RU198525U1 - ENERGY CONVERSION DEVICE - Google Patents

Abstract

The utility model relates to solar energy, namely to power electronics devices for energy conversion. The energy conversion device contains solar panels connected in series in strings, the strings are connected in parallel using bypass diodes, the sub-panel DPP converter is installed inside the panel on the board, the inverter is connected to solar panels, divided into two independent strings with a maximum voltage of 400 V flexible parallel-series configuration, the inverter consists of two devices made in one case: an inverter, which is a DC-AC converter on gallium nitride transistors operating at a frequency of 120 kHz and forming a pure sine at the output from 380 V DC at the input, and MPP tracker, which is a DC-DC converter that monitors the point of maximum efficiency of the string and converts the constant current of the string to obtain a fixed voltage of 380 V at the output to power the inverter module, the inverter has a bridge voltage inverter circuit using a gallium nitride transistor, and also relay d For switching between the home power supply and the inverter circuit line, feedback for measuring the current in the circuit, feedback for measuring input and output voltages and a microcontroller with an integrated mathematical processor, a half-bridge evaluation board was used as an MPPT power converter, which contains elements of a simple converter and two field-effect gallium nitride transistors, united by a simple half-bridge with two field-effect transistors, there are two high-voltage ports, which can serve as input and output, which can be used to connect a storage battery. 4 ill.

Description

The utility model relates to solar energy, namely to power electronics devices for energy conversion.

The prior art knows the design of a single-phase, non-insulated, miniature power inverter for converting direct current into alternating current and designed to create a power inverter with an output specific power of more than 3000 W / dm (see RU 2702103 C2, publ. 04.10.2019) (1). The power inverter is housed in a housing made in the form of an outer electrically conductive shell containing a fan configured to pump air axially to the side surface of the housing, and a multi-level vertical structure, sequentially from the bottom side to the top side, containing: a layer of active filtering capacitors, heatsink, a layer of wide-gap semiconductor switches connected to the printed circuit board with thermal through jumpers, and a layer of active filtering inductors, and the fan and the multilevel structure of the components are made so that during operation the outside temperature of the case does not exceed 60 ° C at any point at the maximum ambient temperature environment 30 ° C and a maximum load of 2 kVA.

The disadvantage of this device (1) is the large losses during conversion of direct current.

It is also known from the prior art, selected as the closest analogue, an inverter (see CN 105978476 A, publ. 09/28/2016) containing an energy storage capacitor and a first circuit breaking module and a second circuit breaking module; the first circuit breaker module is connected between the first input node of the inverter and the first end of the storage capacitor; the second circuit breaker module is connected between the second input node of the inverter and the second end of the capacitor; and turning on and off the first circuit opening unit and the second circuit breaking unit are controlled by the second inverter controller; the inverter also includes a command block used to transmit carrier waves through a transmission line connected to the first input node of the inverter and / or through a transmission line connected to a second input node of the inverter to understand that the inverter is transmitting command information to the street.

The disadvantage of the closest analogue (2) is the low efficiency and controllability of the device.

The technical result of the claimed utility model is to increase the service life and reliability of power converters, increase the conversion efficiency, reduce the number of components and the weight and size characteristics of the inverters.

The technical result is achieved by creating an energy conversion device containing solar panels connected in series into strings, the strings are connected in parallel using bypass diodes, a sub-panel DPP converter is installed inside the panel on a board, the inverter is connected to solar panels, divided into two independent strings with a maximum voltage of up to 400 V in a flexible parallel-series configuration, the inverter consists of two devices made in one housing: an inverter, which is a DC-AC converter on gallium nitride transistors operating at a frequency of 120 kHz and forming a pure sine at the output from 380 VDC at the input, and MPP tracker, which is a DC-DC converter that monitors the point of maximum efficiency of the string and converts the constant current of the string to obtain a fixed voltage of 380 V at the output to power the inverter module, the inverter has a bridge circuit of the voltage inverter with use the use of gallium nitride transistors, as well as a relay for switching between the home power network and the inverter circuit line, feedback for measuring the current in the circuit, feedback for measuring input and output voltages and a microcontroller with a built-in mathematical processor, a half-bridge is used as an MPRT energy converter Evaluation board, which contains elements of a simple converter and two field-effect gallium nitride transistors, combined by a simple half-bridge with two field effect transistors, there are two high-voltage ports that can serve as both input and output.

The claimed utility model is illustrated with the following images:

FIG. 1 is a block diagram of a device with arrays of solar panels with built-in submodules DPP-converters and an inverter;

FIG. 2 - block diagrams of a solar panel with DPP-converters and a functional diagram of the operation of DPP-converters;

FIG. 3 is a block diagram of a gallium-nickel transistor connection;

FIG. 4 is a block diagram of an MPPT converter.

The positions in FIG. 1-4 indicate the following:

1 - solar panel;

2 - DPP converters;

3 - AC / DC converter;

4 - MRPT converter;

5 - DC / DC converter;

6 - battery.

The claimed utility model works as follows.

A traditional solar panel consists of 60-72 cells, each of which can supply 0.5V and 5A direct current. These panels (36V, 5A) are connected in series in strings (strings) to achieve high voltage values, which reduces losses in the connecting wires. The strings are connected in parallel to obtain the desired level of total power / current, thus forming a "solar array."

The power generation of an array of solar panels depends on the characteristics of the panels themselves, the level of illumination and temperature, and the type of load connected. Moreover, it is the level of illumination that can change most rapidly.

Shading can be divided into two types: soft - a slight decrease in illumination caused by a distant object (cloud or tree) and hard - complete blocking of sunlight due to a close obstacle. With soft shading, the voltage changes weakly while maintaining the irradiation level of more than 50 W / m ² , and the current greatly decreases. The voltage depends more on the temperature and the band gap of the semiconducting cell material. When the cells are connected in series, the total amperage is limited by the current produced by the shaded cell itself, since it is the smallest. Moreover, the current generated by the unshaded cells will cause it to pass through the shaded one, heating it up and causing a risk of failure. Therefore, bypass diodes are used, connecting in parallel chains of 24 series cells. These 24 cells form a sub-string of cells.

This panel design makes it possible to form an array by tracking the maximum power point in several places: in the center of the array, in each serial string, on each panel or inside it, replacing the bypass diodes with separate DPP converters.

The inverter allows you to connect up to 6 kW of solar panels, divided into two independent strings with a maximum voltage of up to 400 V in a flexible parallel-serial configuration, which maximizes the use of space for placing panels, and has functions: synchronization with the network, shutdown of panels in case of failure, integration with BMS lithium-ion battery, easy installation and connection with standard wires and connectors, remote monitoring via cloud server and mobile app.

The inverter consists of two devices in one housing:

1. Directly inverter, which is a DC-AC converter on gallium nitride transistors operating at a frequency of 120 kHz and forming a pure sine at the output from 380 V DC at the input.

2. MPP tracker, which is a DC-DC converter that monitors the point of maximum "efficiency of the string and converts" direct current of the string to obtain a fixed voltage of 380 V at the output to power the inverter module.

The inverter can be additionally equipped with built-in DPP (Differential Power Processing) sub-panel converters, designed to redistribute the power difference between two adjacent panel sub-strips.

The DPP converter starts working only when there is a difference in the power of the sub-strings and does not work with the full power of the sub-string, but with the magnitude of the difference in power "of two adjacent sub-strings, redistributing part of the current in such a way that it becomes possible to find the maximum power for both sub-strings. For arrays without rigid "For the shadow, it is enough to use the string MPP tracker built into the inverter with a string power of up to 3 kW. In cases where the installation involves periods of the day when the nearest obstacles (neighboring buildings, trees, etc.) block direct sunlight, a distributed system with sub-panel (for mono- or polysilicon panels) or panel (for thin panels) is more relevant. ) DPP converters. In this configuration, the panels are connected in strings, and the strings can be connected in parallel to achieve the desired current / power.

String DC-DC converter with MPP tracker is a transformerless step-up half-bridge. The choice of the non-isolated half-bridge topology is due to the fact that over a wide power range, the efficiency exceeds 98.5% for full power, a small number of components and compact dimensions.

Each of the two MPP trackers of the DC-DC converter is equipped with standard MC4 connectors for connection. Peak power - 3 kW, input voltage - from 120 to 400 VDC, maximum input current - 8 A, output voltage - 380 VDC, efficiency up to 99.3%

We consider in more detail the overall system architecture as a whole (. Figure 1) and then individually all its elements: panel with sub-panel DPP converters, stringovyi ^- MPPT converter - with integrated tracking algorithm, inverter - generator AC voltage of 220 V, and the module lithium-ion battery pairing.

The task of reducing losses in the process of delivering electricity from an array of solar panels is a priority when choosing a system architecture.

After careful analysis, experimentation and simulation, the choice was made in favor of the following system architecture. The 380V high-voltage DC bus is formed by a DC-DC string boost converter. Moreover, the tracking of the maximum power point occurs in two stages - in the string converter, the global maximum of the string is tracked, and in the sub-panel DPP converter, the problems of maximizing the current strength are solved, which decreases in the case of severe shading, pollution (including snow or foliage), aging and manufacturing defects solar panel. Conversion to 220 VAC takes place in a single phase central inverter. Optionally, a high-voltage battery can be connected to the 380 V bus (or with a DC-DC converter for battery voltage). It is connected to the 220 V network through an inverter.

This architecture gives solar array designers a greater degree of flexibility in string lengths, different panel orientations, and allows panels to be installed in areas of hard shading and different orientations.

Sub-panel DPP (Differential Power Processing) converter is designed to redistribute the power difference between two adjacent sub-strips. The converter is switched on only when a difference in the power of the sub-strings appears and does not work with the full power of the sub-string, but with the magnitude of the difference in the power of two adjacent sub-strings, redistributing part of the current in such a way that it becomes possible to find the maximum power for both sub-strings, increasing the current strength (decreasing " voltage) of each sub-string.

In the event that the current of a sub-string drops due to shading or pollution, in a traditional panel, an anti-parallel bypass diode blocks this sub-string, preventing current backflow, heating and damage to the cells, or reduces the panel output to the current of the weakest cell. ...

The DPP converter equalizes the current of the sagging sub-string to the maximum value of the adjacent sub-strings.

Even taking into account the solution to the problem of optimizing the generation within each panel, the problem of finding the global maximum power of the string needs to be solved.

According to the MPPT (maximum power transfer theorem), the power in the circuit is maximum if and only if the source impedance coincides with the load impedance. Thus, the problem of finding the maximum power is reduced to the problem of matching impedance.

Due to the fact that when the illumination of the panel is above 50 W / m2, mainly the current strength changes, and the voltage remains practically the same, high conversion efficiency is achieved due to a low conversion ratio, not higher than 1: 1.5. If the ratio is higher, then efficiency above 99% is not achieved.

By connecting the panels in series, you can pick up a voltage that is close, but not exceeding 380 V. Moreover, at the point of maximum power for each panel, it will fluctuate around 30 V. Thus, a ratio of 1: 1.5 is observed when the panels are combined into strings of at least 8 and no more than 13 panels. Considering that the average panel power is 250 W, we get a string power from 2 to 3 kW. Without sacrificing efficiency, it will be possible to complete two strings in parallel, receiving from 2 to 6 kW of power. The specified range provides the consumer with sufficient flexibility to generate any desired power without sacrificing efficiency, and the presence of two inputs for tracking MPP has already become the de facto industry standard.

The DC / DC converter generates a DC bus voltage of 380 V. At the input, it receives direct current in the range from 100 to 600 V, with a current strength of up to 15A. A simplified schematic diagram of the DC / DC converter of the inverter MPP string tracker is shown in Fig. 4 Applications.

The selected topology is a half-bridge on two GaN transistors, one of which is the active power switch, and the other “utilizes the freewheeling current. The low level of reverse current makes it possible to eliminate the freewheeling diode, further reducing the number of elements.

Partial power processing efficiency reaches 99.3%. 2 650V GaN FET transistors operate at 250 kHz.

As a realization of the task, it was decided to use the classic bridge inverter circuit.

The choice of using these transistors is due to their high efficiency at high power.

When the current through the low-level shunt resistor reaches a certain threshold level, an overcurrent occurs and the protection circuit prevents damage to the inverter system by disabling the control IC's PWM switching outputs.

An overvoltage error is detected when the DC bus voltage reaches a certain threshold level. If an overvoltage error is detected, the system prevents damage to the inverter system by shutting down

PWM output of the control microcircuit. Fault conditions are restored when the DC bus voltage returns to the normal range.

An undervoltage error is detected when the DC bus voltage falls below a certain threshold. If an undervoltage error is detected, the system prevents damage to the inverter system by disabling the PWM switching of the control IC output. Fault conditions are restored when the DC bus voltage returns to the normal range.

A short circuit protection fault is detected when the AC mains voltage is disconnected. If an anti-islanding error is detected, the system prevents the independent output voltage of the inverter from reaching the AC mains by closing the PWM output of the control IC. Fault conditions recover when the AC line voltage changes.

The MPP tracker is a DC-DC converter that monitors the point of maximum "efficiency of a string of solar panels and converts DC current to obtain a fixed voltage of 380 V at the output to power the inverter module.

A half-bridge evaluation board was used as an MPPT power converter, which contains elements of a simple buck or boost converter.

High switching performance and efficiency are achievable with 650V GaN FETs. In buck or boost mode, the circuit can be configured for synchronous rectification. Jumpers allow the use of one logic input or separate Hi / Lo inputs. The high voltage input and output can operate up to 400 VDC with an output power of up to 2.5 kW. The provided inductor is designed to operate efficiently at 100 kHz, although other inductors and frequencies may also be used.

The circuit contains a simple half-bridge with two GaN FETs.

There are two high-voltage ports that can serve as either input or output, depending on the configuration, a buck or buck converter.

In either case, one field-effect transistor acts as an active power switch and the other acts as a freewheel current. With a GaN FET, the reverse recovery current is low and therefore no additional freewheel diodes are required. There are two input connectors that can be connected to logic level command sources, signals for the hi / lo gate driver. Both inputs can be controlled by external signal sources; or, alternatively, one signal source can be connected to an onboard pulse generator circuit that generates two non-overlapping pulses. Jumpers determine how the input signals are used.

An inductor is provided as a starting point for research. This is a 440 μH toroid for later optimization. It represents a compromise between size and efficiency for power up to 2.5 kW at a switching frequency of 100 kHz.

For operation in buck mode, with an input voltage of 400 V and an output voltage of 48 V; The maximum output current of 50 A is achieved at 2500 W with a 12% duty cycle. Typical load 400V - 200V with 50% duty cycle, 6.5A maximum output current at 2500W. On the other hand, for a boost mode of 200 V - 400 V at 2.5 kW, a maximum output current of 12.5 A with a duty cycle of 50% can be achieved. Thermal cooling must always be ensured for high switching currents.

Thus, when using the claimed utility model, the following is achieved: high conversion efficiency at full and partial load, ease of system management, high energy density, reduced number of components to reduce cost and extend the system life cycle.

Claims (1)

An energy conversion device containing solar panels, characterized in that the solar panels are connected in series in strings, the strings are connected in parallel using bypass diodes, a sub-panel DPP converter is installed inside the panel on a board, the inverter is connected to solar panels, divided into two independent strings with a maximum voltage of up to 400 V in a flexible parallel-series configuration, the inverter consists of two devices made in one housing: an inverter, which is a DC-AC converter on gallium nitride transistors operating at a frequency of 120 kHz and forming a pure sine at the output from 380 VDC at the input, and MPP tracker, which is a DC-DC converter that monitors the point of maximum efficiency of the string and converts the DC current of the string to obtain a fixed voltage of 380 V at the input to power the inverter module, the inverter has a bridge circuit of the voltage inverter with using nitride - gallium transistors, as well as a relay for switching between the home power network and the inverter circuit line, feedback for measuring the current in the circuit, feedback for measuring input and output voltages and a microcontroller with a built-in mathematical processor, a half-bridge evaluation board is used as an MPRT energy converter , which contains elements of a simple converter and two field-effect gallium nitride transistors, combined by a simple half-bridge with two field effect transistors, there are two high-voltage ports, which can serve as input and output.

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