Page 1 of 7 2015-IACC-0418 An Optimized Algorithm for SVPWM Based on Three-Phase Stationary Frame Weiyi Zheng Zhiyong Zeng Huan Yang Zhejiang University Hangzhou, 310027, China weiyizheng@zju.edu.cn Zhejiang University Hangzhou, 310027, China zhyzeng@zju.edu.cn Zhejiang University Hangzhou, 310027, China yanghuan@zju.edu.cn Chong Zhu Qingwei Yuan Rongxiang Zhao Zhejiang University Hangzhou, 310027, China zhuchong@zju.edu.cn Zhejiang University Hangzhou, 310027, China yuanqingwei@zju.edu.cn Zhejiang University Hangzhou, 310027, China rongxiang@zju.edu.cn Abstract--The conventional space vector pulse width modulation (SVPWM), including coordinate transformation, sector identification, and active time calculations of voltage vectors, needs lots of complex irrational number operations such as trigonometric function calculations, which introduces challenges for real-time digital control chips. Considering the shortcomings of traditional algorithm, this paper presents an optimized algorithm based on three-phase stationary frame. In the proposed algorithm, the reference voltage vector is projected onto the three-phase stationary frame firstly, then a unified formula is obtained by utilizing the principle of symmetric, where only normal mathematical operations of modulation wave is required. With the unified formula, the duty ratios of three bridge-arms will be calculated directly. Comparing with conventional algorithm, the proposed algorithm is more suitable for digital system owing to the characteristic of easier programming, faster operating speed, and higher real-time ability. The simulation and experimental results show the validity and feasibility of the proposed algorithm. Index Terms--real-time, space vector pulse width modulation (SVPWM), symmetric, three-phase stationary frame, unified formula. I. INTRODUCTION Due to the high real-time control capability and flexible control algorithm, digital control chips have been widely used in the control systems of power converters [1], [2]. Compared to conventional sinusoidal pulse width modulation (SPWM), space vector pulse width modulation (SVPWM) possesses a better characteristic, such as higher DC voltage utilization ratio, smaller switching losses, lower harmonics, and easier digital implementation [3]-[5]. Thus, the SVPWM strategy is becoming the mainstream of various PWM technologies in the digital control systems. Usually, the switching frequency is required as high as possible to ensure the locus of the voltage space vector closer to a circle, reducing the harmonic of PWM signals. But, due to the restrictions of manufacturing processes and material This work was supported by the National Key Basic Research Program of China (973 Program) under Grant 2013CB035600. properties, the switching frequency for high voltage and power semiconductor is generally between a few kHz to tens kHz, which requires a system with high real-time performance. However, during the realization process of conventional SVPWM modulation, a lot of irrational number operations, such as trigonometric function and square root, are applied to coordinate transformation, sector identification, along with the active time operations of voltage vectors. The complex and redundant calculation process of conventional SVPWM algorithm, not only takes a large number of CPU resources, but also increases the control time delay, which seriously affect the dynamic performance of the system with high switching frequency [6]-[8]. Therefore, how to simplify the conventional algorithm is becoming more and more important. Reference [9] proposed a novel SVPWM algorithm based on non-orthogonal coordinate system to avoid the traditional sector identification process. Although the algorithm was simplified, a large number of trigonometric functions still existed, reducing the system operation precision. In [10], the proposed simplified algorithm utilized line-to-line voltage to express the active time equation of voltage vectors. Reference [11] given the expressions for duty ratios of three bridge-arms directly by calculating the components of reference voltage vector in a special coordinate system which reduced the six sectors in the traditional SVPWM modulation to three. In [12], the switching time of three bridge-arms was obtained directly by the components of reference voltage vector in two-phase stationary coordinate system. Due to the absence of the complicated trigonometric function and square root operations, this kind of methods streamlined the procedure code. However, the look-up table and the sector identification are still required, reducing the real-time performance of the system accordingly. In addition to the selection of reference frame, the synthesis method of voltage space vector will also affect the simplification degree of algorithm. The distinction between all kinds of synthesis methods is mainly reflected by the selection and distribution of zero-voltage vector. The seven-segment switching sequence and fivesegment switching sequence are the most commonly used methods. Considering the advantages and disadvantages of 978-1-4799-8374-0/15/$31.00 © 2015 IEEE Authorized licensed use limited to: WESTERN DIGITAL. Downloaded on June 20,2023 at 02:02:46 UTC from IEEE Xplore. Restrictions apply. 2015-IACC-0418 both methods, the seven-segment switching sequence and the up-down-count mode are used to generate the symmetrical PWM signals, decreasing the harmonica and switching losses [13], [14]. This paper proposes an optimized algorithm for SVPWM based on three-phase stationary frame. According to the geometric relationship reflected in the space vector hexagon, the duty ratios of adjacent voltage space vectors for each sector are calculated respectively by the components of reference voltage vector in three-phase stationary frame. Then, the synthesis method of seven-segment switching sequence is utilized to derive the duty ratios of three bridge-arms for each sector. Finally, a unified formula based on the three-phase stationary frame is presented for SVPWM modulation. The optimized algorithm skips over the procedure of the coordinate transformation, the sector identification, and the active time calculations of voltage vectors existing in conventional SVPWM algorithm. The proposed method calculates the duty ratios of three bridge-arms directly by the simple addition and subtraction operations, as well as a small amount of multiplications. Additionally, the complex irrational number operations are absented, improving the real-time ability. Finally, the simulation and experimental results show the effectiveness of the proposed algorithm. Page 2 of 7 2 sa − sb − sc ­ Vdc °uan = 3 ° 2 sb − sa − sc ° Vdc ®ubn = 3 ° ° 2 sc − sa − sb Vdc ° ucn = 3 ¯ Substituting eight combinations of switching states into (1), and then mapping the obtained phase voltage of AC side into a complex plane, a voltage space vector distribution diagram is shown in Fig. 2. With all possible combination of the switch states, eight basic vectors, including two zero vectors (V0 and V7) and six non-zero vectors (V1 to V6), are derived and show in Fig. 2, where the eight basic vectors are located in the vector plane symmetrically. ȕ V3(010) V2(110) II ur III I V0(000) V4(011) ș TV1 V7(111) IV II. VECTOR PLANE AND SYNTHESIS PRINCIPLE OF SVPWM The topological structure of the digitally controlled threephase PWM rectifier is shown in Fig. 1. In the process of building its mathematical model, utilizing sa, sb, sc to represent the switching state of three bridge-arms respectively. When s=1, the switching device in upper arm is turned on and that in lower arm is turned off, when s=0, the upper arm switching device is turned on and the lower arm switching device is turned off. (1) TV2 V1(100) Į VI V V5(001) V6(101) Fig. 2. Structure of the digitally controlled three-phase PWM rectifier The amplitude of all the six non-zero vectors shown in Fig. 2 is 2Vdc/3. And, a regular hexagon is built by connecting the six vertexes, and the regular hexagon denotes the achievable modulation range of SVPWM strategy. The inscribed circle in the hexagon is the limitation for the linear modulation. Usually, the hexagonal region is divided into six sectors by the six non-zero vectors, where the vector V1 is assigned to sector I, vectors V2 and V3 are assigned to sector II, vector V4 is assigned to sector III, vectors V5 and V6 are assigned to sector V. For the reference voltage ur, it can always be synthetized by the two adjacent basic space vectors. When ur lies on the position shown in Fig. 2, it is synthetized by vectors V1 and V2. According to the volt-second balance principle, the following expression is obtained: ur Ts = V1TV 1 + V2TV 2 (2) where, Ts is the PWM switching cycle, TV1 and TV2 are the active time in a switching cycle Ts for vectors V1 and V2 respectively. Fig. 1. Structure of the digitally controlled three-phase PWM rectifier According to the structure shown in Fig. 1, the expression of three-phase voltage of AC side can be obtained as (1). In addition, (2) can be rewritten as (3) in the form of duty ratio. ur = dV 1V1 + dV 2V2 978-1-4799-8374-0/15/$31.00 © 2015 IEEE Authorized licensed use limited to: WESTERN DIGITAL. Downloaded on June 20,2023 at 02:02:46 UTC from IEEE Xplore. Restrictions apply. (3) Page 3 of 7 2015-IACC-0418 where, dV1 and dV2 are the duty ratios for vectors V1 and V2, respectively. III. DUTY RATIOS OF ACTIVE VECTORS BASED ON THREEPHRASE STATIONARY FRAME In accordance with the sector division manner shown in Fig. 2, the reference voltage is decomposed into uĮ and uȕ in the Į-ȕ coordinate system, then, a novel section identification approach based on three-phase stationary frame is developed. The purpose of the procedure is not to identify which sector that the ur lies on, it is to estimate roughly that whether the expressions for the duty ratios of active vectors are correct or not, and also provides the inductive basis for the derivation of the unified formula for the duty ratios of three bridge-arms. According to the geometric relationship, it can be found that the conventional judgment condition can be replaced by judging the component uȕ whether it is positive or negative and also the value range of cot ș. Assuming: ­ x = uβ ° ® y = uα ° uβ ¯ (4) Therefore, the traditional sector division basis based on variables x and y can be displayed as Table I. Sector TABLE I SECTOR DIVISION BASIS x [ 0, + ∞ ) 2 ( 0, +∞ ) ª 3 3º , «− » 3 3 ¬ ¼ 3 [ 0, + ∞ ) § 3· ¨¨ − ∞ , − 3 ¸¸ © ¹ 4 (−∞ , 0 ) § 3 · , +∞ ¸¸ ¨¨ 3 © ¹ 5 (−∞ , 0 ) ª 3 3º , «− » 3 3 ¬ ¼ 6 (−∞ , 0 ) § 3· ¨¨ − ∞ , − ¸ 3 ¸¹ © ­OB = dV 1V1 ® ¯ BA = dV 2V2 1 ­ °OB = uα − 3 uβ ° ® ° BA = 2 u β °̄ 3 uan > ubn ≥ ucn ubn ≥ uan ≥ ucn ubn ≥ ucn > uan ucn > ubn > uan ucn ≥ uan ≥ ubn uan > ucn > ubn (6) According to the geometric relationship shown in Fig. 3, the expression about OB, BA and uĮ, uȕ can be obtained easily as (7). Substituting the Clark transformation formula to Table I, the criterion of sector division based on three-phase stationary frame can be expressed as (5). ­ Sector 1: ° Sector 2 : ° °° Sector 3 : ® ° Sector 4 : ° Sector 5 : ° °̄ Sector 6 : Fig. 3. The synthesis principle of voltage space vector The physical meanings of segments OB and BA displayed in Fig. 3 are the active time of vectors V1 and V2 respectively. Definition: y § 3 · , +∞ ¸¸ ¨¨ © 3 ¹ 1 Equation (5) provides a more convenient method for sector identification of the conventional SVPWM algorithm, which can be realized just by comparing the values of expected three-phase voltage without the traditional coordinate transformation process. However, in this paper, it is only to estimate roughly the correctness of the expressions for the duty ratios of active vectors, and also provide the inductive basis to the derivation of the unified formula for SVPWM. After determining the sector where the given voltage space vector ur locates with the method described above, the duty ratios of active vectors based on three-phase stationary frame can be derived from (3). Taking sector I for example, the synthesis principle of voltage space vector are shown in Fig. 3. (5) (7) Substituting the Clark transformation formula to the simultaneous equations (6) and (7), the expression for duty ratios of active vectors based on three-phase stationary frame can be received as (8). 1 ∗ ­ ∗ °° dV 1 = 2 ( uan − ubn ) ® °d = 1 ( u ∗ − u ∗ ) °̄ V 2 2 bn cn (8) where, u*an, u*bn, and u*cn are the per-unit values for expected three-phase voltage, and the reference value is Vdc/2. The positive values of dV1 and dV2 denote the condition 978-1-4799-8374-0/15/$31.00 © 2015 IEEE Authorized licensed use limited to: WESTERN DIGITAL. Downloaded on June 20,2023 at 02:02:46 UTC from IEEE Xplore. Restrictions apply. 2015-IACC-0418 u*an>u*bn>u*cn. In addition, the positive value of the dV1 and the zero value of dV2 indicate the situation of u*an>u*bn=u*cn. Summarizing the conclusions above, the relationship between u*an, u*bn, and u*cn can be achieved as u*an>u*bnu*cn, and it is consistent with the identification of sector I. By parity of reasoning, the duty ratio expressions based on three-phase stationary frame for other sectors are shown in Table II, and they all accord with the criterion of sector division. TABLE II DUTY RATIOS OF ACTIVE VECTORS FOR EACH SECTOR Duty1 Duty2 Sector 1(V1,V2) 2(V2,V3) 3(V3,V4) 4(V4,V5) 5(V5,V6) 6(V6,V1) 1 ∗ ( uan − ubn∗ ) 2 1 ∗ ( uan − ucn∗ ) 2 1 ∗ ( ubn − ucn∗ ) 2 1 ∗ ( ubn − uan∗ ) 2 1 ∗ ( ucn − uan∗ ) 2 1 ∗ ( ucn − ubn∗ ) 2 TV 2 TV 1 TV 0 2 2 2 (11) Then, combining with (5), (11) can be rewritten to a unified format as follow: According to the duty ratio expressions of active vectors deduced in the previous section, the duty ratios of three bridge-arms based on three-phase stationary frame can be derived as follow. Taking sector I for example, when the ur locates in linear modulation region, the constraint shown as (9) must be satisfied. (9) Where, the remaining time of a switching cycle Ts is complemented by zero vectors V0 and V7. Considering the harmonic, switching losses and other factors, the symmetric characteristic is applied to generate the pulse sequences, where the zero vector V0 is activated in both the initial state and end state, and the zero vector V7 is also inserted into the midpoint of the given voltage space vector. The calculations for the active time of vectors V0 and V7 are obtained and shown as: 1 (1 − dV 1 − dV 2 ) Ts 2 TV 7 1 1 ∗ ­ ∗ °d a = 2 + 4 ( uan − ucn ) ° 1 1 ∗ ° ∗ ∗ ® d b = − ( uan − 2ubn + ucn ) 2 4 ° 1 1 ∗ ° ∗ ° d c = 2 − 4 ( uan − ucn ) ¯ IV. UNIFIED FORMULA FOR SVPWM STRATEGY BASED ON SYMMETRIC PULSES TV 0 = TV 7 = TV 0 TV 1 TV 2 2 2 2 Fig. 4. The seven-segment switching sequence for sector I 1 ∗ ( ubn − ucn∗ ) 2 1 ∗ ( ubn − uan∗ ) 2 1 ∗ ( ucn − uan∗ ) 2 1 ∗ ( ucn − ubn∗ ) 2 1 ∗ ( uan − ubn∗ ) 2 1 ∗ ( uan − ucn∗ ) 2 TV 1 + TV 2 ≤ Ts Page 4 of 7 (10) where, TV0 and TV7 are the active time in a PWM switching cycle Ts for vectors V0 and V7 respectively. Therefore, the seven-segment switching sequence can be achieved as shown in Fig. 4. From Fig. 4 and equations (8) and (10), the expressions for duty ratios of three bridge-arms based on three-phase stationary frame can be easily obtained as (11). 1 1 ∗ 1 ∗ ­ ∗ °d max = 2 − 4 ( umax + umin ) + 2 umax ° 1 1 ∗ 1 ∗ ° ∗ ® d mid = − ( umax + umin ) + umid 2 4 2 ° 1 1 ∗ 1 ∗ ° ∗ ° d min = 2 − 4 ( umax + umin ) + 2 umin ¯ (12) Analogizing the above derivation of sector I, it is easily to find that the duty ratios of three bridge-arms for all the other sectors can be expressed in the same form of (12). Consequently, the unified formula for SVPWM strategy based on three-phase stationary frame is obtained as (13). 1 1 ∗ + u x + M , ( x = a, b, c ) 2 2 1 ∗ ∗ M = − ( umax + umin ) 4 dx = (13) In accordance with (13), it can be observed that the duty ratios of all the three bridge-arms include a common component M. It just needs to perform simple addition and subtraction operations, as well as a small amount of multiplications on the maximum and minimum values of three-phase voltage, eliminating the complex and redundant irrational number operations. Hence, the optimized algorithm based on threephase stationary frame is more suitable for the high-precision real-time control system, accounting of the easier programming and the faster operating speed. The PWM pulse sequences corresponding to the duty ratios calculated from (13), are generated on the basis of Fig. 5, which is utilizing the intersection of triangular carrier wave and modulation wave as the switching time to toggle the sta- 978-1-4799-8374-0/15/$31.00 © 2015 IEEE Authorized licensed use limited to: WESTERN DIGITAL. Downloaded on June 20,2023 at 02:02:46 UTC from IEEE Xplore. Restrictions apply. Page 5 of 7 2015-IACC-0418 tus of PWM signals. Wherein, the period of the unipolar isosceles triangular carrier wave is Ts, and the amplitude is Ts/2. The modulation waves Taon, Tbon and Tcon are the switching time during a PWM switching cycle of the upper arms switching devices, which can be calculated by (14) and updated at the initial time of each PWM switching cycle. Txon T = s (1 − d x ) , ( x = a, b, c ) 2 the SVPWM strategy can be equivalently implemented by the typical SPWM strategy. Nonetheless, the SVPWM strategy not only achieves a boost of DC voltage utilization ratio, and also avoids the phase synchronization problem of zerosequence component in the improved SPWM strategy. VI. SIMULATION AND EXPERIMENT VERIFICATION (14) Simulation Verification in MATLAB/Simulink To verify correctness of the optimized algorithm proposed in this paper, a 5-kVA three-phase PWM rectifier simulation model is built in MATLAB/Simulink platform, and the system parameters are given in Table III. A. Rs 0.1ȍ Ua/Ub/Uc 110V Fig. 5. The Schematic diagram of generating the PWM pulse sequences In digital system, the interrupt function of the ePWM module and also the up-down-count mode are applied into the generation of the symmetric PWM pulse sequences. Writing the switching time of each switching device to the countcompare register, when the value in the time-base counter is equal to the active count-compare register, toggling the ePWM output (low output signal will be forced high, and a high signal will be forced low). Through this process, the required PWM pulse signals can be generated to trigger the full-controlled switching devices. V. THE ESSENTIAL RELATIONSHIP BETWEEN SVPWM AND SPWM In order to explore further the relation and difference between SVPWM strategy and SPWM strategy, rewriting the united formula for SVPWM strategy to the form of SPWM strategy, that is to calculate the equivalent modulation function corresponding to triangular carrier wave for SVPWM strategy. According to the regular sampling method, the relationship between the duty ratio of each bridge-arm and the expected voltage of the same arm is shown as (15). u x∗ = 2d xspwm − 1, ( x = a, b, c ) TABLE III THE SYSTEM PARAMETERS L 3mH C 2000ȝF Vdc 400V Ts 10kHz The simulation results are shown in Figs. 6, 7 and 8. Fig. 6 displays the comparison between the modulation waveform and the filtered voltage waveform of AC side in case of phase-A. It can be observed that the two waveforms match with each other. Furthermore, analyzing the fundamental component of phase-A real voltage through the FFT window, it can be found that the valid value is 109.4V, and it also has a phase angle of -7.6°, which means lagging the phase-A grid voltage 7.6°. The data observed from FFT window is consistent with the estimated value calculated by the system parameters given in Table III. And, the duty ratios waveform of three bridge-arms shown in Fig. 7 is consistent with the standard saddle waveform obtained from the conventional SVPWM algorithm. Fig. 8 shows the initial status and the stable status of the three-phase current and the DC voltage, which indicates that the simulation model achieves the rectification function with an excellent dynamic and low harmonics. Therefore, according to the above analysis and comparison of the simulation results, the correctness of the optimized algorithm is verified. (15) So, the latent modulation function corresponding to triangular carrier wave for SVPWM strategy is given as (16). u x∗svpwm =u x∗ + 2M , ( x = a, b, c ) (16) From (16), it can be found that comparing with the modulation function for SPWM strategy, there is one more zerosequence component 2M in SVPWM strategy, it is equivalent to inject zero-sequence component to the three-phase sinusoidal modulation wave of SPWM strategy. In other words, Fig. 6. The expected voltage and the real voltage of phase-A 978-1-4799-8374-0/15/$31.00 © 2015 IEEE Authorized licensed use limited to: WESTERN DIGITAL. Downloaded on June 20,2023 at 02:02:46 UTC from IEEE Xplore. Restrictions apply. 2015-IACC-0418 Page 6 of 7 1.0 0.8 0.6 0.4 0.2 0.0 0.03 Fig. 7. The duty ratios of three bridge-arms 0.04 Time (s) 0.06 0.05 Fig. 9. The duty ratios of three bridge-arms 30 20 10 0 -10 -20 -30 -0.02 (a) Three-phase input current 0.00 0.02 Time (s) 0.04 0.06 0.04 0.06 (a) Three-phase input current 420 400 380 360 340 -0.02 0.00 0.02 Time (s) (b) DC voltage (b) DC voltage Fig. 8. Simulation results Fig. 10. Experimental results Experiment Verification In order to further verify the feasibility, the optimized algorithm is applied to a 5-kVA three-phase PWM rectifier experimental platform, which is implemented on a 16-bit DSP TMS320F2808 development board, and the system parameters are given in Table III. Fig. 9 shows the three-phase duty ratios waveform, the standard saddle characteristic is consistent with the simulation result. And the initial status and the stable status of the three-phase current and the DC voltage shown in Fig. 10 indicate that the experimental platform achieves the rectification function with an excellent dynamic and low harmonics. The experimental results shown in Figs. 9 and 10 satisfy the B. 978-1-4799-8374-0/15/$31.00 © 2015 IEEE Authorized licensed use limited to: WESTERN DIGITAL. Downloaded on June 20,2023 at 02:02:46 UTC from IEEE Xplore. Restrictions apply. Page 7 of 7 2015-IACC-0418 required operating characteristic of the three-phase PWM rectifier, which verify the feasibility of the optimized algorithm for SVPWM strategy. VII. [14] D. A. Grant, M. Stevens, and J. A. Houldsworth, "The effect of word length on the harmonic content of microprocessor-based PWM waveform generators," IEEE Trans. Industry Applications, vol. 21, no. 1, pp. 218-225, Jan. 1985. CONCLUSION In this paper, an optimized algorithm of SVPWM strategy based on three-phase stationary frame is proposed for the digital control system with high-precision and real-time characteristic. The proposed algorithm skips over the procedure of coordinate transformation, sector identification, and active time calculations of voltage vectors existing in conventional SVPWM algorithm, and calculates the duty ratios of three bridge-arms in three-phase stationary frame directly without the complex irrational number operations like trigonometric function and square root operations. It streamlines the algorithm, accelerates the operating speed, and improves the realtime ability, making it easier for the implementation of digital systems. Finally, the correctness and the feasibility of the proposed algorithm have been verified through the simulation analyses and experimental tests. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] C. Buccella, C. Cecati, and H. 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