CN114362180B - Compensation method, system, storage medium and computing device for LCL type grid-connected inverter - Google Patents
Compensation method, system, storage medium and computing device for LCL type grid-connected inverter Download PDFInfo
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Abstract
Description
技术领域Technical Field
本发明涉及一种LCL型并网逆变器补偿方法、系统、存储介质及计算设备,属于并网控制技术领域。The invention relates to a compensation method, system, storage medium and computing device for an LCL type grid-connected inverter, belonging to the technical field of grid-connected control.
背景技术Background Art
并网逆变器通常作为分布式发电系统与公共电网的接口,将可再生能源发出的电能以交流电的形式注入电网。随着分布式电源的位置分布越来越广泛,电网逐渐表现出弱网特性,通常用短路比(SCR)描述电网的强弱程度,电网阻抗越大,SCR值越小,系统弱网特性越强,此时并网电流流经电网阻抗的线路压降不可忽略,公共耦合点(PCC)电压不再近似为电网电压。Grid-connected inverters usually serve as the interface between distributed power generation systems and the public power grid, injecting the electricity generated by renewable energy into the grid in the form of alternating current. As the locations of distributed power sources become more and more widespread, the power grid gradually exhibits weak grid characteristics. The short circuit ratio (SCR) is usually used to describe the strength of the power grid. The larger the grid impedance, the smaller the SCR value, and the stronger the weak grid characteristics of the system. At this time, the line voltage drop of the grid-connected current flowing through the grid impedance cannot be ignored, and the voltage at the point of common coupling (PCC) is no longer approximately the grid voltage.
在弱网情况下,锁相环(PLL)对系统稳定性的影响会随着电网阻抗的不断增大而逐渐加剧。对于PLL输出相位而言,电网阻抗和并网电流是干扰量。当电网阻抗增大、并网电流增大时,会影响其输出相位的动静态性能,降低PLL的鲁棒性。锁相环性能的恶化导致了参考电流发生畸变,进一步造成入网电流发生畸变,入网功率发生振荡,严重时甚至使整个逆变器不能稳定运行而被保护装置从电网中切除。现有的考虑PLL影响的并网逆变器控制方法主要从锁相环结构或逆变器输出阻抗重塑来提高并网系统对弱电网的适应性。但在弱电网下,受风电、光伏等分布式新能源发电单元波动性以及负荷等的影响,电网存在背景谐波,且电网电感处于宽范围变化,仅从改进锁相环结构或对逆变器输出阻抗重塑单一方面很难保证并网电流质量和并网系统的稳定性。In the case of weak grid, the impact of the phase-locked loop (PLL) on system stability will gradually increase with the continuous increase of grid impedance. For the PLL output phase, the grid impedance and grid-connected current are interference quantities. When the grid impedance increases and the grid-connected current increases, it will affect the dynamic and static performance of its output phase and reduce the robustness of the PLL. The deterioration of the phase-locked loop performance leads to the distortion of the reference current, which further causes the distortion of the grid current and the oscillation of the grid power. In severe cases, the entire inverter cannot operate stably and is cut off from the grid by the protection device. The existing grid-connected inverter control method considering the influence of PLL mainly improves the adaptability of the grid-connected system to weak grids from the perspective of reshaping the phase-locked loop structure or the inverter output impedance. However, in weak grids, due to the volatility of distributed new energy power generation units such as wind power and photovoltaic power generation units and the load, there are background harmonics in the grid, and the grid inductance varies in a wide range. It is difficult to ensure the quality of the grid-connected current and the stability of the grid-connected system only from the perspective of improving the phase-locked loop structure or reshaping the inverter output impedance.
发明内容Summary of the invention
本发明的目的在于提出一种LCL型并网逆变器补偿方法、系统、存储介质及计算设备,在传统锁相环结构中引入低通滤波器,采用深度强化学习中的深度确定策略梯度(DeepDeterministic Policy Gradient,DDPG)算法,实现自适应小信号补偿,最大程度上抑制电网背景谐波对并网电流的影响。The purpose of the present invention is to propose a LCL type grid-connected inverter compensation method, system, storage medium and computing device, introduce a low-pass filter in the traditional phase-locked loop structure, and adopt the Deep Deterministic Policy Gradient (DDPG) algorithm in deep reinforcement learning to realize adaptive small signal compensation, so as to suppress the influence of grid background harmonics on grid-connected current to the greatest extent.
为达到上述目的,本发明采用的技术方案如下:To achieve the above object, the technical solution adopted by the present invention is as follows:
本发明提供一种LCL型并网逆变器补偿方法,包括:通过在LCL型并网逆变系统的锁相环q轴PI控制器前加入低通滤波器,滤除公共耦合点PCC电压高频扰动分量;The present invention provides a compensation method for an LCL type grid-connected inverter, comprising: adding a low-pass filter before a phase-locked loop q-axis PI controller of the LCL type grid-connected inverter system to filter out a high-frequency disturbance component of a common coupling point PCC voltage;
以及,采用以下方式补偿电网低频谐波扰动分量:And, the low-frequency harmonic disturbance component of the power grid is compensated in the following ways:
以LCL型并网逆变系统的锁相环频率、锁相环频率误差和频率误差的积分为DDPG智能体的输入,得到最优补偿系数和 The phase-locked loop frequency, phase-locked loop frequency error and integral of frequency error of the LCL grid-connected inverter system are used as the input of the DDPG agent to obtain the optimal compensation coefficient. and
最优补偿系数和经锁相环后得到并网电流扰动补偿量和调制电压扰动补偿量;Optimal compensation coefficient and After the phase-locked loop, the grid-connected current disturbance compensation amount and the modulation voltage disturbance compensation amount are obtained;
将并网电流扰动补偿量补偿入q轴并网电流处,将调制电压扰动补偿量补偿入并网电压处。The grid-connected current disturbance compensation amount is compensated into the q-axis grid-connected current, and the modulated voltage disturbance compensation amount is compensated into the grid-connected voltage.
进一步的,所述低通滤波器传递函数为:Furthermore, the low-pass filter transfer function is:
其中,GLPF为低通滤波器传递函数,ωc为低通滤波器截止频率,s为拉普拉斯算子。Where G LPF is the low-pass filter transfer function, ω c is the low-pass filter cutoff frequency, and s is the Laplace operator.
进一步的,锁相环传递函数表示为:Furthermore, the phase-locked loop transfer function is expressed as:
其中,为锁相环传递函数,HPLL(s)=kppll+kipll/s是锁相环PI控制器,kppll、kipll分别为锁相环PI控制器的比例项系数和积分项系数,是d轴公共耦合点电压稳态值。in, is the phase-locked loop transfer function, HPLL (s) = kppll + kipll /s is the phase-locked loop PI controller, kppll and kipll are the proportional term coefficient and the integral term coefficient of the phase-locked loop PI controller respectively, is the steady-state value of the voltage at the common coupling point on the d-axis.
本发明还提供一种LCL型并网逆变器补偿系统,包括DDPG智能体、补偿模块和低通滤波器;The present invention also provides a LCL type grid-connected inverter compensation system, comprising a DDPG intelligent body, a compensation module and a low-pass filter;
所述低通滤波器位于锁相环q轴PI控制器前,用于滤除公共耦合点PCC电压高频扰动分量;The low-pass filter is located before the phase-locked loop q-axis PI controller and is used to filter out the high-frequency disturbance component of the common coupling point PCC voltage;
所述DDPG智能体用于以LCL型并网逆变系统的锁相环频率、锁相环频率误差和频率误差的积分作为输入信号,产生最优补偿系数和 The DDPG agent is used to generate the optimal compensation coefficient using the phase-locked loop frequency, phase-locked loop frequency error and the integral of the frequency error of the LCL type grid-connected inverter system as input signals and
所述补偿模块用于,将最优补偿系数和经锁相环后得到并网电流扰动补偿量和调制电压扰动补偿量;以及将并网电流扰动补偿量补偿入q轴并网电流处,将调制电压扰动补偿量补偿入并网电压处。The compensation module is used to set the optimal compensation coefficient and After the phase-locked loop, the grid-connected current disturbance compensation amount and the modulation voltage disturbance compensation amount are obtained; and the grid-connected current disturbance compensation amount is compensated into the q-axis grid-connected current, and the modulation voltage disturbance compensation amount is compensated into the grid-connected voltage.
进一步的,Furthermore,
所述低通滤波器传递函数为:The low-pass filter transfer function is:
其中,GLPF为低通滤波器传递函数,ωc为低通滤波器截止频率,s为拉普拉斯算子。Where G LPF is the low-pass filter transfer function, ω c is the low-pass filter cutoff frequency, and s is the Laplace operator.
进一步的,所述低通滤波器截止频率ωc取2200Hz。Furthermore, the cut-off frequency ωc of the low-pass filter is 2200 Hz.
进一步的,所述补偿模块中,锁相环传递函数表示为:Furthermore, in the compensation module, the phase-locked loop transfer function is expressed as:
其中,为锁相环传递函数,HPLL(s)=kppll+kipll/s是锁相环PI控制器,kppll、kipll分别为锁相环PI控制器的比例项系数和积分项系数,是d轴公共耦合点电压稳态值。in, is the phase-locked loop transfer function, HPLL (s) = kppll + kipll /s is the phase-locked loop PI controller, kppll and kipll are the proportional term coefficient and the integral term coefficient of the phase-locked loop PI controller respectively, is the steady-state value of the voltage at the common coupling point on the d-axis.
进一步的,所述DDPG智能体采用下式作为奖励函数:Furthermore, the DDPG agent uses the following formula as the reward function:
其中,r为奖励函数,f为锁相环频率,f0为工频。Where r is the reward function, f is the phase-locked loop frequency, and f0 is the power frequency.
本发明第三方面提供一种存储一个或多个程序的计算机可读存储介质,所述一个或多个程序包括指令,所述指令当由计算设备执行时,使得所述计算设备执行根据前述的方法中的任一方法。A third aspect of the present invention provides a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which, when executed by a computing device, cause the computing device to perform any of the methods described above.
本发明第四方面提供一种计算设备,包括,A fourth aspect of the present invention provides a computing device, comprising:
一个或多个处理器、存储器以及一个或多个程序,其中一个或多个程序存储在所述存储器中并被配置为由所述一个或多个处理器执行,所述一个或多个程序包括用于执行根据前述的方法中的任一方法的指令。One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the aforementioned methods.
本发明达到的有益效果为:The beneficial effects achieved by the present invention are:
本发明提供一种LCL型并网逆变器补偿方法及系统,在传统锁相环q轴PI控制器前加入低通滤波器,采用深度强化学习中的深度确定策略梯度算法,对调制电压和并网电流进行自适应补偿,最大程度上抑制电网背景谐波对并网电流的影响。本发明可有效解决弱电网条件下因锁相环导致的并网电流畸变和并网系统失稳等问题,增强了并网逆变器对阻抗宽范围变化的适应能力,即使在存在电网背景谐波的情况下,锁相环频率依然能保持很小的稳态误差,有效地提高了并网逆变器系统的可靠性和鲁棒性。The present invention provides a LCL type grid-connected inverter compensation method and system, which adds a low-pass filter before the traditional phase-locked loop q-axis PI controller, adopts the deep determination policy gradient algorithm in deep reinforcement learning, and adaptively compensates the modulation voltage and grid-connected current, thereby suppressing the influence of the background harmonics of the power grid on the grid-connected current to the greatest extent. The present invention can effectively solve the problems of grid-connected current distortion and grid-connected system instability caused by the phase-locked loop under weak power grid conditions, enhances the adaptability of the grid-connected inverter to wide range impedance changes, and even in the presence of background harmonics of the power grid, the phase-locked loop frequency can still maintain a very small steady-state error, effectively improving the reliability and robustness of the grid-connected inverter system.
附图说明BRIEF DESCRIPTION OF THE DRAWINGS
图1为LCL型并网逆变器系统拓扑结构图;Figure 1 is a topological diagram of an LCL-type grid-connected inverter system;
图2为LCL型并网逆变器q轴控制框图;Figure 2 is a block diagram of the q-axis control of the LCL type grid-connected inverter;
图3为简化后的LCL型并网逆变器q轴控制框图;FIG3 is a simplified block diagram of the q-axis control of the LCL type grid-connected inverter;
图4为本发明改进的PLL的拓扑结构;FIG4 is a topological structure of the improved PLL of the present invention;
图5为本发明提供的LCL型并网逆变器小信号补偿控制框图;FIG5 is a small signal compensation control block diagram of an LCL type grid-connected inverter provided by the present invention;
图6为本发明提供的LCL型并网逆变器自适应小信号补偿控制框图;FIG6 is a block diagram of an adaptive small signal compensation control of an LCL type grid-connected inverter provided by the present invention;
图7为DDPG内部网络架构图;Figure 7 is a diagram of the internal network architecture of DDPG;
图8为本发明实施例中采用传统锁相环未加入补偿前的锁相环频率仿真图;FIG8 is a frequency simulation diagram of a conventional phase-locked loop before compensation is added in an embodiment of the present invention;
图9为本发明实施例中采用传统锁相环未加入补偿前的并网三相电压、电流仿真图;9 is a simulation diagram of the grid-connected three-phase voltage and current using a conventional phase-locked loop before adding compensation in an embodiment of the present invention;
图10为本发明实施例中采用改进锁相环加入自适应小信号补偿后的频率仿真图;FIG10 is a frequency simulation diagram of an improved phase-locked loop with adaptive small signal compensation added in an embodiment of the present invention;
图11为本发明实施例中采用改进锁相环加入自适应小信号补偿后的并网三相电压、电流仿真图。FIG. 11 is a simulation diagram of the grid-connected three-phase voltage and current after an improved phase-locked loop is used to add adaptive small signal compensation in an embodiment of the present invention.
具体实施方式DETAILED DESCRIPTION
下面对本发明作进一步描述。以下实施例仅用于更加清楚地说明本发明的技术方案,而不能以此来限制本发明的保护范围。The present invention is further described below. The following examples are only used to more clearly illustrate the technical solution of the present invention, and are not intended to limit the protection scope of the present invention.
本发明提供一种LCL型并网逆变器补偿方法,包括:The present invention provides a LCL type grid-connected inverter compensation method, comprising:
通过在LCL型并网逆变系统的锁相环q轴PI控制器前加入低通滤波器,滤除公共耦合点PCC电压高频扰动分量;By adding a low-pass filter before the phase-locked loop q-axis PI controller of the LCL type grid-connected inverter system, the high-frequency disturbance component of the PCC voltage at the common coupling point is filtered out;
以及,采用以下方式补偿电网低频谐波扰动分量:And, the low-frequency harmonic disturbance component of the power grid is compensated in the following ways:
以LCL型并网逆变系统的锁相环频率、锁相环频率误差和频率误差的积分为DDPG智能体的输入,得到最优补偿系数和 The phase-locked loop frequency, phase-locked loop frequency error and integral of frequency error of the LCL grid-connected inverter system are used as the input of the DDPG agent to obtain the optimal compensation coefficient. and
最优补偿系数和经锁相环后得到并网电流扰动补偿量和调制电压扰动补偿量;Optimal compensation coefficient and After the phase-locked loop, the grid-connected current disturbance compensation amount and the modulation voltage disturbance compensation amount are obtained;
将并网电流扰动补偿量补偿入q轴并网电流处,将调制电压扰动补偿量补偿入并网电压处。The grid-connected current disturbance compensation amount is compensated into the q-axis grid-connected current, and the modulated voltage disturbance compensation amount is compensated into the grid-connected voltage.
作为一种优选的实施方式,本实施例提供一种LCL型并网逆变器自适应小信号补偿方法,具体如下:As a preferred implementation, this embodiment provides an adaptive small signal compensation method for an LCL type grid-connected inverter, which is specifically as follows:
首先描述弱电网环境下LCL型并网逆变系统的拓扑结构,建立了考虑PLL影响的LCL型并网逆变器的小信号模型。如图1所示,LCL型并网逆变系统基于混合坐标系结构,其中L1,L2,Cf分别为逆变侧电感,网侧电感和滤波电容,Udc为直流侧电压,ua,ub,uc分别为a,b,c三相的桥臂电压,Uga,Ugb,Ugc分别为a,b,c三相电网电压,ω0为电网角频率,a,b,c三相公共耦合点电压Upcc_abc经过PLL输出相角为θ,Kc为电容电流反馈系数,电流环采用PI控制器,其表达式为Gi=(kp+ki/s),kp、ki分别为PI控制器的比例项系数和积分项系数,I1,I2,Ic分别为桥臂电流、并网电流和电容电流。控制原理为:a,b,c三相并网电流I2_abc经过派克变换后得到的I2d,I2q分别为d轴和q轴并网电流实际值,I2d,I2q与d轴和q轴并网电流参考值作差后输入PI控制器,对PI控制器输出信号经解耦后进行派克反变换,为抑制由LCL引入的高频谐振,本发明采用电容电流反馈有源阻尼法将派克反变换后的信号与电容电流反馈信号相减得到SVPWM的输入信号Urα和Urβ,通过SVPWM模块输出PWM信号来控制IGBT的开通和关断,从而实现并网。由于弱电网条件下,公共耦合点(PCC)电压易受干扰从而影响锁相环的动态特性,因此电网电压相角θ与锁相环输出相角θPLL之间存在偏差Δθ。Δθ的存在将dq坐标轴分为系统dq坐标轴和控制器dq坐标轴,现将θPLL和θ的参考坐标轴分别定义为c域和s域。变量x在这两个域间的关系可表示为:Firstly, the topological structure of the LCL grid-connected inverter system under weak power grid environment is described, and the small signal model of the LCL grid-connected inverter considering the influence of PLL is established. As shown in Figure 1, the LCL grid-connected inverter system is based on the hybrid coordinate system structure, where L 1 , L 2 , C f are the inverter side inductance, grid side inductance and filter capacitor respectively, U dc is the DC side voltage, u a , u b , u c are the bridge arm voltages of the three phases a, b, c respectively, U ga , U gb , U gc are the three phase grid voltages a, b, c respectively, ω 0 is the grid angular frequency, the voltage U pcc_abc of the three phases a, b, c common coupling point is θ after PLL output, K c is the capacitor current feedback coefficient, the current loop adopts PI controller, and its expression is G i = (k p + k i / s), k p , k i are the proportional term coefficient and integral term coefficient of the PI controller respectively, I 1 , I 2 , I c are the bridge arm current, grid current and capacitor current respectively. The control principle is: the three-phase grid-connected current I 2_abc obtained after Parker transformation is I 2d and I 2q, which are the actual values of the d-axis and q-axis grid-connected currents respectively. I 2d and I 2q are the reference values of the d-axis and q-axis grid-connected currents. After the difference is made, it is input into the PI controller. The output signal of the PI controller is decoupled and then subjected to Parker's inverse transformation. In order to suppress the high-frequency resonance introduced by LCL, the present invention adopts the capacitor current feedback active damping method to subtract the signal after Parker's inverse transformation from the capacitor current feedback signal to obtain the SVPWM input signals Urα and Urβ . The SVPWM module outputs the PWM signal to control the opening and closing of the IGBT, thereby achieving grid connection. Due to the weak grid condition, the voltage at the common coupling point (PCC) is susceptible to interference, thereby affecting the dynamic characteristics of the phase-locked loop. Therefore, there is a deviation Δθ between the grid voltage phase angle θ and the phase-locked loop output phase angle θ PLL. The existence of Δθ divides the dq coordinate axis into the system dq coordinate axis and the controller dq coordinate axis. The reference coordinate axes of θ PLL and θ are now defined as the c domain and s domain, respectively. The relationship between the variable x in these two domains can be expressed as:
式中:下标“d”和“q”分别代表d轴和q轴;下标“0”表示稳态值;Δx表示小信号扰动变量。Where: the subscripts “d” and “q” represent the d-axis and q-axis respectively; the subscript “0” represents the steady-state value; Δx represents the small signal disturbance variable.
并网逆变器电流环q轴控制框图如图2所示,其中Upccq、Urq和Icq分别为q轴PCC电压、q轴调制电压和q轴电容电流,Gde(s)为控制延时,表达式如下:The q-axis control block diagram of the grid-connected inverter current loop is shown in Figure 2, where U pccq , Urq and I cq are the q-axis PCC voltage, q-axis modulation voltage and q-axis capacitor current respectively, G de (s) is the control delay, and the expression is as follows:
其中,Ts为采样周期。Where Ts is the sampling period.
通过控制框图等效变换,图2可简化为图3,其中,Through the equivalent transformation of the control block diagram, Figure 2 can be simplified to Figure 3, where:
系统环路增益TA可表示为:The system loop gain TA can be expressed as:
TA(s)=Gx1(s)Gx2(s)Gde(s)Gi(s) (5)T A (s)=G x1 (s)G x2 (s)G de (s)G i (s) (5)
锁相环小信号模型为:The small signal model of the phase-locked loop is:
其中,GPLL(s)为锁相环传递函数,其表达式为HPLL(s)=kppll+kipll/s是锁相环PI控制器,kppll、kipll分别为锁相环PI控制器的比例项系数和积分项系数,是d轴PCC电压稳态值,为PCC电压小信号扰动量。将式(6)代入式(1),得:Where G PLL (s) is the phase-locked loop transfer function, which is expressed as H PLL (s) = k ppll + k ipll /s is a phase-locked loop PI controller, k ppll and k ipll are the proportional term coefficient and the integral term coefficient of the phase-locked loop PI controller respectively. is the steady-state value of the d-axis PCC voltage, is the PCC voltage small signal disturbance. Substituting equation (6) into equation (1), we get:
假设在单位功率因数条件下,则系统q轴稳态值为0,且PLL的动态特性仅会影响电网电流I2q和调制电压Urq,即,Assuming the power factor is unity, the system q-axis steady-state value is is 0, and the dynamic characteristics of PLL will only affect the grid current I 2q and the modulation voltage U rq , that is,
其中,分别为控制器q轴调制电压小信号扰动量和系统q轴调制电压小信号扰动量,为系统d轴调制电压稳态值,为控制器q轴并网电流小信号扰动量,为系统d轴并网电流稳态值。in, are the controller q-axis modulation voltage small signal disturbance and the system q-axis modulation voltage small signal disturbance, respectively. is the steady-state value of the system d-axis modulation voltage, is the controller q-axis grid-connected current small signal disturbance, is the steady-state value of the system d-axis grid-connected current.
弱电网下,并网逆变器q轴输出阻抗可表示为:Under weak power grid, the q-axis output impedance of the grid-connected inverter can be expressed as:
其中,in,
q轴并网电流小信号扰动量可表示为,The q-axis grid-connected current small signal disturbance can be expressed as:
由式(13)可知通过补偿q轴并网电流和调制电压可有效减小由锁相环引起的并网电流扰动。It can be seen from formula (13) that the grid current disturbance caused by the phase-locked loop can be effectively reduced by compensating the q-axis grid-connected current and the modulation voltage.
为抑制PCC电压高频扰动分量,减小因电网阻抗增大而产生的对锁相环输出相角的影响,根据前面建立的LCL型并网逆变器的小信号模型,从改造锁相环结构出发,提出含有低通滤波器的锁相环结构,如图4所示。在传统锁相环的基础上,在锁相环q轴PI控制器前加入低通滤波器,其传递函数可表示为,In order to suppress the high-frequency disturbance component of PCC voltage and reduce the In order to determine the influence of the phase-locked loop output phase angle, based on the small signal model of the LCL grid-connected inverter established above, a phase-locked loop structure with a low-pass filter is proposed, as shown in Figure 4. On the basis of the traditional phase-locked loop, a low-pass filter is added before the phase-locked loop q-axis PI controller, and its transfer function can be expressed as:
其中ωc为截止频率,ωc越小,抗干扰能力越好,但较小的ωc将导致较慢的响应速度。综合考虑,本发明选取ωc=2200。Wherein ω c is the cut-off frequency, the smaller ω c is, the better the anti-interference ability is, but a smaller ω c will lead to a slower response speed. After comprehensive consideration, the present invention selects ω c =2200.
由截止频率可知,低通滤波器可有效滤除PCC电压中7次以上的谐波,但电网本身存在丰富的低次背景谐波,这些谐波也会通过锁相环影响并网控制系统,仅通过在改进锁相环结构无法保证并网逆变器输出良好的并网电流质量,加入低通滤波器后的并网逆变器调制电压和并网电流处的小信号扰动可表示为,From the cut-off frequency, it can be seen that the low-pass filter can effectively filter out the 7th harmonics in the PCC voltage, but the power grid itself has abundant low-order background harmonics, which will also affect the grid-connected control system through the phase-locked loop. Only by improving the phase-locked loop structure, it is impossible to ensure that the grid-connected inverter outputs good grid-connected current quality. After adding the low-pass filter, the small signal disturbance at the modulation voltage and grid-connected current of the grid-connected inverter can be expressed as,
由式(13)可知通过补偿q轴并网电流和调制电压可有效减小由锁相环引起的并网电流扰动。假设并网逆变器工作在单位功率因数下且电网电压无波动,则电网电流稳态值等于所设定的d轴电流参考值调制电压稳态值可近似等于电网电压如图5所示,分别在并网电流反馈环和调制电压处加入相应的补偿即可消除锁相环对并网电流的影响。但在考虑存在电网背景谐波时,上述近似等效不再成立。From equation (13), it can be seen that by compensating the q-axis grid-connected current and the modulation voltage, the grid-connected current disturbance caused by the phase-locked loop can be effectively reduced. Assuming that the grid-connected inverter operates at unity power factor and the grid voltage does not fluctuate, the steady-state value of the grid current is Equal to the set d-axis current reference value Modulation voltage steady state value Can be approximately equal to the grid voltage As shown in Figure 5, adding corresponding compensation to the grid-connected current feedback loop and the modulation voltage can eliminate the influence of the phase-locked loop on the grid-connected current. However, when considering the existence of grid background harmonics, the above approximate equivalence is no longer valid.
为改善在存在电网背景谐波下并网逆变器的阻抗宽范围变化适应能力,在改进锁相环结构的基础上,加入自适应补偿,采用深度强化学习中的深度确定策略梯度(DeepDeterministic Policy Gradient,DDPG)算法,对调制电压和并网电流进行自适应补偿,改善弱电网条件下的并网电流畸变。In order to improve the adaptability of the grid-connected inverter to wide range impedance changes in the presence of grid background harmonics, adaptive compensation is added on the basis of improving the phase-locked loop structure. The Deep Deterministic Policy Gradient (DDPG) algorithm in deep reinforcement learning is used to adaptively compensate the modulation voltage and grid current, thereby improving the grid current distortion under weak grid conditions.
基于深度强化学习的深度确定策略梯度策略分为环境和智能体两大模块,环境部分是并网逆变器的物理模型,智能体部分包含策略(深度神经网络)和强化学习算法,训练过程中,强化学习算法依据观测值(Observation)和奖励(Reward)对策略部分不断进行更新,策略部分产生的动作指令(Action)作用到并网逆变器当中,从而形成并网逆变器与智能体之间的闭环控制。The deep deterministic policy gradient strategy based on deep reinforcement learning is divided into two modules: environment and agent. The environment is the physical model of the grid-connected inverter, and the agent includes the strategy (deep neural network) and reinforcement learning algorithm. During the training process, the reinforcement learning algorithm continuously updates the strategy based on the observation value (Observation) and reward (Reward). The action command (Action) generated by the strategy acts on the grid-connected inverter, thus forming a closed-loop control between the grid-connected inverter and the agent.
采用DDPG自适应补偿控制如图6所示,对调制电压扰动量和并网电流扰动量(式15、16、17)进行自适应补偿,即以锁相环频率误差和频率误差的积分为DDPG的输入通过算法得出一个最优补偿系数和来补偿锁相环引入的扰动分量,将补偿系数经锁相环后得到并网电流扰动补偿量(式(17)),补偿入q轴并网电流I2q处,再与q轴并网电流参考值作差后输入q轴PI控制器;q轴PI控制器的输出经解耦后得到并网电压;The DDPG adaptive compensation control is shown in Figure 6. The modulation voltage disturbance and the grid-connected current disturbance (Equations 15, 16, and 17) are adaptively compensated. That is, the phase-locked loop frequency error and the integral of the frequency error are used as the input of the DDPG to obtain an optimal compensation coefficient through the algorithm. and To compensate for the disturbance component introduced by the phase-locked loop, the compensation coefficient After the phase-locked loop, the grid-connected current disturbance compensation value (Equation (17)) is obtained, which is compensated into the q-axis grid-connected current I 2q and then compared with the q-axis grid-connected current reference value The difference is input into the q-axis PI controller; the output of the q-axis PI controller is decoupled to obtain the grid-connected voltage;
将补偿系数经锁相环后得到调制电压扰动补偿量(式(16)),补偿入并网电压处后再进行派克反变换;The compensation factor After the phase-locked loop, the modulation voltage disturbance compensation amount is obtained (Equation (16)), which is compensated into the grid-connected voltage and then subjected to the Park inverse transformation;
最后将派克反变换后的信号与电容电流反馈信号相减得到SVPWM的输入信号通过SVPWM模块输出PWM信号来控制IGBT的开通和关断,从而实现并网。Finally, the signal after Parker inverse transformation is subtracted from the capacitor current feedback signal to obtain the input signal of SVPWM, and the PWM signal is output through the SVPWM module to control the opening and closing of the IGBT, thereby achieving grid connection.
其中,锁相环传递函数为将锁相环频率f、误差信号f0-f以及误差信号积分∫(f0-f)作为DDPG的观测信号,记为s={f,f0-f,∫(f0-f)},其中,f0为工频;The phase-locked loop transfer function is: The phase-locked loop frequency f, the error signal f 0 -f and the error signal integral ∫(f 0 -f) are used as the observation signals of DDPG, denoted as s = {f, f 0 -f, ∫(f 0 -f)}, where f 0 is the power frequency;
被控量f经过奖励函数模块得到的值作为DDPG的奖励,记为r;奖励函数如式(18)所示。The value obtained by the controlled quantity f through the reward function module is used as the reward of DDPG, denoted as r; the reward function is shown in formula (18).
DDPG的输出动作为补偿系数和记为a,基于策略梯度的方法,DDPG的计算策略函数如式(19)所示,The output action of DDPG is the compensation coefficient and Denoted as a, based on the policy gradient method, the calculation strategy function of DDPG is shown in formula (19),
J(πθ)=∫∫ρ(s)πθ(s,a)r(s,a)dads=Es-ρ[r(s,a)] (19)J(π θ )=∫∫ρ(s)π θ (s,a)r(s,a)dads=E s-ρ [r(s,a)] (19)
进一步提升J(πθ)的梯度,即,Further improve the gradient of J(π θ ), that is,
式中,πθ为参数为θ的策略;J为策略函数;ρ为策略的概率分布;Es-ρ为s服从ρ分布的期望;为梯度;Q(s,a)为观测是s、动作是a的条件下,策略π的价值函数。经过迭代,能够给出最佳的补偿量。Where π θ is the strategy with parameter θ; J is the strategy function; ρ is the probability distribution of the strategy; E s-ρ is the expectation that s follows the ρ distribution; is the gradient; Q(s,a) is the value function of strategy π under the condition that the observation is s and the action is a. After iteration, the optimal compensation amount can be given.
为了在稳定范围内获取最佳的补偿量,本发明采用DDPG算法是深度强化学习的一个重要的分支,DDPG内部结构如图7所示,算法采用执行器-评价器结构,经验回放区用以存储智能体和环境之间的交互信息,在离线训练时,为避免经验间耦合,每次从经验回放区随机批量采样以训练网络参数。评价器目标是获取最佳估计值,从所获得奖励中计算价值函数,以正确评价执行器当前的动作。In order to obtain the best compensation amount within the stable range, the present invention adopts the DDPG algorithm, which is an important branch of deep reinforcement learning. The internal structure of DDPG is shown in Figure 7. The algorithm adopts an actuator-evaluator structure. The experience replay area is used to store the interaction information between the agent and the environment. During offline training, in order to avoid coupling between experiences, random batch sampling is performed from the experience replay area each time to train the network parameters. The evaluator's goal is to obtain the best estimate and calculate the value function from the reward obtained to correctly evaluate the current action of the actuator.
实施例Example
采用Matlab/Simulink进行仿真,DDPG算法具体的训练参数如表1所示,表2为LCL型并网逆变器参数设置如表2所示,Matlab/Simulink is used for simulation. The specific training parameters of the DDPG algorithm are shown in Table 1. Table 2 shows the parameter settings of the LCL type grid-connected inverter.
表1 DDPG算法训练参数Table 1 DDPG algorithm training parameters
表2 LCL型并网逆变器参数Table 2 Parameters of LCL grid-connected inverter
在相同的弱电网环境下,将本发明方法与传统方法进行对比。Under the same weak power grid environment, the method of the present invention is compared with the traditional method.
在电网阻抗为15mH时,通过三相可编程电压源加入3%的7次谐波和2%的5次谐波后,采用传统锁相环无补偿仿真结果如图8、图9所示,PLL误差约为15Hz,并网电流受电网电压畸变的影响产生明显的畸变,此时的电流畸变率THD为8.07%。采用本发明所提方法仿真结果如图10、图11所示,PLL误差约为0.7Hz,并网电流波形得到改善,此时的电流畸变率THD为2.07%。When the grid impedance is 15mH, after adding 3% of the 7th harmonic and 2% of the 5th harmonic through the three-phase programmable voltage source, the simulation results of the conventional phase-locked loop without compensation are shown in Figures 8 and 9. The PLL error is about 15Hz, and the grid-connected current is significantly distorted by the grid voltage distortion. At this time, the current distortion rate THD is 8.07%. The simulation results of the method proposed by the present invention are shown in Figures 10 and 11. The PLL error is about 0.7Hz, the grid-connected current waveform is improved, and the current distortion rate THD is 2.07%.
由仿真结果可知,本发明所提的基于深度强化学习的LCL型并网逆变器自适应小信号补偿方法可有效解决弱电网条件下因锁相环导致的并网电流畸变和并网系统失稳等问题,增强了并网逆变器对阻抗宽范围变化的适应能力,即使在存在电网背景谐波的情况下,锁相环频率依然能保持很小的稳态误差,所提控制方法能够有效地提高并网逆变器控制系统的可靠性和鲁棒性。It can be seen from the simulation results that the adaptive small signal compensation method of the LCL type grid-connected inverter based on deep reinforcement learning proposed in the present invention can effectively solve the problems of grid-connected current distortion and grid-connected system instability caused by the phase-locked loop under weak grid conditions, and enhance the adaptability of the grid-connected inverter to wide range of impedance changes. Even in the presence of grid background harmonics, the phase-locked loop frequency can still maintain a very small steady-state error. The proposed control method can effectively improve the reliability and robustness of the grid-connected inverter control system.
本发明另一个实施例提供一种LCL型并网逆变器自适应小信号补偿系统,包括DDPG智能体和补偿模块;Another embodiment of the present invention provides an adaptive small signal compensation system for an LCL type grid-connected inverter, comprising a DDPG agent and a compensation module;
所述DDPG智能体用于以LCL型并网逆变系统的锁相环频率、锁相环频率误差和频率误差的积分作为输入信号,产生最优补偿系数和 The DDPG agent is used to generate the optimal compensation coefficient using the phase-locked loop frequency, phase-locked loop frequency error and the integral of the frequency error of the LCL type grid-connected inverter system as input signals and
所述补偿模块用于,将最优补偿系数和经锁相环后得到并网电流扰动补偿量和调制电压扰动补偿量;以及将并网电流扰动补偿量补偿入q轴并网电流处,将调制电压扰动补偿量补偿入并网电压处。The compensation module is used to set the optimal compensation coefficient and After the phase-locked loop, the grid-connected current disturbance compensation amount and the modulation voltage disturbance compensation amount are obtained; and the grid-connected current disturbance compensation amount is compensated into the q-axis grid-connected current, and the modulation voltage disturbance compensation amount is compensated into the grid-connected voltage.
本实施例中,DDPG智能体采用深度确定策略梯度算法计算得到最优补偿系数和 In this embodiment, the DDPG agent uses a deep deterministic policy gradient algorithm to calculate the optimal compensation coefficient and
本实施例中,DDPG智能体采用下式作为奖励函数:In this embodiment, the DDPG agent uses the following formula as the reward function:
其中,r为奖励函数,f为锁相环频率,f0为工频。Where r is the reward function, f is the phase-locked loop frequency, and f0 is the power frequency.
优选的,还包括低通滤波器,所述低通滤波器位于锁相环q轴PI控制器前,Preferably, it also includes a low-pass filter, wherein the low-pass filter is located before the phase-locked loop q-axis PI controller.
所述低通滤波器传递函数为:The low-pass filter transfer function is:
其中,GLBF为低通滤波器传递函数,ωc为低通滤波器截止频率,s为拉普拉斯算子。Where G LBF is the low-pass filter transfer function, ω c is the low-pass filter cutoff frequency, and s is the Laplace operator.
优选的,所述低通滤波器截止频率ωc取2200Hz。Preferably, the cut-off frequency ω c of the low-pass filter is 2200 Hz.
本发明另一个实施例提供一种存储一个或多个程序的计算机可读存储介质,所述一个或多个程序包括指令,所述指令当由计算设备执行时,使得所述计算设备执行根据前述的方法中的任一方法。Another embodiment of the present invention provides a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which, when executed by a computing device, cause the computing device to perform any of the aforementioned methods.
本发明另一个提供一种计算设备,包括,The present invention further provides a computing device, comprising:
一个或多个处理器、存储器以及一个或多个程序,其中一个或多个程序存储在所述存储器中并被配置为由所述一个或多个处理器执行,所述一个或多个程序包括用于执行根据前述的方法中的任一方法的指令。One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the aforementioned methods.
本领域内的技术人员应明白,本申请的实施例可提供为方法、系统、或计算机程序产品。因此,本申请可采用完全硬件实施例、完全软件实施例、或结合软件和硬件方面的实施例的形式。而且,本申请可采用在一个或多个其中包含有计算机可用程序代码的计算机可用存储介质(包括但不限于磁盘存储器、CD-ROM、光学存储器等)上实施的计算机程序产品的形式。Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.
本申请是参照根据本申请实施例的方法、设备(系统)、和计算机程序产品的流程图和/或方框图来描述的。应理解可由计算机程序指令实现流程图和/或方框图中的每一流程和/或方框、以及流程图和/或方框图中的流程和/或方框的结合。可提供这些计算机程序指令到通用计算机、专用计算机、嵌入式处理机或其他可编程数据处理设备的处理器以产生一个机器,使得通过计算机或其他可编程数据处理设备的处理器执行的指令产生用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的装置。The present application is described with reference to the flowchart and/or block diagram of the method, device (system) and computer program product according to the embodiment of the present application. It should be understood that each process and/or box in the flowchart and/or block diagram, and the combination of the process and/or box in the flowchart and/or block diagram can be realized by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device for realizing the function specified in one process or multiple processes in the flowchart and/or one box or multiple boxes in the block diagram.
这些计算机程序指令也可存储在能引导计算机或其他可编程数据处理设备以特定方式工作的计算机可读存储器中,使得存储在该计算机可读存储器中的指令产生包括指令装置的制造品,该指令装置实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能。These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including an instruction device that implements the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.
这些计算机程序指令也可装载到计算机或其他可编程数据处理设备上,使得在计算机或其他可编程设备上执行一系列操作步骤以产生计算机实现的处理,从而在计算机或其他可编程设备上执行的指令提供用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的步骤。These computer program instructions may also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.
最后应当说明的是:以上实施例仅用以说明本发明的技术方案而非对其限制,尽管参照上述实施例对本发明进行了详细的说明,所属领域的普通技术人员应当理解:依然可以对本发明的具体实施方式进行修改或者等同替换,而未脱离本发明精神和范围的任何修改或者等同替换,其均应涵盖在本发明的权利要求保护范围之内。Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.
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