CN107230975A - A kind of grid stimulating device - Google Patents

Abstract

The invention relates to a power grid simulation device, which is mainly composed of five parts: a real-time digital simulation module, a signal modulator, a power amplifier, a filter and a sampling feedback module. Problem: The switching frequency is greatly increased, effectively simulating the harmonics within 50kHz in the actual power grid, the frequency response range is wide, and the simulation of the drop and high-order harmonic grid form is realistic; the requirements for L and C parameters are reduced, and the filter is simplified The design of the filter reduces the size of the filter; it is easier to build a three-phase power amplifier; the device can easily apply a step-up transformer to increase the output voltage, and increase the output power through a parallel power amplifier chip, which effectively overcomes the impact of the digital power amplifier chip on the output voltage and power. It is convenient to simulate various forms of power grids; it can easily simulate special working conditions of the power grid; the frequency response range is wide, and the simulation of drops, high-order harmonics and other phenomena is realistic.

Description

A network simulation device

technical field

The invention belongs to the field of power state simulation, in particular to a network simulation device.

Background technique

When studying the interaction between distributed generation devices, converters and the grid, it is often necessary for the grid to be under some special working conditions, such as voltage sag, three-phase unbalance, frequency fluctuation, background harmonics, etc. For the actual experimental system, due to the particularity of the power grid, it is often difficult to make the above situation occur in the actual power grid, which brings inconvenience to the study of the interaction between the distributed generation device, the converter and the power grid.

When the research object includes the power grid, we will habitually choose power system simulation software, such as matlab, RTDS, PSASP, etc. However, the results obtained by software simulation often cannot accurately reflect the actual situation. Simulation results are often used as qualitative analysis rather than quantitative research questions. On the other hand, if we do experiments with real objects, the cost is huge. Especially when it comes to a huge power system, it is unrealistic to do experiments on the power system, especially the simulation of special working conditions of the power system.

The device is connected with the actual load and converter or connected with the hardware-in-the-loop simulation device to simulate various grid forms to quantitatively study the interaction between the grid and grid-connected converter or load, and solve the software problems existing in the current research process. The simulation accuracy is poor, and the cost of the actual power grid test is expensive.

Contents of the invention

As described in the background art, in the face of this situation, a power grid simulation device can be designed to connect the simulated power grid with the actual load and converter. Realize the simulation of various special working conditions of the power grid. Considering the rich power system model library and real-time performance of RTDS, it can realize the connection with external objects and is suitable for power grid simulation. However, actual experiments have proved that the power output capability of RTDS is very low, which cannot meet the requirements of simulating a large-capacity power grid. A power amplifier is required to amplify the output signal. A class A push-pull power amplifier can be considered, but the heat generated by the class A power amplifier is amazing. In order to effectively deal with the heat dissipation problem, the class A power amplifier must use a large radiator, and the efficiency is low. The working principle of Class D power amplifier (digital power amplifier) is somewhat similar to the switching power supply, which obtains power conversion by controlling the switch (on/off) of the power tube. Although the switch tube has the largest current when it is turned on, the tube voltage drop is very low. Although the voltage is maximum at the cut-off time, the current is equal to zero. Generally, the efficiency of class D amplification can reach 90% to 95%. Digital power amplifier technology is widely used in audio equipment, mainly to amplify the power of audio signals. The switching frequency of the digital power amplifier chip is at least 200KHz, which is more than 10 times the audio range (20Hz~20KHz) heard by the human ear. It can well reproduce the harmonics within 50kHz in the power grid.

The invention provides a power grid simulation device for simulating various forms. The device can be connected with actual loads and converters, and can also be connected with a half-physical simulation device for researching power grids and grid-connected converters. Or load interaction.

The invention provides a power grid simulation device, which is characterized in that it is mainly composed of five parts: a real-time digital simulation module, a signal modulator, a power amplifier, a filter and a sampling feedback module, the real-time digital simulation module is connected to the signal modulator, and the signal modulator is connected to Power amplifier, the power amplifier is connected to the filter, the filter is connected to the sampling feedback module, the sampling feedback module is connected to the real-time digital simulation module, and the filter outputs an analog signal; the real-time digital simulation module is used to establish and simulate the power grid model to generate sinusoidal signals; the power amplifier adopts The digital power amplifier chip using digital power amplifier technology adopts a two-stage amplification form. The signal modulator converts the sinusoidal signal with a lower amplitude into a 5V PWM signal in the first stage of amplification. The PWM waveform is used as the driving signal to amplify the amplitude and power. The signal output mode adopts bridge-tied load BTL (Bridge Tied load), which has two power amplifier output terminals. The output of one power amplifier is the mirror image of the other output terminal. The two output waveforms are in phase The upper phase difference is 180°, and the amplitude is twice that of the single-ended output waveform; the filter adopts LCL topology to filter out high-order harmonics, ensuring that the waveform is not distorted and does not introduce harmonics to the grid; the sampling feedback module is used to collect The filter outputs the signal and feeds it back to the AD acquisition terminal of the real-time digital simulation module, and the system forms a closed loop to eliminate errors.

The power grid simulation device of the present invention is used to simulate various forms of power grids, such as voltage drop, three-phase unbalance, frequency fluctuation and the like. It connects the RTDS simulation software and the physical object together, and has a reliable semi-physical simulation function; uses the real-time digital simulation module (RTDS) to establish and simulate the power grid model, outputs the voltage and current waveform of a certain node, and amplifies the amplitude of the waveform through an external power amplifier. Value and power, to ensure that the waveform is not distorted and does not introduce harmonics to the grid, and at the same time, the feedback link can be added as needed.

Furthermore, the power grid simulation device mainly includes RTDS and power amplifier. RTDS can use industry-recognized power system simulation software or controller. The latter is a self-developed power amplifier. The power amplifier adopts digital power amplifier technology, and its core is a digital power amplifier chip. Its switching frequency can reach 300kHz.

Furthermore, the power amplifier adopts a two-stage form. The first stage converts the sine wave output by the RTDS into a 5V PWM signal, and the second stage uses the PWM waveform as a driving signal to drive the digital power amplifier chip to output PWM. The output mode adopts the bridge-tied load BTL (Bridge Tied load), the dual output with a mutual difference of 180°, and the final voltage is twice that of the original single-ended output.

Further, for the actual power grid, the power amplifier considers the range of grid harmonics to be within 10KHz, while the switching frequency of the digital power amplifier chip can reach 300KHz, which is 30 times of the former; therefore, the harmonics introduced by the device can be ignored. At the same time relying on the 300kHz switching frequency, the design of the low-pass filter is very simple, and the requirements for LC parameters are very low, and the volume of the filter is also small. The filter adopts an LCL structure, for details, please refer to Figure 6.

Further, in the power amplifier, because the dispersion of digital power amplifier chips is very small, different digital power amplifier chips input the same waveform, and the waveforms after filtering output are almost the same. Therefore, three single-phase amplifiers are connected in parallel to construct a three-phase power amplifier. The power level can be increased by connecting power amplifier chips in parallel.

Furthermore, the output voltage and power of the power amplifier are limited by the digital power amplifier chip. In addition to increasing the power level by connecting the power amplifier chips in parallel, a step-up transformer can also be selected to increase the output voltage.

The English abbreviation of the real-time digital simulation module described in the present invention is RTDS.

The technical effect that the present invention brings is:

1. The device adopts a power amplifier using a digital power amplifier technology chip, which greatly improves the amplification efficiency and solves the problem that RTDS cannot simulate a large-capacity power grid.

2. The device adopts a power amplifier using a digital power amplifier technology chip, which greatly increases the switching frequency, and can effectively simulate the harmonics within 50kHz in the actual power grid, and the frequency response range is wider. more realistic.

3. The device adopts a power amplifier using a digital power amplifier technology chip, which reduces the requirements of L and C parameters, simplifies the design of the filter, and reduces the volume of the filter.

4. The device adopts a power amplifier using a digital power amplifier technology chip. Because of its good consistency, it is easier to construct a three-phase power amplifier.

5. The device can conveniently use a step-up transformer to increase the output voltage, and increase the output power by connecting the power amplifier chip in parallel, which effectively overcomes the limitation of the digital power amplifier chip on the output voltage and power, and can easily simulate various forms of power grids.

6. It is convenient to simulate the special working conditions of the power grid.

7. The frequency response range is wide, and the simulation of drops, high-order harmonics and other phenomena is realistic.

Description of drawings

Fig. 1 is a schematic block diagram of the present invention;

Fig. 2 is TPA2000 circuit diagram of the present invention;

Fig. 3 is a TAS5261 circuit diagram of the present invention;

Fig. 4 is the relationship figure of TAS5261 output power of the present invention and load and voltage;

Fig. 5 is the circuit diagram of filter LCL topological structure of the present invention;

Fig. 6 is a functional block diagram of Embodiment 2 of the present invention;

In the figure: 1 is a real-time digital simulation module; 2 is a signal modulator; 3 is a power amplifier; 4 is a filter; 5 is a sampling feedback module.

detailed description

Referring to accompanying drawings 1-5, the implementation of the present invention will be described in more detail.

Example 1

The invention provides a power grid simulation device, which is mainly composed of five parts: a real-time digital simulation module 1, a signal modulator 2, a power amplifier 3, a filter 4, and a sampling feedback module 5. The real-time digital simulation module 1 is connected to the signal modulator 2, and the signal The modulator 2 is connected to the power amplifier 3, the power amplifier 3 is connected to the filter 4, the filter 4 is connected to the sampling feedback module 5, the sampling feedback module 5 is connected to the real-time digital simulation module 1, and the filter 4 outputs an analog signal; the real-time digital simulation module 1 is used for Establish and simulate the power grid model to generate sinusoidal signals; the power amplifier 3 adopts a digital power amplifier chip using digital power amplifier technology, and adopts a two-stage amplification form. The signal modulator 2 converts the sinusoidal signal with a lower amplitude into a 5V power amplifier in the first stage of amplification. For PWM signal, the power amplifier 3 uses the PWM waveform of the first stage as the driving signal to amplify the amplitude and power of the second-stage amplification, and its signal output method adopts bridge-tied load BTL (Bridge Tied load), with two power amplifier output terminals, The output of one power amplifier is the mirror image of the other output terminal. The phase difference between the two output waveforms is 180°, and the amplitude is twice that of the single-ended output waveform; filter 4 adopts LCL topology to filter out high-order harmonics to ensure The waveform is not distorted and does not introduce harmonics to the power grid; the sampling feedback module 5 is used to collect the output signal of the filter 4 and feed it back to the AD acquisition terminal of the real-time digital simulation module 1, and the system forms a closed loop to eliminate errors.

The power grid simulation device of the present invention is used to simulate various forms of power grids, such as voltage drop, three-phase unbalance, frequency fluctuation and the like. It connects the RTDS simulation software and the physical object together, and has a reliable semi-physical simulation function; uses the real-time digital simulation module (RTDS) to establish and simulate the power grid model, outputs the voltage and current waveform of a certain node, and amplifies the amplitude of the waveform through an external power amplifier. Value and power, to ensure that the waveform is not distorted and does not introduce harmonics to the grid, and at the same time, the feedback link can be added as needed.

Furthermore, the power grid simulation device mainly includes RTDS and power amplifier. RTDS can use industry-recognized power system simulation software or controller. The latter is a self-developed power amplifier. The power amplifier adopts digital power amplifier technology, and its core is a digital power amplifier chip. Its switching frequency can reach 300kHz.

Furthermore, the power amplifier adopts a two-stage form. The first stage converts the sine wave output by the RTDS into a 5V PWM signal, and the second stage uses the PWM waveform as a driving signal to drive the digital power amplifier chip to output PWM. The output mode adopts the bridge-tied load BTL (Bridge Tied load), the dual output with a mutual difference of 180°, and the final voltage is twice that of the original single-ended output.

Further, for the actual power grid, the power amplifier considers the range of grid harmonics to be within 10KHz, while the switching frequency of the digital power amplifier chip can reach 300KHz, which is 30 times of the former; therefore, the harmonics introduced by the device can be ignored. At the same time relying on the 300kHz switching frequency, the design of the low-pass filter is very simple, and the requirements for LC parameters are very low, and the volume of the filter is also small. The filter adopts an LCL structure, for details, please refer to Figure 6.

Further, in the power amplifier, because the dispersion of digital power amplifier chips is very small, different digital power amplifier chips input the same waveform, and the waveforms after filtering output are almost the same. Therefore, three single-phase amplifiers are connected in parallel to construct a three-phase power amplifier. The power level can be increased by connecting power amplifier chips in parallel.

Furthermore, the output voltage and power of the power amplifier are limited by the digital power amplifier chip. In addition to increasing the power level by connecting the power amplifier chips in parallel, a step-up transformer can also be selected to increase the output voltage.

Real-time digital simulation module (RTDS) is a commonly used power system simulation software. It has a rich power system model library and real-time performance, and can realize connection with external objects, which is suitable for power grid simulation.

The first-stage power amplifier (power amplifier modulation) of the power amplifier uses the TPA20000 chip, which can convert the sinusoidal signal into a PWM signal, with an output amplitude of 5V and a power of 2W. Compared with previous products, this product has lower supply voltage, lower noise and higher efficiency.

Power amplifier The second-stage power amplifier (power amplifier amplification) adopts the self-developed TAS5261 digital power amplifier chip, which is a high-performance, integrated, low harmonic loss monophonic digital power amplifier chip, and its size is only 16×11× 3.5mm, its circuit design is simple, only need a simple demodulation filter circuit to achieve high-quality, high-efficiency sound amplification, can achieve a single-phase 300W output, the output single-phase voltage peak value can be adjusted within 50V, the peak-to-peak value is 100V, the frequency is adjustable in the audio range. The switching frequency of the power supply is 300KHz, and a high-quality three-phase power supply can be obtained by using a small inductance and capacitance filter. This chip greatly improves the amplification efficiency and switching frequency, solves the problem that RTDS cannot simulate large-capacity power grids, and can easily simulate various power grid forms.

In the hardware system of the analog power amplifier, TPA20000 is selected for the modulation area of the first stage power amplifier. This chip can change the sinusoidal signal into a PWM signal, and the output amplitude is 5V and the power is 2W. TAS5261 digital power amplifier chip is used in the second-stage power amplifier amplification area. Its size is only 16X11X3.5mm, but it can achieve a single-phase 300W output. adjust. The switching frequency of the power supply is 300KHz, and a high-quality three-phase power supply can be obtained by using a small inductance and capacitance filter.

In Figure 2, because the TPA2000 chip is designed for single power supply and low voltage application, the output tube adopts the BTL connection method. The control signal causes the two output terminals OUT+ and OUT- to have a phase difference of 180°. The audio is modulated in a duty cycle mode, the duty cycle is 50% when there is no signal, and the maximum amplitude of each waveform is 5V. The BTL output is the difference between the two, so the output voltage can be increased to V_pp=10V. But the average current and average voltage of the output are both zero, and there is still no output. If the duty cycles of the output signals at the two output terminals are not the same, signal components will appear when the two are subtracted. It can be seen that the difference of the output signal is the PWM signal we are familiar with.

The filter shown in Figure 5 adopts LCL topology, which is mainly used to filter out high-order harmonics to ensure that the waveform is not distorted and does not introduce harmonics to the power grid.

TPA2000 is the third-generation low-power Class D amplifier launched by TI Corporation of the United States. Compared with previous products, the power supply voltage is lower, the noise floor is lower, and the efficiency is higher. TPA2000 adopts 5V single power supply, when R_L=3Ω, the output is 2W, at this time THD≤0.4%. When switching to 4Ω load and 1W output, the THD+N of 1kHz input signal is less than 0.08%. In order to improve the switch output power at low voltage, the circuit adopts BTL connection, so the input terminal can be directly connected to the balanced input signal. The chip can be used without an output low-pass filter. This is not only convenient for the user, but also reduces the cost of the overall amplifier. Here we use the output PWM signal as the driving signal of the lower stage without filtering.

TAS5261 is a high-performance, integrated, low harmonic loss mono digital power amplifier, which can be used to drive 4Ω to 8Ω speakers. The circuit design is simple, and only a simple demodulation filter circuit is needed to achieve high-quality and efficient sound amplification. TAS5261 integrates a complete protection circuit to protect equipment and speakers from damage. Protection features include short-circuit protection, over-current protection, voltage protection, and input signal PWM loss protection. These protections can be selected as desired. Its output power: 8Ω load, total harmonics less than 0.09%, output 125W at 50V DC voltage; 6Ω load, when total harmonics are 10%, output 220W at 50V DC voltage; 4Ω load, total harmonics At 10%, when the DC voltage is 50V, the output is 315W.

In order to simplify system design, TAS5261 only needs a 12V and a 50V power supply. An internal voltage regulator provides stable power to digital circuits and low-voltage analog circuits. Note that all circuits require a floating power supply. High-side gate drive is provided through a bootstrap circuit built with a small number of peripheral components.

To exhibit excellent electrical and acoustic characteristics, the PWM signals including gate drive and output stage are designed as typically two independent half-bridges. Therefore, each half bridge has independent gate drive power supply, bootstrap circuit and external power supply. Also, an additional pin VDD is used as the power supply for most of the internal circuits. Although the power supply is from the same 12V supply, it is better to separate GVDD_X and VDD by RC filter. These RC filters provide good isolation. Special care is taken to place the decoupling capacitor as close as possible to the pin it is connected to. Be sure to avoid stray inductance between power supply pins and decoupling capacitors.

The 12V power supply should be a power supply with low noise and low input impedance. Similarly, the 50V power supply should be the same. An internal power-on-reset circuit eliminates power-up sequencing. Also, the TAS5261 is able to protect against faults caused by gate parasitic charges. Therefore, the rate of change of the voltage within the specified range need not be considered.

The sampling feedback module 5 is mainly used to collect the output signal, and feed the signal back to the AD collection terminal of the RTDS. The system forms a closed loop to eliminate errors.

Example 2

As in the power grid simulation device described in Embodiment 1, the RTDS is replaced by a controller. The controller generates a three-phase PWM signal by writing a program, controls the inverter bridge to conduct, and generates a PWM wave signal with an amplitude of 0V to the power supply voltage, which is passed through the LC A low-pass filter filters out higher harmonic components. At this time, the controller needs to write SPWM algorithm or SVPWM algorithm program. If a three-phase power supply with flexible adjustment of voltage and frequency is to be obtained, the complexity of controller programming will continue to increase. The device is limited by the switching frequency of the power tube, and the frequency cannot be very high. For example, the maximum frequency of the IGBT is required to be around 50KHz, but its voltage level and power level can be very high. Therefore, this topology is mainly used in occasions that do not require high power quality, and require high voltage and high power, such as motor speed regulation and grid-connected inverters.

Figure 6 Topology 2 Compared with Topology 1, the controller can solidify the program, the controller can also be programmed, the amount of controller programming is greatly reduced, the controller does not need to write complicated programs, and only needs to generate sinusoidal signals with adjustable voltage and frequency , for a controller that supports C language development, it can be realized only by A sin⁡(Bt), where A adjusts the amplitude and B adjusts the frequency. The sinusoidal signal output by the controller, the signal generates a PWM modulation wave through the digital power amplifier chip, and then amplifies the power through the power amplifier chip of the rear stage. Both the microcontroller and the digital power amplifier chip can generate high-frequency signals, so the PWM frequency generated by this method can be very high. Since the digital power amplifier chip material mostly uses MOS tubes, its withstand voltage capability is low, and the power output is often limited. If you want to output high voltage, you can use a transformer to boost the voltage.

In the power grid simulation device, from the sinusoidal signal to the PWM waveform after power amplification, a two-stage form is adopted. The first stage converts the lower sinusoidal signal into a 5V PWM signal; the second stage uses the PWM waveform of the first stage as the driving signal , and then carry out power amplification, the output method adopts bridge-tied load BTL (Bridge Tied load), two power amplifier output terminals, the output of the power amplifier is the mirror image of the other output terminal, that is to say, the signal added to the load has a phase difference of 180 °, so the final waveform is twice the voltage of the original single-ended output. After the final output waveform passes through the conditioning circuit, the AD acquisition terminal of the RTDS collects the output signal as a feedback signal, and the system forms a closed loop to eliminate errors.

Claims (7)

1. A power grid simulation device is characterized in that it is mainly composed of five parts, a real-time digital simulation module, a signal modulator, a power amplifier, a filter and a sampling feedback module, and the real-time digital simulation module is connected to the signal modulator, and the signal modulator is connected to the power Amplifiers, power amplifiers are connected to filters, filters are connected to sampling feedback modules, sampling feedback modules are connected to real-time digital simulation modules, and filters output analog signals; real-time digital simulation modules are used to establish and simulate power grid models to generate sinusoidal signals; power amplifiers use application The digital power amplifier chip of digital power amplifier technology adopts a two-stage amplification form. The signal modulator converts the sinusoidal signal with a lower amplitude into a 5V PWM signal in the first stage of amplification, and the power amplifier converts the PWM signal of the first stage into a 5V PWM signal. The waveform is used as the driving signal to amplify the amplitude and power. The signal output method adopts bridge-tied load BTL (Bridge Tied load), which has two power amplifier output terminals. The output of one power amplifier is the mirror image of the other output terminal. The two output waveforms are in phase The difference is 180°, and the amplitude is twice that of the single-ended output waveform; the filter adopts LCL topology to filter out high-order harmonics, ensuring that the waveform is not distorted and does not introduce harmonics to the grid; the sampling feedback module is used for acquisition and filtering The output signal of the device is fed back to the AD acquisition terminal of the real-time digital simulation module, and the system forms a closed loop to eliminate errors. 2. power grid simulation device as claimed in claim 1, is characterized in that, described power grid simulation device is used for simulating voltage drop, three-phase unbalance, frequency fluctuation; It connects RTDS simulation software and kind together, has reliable half Physical simulation function; use the real-time digital simulation module (RTDS) to establish and simulate the power grid model, output the voltage and current waveform of a certain node, and amplify the amplitude and power of the waveform through an external power amplifier to ensure that the waveform is not distorted and does not introduce harmonics to the power grid , at the same time, feedback links can be added as needed. 3. The power grid simulation device as claimed in claim 1, characterized in that, the power grid simulation device mainly comprises RTDS and power amplifier, and RTDS can select power system simulation software or controller approved by the industry for use, and the latter is a self-developed power amplifier , the power amplifier adopts digital power amplifier technology, its core is a digital power amplifier chip, and its switching frequency can reach 300kHz. 4. The power grid simulation device according to claim 1, wherein the power amplifier adopts a two-stage form, the first stage converts the sine wave output by the RTDS into a 5V PWM signal, and the second stage uses the PWM waveform as a driving signal , to drive the digital power amplifier chip to output PWM; the output method adopts the bridge-tied load BTL (Bridge Tied load), and the dual output with a mutual difference of 180°, the final voltage is twice that of the original single-ended output. 5. The power grid simulation device according to claim 1, characterized in that, for the actual power grid, the power amplifier considers the range of power grid harmonics to be within 10KHz, and the switching frequency of the digital power amplifier chip can reach 300KHz, which is the former 30 times; therefore, the harmonics introduced by the device can be ignored; at the same time relying on the 300kHz switching frequency, the design of the low-pass filter is very simple, and the requirements for LC parameters are very low, and the size of the filter is also small; the filter Adopt LCL structure. 6. The power grid simulation device as claimed in claim 1, characterized in that, said power amplifier, because the dispersion of digital power amplifier chips is very small, different digital power amplifier chips input the same waveform, and the waveforms after filtering output are almost the same , Therefore, three single-phase amplifiers are connected in parallel to build a three-phase power amplifier, and the power level can also be increased by connecting power amplifier chips in parallel. 7. The power grid simulation device as claimed in claim 1, characterized in that, the output voltage and power of the power amplifier are limited by the digital power amplifier chip, in addition to increasing the power level by connecting the power amplifier chips in parallel, a boost voltage can also be selected. The transformer boosts the output voltage.