Abstract: Based on the design of a digital signal controller (DSC) of photovoltaic pump system. 系统以Mimochip Mimochip system to the company's latest dsPIC30F2010 chip as the core, adopted a practical maximum power point tracking (MPPT) control, and the solar maximum power of the real track (TMPPT) function, system main circuit DC / DC part of a Novel Forward push-pull circuit, DC / AC part of the adoption of improved protection of the integration of IPM (ASIPM). Practice has proved that the system has small size, light weight, stable and reliable operation, and other characteristics.
Key words: Inverter; photovoltaic arrays; push-pull forward; constant voltage tracking; maximum power point tracking: PV pumps
0 introduction to China's remote western region of millions of farmers and herdsmen still have no electricity supply, climate and drought in the region, land desertification and grassland degradation has become increasingly serious, rational use of photovoltaic systems to pump the development of groundwater resources, to address the region's drinking water and Agricultural water issues, improve the ecological environment, is of great significance. The photovoltaic pump technology is the core of the converter for the design, how to design and solar arrays match, with maximum power point tracking solar photovoltaic pumping systems and the protection of the unique features of the inverter, is the focus of this paper.
1 And a system of principle
1.1 photovoltaic system pumps from the structure of the Figure 1 indicates that system will use solar arrays of solar energy directly into electrical energy. After DC / DC boost, and a function of frequency converter TMPPT after the three-phase AC voltage output driver induction motor and pump load, water towers to complete the function. Which mainly includes four parts: solar arrays; TMPPT a function of frequency converter; pumps load; storage devices.
1.2 inverter main circuit and hardware of the system used by the main circuit and hardware control diagram shown in Figure 2. Main circuit DC / DC part of a superior performance of the push-pull Forward-circuit boost; DC / AC inverter part of a three-phase bridge circuit. 。 The main power devices used ASIPM (integration IPM) PS12036, the core system control from 16-bit digital signal controller dsPIC30F2010 pose. External control circuit including the array bus voltage level detection and a dry detection circuit. First of all initial system set up by the working methods and parameters of PI work, and then by the real-time search MPPT subroutine to voltage values as the CVT inner ring given by PI work by regulating the frequency value, calculated PWM signal duty cycle, Photovoltaic arrays to achieve the maximum power of the real track (TMPPT), and to maintain the induction motor V / f ratio constant. MPPT system and inverter combination of ASIPM module built-in functions to detect fault detection and protection, simple, convenient control.
1 2 DC / DC boost circuit briefly
1 2 1.1 main circuit of choice for small and medium-sized photovoltaic power pumps, voltage photovoltaic arrays are mostly low-voltage (24 v, 36v, 48V), the main circuit to boost the choice, people generally choose push-pull circuit Because the push-pull circuit-voltage transformer is the original DC input voltage, while driving without isolation, and therefore more suitable for low input voltage occasions. However, magnetic bias restricting its application is a major unfavorable factors, differences in the parameters of power transformers around the system and process are likely to push-pull circuit in a state of instability. Based on the many factors to consider, the system uses a novel structure of the push-pull forward circuit, the circuit topology not only overcome the magnetic bias, but also relatively easy to closed-loop control (second-order system).
1. 2. L.2 push-pull forward circuit simple analysis
Forward push-pull circuit shown in Figure 2, by the power of the S1 and S2, capacitors and transformers T C8 composed of the original T-transformer winding N1 and N2 have the same turns, the same name-as shown in Figure 2. When the S1 and S2 at the same time off when the voltage capacitors at both ends of C8 are negative, and the equivalent array voltage, when the S1 opened, S1, N2 and a photovoltaic array circuit, N2 is on the negative, while C8, N1 S1 and a loop, C8 discharge, N1 is on the negative, then the work of the equivalent of two parallel forward converter. Similarly, when the S2 opened S1 shutdown, the equivalent of two parallel forward converter. Through theoretical analysis, push-pull forward circuit is a second-order system, so simple closed-loop control, while the output filter capacitance and inductance greatly reduced.
1.2.2 dsPIC30F2010 brief
Through micro-chip companies in 16-bit microcontrollers, cleverly add DSP functions, so that micro-chip dsPIC30F digital signal controller (DSC) at the same time a microcontroller (MCU) of the control and digital signal processor (DSP) of calculation Capacity and data throughput capacity. Because of its function of the DSP, with the volume and price of SCM, the system uses this chip as a controller. This chip is mainly suitable for motor control, such as brushless DC motors, single-phase and three-phase induction motor and SRM at the same time also applies to an uninterruptible power supply (UPS), inverters, switching power supply and power factor correction, and so on. dsPIC30F2010 pin indicated as shown in Figure 3.
1. 2.2. A main structure
12KB program memory;
512 bytes SRAM:
1024-byte EEPROM;
3 16 timer;
Four-channel input capture;
2 output compare / PWM standard channels;
6 motor control PWM channels;
6 10 500 kspsSA / D converter channels.
l 2. 2. 2 main features
/ D sampling speed and multi-channel can be sampled;
6 independent / complementary / center alignment / Align the edge PWM:
2 programmable dead;
In the noisy environment 5 V power supply can work properly;
The minimum voltage 3 V;
/ D sampling and PWM synchronous the same period.
2 photovoltaic pump the maximum power point tracking (MPPT) Design
2.1 conventional constant voltage tracking (CVT) means the characteristics and shortcomings
CVT way can be similar to the solar maximum power output, software to deal with relatively simple. However, sunlight intensity and the temperature is always changing, especially in the western region, the same day in different time, temperature and sunlight intensity changes are significant, these solar arrays will cause the maximum power of the offset voltage, Especially the change in temperature most affected. 。 Under such circumstances, the use of CVT can not be a good way to track the most points.
2. 2 TMPPT and realization of the principle
CVT way to overcome the disadvantages of the proposed TMPPT (TrueMaximum forces that tracking) concept, its meaning is "the real maximum power tracking" control system that is guaranteed regardless of the duration of bright sunshine and temperatures in the conditions, always to work in the largest solar power Points. As inverter with constant V / f control, the pump motor speed is proportional to its input voltage, therefore, adjust the output voltage inverter, the load is equivalent to regulate the electrical power output. Therefore, this system uses solar TMPPT way to work in as much as possible the maximum power point, to provide the maximum load of energy.
By the solar arrays of the curve (see Figure 4) tells us that
dP ／ dV In maximum power point, dP / dv = O, the maximum power point to the left, when dP / dV> O when, P showed an upward trend, dP ／ dv When O, P trend to decrease, dP / dv
Figure 5-for TMPPT largest «0 Qiao is Shu Dao bottles Nao muscle» system input «0 Sc drop» 0, feedback 000? DP? 0dV dV, assuming Z3 status is +1, Usp * command voltage increase, the CVT link adjustment, the system's output voltage V tracking Usp * increase output current sampling I, as part of computing power and power differential link, access to dP / dV value, such as dP / dV> 0, then Z1 to +1, Z2 is + 1, Z3 to + l, Usp * command voltage continue to increase. 如dP ／ dV If dP / dV
3 protection system design
1) flow and short-circuit protection under the arm as ASIPM IGBT bus on a string sample resistance, by detecting bus current protection can be achieved. When the current value of more than testing a given value, was considered over-current or short-circuit, this time under the bridge IGBT gate was off, while the output signal failures, dsPIC detect this signal blockade PWM pulse further protect circuit.
2) under-voltage protection ASIPM testing arm of the bridge under the control of the supply voltage, if the power supply voltage for a given less than 1 OMs, then under the arm of the bridge were IGBT shutdown, while the output signal failures, failures in the period, under the bridge Three-phase IGBT arm of the gate does not accept external signals.
3) overheating protection features built-in detection ASIPM substrate temperature thermal resistance, thermistor resistance was the direct output, dsPIC by testing its resistance to be completed overheating protection.
More protection is to use the ASIPM with its own function, without additional circuits, further simplifying the hardware design. In addition to the above system protection, also has photovoltaic pump system unique low-frequency, low sunshine, a stem (a dry automatic and manual), and other protection. The pump load, when the speed below the lower limit, photovoltaic arrays provided by the vast majority of energy into a loss, long-term low-speed operation, will cause fever and affect pump life, so the system is designed to protect low-frequency , The pump, when pump inlet below the surface, the pumps are empty, and not to take measures to long run will damage lubricating bearings, and the system to work outdoors unattended, it System To increase the reliability of detection, the use of automatic and manual stem a two identification of a stem, including automatic system is based on a dry output power and electrical work carried out to determine the frequency; manually through a dry is to identify the current water level sensors To achieve the high and low water level. As low-frequency, low sunshine, a dry, and other functions are to complete by the software, hardware circuits do not need to increase, the system is simple.
4 conclusion of the system DC / DC link using the push-pull Forward-circuit, in performance, superior to the traditional economic and other aspects of the topology, is very applicable to the photovoltaic pump system. DC / AC link by using the latest ASIPM module greatly simplifies the circuit, improving the reliability of the system. TMPPT control strategy on the use of the maximum power point tracking control methods, improve the efficiency of the system, simplify the structure of the system, the system also uses a digital signal controllers (DSC) dsPIC30F2010 system for improving the speed and improve system performance plays an important role. In short, based on the structure of photovoltaic pump controller, both in structure, function, cost and reliability of such areas have obvious advantages and market competitiveness.