CN108199601A - A kind of single-phase cascade ac high frequency chain bidirectional converter modulator approach - Google Patents

Abstract

The present invention discloses a kind of single-phase cascade ac high frequency chain bidirectional converter modulator approach, and the DC power supply of each high frequency chain element generates the identical d. c. voltage signal of amplitude；Preceding-stage inversion device is modulated d. c. voltage signal, generates identical high frequency square wave voltage signal；High frequency transformer carries out voltage class transformation and electrical isolation；Matrix converter carries out coupling modulation of unhitching, and matrix converter is equivalent to the inverter of two groups of independence, is respectively controlled；Using carrier phase cascade modulation between each high frequency chain element, each high frequency chain element output voltage level is joined, stable sine wave is generated after filtered.The method of the present invention flexibility and reliability can obtain higher equivalent switching frequency, improve output voltage waveforms, reduce output harmonic wave under relatively low devices switch frequency.

Description

A single-phase cascaded AC high-frequency link bidirectional converter modulation method

technical field

The invention relates to micro-grid and energy storage technology, in particular to a single-phase cascaded AC high-frequency link bidirectional converter modulation method.

Background technique

Energy storage converter technology is developing towards the direction of large capacity, high conversion efficiency, high frequency isolation and low application cost. Single-phase cascaded AC high-frequency link topology. The AC side is composed of N high-frequency link units cascaded. By increasing the rated current of the AC high-frequency link power unit and the capacity of the single battery, the energy storage system can be increased in capacity. The cascaded AC high-frequency link structure can be directly connected to the 10kV power grid, avoiding the loss of power frequency transformers and filters, and improving efficiency; it can reduce the insulation design requirements for energy storage batteries through high-frequency isolation; in a certain AC high-frequency link power unit In case of failure, it can be bypassed to achieve redundant fault-tolerant operation, especially suitable for high-power applications.

At present, the modulation methods commonly used in high-frequency chain circuits include unipolar phase-shift SPWM modulation, bipolar phase-shift SPWM modulation, decoupling and coupling modulation, etc.; the modulation methods commonly used in cascaded multi-level circuits include ladder wave modulation, space Vector modulation method, phase shift PWM modulation method. These modulation methods are widely used, and the research is relatively mature. However, at this stage, the research on the comprehensive modulation of combining these two circuit modulation methods to generate cascaded AC high-frequency chain circuits is still relatively lacking, and there are problems such as poor output waveform quality, poor scalability, High system cost and other issues.

Contents of the invention

The purpose of the present invention is to provide a single-phase cascaded AC high-frequency link bidirectional converter modulation method, which combines the decoupling and coupling modulation strategy of the AC high-frequency link with the cascaded multi-level carrier phase-shift modulation technology to reduce the output voltage harmonics , Improve the equivalent switching frequency and transmission bandwidth.

The technical solution to realize the purpose of the present invention is: a single-phase cascaded AC high-frequency link bidirectional converter modulation method, including the following steps:

Step 1. The DC power supply of each high-frequency chain unit generates a DC voltage signal with the same amplitude;

Step 2. The front-stage inverters of each high-frequency chain unit modulate the DC voltage signal to generate the same high-frequency square wave voltage signal;

Step 3, the high-frequency transformer of each high-frequency chain unit performs voltage level conversion and electrical isolation;

Step 4. The matrix converters of each high-frequency link unit adopt decoupling and coupling modulation, and the matrix converters are equivalent to two sets of independent inverters, which are controlled separately;

Step 5. Carrier phase-shift cascade modulation is adopted between each high-frequency chain unit, and the output voltage of each high-frequency chain unit is cascaded, and a stable sine wave is generated after filtering.

Compared with the prior art, the present invention has the remarkable advantages: 1) each AC high-frequency link unit of the present invention adopts the same decoupling and coupling modulation mode, and the control method is simple and effective; 2) the present invention can realize The cascading of AC high-frequency chain units further improves the system capacity; 3) The present invention adopts the method of carrier phase shift, which can effectively increase the equivalent switching frequency, offset the low-order harmonic components of the system, and improve the output waveform quality.

Description of drawings

Figure 1 is a topology diagram of a single AC high-frequency chain unit;

Fig. 2 is a topological structure diagram after each unit of N is cascaded;

Figure 3 is a schematic diagram of the decoupling of the decoupled SPWM modulation strategy;

FIG. 4 is a driving waveform diagram of a decoupling modulation strategy;

Figure 5 is a partial expanded view of the output waveform of a single high-frequency chain unit;

Figure 6 is an FFT analysis diagram of the output waveform of a single high-frequency chain unit;

Figure 7 is a waveform diagram of the output voltage of the cascaded high-frequency chain converter;

Figure 8 is an FFT analysis diagram of the output voltage waveform of the cascaded high-frequency link converter.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Figure 1 is the topological structure of a single AC high-frequency chain unit, which includes several parts such as a DC power supply, a pre-stage inverter bridge, a high-frequency transformer, and a matrix converter. Figure 2 is the circuit topology after N units are cascaded, and each unit uses a DC power supply independently. For the circuit topology in Fig. 2, the present invention provides a single-phase cascaded AC high-frequency link bidirectional converter modulation method, which combines the AC high-frequency link decoupling and coupling modulation strategy with the cascaded multi-level carrier phase-shift modulation technology. The principle of modulation is introduced below to facilitate the understanding of subsequent schemes.

The decoupling principle of decoupling SPWM modulation strategy is: in a high-frequency cycle, the high-frequency inverter bridge produces a bipolar square wave signal with a duty ratio of 0.5. If only half of the high-frequency cycle is considered, the matrix The input of the formula converter can be regarded as a constant DC signal. When the output voltage on the primary side of the transformer is positive, the inverter bridge composed of S1a, S2a, S3a, and S4a works; when the output voltage on the primary side of the transformer is negative, the inverter bridge composed of S1b, S2b, S3b, and S4b works. The coupling principle is shown in Figure 3. In this way, the matrix converter is decoupled into two independent common inverters connected in series, and when one set of inverter bridges is working, all the switch tubes of the other set of inverter bridges remain on.

The principle of decoupling and coupling SPWM modulation strategy is: triangular carrier and sinusoidal modulation wave intersect to generate two complementary SPWM waveforms, and then logically combine them with square wave signals generated by high frequency inverters to generate matrix respectively The driving signal of each switching tube of the type converter. The driving signal waveform of the decoupling modulation strategy is shown in Figure 4, where SPWM1 and SPWM2 are two complementary SPWM signals generated by comparing the sinusoidal modulation wave with the triangular carrier wave, and V1 and V2 are the duty cycles generated by the high-frequency inverter is a complementary square wave signal of 0.5, the logic relationship of the driving signals of each switch tube of the matrix converter is:

S1a/S4a=V2+SPWM1 S2a/S3a=V2+SPWM2

S2b/S3b=V1+SPWM1 S1b/S4b=V1+SPWM2 (1)

The single-phase cascaded AC high-frequency link bidirectional converter modulation method includes the following steps:

Step 1. Each high-frequency chain unit uses an independent DC power supply to generate DC voltage signals with the same amplitude.

Step 2. The front-stage inverter of the high-frequency chain unit modulates the DC voltage signal. The modulation mode of the front-stage inverter in each high-frequency chain unit is the same, and the same high-frequency square wave voltage signal is generated. The amplitude is the value of the DC power supply voltage, and the cycle Twice the period of the triangular carrier.

Step 3. Each high-frequency chain unit uses the same high-frequency transformer with the same parameters such as operating frequency, transformation ratio, and capacity, and performs voltage level conversion and electrical isolation.

Step 4. The matrix converters of each high-frequency link unit are modulated by decoupling, and the matrix converters are equivalent to two sets of independent inverters, which are controlled separately. During decoupling modulation, the triangular carrier wave is compared with the sine modulation wave to generate two complementary SPWM signals. When the output voltage of the transformer is positive, the positive inverter works; when the output voltage of the transformer is negative, the negative inverter works. Inverter works, when one group of inverters is working, the switching tube of the other group of inverters remains on.

Step 5. Carrier phase-shift cascade modulation is adopted between each high-frequency chain unit, and the output voltage of each high-frequency chain unit is cascaded, and a stable sine wave is generated after filtering. During carrier phase shift modulation, the sinusoidal modulation wave is exactly the same, the triangular carrier frequency and amplitude are the same, but the phase difference is 1/N of the period, where N is the number of high frequency chain units.

Example 1

The experimental simulation model is built in Matlab. The system parameters are as follows: sine modulation wave frequency 50Hz, triangular carrier frequency 20kHz, DC power supply voltage 24V, transformer ratio 48:300, and the partially expanded waveform of the output voltage of a single AC high-frequency link unit is shown in Figure 5. , whose amplitude is ±150V two-state SPWM wave. The Fourier analysis of the output voltage is shown in Figure 6, and its harmonics are mainly distributed around the carrier frequency and its multiplier.

The cascading of four high-frequency chain units is realized by means of triangular carrier phase shifting. The phase difference of each unit’s triangular carrier is 1/4 of the carrier period from the adjacent unit. Figure 7 is the output voltage waveform after cascading, and its voltage amplitude is a single The output voltage amplitude of the high-frequency chain unit is 4 times, and the number of levels is increased at the same time. Figure 8 is the Fourier analysis of the output voltage after cascading, and its main harmonics are concentrated around 80kHz, which is equivalent to 4 times the triangular carrier frequency. It can be seen that cascading N high-frequency chain units by using carrier phase-shift modulation can increase the equivalent switching frequency by N times without fundamental wave loss, and greatly improve the harmonic characteristics of the output waveform.

Claims (6)

1. a kind of single-phase cascade ac high frequency chain bidirectional converter modulator approach, which is characterized in that include the following steps：

The identical d. c. voltage signal of step 1, the DC power supply generation amplitude of each high frequency chain element；

Step 2, each high frequency chain element preceding-stage inversion device d. c. voltage signal is modulated, generate identical high frequency square wave electricity Press signal；

Step 3, the high frequency transformer progress voltage class transformation of each high frequency chain element and electrical isolation；

Step 4, each high frequency chain element matrix converter using unhitch coupling modulation, by matrix converter be equivalent to two groups it is only Vertical inverter, is respectively controlled；

Using carrier phase cascade modulation between step 5, each high frequency chain element, each high frequency chain element output voltage level is joined, through filter Stable sine wave is generated after wave.

2. single-phase cascade ac high frequency chain bidirectional converter modulator approach according to claim 1, which is characterized in that step Each high frequency chain element uses independent DC power supply in 1.

3. single-phase cascade ac high frequency chain bidirectional converter modulator approach according to claim 1, which is characterized in that step The modulation system of each high frequency chain element preceding-stage inversion device is identical in 2, and the high-frequency square-wave signal amplitude of generation is direct current power source voltage Value, period are coupling modulation twice of the triangular carrier cycle of unhitching.

4. single-phase cascade ac high frequency chain bidirectional converter modulator approach according to claim 1, which is characterized in that step Each high frequency chain element uses identical high frequency transformer in 3, and working frequency, no-load voltage ratio, capacity are consistent.

5. single-phase cascade ac high frequency chain bidirectional converter modulator approach according to claim 1, which is characterized in that step 4 unhitch coupling modulation in triangular carrier and sinusoidal modulation wave are compared, generation two-way complementation SPWM signals, when transformer is defeated Go out voltage for timing, it is positive to organize inverter work, when transformer output voltage is negative, bear group inverter work, one group of inverter During work, the switching tube of another group of inverter is held on.

6. single-phase cascade ac high frequency chain bidirectional converter modulator approach according to claim 1, which is characterized in that step Sinusoidal modulation wave is identical in the modulation of 5 carrier phases, and triangular carrier frequency, amplitude are identical, but the 1/ of the period is differed in phase N, wherein N are the number of high frequency chain element.