Experimental Verification of a One-turn Transformer Power Supply Circuit for Gate Drive Unit

Transcription

1 Experimental Veriication o a One-turn Transormer Power Supply Circuit or Gate Drive Unit Jun-ichi Itoh, Takeshi Kinomae *agaoka University o Technology/Department o Electrical, Electronics and Inormation Engineering, agaoka, Japan, itoh@vos.nagaokaut.ac.jp, kinome@stn.nagaokaut.ac.jp Abstract This paper proposes a power supply circuit or gate drive units (GDU) that uses a one-turn transormer which is given advantages in term o cost and loss. The structure o this one turn transormer consists o one turn in the primary winding and multiple turns in the secondary winding. Then the circuit is connected in series to a main switching device to obtain a power or the GDUs. The proposed circuit can be applied to all kinds o main circuit topologies such as a multilevel converter topology or a matrix converter in addition to a conventional 6-arm inverter. In this paper, the design method o the one-turn transormer and the characteristics are described accordingly based on the undamental experimental results. Besides, the proposed circuit with GDUs is tested in a three-phase inverter or veriication purpose. The results conirmed that the proposed gate drive circuit is working without an external power source circuit when the output current is /0 times over the rated current o the switching device. Keywords Power supplies, Power transormer Gate Drive Unit, I. ITRODUCTIO A gate drive unit (GDU) is generally used or power converters to operate the switching devices such as IGBT, MOS-FET and others [-4]. The GDUs required additional power supply units because the electric potential o emitter o the switching device is dierence depending on the switching device in the main circuit. Generally, an isolated DC-DC converter is used or a gate power supply; however extra cost is implemented. There are some design approaches or cost reduction, such as a charge pump circuit, a bootstrap circuit, and a sel-supplying power circuit using a series regulator [5-8]. The bootstrap circuit has a simple coniguration, and the charge pump circuit can reduce the volume o the capacitor, urthermore these two circuits can be applied easily to a conventional inverter topology. However, when these two circuits apply to other main circuit topologies such as matrix converters or multi-level converters, several problems are encountered. The number o parts in the gate power supply will increase [8], urthermore the voltage rating o the components in the gate power supply are depended on that o the main circuits. On the other hand, the sel-supplying power circuit using a series regulator provides some advantages in comparison to other two circuits. This gate power supply does not require high voltage rating parts as the other two circuits. In addition, the coniguration o the gate power supply is not inluenced by the main circuit, so this circuit can be accepted in all kinds o main circuit topologies. However, a large loss occurs at the series regulator in the sel-supplying power circuit. This paper proposes a sel-supplying type o gate power circuit by using a transormer, which has a one-turn coil in the primary side. The purpose o the proposed circuit is achieving the cost reduction and low power loss in the gate power circuit. The proposed gate power supply delivers the ollowing eatures; The proposed circuit is isolated rom the main circuit; The voltage rating o the components does not depend on the main circuit; An easy coniguration that is composed o a transormer and a rectiier. A complicated control is unnecessary. However, the output power o the transormer depends on the primary current and the switching requency o the main circuit. In addition, these characteristics o the proposed circuits are analyzed and conirmed with a steady operation. At irst, this paper describes the characteristics o the oneturn coil transormer with an equivalent circuit. Then, the design method o a transormer is established. Secondly, the power supply characteristic or the GDU is investigated by experimented with a step-down chopper. Thirdly, the optimization o the connection point o the proposed transormer in a three-phase inverter is discussed. Finally, the experimental results rom an inverter with the proposed sel-supplying gate power circuit will be demonstrated. II. IVESTIGATIO OF OE-TUR TRASFORMER This chapter shows an equivalent circuit o the one-turn coil transormer, then the adequacy o the equivalent circuit is veriied by simulation results and experimental results. A. Identiication o equivalent circuit parameters Fig. shows the basic coniguration o the proposed selsupplying power circuit is connecting to a step-down chopper. The proposed circuit consists o a diode rectiier and a transormer using one-turn coil in the primary side. The output power P is supplied to the GDU. ote that a resistor is connected instead o a GDU in order to investigate the characteristics o the proposed circuit. The power consumption o the proposed power circuit is lower than the conventional series regulated sel-supplying power

2 Fig. 3. Operation waveorms o proposed circuit. ( sw=0 khz, =0 turn, Duty=35 %, I out=0 A). i Fig.. Experimental circuit or the proposed sel supplying using one-turn transormer. : R l ' ai L l ' R M = Q M i m i out L l R l e l L m e m C p I out Fig.. Equivalent circuit with the secondary side mode o the transormer. C + E out R g circuit because the step-down unction o the voltage in the proposed circuit is implemented by a transormer instead o a series regulator. Fig. shows an equivalent circuit with the secondary side model o the transormer. The equivalent circuit is composed by an ideal transormer and T type circuit, which is expressed by a mutual inductance, leakage inductance and winding resistances. The primary side o the transormer is connected with a current source as the primary current. The identiication o the circuit parameter is obtained as ollowing. At irst, the compositional leakage inductance L sc on the secondary side is measured by a LCR meter when the primary side terminal is shorted. In addition, the secondary side sel inductance L is obtained by a LCR meter when the primary side terminal is opened. Then, the coupling actor k o the transormers is deined by k = LSC L (). The mutual inductance L m in the equivalent circuit is obtained by L m kl = k L L = (), where is the number o primary winding turns, is the number o secondary winding turns. On the other hand, the primary leakage inductance L l, which is transormed to the secondary side rom the primary side, and the secondary leakage inductance L l are expressed by Ll = Ll' = L ( k) = L ( k) (3). i 5A/div 0A e 0V/div 0V i out 0.5A/div 0A Fig. 4. Operation waveorms o equivalent circuit ( sw=0 khz, =0 turn, Duty=35 %, I out=0 A). 0μs/div B. Comparison o experimental waveorms with a simulation waveorms Fig. 3 shows the waveorms o the secondary side output voltage e and the secondary side current i out with the primary current i. The experimental conditions are; the step down chopper switching requency sw =0 khz, Duty=35%, output current I out =0 A, the coupling actor k=0.9, the number o secondary winding turn =0 turn, mutual inductance L m =440 μη. Fig. 4 shows the simulation waveorms by using the equivalent circuit as shown in Fig.. The simulation conditions are the same as the experimental conditions. From Fig.4, the simulation waveorms are similar to the experimental waveorms. The secondary voltage waveorm e is oscillating rapidly at two points; when the positive voltage is reducing to zero and when the negative voltage is returning to zero. The oscillation requency in e at the irst point (positive voltage) is dierent to that o e at the second point (negative voltage). At the irst point, the leakage inductance L sc appears in the secondary side because the induced electromotive orce becomes zero since the primary current is constant; i.e. the primary side is the same as the short circuit. Thereore, the resonant requency pon is obtained by pon = (4). π LSC C p On the other hand, the sel inductance L appears at the second point is because the primary current is zero; i.e. the primary side is the same as open circuit. Thereore, the resonant requency pon is obtained by po = (5). π L C p

3 Thus, these resonant waveorms are generated by the capacitance C p, which is connected in parallel with the input o the rectiier. ote that the oscillation is gradually reduced by the iron loss; resistance R M. Using C p and R M the simulation waveorms agree well with the experimental waveorms including resonant requency. Thereore, the validation o the equivalent circuit is conirmed. III. EXPLAATIO OF SECODARY POWER OUTPUT POWER This chapter discusses the relation between the output power P and parameter o the transormer. The output power o the transormer depends on the core size and switching requency i the number o turns in the primary side is only one-turn. The output power P is calculated by the output current I out and the output voltage E out. At irst, the output current I out o the proposed circuit is introduced by a simple operation model. Fig. 5 shows the current waveorms in the equivalent circuit. Each waveorms are shown as ollowing; ai is the primary current, which will be converted to the secondary side, i m is the exciting current, which lows in the mutual inductance L m, and i out is the output current (instantaneous value). ote that a is the turn ratio o the transormer which is given by a = (6) Fig. 5 assumes that the resistance in the transormer can be neglected and the primary current is constant during one switching cycle. The exciting current is increased because the primary current commutates to the mutual inductance. Thus, the output current becomes triangle shape. The peak value o the output current is deined as ai. Then the output current I out (average value or switching one cycle) is obtained by (7) rom the area o the triangle waveorm i out ; aiti I out = = aiti sw (7), T where t i is the current low time and sw is the switching requency. ext, the output voltage o the proposed circuit E out is considered. The output voltage E out is given by dim di Eout = Lm + Ll (8). dt dt ow, the dierential o the current are approximately obtained by (9) and (0) rom Fig. 5. dim ai = (9) dt ti di ai dt = (0) t i Thereore, the output voltage E out is obtained by () rom (8), (9) and (0). ai ai Eout = Lm Ll = ai( Lm ll ) () ti ti ti Thus, the output power P o the transormer is obtained by () rom (8) and (). P = I out Eout = ( Lm Ll )( ai) sw (), Thus the relation between the output power P and the secondary side sel inductance L is expressed by (3) rom (), (3), and (). P = ( k ) L ( ai) sw (3). On the other hand, the relation between the primary current I and the input current or the equivalent circuit ai is given by (4) ai = I (4), where is the number o turns on the primary side and is the number o turns on the secondary side. When the toroidal core is used in the transormer, the relation between the coil parameters and the secondary side sel inductance L is obtained by Ae L = μ 0 μe l (5), e where μ 0 is the space permeability, μ e is the eective permeability, A e is the eective cross section, and l e is the eective magnetic path length. Thus the output power P is obtained by (6) rom (3), (4), and (5). Ae P = ( k ) I swμ 0 μe (6) le Thereore, the output power P is increased by the primary current I, the switching requency sw, and the parameter o the core. It should be noted that the output power P does not depend on the number o turns in the secondary side. IV. DESIG OF THE OE-TUR COIL TRASFORMER This chapter discusses the design o the one-turn coil transormer. In addition, an example o design example is discussed in section C. A. The design o the one-turn coil transormer Fig. 6 shows the design low chart o the transormer. Each o the parameters o the transormer is decided according to the circuit speciications given in shown Fig 6. Fig.5 Current waveorm o the equivalent circuit Fig.6. Design low chart or one-turn coil.

4 The given circuit speciications are ollowing; the maximum current o the main circuit is I max, the minimum current o the main circuit is I min, the switching requency is sw, the minimum power o operation or GDU is P min, and the maximum allowable current o diode or rectiier is I D_max. Besides, the number o turn on the primary side is oneturn and the coupling actor k is assumed to be more than 0.9. The design procedures o the transormer are ollowing: First, the minimum value o the primary side sel inductance L min is decided to conirm an enough power or the GDU can be obtained. ext, the number o turns is designed rom the maximum current I D_max o the diode rectiier. Finally, the core size o the transormer is selected according to the speciications. B. Design method o the one-turn coil transormer At irst, the primary side sel inductance L is obtained by Ae L = μ 0 μ e l (7). e Thereore, the relation the output power P using L is obtained by P = ( k ) L I sw (8). Thereore, the minimum value o the primary side sel inductance L min is obtained by (4) rom (3) using the ollowing components, I min, P min, and sw ; Pmin Lmin (9). ( k ) Imin sw ext, the minimum turns o the secondary side winding turn is designed. The number o turns is calculated by (0) rom (4) using I max, and I D_max ; Output Power P [W] P /(k-) TABLE I. CIRCUIT SPECIFICATIOS. I min I max sw P min I D_max k 7.A 4A 0kHz 0.3W A Secondary Windings [turn] (a) Output power P (b) Output power divided by (k-) Fig. 7. Characteristics o the number o turns in the secondary side ( sw=0 khz, =vary, Duty=35%, I out= A) I (0) max I D _ max Finally, the core o the transormer is selected to meet (9) and (0). The value o the sel inductance is decided by the only core size because the number o primary turns is constrained as only one-turn. Thereore, the core parameters should be selected by () rom (7). Ae L μe () le μ0 The speciication o the core is decided by (0) and () C. The design example o the one-turn coil transormer At irst, the circuit speciications are provided. The circuit speciication in Table is shown as an example. The minimum value o the primary side sel inductance L min is calculated by (), on the other hand the minimum turns in the secondary side windings turn is calculated by (3). Pmin L min = 0.73μH () (k ) I sw Imax (3) = I D _ max Thereore, the core that meets the conditions in () and (3) is selected. As a result, we ined the core, which has parameters as ollows; A e =50 mm, l e =56.5 mm, and μ e =9. Using this core, L o 0.79 μh is obtained with o turns. D. Evaluation o the analysis results The analysis results are evaluated by a basic experimental circuit in Fig.. The transormer was used in the experimental, which was designed in the previous chapter. Fig. 7(a) shows the relation between the output power P and the number o turns in the secondary side which is obtained by the experimental results. ote that the output power P is increasing as the increased. This reason is because o the coupling actor k is changed by. On the other hands, Fig. 7(b) shows the relation between the number o the secondary winding turn and the value o the output power P divided by (k-) to exclude the variation o k. Then, the output power is standalone rom the number o turns on secondary side while the coupling actor is constant. Fig. 8 shows the relation between the output power P and the primary current based on the experimental result and the theoretical analysis rom (8). The output power is increasing according to the primary current. Experimental result Theoretical curve Primary current I [A] Fig.8 Output power P according to the main circuit current. ( sw=0 khz, =turn, Duty=35%, R =changing)

5 Fig. 9. Output power P according to the switching requency ( = turn, Duty = 35%, I out =3.5 A) Fig.. Experiment circuit o sel-supplying power circuit. Output Power P[W] (a) Current rom sub supply e sub and output voltage o the GDU V ge without proposed circuit Fig. 0. Output power P characteristic by changing the P. ( sw=0 khz, =turn, Duty=35%, I out=0 A, E in=changing) Fig. 9 shows the relation between the output power P and the switching requency. Fig. 9 conirms that the proposed method could obtain an enough output power P to operate the GDU. It is noted that the GDU only requires the power o a ew watt (0.3W) to drive the power device. Fig. 0 shows the output power P with the output power o the main circuit. The output power P is not increase even the output power o the main circuit has been increased. The output power o the main circuit is controlled by the DC link voltage. Thereore, the output power o the gate power supply does not depend on the active power o the main circuit. In each result, the experimental results agreed with the theoretical line. In addition, these experimental veriications concluded that the proposed sel-supplying power circuit could generate enough power to operate the GDU. Besides, the output power o the gate power supply is increased by a larger primary current or a higher switching requency even the output power o the main circuit is still kept small. V. EVALUATIO OF THE PROPOSED CIRCUIT AS A GATE POWER SUPPLY A. Fundamental operation in a DC chopper Fig. shows the evaluation circuit o the proposed circuit. In this chapter, the operation o a GDU using the proposed power source circuit will be conirmed by the experiment circuit. The power consumption o a GDU is 0.35 W, and the operation voltage is more than 4 V. When the output voltage o the proposed gate power circuit is less than 4 V, an auxiliary DC power source (e sub ) is used or the initial operation. It should be noted that when the DC i sub 0. A/div 0 A V ge 5 V/div 0 V (b) Current rom proposed circuit and output voltage o the GDU V ge with proposed circuit Fig. Operation waveorms o the GDU using the proposed circuit at step down chopper power supply current i sub is equaled to zero, this means that only the proposed circuit supplies the power to the GDU. The gate voltage is designed as 6 V or on-state period and 7 V or o-state period respectively. Fig. shows the operation waveorms o the GDU with using the proposed power circuit; V ge is the voltage between the gate and emitter, the supply current i sub is rom the proposed circuit and the current i sub is rom the sub power supply. The experimental conditions are ollowing; the output current o step-down chopper I out =7.8A, the requency o the switching device sw =6kHz, the switching duty ratio=35%. In Fig. (a), the current or the GDU is supplied rom the sub power supply e sub without the proposed circuit. On the other hands, in Fig. (b), the current or the GDU is i sub rom the proposed circuit. The same gate voltage waveorms are obtained in Fig. (a) and (b). These results conirmed that the proposed circuit is able to supply enough power or the GDU initially and operate normally onwards. B. Connection point in a Three-phase inverter Fig. 3 illustrates several connection points o the transormer in a three-phase inverter. In the previous undamental veriication, the sel-supplying transormer is connected in series to the switching device. Practically, the

6 Fig. 6. Operation waveorms o the GDU with the proposed circuit Fig. 3. The possible connection points o the transormer in a three phase inverter. Output power P [W] Fig. 4. Output power P at the selected connection point o the transormer. Fig. 7. Operation waveorms o the inverter with the GDU using the proposed circuit Current [%] Fig. 5. Harmonics components o the primary current at each connection point. (The reerence value is in DC current at connection point α) transormer can be connected in series to (α) the DC-link part, (β) the smoothing capacitor, or (γ) the current o each leg in order to reduce the cost. Fig. 4 shows the output power P o the secondary side according to the connected location o the transormer. The output power P obtains more than 4 W when the primary side o the transormer is connected to the point (α) and (β). The proposed gate power circuit is able to supply enough power to operate up to six GDUs. On the other hand, the proposed circuit can be only generated 0.7W when the primary side o the transormer is connected to the point (γ). Fig. 5 shows the harmonics components o the primary current at each connection point. The harmonics components o the switching requency at the point (γ) are smaller than other connection points as shown in Fig. 3. In addition, a same output power is obtained by the proposed circuit when the primary side is connected to the point (α) and (β) because the output power is dominated by the harmonics components o the switching requency in the primary current. It should be noted that the output power P is proportional to the switching requency and the square o the primary current as shown in (6). However, the connection point (α) aces the magnetic saturation rom the current at the DC component o the main circuit. Thereore, a large core is required or the transormer i connecting at this point. Because o these reasons, the connection point (β) is the best connection point because point β can obtain the largest power and use a smaller core. C. Application in a three-phase inverter In this section, the perormance o the gate drive unit will be evaluated. A three-phase inverter is used as the main circuit, and the GDU is supplied by the proposed gate power circuit. ote that only the GDU or U-phase is supplied by the proposed gate power circuit where the primary side o the transormer is connected to point (β). Fig. 6 shows the operation waveorms o the proposed circuit in Fig. 3. Start rom the top, V ge is the voltage between the gate and emitter; i g is the gate current, i sub is the supply current or the GDU and e sub is the power supply voltage or the GDU. The power supply voltage e sub is at constant while the gate current i g is operated in charge or discharge mode. Besides, the actual gate voltage almost agrees with the design value. It is noted that the auxiliary power source did not work in this situation because the output voltage o the auxiliary power source is up to 4 V only; however the power supply voltage is kept to 7 V. The voltage between the gate and the emitter does not contain a large distortion. Thereore the GDU is then conirmed to operate normally even i the proposed power supply is used. Fig. 7 shows the operation waveorms o the three-phase inverter which are the collector-emitter voltage o the switching device e sup, the U phase current I u, the V phase

7 (a) 3 0 Gate power supply voltage according to the output current. s =6 khz s =.5 khz Output current I out [A] Consumption Power o GDU (b) Output power o the gate power supply according to the output current. Fig. 8. The relationships between the three-phase inverter circuit and the gate power circuit current I v, and the power supply voltage e sub or the GDU. Sinusoidal current waveorms are obtained in U-phase and V-phase and without any distortion. Besides, the gate power supply shows a constant voltage. Thereore, the results conirmed that the inverter is able to operate normally by using the GDU with the proposed gate power circuit. Fig. 8(a) shows the relations between the output current o the main circuit with the supply voltage e sub o the GDU and Fig. 8(b) shows the relations between the output current o the main circuit with supply power P sub o the GDU. Two switching requency o 6 khz and.5 khz were tested to investigate the inluence o the switching requency. The results conirmed that the GDU can be operated by the proposed gate power circuit when the output current is more than 4A. It should be noted that the gate power supply voltage increases when the output current is larger. This reason is that the output power o the transormer is higher than the power consumption o the GDU. Thereore, the proposed gate power circuit should be designed in a way that the gate power supply voltage is at the maximum load condition and the switching requency is lower than the absolute operation voltage o the GDU. (i) The secondary power is almost proportional to the primary current and its requency. On the other hands, the active output power or the load does not inluence the gate drive perormance. (ii) The primary side o the transormer should be connected in series to the smoothing capacitor at the DC link o the inverter in order to reduce the core size and to obtain the maximum power. (iii) The same gate voltage is obtained by the proposed circuit in comparison to that o a conventional gate drive unit. (iv) The proposed gate power supply circuit is applied to a three-phase inverter, and sinusoidal output current waveorms are obtained as similarly to the conventional inverter. As a result, the validity o the proposed sel-supplying gate power circuit is conirmed. In uture study, the eect o the noise reduction will be investigated in the proposed circuit because the rise time o the switch current is reduced by the series transormer. In addition, the initial operation o the proposed circuit without the auxiliary power supply will be considered. REFERECES [] John, V.; Bum-Seok Suh; and Lipo, T.A.; High-Perormance Active Gate Drive or High-Power IGBT's, IEEE Transactions on Industry Applications, Vol. 35, Issue. 5, pp. 08-7, Oct. 999 [] Kaiwei Yao; and Lee, F.C.; A novel resonant gate driver or high requency synchronous buck converters, IEEE Transactions on Power Electronics, Vol. 7, Issue., pp.80-86, Mar. 00 [3] Wiegman, H.L..; A resonant pulse gate drive or high requency applications, Seventh Annual Applied Power Electronics Conerence and Exposition, Boston, MA, pp , Feb.99 [4] Zhihua Yang; Sheng Ye; and Yan-Fei Liu; A ew Dual-Channel Resonant Gate Drive Circuit or Low Gate Drive Loss and Low Switching Loss, IEEE Transactions on Power Electronics, Vol. 3, Issue. 3, pp , May [5] International Rectiier, Application note A-978: HV Floating MOS-Gate Driver ICs, Mar [Online]. Available: [Accessed: May. 008] [6] J.Adams; Design Tip: Bootstrap Component Selection For Control IC s, 4. Sept. 00. [Online]. Available: [Accessed: May. 008] [7] Shihong Park; and Jahns, T.M.; A sel-boost charge pump topology or a gate drive high-side power supply, IEEE Transactions on Power Electronics, Vol. 0, Issue., pp , Mar [8] Moe. Imaizumi and Yukihiko. Sato, Application and evaluation o loating methods or gate drive power supplies, IEEJ on Semiconductor Power Conversion, SPC-08-9,pp.49-54, Jan [In Japanese] VI. COCLUSIO This paper proposed a sel-supplying gate power circuit or the gate drive unit which is using a one-turn transormer. The characteristics o the proposed gate power circuit are conirmed by the experimental results as ollowing;