CN202159982U - Solar photovoltaic grid-connected inverter based on digital signal processor (DSP) - Google Patents

Abstract

The utility model discloses a solar photovoltaic gird-connected inverter based on a digital signal processor (DSP), which comprises a maximum power point tracking (MPPT) module, a voltage current converting module, a DSP control module, a user power management module and a man-machine interaction module. The solar photovoltaic grid-connected inverter based on the DSP can track a maximum power point, guarantees sufficient utilization of light energy, simultaneously has a phase locking function, and can guarantee that voltage and current which are output by the inverter are consistent with those of a power grid. The solar photovoltaic grid-connected inverter based on the DSP not only has the advantages of being high in efficiency and reliability, small in harmonic pollution to the power gird and the like, but also has a user power management function. The inverter utilizes electric energy generated by solar battery arrays to the maximum limit, thereby greatly reducing cost.

Description

DSP-based solar photovoltaic grid-connected inverter

technical field

The utility model belongs to the technical field of solar grid-connected power generation, in particular to an inverter for solar grid-connected power generation, in particular to a DSP-based solar photovoltaic grid-connected inverter.

Background technique

The rapid economic development has made the development and utilization of green new energy a top priority for governments of all countries. Solar energy is a renewable energy source that does not pollute the environment. Under this background, solar photovoltaic power generation has developed rapidly as a new energy industry.

Incorporating the electricity generated by solar cells into the grid can not only alleviate the power shortage during the peak power consumption period, but also save electricity storage costs. The key component that connects solar cell power generation to the grid is the photovoltaic inverter, whose main function is to convert the direct current generated by the solar cell into alternating current with the same frequency and phase as the grid. It can be said that the performance (efficiency, reliability) of the photovoltaic inverter , security, detectability and environmental adaptability, etc.) determine the performance of the entire grid-connected power generation system. However, the current solar photovoltaic grid-connected inverters have low efficiency, poor reliability, weak stability, insufficient maximum power point tracking, and lack of user power consumption management functions, all of which cannot meet the needs of the existing solar photovoltaic power generation industry.

Contents of the invention

The purpose of this utility model is to provide a high efficiency, strong reliability, strong adaptability, and user-friendly DSP-based solar photovoltaic grid-connected inverter with power management function. The utility model has the following advantages:

1. High efficiency: The power factor is 1, which can maximize the use of solar cells, thereby improving the efficiency of the entire solar photovoltaic grid-connected system and reducing costs.

2. High reliability: It has various protection functions, such as input DC polarity reverse protection, AC output short-circuit protection, overheating, overload protection, etc. It does not need to be manned and maintained, and is especially suitable for various remote areas.

3. The DC input voltage has a wide range of adaptation: because the terminal voltage of the battery changes with the load and the intensity of sunlight, although the battery plays an important role in the voltage of the battery, the voltage of the battery varies with the remaining capacity and internal resistance of the battery. Fluctuations, especially when the battery ages, its terminal voltage varies greatly, which requires the inverter to ensure normal operation within a wide DC input voltage range and ensure the stability of the AC output voltage.

4. It has the user power management function: it can judge whether the current photovoltaic power supplies power to the grid, whether the user takes power from the grid, etc., and then turn off/on the corresponding switch.

The technical scheme of the utility model to realize the above advantages is: a DSP-based solar photovoltaic grid-connected inverter, including a maximum power point tracking MPPT module, a voltage and current conversion module, a DSP control module, a user power management module and a human-computer interaction module.

Among them, the maximum power point tracking MPPT module includes a pre-stage voltage matching sub-module. The voltage and current conversion module includes a DC/DC boost circuit, a DC/AC inverter circuit and a drive circuit; the DC current of the solar array battery becomes a higher DC current after passing through the DC/DC boost circuit, and then passes through the DC/AC inverter circuit. The transformer circuit converts it into 220V AC and sends it to the grid. The DC/AC inverter is modulated by the deadbeat SVPWM algorithm, which is easy to digitize, reduces the size of the device, can improve the dynamic performance of the power supply, and increase the utilization rate of the DC voltage. The user power management module includes a grid detection circuit and a sampling circuit. The DSP control module is the core of the entire inverter. It tracks the maximum power point through an algorithm based on the voltage and current of the sampled solar cell array. If the power generation is greater than the power consumption, the excess power will be sent to the grid; if the power generation is less than the power consumption, the gap part of the power will be obtained from the grid for power management. At the same time, the inverter also has the function of synchronous locking.

The DSP-based solar photovoltaic grid-connected inverter is characterized in that: the implementation method of the maximum power point tracking MPPT module maximum power control adopts the "voltage disturbance method" and its improvement. The principle of the voltage disturbance method is to determine whether to increase or decrease the working voltage of the solar cell array by comparing the output power of the photovoltaic array this time with the previous one.

The DSP-based solar photovoltaic grid-connected inverter is characterized in that: the DC/DC boost circuit in the voltage-current conversion module adopts BOOST mode; the DC/AC circuit adopts a three-phase bridge inverter circuit, and the power device Using an IPM module integrated with drive and protection circuits, the switching frequency is 10 kHz. In order to prevent electric energy from flowing into the solar photovoltaic array from the grid, anti-reverse diodes are added on the DC side; the output of the inverter uses an LC filter circuit to filter out high-frequency components, and contactors are installed at both the input and output ends of the inverter. Inverter, to achieve reliable isolation and protection of the inverter. The inverter uses a large capacitor for decoupling, and power resistors are installed at both ends of the decoupling capacitor to realize discharge, so as to ensure the personal safety of maintenance personnel. The inverter circuit adopts a voltage-type single-phase bridge inverter circuit.

The DSP-based solar photovoltaic grid-connected inverter is characterized in that: the DSP control module can effectively prevent the islanding effect.

The DSP-based solar photovoltaic grid-connected inverter is characterized in that: the user power management module determines the current power consumption of the user by measuring the total current of the current user, and compares it with the power generation of the photovoltaic system to determine the power How the management module works.

The DSP-based solar photovoltaic grid-connected inverter is characterized in that: the phase-locking function is a digital phase-locking based on DSP, so that the current output by the inverter is synchronized with the grid voltage phase and frequency.

Description of drawings

Fig. 1 is a block diagram of modules provided by the utility model;

Fig. 2 is the overall frame diagram of the detailed point provided by the utility model;

Fig. 3 is the MPPT control process that the utility model provides;

Fig. 4 is the schematic diagram of the inverter circuit provided by the utility model;

Fig. 5 is a detection block diagram of the grid voltage frequency and phase provided by the utility model.

Detailed ways

The DSP-based solar photovoltaic grid-connected inverter of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

DSP (digital signal processor) is a unique microprocessor, a device that processes a large amount of information with digital signals. Its working principle is to receive an analog signal and convert it into a digital signal of 0 or 1. Then modify, delete, and strengthen the digital signal, and interpret the digital data back to analog data or the actual environment format in other system chips. Not only is it programmable, but its real-time running speed can reach tens of millions of complex instruction programs per second, far exceeding that of general-purpose microprocessors. It is an increasingly important computer chip in the digital electronics world. Its powerful data processing capability and high operating speed are the two most commendable features.

The full name of the MPPT controller is "Maximum Power Point Tracking" (MPPT for short). , so that the system charges the battery with the highest efficiency. The MPPT control system is an electrical system that controls the working state of the electrical module and enables the photovoltaic panel to output more electrical energy. The maximum power point is mainly affected by ambient temperature and sunlight intensity. In the case of constant sunlight intensity, as the temperature increases, the open circuit voltage of photovoltaic cells decreases, and the maximum output power decreases accordingly. When the temperature remains unchanged and the intensity of sunlight increases, the open circuit voltage of the photovoltaic cell remains basically unchanged. The short-circuit current is greatly increased, and the maximum output power is greatly increased. Since the photovoltaic cell system is affected by various factors such as light intensity, temperature, and sunlight incident angle, its output voltage Ub, output current Ib, and internal resistance R are also constantly changing. Only by using the DC/DC converter to realize the dynamic change of the load, can the photovoltaic cell always output the maximum power.

The most basic module of the solar inverter is the voltage-current conversion module. The terminal voltage and terminal current of the solar cell array are sampled, and then sent to the DC/DC booster circuit to obtain a higher and more stable DC voltage UA. At the same time, the DC/DC converted voltage UA is then passed through the DC/AC inverter The transformer circuit obtains the required alternating current and merges it into the grid. In the utility model, the DC/DC boost circuit adopts a BOOST boost mode, and the DC/AC inverter circuit adopts a single-phase bridge inverter circuit. The DC/AC inverter is modulated by the deadbeat SVPWM algorithm. SVPWM and deadbeat control technology are applied to the tracking control of the inverter power supply, which is not only easy to digitize, reduces the size of the device, but also improves the dynamic performance of the power supply and optimizes the switching times. Reduce switching loss and improve DC voltage utilization. In the modulation process, the dead zone problem should be considered, and corresponding mechanisms should be adopted to solve it, so as to enhance the reliability of the inverter.

Photovoltaic cell is a nonlinear power supply, its output voltage and current are not only affected by light intensity and temperature, but also determined by the nature and condition of the load. In the volt-ampere curve of photovoltaic cell, the output characteristic of photovoltaic cell The intersection point is the operating point of the photovoltaic cell. If the operating point is at the maximum power point, the system is in a matching state, and the electric energy generated by the photovoltaic cell is fully utilized; otherwise, the electric energy generated by it is not fully utilized. The maximum power point tracking MPPT module of the utility model is a designed control method for the maximum power of solar energy, which is "voltage disturbance method" and is improved. The principle of the voltage disturbance method is to determine whether to increase or decrease the operating voltage of the photovoltaic cell by comparing the output power of the photovoltaic array this time with the previous one. If the power increases, the photovoltaic cell voltage maintains the original voltage disturbance direction; if the power decreases, the photovoltaic cell voltage perturbs in the opposite direction. Through repeated disturbance, observation and comparison, the output power of photovoltaic cells reaches the maximum power point to realize MPPT. The output voltage of the photovoltaic cell is adjusted by changing the duty cycle D of the step-down chopper circuit. It can be seen from D=Uo/Uin that since the size of Uo cannot be controlled artificially, it is necessary to adjust D in the opposite direction to make Uin change in the ideal direction. For example, assuming that the power output can be increased when Uin is increased, only by reducing D can Uin be increased. The change of duty cycle D is obtained by changing the value of PWM. The MPPT control process is shown in Figure 3.

The DSP control module with anti-islanding effect is the main module of this utility model, and its circuit is shown in Figure 4. The so-called isolated island phenomenon refers to: when the grid power supply trips due to fault accidents or power outage maintenance, the distributed grid-connected power generation systems (such as: photovoltaic power generation, wind power generation, fuel cells, etc.) Cut itself off from the network, and form a self-sufficient power supply island known by the grid-connected power generation system of the distributed power station and the surrounding loads. Once the island is generated, it will endanger the safety of the maintenance personnel on the transmission line of the power grid; affect the action program of the protection switch on the power distribution system and impact the protection device of the power grid; affect the quality of transmitted electric energy, and the power supply voltage and frequency in the power island area will be unstable ; When the grid power supply is restored, the phases will be out of sync; the single-phase distributed power generation system will cause the three-phase load of the system to lose phase power supply. Therefore, for a grid-connected system, it is necessary to be able to perform anti-islanding detection. the

There are two main methods of island detection: passive detection and active detection. The parameters of the DG output at the moment of island formation usually have spikes. The passive method mainly uses this instantaneous fluctuation to detect the formation of islands by calculating the total harmonic distortion (THD) or voltage unbalance (VU).

The active method is to artificially introduce a small voltage or frequency disturbance in the output of the inverter. Under the islanding condition, this kind of disturbance will cause voltage or frequency instability, and then the frequency protection circuit will detect the protection circuit to detect the islanding phenomenon. generation, which eventually leads to the disconnection of the inverter.

The disadvantage of this type of method is that: on the one hand, it is easy to malfunction when the regional power grid is heavily loaded. On the other hand, when a large number of DGs are connected to the system, these artificially introduced positive feedbacks will have a relatively large impact on the power quality of the public network. This design uses a hybrid detection method, which combines the active method and the passive method to detect THD and VU first, and when a possible island formation is found, it is reflected in the disturbance to confirm. In this way, the advantages of the two methods are played, and the interference to the power grid is minimized.

In the photovoltaic grid-connected power generation system, it is necessary to detect the phase and frequency of the grid voltage in real time to control the grid-connected inverter so that its output current is synchronized with the phase and frequency of the grid voltage, that is, genlock. Genlock is a key technology of photovoltaic grid-connected system, and its control accuracy directly affects the grid-connected operation performance of the system. This design uses a DSP chip to realize the digital phase-locking of the photovoltaic grid-connected system, as shown in Figure 5. This method can effectively eliminate the shortcomings of the simulation method, and at the same time has the advantages of flexible control, convenient device upgrades, online modification and debugging, high reliability, and convenient maintenance. The goal of digital phase-locking is to make the output current have the same frequency and phase as the grid voltage, that is, let the inverter current track the change of the grid voltage. The detection of the synchronous signal is divided into the detection of the grid voltage and the inverter output current. The grid voltage is first sampled by the sampling transformer, and then the sampled voltage is sent to the zero-crossing comparator for zero-crossing detection, and a square wave signal with the same frequency and phase as the grid voltage is obtained, and then the optocoupler is isolated, and the high-frequency interference is filtered out by voltage limiting. Finally, it is sent to a certain CAP port of the DSP. The detection of the inverter current is the same as the grid voltage sampling, and the inverter current signal is sent to another CAP port of the DSP. The function of the DSP capture unit is to capture the level change on the pin and record the moment when the level changes. The port input signal is a square wave signal, so the interval between two adjacent rising edges is exactly one cycle, and the moment when the rising edge occurs is the zero-crossing point of the sampling signal from negative to positive, so as to realize the control of the grid voltage and output current frequency and phase detection.

The process of frequency adjustment is that when a rising edge is caught and an interrupt is generated, the interrupt service routine is entered to first protect the site, and then determine whether the interrupt source is CAP_A or CAP_B. If it is CAP_B, it means that the moment when the interruption occurs is the zero-crossing point of the grid voltage. Store the captured value into the relevant register, and then subtract the last captured value, the difference between the two is exactly the period of the grid voltage. Then compare this period with the current inverter current period, and return if there is no difference between the two; if there is an error, make corresponding adjustments to the period register.

The output current phase is realized by adjusting the moment when the first point in the sine wave discrete value of the SVPWM signal occurs. When the zero-crossing point of the grid voltage is captured, the pointer of the sine wave discrete value in the corresponding comparison register is adjusted immediately, and Make some time compensation. The process of phase adjustment is to compare the current grid voltage and the zero-crossing value captured by the inverter current to obtain the phase difference. If the phase difference is less than or equal to the allowable value, it means that the two are in phase; if the phase difference is greater than the allowable value, then PI adjustment is performed, and then it is judged whether the sinusoidal count value is greater than the limit value, if not, directly convert the adjacent two The difference is used as the adjustment amount; if it is greater than the limit value, only the limit value will be adjusted, and further adjustment will be made at the next interruption. the

The user power management module measures the total current of the current user through the current detection circuit, determines the current power consumption of the user, and then compares it with the power generation of the photovoltaic system, and realizes the working mode of the power management module through an algorithm.

Claims (6)

1. based on the solar photovoltaic interconnected inverter of DSP, comprise inverter, it is characterized in that: this inverter comprises MPPT maximum power point tracking MPPT module, voltage current transformation module, DSP control module, custom power administration module and human-computer interaction module; MPPT maximum power point tracking MPPT module was the custom power administration module after the voltage current transformation module before the voltage current transformation module, and these three modules are communicated by letter simultaneously and between the DSP control module, and human-computer interaction module only is connected with the DSP control module.

2. the solar photovoltaic interconnected inverter based on DSP according to claim 1 is characterized in that: described MPPT maximum power point tracking MPPT module includes prime voltage matches submodule.

3. the solar photovoltaic interconnected inverter based on DSP according to claim 1 is characterized in that: described voltage current transformation module comprises DC/DC booster circuit, DC/AC inverter circuit and drive circuit.

4. voltage current transformation module according to claim 3 is characterized in that: described DC/AC inverter circuit adopts the single-phase bridge inverter circuit that includes power device; The IPM module of described power device use is integrated driving and protective circuit.

5. the solar photovoltaic interconnected inverter based on DSP according to claim 1 is characterized in that: described custom power administration module comprises electrical network testing circuit and sample circuit.

6. the solar photovoltaic interconnected inverter based on DSP according to claim 1 is characterized in that: described inverter is provided with the counnter attack diode at DC side; Output uses LC filter circuit filtering high fdrequency component; Input and output are all installed contactor; Inverter adopts big capacitor-decoupling, installs power resistor additional at the two ends of decoupling capacitance.

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