Pure Sine Wave Inverter Simulation in Proteus

Hello friends! Today we will study a pure sine wave inverter simulation in Proteus, following the signal path from a DC source through the controller, bridge, filter and transformer. The original project uses a PIC16F877A and illustrates a nominal 12 V DC to 220 V AC conversion. We will keep its diagrams while explaining the assumptions needed to interpret them correctly.

The first point to understand is that waveform quality and efficiency are different properties. A smooth sinusoidal output does not imply zero losses, and a highly efficient converter does not automatically have low distortion. We need separate measurements for output voltage, frequency, harmonic content and power conversion efficiency.

This tutorial explains the historical simulation and how to evaluate such a model. The screenshots alone do not establish a hardware-ready power converter or a measured 220 V rating. Begin with our pure sine wave inverter design introduction if you want background on the overall architecture before examining the blocks below.

What Does a Sine Wave Inverter Do?

An inverter converts DC electrical power into an alternating output. A bridge changes the polarity applied to a load or transformer. With suitable pulse-width modulation and filtering, the low-frequency component can approximate a sine wave. The switching waveform at the bridge is not itself a smooth sine.

For a sinusoidal voltage, v(t) = Vpk sin(2πft), where Vpk is the peak voltage and f is the frequency. Its RMS value is Vpk / √2. Therefore a 220 V RMS sine has a peak of approximately 311 V, while a 12 V RMS sine has a peak of approximately 17.0 V.

That distinction matters immediately: an ideal full bridge supplied by 12 V cannot produce a 17 V peak sinusoidal fundamental directly under ordinary linear sinusoidal modulation. A statement such as “the bridge produces 12 V AC” must specify whether it means switching amplitude, RMS of a square waveform or RMS of the sinusoidal fundamental.

Efficiency Is a Power Ratio

Efficiency = average real output power / average input power × 100%.

If a converter supplies a 100 W load and operates at 85% efficiency, its DC input power is approximately 117.6 W. At a steady 12 V input, that corresponds to about 9.8 A before considering additional battery voltage variation. The remaining 17.6 W becomes losses in switching devices, magnetics, conductors, control circuits and other components.

This example is a calculation, not a measured efficiency for the illustrated project. A waveform screenshot cannot supply either of the required power measurements. For a reactive load, multiplying RMS voltage by RMS current gives apparent power, not necessarily real power.

Follow the Functional Blocks

The conceptual diagram is a useful map, but the detailed schematic determines actual component placement. In the retained power-stage image, the inductors and two shunt capacitors appear on the transformer primary side, while another capacitor is across the secondary. It should not be described as only a small LC filter placed after the transformer.

Filtering mainly addresses switching-frequency content and other unwanted spectral components. It is misleading to say that the transformer is normally the source of all noise. Switching edges, parasitic capacitance, leakage inductance and control behavior all influence the observed waveform.

The 5 V Controller Supply

The historical circuit uses a 7805 regulator to derive a controller supply from the nominal 12 V source. This is a linear regulator, so the voltage difference is largely dissipated as heat. At a 50 mA load, the approximate regulator dissipation is (12 − 5) × 0.05 = 0.35 W, plus its own operating losses.

A simulation using an idealized regulator may not reveal the resulting junction temperature. Check the actual regulator package, thermal conditions, input range and required bypass capacitors before translating the supply into hardware. Place local decoupling near the PIC's power pins rather than relying only on a distant capacitor.

The controller should also have a defined reset condition and a deliberate output state during startup. If bridge commands are undefined while the supply rises, a correct steady-state PWM routine may still be insufficient. Power-stage enable logic should remain inactive until the controller and driver supplies are valid.

PIC16F877A PWM and Switching Logic

The PIC16F877A contains two CCP modules, not a universal single CCP pin shared by all microcontrollers. The illustrated design uses a PWM-related signal together with logic gates to route pulses according to the intended half-cycle. An AND gate selects a logical condition; it does not generate a negative power voltage or provide a high-current MOSFET gate driver.

The schematic also includes an inverter gate. Its logical complement is useful for constructing control signals, but logical inversion alone does not guarantee safe non-overlapping transistor conduction. Propagation delay and the actual gate-charge dynamics must be considered in the complete driver arrangement.

The PIC16F87XA datasheet describes Timer2-based PWM. For the standard CCP PWM arrangement:

fPWM = fOSC / [4 × (PR2 + 1) × Timer2 prescaler].

As a worked configuration example, choose a 20 MHz oscillator, a prescaler of one and PR2 = 249. The resulting carrier is 20,000,000 / (4 × 250) = 20,000 Hz. This is an example calculation, not confirmation of the oscillator or register values inside the historical compiled file.

The effective duty setting also depends on the timer period. With PR2 = 249, the period contains 4 × 250 = 1000 duty increments in the standard PWM expression. A nominal ten-bit duty register does not mean that every carrier setting provides 1024 distinct useful pulse widths.

Carrier Frequency Is Not Output Frequency

The original description identifies a 20 kHz carrier. A 50 Hz output has a 20 ms period, so 20,000 / 50 = 400 carrier periods fit in one output cycle. The duty pattern must evolve through that cycle in a way that produces the intended fundamental component.

If the firmware updates one lookup-table entry per carrier period, table length and update rate determine the synthesized frequency. A 400-entry full-cycle table updated at 20 kHz produces 50 Hz. A different table arrangement, such as a quarter-wave table with symmetry handling, requires corresponding indexing logic rather than simply assuming the same count.

Inspect the pulse widths over both a carrier-scale time window and a complete output cycle. A scope display that is too compressed may show a convincing envelope while hiding missing pulses, excessive minimum widths or an incorrect polarity transition.

Read the Bridge Schematic Carefully

The power-stage image labels the upper devices IRF5210 and the lower devices IRF3205. These are different device types: IRF5210 is a P-channel MOSFET, while IRF3205 is an N-channel MOSFET. The gate-drive polarity and source reference must match each device.

For a high-side P-channel transistor with its source near 12 V, bringing its gate close to 12 V turns it off. Pulling the gate sufficiently below its source turns it on. A direct 5 V logic HIGH would leave approximately −7 V between gate and source in that simplified situation, so it cannot be assumed to provide the required off state.

Likewise, a lower N-channel device needs adequate positive gate-to-source voltage for its specified on-resistance. Its threshold voltage merely describes the onset of conduction under a small test current; it is not a guarantee of low resistance at a useful load current. Consult the exact device data rather than choosing drive voltage from the threshold number.

The historic image shows logic-level connections but does not establish a complete practical gate-drive design. A working implementation needs correctly referenced drivers, gate resistors, defined off-state biasing and suitable protection. These requirements should be represented in a more detailed simulation before the circuit is considered for hardware.

Prevent Shoot-Through and Flux Imbalance

Infineon's IRF5210 information identifies the upper device as P-channel, and its IRF3205 information identifies the lower device's specified operating characteristics. Use the corresponding datasheets to check on-resistance at the intended gate voltage, maximum gate stress and switching charge. Selecting a device only by its large headline current rating leaves the driver and thermal design unresolved.

If the upper and lower devices in the same leg conduct together, they create a low-impedance path across the DC source. This is shoot-through. Insert appropriate dead time between their switching commands and account for turn-off delay and driver behavior. Choose that timing from device and driver characteristics rather than copying an arbitrary value.

Dead time also changes the waveform, particularly around current reversals, so increasing it indefinitely is not a free solution. Observe bridge current and output distortion as well as the digital gate commands. A logic waveform can look non-overlapping while a transistor is still conducting because of stored gate charge.

The transformer also requires balanced volt-seconds. A sustained DC component or unequal positive and negative excitation can drive its core toward saturation. An ideal transformer model may conceal this failure because it does not necessarily include realistic magnetizing behavior and core limits.

Transformer Ratio and Output Voltage

For an ideal full bridge using ordinary linear sinusoidal PWM, the fundamental peak can be expressed approximately as ma × VDC, where ma is the modulation index under that definition. Its fundamental RMS value is ma × VDC / √2. At VDC = 12 V and ma = 0.9, this is approximately 7.64 V RMS.

An ideal transformer would then require a secondary-to-primary ratio of roughly 220 / 7.64 = 28.8 to obtain a 220 V RMS fundamental, ignoring filter response and losses. This differs from simply dividing 220 by 12. The calculation must begin with the actual fundamental applied to the transformer.

These relationships depend on topology and modulation. A transformer nameplate voltage is specified under particular frequency and loading conditions, not as an unconditional multiplication factor for every pulse waveform. Include winding resistance, leakage and magnetizing effects when evaluating regulation and current.

Do not treat this numerical example as a transformer construction specification. It explains why the DC-source label alone is insufficient to establish the output rating. The retained simulation screenshots do not provide the complete transformer design data.

Filter Design and Resonance

A simple ideal LC pair has a natural frequency f0 = 1 / (2π√LC). For illustration, L = 10 mH and C = 1 µF give approximately 1592 Hz. That lies above a 50 Hz fundamental and below a 20 kHz carrier, but this fact alone does not make it a finished inverter filter.

The complete response depends on the connection, load impedance, component losses and any transformer between the filter and load. A lightly damped filter can ring or magnify voltage near resonance. A capacitor also draws reactive current at the fundamental, so its value affects more than switching ripple.

In the historical diagram, the two primary-side branches and the secondary capacitor form a more complicated network than a single isolated LC pair. Analyze that actual network, including the transformer model and load, rather than substituting the simple formula for a full transfer-function or transient study.

TI's voltage-source inverter reference design demonstrates an engineering workflow that includes an LC filter, control and measured performance. Its component values and control software belong to its own hardware and should not be transplanted into this PIC project without a new design calculation.

Measure the Simulation Correctly

Measure the voltage across the load, not merely each output terminal relative to a convenient ground. If two terminals move in opposite directions, the useful differential voltage is their difference. Comparing the amplitude of one trace with a differential output specification can produce a factor-of-two misunderstanding.

Allow startup to settle, then select a measurement window containing an integer number of fundamental cycles. Record RMS voltage, fundamental frequency, DC offset and load current. Use a sufficiently fine simulation time step to resolve switching events, then reduce it and check whether the calculated results materially change.

Harmonic distortion requires spectral information. For harmonic RMS voltages V2, V3 and so on, THD = √(V2² + V3² + …) / V1, where V1 is the fundamental RMS voltage. Specify the included harmonic range and measurement bandwidth. A smooth-looking trace at one screen scale does not establish a particular THD.

A Useful Validation Sequence

1. Check the controller supply and reset behavior before enabling the bridge.
2. Inspect PWM frequency and duty evolution with the power stage disabled.
3. Check gate-to-source voltages and overlap at each switch.
4. Begin the power-stage model with a reduced DC voltage and a defined resistive load.
5. Measure differential bridge and load voltages separately.
6. Observe transformer magnetizing current and average primary voltage.
7. Change load and input voltage while checking regulation, current and device stress.
8. Refine time step and measurement windows before reporting numerical performance.

A resistive test load makes the first power calculation straightforward: P = Vrms² / R. For example, 220 V RMS across 484 ohms represents 100 W. In a real circuit that load needs a suitable power rating and voltage rating; a schematic resistor symbol does not establish either.

Project Files and Scope of This Tutorial

The original project directs readers to the Proteus inverter project listing for its simulation and PIC firmware package. Refer to that listing for current availability and contents. The historical price is not repeated here because it should not be treated as a verified current offer.

This article does not include a replacement firmware download or claim that the commercial archive has been rebuilt and tested during the revision. Before using any supplied HEX file, match its processor, oscillator assumptions and project configuration. A file that loads into a simulated PIC can still produce the wrong timing if the clock configuration differs.

A mains-voltage inverter also requires insulation, protection and construction measures that are not established by these screenshots. Treat the model as an educational starting point. Keep initial investigations at reduced voltage and use equipment and procedures appropriate to any later power-stage work.

Frequently Asked Questions

Does pure sine wave mean 100 percent efficiency?

No. Distortion describes waveform shape, while efficiency compares average real output and input power. Real switching devices, conductors and magnetics dissipate energy even when the output waveform is good.

Does the PIC produce a 220 V sine wave?

No. It produces control signals. The driver, bridge, transformer and filter handle the power conversion and determine the available output under load.

Can AND gates directly drive the illustrated bridge?

The logic functions do not establish adequate gate voltage, current or source referencing. The P-channel and N-channel devices require an appropriate drive circuit and defined switching interlocks.

Why does the output change when I attach a load?

Source impedance, semiconductor drops, transformer impedance and filter response affect regulation. An open-loop modulation pattern does not automatically compensate for those changes.

Is a sine-shaped scope trace enough to verify the design?

No. Check RMS amplitude, frequency, distortion, current, losses, switching stress and startup behavior under stated conditions. Each measurement answers a different engineering question.