PV inverter from Prius inverter

[NiHaoMike]

I'm still working on getting the PLC transmitter to work as I want it to. The CD4046 did not really perform that much better than the 74LV4046A since it was getting pushed close to its operating frequency limit, what performed the best was the 74LV4046A with a very carefully tuned VCO circuit. Next comes the compander circuit, which I'm going to base around photoresistors illuminated by LEDs as the basis for a variable gain cell. I'll have to tune the gain control rates to get the best overall signal. (This is very much getting up to the Jim Williams level of analog circuit design!)

To help with testing, I have built a current signal simulator by connecting a coil of wire to an audio amplifier that I can play signals through with a PC. With 100 turns, the amplifier will only have to source 2A to emulate a 200A current.

I also got a 90A contactor that will be used to connect the grid, running the coil from 240V AC as intended, it uses 12W just to stay on and buzzes pretty loudly. But if I use a 170V DC pulse to turn it on and then supply 12V DC to hold it on, it's silent after switching on and uses just 0.8W! (I selected the voltage based on the current that was drawn when powered from AC. I have found that even in its worst case orientation, it will stay on with a mere 4V applied to the coil.)

[randen]

NiHaoMike

Just curious if there is any update on the progress of your inverter??? Our late winter early spring was quite disappointing for any serious product , alas we had to buy electricity

Randen

[NiHaoMike]

I got a lot more parts for the inverter (the inverter module itself, capacitor bank, inductor cores, various control circuit parts) and I'm working on it. It will be a long project for sure, one with a lot of learning opportunities.

[randen]

NiHaoMike

Just wondered if you were able to get any electrons to flow yet. Here days are the longest and of recent quite warm. Our biggest consumers of current such as the Geo-heatpump and car charging are using most of the days production. Today being the longest is quite cloudy with thundershowers.. Oh well.

One of our fellow members is quite eager to follow in our footsteps with a single phase inverter. At this point of time I'm extremely busy with another huge project and can't possibly take on another.

Thought I would check in

Randen

[NiHaoMike]

Working on the wireless sensor - managed to get it outputting a nice, low jitter signal. For a test, I had it transmitting music over the power line and the quality is surprisingly good - not HD but about as good as expected for FM. Next up will be implementing the subcarriers for the phase current imbalance and digital data transmission. I now understand why no commercial zero export inverter uses PLC for the sensors - it's hard to get right.

I also started planning out the FPGA design. The FPGA I chose is a Spartan 6 LX100-3, because it's relatively cheap (about $10 for the board!) and quite large with 180 DSP cores and just over 100k general purpose logic cells. It's not as energy efficient as the (much more expensive) Artix 7 I have, but it doesn't use enough power (just a few watts at most) to significantly impact the efficiency of the whole system and is unlikely to be pushed near the limits of what it can do, unlike the Artix 7 that was stuffed full of BLAKE256 instances and run at basically the maximum clock speed it's capable of when it was helping Naomi Wu.

[NiHaoMike]

Pretty big Pi Day update. I connected a pair of AK5558 ADCs to the FPGA and managed to program the FPGA to work with them. I then used a Raspberry Pi to send the data stream over Ethernet to my PC so I can use baudline to analyze it.

There was a lot of work leading up to it. The AK5558 ADCs are very high performance ADCs, able to digitize 8 channels at 768kHz and 32 bit. As such, there's very high requirements on the analog design to allow the ADCs to meet their specifications. Two things that took a lot of research were a low noise power supply and a very low jitter crystal oscillator.

768kHz is not fast enough to directly digitize the PLC signal which is on the order of 1.2MHz. For that, I would use a Quadrature Sampling (Tayloe) mixer to downconvert the signal. There will be two of those implemented in order to allow implementation of coherent diversity MIMO, the PLC version of wireless beamforming. Basically, there are two analog front ends picking the signals from the two hot lines. Noise tends to affect each line differently, so with some DSP trickery, the noise can be largely nulled out making the system more robust. The high dynamic range of the ADCs and mixer also greatly improves robustness against impulse noise.

The FPGA programming turned out to be the most difficult part by far. I started with implementing an internal data bus to allow the Pi to change and read back registers implemented in the FPGA. The Pi side of the interface is clocked by the Pi while the internal side of the interface is on its own clock domain that's tied to the ADC clock. I got to deal with the issues of clock domain crossing right at the start since it would be a lot easier to solve it in one place rather than have to deal with it throughout my design. The MASIE (Mixed Architecture System Integration Extended) bus specifies that the CPU (Pi in this case) acts as the master for the I2C, SPI, JTAG, and eUSB/HSIC interfaces, but the PCM interface can be clocked by whichever side that makes more sense for the design. Thus, the PCM interface in my design is tied to the ADC clock so no clock domain crossing needed in this case. (Which is good because retiming PCM data is really complex...)

While doing all that, I now understand just how smart my friend Tiffany Yep really is. I knew that she was smart but only now do I truly understand how complex the stuff she does is. So far, I'm only aware of one other model - Xyla Foxlin - to have participated in a beauty pageant and have such advanced technical skills. (I know quite a few other models who are engineers, but it's one thing to look good enough for stuff like appearing on TV or at live events, quite another to compete with other models.)

And for the Pi Day bit, I used a 3.14kHz sine wave test signal, one phase shifted so that it's about 90 degrees out of phase with the first. (A sine wave is in fact a 2D projection of Euler's Formula.) The sample rate reported by the Pi is not correct due to a quirk of how it handles the MASIE PCM data.

[NiHaoMike]

Mostly completed the wireless sensor, what's left is to validate that all of the features work properly and then conformal coat for installing into an outdoor breaker box.