Everyone come and join me, I made a photovoltaic inverter control (MPPT) all-in-one machine[Copy link]
This project is a device that integrates off-grid inverter, MPPT battery charging, and grid energy interaction. It is a machine that completes all application scenarios in off-grid solar power generation; Due to the large number of integrated functions, it may need to be upgraded before it is finally perfected! The technical information will be updated step by step after the hardware is perfected, and shared with everyone! This is good news for those who want to make their own MPPT or high-performance inverter switcher, because the second version will have a separate control board, which can be provided for everyone to make. The dream of DIY is to use the simplest and least things to make the perfect thing that meets your imagination. Imagine if you have a photovoltaic integrated machine that you built yourself, with MPPT, inverter with AC power, inverter priority switching, and automatic charging management, what a pleasant thing it would be. However, there are too few such machines that can accomplish this at present. There needs to be a solution and a platform to start with. At present, we have come up with the simplest thing that completes the above functions and meets the various requirements of photovoltaic power generators. At present, many inverters do not have MPPT, and the inverters are not mature enough to switch between mains priority and inverter priority. This is because there is no mature solution in terms of core control, which requires multiple chips to work together. Therefore, in order to simplify the circuit, we must start from the core control chip and redesign a single-chip solution that can include the following functions: 1. Integrated MPPT charging. In order to improve the efficiency, it is designed as a single-phase BUCK DC-DC method, combined with the previous mature experience of MPPT, and specially matched with the inverter. 2. Integrated photovoltaic charging current detection. Through an external op amp, the photovoltaic current is given to the CPU for MPPT calculation, eliminating too many cumbersome processes. 3. 4-way PWM of integrated inverter H-bridge, PWM adopts the most efficient and stable bilateral modulation SPWM output, 4-way SPWM directly output from the chip, further simplifying the periphery, 4. Integrated AC phase lock, using a unique hardware phase lock method, processing a series of interferences such as interference clutter and wave loss on the AC power in the chip, making the AC voltage output by the inverter and the AC signal of the AC power strictly symmetrical. When the AC power is available, the inverter voltage follows the frequency and phase of the AC power, and even when switching, it tracks the current voltage of the AC power to complete the inverter and the AC power voltage. After switching, the voltage returns to the default value again. The purpose of this is to maximize the guarantee of perfect switching, smooth transition of switching, and switching without voltage difference. 5. Integrated communication control function allows users to set inverter priority or mains priority, and can output MPPT data, inverter data, and mains data to the outside world in real time. For example, some lithium battery systems need such data for further control, which is very useful. With these, there is a basis for remote control and monitoring. Some brothers have started to make upper computer software. When they have this, they can provide monitoring. 6. With the specially developed current sensing element, the short-circuit protection circuit is simplified, and the unique chip internal short-circuit protection action circuit, when a short circuit occurs externally, the inverter executes the constant current + current inner loop mode to avoid burning IGBT and drive. In addition, this mode will optimize the load function. 3KW high-frequency machine, directly starting the 2P air conditioner will not have any problems. The inverter basically feels no pressure and can start smoothly. 7. It integrates 5 major protection functions: overvoltage, undervoltage, overtemperature, short circuit and overload. 8. This time, the STM32 chip is used to realize the above functions. The current preliminary model is: STM32F103RET6. For the hardware platform, I use the control board + power motherboard separate mode, and use the pin plug structure for easy debugging. This project is currently open in the QQ group. Since the forum is inconvenient, you can contact me privately and provide it to everyone. The basic parameters of this time are as follows: The rated input voltage of the inverter is 24V, and the voltage range is DC21-DC30V Output voltage: AC220V, pure sine wave Output frequency: 50hz, 60hz (automatically follows the mains frequency and memorizes it) Output rated power: 2000W MPPT input voltage range: PV/30V-180VDC MPPT charging current: 30A Mains and inverter switching time <10ms Below is the circuit analysis step by step. Starting from the motherboard... The actual photo of the control panel is as follows: Control board, small signal circuit part analysis: 1: Auxiliary power supply control part: Since the design is for DC24V battery input, the CPU and other chips are powered by low voltage, so an auxiliary power supply is needed to reduce the input DC24V to several suitable voltages to provide power to the chip and drive circuit. Here, the classic UC3845 chip is used to make a flyback power supply, as shown in the figure below. The transformer is not drawn because it is on the motherboard. When the motherboard circuit diagram is updated later, the connection of the auxiliary transformer can be seen. Only the small signal control part is analyzed here. The auxiliary power supply generates 12V, 5V and 3.3V voltages. There is also a set of isolation for the 12V voltage. The isolation will be provided to the inverter IGBT drive, 5V to the op amp, and 3.3V to the CPU. These are the auxiliary power supply parts. 1: Inverter boost DC-DC part: In order to simplify the boost part, I still use the classic SG3525 chip to implement push-pull boost. At present, push-pull should be the most suitable circuit for boosting DC24V to DC400V, and the drive is relatively simple. The optocoupler at the bottom of this circuit is used to isolate feedback and directly control the SD pin of SG3525. As long as the boost voltage exceeds DC400V, the optocoupler will be turned on, the SD pin voltage will increase, and the PWM duty cycle will automatically decrease. A similar voltage regulation is achieved. Since the voltage regulation does not need to be precise here, the simpler the circuit, the better! 3:CPU part: This time STM32F103RET6 is used as the main control part. It is a 64pin chip. The resources and IO are enough to realize the functions of this board. Since this chip is quite fast, you can search Baidu for its specific performance. I won't type it again here. This simplifies many things, especially the hardware, as follows: Let's look at the definition of the signal step by step. The following 4 PWM channels correspond to the inverter H-bridge, which drive the upper and lower tubes of the left and right bridge arms respectively to generate SPWM and achieve sine wave output. The following two groups of PWM are used to generate a phase staggered 180-degree duty cycle, which is used for MPPT charging in BUCK mode, and the duty cycle is set to 0-96%. The one below is used as the fault detection pin for the wave-by-wave current limiting of the inverter SPWM, which realizes the short-circuit protection of the inverter part and takes into account the load capacity and does not explode the tube. It depends on it. 4WM output level conversion part: In order to isolate the PWM signal from the CPU and prevent the CPU from being disturbed by the noise of the external driver, the PWM signal is isolated with a level buffer chip: In this way, the 3.3V PWM can be buffered by this chip to further improve the noise resistance, which is beneficial for the subsequent input to the driver. 5: Optocoupler drive part: The design is for the TLP250 optocoupler drive, and the secondary power supply adopts the bootstrap method. Simplify the circuit on the power supply side. 6: Solar panel current detection required for MPPT. Use an op amp to amplify the voltage on the sampling resistor, with an amplification factor of 51 times. 7: Mains phase lock, synchronization, VRMS detection First, use the differential to reduce the mains voltage to 0-3.3V, the range that the CPU ADC can detect. In addition, use a comparator to generate a mains frequency synchronized square wave, which enters the DSP to calculate the zero point and the mains cycle. The program needs these parameters for phase lock and synchronization. 8: Inverter AC220V voltage detection uses differential to attenuate the invertered 220V voltage to a signal corresponding to 0-3.3V, and inputs it to the ADC port of the CPU. The program uses this parameter to implement the AC220V voltage closed loop and instantaneous value feedback. 9: Inverter load current detection The output signal of the transformer on the mainboard is used to obtain a sine wave voltage on the sampling resistor. After being conditioned by the op amp, it is sent to the CPU's ADC for IRMS detection. Overload protection and power and current display are realized according to the parameters. 10: 1.65V reference bias voltage generation The 3.3V voltage is divided by two resistors of the same size, and the op amp follows it, and then a 1.65V stable bias is used. Due to the AC parameters, this 1.65 is used as an adder for each AC signal.
The above has updated the motherboard circuit diagram.Let's take a look at the parts on the motherboard step by step. The mainboard has a first-level DCDC push-pull boost, plus an inverter part and an MPPT charging part. First, let's take a look at the DCDC push-pull part, as follows: It's a very classic push-pull. Since the input of this circuit is 24V, the push-pull switch tube is actually enough with a voltage resistance of 80-100V. The parameters in the figure are IXTQ96N20, which can be used for DC48V. In fact, you can directly use the 100V tube of IRFB4310. D5-D6 in the figure is used to absorb the push-pull switch tube spikes and increase the safety of the tube. Fan power supply part: a secondary winding of the transformer is used for rectification output to provide power for fan control. sans-serif]
Hello, I would like to seek technical cooperation and help. We make solar controllers and want to develop all-in-one machines. If you receive a message, please contact me by phone or WeChat, QQ664303381. Looking forward to your reply.
Posted by Mufan001 on 2018-6-26 14:40 The above is an updated mainboard circuit diagram. Let's look at the mainboard part step by step. The mainboard has a first-level DCDC push-pull boost, plus an inverter part and MPPT...
I am very interested and hope to pay for cooperation. My WeChat is 15275410718