Điều khiển trượt bộ lọc công suất tích cực một pha

T \ P CHJ KHOA HOC & CONG NGHE C.^C TRLONG DAI HOC KV THUAT * SO 80-2011 SLIDING-MODE CONTROL FOR A SINGLE-PHASE ACTIVE POWER FILTER DIEU KHIEN TRUOT BO LOC CONG SUAT TICH CUC M O T PHA Son T.Nguyen, Thanh V.Sguyen Hanoi University of Science and Technology ABSTRACT This paper presents the methgd of designing a non-linear controller for a single-phase active power filter (APF) that is connected power electronic loads in parallel In particular, a controller with sliding-mode control is developed for this application A single-phase APF has the topology of an Hbridge with four MOSFET switches connected the load via an inductor and connected a capacitor In the DC bus With the structure like this, the model of the APF can be seen as a variable structure model and is well suited with the sliding-mode control In this application, the sliding mode control always guarantees the shape of the main current to be sinusoidal and coincide with the phase of the main voltage The simulation results show that the sliding-mode control always maintains the good performance of the APF when working at different conditions Moreover, the control algorithm is easily deployed on low-cost digital control systems TOM T.\T Bii bio niy trinh biy phwong phip thiit ki mdt bd diiu khiin phi tuyin cho bd iQc cdng suit tich cwc mdt pha mic song song vdi tii li thiit bi dien tir cdng suit, cu thi li thiit ki mdt bd diiu khiin phi tuyin vdi diiu khiin trwgt Bd Igc cdng suit mdt pha cd ciu hinh bao gdm mdt ciu H vdi bin khda chuyin mach MOSFET nil song song vdt til qua mdt dien cim vi mdt tij dien phia mdt chiiu Vdi thiit ki nhw viy, md hinh ciia bd lgc tich cwc mdt pha dwgc xem nhw li md hinh cd ciu true thay ddi vi phii hgp vdl diiu khiin trwgt Trong irng dung niy, bd diiu khiin trwgt ludn dam bao cho ddng diin cua ngudn cd dang hinh sin va triing pha vdi dien ip ngudn Kit qui md phdng cho thiy diiu khiin trwgt ludn tri tit ning lim vlec cua bd Igc die biet til lam viec d dc chi dd khic Hon thi nu'a, thuit toin diiu khiin de ding thirc thi vdi dc he thing diiu khtin si chi phi thip • I INTRODUCTION The wide application of power electronic dev ices causes the distortion of the main current due to the power electronic devices work as non-linear loads One of the methods for eliminating the harmonic distortion of the single-phase load is using the active power niter (.-VPF) connected with the load in parallel, •fhe function of the active filtere is generating a hamionie compensation current that is able to eliminate harmonic components generated by the load Essentially, the compensation current is the inverse of the hannonic current via the load According to [1, 2], there are some methods of determining the hannonic current such as Fast Fourier Transform (FFT), instantaneous power theorv', synchronous d-q theory, instantaneous p-q theory For FFT method, the exact computation method requires two cycles of the wave needed to be analysed: the first cvcle for data acquisition and another cycle for analyzing data For other method, the implementation is quite complicated Recently, the use of adaptive linear neural networks can be seen one of the methods for determining the compensation current [3], However, this method requires costly hardware such as digital signal processor (DSP) or specific digital control svstems Recenllv there have been some methods of designing the single-phase APF Most of these methods include two following steps: • Step 2: Designing the controller for AC current of the filter computed in step I Step 1: Detennining the compensation current for the active fitlter with the line frequenev of the non-linear load 67 T.AP CHi KHOA HOC & CONG NGHE CAC T R L > G DAI HOC K\ THL.\T • SO 80 - 2011 This paper decribes a simple method that is able to combine Uvo steps when designing the single-phase APF In particular, a slidingmode control is developed to guarantee the main current to be sinusoidal and coincide with the phase of the main voltage The main advantage of this method is that it has the fast computation and is easy to be deployed on cheap digital control systems The model of the single-phase APF is a votage source inverter with the DC votage is formed on the capacitor (depending on switching status of the swiches on the H-bridge as shown in Figure.2 Another matter is that the law of switching 5, and S, has to guarantee the voltage on the capacitor greater than the maximum voltage of the AC source at am moment Therefore, the control law has to be satified the first condition as follows: This paper is organized as follows Section summarizes the model of a singlephase APF In section the authors mention the development of sliding-mode control for this application Section are simulation results obtained bv using Matlab/Simulink Finally, Section is the conclusion of this research c: • '•o)>^'; (1) where V,, is the voltage on the capacitor C, K, is the reference voltage and !', the r.m.s votlage of the AC source II MODEL OF A SINGLE-PHASE APF The single-phase APF is connected with a non-linear load in parallel as shown in Figure The power of the resistive load is changed by adjusting the firing angle of the Triac The APF has four controllable switches 5",,.S,,,S', and S'^ and is connected with the non-linear load via an inductor L and connected with a capacitor ('in the DC bus The values of the inductor L and the capacitor ('depend on the maximum power of the resistive load Fig.2 The APF is developed by the principle oj a voltage-source inverter If ^', and »j are called logic signals (Oor I) for closing and opening the switches 5, and S, with the rule below: In order to guarantee the APF working correctly, the switches in the same legs of the H-bridge have to work in reverse order This means that if ,9, is closed then ,S', is open, if V, is closed then S^ is open Therefore, the control of the H-bridge is essentially controlling tw o switches 5, and 9^ • If i/| = then 5", is closed, if u^ = then 5", is open • If t/j = then S', is closed, if »_, = then S.^ is open Two equations of the inverter have the following forms: ^.' •S y = (21 ^.(u.^iu \)i,] (3! According to equations (2) and (3), the current ;, is governed bv the voltage on the capacitor and the switching status ol ,S' and S', Fig I .1 single-phase 4PF is connected with a power electronic load in parallel 68 TAPCHl KHOA HOC & CONG NGHE CAC TRLOAG DAI HOC KV T H U A T * SO 80-2011 III SLIDING-MODE CONTROL due to the switching status of the switches on the H-bridge In addition, the procedure of designing a correct power circuit will always In control theory, sliding-mode control (SMC) is a control form that has variable structure This is a non-linear control method that changes the dynamics of a non-linear system by high-frequency switching control SMC is concemed with forcing one or more force variables (often, but not necessary, state variables) to follow a specific trajectory The trajectory is known as the sliding surface The location of the variables relative to the sliding surface governs the control law which is applied to the system As the system variables of interest pass through the sliding surface, the control law changes The nonlinear control law is chosen so that regardless of where the system is with respect to the sliding surface, control actions always drive the system toward the sliding surface Power electronic systems are natural candidates for sliding-mode control because topologies of power electronic circuits always change with the operation of semiconductor switches s following the non-linear control law as shows in Table.I In other words, we have: S i ? '+yf, -f-sgn{V^) (9) i; < Substitute (9) into (8) and solve equation (8) with variable u, we have: • ^'( , , ] K l-sgn(F) "' "Fl'" T "f^^—2^ ^'°^ Equation (10) is popularly used in inverter simulations Table I The non-linear conirol law used to implement Ihe sliding mode control for the APF when the source current is on the sliding surface In order to guarantee the sv stem on the sliding surface, the following condition has to be satisfied at any moment: "• " (6) / A t ; 1 In order to have condition (6) to be '•, < o f alwavs satislled, the sign of s has to be ", controlled approximately .Al anv time, the APF can make the sign csi i (8) where sgn{Tj = \ if (;>0 and sgn(V^) = -\ if (5) ss