A gate signal shifted by δ is required for power factor correction δ depends on the load impedance ratio XC / XL Computed waveforms (X C < X L ) S1,S3 ON Voltages (V) 200 vc δ id vd v vd -200 40 Current (A) vc S2,S4 ON v 20 40 id δ should be fixed at π/2 regardless of XC , X L and frequency -40 Discharging time of C is much longer than the switching cycle v c is almost constant 20 time (ms) 40 Power factor automatically becomes 7 Gate angle for power factor 90 XC / XL < δ = 90(deg) (constant) δ (deg) Normalized VCmax δ 60 VCmax Gate angle δ should be always fixed at 90(deg) VC ≒ 0.7~1 p.u 30 XC / XL > δ < 90(deg) 0.1 To maintain the power factor at XC / XL 10 Gate angle δ should be fixed at an appropriate value within 0~90(deg) VC > p.u Automatic power factor correction is realized under the conditionof XC / XL < 8 Single-phase induction motor Single-phase induction motors are widely used (home, agriculture, factory ) Low cost Easy to use Bad power factor The power factor is 0.3~0.7 (at the best) It requires large power capacity and causes an increase in cost Costly power converter is not suitable Capacitor start type single-phase induction motor (400W) MERS is suitable because of its simple circuit and simple control 9 Experimental setup Phase shifting control Controller IGBTs of MERS are controlled synchronusly with the AC system Gate signals advances in phase by π/2 Load machine V1 is controlled to maintain V2 at 100 V Tested machine Vmers I1 I2 V1 V0 100V (rms) 50Hz Single-phase induction motor 400 W / 100 V / 9.0 A VC V2 Gate Control Circuit IM DC Load machine DC motor 10 Voltage (V) Experimental wafeforms VC 100 I2 VC V1 -100 V1 20 20 40 I2 The current waveforms are distorted The power factor of the fundamental component of V1 and I1 is nearly I1 -20 V2 IM V2 Current (A) I1 20 time (ms) 40 The power factor of input is improved 11 Power factor Power factor with MERS(820µF) 0.8 without MERS 0.6 0.4 200 400 The power factors without MERS are varying between 0.8~0.4 The power factors with MERS are maintained within 0.9~1.0 600 Load (W) MERS can automatically correct the power factor regardless of load conditon 12 Input current Input current I1 (A) 15 10 without MERS 0 The power factor correction decreases input current with MERS(820µF) 200 400 Load (W) 600 Improves utilization of electrical equipment (decreases required power capacity.) Decreases transmission losses 13 Efficiency Efficiency = Efficiency (%) 60 Mechanical output Input power without MERS Includes losses of motor and MERS 40 20 with MERS(820µF) 200 400 Load (W) 600 Efficiecy does not decreases, although the current waveform is distorted MERS improve the power factor while it does not affect the load side 14 Experiments by PWM control The current waveforms by phase shifting control have large distotion and harmonic components PWM control can be used for applications which require clean sinusoidal waveforms PWM control A reference current i* is determined by input voltage to maintain the power factor at MERS is controlled to make a difference (i * - i ) to be zero by PI control and PWM control VC i* i S1,S3 S2,S4 K kHz 15 Voltage (V) Experimental waveforms VC 100 V2 includes high frequency components V1 -100 Voltage (V) 20 100 40 V2 I is almost sinusoidal without distortion The phase of I is almost the same as that of V1 -100 Currnet (A) 10 I1 20 40 I2 MERS with PWM control also achieves the power factor correction -10 20 time (ms) 40 16 Power factor Power factor 0.8 with MERS(PWM) The power factor by phase shifting control decreases to 0.9 at low load (Higher harmonic components cause insufficient power factor correction.) with MERS (Phase shifting) 0.6 without MERS 0.4 200 400 Load (W) 600 The power factor by PWM control is always maintained to be The sinusoidal current generated by the PWM control improves the power factor more efficiently 17 Efficiency Efficiecy of PWM control is almost the same as that of phase shifting without MERS Efficiency (%) 60 with MERS(PWM) Although the sinusoidal current waveform decreases losses of motor, switching losses are increased by PWM 40 with MERS(Phase shifting) 20 200 400 Load (W) 600 The PWM control of MERS does not have significant effect in efficiency 18 Energy saving by MERS The experiment to demonstrate energy saving by MERS were carried out Refrigerator(100W) Electric power company side Custumer side I Wattmeter Using single-phase induction motor The power factor is 0.72 MERS Long wire (100m 5.6 Ω) The voltage applied to the refrigerator is fixed at 100V V ... principles of MERS Power factor correction of singlephase induction motor PWM control of MERS Energy saving by MERS 1 Magnetic Energy Recovery Switch S2 MERS S1 (Magnetic Energy Recovery Switch) L... factor with MERS( 820µF) 0.8 without MERS 0.6 0.4 200 400 The power factors without MERS are varying between 0.8~0.4 The power factors with MERS are maintained within 0.9~1.0 600 Load (W) MERS can... Input power without MERS Includes losses of motor and MERS 40 20 with MERS( 820µF) 200 400 Load (W) 600 Efficiecy does not decreases, although the current waveform is distorted MERS improve the power