Abstract: Regarding uses SPWM the invertor, the unipolarity inversion way only uses to a pair of high frequency switch, is opposite has in the bipolarity inversion loses, the electromagnetic interference lowly few and so on merits. Introduced separately the unipolarity inverts unilateral with the bilateral SPWM production method as well as the respective control method, has analyzed these two control method in the sine wave voltage zero crossing nearby vibration situation, had proven after the simulation and circuit experiment the bilateral SPWM way performance is more superior.
Key word: Unipolarity; Sine wave pulse-duration modulation; Zero crossing vibration
Introduction
Along with control technology development and to equipment performance request unceasing enhancement, 
many profession current collector no longer direct turning on exchange electrical networks, but obtains the electrical energy through the electric power electron power transformation, their peak-to-peak value, the frequency, the stability and the change form different are different because of the current collector. Like the correspondence power source, the arc welding power source, the electric motor frequency conversion velometer, heats up the power source, the automobile power source, green illumination power source, UPS, medical power source, battery charger and so on, they use the electrical energy is through carries on the rectification and the contravariant transformation after the electrical network electrical energy obtains. Therefore, the high grade contravariant power source already became the Chinese Journal of Power Sources the important object of study.
1 principle of work
1.1 main circuit analysis situses and SPWM production
Unipolarity SPWM inversion electric circuit’s analysis situs as shown in Figure 1,
2 groups bridge arms which is composed of the entire bridge 4 switching valves constitute, a group by the high frequency switch operating frequency work, is called the high frequency arm (S3, S4); Another group outputs the sine wave frequency carries on the cut, becomes the low frequency arm (S1, S2).
The unipolarity inversion has two kinds to have the SPWM method. The first control method is the carrier which assigns (sine wave) rectification Cheng Zheng, the modulating wave (triangular wave) is also, like Figure 2 (a) shows, is called the unilateral SPWM control; The second control method is the carrier which assigns (sine wave) is a complete sine wave, the modulating wave (triangular wave) works as the sine wave is positive when is, when sine wave for negative is negative, like Figure 2 (b) shows, is called the bilateral SPWM control.
The above two control method produces the SPWM mechanism not to be dissimilar, the respective control circuit also differs from.
1.2 unipolarity SPWM two control methods
1.2.1 unilateral SPWM controls
Unilateral SPWM control circuit as shown in Figure 3. Figure 3 Sg3 and Sg4 correspond the high frequency arm high and low tube’s driving signal separately; Sg1 and Sg2 correspond the low frequency arm high and low tube’s driving signal separately. As a result of low frequency arm’s cut function, high frequency arm PWM output nature along with it change. For example, originally when zero crossing Sg1 narrow pulse correspondence output low voltage, after low frequency arm cut, becomes the high voltage suddenly. Therefore, PWM has a sudden change process.
What shown in Figure 4 is the unilateral SPWM control method in the zero hour schematic drawing. Figure 4 E1 is theoretically with the datum (voltage waveform) with the phase error signal, because in the electricity pressure ring and the electric current surround in two links to have the integration element, according to the load nature and the weight, actual outlet error signal E2 and the reference signal has a phase difference. In the chart SPWM1 is the high frequency arm on theoretically tube’s driving signal, SPWM2 is on the actual high frequency arm tube’s driving signal.
1) the t0~t1 time by Figure 4 may see that in the t0~t1 time, because assigns the low frequency arm signal is 1, corresponding chart 3 may know that under main circuit low frequency arm tube breakover, what Figure 4 SPWM correspondence is on the high frequency arm tube’s driving signal, on tube’s SPWM driving signal changes gradually is small. By Figure 1 may know that in the t0~t1 time, the output sine wave signal by is becoming gradually 0.
2) the t1 time in the t1 time, the low frequency arm signal by 1 becomes 0, therefore, the low frequency arm becomes on the tube breakover by under tube breakover, may analyze by Figure 3, while the low frequency arm cuts, produced the SPWM comparator also to carry on the cut, therefore, produced by the E1 error signal SPWM (on high frequency arm tube) became close 100% SPWM immediately in the t1 time, then changed gradually is small. Under high frequency arm tube’s actuation supplementary on high frequency arm tube’s actuation, therefore under the high frequency arm tube’s actuation by 0 increases gradually. May know by Figure 1 that the output sine wave signal by 0 changes gradually negative.
3) t1~t2 time actual outlet error signal E2 can differ a phase with E1, therefore, produces SPWM2 and SPWM1 are different. May see by Figure 4: t1 time later, SPWM2 is 0 immediately, because under high frequency arm tube signal supplementary in SPWM2, corresponds in the main circuit, under the t1 high frequency arm the tube by a quite big dutyfactor breakover, then the dutyfactor changes slowly immediately frequently small (in chart SPWM2 gradually fill-out), under the high frequency arm the tube signal is not by 0 increases gradually, the SPWM sudden change definitely will cause the output sine wave signal in a zero crossing vibration. May supply the choice the solution to be as follows:
(1) while the low frequency arm cuts, artificial discharges the outlet error signal, causes it is 0, like this may weaken the vibration which causes in a zero crossing time;
(2) artificial low frequency arm signal in advance or lag certain phase, but, this plan, because the low frequency arm signal’s phase the load weight’s influence, in fact with difficulty is achieved accurately.
1.2.2 bilateral SPWM control
Bilateral SPWM control circuit as shown in Figure 5. As a result of low frequency arm’s cut function, high frequency arm PWM output nature along with it change. For example, before the zero crossing, the Sg1 narrow pulse correspondence is the output low voltage, after low frequency arm cut, becomes the high voltage suddenly. What however is different with the unilateral SPWM control, in the bilateral SPWM opposition movement is and the low frequency arm simultaneously carries on. Because in controller’s output has not changed suddenly, the low frequency arm’s cut will not create the output the sudden change.
What shown in Figure 6 is the bilateral SPWM control method in the zero crossing nearby SPWM schematic drawing. Figure 6 E1 is theoretically with the datum (voltage waveform) with the phase error signal, because in the electricity pressure ring and the electric current surround in two links to have the integration element, actual error signal E2 can differ a phase with the reference signal. In the chart SPWM1 is the high frequency arm on theoretically tube’s driving signal, SPWM2 is on the actual high frequency arm tube’s driving signal.
1) the t0~t1 time by Figure 6 may see that in the t0~t1 time, because assigns the low frequency arm signal is 1, corresponding chart 5 may know that under the main circuit low frequency arm the tube breakover, Figure on 6 SPWM correspondence’s high frequency arm tube’s driving signal, by Figure 1 may know in the t0~t0 time, the output sine wave signal by is becoming gradually 0.
2) the t1 time in the t1 time, the low frequency arm signal by 1 becomes 0, therefore the low frequency arm becomes on the tube breakover by under tube breakover, may analyze by Figure 5, while the low frequency arm cuts, produced the SPWM comparator also to carry on the cut, therefore, produced by the E1 error signal SPWM (on high frequency arm tube) became 100% SPWM immediately in the t1 time, then changed gradually is small. Under high frequency arm tube’s actuation supplementary on high frequency arm tube’s actuation, therefore, under the high frequency arm tube’s actuation by 0 increases gradually. May know by Figure 1 that the output sine wave signal by 0 changes gradually negative. 3) t1~t2 time actual outlet error signal E2 can differ a phase with E1, therefore, produces SPWM2 and SPWM1 are different, may see by Figure 6, in t1 to the t2 time, on the high frequency arm the tube actuates has been the high level, because under the high frequency arm the tube supplementary actuates on tube, therefore, in t1 to the t2 time, under the high frequency arm the tube breakover, hereafter does not have a soft clear process. SPWM1 and the SPWM2 comparison may see by Figure 6, the error signal lag is advantageous to the reference signal in suppresses the sine wave output signal in a zero crossing vibration.
2 computer simulations and experimental result
Using the electronic circuit computer auxiliary analysis in design software Matlab, has carried on the simulation separately to the above two control method.
Simulation condition: Outputs 220V, f=25Hz
2.1 unilateral SPWM control simulation profile
Unilateral SPWM control’s simulation profile as shown in Figure 7. From Figure 7 may see obviously, sine wave at a zero crossing time has the obvious vibration, tallies completely with the theoretical analysis.
simulation of profile 2.2 both sides control method
Bilateral SPWM control’s simulation profile as shown in Figure 8. From Figure 8 may see obviously, sine wave at a zero crossing time has not vibrated, tallies completely with the theoretical analysis.
3 experimental results and discussion
experiment of profile 3.1 unilateral SPWM control method
Experiment profile like chart 9, shown in Figure 10.
experiment of profile 3.2 bilateral SPWM control method
Experiment profile as shown in Figure 11.
3.3 discussions
By the simulation profile and the experiment profile may see that the unilateral SPWM control method has the very big vibration in the zero crossing spot, and may know by the experiment, the unilateral SPWM control method before not having the closed loop to vibrate fiercely, moreover the inductance has the very big noise, the unilateral SPWM control method also will later have the vibration in the closed loop, the inductance still has the noise.
The bilateral SPWM control method has when very good suppresses a zero crossing vibration the function, the experiment, bilateral SPMW control method after the closed loop and closed loop zero crossing has not vibrated, the inductance noise is also very small.
4 conclusions
Inverts on the unipolarity, this article separately to unilateral as well as it has carried on the analysis with the bilateral SPWM production method and the control method in the sine wave voltage zero crossing nearby vibration situation. The theoretical analysis indicated that and through the simulation and circuit experiment proof, in the bilateral SPWM controller outputs, because has not had the big sudden change nearby zero crossing, its performance is more superior.
