The principle of waveform generator based on 80C196MC and its application in inverter power supply-EEWORLD

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These integrated circuits include HFE4752, SLE4520, MA8X8/SA8X8, SAXXXX, etc. Most of them need to be connected to a single-chip microcomputer to complete the SPWM control function, which is still not simple enough for inverter systems with higher requirements. The 16-bit single-chip microcomputer 8XC196MC launched by INTEL integrates a three-phase SPWM waveform generator WFG (Wave Form Generator, hereinafter referred to as WFG) [1], which provides strong hardware support for the full digital design of the inverter control circuit. It has rich software instructions and is basically compatible with other 196XX single-chip microcomputers. This article focuses on the working principle of WFG in 80C196MC and the design points of the software.

1 WFG Working Principle

There are four control modes to choose from: Mode 0 to Mode 3. Mode 0 and Mode 1 are center-aligned modes, that is, the SPWM pulse is arranged at the center point of the switching cycle, which corresponds to the triangle wave carrier (double-sided modulation) in the analog circuit. The difference between Mode 0 and Mode 1 is the different reloading time and number of waveform parameters. Modes 2 and 3 are edge-aligned modes, that is, the SPWM pulse wave is arranged at the starting point of the switching cycle, which corresponds to the sawtooth wave carrier (single-sided modulation) in the analog circuit. The difference is also the different timing of reloading. The harmonics caused by the center-aligned SPWM waveform are small, and do not contain ωs±ω0 and 2 ωs ( ωs is the switching angular frequency, ω0 is the signal wave angular frequency) harmonics [2]. The center-aligned mode is usually used. In the following description, Mode 0 is taken as an example (M0 (B12) = M1 (B13) = 0).

The value first written into WG-RELOAD is loaded into WG-COUNT after one crystal oscillator cycle. If EC=1 in WG-CON, it starts to count down by 1 to 0001H, waits for one clock cycle and then counts up by 1 until the value in WG-COUNT equals the value of the count comparison register, at which time one carrier cycle is completed, as shown in t1~t2 in Figure 1. The content of WG-RELOAD is loaded into WG-COUNT and the count comparison register; the content of WG-COMPx is loaded into the phase comparison register; the content of the output buffer register is loaded into WG-OUT; the WG interrupt in the PI-PEND register is set to 1.

μs), WG-RELOAD-16-bit binary number; Fxtal-the crystal frequency on the Xtal pin, ignoring the effective pulse width of the dead time; tp=WG-COMP/Fxtal ( μs ).

2 Software Design

The WFG of 80C196MC generates 6-way SPWM signals to control the on and off of 6 power switch devices in the three-phase bridge of the main circuit. Therefore, it is necessary to first establish a three-phase sinusoidal pulse width data table, which is calculated by the microcontroller when it is initialized, and stored in RAM in a certain format (i.e. considering the phase sequence and the pulse width sequence in the same phase, etc.), and establish a data pointer so that it can be queried in a certain addressing mode.

Δu(k)=u(k)-u(k-1)=kp[e(k)-e(k-1)]+k1e(k)+kD[e(k)-2e(k-1) +e(k-2)]

Δu(k)=q0e(k)+q1e(k-1)+q2e(k-2)

q0=kp(1+T/T1+TD/T) kp=1/δ Proportional coefficient

3 Overall composition of variable frequency power supply

4 Test results

μs. (WG-CON) = 418H, (WG-RELOAD) = 12FH, (WG-OUT) = 7FFFH. The output of the SPWM waveform generates an interrupt when WG-RELOAD is reduced to 1. In the interrupt service subroutine, the content in WG-COMPx is refreshed by the calculation result (that is, the next pulse width is set), and the cycle continues. Figure 6 (a) is the SPWM waveform output by 80C196MC, and Figure 6 (b) is the waveform of one phase of the power supply output. The relevant technical indicators are as follows:

The 16-bit single-chip microcomputer 80C196MC minimum system is used to greatly simplify the entire control circuit and realize full digitalization. The number of components is reduced, the structure is compact, and the cost performance is high. The test shows that the system has good dynamic characteristics and high reliability.

Keywords：80C196MC Reference address：The principle of waveform generator based on 80C196MC and its application in inverter power supply

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