introduction
With the development of modern technology, inverter power is widely used in various industries, and higher requirements are put forward for its performance. The traditional inverter power supply is mostly a control system combining analog control or digital. The good inverter power supply voltage output waveform mainly includes high steady state precision and good dynamic performance. At present, the structure and control of the inverter can obtain a good sinusoidal output voltage waveform, but the effect is not ideal for a waveform with a relatively fast mutation.
The function signal generator is a commonly used device in experimental teaching. Waveforms that can produce different frequencies and voltage levels: square wave signals, triangular waves, sinusoidal signal waveforms. A new DDS technology that has emerged in recent years is the direct digital frequency synthesis technology. But they are all small signal waves, no power output, and can not carry a certain load.
The multi-function inverter power supply proposed in this paper adopts a double-phase single-phase full-bridge inverter structure. The output voltage waveform tracks the given reference waveform and has power output, which can carry a certain load. The control adopts the hysteresis control added to the differential link to fully realize the digital control.
Main circuit design
The principle of the multi-function inverter power supply is shown in Figure 1. It consists of two parts: the main circuit and the control part. The reference signal of the main circuit can be obtained by communication with a computer or other circuits.
Figure 1: Principle of multi-function inverter power supply
In the design of the main circuit, the multi-inverter structure is borrowed, and a double-phase single-phase full-bridge inverter connection is adopted. The schematic diagram is shown in Figure 2. The DC side voltages of the two inverters are different. The DC side voltage of the main inverter is Udc, and the DC side voltage of the inverter is 3Udc. The transmission voltage waveform has 9 levels: ± 4Udc, ±3Udc, ±2Udc, ±Udc, 0. Since the number of output levels is more than a single inverter, the output waveform is better. The main inverter works at a higher frequency, and the operating frequency from the inverter is lower, which greatly reduces the switching loss. In the slow phase of the reference waveform change, only the main inverter bridge needs to work, and the reference signal can be well tracked; when the reference signal changes quite rapidly, the auxiliary inverter bridge and the main inverter bridge need to work at the same time, and the fast and accurate tracking reference is needed. signal.
Figure 2: Double cascade single phase full bridge inverter topology
Control design
In the control part, hysteresis is used for complete digital control. Hysteresis control has fast response, high accuracy, high tracking accuracy, and the output voltage does not contain harmonic components of a specific frequency. It can be digitally controlled using DSP. Hysteresis control is used for the main inverter of the main circuit and the slave inverter.
Figure 3: Hysteresis control principle
As shown in Figure 3, the hysteresis width of the main switch is h, the hysteresis width of the slave switch is hs, and hs "h. The main inverter is always working, the switches V1 and V4; V2 and V3 are alternately turned on. Broken. There are three working states from the inverter. At the time t1~t2, the error voltage does not exceed the hysteresis width of the inverter, only the main inverter needs to work, and the four switching tubes are all turned off; at time t3, the error voltage Δu"hs, the switching tube VS2 When VS3 is turned on, the switching transistors VS1 and VS4 are turned off; the error voltage at time t4 is -Δu "-hs switching transistors VS1 and VS4 are turned on, and the switching transistors VS2 and VS3 are turned off.
Considering the difficulty of following the abrupt signal, a differential link is introduced before the hysteresis controller, as shown in Figure 4, to improve the following effect.
Figure 4: Hysteresis control with differential links
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