基于IEEE和英国G5/5的谐波研究

进行谐波研究以证明符合公用事业标准是将现代电力系统连接到电网的关键技术过程. 随着基于逆变器的资源和非线性负载的激增, 公用事业公司现在严格执行 IEEE 等标准 519 或英国G5/5，确保电能质量和系统稳定性.

以下技术指南概述了进行谐波研究的系统方法, 基于现行国际标准.

1. 基本概念和监管框架

开始计算之前, 了解管理标准和起作用的物理现象至关重要.

1.1 了解谐波失真

谐波是频率为基频整数倍的正弦电压或电流 (例如, 60 Hz或 50 赫兹) . 它们是由非线性负载（例如变频驱动器）产生的, LED照明, 和逆变器. 这些扭曲可能导致设备过热, 变压器损耗, 及保护误动作 .

1.2 适用标准

标准的选择取决于您的地理位置和公用设施要求:

IEEE StD里 519-2014: 主要用于北美, 该标准规定了公共耦合点的电力质量 (PCC). 它限制了个别谐波失真 (内出血) 和总谐波失真 (总谐波失真) 电压和电流的 .
工程建议 G5/5: 英国强制要求, 该标准要求对增量和增量进行更严格的评估 (您工厂的贡献) 和总计 (背景 + 增量式) 谐波电压, 通常评估高达 100 次谐波 .

2. 数据采集和系统建模

The accuracy of a harmonic study is entirely dependent on the quality of input data.

2.1 Utility Data (Point of Common Coupling)

You must obtain the following from the Distribution Network Operator (DNO) or utility:

Background Harmonic Voltages: Typically based on two weeks of measured data at the PCC to capture normal operating variations .
Harmonic Impedance Loci: This describes how the network impedance varies with frequency. It is critical for identifying potential resonance. The preferred format is ungrouped envelopes for each harmonic order .
Grid Strength: Usually expressed as the Short Circuit Ratio (SCR) at the PCC.

2.2 Equipment Data (OEM)

The Original Equipment Manufacturer (OEM) must provide a Norton Equivalent Model of the plant (inverter, 驱动器, 等等). This model, essential for accurate simulation, consists of two parts for each frequency :

Norton Current Source: The magnitude and phase angle of the harmonic current injected by the device.
诺顿阻抗: The internal impedance of the device, which affects how it interacts with grid resonances.

根本 (50 赫兹) 谐波 Distorted waveform

3路 12%

5日 20%

7日 10%

11日 5%

13日 4%

THD = 23.1% Crest factor = 1.38 Peak = 1.32 可以

图 1: Harmonics Example (Interactive)

Distorted waveform resulting from the combination of fundamental and harmonic frequencies (Fully interactive).

3. Step-by-Step Harmonic Analysis Methodology

Once the data is gathered, the study proceeds through a series of analytical steps using specialized software (例如, ETAP, DIgSILENT PowerFactory).

3.1 Frequency Scan Analysis

The first step is a frequency sweep to identify resonant conditions. The software injects a current of varying frequency and measures the impedance.

目标: Identify parallel (high impedance) and series (low impedance) resonance points.
Risk: If a resonance peak aligns with a characteristic harmonic frequency (例如, 5日, 7日, 11日), harmonic voltages will be amplified, leading to high distortion .

Impedance |在| (Ž) Inductive ωL Capacitive 1/ωC Resonance (300 赫兹)

f₁ = 60 赫兹 — fundamental f_res = 300 赫兹 — 5th harmonic order 在_高峰 ≈ 38 Ž — parallel resonance Q ≈ 8 — quality factor

图 2: Harmonics Resonance at the 5th harmonic (example)

Impedance vs. Frequency plot showing a parallel resonance peak.

Using the Norton model of the plant and the grid impedance, calculate the voltage distortion caused only by your new equipment.

3.2 Calculate Incremental Harmonic Voltages

公式:

V_{Ĥ} = I_{Ĥ} \times Z_{Ĥ}

哪里: 在_Ĥ is the harmonic voltage, 我_Ĥ is the harmonic current, 和 在_Ĥ is the grid impedance at harmonic order Ĥ.

Compliance Check: This value must be below the "Incremental Limits" set by the utility or standard (例如, G5/5 Stage 1 范围) .

3.3 Calculate Total Harmonic Distortion

This combines the incremental contribution with pre-existing background distortion.

Total Voltage Harmonic Distortion (THDv): The root mean square (有效值) of all harmonic voltages, expressed as a percentage of the fundamental voltage.
Compliance Check: The THDv and individual harmonic voltages must remain below the "Total Limits" (例如, IEEE 519 limits for voltage quality or G5/5 Planning Levels) .

系统: 50 赫兹 60 赫兹 Voltage level (IEEE 519):

Measured IHD (%在) IEEE 519 limit G5/5 planning level

THDv = - IEEE 519 THD limit = - Status: -

图 3: Voltage Harmonics (Interactive)

Bar chart representation of individual harmonic voltages (VN) as a percentage of the fundamental .

G5/5 and similar standards require checking that the new connection does not negatively affect neighboring customers. This involves simulating the impact at adjacent substations or sensitive locations (hospitals, data centers) .

Plant — Norton model (OEM) Utility / 格 Point of common coupling Iₙ(Ĥ) Norton 当前 Zₙ(Ĥ) Norton 阻抗 Iₕ → Vₕ Zg(Ĥ) 格阻抗 Vₕ = Iₙ(Ĥ) · Zg(Ĥ) · Zₙ(Ĥ) / ( Zₙ(Ĥ) + Zg(Ĥ) ) Simplified when Zₙ >> Zg : Vₕ ≈ Iₙ(Ĥ) · Zg(Ĥ)

图 4: Harmonics Impedance Loci

Impedance loci plotted on the R-X plane, showing how impedance changes with frequency [citation:4].

The final step is to compile the results into a formal report for the utility.

4. Compliance Verification and Reporting

4.1 Comparison with Limits

Create a summary table comparing the calculated values against the standard limits. For IEEE 519, this involves checking:

IEEE 519 表 1: Voltage distortion limits at the PCC.
IEEE 519 表 2: Current distortion limits based on the I_{资深大律师}/I_L ratio (Short circuit current vs. Load current) .

4.2 Mitigation Strategies

如果超出限制, 研究必须提出解决方案:

无源滤波器: Tuned to shunt specific harmonic frequencies.
有源谐波滤波器: Inject opposing currents to cancel harmonics.
Impedance Modification: Changing transformer connections or adding reactors to detune the system .

4.3 The Three-Step Verification Guideline

As outlined in recent IEEE guidelines, compliance can be summarized in a three-step process :

1. Measure data at the Point of Interconnection (POI).
2. Perform a statistical evaluation on the data.
3. Compare the results to the correct IEEE limits.