Digital Control Implementation for a Single-PWM Multiple- Output Switching Converter

Transcription

1 Digital ontrol Imlementation for a SinglePWM Multile Outut Switching onverter Kyusik hoi, B.H.ho School of Electrical Engineering and omuter Science, Seoul ational University #043, San 56, Shinlimdong, Kwanakgu, Seoul 574, Korea ezto84@snu.ac.kr Abstract A digital control imlementation method is roosed for a singlepwm, reciselycontrolled multioutut converter. Each outut voltage is regulated indeendently with only single itch or itch air by Suerosed Sinusoidal Pulse Width Modulation (SSPWM) and Pulse Frequency Modulation (PFM) control. The static and dynamic roerties are introduced on this novel multileoutut converter using BandPass Filters (BPFs). The exerimental verifications are erformed using a 550W twooutut DD converter for Plasma Dislay Panels (PDP) ower system with a Digital Signal Processor (DSP). Keywords Band Pass Filter, Multile Outut. I. ITRODUTIO With recent advantages in digital systems, digital control has become increasingly feasible even for high frequency, low to medium ower itching converters. Digital control offers the otential advantages of immunity to analog comonent variations, rogrammability and ossibilities to imrove erformance using more advanced and sohisticated algorithms [9]. Most electrical equiments require several different voltage levels for their own oeration. Taking a converter for each voltage level is undesirable solution due to its high cost and bulky size. For this reason, multileoutut converters have been focused on because of their advantages, such as small size and low cost [05]. However, these conventional multileoutut converters are not used widely due to their limitation like low controllability or necessity of additional itches for tight regulation, which is a significant tradeoff between the efficiency and the accuracy of the multioutut regulation. Tyically there are threetye of conventional multileoutut converters. One is the cross regulation multileoutut converter. The cross regulation converter can regulate only one main outut voltage and the other auxiliary outut voltages are just determined by transformer turn ratio, so dynamic erformances of outut voltages excet main outut voltage are oor. Similar one is the weighted function multileoutut converter, as shown in Fig.. Because the converter emloys only one controller, the outut regulation erformance is oor due to the single control variable following the weighted function. To solve this roblem, the ost regulation multileoutut converter was roosed. This method is adding a linear regulator or a converter like buck or boost in each of auxiliary outut to regulate all of outut voltages indeendently. This method guarantees the dynamic erformance of the all outut voltages, even though the cost and the ower loss increase because it needs additional itches to regulate each outut voltage. In this aer, a novel multileoutut converter, which regulates each outut voltage indeendently without any additional itches by Suerosed Sinusoidal Pulse Width Modulation (SSPWM) and Pulse Frequency Modulation (PFM) control, is introduced and a digital controller imlementation method is roosed. This converter is based on the multileband modulation and demodulation which are oerated by SSPWM, PFM and bandass filtering. The each outut can be regulated recisely by this technique. Also, it has high efficiency due to the resonant network of BandPass Filters (BPFs), and can be imlemented with low cost because of the single PWM generator and single ower itch (air) in ower stage as well. However, the roosed control scheme requires a comlicated controller imlementation in analog control, which can be easily realized through digital control aroach. An isolated 550W halfbridge tye twooutut DD converter for Plasma Dislay Panels (PDP) ower system with a Digital Signal Processor (DSP) is imlemented for the verification. Fig. Block diagram of the conventional weightedfunction MultileOutut onverter

2 Switched oltage Source 3 in Bandass Filter ( ) Rectifier oad Bandass Filter ( ) Bandass Filter 3 ( 3) II. MUTIPEOUTPUT OERTER USIG BADPASS FITER A. Oeration Princile The basic concet of the singlepwm multileoutut converter is shown in Fig.. The ower system is comosed of a itched voltage source and several BPFs, which are connected each other in arallel. The itched voltage source generates several frequency comonents by SSPWM and/or PFM. There are dominant and controllable comonents of the generated PWM comonents. One of them is at itching frequency which is controlled by PFM and the other comonents are at sinusoidal reference waves which are controlled by SSPWM. A number of sinusoidal signals with each own frequency band are suerimosed right before the ulsewidth modulation rocess. Then, the final SSPWM signal includes all the frequency comonent of each frequency signal as well as PFM triangular frequency. When this modulation signal is alied to the ower stage amlifier, each of the outut ort receiving the amlified PWM signal selects one of the frequency comonents through BPF of its own. In Fig. 3, the Fast Fourier Transform (FFT) result of shows that it has three frequency comonents at, r and r because the PWM signal is generated by comarison between the triangular waveform whose frequency is, and the sum of the sinusoidal reference. waveforms ( ) and ( ) r cos r Rectifier Rectifier SSPWM & PFM ontroller r cos r oad oad 3 Fig. Block diagram of the singlepwm MultileOutut onverter using BandPass Filters Fig. 4 ombination of the BPFs and the frequency comonents Each of the BPFs asses only one frequency comonent as shown in Fig. 4. The center frequency of the bandass filter (BPF) is near the itching frequency, and the center frequency of bandass filter (BPF) is which is the same as the frequency of sinusoidal reference wave, r, and the center frequency of the bandass filter 3 (BPF3), 3, is the same as the frequency of the sinusoidal reference wave, r. For BPF, series resonant branch or arallel resonant branch can be used. The controller can be imlemented with a SSPWM controller and/or a PFM controller. The SSPWM controller varies the amlitude of sinusoidal reference waveforms r, r and so on. These values change the magnitude of frequency comonents at r and r. The SSPWM controller can also change the frequency of the sinusoidal reference waves to regulate the outut voltage. However, this aer rooses SSPWM controller changing only the amlitudes of the sinusoidal reference waveforms in order to revent the varied frequency comonents, which may ass another BPFs undesired to ass. The other controller of PFM varies the itching frequency,, like a frequency control method for the conventional resonant tye converters. B. ontrol Method Fig. 5 shows the simlified halfbridge tye multileoutut DD converter using the roosed method. The center frequency of BPF is designed near the itching frequency,, and the center frequency of BPF is at r r PWM c f ( ) rcos rt omarator r r rcos rt <FTT result of PWM> Fig. 3 Modulation methods of SSPWM and PFM Fig. 5 Simlified halfbridge tye twooutut DD converter using SSPWM and PFM

3 sinusoidal reference frequency, r. The first outut voltage, o, is controlled by varying itching frequency,, and the second outut voltage, o, is controlled by varying the amlitude of sinusoidal reference voltage, r, and so on. To regulate o, a frequency control method can be alied for the conventional resonant converter because its structure and roerties are the same. However, to guarantee indeendency between each of the outut voltage, the itching frequency at above resonance frequency region is better than the itching frequency at below resonance frequency region which may affect the outut voltage o by assing its frequency comonent through BPF. For the simlicity of controllability analysis, only two outut voltages are considered in this aer. The rimary voltage, ri, in Fig. 5 which is generated through sinusoidal ulse width modulation (SPWM) is a comarison between the triangular carrier and the sinusoidal reference waveform. The itched voltage v ri (t) can be exressed in terms of its harmonic comonents as eq. () by Double Fourier Integral analysis [6, 7]. in v ri ( t) = M 4 in 4 When the Qfactor of the BPF is large enough and the center frequencies of BPF and BPF are designed to be aart from each other, the second and third terms in eq. () can be neglected by bandass filtering. Thus, the aroximated outut voltages are derived as follows: If the BPF is realized by using the series or arallel resonant branch, the voltage gain of the BPF is driven as follows [8]: in π π cos( rt ) J 0 m M sin m cos( mt) π m= m in π π J n m M sin [ m n] cos( mt nrt ) π m= n= m where M = Modulation index or modulation deth, r c with range 0 < M < Ji = ith Bessel function = Inut voltage where o, rms o, rms G n = G = G ( ) ( ) r in r tri in s s ( n ) = voltage gain of nth BPF at n in Eq. () shows that the outut voltage is varied by only itching frequency,. Thus, the o is controlled by changing the itching frequency. Otherwise, the outut voltage o is varied by the reference frequency, r, and the eak ratio between the reference and the triangular carrier waveform, r tri. Since the tri is a constant value, the o is controlled by only using the when the reference frequency is fixed. r n a an s s c f (, t) f ( r, t) cos( rt) Fig. 6 The structure of hardware rototye Frequency ontroller Amlitude ontroller III. DIGITA OTRO IMPEMETATIO AD EXPERIMETA To verify the controllability of the converter, a hardware rototye for a 550W PDP ower system has been built and imlemented as shown in Fig. 6. The main outut stage is comosed of a arallel resonant branch for BPF and a full wave rectifier. The auxiliary outut stage is comosed of a series resonant branch for BPF and a full wave rectifier. The circuit arameters of hardware rototye are shown in Table I. In oerating condition, the itching frequency,, is about 96kHz and the sinusoidal reference frequency, r, is about 35kHz. The FFT result of ri by PSIM software is shown in Fig. 7. Each major section begins with a Heading in 0oint Times centered within the column and number using Roman numerals (excet for AKOWEDGEMET and REFEREES) followed by a eriod, a single sace, and the title using an initial caital letter for each word. The remaining letters are in SMA APITAS. The aragrah descrition of the section heading line should be set for 8 oints before, 6 oints after, and the line sacing should be set to exactly oints. Hyhenation is encouraged throughout. Harmonic Magnitude 50 [] IO O IO O O O Series resonance tye Parellel resonance tye: : G G ( ) s ( ) s = =, Qs = R s o Qs o s, o Q o Q = R Frequency (khz) Fig. 7 FFT result of the rimary side voltage

4 TABE I. IRUIT PARAMETERS OF PROTOTYPE HARDWARE Parameters in o R o For the body of your aer, use 0oint Times and set your line sacing at exactly oints with 0 oints before and after. Indent each aragrah by.5 mm. Further details are rovided in the remainder of this aer on some secific situations. A.. Digital ontrol Method alues 400 [] 00 [] 5 [Ohm] o 00 [] R o 50 ~ 00 [Ohm] 3:3:. : : s s o 4 [uh] 33 [nf] 6 [uh] 33 [nf] 470 [uf] 300 [uf] o In order to realize the roosed control scheme in analog domain, a very comlex hardware is required such as PWM generator, Adder, two omensator, two oltage ontrolled Oscillator (O) for PFM and sine function generation, Multilier and etc. However, in digital control, the control algorithm can be easily realized through the rogramming of a single DSP. Fig. 8 deicts the PWM duty ratio generation and the exact samling frequency generation using the synchronous PWM as well as the signal samling method without the use of a sensingsignalconditioning filter. This is because the samling measurements of voltage o, ref o, ref o o omensator omensator τ τ z z r Discrete Integrator OS Duty Period ounter alculation omarator ounter alculation DPWM nt( k ) nt( k) To om( k ) om( k) Gate Driver Fig. 9 The comlete digital controller structure and current information are erformed in the exactly middle of O and OFF itching eriod to avoid the itching noise of active devices. Taking into account the AnalogtoDigital (A/D) conversion time and the control algorithm calculation time, the duty cycle is udated at the next samling time. This rovision reduces control delays in the feedback loo. The comlete digital controller for the roosed control system is shown in Fig. 9. The itching eriod is generated by the comensator, which is fed to the Fig. 0 Steadystate exerimental results of the roosed digital control system Fig. 8 DSP control strategy Fig. Transient resonse at load steu transition in (00 [Ohm] to 50 [Ohm])

5 method is using the SSPWM and/or PFM to regulate all outut voltage recisely without any additional itches. It has been ractically roved by hardware rototye imlementation. Also, it has been confirmed that the digital control method can easily imlement the comlicated control algorithm for the singlepwm multileoutut control method. The exerimental results show that this new converter can be controlled indeendently and stably by using a simle digital control aroach.. REFEREES Fig. Transient resonse at load stedown transition in (50 [Ohm] to 00 [Ohm]) eriod count calculation block for DPWM itching frequency and the discrete integrator for the sine reference generation. The duty ratio is determined by multilication between the outut of comensator and the sine reference, which is fed to the comarator count calculation block for duty cycle. As shown in Fig. 9, this simle digital algorithm can solve the comlexity of analog controller. B. Exerimental Results Fig. 0 shows the steadystate erformance of the roosed digital control system. It is observed that the first and second outut voltage is well regulated to its desired values as 00 [] and 00 [] each. Fig. and show the transient resonse under a ste load change from 00 [Ohm] to 50 [Ohm] and vice versa. The first outut voltage is constantly regulated while the steed load transition occurs in the second outut voltage side. These exerimental results mean that the outut voltage sides are not influenced by each other and each side has an indeendent control variable for the regulation of its outut voltage. Therefore, it is confirmed that the roosed multileoutut converter using BPF and digital control scheme can regulate each outut voltage recisely and indeendently with only single itching network. The efficiency of the rototye hardware at rated condition is about 94% while the efficiency of conventional PDP ower system using a cross regulation method is less than that of the roosed control system in site of the oor indeendency. I. OUSIO This aer introduced a novel singlepwm multileoutut DD converter for a PDP ower system alication, and the digital controller imlementation method is roosed. The roosed [] Y. Duan and H. Jin, Digital ontroller Design for Switch Mode Power onverters, in Proc. IEEE Annu. Al. Power Electron. onf., 999, vol., [] A.. Perterchev and S. R. Sanders, Quantization Resolution and imit ycling in Digitally ontroller PWM onverters, IEEE Trans. Power Electron., vol. 8, no., , Jan [3] J. hen, A. Prodic, R. W. Ericson and D. Maksimovic, Predictive Digital urrent Programmed ontrol, IEEE Trans. Power Elecron., vol. 8, no.,. 449, Jan [4] Angel. Peterchev and Seth R. Sanders, Quantization Resolution and imit ycling in Digitally ontrolled PWM onverters, IEEE Trans. Power Electronics, ol. 8, o., Jan [5] P. Mattavelli, Digital ontrol of dcdc Boost onverters with Inductor urrent Esti mation, Alied Power Electronics onference and Exosition, 004. [6] S. Saggini, M. Ghioni and A. Geraci, An Innovative Digital ontrol Architecture for owvoltage, Highcurrent DD onverters with Tight oltage Regulation, IEEE Trans. Power Electron., vol. 9, no.,. 08, Jan [7] G. Feng, E. Meyer and Y. F. iu, A ew Digital ontrol Algorithm to Achieve Otimal Dynamic Performance in DtoD onverters, IEEE Trans. Power Electron., vol., no. 4, , Jul [8] Hyunsu Bae, Jaeho ee, Jeonghwan Yang and Bo Hyung ho, Digital Resistive urrent (DR) ontrol for the Parallel Interleaved DD onverters, IEEE Trans. Power Electron., vol. 3, no. 5, , Se [9] Xu Zhang, uca orradini and Dragan Maksimovic, Sensorless urrent Sharing in Digitally ontrolled Two Phase Buck DD onverters, IEEE Annu. Al. Power Electron. onf. Exosition, Feb. 009, [0] in. Y.., iu. K.H., A ew SynchronousSwitch Post Regulator for MultiOutut Forward onverters., in Proc. IEEE APE 90, , 990. [] Kim, E. H. ee, J. J. Kwon, J. M. hoi, W. Y. Kwon, B.H., Asymmetrical PWM Halfbridge onvertor with Indeendently Regulated Multile Oututs, Electric Power Alications, IEE Proceedings, olume: 53, Issue:,. 4, Jan [] Q. hen, F.. ee, M.M. Jovanovic, Analysis and Design of Weighted oltagemode ontrol for a MultileOutut Forward onverter, in Proc. IEEE APE 93, , March [3] hongeun Kim, KiBum Park, GunWoo Moon, and Jun Young ee, ew Multioutut Resonant onverter

6 for High Efficiency and ow ost PDP Power Module, PES,. 7, June [4] huanwen Ji, K. Mark Smith, Keyue M. Smedley, Ken King, ross Regulation in Flyback onverters: Analytic Model and Solution, IEEE Transactions on Power Electronics, vol. 6, o., March 00. [5] Hirofumi Matsuo, omarison of MultileOutut D D onverters Using ross Regulation, Industrial Electronics and ontrol Instrumentation, IEEE Transactions on, vol. IEI7,. 7689, August 980. [6] ed Mohan, Tore M. Undeland, William P. Robbins, Power Electronics, 3rd ed, WIEY, 003, [7] D. Grahame Holmes, Thomas A. io, Pulse Width Modulation for Power onverters, WIEY, 003,. 49. [8] Marian K. Kazimierczuk, Dariusz zarkowski, Resonant Power onverters, WIEY, 995,