CN117220340A - SPWM (sinusoidal pulse Width modulation) method of photovoltaic grid-connected micro inverter based on phase detection - Google Patents
SPWM (sinusoidal pulse Width modulation) method of photovoltaic grid-connected micro inverter based on phase detection Download PDFInfo
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Abstract
The invention relates to a photovoltaic grid-connected micro inverter SPWM (sinusoidal pulse Width modulation) modulation method based on phase detection, which comprises the steps of firstly realizing high-speed and high-precision sampling of grid voltage through an acquisition module; then establishing a power grid voltage phase angle set; then the control system judges whether the power grid voltage is in a power grid zero crossing interval according to the sampled power grid voltage amplitude, and the power grid zero crossing interval is correspondingly divided into two states: zero-crossing state T1, non-zero-crossing state T2; the control system respectively performs phase angle control on the two states, if the state is in a zero crossing state T1, the current phase angle is set to 0, and if the state is in a non-zero crossing state T2, the current phase angle is the sum of the phase angle at the last moment and a fixed difference value; and finally, the control system multiplies the current phase angle information by the amplitude of the modulation wave, and compares the multiplied value with a carrier wave to further realize SPWM (sinusoidal pulse Width modulation). Compared with other SPWM (sinusoidal pulse Width modulation) strategies based on detection of grid-connected voltage phases, the method has higher accuracy.
Description
Technical Field
The invention relates to a photovoltaic grid-connected control method, in particular to a SPWM (sinusoidal pulse Width modulation) method of a photovoltaic grid-connected micro inverter.
Background
With the irreproducibility of traditional energy sources and irreversible damage to the environment caused by unlimited exploitation of traditional energy sources, people tend to use renewable energy sources, and solar energy is widely applied due to the excellent characteristics of safety, universality, cleanliness, large storage capacity and the like, so that the photovoltaic power generation technology is also developed rapidly. Sinusoidal pulse width modulation (Sinusoidal Pulse Width Modulation, SPWM) is used as a supporting technology of a photovoltaic power generation technology, and the core is that a pulse width is changed according to a sinusoidal rule and a PWM waveform equivalent to the sinusoidal wave drives a high-frequency switching tube of direct current chopper (DC/DC) and alternating current inverter (DC/AC) in a photovoltaic micro-inverter so as to realize energy grid connection, and the photovoltaic micro-inverter is a common photovoltaic grid connection modulation strategy.
The core part of SPWM modulation in the photovoltaic micro inverter is that the public power grid voltage is subjected to phase-locked loop control to obtain the power grid angle, and the traditional phase-locked loop has the following defects that firstly, the phase angle of the acquired power grid voltage and the real angle of the power grid voltage have larger errors; secondly, after the power grid voltage amplitude is distorted, the phase angle acquired by the phase-locked loop is too large in difference with the actual value; finally, the traditional phase-locked loop needs to increase the material cost of the photovoltaic micro-inverter in hardware design, and if the traditional phase-locked loop is realized by software design, the task amount of an execution program is increased, and the calculation burden of data acquisition and numerical analysis of a photovoltaic system is increased.
Disclosure of Invention
The invention aims to: aiming at the problems, the SPWM modulation method of the photovoltaic grid-connected micro inverter based on phase detection is provided, and the performance of accurately tracking the voltage phase of a power grid by an SPWM driving signal is improved.
The technical scheme is as follows: the SPWM (sinusoidal pulse Width modulation) method for the photovoltaic grid-connected micro inverter based on phase detection comprises the following steps of:
s1: the acquisition module is used for acquiring the power grid voltage v g Sampling at a high rate;
s2: dividing a half period of the power grid voltage into a limited number of phase angles with equal spacing according to the sampling frequency of the acquisition module to obtain a phase angle sample set R θ {θ 1 ,θ 2 ,θ 3 … and phase angle fixed difference θ e ；
S3: the control module judges whether the power grid voltage is in a zero crossing point interval according to the amplitude of the acquired power grid voltage and correspondingly divides the power grid voltage into two states: zero-crossing state T1, non-zero-crossing state T2; then, respectively performing phase angle control according to the states, if the system is in a zero crossing state T1, setting the current phase angle to 0, and if the system is in a non-zero crossing state T2, setting the current phase angle to be the sum of the fixed difference value of the angle and the phase angle at the last moment;
s4: the control module multiplies the current discrete phase angle information by the amplitude of the modulation wave, and compares the multiplied value with a carrier wave to realize SPWM modulation.
Further, in S1, the sampling frequency of the acquisition module is nHz, and n is not less than 10 3 For the instantaneous continuous value v of the grid voltage g (t) performing high-rate discrete point sampling to respectively obtain sampling values of the power grid voltage at the current moment and the power grid voltage at the previous moment:
in the formula, v g [k]K is the sampling moment point for sampling the instantaneous value of the power grid voltage; v (V) ac Amplitude value of the grid voltage; ω is the grid angular frequency.
Further, in S2, the phase angle set R θ Fixed phase angle difference θ e Expressed as:
wherein n is the sampling frequency of the acquisition module, the unit is Hz, and n is more than or equal to 10 3 。
Further, in the step S3, according to the collected grid voltage amplitude v g [k]Judging whether the power grid voltage is in a zero crossing point interval or not according to the magnitude of the power grid voltage, and corresponding to a system state X k The basis of the judging formula is as follows:
wherein X is k In the system state, T1 represents a zero-crossing state, and T2 represents a non-zero-crossing state; v (V) ac Amplitude value of the grid voltage; n is the sampling frequency of the acquisition module, the unit is Hz, and n is more than or equal to 10 3 。
Further, in the step S4, the amplitude D of the modulated wave is obtained after tracking and controlling the photovoltaic micro inverter through the maximum power point s Then updating the phase angle value theta [ k ] of the current time obtained in the step S4]Amplitude D of modulated wave s And (3) multiplying, wherein the multiplied value d is a modulation wave signal value for realizing SPWM, namely:
wherein X is k Representing a system state;
comparing the modulated wave signal value d with a carrier wave to generate a high-frequency switching tube control signal; when the modulated wave signal value d is larger than the carrier signal value, the high-frequency switching tube driving signal in the photovoltaic micro-inverter is set to be in a high-level state, and the high-frequency switching device S m Opening; when the modulated wave signal value d is smaller than the carrier signal value, the high-frequency switching tube driving signal in the photovoltaic micro-inverter is set to be low level, and the high-frequency switching device S m Turning off; and the phase angle is updated again every half of the grid cycle.
The beneficial effects are that: the invention provides an SPWM (sinusoidal pulse Width modulation) method based on a traditional phase-locked loop, which is characterized in that a high-precision phase detection-based SPWM strategy of a photovoltaic grid-connected micro inverter is provided, a phase angle set is established after grid voltage signals are acquired at a high speed and high precision, a control system judges the grid voltage signals and completes phase angle control, the synchronization precision of the SPWM driving signals and grid-connected voltage is improved, the problem that the actual phase of the grid and the phase error obtained by phase locking are overlarge due to the traditional phase-locked loop after sampling and equal discrimination operations is solved, and meanwhile, the wrong phase angle caused by sudden change of the grid-connected voltage can be filtered out.
Drawings
FIG. 1 is an overall control block diagram of the SPWM modulation method of the photovoltaic grid-connected micro inverter of the present invention;
fig. 2 is a phase angle control mechanism diagram of the SPWM modulation method of the photovoltaic grid-connected micro inverter of the present invention;
fig. 3 is a schematic diagram of SPWM modulation of the SPWM modulation method of the photovoltaic grid-connected micro inverter of the present invention.
Detailed Description
The present invention will be described in further detail by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and not limited to the following examples.
The integral control block diagram is shown in fig. 1, a phase angle set is established after grid voltage signals are acquired at high speed and high precision, then a control module judges the grid voltage state according to the grid voltage signal amplitude obtained by sampling and completes phase angle control, the angle information of the phase angle control is multiplied by the modulation wave amplitude, and the multiplication value is compared with a carrier wave to finally realize SPWM modulation.
Specifically, the method comprises the following steps:
s1: the sampling frequency of the designed acquisition module is nHz, and n is more than or equal to 10 3 For instantaneous continuous value v of public network voltage g (t)＝V ac sin (ωt) performs high-rate discrete point sampling to respectively obtain sampling values of the power grid voltage at the current moment and the power grid voltage at the previous moment:
in the formula, v g [k]K is a discrete point in the sampling moment; v (V) ac The amplitude value is 311, which is the amplitude value of the grid voltage; omega is the angular frequency of the power grid; n is the sampling frequency of the acquisition module.
Step 2: power grid according to sampling frequency of acquisition moduleDividing the voltage half period into a limited number of equal phase angle information to obtain a phase angle set R θ And a phase angle fixed difference value theta e Expressed as:
step 3: according to the acquired power grid voltage amplitude v g [k]Judging whether the power grid voltage is in a zero crossing point interval or not according to the magnitude of the power grid voltage, and corresponding to a system state X k The basis of the judging formula is as follows:
wherein X is k Is a system state; t1 represents a zero-crossing state; t2 represents a non-zero crossing state. If the system state X k Will be T1, then it means now in the zero crossing interval; if the system state X k Will be T2, then this indicates that it is now in a non-zero crossing interval.
The phase angle of the power grid voltage at the current moment and the phase angle of the power grid voltage at the last moment are respectively expressed as theta [ k ]]And theta [ k-1 ]]If the system state X k In the zero crossing state T1, the current phase angle is set to 0, if the system state X k In the non-zero crossing state T2, the current phase angle is set as the fixed difference value theta between the angle and the phase angle at the last moment e The sum corresponds to the formula:
thereby obtaining the latest phase angle value theta k at the current moment.
Step 4: photovoltaic micro-inverter via Maximum power point tracking control (Maximum Power Point Tracking (MPPT) to obtain amplitude D of modulated wave s Then the phase angle information theta [ k ] at the current moment]Amplitude D of modulated wave s And (3) multiplying, wherein the multiplied value d is a modulation wave signal value for realizing SPWM, namely:
comparing the modulated wave signal value d with a carrier wave to generate a high-frequency switching tube control signal; when the modulated wave signal value d is larger than the carrier signal value, the high-frequency switching tube driving signal in the photovoltaic micro-inverter is set to be in a high-level state, and the high-frequency switching device S m Opening; when the modulated wave signal value d is smaller than the carrier signal value, the high-frequency switching tube driving signal in the photovoltaic micro-inverter is set to be low level, and the high-frequency switching device S m Turning off; and since the phase angle will be updated again every half grid period (100 Hz), the generated SPWM (Sinusoidal Pulse Width Modulation) modulated signal will track the grid voltage phase angle with high accuracy.
According to the SPWM control method for the photovoltaic grid-connected micro inverter, the acquisition module acquires the power grid voltage amplitude at a high speed and with high precision, data are transmitted to the control module, the control module judges zero crossing points and completes phase angle control by comparing phase angle sets, and finally SPWM control is carried out on the product value, so that a modulation signal synchronous with the power grid voltage is generated. Fig. 2 shows a phase angle control mechanism, i.e. when the grid voltage is in a zero crossing state of the area or in a non-zero crossing state outside the area, respectively, the phase angle control is performed, wherein the frequency of the phase angle cycle update is twice the grid period (i.e. 100 Hz), which simplifies the phase angle detection mechanism to a certain extent; FIG. 3 shows the SPWM modulation principle, the current phase angle and the amplitude D of the modulated wave obtained by the photovoltaic micro-inverter through maximum power point tracking control (Maximum Power Point Tracking, MPPT) s And (3) multiplying to obtain a modulated wave d, and comparing the modulated wave with a carrier wave to finally realize high-precision SPWM modulation. Compared with the traditional phase-locked loop, the SPWM strategy of the photovoltaic grid-connected micro inverter based on high-precision phase detection is further improvedThe phase synchronization precision of the SPWM driving signal and the grid-connected voltage is improved.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (5)
1. The SPWM (sinusoidal pulse Width modulation) method for the photovoltaic grid-connected micro inverter based on phase detection is characterized by comprising the following steps of:
s1: the acquisition module is used for acquiring the power grid voltage v g Sampling at a high rate;
s2: dividing a half period of the power grid voltage into a limited number of phase angles with equal spacing according to the sampling frequency of the acquisition module to obtain a phase angle sample set R θ {θ 1 ,θ 2 ,θ 3 … and phase angle fixed difference θ e ；
S3: the control module judges whether the power grid voltage is in a zero crossing point interval according to the amplitude of the acquired power grid voltage and correspondingly divides the power grid voltage into two states: zero-crossing state T1, non-zero-crossing state T2; then, respectively performing phase angle control according to the states, if the system is in a zero crossing state T1, setting the current phase angle to 0, and if the system is in a non-zero crossing state T2, setting the current phase angle to be the sum of the fixed difference value of the angle and the phase angle at the last moment;
s4: the control module multiplies the current discrete phase angle information by the amplitude of the modulation wave, and compares the multiplied value with a carrier wave to realize SPWM modulation.
2. The phase detection-based SPWM (sinusoidal pulse Width modulation) method for a photovoltaic grid-connected micro inverter according to claim 1, wherein in S1, the sampling frequency of the acquisition module is nHz, and n is more than or equal to 10 3 For the instantaneous continuous value v of the grid voltage g (t) performing high-rate discrete point sampling to respectively obtain sampling values of the power grid voltage at the current moment and the power grid voltage at the previous moment:
in the formula, v g [k]K is the sampling moment point for sampling the instantaneous value of the power grid voltage; v (V) ac Amplitude value of the grid voltage; ω is the grid angular frequency.
3. The phase detection-based SPWM (sinusoidal pulse Width modulation) method for a photovoltaic grid-connected micro-inverter according to claim 1, wherein in S2, the phase angle set R θ Fixed phase angle difference θ e Expressed as:
wherein n is the sampling frequency of the acquisition module, the unit is Hz, and n is more than or equal to 10 3 。
4. The phase detection-based SPWM (sinusoidal pulse Width modulation) method for a photovoltaic grid-connected micro-inverter according to claim 1, wherein in S3, according to the collected grid voltage amplitude v g [k]Judging whether the power grid voltage is in a zero crossing point interval or not according to the magnitude of the power grid voltage, and corresponding to a system state X k The basis of the judging formula is as follows:
wherein X is k In the system state, T1 represents a zero-crossing state, and T2 represents a non-zero-crossing state; v (V) ac Amplitude value of the grid voltage; n is the sampling frequency of the acquisition module, the unit is Hz, and n is more than or equal to 10 3 。
5. The method for SPWM modulation of a photovoltaic grid-connected micro-inverter based on phase detection according to claim 1, wherein in S4, the amplitude D of the modulated wave is obtained after tracking and controlling the photovoltaic micro-inverter via the maximum power point s Then updating the phase angle value theta [ k ] of the current time obtained in the step S4]Amplitude D of modulated wave s And (3) multiplying, wherein the multiplied value d is a modulation wave signal value for realizing SPWM, namely:
wherein X is k Representing a system state;
comparing the modulated wave signal value d with a carrier wave to generate a high-frequency switching tube control signal; when the modulated wave signal value d is larger than the carrier signal value, the high-frequency switching tube driving signal in the photovoltaic micro-inverter is set to be in a high-level state, and the high-frequency switching device S m Opening; when the modulated wave signal value d is smaller than the carrier signal value, the high-frequency switching tube driving signal in the photovoltaic micro-inverter is set to be low level, and the high-frequency switching device S m Turning off; and the phase angle is updated again every half of the grid cycle.
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